Comparison of the Dacron ring and suture annuloplasty for aortic root repair: an in vitro evaluation

Comparison of the Dacron ring and suture annuloplasty for aortic root repair: an in vitro evaluation Abstract OBJECTIVES Increasing evidence shows that annular stabilization is essential in most aortic valve repair procedures. However, a standardized comparison of the 2 commonly used annuloplasty procedures is lacking. We hypothesized that the Dacron ring is more rigid than the polytetrafluoroethylene suture, whereas both procedures decrease annular dimensions. The aim of this study was to compare the biomechanical properties of the ring and suture techniques with native aortic roots in vitro. METHODS Eighteen aortic roots explanted from 80-kg pigs were randomized into a Dacron ring group, a suture annuloplasty group and a native control group. Each sample was tested in a pulsatile in vitro model with a force transducer attached to the aortic annulus to obtain radial force measurements, and annular dynamics was evaluated using 2-dimensional echography. RESULTS Among the 2 annuloplasty procedures, only the Dacron ring group provided a significant reduction in the annular diameter compared with the native group (P < 0.006). Both annuloplasty procedures significantly reduced the geometric orifice area, tenting area and sinus diameter while increasing the coaptation length compared with the native group. Systolic annular distension was retained between groups, although the total radial forces were significantly reduced in the procedure groups compared with the native group (ring 1.07 ± 0.45 N, suture 1.13 ± 0.39 N and native 3.55 ± 1.34 N, P < 0.001). CONCLUSIONS Although both annuloplasty procedures increase coaptation length and decrease geometric orifice area, a significant downsizing of the annulus was achieved using the Dacron ring only. The systolic annular distension was similar to the native aortic root, whereas the radial annular forces were evenly decreased by both annuloplasty procedures. Long-term studies are needed to disclose any difference in long-term effect of the annuloplasty procedures. Aortic insufficiency , Aortic valve repair , Annular dilation , Annuloplasty , Dacron ring , Gore-Tex polytetrafluoroethylene suture annuloplasty INTRODUCTION For patients with aortic valve regurgitation with or without aortic root dilatation, aortic valve-sparing procedures have proved to be an advantageous treatment alternative to aortic valve replacement, in particular because anticoagulation- and valve prosthesis-related complications are avoided [1]. If aortic annulus dilatation is present and left untreated, this represents a risk of failure for the aortic valve-sparing procedures, and evidence shows that a subvalvular annuloplasty is crucial for improving long-term durability of these procedures [2–7]. Over time, different annuloplasty procedures have been proposed [8]. The 2 most commonly used procedures are the Dacron ring annuloplasty and the polytetrafluoroethylene (PTFE) suture annuloplasty. The Dacron ring annuloplasty has demonstrated encouraging results when combined with the remodelling procedure [9–13]. Previous studies have shown that the tubular Dacron graft tends to expand in diameter over time when used as a vascular aortic conduit [14], which has led to concerns regarding the durability of the Dacron material when used as an external subvalvular annuloplasty. However, Basmadjian et al. [10] recently found that the Dacron ring preserved its size at 2-year follow-up when used as a subvalvular annuloplasty, suggesting that the standardized technique of fixating the Dacron ring using 6 anchoring sutures may limit radial expansion. Nevertheless, the drawback of the Dacron ring annuloplasty is the need for deep para-aortic dissection with the risk of coronary artery and right ventricular perforation or irregular dissection [15, 16]. As an alternative to Dacron ring annuloplasty, Schäfers et al. developed a PTFE suture annuloplasty procedure, which have shown excellent early and mid-term results in patients with bicuspid aortic valves [5, 6, 17]. The major benefits of the suture annuloplasty are less extensive root dissection and fast and simple application technique [18]. However, the lack of standardization represents a drawback with this technique. Although treating a dilated aortic annulus is considered essential for a durable aortic valve repair, the 2 annuloplasty procedures have never been examined in a consistent, standardized setting earlier. Based on material and surgical procedure, it is hypothesized that the Dacron ring annuloplasty is more rigid and has a more mechanical supporting effect on the aortic annulus than the PTFE suture annuloplasty. On the other hand, one could also speculate that the PTFE suture annuloplasty is more flexible with more physiological properties, which could result in better leaflet dynamics. Hence, the aim of this in vitro study was to analyse the biomechanical characteristics of the Dacron ring annuloplasty and PTFE suture annuloplasty and compare both with the native aortic root. MATERIALS AND METHODS Study material and surgical preparation Eighteen porcine hearts (bodyweight 80 kg) were collected from a slaughter house and randomized into 3 groups: the Dacron ring annuloplasty group, the PTFE suture annuloplasty group and the native aortic root group serving as controls. The aorta was carefully transected 2 cm distal to the sinotubular junction and 3 cm proximal to the aortic annulus. Only aortic roots with an annular diameter of 19–22 mm were included in the study. They were inspected for pathological abnormalities. The intraluminal diameters of the aortic annulus and sinotubular junction were measured using Hegar dilators. The annular base of the aortic root was dissected free, and the coronary arteries were ligated at the level of the sinuses. A standardized approach was used for the annuloplasty procedures and force attachment as illustrated in Fig. 1. Figure 1: View largeDownload slide The annuloplasty procedures and the force transducer. A schematic representation (left) and photographs (right) of (A) the Dacron ring annuloplasty, (B) the polytetrafluoroethylene suture annuloplasty and (C) the force transducer positioned below the aortic interleaflet triangles at the annular plane. The blue square of the transducer arm indicates the location of the strain gauges, and the black arrows indicate the extraluminal radial force directions. Figure 1: View largeDownload slide The annuloplasty procedures and the force transducer. A schematic representation (left) and photographs (right) of (A) the Dacron ring annuloplasty, (B) the polytetrafluoroethylene suture annuloplasty and (C) the force transducer positioned below the aortic interleaflet triangles at the annular plane. The blue square of the transducer arm indicates the location of the strain gauges, and the black arrows indicate the extraluminal radial force directions. For the Dacron ring procedure (Fig. 1A), a circular band of 3 mm in height was excised from a straight Dacron tube graft with a diameter of 22 mm (Gelweave™, Vascutek Ltd., Renfrewshire, UK). The diameter of the Dacron ring was derived from the sizing criterion proposed by Lansac et al. Six anchoring ‘U’ stiches were passed inside-out at the subvalvular plane and through the ring. Hereafter, the ‘U’ stitches were tied down to fasten the ring in the subvalvular position [11] and might reduce the circumference further. The suture annuloplasty procedure (Fig. 1B) was performed using a CV-0 PTFE double-needle suture (GORE-TEX®, W.L.Gore & Associates, Flagstaff, AZ, USA). The suture was passed through the septal myocardium from outside at the right–left commissure. Then, each needle end of the suture was passed below each coronary artery through the connective tissue outside the non-coronary sinus. Here, the suture was tied around a 22-mm Hegar dilator for sizing control to perform the procedure as close to the clinical setting [17]. Following the surgical preparation of the aortic root, a force transducer was attached inside the aortic annulus directly below the interleaflet triangles using 3 sutures (Fig. 1C). Finally, the left ventricular outflow tract was elongated by a 3-cm Dacron tube graft to fixate the aortic root in the in vitro setup. In vitro setup The pulsatile left heart in vitro model presented in Fig. 2 was used for the experiments. The model consisted of an atrial chamber (Fig. 2A) and a ventricular chamber (Fig. 2B) separated by a mechanical mitral valve. The ventricular chamber was connected to a digitally controlled piston pump (SuperPump AR Series, ViVitro Labs, Victoria, Canada), providing pulsatile flow to simulate left ventricular ejection into the aortic root. The annuloplasty-modified aortic root was inserted into the replaceable aortic section in the model (Fig. 2C), and a compliance chamber was attached (Fig. 2D) simulating arterial elasticity. The systemic vascular resistance was adjusted through an adjustable clamp (Fig. 2E). Figure 2: View largeDownload slide An illustration of the pulsatile in vitro model. (A) Atrial chamber, (B) ventricular chamber, (C) replaceable aortic section, (D) compliance chamber and (E) adjustable resistance. Figure 2: View largeDownload slide An illustration of the pulsatile in vitro model. (A) Atrial chamber, (B) ventricular chamber, (C) replaceable aortic section, (D) compliance chamber and (E) adjustable resistance. Instantaneous aortic flow and peripheral venous flow were measured using an ultrasonic transit time flow system (PXL11, PXL25, TS410, Transonic Systems Inc., Ithaca, NY, USA). Pressures of the left ventricular chamber and the aortic chamber were measured using Mikro-Tip pressure catheters (SPR-350S, Millar Instruments, Houston, TX, USA) and amplified using a 2-channel pressure control unit (PCU-2000, Millar Instruments). Force- and hydrodynamic analogue signals were recorded using dedicated data acquisition hardware at a sample rate of 1613 Hz (cDAQ model 9172, NI-9237, NI-9215, National Instruments, Austin, TX, USA). The data acquisition was handled using custom-made software (LabVIEW 11.0, National Instruments). Study design Hydrodynamic and force measurements were recorded during the first data collection. After the first data acquisition, the force transducer was released from the aortic root to avoid interference with the echographic recordings. In the second data collection, another round of hydrodynamic measurements was obtained using 2-dimensional (2D) echography. Physiological conditions were adjusted to a fixed heart rate of 70 beats⋅min−1, a flow of 6–7 l/min and an arterial pressure of 110/70 mmHg throughout all acquired measurements. Force transducer A dedicated force transducer was developed to measure the annular radial forces (Fig. 1C). The transducer consisted of a basal ring with 3 equidistantly placed arms. The outer diameter of its basal ring and the arms of the transducer was 20 mm and 19 mm, respectively. On each arm, 2 strain gauges were setup in a Wheatstone half-bridge configuration. The force transducer measured strain corresponding to luminal bending and extraluminal distension. Prior to each experiment, the strain measurements were calibrated to radial forces as previously described [19]. Each transducer arm measured the radial distension forces at annular level below the right/left coronary interleaflet triangle, right/non-coronary interleaflet triangle and left/non-coronary interleaflet triangle, providing the specific radial force development at each segment acting on the aortic annulus and the annuloplasty. Echography Echographic recordings of annular and leaflet dynamics were performed using a 2D-linear probe (GE 9 l-RS Probe, GE Vingmed Ultrasound AS, Horten, Norway). One short-axis view was obtained at the sinus plane and 3 long-axis views projecting through adjacent leaflets (right/left coronary interleaflet triangle, right/non-coronary interleaflet triangle and left/non-coronary interleaflet triangle) involving the whole aortic root. The echographic systole and diastole were defined from the maximum and minimum annular diameters. The acquired echographic parameters were annular base internal diameter at the level of the nadir of the 3 leaflets (systole and diastole); mid-sinus internal diameter (systole and diastole); coaptation length (length of direct leaflet contact); tenting area (area between the aortic annulus and the lower border of leaflet coaptation); geometric orifice area (planimetric opening area formed by the free edges of the leaflets in the systole [20]) and planimetric cross-sectional sinus area (entire area at the level of the sinuses). Data analysis The acquired data were analysed off-line using dedicated virtual instrumentation software (LabVIEW 11.0, National Instruments). The systolic and diastolic pressures were determined from maximum and minimum aortic pressures, whereas the maximum pressure gradient drop was calculated as the difference between the maximum ventricular pressure and maximum aortic pressure. The radial forces were defined as maximum–minimum force at each measuring site. Echographic data were analysed using OsiriX MD v8.5 (Pixmeo Sarl, Bernex, Switzerland). The echographic analysis was performed using inner-edge to inner-edge measurements [21]. The distensibility was defined as the difference between the systolic and diastolic diameters at the respective level. Radial forces were compared with the annular distensibility acquired from echography to evaluate the radial force development per millimetre of distension for each of the 3 groups defined as the force–distensibility ratio. Statistical analysis All data are presented as mean ± standard deviation and are based on 10 consecutive cardiac cycles for each aortic root. The repeated measurements for hydrodynamics and forces were analysed in a mixed model with nested random effects to take into account the repeated measurements on animals and anatomical location within animals. Following the mixed model, residuals were inspected for normality, and no reason was found to refute this. The statistical methods were provided by the Biostatistical Advisory Service (BIAS, Aarhus University, Denmark). The echographic parameters were analysed using the one-way analysis of variance with a Bonferroni post hoc test. All statistical comparisons were performed using Stata 13.0 (StataCorp LLC, Texas, USA), and P-values <0.05 were considered statistically significant. RESULTS Hydrodynamic results All aortic valves were competent at all time points, and the baseline hydrodynamic parameters are summarized in Table 1. There were no statistical differences regarding the hydrodynamics between groups. Table 1: Baseline hydrodynamics (n = 6) Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Baseline hydrodynamics with the force transducer attached inside the aortic annulus. Øannulus, ØSTJ: sample diameter of the intraluminal aortic annulus and sinotubular junction before surgical preparation; pdiastolic, psystolic: diastolic and systolic pressure determined from maximum and minimum aortic pressures; pgradient: systolic pressure drop over the valve measured as the difference between left ventricular and aortic pressure; Qmean: applied flow rate; SD: standard deviation. Table 1: Baseline hydrodynamics (n = 6) Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Baseline hydrodynamics with the force transducer attached inside the aortic annulus. Øannulus, ØSTJ: sample diameter of the intraluminal aortic annulus and sinotubular junction before surgical preparation; pdiastolic, psystolic: diastolic and systolic pressure determined from maximum and minimum aortic pressures; pgradient: systolic pressure drop over the valve measured as the difference between left ventricular and aortic pressure; Qmean: applied flow rate; SD: standard deviation. After removing the force transducer, the pressure gradient was unaffected in the suture group (23 ± 8.0 mmHg). However, the pressure gradient significantly decreased in the native (10.7 ± 2.6 mmHg, P = 0.01) and ring groups (19.2 ± 2.7 mmHg, P < 0.001), compared with measurements of the force transducer presented in Table 1. Apart from this, the hydrodynamics were unchanged after the removal of the force transducer. Echographic results The echographic data are summarized in Table 2, and a representative visualization of 1 aortic root from each group is shown in Fig. 3. Table 2: Echographic measurements Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns ns: not statistically significantly different; SD: standard deviation. Table 2: Echographic measurements Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns ns: not statistically significantly different; SD: standard deviation. Figure 3: View largeDownload slide Representative echographic series from each group in the long-axis view (left panel) and the short-axis view (right panel) for the diastole and systole. Figure 3: View largeDownload slide Representative echographic series from each group in the long-axis view (left panel) and the short-axis view (right panel) for the diastole and systole. Long-axis views revealed a reduction in annular diameter in the procedure groups compared with the native aortic roots, although only the Dacron ring provided a statistically significant annular diameter reduction (Table 2). The relative annular distensibility was retained between all 3 groups (native 14%, ring 12% and suture 16%). No significant differences were found in the sinotubular junction diameter between groups. The geometric heights of each cusp measured echographically did not differ between groups (P-value ≥0.5). The short-axis view revealed a significant reduction in the geometric orifice area of 57% and 46% for the ring and suture groups, respectively, compared with the native group (Table 2). The planimetric cross-sectional area at sinus level was statistically significantly reduced by both procedures compared with the native group. Figure 4 depicts coaptation length and tenting area. The coaptation length increased significantly after both procedures compared with the native group corresponding to 40% by the suture (P = 0.01) and 32% by the ring (P = 0.04). As the coaptation length increased and annular dimensions decreased, the tenting area significantly decreased correspondingly in both procedure groups (P < 0.002). Figure 4: View largeDownload slide Valve geometry for each group. (A) Leaflet coaptation length was significantly increased in both procedure groups. (B) Tenting area was significantly decreased in both procedure groups. *P < 0.05 compared with the native group. Figure 4: View largeDownload slide Valve geometry for each group. (A) Leaflet coaptation length was significantly increased in both procedure groups. (B) Tenting area was significantly decreased in both procedure groups. *P < 0.05 compared with the native group. None of the examined echographic parameters indicated any significant differences between the 2 procedure groups. Force development The radial forces for each measuring site are presented in Fig. 5. Both procedures significantly reduced the radial force for each segment compared with the native group. The total radial forces were significantly lower in the procedure groups compared with the native group (ring 1.07 ± 0.45 N; suture 1.13 ± 0.39 N; native 3.55 ± 1.34 N, P < 0.001). However, no individual segmental differences were observed between the annular forces within each group. Figure 5: View largeDownload slide The difference between maximum and minimum radial forces at the annulus for each group in each segment. NL: non-coronary/left-coronary interleaflet triangle; RL: right/left coronary interleaflet triangle; RN: right/non-coronary interleaflet triangle. *P < 0.001 compared with the native group. Figure 5: View largeDownload slide The difference between maximum and minimum radial forces at the annulus for each group in each segment. NL: non-coronary/left-coronary interleaflet triangle; RL: right/left coronary interleaflet triangle; RN: right/non-coronary interleaflet triangle. *P < 0.001 compared with the native group. Force–distensibility ratio Figure 6 illustrates the ratio between the mean radial forces (ring 0.38 ± 0.16 N, suture 0.38 ± 0.12 N and native 1.18 ± 0.39 N, P < 0.001) and the annular distensibility. The suture group exhibited a significantly decreased force–distensibility ratio compared with the native group (P = 0.038), whereas there were no significant differences between ring vs native or ring vs suture groups. Figure 6: View largeDownload slide Combined radial forces and echography showing the force–distensibility ratio. The bars represent the radial force development per millimetre annular distension for each group. *P-value <0.04 compared with the native group. Figure 6: View largeDownload slide Combined radial forces and echography showing the force–distensibility ratio. The bars represent the radial force development per millimetre annular distension for each group. *P-value <0.04 compared with the native group. DISCUSSION In the present study, echography demonstrated that both annuloplasty procedures fulfilled their intended purpose. Both procedures significantly increased coaptation length and reduced tenting area in consistency with the results from other studies [10, 22–24]; however, a statistically significant downsizing of the annulus was only achieved with the Dacron ring. Furthermore, both annuloplasty procedures reduced the radial force development while preserving the relative annular distensibility similar to the native aortic annulus. However, the suture annuloplasty expresses a more flexible behaviour at the same radial forces when compared with the ring group, although not statistically significant compared with the ring group. This is illustrated by the significantly reduced force–distensibility ratio of the suture group when compared with the native group. Although these findings demonstrate the acute effect of the annuloplasty procedures, the Dacron ring has shown to preserve its size and distensibility in a recent 2-year follow-up study [10]. In this acute setup, the suture annuloplasty reduced the annular diameter; however, this was not statistically significant. Therefore, the downsizing capacity over time of the suture annuloplasty should be considered. Nevertheless, the suture annuloplasty has shown to improve valve stability, freedom from aortic regurgitation and reoperation in patients with regurgitant bicuspid valves when compared with repair procedure without a suture annuloplasty at 5-year follow up [5]. However, in clinical assessment of complex surgery, such as aortic root repair, it is difficult to distinguish and interpret the isolated impact of the annuloplasty due to several coexisting factors such as anatomy, comorbidities and pathology. Furthermore, when several parameters are changed during surgery as part of the repair procedure by different surgeons with different expertise and approaches, results may not be entirely comparable. These issues are overcome in this in vitro study, which is the first to compare the isolated functional and biomechanical effect of the PTFE suture annuloplasty and the Dacron ring annuloplasty to the native aortic root under standardized conditions with the same operator. We hypothesized that the Dacron ring would show a more pronounced mechanical stabilizing effect than the suture annuloplasty assessed from the force development, but this has not been confirmed in the present study. In the long-axis echographic view, the annular diameter was downsized by both procedure groups, although the annular distension was similar between all groups. These results indicate that both annuloplasty procedures support the aortic annulus equally and efficiently immediately after surgery, without impairing root dynamics, which is a drawback of the reimplantation procedure. However, the short-axis view of the aortic annulus (Fig. 3) demonstrated a perfect circle in the ring group, whereas the suture group displayed an irregular circle similar to the native annulus. This difference might explain why the annulus diameter is significantly decreased by the ring group—and not by the suture group—when compared with the native group. The distensibility of the sinuses was also similar between groups in the long-axis view. However, when examined in the short-axis view, the sinus area distension was significantly smaller in the procedure groups compared with the native group. This discrepancy can be explained by the measuring method in different projections. The cross-sectional distension likely occurs in several segments, which is difficult to measure in one long-axis view. Additionally, the 2D long-axis view presumes a circular shape of the left ventricular outflow tract area, which often results in an underestimation of the annular diameter. This could have been overcome using 3-dimensional echography, enabling simultaneous display of the aortic root in both the short-axis view and the long-axis view [25]. Furthermore, the aortic root tends to change from a clover shape in the diastole to a cylindrical shape during ejection of blood, which has previously been described [26]. Although echography showed similar annular distension for all groups in the study, the force transducer revealed a significantly reduced radial force development in the procedure groups compared with the native group. When combining the findings of annular distension and radial forces (Fig. 6), it seems that the annuloplasty absorb and reduce the distension forces while preserving root dynamics. The radial forces were similar between the procedure groups although the annular diameters differed, suggesting that the annular diameter does not influence the radial forces, as much as the annuloplasty itself, by absorbing the forces. Absorption of radial forces is indicative for an external supporting mechanism in both annuloplasty groups and, hence, protection of the vulnerable aortic root, where it is essential to avoid redilation. These results indicate that the annuloplasty procedures are excellent supportive techniques for the potential avoidance of redilation, which is the main limitation of the remodelling procedure without an added annuloplasty—especially as the Dacron ring has shown not to dilate over time. This supports the concept of a protective annuloplasty in root repair in agreement with recent follow-up studies [5, 7]. The force–distensibility ratio was lower in the procedure groups compared with the native aortic roots, although only significant for the suture group. This may be due to the larger distensibility of the suture group compared with the ring group, although this was not shown to be significant. The force–distensibility ratio suggests that the suture group is capable of distending more throughout the cardiac cycle while maintaining the same low radial force development as seen in the ring group. However, the findings of the force–distensibility ratio could also be due to a more extensive downsizing in the Dacron group. We deliberately chose the sizing criterion made by Lansac et al. [11] derived from dilated aortic roots as the basis of choice for the Dacron ring size. It can be argued that a bigger size of the Dacron rings should have been used when compared with the sizing formula of Kerchove et al. [22] used for healthy porcine aortic roots. Another explanation is that the sutures of the Dacron ring fixates the ring and reduces the functional ring diameter more than expected. For the suture procedure, it could be speculated that a smaller Hegar dilator should be used to align the intervention groups; however, we chose to perform the study as close to the real clinical procedure. Nevertheless, these results indicate that the Dacron ring might reduce the annular distension more than the suture group, although not significantly. Overall, both the suture annuloplasty and ring annuloplasty seem to reduce the annular diameter efficiently and improve the coaptation geometry immediately after surgery without significant differences between the 2 types of annuloplasty procedures. What needs to be established in the future is long-term durability of each procedure. As the acute effect of both suture and ring seems comparable in this in vitro study, there is no evidence towards one method being immediately technically superior to the other; hence, the choice of annuloplasty procedure relies on the personal preference of the surgeon until long-term clinical durability studies are performed to clarify the impact of the annuloplasty procedures over time. Limitations The annuloplasty procedures were evaluated in an in vitro setup using healthy porcine aortic roots. The lack of aortic root pathology and the differences between porcine and human anatomy are limitations associated with a study such as this. Even though fresh aortic tissue was used, the rest of the in vitro system comprised acrylic chambers mimicking the circulatory system. Meticulous preparation was made to fine tune compliance and hydrodynamic impedances to obtain physiological pressure and flow waveforms; however, the in vitro model still differs from an in vivo situation. The presented results could differ if the study was made in vivo and even in humans, and hence, long-term clinical or pathological in vivo porcine studies are needed. Nevertheless, a study on healthy aortic roots is more reproducible, and it is more apparent to evaluate techniques made by the same operator in homogenous aortic roots. The dedicated force transducer was designed to interfere minimally with the hydrodynamic flow. However, interference cannot be avoided entirely. We expect any interference induced by the transducer to be equal between groups, and therefore, it does not affect our results as the measurements are used for comparison between groups. As there was no electrocardiogram, it was not technically possible to make a direct correlation between the time points of the force measurements and the echography. Therefore, we defined the systole and diastole as the maximum and minimum forces, and the maximum and minimum diameters of the echographic annular diameters. Finally, as the echographic parameters were measured visually, data analysis was blinded to the operator to avoid operator-induced bias. Intraobserver and interobserver variability tests were performed, and the differences were satisfactory (<10%). CONCLUSION From this in vitro study, a comprehensive biomechanical comparison of the Dacron ring and PTFE suture annuloplasty procedures was obtained. The Dacron ring annuloplasty and suture annuloplasty effectively downsized the annular diameter although only statistically significant by the Dacron ring. Furthermore, both procedures reduced the radial force development in the aortic annulus while maintaining relative annular distensibility similar to the native aortic root. Hence, both annuloplasty techniques preserve the dynamics of the aortic annulus while providing external support as intended, indicating that the material is less important than the surgical technique, when choosing an annuloplasty procedure for the dilated aortic root in the acute setting. Funding This work was supported by the Graduate School, Health, Aarhus University and Købmand Sven Hansen og Hustru Ina Hansens fond. Conflict of interest: none declared. REFERENCES 1 David TE. Aortic root aneurysms: remodeling or composite replacement? Ann Thorac Surg 1997 ; 64 : 1564 – 8 . Google Scholar CrossRef Search ADS PubMed 2 Kunihara T , Aicher D , Rodionycheva S , Groesdonk H-V , Langer F , Sata F et al. . Preoperative aortic root geometry and postoperative cusp configuration primarily determine long-term outcome after valve-preserving aortic root repair . J Thorac Cardiovasc Surg 2012 ; 143 : 1389 – 95 . Google Scholar CrossRef Search ADS PubMed 3 Schäfers H-J , Raddatz A , Schmied W , Takahashi H , Miura Y , Kunihara T et al. . Reexamining remodeling . J Thorac Cardiovasc Surg 2015 ; 149(2 Suppl) : S30 – 6 . Google Scholar CrossRef Search ADS 4 Hanke T , Charitos EI , Stierle U , Robinson D , Gorski A , Sievers H-H et al. . Factors associated with the development of aortic valve regurgitation over time after two different techniques of valve-sparing aortic root surgery . J Thorac Cardiovasc Surg 2009 ; 137 : 314 – 9 . Google Scholar CrossRef Search ADS PubMed 5 Schneider U , Hofmann C , Aicher D , Takahashi H , Miura Y , Schäfers H-J. Suture annuloplasty significantly improves the durability of bicuspid aortic valve repair . Ann Thorac Surg 2017 ; 103 : 504 – 10 . Google Scholar CrossRef Search ADS PubMed 6 Aicher D , Schneider U , Schmied W , Kunihara T , Tochii M , Schäfers H-J. Early results with annular support in reconstruction of the bicuspid aortic valve . J Thorac Cardiovasc Surg 2013 ; 145(3 Suppl) : S30 – 4 . Google Scholar CrossRef Search ADS 7 Lansac E , Di Centa I , Sleilaty G , Lejeune S , Berrebi A , Zacek P et al. . Remodeling root repair with an external aortic ring annuloplasty . J Thorac Cardiovasc Surg 2017 ; 153 : 1 – 13 . Google Scholar CrossRef Search ADS PubMed 8 Schäfers H-J. Aortic annuloplasty: a new aspect of aortic valve repair . Eur J Cardiothorac Surg 2012 ; 41 : 1124 – 5 . Google Scholar CrossRef Search ADS PubMed 9 Lansac E , Di Centa I , Sleilaty G , Lejeune S , Khelil N , Berrebi A et al. . Long-term results of external aortic ring annuloplasty for aortic valve repair . Eur J Cardiothorac Surg 2016 ; 50 : 350 – 60 . Google Scholar CrossRef Search ADS PubMed 10 Basmadjian L , Basmadjian AJ , Stevens L-M , Mongeon F-P , Cartier R , Poirier N et al. . Early results of extra-aortic annuloplasty ring implantation on aortic annular dimensions . J Thorac Cardiovasc Surg 2016 ; 151 : 1280 – 1 . Google Scholar CrossRef Search ADS PubMed 11 Lansac E , Di Centa I , Vojacek J , Nijs J , Hlubocky J , Mecozzi G et al. . Valve sparing root replacement: the remodeling technique with external ring annuloplasty . Ann Cardiothorac Surg 2013 ; 2 : 117 – 23 . Google Scholar PubMed 12 Lansac E , Di Centa I , Bonnet N , Leprince P , Rama A , Acar C et al. . Aortic prosthetic ring annuloplasty: a useful adjunct to a standardized aortic valve-sparing procedure? Eur J Cardiothorac Surg 2006 ; 29 : 537 – 44 . Google Scholar CrossRef Search ADS PubMed 13 Holubec T , Higashigaito K , Belobradek Z , Dergel M , Harrer J , Alkadhi H et al. . 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Suture annuloplasty in aortic valve repair . Ann Thorac Surg 2016 ; 101 : 783 – 5 . Google Scholar CrossRef Search ADS PubMed 18 Kunihara T. Annular management during aortic valve repair: a systematic review . Gen Thorac Cardiovasc Surg 2016 ; 64 : 63 – 71 . Google Scholar CrossRef Search ADS PubMed 19 Bechsgaard T , Hønge JL , Nygaard H , Nielsen SL , Johansen P. Biomechanical assessment of the aortic root using novel force transducers . J Biomech 2017 ; 61 : 58 – 64 . Google Scholar CrossRef Search ADS PubMed 20 Saikrishnan N , Kumar G , Sawaya FJ , Lerakis S , Yoganathan AP. Accurate assessment of aortic stenosis: a review of diagnostic modalities and hemodynamics . Circulation 2014 ; 129 : 244 – 53 . Google Scholar CrossRef Search ADS PubMed 21 Baumgartner H , Hung J , Bermejo J , Chambers JB , Edvardsen T , Goldstein S et al. . Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography . J Am Soc Echocardiogr 2017 ; 30 : 372 – 92 . Google Scholar CrossRef Search ADS PubMed 22 de Kerchove L , Vismara R , Mangini A , Fiore GB , Price J , Noirhomme P et al. . In vitro comparison of three techniques for ventriculo-aortic junction annuloplasty . Eur J Cardiothorac Surg 2012 ; 41 : 1117 – 24 . Google Scholar CrossRef Search ADS PubMed 23 Wuliya M , Sleilaty G , Di Centa I , Khelil N , Berrebi A , Czitrom D et al. . An expansible aortic ring to preserve aortic root dynamics after aortic valve repair . Eur J Cardiothorac Surg 2015 ; 47 : 482 – 90 ; discussion 490. Google Scholar CrossRef Search ADS PubMed 24 Marom G , Haj-Ali R , Rosenfeld M , Schäfers H-J , Raanani E. Aortic root numeric model: annulus diameter prediction of effective height and coaptation in post-aortic valve repair . J Thorac Cardiovasc Surg 2013 ; 145 :406–11.e1. 25 Lang RM , Badano LP , Tsang W , Adams DH , Agricola E , Buck T et al. . EAE/ASE recommendations for image acquisition and display using three-dimensional echocardiography . Eur Heart J Cardiovasc Imaging 2012 ; 13 : 1 – 46 . Google Scholar CrossRef Search ADS PubMed 26 Cheng A , Dagum P , Miller DC. Aortic root dynamics and surgery: from craft to science . Philos Trans R Soc Lond B Biol Sci 2007 ; 362 : 1407 – 19 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. 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Comparison of the Dacron ring and suture annuloplasty for aortic root repair: an in vitro evaluation

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
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Abstract

Abstract OBJECTIVES Increasing evidence shows that annular stabilization is essential in most aortic valve repair procedures. However, a standardized comparison of the 2 commonly used annuloplasty procedures is lacking. We hypothesized that the Dacron ring is more rigid than the polytetrafluoroethylene suture, whereas both procedures decrease annular dimensions. The aim of this study was to compare the biomechanical properties of the ring and suture techniques with native aortic roots in vitro. METHODS Eighteen aortic roots explanted from 80-kg pigs were randomized into a Dacron ring group, a suture annuloplasty group and a native control group. Each sample was tested in a pulsatile in vitro model with a force transducer attached to the aortic annulus to obtain radial force measurements, and annular dynamics was evaluated using 2-dimensional echography. RESULTS Among the 2 annuloplasty procedures, only the Dacron ring group provided a significant reduction in the annular diameter compared with the native group (P < 0.006). Both annuloplasty procedures significantly reduced the geometric orifice area, tenting area and sinus diameter while increasing the coaptation length compared with the native group. Systolic annular distension was retained between groups, although the total radial forces were significantly reduced in the procedure groups compared with the native group (ring 1.07 ± 0.45 N, suture 1.13 ± 0.39 N and native 3.55 ± 1.34 N, P < 0.001). CONCLUSIONS Although both annuloplasty procedures increase coaptation length and decrease geometric orifice area, a significant downsizing of the annulus was achieved using the Dacron ring only. The systolic annular distension was similar to the native aortic root, whereas the radial annular forces were evenly decreased by both annuloplasty procedures. Long-term studies are needed to disclose any difference in long-term effect of the annuloplasty procedures. Aortic insufficiency , Aortic valve repair , Annular dilation , Annuloplasty , Dacron ring , Gore-Tex polytetrafluoroethylene suture annuloplasty INTRODUCTION For patients with aortic valve regurgitation with or without aortic root dilatation, aortic valve-sparing procedures have proved to be an advantageous treatment alternative to aortic valve replacement, in particular because anticoagulation- and valve prosthesis-related complications are avoided [1]. If aortic annulus dilatation is present and left untreated, this represents a risk of failure for the aortic valve-sparing procedures, and evidence shows that a subvalvular annuloplasty is crucial for improving long-term durability of these procedures [2–7]. Over time, different annuloplasty procedures have been proposed [8]. The 2 most commonly used procedures are the Dacron ring annuloplasty and the polytetrafluoroethylene (PTFE) suture annuloplasty. The Dacron ring annuloplasty has demonstrated encouraging results when combined with the remodelling procedure [9–13]. Previous studies have shown that the tubular Dacron graft tends to expand in diameter over time when used as a vascular aortic conduit [14], which has led to concerns regarding the durability of the Dacron material when used as an external subvalvular annuloplasty. However, Basmadjian et al. [10] recently found that the Dacron ring preserved its size at 2-year follow-up when used as a subvalvular annuloplasty, suggesting that the standardized technique of fixating the Dacron ring using 6 anchoring sutures may limit radial expansion. Nevertheless, the drawback of the Dacron ring annuloplasty is the need for deep para-aortic dissection with the risk of coronary artery and right ventricular perforation or irregular dissection [15, 16]. As an alternative to Dacron ring annuloplasty, Schäfers et al. developed a PTFE suture annuloplasty procedure, which have shown excellent early and mid-term results in patients with bicuspid aortic valves [5, 6, 17]. The major benefits of the suture annuloplasty are less extensive root dissection and fast and simple application technique [18]. However, the lack of standardization represents a drawback with this technique. Although treating a dilated aortic annulus is considered essential for a durable aortic valve repair, the 2 annuloplasty procedures have never been examined in a consistent, standardized setting earlier. Based on material and surgical procedure, it is hypothesized that the Dacron ring annuloplasty is more rigid and has a more mechanical supporting effect on the aortic annulus than the PTFE suture annuloplasty. On the other hand, one could also speculate that the PTFE suture annuloplasty is more flexible with more physiological properties, which could result in better leaflet dynamics. Hence, the aim of this in vitro study was to analyse the biomechanical characteristics of the Dacron ring annuloplasty and PTFE suture annuloplasty and compare both with the native aortic root. MATERIALS AND METHODS Study material and surgical preparation Eighteen porcine hearts (bodyweight 80 kg) were collected from a slaughter house and randomized into 3 groups: the Dacron ring annuloplasty group, the PTFE suture annuloplasty group and the native aortic root group serving as controls. The aorta was carefully transected 2 cm distal to the sinotubular junction and 3 cm proximal to the aortic annulus. Only aortic roots with an annular diameter of 19–22 mm were included in the study. They were inspected for pathological abnormalities. The intraluminal diameters of the aortic annulus and sinotubular junction were measured using Hegar dilators. The annular base of the aortic root was dissected free, and the coronary arteries were ligated at the level of the sinuses. A standardized approach was used for the annuloplasty procedures and force attachment as illustrated in Fig. 1. Figure 1: View largeDownload slide The annuloplasty procedures and the force transducer. A schematic representation (left) and photographs (right) of (A) the Dacron ring annuloplasty, (B) the polytetrafluoroethylene suture annuloplasty and (C) the force transducer positioned below the aortic interleaflet triangles at the annular plane. The blue square of the transducer arm indicates the location of the strain gauges, and the black arrows indicate the extraluminal radial force directions. Figure 1: View largeDownload slide The annuloplasty procedures and the force transducer. A schematic representation (left) and photographs (right) of (A) the Dacron ring annuloplasty, (B) the polytetrafluoroethylene suture annuloplasty and (C) the force transducer positioned below the aortic interleaflet triangles at the annular plane. The blue square of the transducer arm indicates the location of the strain gauges, and the black arrows indicate the extraluminal radial force directions. For the Dacron ring procedure (Fig. 1A), a circular band of 3 mm in height was excised from a straight Dacron tube graft with a diameter of 22 mm (Gelweave™, Vascutek Ltd., Renfrewshire, UK). The diameter of the Dacron ring was derived from the sizing criterion proposed by Lansac et al. Six anchoring ‘U’ stiches were passed inside-out at the subvalvular plane and through the ring. Hereafter, the ‘U’ stitches were tied down to fasten the ring in the subvalvular position [11] and might reduce the circumference further. The suture annuloplasty procedure (Fig. 1B) was performed using a CV-0 PTFE double-needle suture (GORE-TEX®, W.L.Gore & Associates, Flagstaff, AZ, USA). The suture was passed through the septal myocardium from outside at the right–left commissure. Then, each needle end of the suture was passed below each coronary artery through the connective tissue outside the non-coronary sinus. Here, the suture was tied around a 22-mm Hegar dilator for sizing control to perform the procedure as close to the clinical setting [17]. Following the surgical preparation of the aortic root, a force transducer was attached inside the aortic annulus directly below the interleaflet triangles using 3 sutures (Fig. 1C). Finally, the left ventricular outflow tract was elongated by a 3-cm Dacron tube graft to fixate the aortic root in the in vitro setup. In vitro setup The pulsatile left heart in vitro model presented in Fig. 2 was used for the experiments. The model consisted of an atrial chamber (Fig. 2A) and a ventricular chamber (Fig. 2B) separated by a mechanical mitral valve. The ventricular chamber was connected to a digitally controlled piston pump (SuperPump AR Series, ViVitro Labs, Victoria, Canada), providing pulsatile flow to simulate left ventricular ejection into the aortic root. The annuloplasty-modified aortic root was inserted into the replaceable aortic section in the model (Fig. 2C), and a compliance chamber was attached (Fig. 2D) simulating arterial elasticity. The systemic vascular resistance was adjusted through an adjustable clamp (Fig. 2E). Figure 2: View largeDownload slide An illustration of the pulsatile in vitro model. (A) Atrial chamber, (B) ventricular chamber, (C) replaceable aortic section, (D) compliance chamber and (E) adjustable resistance. Figure 2: View largeDownload slide An illustration of the pulsatile in vitro model. (A) Atrial chamber, (B) ventricular chamber, (C) replaceable aortic section, (D) compliance chamber and (E) adjustable resistance. Instantaneous aortic flow and peripheral venous flow were measured using an ultrasonic transit time flow system (PXL11, PXL25, TS410, Transonic Systems Inc., Ithaca, NY, USA). Pressures of the left ventricular chamber and the aortic chamber were measured using Mikro-Tip pressure catheters (SPR-350S, Millar Instruments, Houston, TX, USA) and amplified using a 2-channel pressure control unit (PCU-2000, Millar Instruments). Force- and hydrodynamic analogue signals were recorded using dedicated data acquisition hardware at a sample rate of 1613 Hz (cDAQ model 9172, NI-9237, NI-9215, National Instruments, Austin, TX, USA). The data acquisition was handled using custom-made software (LabVIEW 11.0, National Instruments). Study design Hydrodynamic and force measurements were recorded during the first data collection. After the first data acquisition, the force transducer was released from the aortic root to avoid interference with the echographic recordings. In the second data collection, another round of hydrodynamic measurements was obtained using 2-dimensional (2D) echography. Physiological conditions were adjusted to a fixed heart rate of 70 beats⋅min−1, a flow of 6–7 l/min and an arterial pressure of 110/70 mmHg throughout all acquired measurements. Force transducer A dedicated force transducer was developed to measure the annular radial forces (Fig. 1C). The transducer consisted of a basal ring with 3 equidistantly placed arms. The outer diameter of its basal ring and the arms of the transducer was 20 mm and 19 mm, respectively. On each arm, 2 strain gauges were setup in a Wheatstone half-bridge configuration. The force transducer measured strain corresponding to luminal bending and extraluminal distension. Prior to each experiment, the strain measurements were calibrated to radial forces as previously described [19]. Each transducer arm measured the radial distension forces at annular level below the right/left coronary interleaflet triangle, right/non-coronary interleaflet triangle and left/non-coronary interleaflet triangle, providing the specific radial force development at each segment acting on the aortic annulus and the annuloplasty. Echography Echographic recordings of annular and leaflet dynamics were performed using a 2D-linear probe (GE 9 l-RS Probe, GE Vingmed Ultrasound AS, Horten, Norway). One short-axis view was obtained at the sinus plane and 3 long-axis views projecting through adjacent leaflets (right/left coronary interleaflet triangle, right/non-coronary interleaflet triangle and left/non-coronary interleaflet triangle) involving the whole aortic root. The echographic systole and diastole were defined from the maximum and minimum annular diameters. The acquired echographic parameters were annular base internal diameter at the level of the nadir of the 3 leaflets (systole and diastole); mid-sinus internal diameter (systole and diastole); coaptation length (length of direct leaflet contact); tenting area (area between the aortic annulus and the lower border of leaflet coaptation); geometric orifice area (planimetric opening area formed by the free edges of the leaflets in the systole [20]) and planimetric cross-sectional sinus area (entire area at the level of the sinuses). Data analysis The acquired data were analysed off-line using dedicated virtual instrumentation software (LabVIEW 11.0, National Instruments). The systolic and diastolic pressures were determined from maximum and minimum aortic pressures, whereas the maximum pressure gradient drop was calculated as the difference between the maximum ventricular pressure and maximum aortic pressure. The radial forces were defined as maximum–minimum force at each measuring site. Echographic data were analysed using OsiriX MD v8.5 (Pixmeo Sarl, Bernex, Switzerland). The echographic analysis was performed using inner-edge to inner-edge measurements [21]. The distensibility was defined as the difference between the systolic and diastolic diameters at the respective level. Radial forces were compared with the annular distensibility acquired from echography to evaluate the radial force development per millimetre of distension for each of the 3 groups defined as the force–distensibility ratio. Statistical analysis All data are presented as mean ± standard deviation and are based on 10 consecutive cardiac cycles for each aortic root. The repeated measurements for hydrodynamics and forces were analysed in a mixed model with nested random effects to take into account the repeated measurements on animals and anatomical location within animals. Following the mixed model, residuals were inspected for normality, and no reason was found to refute this. The statistical methods were provided by the Biostatistical Advisory Service (BIAS, Aarhus University, Denmark). The echographic parameters were analysed using the one-way analysis of variance with a Bonferroni post hoc test. All statistical comparisons were performed using Stata 13.0 (StataCorp LLC, Texas, USA), and P-values <0.05 were considered statistically significant. RESULTS Hydrodynamic results All aortic valves were competent at all time points, and the baseline hydrodynamic parameters are summarized in Table 1. There were no statistical differences regarding the hydrodynamics between groups. Table 1: Baseline hydrodynamics (n = 6) Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Baseline hydrodynamics with the force transducer attached inside the aortic annulus. Øannulus, ØSTJ: sample diameter of the intraluminal aortic annulus and sinotubular junction before surgical preparation; pdiastolic, psystolic: diastolic and systolic pressure determined from maximum and minimum aortic pressures; pgradient: systolic pressure drop over the valve measured as the difference between left ventricular and aortic pressure; Qmean: applied flow rate; SD: standard deviation. Table 1: Baseline hydrodynamics (n = 6) Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Native mean ± SD Ring mean ± SD Suture mean ± SD Qmean (l/min) 6.4 ± 0.4 6.4 ± 0.3 6.4 ± 0.2 psystolic (mmHg) 112 ± 2.5 110 ± 5 112 ± 2.5 pdiastolic (mmHg) 68 ± 2.6 66 ± 2.5 69 ± 2.5 pgradient (mmHg) 17.9 ± 6.1 22.8 ± 1.9 22.2 ± 8.9 Øannulus (mm) 21.2 ± 0.8 20.0 ± 0.8 20.3 ± 0.8 ØSTJ (mm) 20.0 ± 0.9 18.7 ± 0.5 19.3 ± 0.5 Baseline hydrodynamics with the force transducer attached inside the aortic annulus. Øannulus, ØSTJ: sample diameter of the intraluminal aortic annulus and sinotubular junction before surgical preparation; pdiastolic, psystolic: diastolic and systolic pressure determined from maximum and minimum aortic pressures; pgradient: systolic pressure drop over the valve measured as the difference between left ventricular and aortic pressure; Qmean: applied flow rate; SD: standard deviation. After removing the force transducer, the pressure gradient was unaffected in the suture group (23 ± 8.0 mmHg). However, the pressure gradient significantly decreased in the native (10.7 ± 2.6 mmHg, P = 0.01) and ring groups (19.2 ± 2.7 mmHg, P < 0.001), compared with measurements of the force transducer presented in Table 1. Apart from this, the hydrodynamics were unchanged after the removal of the force transducer. Echographic results The echographic data are summarized in Table 2, and a representative visualization of 1 aortic root from each group is shown in Fig. 3. Table 2: Echographic measurements Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns ns: not statistically significantly different; SD: standard deviation. Table 2: Echographic measurements Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns Native mean ± SD Ring mean ± SD Suture mean ± SD P-values Native vs ring Native vs suture Ring vs suture Long-axis view  Annulus diameter   Systole (mm) 19.6 ± 2.2 14.3 ± 2.9 16.9 ± 2.1 0.006 ns ns   Diastole (mm) 17.1 ± 2.2 12.8 ± 3.0 14.6 ± 2.0 0.021 ns ns   Distensibility (mm) 2.4 ± 0.8 1.5 ± 0.8 2.3 ± 0.3 ns ns ns  Sinus diameter   Systole (mm) 31.6 ± 1.4 27.4 ± 1.8 27.9 ± 1.1 <0.001 0.002 ns   Diastole (mm) 30.6 ± 1.7 27.5 ± 2.1 27.3 ± 1.8 0.036 0.025 ns   Distensibility (mm) 0.1 ± 0.1 0.0 ± 0.1 0.1 ± 0.1 ns ns ns Short-axis view  Geometric orifice area (cm2) 3.5 ± 0.5 1.5 ± 0.1 1.9 ± 0.3 <0.001 <0.001 ns  Sinus area systole (cm2) 8.8 ± 1.1 5.2 ± 0.7 6.0 ± 0.7 <0.001 <0.001 ns  Sinus area diastole (cm2) 7.9 ± 0.9 4.7 ± 0.6 5.6 ± 0.8 <0.001 <0.001 ns  Sinus area distensibility (cm2) 0.9 ± 0.2 0.5 ± 0.4 0.4 ± 0.1 0.038 0.011 ns ns: not statistically significantly different; SD: standard deviation. Figure 3: View largeDownload slide Representative echographic series from each group in the long-axis view (left panel) and the short-axis view (right panel) for the diastole and systole. Figure 3: View largeDownload slide Representative echographic series from each group in the long-axis view (left panel) and the short-axis view (right panel) for the diastole and systole. Long-axis views revealed a reduction in annular diameter in the procedure groups compared with the native aortic roots, although only the Dacron ring provided a statistically significant annular diameter reduction (Table 2). The relative annular distensibility was retained between all 3 groups (native 14%, ring 12% and suture 16%). No significant differences were found in the sinotubular junction diameter between groups. The geometric heights of each cusp measured echographically did not differ between groups (P-value ≥0.5). The short-axis view revealed a significant reduction in the geometric orifice area of 57% and 46% for the ring and suture groups, respectively, compared with the native group (Table 2). The planimetric cross-sectional area at sinus level was statistically significantly reduced by both procedures compared with the native group. Figure 4 depicts coaptation length and tenting area. The coaptation length increased significantly after both procedures compared with the native group corresponding to 40% by the suture (P = 0.01) and 32% by the ring (P = 0.04). As the coaptation length increased and annular dimensions decreased, the tenting area significantly decreased correspondingly in both procedure groups (P < 0.002). Figure 4: View largeDownload slide Valve geometry for each group. (A) Leaflet coaptation length was significantly increased in both procedure groups. (B) Tenting area was significantly decreased in both procedure groups. *P < 0.05 compared with the native group. Figure 4: View largeDownload slide Valve geometry for each group. (A) Leaflet coaptation length was significantly increased in both procedure groups. (B) Tenting area was significantly decreased in both procedure groups. *P < 0.05 compared with the native group. None of the examined echographic parameters indicated any significant differences between the 2 procedure groups. Force development The radial forces for each measuring site are presented in Fig. 5. Both procedures significantly reduced the radial force for each segment compared with the native group. The total radial forces were significantly lower in the procedure groups compared with the native group (ring 1.07 ± 0.45 N; suture 1.13 ± 0.39 N; native 3.55 ± 1.34 N, P < 0.001). However, no individual segmental differences were observed between the annular forces within each group. Figure 5: View largeDownload slide The difference between maximum and minimum radial forces at the annulus for each group in each segment. NL: non-coronary/left-coronary interleaflet triangle; RL: right/left coronary interleaflet triangle; RN: right/non-coronary interleaflet triangle. *P < 0.001 compared with the native group. Figure 5: View largeDownload slide The difference between maximum and minimum radial forces at the annulus for each group in each segment. NL: non-coronary/left-coronary interleaflet triangle; RL: right/left coronary interleaflet triangle; RN: right/non-coronary interleaflet triangle. *P < 0.001 compared with the native group. Force–distensibility ratio Figure 6 illustrates the ratio between the mean radial forces (ring 0.38 ± 0.16 N, suture 0.38 ± 0.12 N and native 1.18 ± 0.39 N, P < 0.001) and the annular distensibility. The suture group exhibited a significantly decreased force–distensibility ratio compared with the native group (P = 0.038), whereas there were no significant differences between ring vs native or ring vs suture groups. Figure 6: View largeDownload slide Combined radial forces and echography showing the force–distensibility ratio. The bars represent the radial force development per millimetre annular distension for each group. *P-value <0.04 compared with the native group. Figure 6: View largeDownload slide Combined radial forces and echography showing the force–distensibility ratio. The bars represent the radial force development per millimetre annular distension for each group. *P-value <0.04 compared with the native group. DISCUSSION In the present study, echography demonstrated that both annuloplasty procedures fulfilled their intended purpose. Both procedures significantly increased coaptation length and reduced tenting area in consistency with the results from other studies [10, 22–24]; however, a statistically significant downsizing of the annulus was only achieved with the Dacron ring. Furthermore, both annuloplasty procedures reduced the radial force development while preserving the relative annular distensibility similar to the native aortic annulus. However, the suture annuloplasty expresses a more flexible behaviour at the same radial forces when compared with the ring group, although not statistically significant compared with the ring group. This is illustrated by the significantly reduced force–distensibility ratio of the suture group when compared with the native group. Although these findings demonstrate the acute effect of the annuloplasty procedures, the Dacron ring has shown to preserve its size and distensibility in a recent 2-year follow-up study [10]. In this acute setup, the suture annuloplasty reduced the annular diameter; however, this was not statistically significant. Therefore, the downsizing capacity over time of the suture annuloplasty should be considered. Nevertheless, the suture annuloplasty has shown to improve valve stability, freedom from aortic regurgitation and reoperation in patients with regurgitant bicuspid valves when compared with repair procedure without a suture annuloplasty at 5-year follow up [5]. However, in clinical assessment of complex surgery, such as aortic root repair, it is difficult to distinguish and interpret the isolated impact of the annuloplasty due to several coexisting factors such as anatomy, comorbidities and pathology. Furthermore, when several parameters are changed during surgery as part of the repair procedure by different surgeons with different expertise and approaches, results may not be entirely comparable. These issues are overcome in this in vitro study, which is the first to compare the isolated functional and biomechanical effect of the PTFE suture annuloplasty and the Dacron ring annuloplasty to the native aortic root under standardized conditions with the same operator. We hypothesized that the Dacron ring would show a more pronounced mechanical stabilizing effect than the suture annuloplasty assessed from the force development, but this has not been confirmed in the present study. In the long-axis echographic view, the annular diameter was downsized by both procedure groups, although the annular distension was similar between all groups. These results indicate that both annuloplasty procedures support the aortic annulus equally and efficiently immediately after surgery, without impairing root dynamics, which is a drawback of the reimplantation procedure. However, the short-axis view of the aortic annulus (Fig. 3) demonstrated a perfect circle in the ring group, whereas the suture group displayed an irregular circle similar to the native annulus. This difference might explain why the annulus diameter is significantly decreased by the ring group—and not by the suture group—when compared with the native group. The distensibility of the sinuses was also similar between groups in the long-axis view. However, when examined in the short-axis view, the sinus area distension was significantly smaller in the procedure groups compared with the native group. This discrepancy can be explained by the measuring method in different projections. The cross-sectional distension likely occurs in several segments, which is difficult to measure in one long-axis view. Additionally, the 2D long-axis view presumes a circular shape of the left ventricular outflow tract area, which often results in an underestimation of the annular diameter. This could have been overcome using 3-dimensional echography, enabling simultaneous display of the aortic root in both the short-axis view and the long-axis view [25]. Furthermore, the aortic root tends to change from a clover shape in the diastole to a cylindrical shape during ejection of blood, which has previously been described [26]. Although echography showed similar annular distension for all groups in the study, the force transducer revealed a significantly reduced radial force development in the procedure groups compared with the native group. When combining the findings of annular distension and radial forces (Fig. 6), it seems that the annuloplasty absorb and reduce the distension forces while preserving root dynamics. The radial forces were similar between the procedure groups although the annular diameters differed, suggesting that the annular diameter does not influence the radial forces, as much as the annuloplasty itself, by absorbing the forces. Absorption of radial forces is indicative for an external supporting mechanism in both annuloplasty groups and, hence, protection of the vulnerable aortic root, where it is essential to avoid redilation. These results indicate that the annuloplasty procedures are excellent supportive techniques for the potential avoidance of redilation, which is the main limitation of the remodelling procedure without an added annuloplasty—especially as the Dacron ring has shown not to dilate over time. This supports the concept of a protective annuloplasty in root repair in agreement with recent follow-up studies [5, 7]. The force–distensibility ratio was lower in the procedure groups compared with the native aortic roots, although only significant for the suture group. This may be due to the larger distensibility of the suture group compared with the ring group, although this was not shown to be significant. The force–distensibility ratio suggests that the suture group is capable of distending more throughout the cardiac cycle while maintaining the same low radial force development as seen in the ring group. However, the findings of the force–distensibility ratio could also be due to a more extensive downsizing in the Dacron group. We deliberately chose the sizing criterion made by Lansac et al. [11] derived from dilated aortic roots as the basis of choice for the Dacron ring size. It can be argued that a bigger size of the Dacron rings should have been used when compared with the sizing formula of Kerchove et al. [22] used for healthy porcine aortic roots. Another explanation is that the sutures of the Dacron ring fixates the ring and reduces the functional ring diameter more than expected. For the suture procedure, it could be speculated that a smaller Hegar dilator should be used to align the intervention groups; however, we chose to perform the study as close to the real clinical procedure. Nevertheless, these results indicate that the Dacron ring might reduce the annular distension more than the suture group, although not significantly. Overall, both the suture annuloplasty and ring annuloplasty seem to reduce the annular diameter efficiently and improve the coaptation geometry immediately after surgery without significant differences between the 2 types of annuloplasty procedures. What needs to be established in the future is long-term durability of each procedure. As the acute effect of both suture and ring seems comparable in this in vitro study, there is no evidence towards one method being immediately technically superior to the other; hence, the choice of annuloplasty procedure relies on the personal preference of the surgeon until long-term clinical durability studies are performed to clarify the impact of the annuloplasty procedures over time. Limitations The annuloplasty procedures were evaluated in an in vitro setup using healthy porcine aortic roots. The lack of aortic root pathology and the differences between porcine and human anatomy are limitations associated with a study such as this. Even though fresh aortic tissue was used, the rest of the in vitro system comprised acrylic chambers mimicking the circulatory system. Meticulous preparation was made to fine tune compliance and hydrodynamic impedances to obtain physiological pressure and flow waveforms; however, the in vitro model still differs from an in vivo situation. The presented results could differ if the study was made in vivo and even in humans, and hence, long-term clinical or pathological in vivo porcine studies are needed. Nevertheless, a study on healthy aortic roots is more reproducible, and it is more apparent to evaluate techniques made by the same operator in homogenous aortic roots. The dedicated force transducer was designed to interfere minimally with the hydrodynamic flow. However, interference cannot be avoided entirely. We expect any interference induced by the transducer to be equal between groups, and therefore, it does not affect our results as the measurements are used for comparison between groups. As there was no electrocardiogram, it was not technically possible to make a direct correlation between the time points of the force measurements and the echography. Therefore, we defined the systole and diastole as the maximum and minimum forces, and the maximum and minimum diameters of the echographic annular diameters. Finally, as the echographic parameters were measured visually, data analysis was blinded to the operator to avoid operator-induced bias. Intraobserver and interobserver variability tests were performed, and the differences were satisfactory (<10%). CONCLUSION From this in vitro study, a comprehensive biomechanical comparison of the Dacron ring and PTFE suture annuloplasty procedures was obtained. The Dacron ring annuloplasty and suture annuloplasty effectively downsized the annular diameter although only statistically significant by the Dacron ring. Furthermore, both procedures reduced the radial force development in the aortic annulus while maintaining relative annular distensibility similar to the native aortic root. Hence, both annuloplasty techniques preserve the dynamics of the aortic annulus while providing external support as intended, indicating that the material is less important than the surgical technique, when choosing an annuloplasty procedure for the dilated aortic root in the acute setting. Funding This work was supported by the Graduate School, Health, Aarhus University and Købmand Sven Hansen og Hustru Ina Hansens fond. Conflict of interest: none declared. REFERENCES 1 David TE. Aortic root aneurysms: remodeling or composite replacement? Ann Thorac Surg 1997 ; 64 : 1564 – 8 . 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Aortic root numeric model: annulus diameter prediction of effective height and coaptation in post-aortic valve repair . J Thorac Cardiovasc Surg 2013 ; 145 :406–11.e1. 25 Lang RM , Badano LP , Tsang W , Adams DH , Agricola E , Buck T et al. . EAE/ASE recommendations for image acquisition and display using three-dimensional echocardiography . Eur Heart J Cardiovasc Imaging 2012 ; 13 : 1 – 46 . Google Scholar CrossRef Search ADS PubMed 26 Cheng A , Dagum P , Miller DC. Aortic root dynamics and surgery: from craft to science . Philos Trans R Soc Lond B Biol Sci 2007 ; 362 : 1407 – 19 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

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Interactive CardioVascular and Thoracic SurgeryOxford University Press

Published: Jun 1, 2018

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