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/lp/ou_press/morphological-features-of-the-thoracic-aorta-and-supra-aortic-branches-0ejhrBPvp9
- Publisher
- Oxford University Press
- Copyright
- © The Author(s) 2018. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.
- ISSN
- 1569-9293
- eISSN
- 1569-9285
- DOI
- 10.1093/icvts/ivy110
- Publisher site
- See Article on Publisher Site
Abstract
Abstract OBJECTIVES This study aimed to investigate the morphological characteristics of the dissected thoracic aorta and brachiocephalic arteries within the Chinese population. METHODS A retrospective analysis of computed tomography scans of 387 patients with acute Type A aortic dissection was carried out. The dimensions of the thoracic aorta at multiple levels and other imaging characteristics were studied. RESULTS The patients with a maximum diameter ≥55 mm accounted for less than one-third of the population. Among those without Marfan syndrome (MFS) (n = 349), only 114 (32.8%) patients had a maximal aortic diameter ≥ 55 mm, whereas among those with MFS (n = 38), 20 (78.9%) had a maximal aortic diameter ≥ 45 mm. The predicted maximum aortic diameter is 88.46 − 0.81 × height (cm) + 63.02 × body surface area (m2) + 5.50 × (if diabetes, 1, if not, 0) − 6.63 × (if hypertension, 1, if not, 0). A positive correlation was established between a circular false lumen and the probability that brachiocephalic arteries were involved by dissection. The size ratio of false lumen to true lumen was greater in the circumferential group when compared with the crescent group. The independent predictors for the circumferential false lumen were age, atherosclerosis and smoking. CONCLUSIONS Herein, the morphological characteristics of the thoracic aorta among Chinese patients with acute Type A aortic dissection were described. The currently recommended criteria for prophylactic aorta surgery were applied to most patients with MFS but not to those without MFS within the Chinese population. Furthermore, the shape of the false lumen was identified as a putative risk factor that might affect the prognosis of the patients. Aorta , Morphological features , Dissection , Asian INTRODUCTION Aortic dissection (AD), especially acute Type A AD (AAAD), remains a major challenge in the field of cardiovascular surgery. In recent years, some investigators have attempted to perform extended total arch replacement with the open placement of a triple-branched stent graft [1, 2] and even totally endovascular therapy [3]. These emerging techniques have simplified the operation and are gaining increasing attention. However, the success of these operation techniques depends highly on how well the artificial graft fits within the dissected aortic wall, which necessitates an in-depth study of morphological characteristics of the aorta after dissection as the morphological features of the thoracic aorta in Asian patients with AAAD have been poorly investigated. On the other hand, although the incidence of AD in China is continually increasing, the majority of the studies concerning AAAD originate from Western countries. The maximum aortic diameter ≥55 mm serves as a predictor for AD, and hence, the criteria for prophylactic aorta replacement have long been adopted in China, despite these having been derived from Western studies [4, 5]. Nevertheless, the reliability of these criteria is under investigation in recent years even in Western countries [6–9]. Reportedly, cardiovascular anatomy with its associated normal reference values, disease manifestations and progression are associated with geographical and ethnic variations [10]. Thus, this study aimed to analyse the morphological characteristics of the thoracic aorta and brachiocephalic arteries of patients with a normal aortic arch in the setting of AAAD and test the validity of current criteria for prophylactic surgery criteria within the Chinese population. MATERIALS AND METHODS A retrospective analysis was carried out on patients with AAAD admitted to the Fuwai Hospital, Beijing, China, from February 2010 to March 2013. The local institutional review board approved this observational study and waived the requirement of informed consent from the patients. The exclusion criteria included (i) >14 days after onset (chronic phase); (ii) younger than 18 years; (iii) variant aortic arch such as bovine arch; (iv) complicated with severe lung diseases or thoracic deformity, which might affect the shape of the thoracic aorta and (v) AD due to Loeys–Dietz syndrome, Ehlers–Danlos syndrome, trauma and bicuspid aortic valve as these aetiological factors were rarely observed at our centre. Moreover, variables with respect to demographics and cardiovascular risk factors were collected. Marfan syndrome (MFS) was diagnosed in line with the Ghent criteria. Hypertension implied a systolic pressure >140 mmHg or on antihypertensive medication. Diabetes mellitus was defined as a self-reported history of the disorder either on medication or insulin injection. Smoking was defined as 1 cigarette per day for at least 1 year. Drinking was defined as alcohol consumption at least once a week. All imaging data were processed using the specialized software (Medtronic 3D Recon EVAR 6.0, MN, USA). The system automatically generated a centreline along the aorta and performed 3-dimensional reconstruction. The aortic arch could be classified into 3 types according to Myla classification [11]. The vertebral arteries were classified into left vertebral artery dominance, right vertebral artery dominance and balanced vertebral arteries based on the dimension of the bilateral vertebral arteries. The diameters of the thoracic aorta were measured at 6 levels perpendicular to the centreline: (i) sinotubular junction; (ii) the mid-ascending aorta; (iii) immediately prior to the origin of the innominate artery (IA); (iv) between the IA and the left common carotid artery (LCCA); (v) between the LCCA and the left subclavian artery (LSA) and (iv) 2 cm distal to the origin of the LSA. The length of the thoracic aorta was measured at 3 segments that are formed by the appropriate planes perpendicular to the centreline: (i) the ascending aorta; (ii) the distance from the IA to the LCCA and (iii) the distance from the LCCA to the LSA. We measured the diameters of 3 brachiocephalic arteries at 2 levels: (i) ostium of brachiocephalic arteries; (ii) 2 cm distal to the ostium of arteries. Then, the false lumen at the ascending aorta was classified into 2 groups according to its shape: crescent and circumferential (Fig. 1). The dimensions of true lumen and false lumen at the ascending aorta were measured perpendicular to the intimal flap and compared. The size ratio of false lumen to true lumen was classified into 6 levels: 1/3, 1/2, 1/1, 2/1, 3/1 and >3/1. Figure 1: View largeDownload slide The shape of the false lumen at the ascending aorta could be classified into 2 groups: crescent (A) and circumferential (B). F: false lumen; T: true lumen. Figure 1: View largeDownload slide The shape of the false lumen at the ascending aorta could be classified into 2 groups: crescent (A) and circumferential (B). F: false lumen; T: true lumen. Statistical analysis Continuous variables are expressed as mean x- ± standard deviation and compared using the independent t-test or Wilcoxon rank sum test. Categorical variables are presented as frequencies and percentages and compared using the χ2 test or Fisher’s exact test as appropriate. We used multivariate linear regression (backwards) to predict the maximum diameter of the thoracic aorta in AAAD. Thus, the clinical decision-making would be more individualized rather than relying on a fixed rule. Receiver operating characteristic curve was used to evaluate the predictive value of the formula. We obtained the independent predictors for the circumferential false lumen using multivariate logistical regression (backwards). All data analyses were performed using IBM SPSS Statistics for Windows, version 20.0 (IBM Corp, Armonk, NY, USA). A P-value <0.05 in the 2-tailed test was considered statistically significant. RESULTS Baseline characteristics From a total of 426 patients with AAAD, 39 (9.2%) patients, who met the exclusion criteria, were excluded. The baseline demographics and cardiovascular risk factors of 387 (91.8%) patients are listed in Table 1. When compared with those of the International Registry of Aortic Dissection (IRAD), the patients in China were much younger (48.8 vs 63.1 years), with more men (81.1% vs 65.3%) and more likely to have hypertension (78.6% vs 72.1%). All patients were divided into 2 groups according to whether they had MFS. In contrast to patients without MFS, those with MFS tended to be younger (P < 0.001), taller (P < 0.001), heavier (P = 0.007) and with a larger body surface area (BSA) (P < 0.001) but a smaller body mass index (P = 0.001) and less likely to suffer from hypertension (P < 0.001). Table 1: Baseline demographics and cardiovascular risk factors Variables All (n = 387) MFS (n = 38) Non-MFS (n = 349) P-value Demographics Age (years), mean ± SD 48.8 ± 12.5 36.8 ± 15.0 50.2 ± 11.5 <0.001 Male, n (%) 314 (81.1) 28 (73.7) 286 (81.9) 0.216 Height (cm), mean ± SD 168.2 ± 7.0 178.3 ± 7.3 167.1 ± 6.1 <0.001 Weight (kg), mean ± SD 63.4 ± 8.2 66.8 ± 8.3 63.0 ± 8.1 0.007 BMI (kg/m2), mean ± SD 22.4 ± 2.6 21.0 ± 2.3 22.6 ± 2.6 0.001 BSA (m2), mean ± SD 1.68 ± 0.13 1.79 ± 0.13 1.67 ± 0.12 <0.001 Cardiovascular risk factors, n (%) Hypertension 304 (78.6) 17 (44.7) 287 (82.2) <0.001 Diabetes 26 (6.7) 1 (2.6) 25 (7.2) 0.495 Atherosclerosis 57 (14.7) 3 (7.9) 54 (15.5) 0.211 Prior cardiac surgery 4 (1.0) 1 (2.6) 3 (0.9) 0.340 Catheterization/angiography 10 (2.6) 2 (5.3) 8 (2.3) 0.256 Family history of cardiovascular disease 14 (3.6) 2 (5.3) 12 (3.4) 0.637 Smoking 82 (21.2) 7 (18.4) 75 (21.5) 0.660 Alcohol consumption 41 (10.6) 2 (5.3) 39 (11.2) 0.397 Variables All (n = 387) MFS (n = 38) Non-MFS (n = 349) P-value Demographics Age (years), mean ± SD 48.8 ± 12.5 36.8 ± 15.0 50.2 ± 11.5 <0.001 Male, n (%) 314 (81.1) 28 (73.7) 286 (81.9) 0.216 Height (cm), mean ± SD 168.2 ± 7.0 178.3 ± 7.3 167.1 ± 6.1 <0.001 Weight (kg), mean ± SD 63.4 ± 8.2 66.8 ± 8.3 63.0 ± 8.1 0.007 BMI (kg/m2), mean ± SD 22.4 ± 2.6 21.0 ± 2.3 22.6 ± 2.6 0.001 BSA (m2), mean ± SD 1.68 ± 0.13 1.79 ± 0.13 1.67 ± 0.12 <0.001 Cardiovascular risk factors, n (%) Hypertension 304 (78.6) 17 (44.7) 287 (82.2) <0.001 Diabetes 26 (6.7) 1 (2.6) 25 (7.2) 0.495 Atherosclerosis 57 (14.7) 3 (7.9) 54 (15.5) 0.211 Prior cardiac surgery 4 (1.0) 1 (2.6) 3 (0.9) 0.340 Catheterization/angiography 10 (2.6) 2 (5.3) 8 (2.3) 0.256 Family history of cardiovascular disease 14 (3.6) 2 (5.3) 12 (3.4) 0.637 Smoking 82 (21.2) 7 (18.4) 75 (21.5) 0.660 Alcohol consumption 41 (10.6) 2 (5.3) 39 (11.2) 0.397 BSA = 0.0061 × height (cm) + 0.0128 × weight (kg) − 0.1529. BMI: body mass index; BSA: body surface area; MFS: Marfan syndrome; SD: standard deviation. Table 1: Baseline demographics and cardiovascular risk factors Variables All (n = 387) MFS (n = 38) Non-MFS (n = 349) P-value Demographics Age (years), mean ± SD 48.8 ± 12.5 36.8 ± 15.0 50.2 ± 11.5 <0.001 Male, n (%) 314 (81.1) 28 (73.7) 286 (81.9) 0.216 Height (cm), mean ± SD 168.2 ± 7.0 178.3 ± 7.3 167.1 ± 6.1 <0.001 Weight (kg), mean ± SD 63.4 ± 8.2 66.8 ± 8.3 63.0 ± 8.1 0.007 BMI (kg/m2), mean ± SD 22.4 ± 2.6 21.0 ± 2.3 22.6 ± 2.6 0.001 BSA (m2), mean ± SD 1.68 ± 0.13 1.79 ± 0.13 1.67 ± 0.12 <0.001 Cardiovascular risk factors, n (%) Hypertension 304 (78.6) 17 (44.7) 287 (82.2) <0.001 Diabetes 26 (6.7) 1 (2.6) 25 (7.2) 0.495 Atherosclerosis 57 (14.7) 3 (7.9) 54 (15.5) 0.211 Prior cardiac surgery 4 (1.0) 1 (2.6) 3 (0.9) 0.340 Catheterization/angiography 10 (2.6) 2 (5.3) 8 (2.3) 0.256 Family history of cardiovascular disease 14 (3.6) 2 (5.3) 12 (3.4) 0.637 Smoking 82 (21.2) 7 (18.4) 75 (21.5) 0.660 Alcohol consumption 41 (10.6) 2 (5.3) 39 (11.2) 0.397 Variables All (n = 387) MFS (n = 38) Non-MFS (n = 349) P-value Demographics Age (years), mean ± SD 48.8 ± 12.5 36.8 ± 15.0 50.2 ± 11.5 <0.001 Male, n (%) 314 (81.1) 28 (73.7) 286 (81.9) 0.216 Height (cm), mean ± SD 168.2 ± 7.0 178.3 ± 7.3 167.1 ± 6.1 <0.001 Weight (kg), mean ± SD 63.4 ± 8.2 66.8 ± 8.3 63.0 ± 8.1 0.007 BMI (kg/m2), mean ± SD 22.4 ± 2.6 21.0 ± 2.3 22.6 ± 2.6 0.001 BSA (m2), mean ± SD 1.68 ± 0.13 1.79 ± 0.13 1.67 ± 0.12 <0.001 Cardiovascular risk factors, n (%) Hypertension 304 (78.6) 17 (44.7) 287 (82.2) <0.001 Diabetes 26 (6.7) 1 (2.6) 25 (7.2) 0.495 Atherosclerosis 57 (14.7) 3 (7.9) 54 (15.5) 0.211 Prior cardiac surgery 4 (1.0) 1 (2.6) 3 (0.9) 0.340 Catheterization/angiography 10 (2.6) 2 (5.3) 8 (2.3) 0.256 Family history of cardiovascular disease 14 (3.6) 2 (5.3) 12 (3.4) 0.637 Smoking 82 (21.2) 7 (18.4) 75 (21.5) 0.660 Alcohol consumption 41 (10.6) 2 (5.3) 39 (11.2) 0.397 BSA = 0.0061 × height (cm) + 0.0128 × weight (kg) − 0.1529. BMI: body mass index; BSA: body surface area; MFS: Marfan syndrome; SD: standard deviation. Aortic arch type and vertebral artery dominance Of the 387 patients, 249 (64.3%) patients presented with Type I aortic arch, 73 (18.9%) patients with Type II and 65 (16.8%) patients with Type III. There was no statistical difference between the MFS and non-MFS groups (P = 0.347). The proportions of the balanced vertebral artery, right dominant vertebral artery and left dominant vertebral artery were 260 (67.1%), 42 (10.9%) and 85 (22.0%), respectively. No statistically significant difference was observed between the MFS and non-MFS groups with respect to these parameters (P = 0.245). Dimensions of the thoracic aorta and brachiocephalic artery The diameters at 6 cross-sectional planes of the thoracic aorta and the maximum diameter are listed in Table 2. The mid-ascending aorta had the largest diameter. The aorta tapered off gradually from 51.5 ± 13.7 mm at the level of the mid-ascending aorta to 36.5 ± 10.3 mm at the proximal descending aorta. Among all patients, those with a maximum diameter <45 mm, between 45 and 54 mm and ≥55 mm were 66 (17.1%), 194 (50.1%) and 127 (32.8%), respectively. Patients with a maximum diameter ≥55 mm accounted for less than one-third of the cohort. Among individuals without MFS, only 114 (32.8%) patients had a maximal aortic diameter ≥55 mm, whereas among those with MFS, only 13 (34.2%) patients had a maximal aortic diameter ≥55 mm and 20 (78.9%) patients ≥45 mm. Table 2: Diameters of the thoracic aorta Levels of the thoracic aorta (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value STJ 47.6 ± 11.3 48.8 ± 16.1 47.5 ± 10.6 0.638 Mid-ascending aorta 51.5 ± 13.7 54.0 ± 18.3 51.3 ± 13.1 0.236 Upper ascending aorta 44.0 ± 8.9 40.5 ± 9.1 43.9 ± 8.8 0.025 Between IA and LCCA 40.7 ± 8.0 37.9 ± 7.4 41.0 ± 8.0 0.023 Between LCCA and LSA 38.1 ± 7.3 34.7 ± 5.9 38.5 ± 7.4 0.002 Distal to LSA 36.5 ± 10.3 33.8 ± 7.6 36.8 ± 10.6 0.086 Maximal 53.8 ± 14.3 54.8 ± 17.9 53.7 ± 14.0 0.645 Levels of the thoracic aorta (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value STJ 47.6 ± 11.3 48.8 ± 16.1 47.5 ± 10.6 0.638 Mid-ascending aorta 51.5 ± 13.7 54.0 ± 18.3 51.3 ± 13.1 0.236 Upper ascending aorta 44.0 ± 8.9 40.5 ± 9.1 43.9 ± 8.8 0.025 Between IA and LCCA 40.7 ± 8.0 37.9 ± 7.4 41.0 ± 8.0 0.023 Between LCCA and LSA 38.1 ± 7.3 34.7 ± 5.9 38.5 ± 7.4 0.002 Distal to LSA 36.5 ± 10.3 33.8 ± 7.6 36.8 ± 10.6 0.086 Maximal 53.8 ± 14.3 54.8 ± 17.9 53.7 ± 14.0 0.645 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; MFS: Marfan syndrome; SD: standard deviation; STJ: sinotubular junction. Table 2: Diameters of the thoracic aorta Levels of the thoracic aorta (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value STJ 47.6 ± 11.3 48.8 ± 16.1 47.5 ± 10.6 0.638 Mid-ascending aorta 51.5 ± 13.7 54.0 ± 18.3 51.3 ± 13.1 0.236 Upper ascending aorta 44.0 ± 8.9 40.5 ± 9.1 43.9 ± 8.8 0.025 Between IA and LCCA 40.7 ± 8.0 37.9 ± 7.4 41.0 ± 8.0 0.023 Between LCCA and LSA 38.1 ± 7.3 34.7 ± 5.9 38.5 ± 7.4 0.002 Distal to LSA 36.5 ± 10.3 33.8 ± 7.6 36.8 ± 10.6 0.086 Maximal 53.8 ± 14.3 54.8 ± 17.9 53.7 ± 14.0 0.645 Levels of the thoracic aorta (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value STJ 47.6 ± 11.3 48.8 ± 16.1 47.5 ± 10.6 0.638 Mid-ascending aorta 51.5 ± 13.7 54.0 ± 18.3 51.3 ± 13.1 0.236 Upper ascending aorta 44.0 ± 8.9 40.5 ± 9.1 43.9 ± 8.8 0.025 Between IA and LCCA 40.7 ± 8.0 37.9 ± 7.4 41.0 ± 8.0 0.023 Between LCCA and LSA 38.1 ± 7.3 34.7 ± 5.9 38.5 ± 7.4 0.002 Distal to LSA 36.5 ± 10.3 33.8 ± 7.6 36.8 ± 10.6 0.086 Maximal 53.8 ± 14.3 54.8 ± 17.9 53.7 ± 14.0 0.645 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; MFS: Marfan syndrome; SD: standard deviation; STJ: sinotubular junction. Furthermore, we analysed the independent predictors for maximum aortic diameter using multivariate linear regression. The aortic maximum diameter prediction formula is as follows: predicted maximum aortic diameter = 88.46 − 0.81 × height (cm) + 63.02 × BSA (m2) + 5.50 × (if diabetes, 1, if not, 0) − 6.63 × (if hypertension, 1, if not, 0). The P-values for coefficients of height, BSA and hypertension were <0.001 and that for diabetes was 0.035. Then, the predicted maximum aortic diameters were calculated and compared with the actual value using the receiver operating characteristic curve to evaluate the predictive power of the formula (Fig. 2). The area under the curve was 0.80, thereby indicating that the predictive power of the formula was good. Figure 2: View largeDownload slide Receiver operating characteristic curve to evaluate the predictive power of the formula whether the maximum aortic diameter after dissection would be ≥55 mm. The area under the curve was 0.8, which indicated the excellent predictive power. Figure 2: View largeDownload slide Receiver operating characteristic curve to evaluate the predictive power of the formula whether the maximum aortic diameter after dissection would be ≥55 mm. The area under the curve was 0.8, which indicated the excellent predictive power. The length of the thoracic aorta is listed in Table 3. Patients with MFS were inclined to have a longer ascending aorta in contrast to those without MFS (76.0 ± 18.3 mm vs 62.6 ± 5.8 mm, P = 0.001). The diameters of the brachiocephalic arteries are summarized in Table 4. The diameters at the ostium of the brachiocephalic artery were greater than that of 2 cm distal to the ostium. Moreover, the difference between the 2 levels increased markedly when brachiocephalic arteries were involved in the dissection. The diameters of brachiocephalic arteries involved in the dissection were significantly greater than those not involved at both levels (P < 0.001). Table 3: Length of the thoracic aorta Distance (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value Ascending aorta 64.0 ± 8.9 76.0 ± 18.3 62.6 ± 5.8 <0.001 IA-LCCA 12.5 ± 4.6 11.5 ± 5.3 12.6 ± 4.5 0.174 LCCA-LSA 19.7 ± 5.8 17.8 ± 4.8 18.9 ± 5.6 0.254 Distance (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value Ascending aorta 64.0 ± 8.9 76.0 ± 18.3 62.6 ± 5.8 <0.001 IA-LCCA 12.5 ± 4.6 11.5 ± 5.3 12.6 ± 4.5 0.174 LCCA-LSA 19.7 ± 5.8 17.8 ± 4.8 18.9 ± 5.6 0.254 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; MFS: Marfan syndrome; SD: standard deviation. Table 3: Length of the thoracic aorta Distance (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value Ascending aorta 64.0 ± 8.9 76.0 ± 18.3 62.6 ± 5.8 <0.001 IA-LCCA 12.5 ± 4.6 11.5 ± 5.3 12.6 ± 4.5 0.174 LCCA-LSA 19.7 ± 5.8 17.8 ± 4.8 18.9 ± 5.6 0.254 Distance (mm) All (n = 387), mean ± SD MFS (n = 38), mean ± SD Non-MFS (n = 349), mean ± SD P-value Ascending aorta 64.0 ± 8.9 76.0 ± 18.3 62.6 ± 5.8 <0.001 IA-LCCA 12.5 ± 4.6 11.5 ± 5.3 12.6 ± 4.5 0.174 LCCA-LSA 19.7 ± 5.8 17.8 ± 4.8 18.9 ± 5.6 0.254 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; MFS: Marfan syndrome; SD: standard deviation. Table 4: Diameters of the brachiocephalic arteries by dissection involvement or not Levels of brachiocephalic arteries (mm) All (n = 387), mean ± SD Involved, mean ± SD Not involved, mean ± SD P-value Ostium of IA 16.3 ± 4.1 18.4 ± 4.2 14.7 ± 3.3 <0.001 2 cm distal to IA 12.1 ± 3.0 13.1 ± 3.3 11.3 ± 2.6 <0.001 Ostium of LCCA 12.0 ± 2.7 13.4 ± 3.4 11.4 ± 2.0 <0.001 2 cm distal to LCCA 9.3 ± 2.0 10.0 ± 2.3 9.0 ± 1.8 <0.001 Ostium of LSA 13.0 ± 3.5 14.7 ± 3.6 12.1 ± 3.0 <0.001 2 cm distal to LSA 10.0 ± 2.1 10.6 ± 2.3 9.7 ± 2.0 <0.001 Levels of brachiocephalic arteries (mm) All (n = 387), mean ± SD Involved, mean ± SD Not involved, mean ± SD P-value Ostium of IA 16.3 ± 4.1 18.4 ± 4.2 14.7 ± 3.3 <0.001 2 cm distal to IA 12.1 ± 3.0 13.1 ± 3.3 11.3 ± 2.6 <0.001 Ostium of LCCA 12.0 ± 2.7 13.4 ± 3.4 11.4 ± 2.0 <0.001 2 cm distal to LCCA 9.3 ± 2.0 10.0 ± 2.3 9.0 ± 1.8 <0.001 Ostium of LSA 13.0 ± 3.5 14.7 ± 3.6 12.1 ± 3.0 <0.001 2 cm distal to LSA 10.0 ± 2.1 10.6 ± 2.3 9.7 ± 2.0 <0.001 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; SD: standard deviation. Table 4: Diameters of the brachiocephalic arteries by dissection involvement or not Levels of brachiocephalic arteries (mm) All (n = 387), mean ± SD Involved, mean ± SD Not involved, mean ± SD P-value Ostium of IA 16.3 ± 4.1 18.4 ± 4.2 14.7 ± 3.3 <0.001 2 cm distal to IA 12.1 ± 3.0 13.1 ± 3.3 11.3 ± 2.6 <0.001 Ostium of LCCA 12.0 ± 2.7 13.4 ± 3.4 11.4 ± 2.0 <0.001 2 cm distal to LCCA 9.3 ± 2.0 10.0 ± 2.3 9.0 ± 1.8 <0.001 Ostium of LSA 13.0 ± 3.5 14.7 ± 3.6 12.1 ± 3.0 <0.001 2 cm distal to LSA 10.0 ± 2.1 10.6 ± 2.3 9.7 ± 2.0 <0.001 Levels of brachiocephalic arteries (mm) All (n = 387), mean ± SD Involved, mean ± SD Not involved, mean ± SD P-value Ostium of IA 16.3 ± 4.1 18.4 ± 4.2 14.7 ± 3.3 <0.001 2 cm distal to IA 12.1 ± 3.0 13.1 ± 3.3 11.3 ± 2.6 <0.001 Ostium of LCCA 12.0 ± 2.7 13.4 ± 3.4 11.4 ± 2.0 <0.001 2 cm distal to LCCA 9.3 ± 2.0 10.0 ± 2.3 9.0 ± 1.8 <0.001 Ostium of LSA 13.0 ± 3.5 14.7 ± 3.6 12.1 ± 3.0 <0.001 2 cm distal to LSA 10.0 ± 2.1 10.6 ± 2.3 9.7 ± 2.0 <0.001 IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery; SD: standard deviation. Imaging characteristics of aortic dissection Among 387 patients with AAAD, 242 (62.6%) showed a primary tear located at the ascending aorta, 100 (25.8%) at the aortic arch, 14 (3.6%) at the descending aorta and 31 (8%) with an unknown primary tear. However, no statistically significant difference was observed between the MFS and non-MFS groups (P = 0.502). Subsequently, we divided all patients into 2 groups according to the shape of false lumen in the ascending aorta: crescent and circumferential. In patients with the circumferential false lumen at the ascending aorta (n = 60), the number of patients with the IA, LCCA and LSA involved in the dissection were 36 (60%, P = 0.003), 31 (51.7%, P = 0.001) and 29 (48.3%, P = 0.015), respectively. In addition, we classified the size of false lumen into 6 levels according to the size when compared with true lumen (Table 5). It was more common in the circumferential group that the size ratio of false lumen to true lumen was ≥3:1 (P = 0.001). We also used multivariate logistic regression to explore the independent risk factors for the circumferential false lumen, which indicated age [odds ratio (OR) 0.96, 95% confidence interval (CI) 0.93–0.98; P = 0.002], atherosclerosis (OR 2.75, 95% CI 1.06–7.17; P = 0.038) and smoking (OR 5.25, 95% CI 2.78–9.91; P = 0.001) as independent predictors. Table 5: Size ratio of false lumen to true lumen between 2 groups with different false lumen shape Size ratio of false lumen to true lumen Crescent (n = 327), n (%) Circumferential (n = 60), n (%) P-value 1:3 7 (2.1) 1 (1.7) 1.000 1:2 7 (2.1) 0 (0.0) 0.602 1:1 103 (31.5) 13 (21.7) 0.127 2:1 98 (30.0) 7 (11.7) 0.003 3:1 53 (16.2) 13 (21.7) 0.301 >3:1 59 (18.0) 26 (43.3) <0.001 Size ratio of false lumen to true lumen Crescent (n = 327), n (%) Circumferential (n = 60), n (%) P-value 1:3 7 (2.1) 1 (1.7) 1.000 1:2 7 (2.1) 0 (0.0) 0.602 1:1 103 (31.5) 13 (21.7) 0.127 2:1 98 (30.0) 7 (11.7) 0.003 3:1 53 (16.2) 13 (21.7) 0.301 >3:1 59 (18.0) 26 (43.3) <0.001 Table 5: Size ratio of false lumen to true lumen between 2 groups with different false lumen shape Size ratio of false lumen to true lumen Crescent (n = 327), n (%) Circumferential (n = 60), n (%) P-value 1:3 7 (2.1) 1 (1.7) 1.000 1:2 7 (2.1) 0 (0.0) 0.602 1:1 103 (31.5) 13 (21.7) 0.127 2:1 98 (30.0) 7 (11.7) 0.003 3:1 53 (16.2) 13 (21.7) 0.301 >3:1 59 (18.0) 26 (43.3) <0.001 Size ratio of false lumen to true lumen Crescent (n = 327), n (%) Circumferential (n = 60), n (%) P-value 1:3 7 (2.1) 1 (1.7) 1.000 1:2 7 (2.1) 0 (0.0) 0.602 1:1 103 (31.5) 13 (21.7) 0.127 2:1 98 (30.0) 7 (11.7) 0.003 3:1 53 (16.2) 13 (21.7) 0.301 >3:1 59 (18.0) 26 (43.3) <0.001 DISCUSSION The demographics and cardiovascular risk factors for AAAD differed between the Chinese and Western populations as follows: the patients in this study were much younger compared to those in the IRAD (48.8 vs 63.1 years), which is consistent with several previous studies [12, 13]. Also, racial differences might play a role. This study had more hypertensive patients than the IRAD (78.6% vs 69.3%). In our experience, the majority of patients admitted to our hospital came from rural areas of northern China where hypertension was prevalent due to the high-salt diet of the region. Furthermore, many hypertensive patients were unaware of their high blood pressure due to low education and lack of routine physical examination [14]. Male sex was more dominant in our study than that in the IRAD, which might be attributed to men being more prone to hypertension in China. Moreover, men are usually exposed to heavier physical labour than women in rural areas of China, which could trigger the AD. The broad discrepancies in the baseline characteristics indicate that the differences between Asians and Westerners do exist, thereby questioning applicability of conclusions derived from Western countries. Furthermore, the LSA coverage in endovascular therapy for AD was reported when the proximal landing zone was not sufficient [15]. This technique requires a careful assessment of the dominance of bilateral vertebral arteries and the integrity of cerebral arterial circle. Our study found that only a small portion (10.9%) of patients had right vertebral dominance in China. The direct coverage of LSA might lead to posterior circulation ischaemia in most patients, so LSA should be reconstructed maximally. Total arch replacement with endovascular therapy is attractive; however, it is hard to achieve presently. Therefore, some investigators have considered total aortic arch replacement with the open placement of a triple-branched stent graft for AAAD [2]. Instead of removing the aortic arch, a triple-branched stent graft is inserted from the aortic arch incision immediately prior to the IA. To design such new types of grafts, large amounts of detailed anatomical data in the setting of AAAD in China are essential, which is rare at present. We studied the dimensions of the thoracic aorta and brachiocephalic arteries at multiple planes (Tables 2–4). In addition, the distance between the IA and the LCCA was shorter than that between the LCCA and the LSA, instead of equidistance as designed in many artificial grafts. Moreover, the brachiocephalic arteries tapered off from the origin to the 2 cm distal, with an average difference of 3 mm. The difference between the 2 levels widened when brachiocephalic arteries were involved in AD. The artificial graft with cylindrical stent branches may not be a reasonable option, because the distal end of aortic branches would bear greater radial tension. Then, we measured the diameters of the thoracic aorta at 6 planes and found that the largest diameter was located at the mid-ascending aorta (51.5 ± 31.7 mm). This preliminary study describes the patterns of aortic morphology after dissection in China. Notably, considering the huge heterogeneity in AD, it is difficult to design a universally applicable artificial graft. This first database on the morphological features of AD in China could guide and improve the design of the new graft mentioned above. In turn, we could use these data to verify the applicability of the new graft. Although customized grafts are more practical, the death rate of Type A AD remains high, and it requires an extended period to customize the graft. Our database is still continually updated, and as the amount of data increases, it will become increasingly reliable. Recently, the reliability of current criteria on prophylactic aorta replacement has been questioned a lot in Western countries [6–9]. This study encompassed an Asian population, wherein the patients with a maximum aortic diameter ≥55 mm accounted for less than one-third of the population. In other words, Chinese patients do usually not dissect on the basis of aneurysms, and thus, the guidelines’ threshold for prophylactic replacement does not address most of these patients. In the non-MFS group (n = 349), only 114 (32.8%) patients exhibited a maximum aortic diameter ≥ 55 mm. In the MFS group (n = 38), only 13 (34.2%) patients had the maximum diameter ≥55 mm but 20 (78.9%) patients had ≥ 45 mm, which is currently the recommended criterion for prophylactic surgery for patients with MFS. Thus, a majority of the patients with MFS could benefit from the currently recommended surgery criteria. In this study, to test the reliability of criteria mentioned above, we assessed the dimension of the thoracic aorta prior to AD by measuring the dimension after AD and made no corrections. Some studies have shown that the aorta would expand after AD [16, 17]. In such a case, fewer patients would fulfil the current surgery criteria, thereby lending credibility to our conclusion. However, we do not recommend decreasing the threshold of the prophylactic surgery, as it would expose a large number of innocent individuals to the trauma of surgery. Thus, for a customized clinical decision, we proposed a formula as follows: predicted maximum aortic diameter = 88.46 − 0.81 × height (cm) + 63.0 × BSA (m2) + 5.50 × (if diabetes, 1, if not, 0) − 6.63 × (if hypertension, 1, if not, 0). The equation could act as a risk stratification tool to help identify patients who are more likely to develop AD at a diameter less than 55 mm, hence alerting both the doctor and the patient. If the predicted maximum aortic diameter after dissection is <55 mm, the patient should then be monitored more closely and followed up more regularly. Our study also found that most primary entries in AAAD were located at the ascending aorta, which was consistent with previous reports [18]. However, the primary entry located at aortic arch was more common in our study than that in the IRAD (25.8% vs 6.4%). This phenomenon could partially explain why extended total arch replacement was more preferred in China than in Western countries. Then, we divided all patients into 2 groups according to the shape of the false lumen at the ascending aorta: crescent and circumferential. When compared with the crescent group, the size ratio of false lumen to true lumen in the circumferential group was greater, and a positive correlation was established between the circumferential false lumen and the incidence of the IA and the LCCA being involved by dissection. Thus, the circumferential false lumen may portend a worse prognosis, as it might indicate intensive tearing and high pressure in false lumen. Also, a higher probability of brachiocephalic arteries being involved in the dissection may lead to a higher incidence of neurological complications. Next, we used multivariate logistic regression to explore the independent predictors for the circumferential false lumen and found that a young smoker concomitant with aortic atherosclerosis was prone to develop AD with the circumferential false lumen. The risk of smoking was the highest (OR 5.25, 95% CI 2.78–9.91; P = 0.001). However, the small proportion of patients with circumferential false lumen may lead to bias in the results of this study. Therefore, additional studies are essential in the future with a larger sample to verify whether the shape of false lumen would affect prognosis of the patients. Limitations Nevertheless, this study has several limitations. First, because of the abrupt onset and high mortality of AAAD, a large proportion of patients might have been deceased before being transferred to the hospital. Thus, our data could only partially reflect the real-world situation of AD. Second, this was a single-centre study which might not represent the conditions of a whole country. However, our hospital is a tertiary referral centre admitting more than 100 patients with AAAD annually, and the patients were from all over the country. CONCLUSIONS The morphological features of the thoracic aorta in the setting of AAAD such as aortic arch type, vertebral artery dominance, dimensions of the thoracic aorta, entry tear location and shape of false lumen were investigated. The currently recommended criteria for prophylactic aorta surgery were applicable to most patients with MFS in China; however, in the case of those without MFS, it was less valuable. A formula was developed to estimate the post-dissection maximum aortic diameter and assist in clinical decision-making. ACKNOWLEDGEMENTS We thank Yan Huang for statistical analysis and Qi-Peng Luo for data collection. We are also grateful to Lilu for advice regarding image processing. Conflict of interest: none declared. 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Journal
Interactive CardioVascular and Thoracic Surgery – Oxford University Press
Published: Apr 24, 2018