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Leaflet kinematics after the Yacoub and Florida-sleeve operations: results of an in vitro study

Leaflet kinematics after the Yacoub and Florida-sleeve operations: results of an in vitro study Abstract Open in new tabDownload slide Open in new tabDownload slide OBJECTIVES The Florida-sleeve is a valve-sparing technique that causes minimal interference to leaflet kinematics and aortic root dynamism. The aim of this in vitro study was to evaluate the effects of the Florida-sleeve and Yacoub techniques on aortic leaflet kinematics. METHODS Two groups of 6 whole porcine hearts were treated with either the Florida-sleeve technique or the Yacoub technique and tested in a pulsatile loop. Valve fluid dynamics, coronary flow analysis and valve echocardiograms were performed both before and after the procedures. RESULTS Both procedures showed no difference in rapid valve opening time as compared with their respective baseline values. The Florida-sleeve procedure showed a shorter slow closing time (192 ± 19 ms vs baseline 244 ± 14 ms, P = 0.016) and increased slow closing velocity (−1.5 ± 0.4 cm/s vs baseline −0.8 ± 0.4 cm/s, P = 0.038). In the rapid valve closing phase, the Yacoub procedure showed a trend towards slower closing valve velocity (−16 ± 9 cm/s vs baseline −25 ± 9 cm/s, P = 0.07). The Yacoub procedure showed larger leaflet displacement at the end of the slow valve closing time that was 2.0 ± 0.5 cm vs baseline 1.5 ± 0.3 cm, P = 0.044. When comparing the Florida-sleeve and Yacoub procedures, the former showed statistically significant shorter slow valve closing time (P = 0.017). CONCLUSIONS This study showed that the Florida-sleeve technique alters the slow closing phase of the aortic valve leaflet kinematics when compared with both the normal baseline and Yacoub procedure, while the latter showed a larger leaflet displacement before the rapid closing valve phase. Adult, Aortic valve sparing, Leaflet kinematics INTRODUCTION Aortic valve (AV)-sparing operations are widely accepted techniques to treat aortic root (AR) aneurysms with or without AV regurgitation. Long-term follow-up results have confirmed the efficacy and safety of these procedures [1]. The Yacoub technique, or ‘remodelling’ procedure, is considered the most physiological method with less interference to the AR dynamics and less alteration of leaflet kinematics when compared with the reimplantation technique [2–4]. This is thought to be associated with low degree of leaflet stress with, possibly, a long-term benefit on AV function durability [5]. In the last decade, a new technique known as the Florida-sleeve procedure, has been proposed that appears to be effective in treating AR disease [6–11]. This technique aims to restore a near normal AR size, geometry and possibly dynamics through the preservation of the ‘leaflet-sinus’ unit, i.e. the continuity between the leaflet and sinus of Valsalva, by sheathing the AR with a sinus-shaped graft. AV leaflet kinematics depends on AR geometry [2, 12, 13] and dynamics [4, 14, 15] as well as transvalvular flow, heart rate, aortic pressure and coronary flow [16, 17]. Valve-sparing procedures require an inelastic artificial graft for the reconstruction of the sinuses of Valsalva, which interferes with the AR dynamics and, in turn, can alter the leaflet kinematics [2, 3]. Thus, the extent of the kinematic disruption may be an indicator of the biomechanical comportment of the AR [14, 15]. In this study, we aimed to evaluate in an ex vivo set-up, the effects of the Florida-sleeve and Yacoub techniques on aortic leaflet kinematics, fluid dynamics and coronary perfusion. MATERIALS AND METHODS Passive beating heart platform Figure 1 shows a schematic representation of the mock loop. This consisted of a porcine heart stimulated by a computer-controlled volumetric pump able to replicate left ventricular flow waveforms, and of an adjustable hydraulic afterload mimicking the input impedance of systemic circulation. The platform is described in detail elsewhere [18]. Figure 1: Open in new tabDownload slide Schematic representation of the mock loop with a porcine heart (A) activated by a computer-controlled volumetric pump (B) able to replicate left ventricular flow waveforms and an adjustable hydraulic afterload (C) mimicking the hydraulic input impedance of the systemic circulation and (D) constant atrial pressure. Figure 1: Open in new tabDownload slide Schematic representation of the mock loop with a porcine heart (A) activated by a computer-controlled volumetric pump (B) able to replicate left ventricular flow waveforms and an adjustable hydraulic afterload (C) mimicking the hydraulic input impedance of the systemic circulation and (D) constant atrial pressure. Coronary perfusion simulator Coronary perfusion was evaluated using the coronary impedance simulator (CIS) module of the experimental set-up. The CIS consisted of 2 adjustable hydraulic loops designed to reproduce the impedance of left and right coronary circulation during the systole and diastole. The loops were connected to the left and right coronary ostia of the AR of the heart sample. A detailed description of the CIS has been published elsewhere [19]. Sample preparation A total of 12 whole porcine hearts with 23-mm ventricular-aortic junction were selected. These samples were randomly assigned to be treated by either the Yacoub or the Florida-sleeve technique (n = 6 in each group). Both techniques were based on the Cardioroot prosthesis graft technique (MAQUET Cardiovascular LLC, Wayne, NJ, USA). Experimental design Each heart sample was first tested untreated (baseline condition) and then retested after the surgery (post-treatment conditions). Each sample was tested simulating the rest conditions (stroke volume: 70 ml, heart rate: 60 bpm, systolic ejection time: one-third of the entire cardiac cycle, mean systemic pressure: 100 mmHg). At baseline conditions, the CIS was set to obtain close to physiological left/right diastolic/systolic mean flow rate values [19]. The same settings were used for post-treatment conditions, which allowed assessment of possible changes in coronary perfusion induced by the treatments. Haemodynamics was evaluated with a transit-time flowmeter (HT110R equipped with 6PXL probe and TS410 equipped with 2 4PXN probes for aortic and coronary flow measurements, respectively; Transonic System, Inc., Ithaca, NY, USA) and 3 pressure transducers (PC140 series, Honeywell Inc., Morristown, NJ, USA): one upstream AV in the left ventricle, one downstream the AV and a third one placed at the inlet section of the hydraulic afterload (Pven, Pao, Psyst, respectively; Fig. 1). The haemodynamic signals were acquired at a sampling rate of 200 Hz via an A/D acquisition board. Echocardiographic data acquisition and measurements Ultrasound acquisitions were performed in M-mode at 23 Hz and recorded at a speed of 150 mm/s (Philips IE 33 with transoesophageal probe CX7-2t) to evaluate opening and closing kinematics of the right aortic leaflets and the non-coronary leaflets. The leaflet movements in systole were divided into 3 phases: rapid valve opening time (RVOT), slow valve closing time (SVCT) and rapid valve closing time [2]. The maximal leaflet displacement at the end of RVOT and SVCT were labelled D1 and D2, respectively. The slow closing displacement was expressed in percentage as (D1 − D2/D1) × 100. The average value of 3 consecutive cycles was calculated for each of the abovementioned parameters. Rapid valve opening velocity, slow valve closing velocity and the rapid valve closing velocity were calculated as the ratios between D1 and RVOT, slow closing displacement and SVCT and D2 and rapid valve closing time, respectively. Effective height was measured in 2-dimensional B-mode long-axis view by measuring the distance between the annulus and highest coaptation leaflet point at peak diastole. Statistical analysis After confirming normality of data distribution by the Shapiro–Wilk test, data were reported as mean ± standard deviation with 95% confidence interval values. The continuous variables of the post-treatment conditions were tested with that of pretreatment using the paired t-test, while the comparison between sleeve and Yacoub techniques was performed using the unpaired t-test. P-value <0.05 was considered to indicate statistical significance. All statistical analyses were performed using the Systat 13, Systat Software (Inc.), San Jose (CA) USA. RESULTS Fluid dynamics The fluid dynamics data are reported in Table 1. No statistical differences were found when comparing pre- and post-treatment data, except for the stroke volume following the Florida-sleeve procedure, which decreased from 74 ± 4 ml measured in the untreated samples to 67 ± 5 ml (P < 0.001), and could cause underestimation of the pressure gradient at post-treatment. When the 2 surgical techniques were compared, no statistical differences were found. Table 1: Fluid dynamic results . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 LCF: left coronary flow; RCF: right coronary flow; SV: stroke volume. Open in new tab Table 1: Fluid dynamic results . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 LCF: left coronary flow; RCF: right coronary flow; SV: stroke volume. Open in new tab Leaflet kinematics The leaflet kinematics data are reported in Table 2. Both surgical techniques showed no difference in RVOT compared with the respective baseline value. The Florida-sleeve procedure showed a shorter SVCT (192 ± 19 ms vs  244± 14 ms; P = 0.016) and higher slow valve closing velocity (−1.5 ± 0.4 cm/s vs –0.8 ± 0.4 cm/s; P = 0.038) than the respective baseline values. In the rapid valve closing phase, the Yacoub procedure showed a trend to slower closing valve velocity (rapid valve closing velocity) with −16 ± 9 cm/s compared with the baseline −25 ± 9 cm/s (P = 0.07). Furthermore, the Yacoub procedure showed larger leaflet displacement at the end of the SVCT with a D2 value of 2.0 ± 0.5 cm compared with the baseline value of 1.5 ± 0.3 cm (P = 0.044). Upon comparing the Florida-sleeve and Yacoub procedures, the former showed statistically significant shorter SVCT (P = 0.017). Neither technique affected the effective height (Table 2), and no systolic contact was observed between the aortic cusps and aortic wall. Table 2: Leaflets kinematics . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 a P = 0.017 between Yacoub versus sleeve. D: diameter; eH: effective height; RVCT: rapid valve closing time; RVCV: rapid valve closing velocity; RVOT: rapid valve opening time; RVOV: rapid valve opening velocity; SCD: slow closing displacement; SVCT: slow valve closing time; SVCV: slow valve closing velocity.[] Open in new tab Table 2: Leaflets kinematics . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 a P = 0.017 between Yacoub versus sleeve. D: diameter; eH: effective height; RVCT: rapid valve closing time; RVCV: rapid valve closing velocity; RVOT: rapid valve opening time; RVOV: rapid valve opening velocity; SCD: slow closing displacement; SVCT: slow valve closing time; SVCV: slow valve closing velocity.[] Open in new tab Comment The results of this experimental study showed that while neither tested procedure disrupted the dynamics of valve opening, both affected the valve closing phase. In the Florida-sleeve procedure, the rapid valve closing phase was triggered earlier than the baseline value, while the Yacoub procedure affected the leaflet displacement at the end of SVCT. The findings for both procedures with respect to valve fluid dynamics (gradients and flow curve shape) and coronary flows remained similar. The AR has a well-defined geometry and, functionally, it may be conceptualized as organized in 2 compartments: 1 proximal, i.e. beneath the AV and subjected to the ventricular dynamics, and 1 distal, i.e. above the AV, and subjected to aortic haemodynamics. In normal ARs, these 2 compartments interact with each other throughout the cardiac cycle, storing and releasing elastic potential energy that generates a complex, and yet finely harmonized pattern of displacements and deformations of their components [20–23]. Because AV-sparing procedures require the use of artificial grafts for the AR reconstruction, the graft stiffness may alter the complex biomechanical equilibrium between the 2 compartments with an impact on valve kinematics and, ultimately, on leaflet stress [24]. In this study, by maintaining the anatomical continuity between the AR and the surrounding structures in addition to the simulating coronary perfusion, we could explore the disruption caused by the sparing valve on leaflet kinematics. To our best knowledge, the Florida-sleeve technique has never been evaluated in in vitro settings, and the results could provide some insight for clinical practice, given that this technique is gaining more popularity [6–11]. Mechanics of valve opening The opening phase of a normal AV is a highly dynamic phenomenon, wherein the valve leaflets change position and geometric configuration [25]. If any disruption takes place during this phase, high flexural stress concentration may occur in specific areas [4, 5, 24], ultimately leading to irreversible damage. The opening phase may be split into 2 parts, where the first part occurs in the isovolumetric contraction interval during which, despite the flow still being nil, the valve begins to unfold accounting for up to 20% of the maximal opening [11, 20–23, 26]. This part of the opening phase is highly dependent on passive mechanical properties of the AR, mainly to the outward movement of the commissures, owing to leaflets unloading, as well as the elastic properties of the leaflets [20]. Indeed, the unfolding can be suppressed if the motion of the commissures is restricted or the leaflets are stiffened, causing the shortening of the RVOT interval as a result [11]. The second part of the opening phase is due to the thrust from the blood flow, which displaces the leaflets to their maximal aperture position [20]. Our findings suggested that the type of sparing procedure does not influence the valve opening (Table 2 and Fig. 2) in terms of time, leaflets velocity and maximal leaflets displacement, when compared with their baseline values. This implies that both procedures may preserve a normal outward displacement of the commissures, as has already been reported [3, 11, 24]. As for the Yacoub procedure, our results were consistent with those reported by Fries et al. [3], although our data showed shorter RVOT intervals, which might be explained by the different experimental set-up. Figure 2: Open in new tabDownload slide Aortic leaflet displacement during the systolic ejection period. (A) Comparison of leaflets displacement between the basal and after the Yacoub technique. (B) Comparison of leaflets displacement between the basal and after the Florida-sleeve technique. Figure 2: Open in new tabDownload slide Aortic leaflet displacement during the systolic ejection period. (A) Comparison of leaflets displacement between the basal and after the Yacoub technique. (B) Comparison of leaflets displacement between the basal and after the Florida-sleeve technique. Mechanics of the valve closure The dynamics of valve closing phase is a complex phenomenon that, in turn, may be divided into 2 parts. The first part is featured by a slow movement of the leaflets towards the AR axis, while the second phase is characterized by a fast, quasi impulsive movement of the leaflets which ends with complete valve closure. Similar to the opening, the closing phase is driven by the time variation of the pressure difference across the leaflets, and additionally depends upon mechanical properties of the AR structures [15, 20], coronary flow [16, 17] and geometry of the sinuses of Valsalva with vortexes formation. Our findings, as for the Yacoub technique during the closure phase, are in agreement with those reported by Fries et al. [3] and confirmed that this technique does not significantly influence the time interval and velocity of both slow and rapid closing phases, but rather affects the leaflets position as shown by the breadth of the leaflets displacement distance or D2. In this regard, we can speculate that the stiffness of the graft and the unnatural shape of the sinus of Valsalva might be the reason for these findings. Indeed, the position of the leaflets, in this phase, depends upon the trans-leaflet pressure balance affected by the amplitude and the strength of vortexes generated in the sinuses of Valsalva. Conversely, the Florida-sleeve technique showed a significantly shorter and faster slow closing phase than the respective baseline values. This could be explained by the restrained effect on the ventricular–arterial junction related to the technique [11]. Indeed, the Florida-sleeve could have triggered an earlier valve closure by reducing the outward movement of the ventricular–arterial junction [27, 28]. This finding is corroborated by the unaffected closure phase in the Yacoub technique, wherein the ventricular–arterial junction dynamics tend to be more preserved [2] unless a restriction is imposed by implanting an external ring or a Gore-Tex stitch. The possible implications of these differences on long-term clinical results are not obvious. In the case of Florida-sleeve, these deviations from the normal appear due to the annulus movement restriction imposed by the technique itself. Nevertheless, stabilization of the annulus prevents its dilatation over time and thereby also prevents valve function failure [7]. In this regard, long-term clinical studies are needed. If the annulus is left untreated in the Yacoub technique, it may dilate and affect the valve function in some cases. After a further flow deceleration, the axial flow reverses its direction, triggering rapid closure of the valve. However, neither sparing procedure seemed to affect the rapid valve closure phase. The rapid movement of leaflets in this phase was reasonably driven mainly by transvalvular fluid dynamics, with a negligible role of the biological structure involved. The geometry of the leaflets’ resting position, or effective height, was unaffected by either technique. The Yacoub versus Florida-sleeve technique No substantial inter-technique differences were found with respect to leaflet dynamics, except for a shorter slow closing time with the Florida-sleeve (Table 2). We speculated that this was likely associated with the movement restriction at the level of ventricular–arterial junction discussed in the previous paragraph. Moreover, kinematic assessment of the aortic leaflets in AR treated with the David technique by using a straight graft has suggested significant shortening of the rapid valve opening and closing phases with respect to normal valves [3, 12, 13, 28]. This is not the case for both the Yacoub and Florida-sleeve techniques as evaluated in this work. Respecting the geometrical relationships and dynamisms of the AR is paramount to minimizing mechanical stress, in the leaflets, in both opening and closing phases. That may have a favourable impact on the long-term AV function durability. More specifically, preserving the first opening phase during the isovolumetric contraction, allows leaflets to assume a more favourable geometry while, in the second opening phase, the preservation of the AR dynamics allows the leaflets to be accommodated with a more appropriate geometry [14, 21] which minimizes flexural stress and prevents the leaflets from ramming into the sinus of Valsalva. During diastole, the presence of the sinuses of Valsalva may allow the leaflets to lodge with a more proper geometry, reducing their tensile stress [11]. In addition, in case of anatomical integrity of the ‘leaflet-sinus unit’ as in the Florida-sleeve, which implies an anatomical and mechanical continuity, the forces acting on leaflet may partly be transferred into the adjacent native sinus and, as such, reducing the tensile stress experienced by the leaflet [11, 21]. The benefits of preserving the sinuses of Valsalva from the kinematic point of view provided indirectly by this study are of interest and may complement the fluid dynamic findings [29]. CONCLUSION In this ex vivo set-up, the Florida-sleeve technique appeared to alter the slow closing phase of the AV leaflet kinematics when compared with both the normal baseline and Yacoub procedure, while the latter showed a larger displacement of the leaflets before the rapid closing valve phase. Long-term clinical studies are required to confirm any impact on valve durability, by these different leaflet kinematics patterns. Limitations The main limitation of this study concerns the use of an ex vivo heart sample, which does not present the natural contractility that might influence the AR dynamic changes within the cardiac cycle. In a clinical scenario, only the initial phase of the systole is characterized by AR expansion, whereas in the adopted experimental set-up, the AR was subjected to an expansion throughout the whole systole. The subvalvular portion of the porcine model has more muscular asymmetry than that of humans. However, we compared the porcine ARs pre- and post-treatments to mitigate any effect related to the shape of the LVOT. Because of the relatively small sample size, some differences between the groups might have been undetected. Conflict of interest: none declared. Author contributions Giordano Tasca: Conceptualization; Data curation; Formal analysis; Methodology; Writing—original draft. Michal Jaworek: Conceptualization; Data curation; Formal analysis. Federico Lucherini: Data curation; Formal analysis; Writing—review & editing. Francesco Trinca: Investigation. Paola Redaelli: Investigation; Writing—review & editing. Carlo Antona: Writing—review & editing. Riccardo Vismara: Conceptualization; Methodology; Supervision; Writing—review & editing. Reviewer information European Journal of Cardio-Thoracic Surgery thanks Diana Aicher, Rüdiger Autschbach, Stefano Benussi and the other, anonymous reviewer(s) for their contribution to the peer review process of this article. REFERENCES 1 David TE. Aortic valve sparing operations: outcomes at 20 years . Ann Cardiothorac Surg 2013 ; 2 : 24 – 9 . Google Scholar PubMed OpenURL Placeholder Text WorldCat 2 Leyh RG Schmidtke C Sievers HH Yacoub MH. Opening and closing characteristics of the aortic valve after different types of valve-preserving surgery . Circulation 1999 ; 100 : 2153 – 60 . Google Scholar Crossref Search ADS PubMed WorldCat 3 Fries R Graeter T Aicher D Reul H Schmitz C Böhm M et al. In vitro comparison of aortic valve movement after valve-preserving aortic replacement . J Thorac Cardiovasc Surg 2006 ; 132 : 32 – 7 . Google Scholar Crossref Search ADS PubMed WorldCat 4 Soncini M Votta E Zinicchino S Burrone V Mangini A Lemma M et al. Aortic root performance after valve sparing procedure: a comparative finite element analysis . Med Eng Phys 2009 ; 31 : 234 – 43 . Google Scholar Crossref Search ADS PubMed WorldCat 5 Robicsek F Thubrikar MJ Fokin AA. Cause of degenerative disease of the trileaflet aortic valve: review of subject and presentation of a new theory . Ann Thorac Surg 2002 ; 73 : 1346 – 54 . Google Scholar Crossref Search ADS PubMed WorldCat 6 Gamba A Tasca G Giannico F Lobiati E Skouse D Galanti A et al. 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Comparison of distensibility of the aortic root and cusp motion after aortic root replacement with two reimplantation techniques: Valsalva graft versus tube graft . Interact CardioVasc Thorac Surg 2006 ; 6 : 177 – 81 . Google Scholar Crossref Search ADS WorldCat 14 Robicsek F Thubrikar MJ. Role of sinus wall compliance in aortic leaflet function . Am J Cardiol 1999 ; 84 : 944 – 6 . Google Scholar Crossref Search ADS PubMed WorldCat 15 Sripathi VC Kumar RK Balakrishnan KR. Further insights into normal aortic valve function: role of a compliant aortic root on leaflet opening and valve orifice area . Ann Thorac Surg 2004 ; 77 : 844 – 51 . Google Scholar Crossref Search ADS PubMed WorldCat 16 Moore BL Dasi LP. Coronary flow impacts aortic leaflets mechanics and aortic sinus hemodynamics . Ann Biomed Eng 2015 ; 43 : 2231 – 41 . Google Scholar Crossref Search ADS PubMed WorldCat 17 Cao K Sucosky P. Aortic valve leaflet wall shear stress characterization revisited impact of coronary flow . 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Novel insights by 4D flow imaging on aortic flow physiology after valve-sparing root replacement with or without neosinuses . Interact CardioVasc Thorac Surg 2018 ; 26 : 957 – 64 . Google Scholar Crossref Search ADS PubMed WorldCat ABBREVIATIONS ABBREVIATIONS AR Aortic root AV Aortic valve CIS Coronary impedance simulator RVOT Rapid valve opening time SCD Slow closing displacement SVCT Slow valve closing time © The Author(s) 2020. 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/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png European Journal of Cardio-Thoracic Surgery Oxford University Press

Leaflet kinematics after the Yacoub and Florida-sleeve operations: results of an in vitro study

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Publisher
Oxford University Press
Copyright
Copyright © 2021 European Association for Cardio-Thoracic Surgery
ISSN
1010-7940
eISSN
1873-734X
DOI
10.1093/ejcts/ezaa370
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See Article on Publisher Site

Abstract

Abstract Open in new tabDownload slide Open in new tabDownload slide OBJECTIVES The Florida-sleeve is a valve-sparing technique that causes minimal interference to leaflet kinematics and aortic root dynamism. The aim of this in vitro study was to evaluate the effects of the Florida-sleeve and Yacoub techniques on aortic leaflet kinematics. METHODS Two groups of 6 whole porcine hearts were treated with either the Florida-sleeve technique or the Yacoub technique and tested in a pulsatile loop. Valve fluid dynamics, coronary flow analysis and valve echocardiograms were performed both before and after the procedures. RESULTS Both procedures showed no difference in rapid valve opening time as compared with their respective baseline values. The Florida-sleeve procedure showed a shorter slow closing time (192 ± 19 ms vs baseline 244 ± 14 ms, P = 0.016) and increased slow closing velocity (−1.5 ± 0.4 cm/s vs baseline −0.8 ± 0.4 cm/s, P = 0.038). In the rapid valve closing phase, the Yacoub procedure showed a trend towards slower closing valve velocity (−16 ± 9 cm/s vs baseline −25 ± 9 cm/s, P = 0.07). The Yacoub procedure showed larger leaflet displacement at the end of the slow valve closing time that was 2.0 ± 0.5 cm vs baseline 1.5 ± 0.3 cm, P = 0.044. When comparing the Florida-sleeve and Yacoub procedures, the former showed statistically significant shorter slow valve closing time (P = 0.017). CONCLUSIONS This study showed that the Florida-sleeve technique alters the slow closing phase of the aortic valve leaflet kinematics when compared with both the normal baseline and Yacoub procedure, while the latter showed a larger leaflet displacement before the rapid closing valve phase. Adult, Aortic valve sparing, Leaflet kinematics INTRODUCTION Aortic valve (AV)-sparing operations are widely accepted techniques to treat aortic root (AR) aneurysms with or without AV regurgitation. Long-term follow-up results have confirmed the efficacy and safety of these procedures [1]. The Yacoub technique, or ‘remodelling’ procedure, is considered the most physiological method with less interference to the AR dynamics and less alteration of leaflet kinematics when compared with the reimplantation technique [2–4]. This is thought to be associated with low degree of leaflet stress with, possibly, a long-term benefit on AV function durability [5]. In the last decade, a new technique known as the Florida-sleeve procedure, has been proposed that appears to be effective in treating AR disease [6–11]. This technique aims to restore a near normal AR size, geometry and possibly dynamics through the preservation of the ‘leaflet-sinus’ unit, i.e. the continuity between the leaflet and sinus of Valsalva, by sheathing the AR with a sinus-shaped graft. AV leaflet kinematics depends on AR geometry [2, 12, 13] and dynamics [4, 14, 15] as well as transvalvular flow, heart rate, aortic pressure and coronary flow [16, 17]. Valve-sparing procedures require an inelastic artificial graft for the reconstruction of the sinuses of Valsalva, which interferes with the AR dynamics and, in turn, can alter the leaflet kinematics [2, 3]. Thus, the extent of the kinematic disruption may be an indicator of the biomechanical comportment of the AR [14, 15]. In this study, we aimed to evaluate in an ex vivo set-up, the effects of the Florida-sleeve and Yacoub techniques on aortic leaflet kinematics, fluid dynamics and coronary perfusion. MATERIALS AND METHODS Passive beating heart platform Figure 1 shows a schematic representation of the mock loop. This consisted of a porcine heart stimulated by a computer-controlled volumetric pump able to replicate left ventricular flow waveforms, and of an adjustable hydraulic afterload mimicking the input impedance of systemic circulation. The platform is described in detail elsewhere [18]. Figure 1: Open in new tabDownload slide Schematic representation of the mock loop with a porcine heart (A) activated by a computer-controlled volumetric pump (B) able to replicate left ventricular flow waveforms and an adjustable hydraulic afterload (C) mimicking the hydraulic input impedance of the systemic circulation and (D) constant atrial pressure. Figure 1: Open in new tabDownload slide Schematic representation of the mock loop with a porcine heart (A) activated by a computer-controlled volumetric pump (B) able to replicate left ventricular flow waveforms and an adjustable hydraulic afterload (C) mimicking the hydraulic input impedance of the systemic circulation and (D) constant atrial pressure. Coronary perfusion simulator Coronary perfusion was evaluated using the coronary impedance simulator (CIS) module of the experimental set-up. The CIS consisted of 2 adjustable hydraulic loops designed to reproduce the impedance of left and right coronary circulation during the systole and diastole. The loops were connected to the left and right coronary ostia of the AR of the heart sample. A detailed description of the CIS has been published elsewhere [19]. Sample preparation A total of 12 whole porcine hearts with 23-mm ventricular-aortic junction were selected. These samples were randomly assigned to be treated by either the Yacoub or the Florida-sleeve technique (n = 6 in each group). Both techniques were based on the Cardioroot prosthesis graft technique (MAQUET Cardiovascular LLC, Wayne, NJ, USA). Experimental design Each heart sample was first tested untreated (baseline condition) and then retested after the surgery (post-treatment conditions). Each sample was tested simulating the rest conditions (stroke volume: 70 ml, heart rate: 60 bpm, systolic ejection time: one-third of the entire cardiac cycle, mean systemic pressure: 100 mmHg). At baseline conditions, the CIS was set to obtain close to physiological left/right diastolic/systolic mean flow rate values [19]. The same settings were used for post-treatment conditions, which allowed assessment of possible changes in coronary perfusion induced by the treatments. Haemodynamics was evaluated with a transit-time flowmeter (HT110R equipped with 6PXL probe and TS410 equipped with 2 4PXN probes for aortic and coronary flow measurements, respectively; Transonic System, Inc., Ithaca, NY, USA) and 3 pressure transducers (PC140 series, Honeywell Inc., Morristown, NJ, USA): one upstream AV in the left ventricle, one downstream the AV and a third one placed at the inlet section of the hydraulic afterload (Pven, Pao, Psyst, respectively; Fig. 1). The haemodynamic signals were acquired at a sampling rate of 200 Hz via an A/D acquisition board. Echocardiographic data acquisition and measurements Ultrasound acquisitions were performed in M-mode at 23 Hz and recorded at a speed of 150 mm/s (Philips IE 33 with transoesophageal probe CX7-2t) to evaluate opening and closing kinematics of the right aortic leaflets and the non-coronary leaflets. The leaflet movements in systole were divided into 3 phases: rapid valve opening time (RVOT), slow valve closing time (SVCT) and rapid valve closing time [2]. The maximal leaflet displacement at the end of RVOT and SVCT were labelled D1 and D2, respectively. The slow closing displacement was expressed in percentage as (D1 − D2/D1) × 100. The average value of 3 consecutive cycles was calculated for each of the abovementioned parameters. Rapid valve opening velocity, slow valve closing velocity and the rapid valve closing velocity were calculated as the ratios between D1 and RVOT, slow closing displacement and SVCT and D2 and rapid valve closing time, respectively. Effective height was measured in 2-dimensional B-mode long-axis view by measuring the distance between the annulus and highest coaptation leaflet point at peak diastole. Statistical analysis After confirming normality of data distribution by the Shapiro–Wilk test, data were reported as mean ± standard deviation with 95% confidence interval values. The continuous variables of the post-treatment conditions were tested with that of pretreatment using the paired t-test, while the comparison between sleeve and Yacoub techniques was performed using the unpaired t-test. P-value <0.05 was considered to indicate statistical significance. All statistical analyses were performed using the Systat 13, Systat Software (Inc.), San Jose (CA) USA. RESULTS Fluid dynamics The fluid dynamics data are reported in Table 1. No statistical differences were found when comparing pre- and post-treatment data, except for the stroke volume following the Florida-sleeve procedure, which decreased from 74 ± 4 ml measured in the untreated samples to 67 ± 5 ml (P < 0.001), and could cause underestimation of the pressure gradient at post-treatment. When the 2 surgical techniques were compared, no statistical differences were found. Table 1: Fluid dynamic results . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 LCF: left coronary flow; RCF: right coronary flow; SV: stroke volume. Open in new tab Table 1: Fluid dynamic results . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . SV (ml) 74 ± 4 67 ± 5 −6 (−9 to −4) 0.001 70 ± 5 67 ± 6 −3 (−9 to 3) 0.26 Aortic pressure (mmHg) 103 ± 3 99 ± 3 −4 (−8 to 1) 0.1 101 ± 2 101 ± 2 0 (−3 to 3) 0.82 Mean gradient (mmHg) 6 ± 3 8 ± 3 1 (−3 to 6) 0.41 8 ± 5 9 ± 4 2 (−2 to 6) 0.35 LCF diastole (ml/min) 241 ± 18 225 ± 26 −16 (−48 to 16) 0.26 215 ± 15 217 ± 12 2 (−6 to 10) 0.52 LCF systole (ml/min) 144 ± 12 147 ± 23 2 (−13 to 17) 0.71 142 ± 14 132 ± 29 −10 (−39 to 18) 0.38 RCF diastole (ml/min) 96 ± 2 77 ± 25 −19 (−47 to 9) 0.15 98 ± 7 99 ± 6 1 (−6 to 6) 0.81 RCF systole (ml/min) 68 ± 6 71 ± 11 3 (−8 to 14) 0.54 72 ± 7 71 ± 8 −1 (−6 to 5) 0.77 LCF: left coronary flow; RCF: right coronary flow; SV: stroke volume. Open in new tab Leaflet kinematics The leaflet kinematics data are reported in Table 2. Both surgical techniques showed no difference in RVOT compared with the respective baseline value. The Florida-sleeve procedure showed a shorter SVCT (192 ± 19 ms vs  244± 14 ms; P = 0.016) and higher slow valve closing velocity (−1.5 ± 0.4 cm/s vs –0.8 ± 0.4 cm/s; P = 0.038) than the respective baseline values. In the rapid valve closing phase, the Yacoub procedure showed a trend to slower closing valve velocity (rapid valve closing velocity) with −16 ± 9 cm/s compared with the baseline −25 ± 9 cm/s (P = 0.07). Furthermore, the Yacoub procedure showed larger leaflet displacement at the end of the SVCT with a D2 value of 2.0 ± 0.5 cm compared with the baseline value of 1.5 ± 0.3 cm (P = 0.044). Upon comparing the Florida-sleeve and Yacoub procedures, the former showed statistically significant shorter SVCT (P = 0.017). Neither technique affected the effective height (Table 2), and no systolic contact was observed between the aortic cusps and aortic wall. Table 2: Leaflets kinematics . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 a P = 0.017 between Yacoub versus sleeve. D: diameter; eH: effective height; RVCT: rapid valve closing time; RVCV: rapid valve closing velocity; RVOT: rapid valve opening time; RVOV: rapid valve opening velocity; SCD: slow closing displacement; SVCT: slow valve closing time; SVCV: slow valve closing velocity.[] Open in new tab Table 2: Leaflets kinematics . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 . Basal . Sleeve . Mean difference (95% CI) . P-value . Basal . Yacoub . Mean difference (95% CI) . P-value . RVOT (ms) 24.3 ± 7 24.9 ± 2 0.6 (−8.4 to 9.6) 0.45 25.8 ± 4 29.3 ± 11 3.4 (−7.5 to 14.3) 0.49 RVOV (cm/s) 54 ± 11 47 ± 10 −7 (−21 to 6) 0.20 51.5 ± 13 46 ± 27 −6 (−35 to 23) 0.63 SVCT (ms) 244 ± 14 192 ± 19 −52 (−88 to −16) 0.016 253 ± 31 238 ± 30a −16 (−56 to 26) 0.4 SVCV (cm/s) −0.8 ± 0.4 −1.5 ± 0.4 −0.7 (−1.3 to −0.1) 0.04 −1.1 ± 0.3 −1.4 ± 0.5 −0.3 (−0.7 to 0.2) 0.2 RVCT (ms) 62 ± 11 70 ± 13 12 (−8 to 33) 0.15 47 ± 21 63 ± 34 17 (−27 to 61) 0.4 RVCV (cm/s) −18 ± 4 −13 ± 3 5.0 (−2.2 to 12.2) 0.12 −25 ± 9 −16 ± 9 8.6 (−1.0 to 18.2) 0.07 SCD (%) 17 ± 7 27 ± 12 12 (−2 to 27) 0.07 20 ± 11 30 ± 15 10 (−2 to 22) 0.11 D1 (cm) 2.5 ± 0.3 2.3 ± 0.3 −0.2 (−0.7 to 0.2) 0.22 2.6 ± 0.4 2.2 ± 0.5 −0.4 (−0.9 to 0.2) 0.13 D2 (cm) 2.1 ± 0.3 1.7 ± 0.4 −0.4 (−1.0 to 0.2) 0.15 2.0 ± 0.5 1.5 ± 0.3 −0.5 (−0.9 to −0.02) 0.044 eH (mm) 15.4 ± 1.1 16.6 ± 1.2 1.2 (−2.7 to 5.1) 0.31 14.8 ± 2.8 13.5 ± 1.6 −1.3 (−4.1 to 1.5) 0.28 a P = 0.017 between Yacoub versus sleeve. D: diameter; eH: effective height; RVCT: rapid valve closing time; RVCV: rapid valve closing velocity; RVOT: rapid valve opening time; RVOV: rapid valve opening velocity; SCD: slow closing displacement; SVCT: slow valve closing time; SVCV: slow valve closing velocity.[] Open in new tab Comment The results of this experimental study showed that while neither tested procedure disrupted the dynamics of valve opening, both affected the valve closing phase. In the Florida-sleeve procedure, the rapid valve closing phase was triggered earlier than the baseline value, while the Yacoub procedure affected the leaflet displacement at the end of SVCT. The findings for both procedures with respect to valve fluid dynamics (gradients and flow curve shape) and coronary flows remained similar. The AR has a well-defined geometry and, functionally, it may be conceptualized as organized in 2 compartments: 1 proximal, i.e. beneath the AV and subjected to the ventricular dynamics, and 1 distal, i.e. above the AV, and subjected to aortic haemodynamics. In normal ARs, these 2 compartments interact with each other throughout the cardiac cycle, storing and releasing elastic potential energy that generates a complex, and yet finely harmonized pattern of displacements and deformations of their components [20–23]. Because AV-sparing procedures require the use of artificial grafts for the AR reconstruction, the graft stiffness may alter the complex biomechanical equilibrium between the 2 compartments with an impact on valve kinematics and, ultimately, on leaflet stress [24]. In this study, by maintaining the anatomical continuity between the AR and the surrounding structures in addition to the simulating coronary perfusion, we could explore the disruption caused by the sparing valve on leaflet kinematics. To our best knowledge, the Florida-sleeve technique has never been evaluated in in vitro settings, and the results could provide some insight for clinical practice, given that this technique is gaining more popularity [6–11]. Mechanics of valve opening The opening phase of a normal AV is a highly dynamic phenomenon, wherein the valve leaflets change position and geometric configuration [25]. If any disruption takes place during this phase, high flexural stress concentration may occur in specific areas [4, 5, 24], ultimately leading to irreversible damage. The opening phase may be split into 2 parts, where the first part occurs in the isovolumetric contraction interval during which, despite the flow still being nil, the valve begins to unfold accounting for up to 20% of the maximal opening [11, 20–23, 26]. This part of the opening phase is highly dependent on passive mechanical properties of the AR, mainly to the outward movement of the commissures, owing to leaflets unloading, as well as the elastic properties of the leaflets [20]. Indeed, the unfolding can be suppressed if the motion of the commissures is restricted or the leaflets are stiffened, causing the shortening of the RVOT interval as a result [11]. The second part of the opening phase is due to the thrust from the blood flow, which displaces the leaflets to their maximal aperture position [20]. Our findings suggested that the type of sparing procedure does not influence the valve opening (Table 2 and Fig. 2) in terms of time, leaflets velocity and maximal leaflets displacement, when compared with their baseline values. This implies that both procedures may preserve a normal outward displacement of the commissures, as has already been reported [3, 11, 24]. As for the Yacoub procedure, our results were consistent with those reported by Fries et al. [3], although our data showed shorter RVOT intervals, which might be explained by the different experimental set-up. Figure 2: Open in new tabDownload slide Aortic leaflet displacement during the systolic ejection period. (A) Comparison of leaflets displacement between the basal and after the Yacoub technique. (B) Comparison of leaflets displacement between the basal and after the Florida-sleeve technique. Figure 2: Open in new tabDownload slide Aortic leaflet displacement during the systolic ejection period. (A) Comparison of leaflets displacement between the basal and after the Yacoub technique. (B) Comparison of leaflets displacement between the basal and after the Florida-sleeve technique. Mechanics of the valve closure The dynamics of valve closing phase is a complex phenomenon that, in turn, may be divided into 2 parts. The first part is featured by a slow movement of the leaflets towards the AR axis, while the second phase is characterized by a fast, quasi impulsive movement of the leaflets which ends with complete valve closure. Similar to the opening, the closing phase is driven by the time variation of the pressure difference across the leaflets, and additionally depends upon mechanical properties of the AR structures [15, 20], coronary flow [16, 17] and geometry of the sinuses of Valsalva with vortexes formation. Our findings, as for the Yacoub technique during the closure phase, are in agreement with those reported by Fries et al. [3] and confirmed that this technique does not significantly influence the time interval and velocity of both slow and rapid closing phases, but rather affects the leaflets position as shown by the breadth of the leaflets displacement distance or D2. In this regard, we can speculate that the stiffness of the graft and the unnatural shape of the sinus of Valsalva might be the reason for these findings. Indeed, the position of the leaflets, in this phase, depends upon the trans-leaflet pressure balance affected by the amplitude and the strength of vortexes generated in the sinuses of Valsalva. Conversely, the Florida-sleeve technique showed a significantly shorter and faster slow closing phase than the respective baseline values. This could be explained by the restrained effect on the ventricular–arterial junction related to the technique [11]. Indeed, the Florida-sleeve could have triggered an earlier valve closure by reducing the outward movement of the ventricular–arterial junction [27, 28]. This finding is corroborated by the unaffected closure phase in the Yacoub technique, wherein the ventricular–arterial junction dynamics tend to be more preserved [2] unless a restriction is imposed by implanting an external ring or a Gore-Tex stitch. The possible implications of these differences on long-term clinical results are not obvious. In the case of Florida-sleeve, these deviations from the normal appear due to the annulus movement restriction imposed by the technique itself. Nevertheless, stabilization of the annulus prevents its dilatation over time and thereby also prevents valve function failure [7]. In this regard, long-term clinical studies are needed. If the annulus is left untreated in the Yacoub technique, it may dilate and affect the valve function in some cases. After a further flow deceleration, the axial flow reverses its direction, triggering rapid closure of the valve. However, neither sparing procedure seemed to affect the rapid valve closure phase. The rapid movement of leaflets in this phase was reasonably driven mainly by transvalvular fluid dynamics, with a negligible role of the biological structure involved. The geometry of the leaflets’ resting position, or effective height, was unaffected by either technique. The Yacoub versus Florida-sleeve technique No substantial inter-technique differences were found with respect to leaflet dynamics, except for a shorter slow closing time with the Florida-sleeve (Table 2). We speculated that this was likely associated with the movement restriction at the level of ventricular–arterial junction discussed in the previous paragraph. Moreover, kinematic assessment of the aortic leaflets in AR treated with the David technique by using a straight graft has suggested significant shortening of the rapid valve opening and closing phases with respect to normal valves [3, 12, 13, 28]. This is not the case for both the Yacoub and Florida-sleeve techniques as evaluated in this work. Respecting the geometrical relationships and dynamisms of the AR is paramount to minimizing mechanical stress, in the leaflets, in both opening and closing phases. That may have a favourable impact on the long-term AV function durability. More specifically, preserving the first opening phase during the isovolumetric contraction, allows leaflets to assume a more favourable geometry while, in the second opening phase, the preservation of the AR dynamics allows the leaflets to be accommodated with a more appropriate geometry [14, 21] which minimizes flexural stress and prevents the leaflets from ramming into the sinus of Valsalva. During diastole, the presence of the sinuses of Valsalva may allow the leaflets to lodge with a more proper geometry, reducing their tensile stress [11]. In addition, in case of anatomical integrity of the ‘leaflet-sinus unit’ as in the Florida-sleeve, which implies an anatomical and mechanical continuity, the forces acting on leaflet may partly be transferred into the adjacent native sinus and, as such, reducing the tensile stress experienced by the leaflet [11, 21]. The benefits of preserving the sinuses of Valsalva from the kinematic point of view provided indirectly by this study are of interest and may complement the fluid dynamic findings [29]. CONCLUSION In this ex vivo set-up, the Florida-sleeve technique appeared to alter the slow closing phase of the AV leaflet kinematics when compared with both the normal baseline and Yacoub procedure, while the latter showed a larger displacement of the leaflets before the rapid closing valve phase. Long-term clinical studies are required to confirm any impact on valve durability, by these different leaflet kinematics patterns. Limitations The main limitation of this study concerns the use of an ex vivo heart sample, which does not present the natural contractility that might influence the AR dynamic changes within the cardiac cycle. In a clinical scenario, only the initial phase of the systole is characterized by AR expansion, whereas in the adopted experimental set-up, the AR was subjected to an expansion throughout the whole systole. The subvalvular portion of the porcine model has more muscular asymmetry than that of humans. However, we compared the porcine ARs pre- and post-treatments to mitigate any effect related to the shape of the LVOT. Because of the relatively small sample size, some differences between the groups might have been undetected. Conflict of interest: none declared. 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Novel insights by 4D flow imaging on aortic flow physiology after valve-sparing root replacement with or without neosinuses . Interact CardioVasc Thorac Surg 2018 ; 26 : 957 – 64 . Google Scholar Crossref Search ADS PubMed WorldCat ABBREVIATIONS ABBREVIATIONS AR Aortic root AV Aortic valve CIS Coronary impedance simulator RVOT Rapid valve opening time SCD Slow closing displacement SVCT Slow valve closing time © The Author(s) 2020. 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/open_access/funder_policies/chorus/standard_publication_model)

Journal

European Journal of Cardio-Thoracic SurgeryOxford University Press

Published: Nov 21, 2020

Keywords: aortic valve; florida; in vitro study; kinematics; heart; fluid dynamics; supraaortic valve area; fluid flow; aorta; ascending aortic graft with valve suspension and coronary reconstruction with valve sparing aortic annulus remodeling; echocardiography

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