Clinical Analysis And Mechanism Study Of Ascending Aorta Dilatation After Bicuspid Aortic Valve Surgery

Background:Bicuspid aortic valve(BAV)is the most common congenital cardiac disorder,affecting about 1%-2% of the population worldwide.A normal tricuspid aortic valve(TAV)consists of three aortic-valve cusps with each semilunar in appearance,which can be divided into left,right and noncoronary valves according to their corresponding relationship with the coronary artery orifice,while a bicuspid aortic valve is typically composed of two leaflets of unequal size.Sievers et al.classified BAV and created Sievers’ classification system based on the number of raphes and spatial position of cusps or raphes,which is widely used in cardiac surgery literature.With age,a variety of complications will occur,such as aortic stenosis or insufficiency,aortic aneurysm or dissection,etc.And aortic dilatation is the most common complication of all.Most BAV patients with aortic dilatation require surgical treatment such as aortic valve and aortic root replacement.The guidelines set the maximum diameter of the ascending aorta as the main reference for surgical treatment in BAV patients.However,the aorta of BAV involves many pathophysiological factors,including hemodynamic factors,molecular and cellular changes determined by genetic factors.This makes it limited to determine surgical intervention only by the maximum diameter of ascending aorta for BAV patients whose ascending aorta is widened to moderate dilation(35 mm < d < 50 mm).Girdauskas et al.considered that preoperative aortic regurgitation in BAV patients was 10 times more likely to develop aortic dissection than those with aortic stenosis.However,Zhang et al.found that aortic stenosis was significantly related to the dilatation of ascending aorta in BAV.Therefore,more and more evidence suggests that valve morphology may have a greater impact on aortic dilatation than ascending aortic diameter in BAV patients.In addition,Mahadevia et al found that bicuspid aortic cusp fusion morphology alters aortic three-dimensional outflow patterns,wall shear stress,and expression of aortopathy compared with TAV patients.Ren et al.also found that there were significant differences in the types of ascending aortic dilatation among different types of BAV patients through clinical follow-up study.Therefore,we need to find more clinical indicators to conduct the current surgical strategy,rather than simply taking the ascending aorta diameter as standard.In addition,Chim et al.found BAV had a greater loss of aortic wall compliance and more serious matrix degradation relative to TAV.The main pathophysiological mechanism of aortic aneurysm is the loss of vascular smooth muscle cells(VSMCs)and the degradation of extracellular matrix(ECM).In this pathological process,the imbalance of matrix metalloproteinases(MMPs)and tissue inhibitor of metalloproteinases(TIMPs)plays an important role.MMP-2 and MMP-9 are considered to be the most important MMPs in the degradation of ECM.The current literature shows that TIMP-1,TIMP-3 and TIMP-4 can inhibit the activity of MMP-2 and MMP-9 significantly.Ikonomidis et al.found that the expression of MMPs and TIMPs in aortic tissues was also significantly different among type 1 BAV patients,but there were still limitations in the analysis of other types of BAV.Objectives:In this study,based on the classification system of BAV and the technique of propensity score matching(PSM),we compared the clinical data of BAV and TAV after AVR(mechanical valve)and tried to find out the risk factors of ascending aortic dilatation in BAV,so as to provide reference for the development of surgical strategy for BAV patients.Furthermore,the pathological differences of ascending aorta wall in BAV,TAV and Control groups were compared,as well as the distribution and expression of MMP-2,MMP-9 and TIMP-1,TIMP-3 and TIMP-4 in each group.Methods:1.According to inclusion and exclusion criteria,consecutive patients who only received AVR(mechanical valve)in the Second Affiliated Hospital of Army Medical University from January 2014 to June 2019 were collected and divided into TAV group and BAV group.The baseline data of the two groups before operation were balanced by PSM.The intraoperative and mid-term clinical data of the two groups were compared,and the risk factors affecting the continuous dilatation of BAV ascending aorta were found.2.Compare the pathological differences of ascending aorta wall and the expression of matrix metalloproteinase and its inhibitor in BAV,TAV and Control groups.2.1 Collection of human aortic tissue specimens.Aorta tissue was obtained from BAV or TAV patients who underwent ascending aortic replacement(including David operation,Bentall operation and sun’s operation)and control tissue was obtained from punch biopsies during coronary artery bypass grafting(CABG)operation.The BAV patients were classified according to the Sievers’ classification.2.2 After paraffin section,the pathological differences of ascending aorta wall in each group were compared by hematoxylin eosin staining(HE),Verhoeff’s van Gieson staining(EVG)and Masson staining.2.3 The expression and distribution of MMP-2,MMP-9 and TIMP-1,TIMP-3,TIMP-4in each group were detected by immunofluorescence after frozen section.2.4 The expression of MMP-2,MMP-9 and TIMP-1,TIMP-3,TIMP-4 was detected by Western blot.Results:1.A total of 245 patients were included in the clinical study,including 158 TAV patients and 87 BAV patients.According to Sievers’ classification,BAV patients were further divided into 15 cases of type 0 Ap,21 cases of type 0 Lat,45 cases of type 1 and 6 cases of type 2.2.69 pairs were successfully matched by PSM.After PSM,the preoperative clinical baseline data of TAV group and BAV group were comparable(P > 0.05),and there were no significant differences in intraoperative and perioperative outcomes(P > 0.05).During the median follow-up time of 45 months,there were no significant differences in the diameter of the ascending aorta,diameter of the aortic sinus and its changes,incidence of adverse aortic events,functional status of the prosthetic valve,and classification of cardiac function between the two groups(P>0.05),while the difference of ascending aorta change,annual change rate,and proportion of continuous dilation of ascending aorta were significantly higher in the BAV group than the TAV group(P=0.016,0.010 and 0.041 respectively).3.Multivariate logistic regression analysis of PSM cohort showed that BAV types(OR=3.296,95%CI: 1.473～7.372),aortic regurgitation(OR=6.491,95%CI: 2.691～15.657)and aortic valve stenosis with regurgitation(OR=8.233,95%CI: 2.565 ～ 26.429)were positively correlated with the continued dilatation of the ascending aorta after AVR.Furthermore,after the BAV cohort was screened out from the PSM cohort,multivariate logistic regression analysis indicated that type 1 in BAV(OR=10.378,95%CI: 1.587～67.853)],smoking(OR=4.959,95%CI: 1.158～21.231)and aortic regurgitation(OR=8.070,95%CI: 1.729～37.674)were positively correlated with the continued dilatation of the ascending aorta after AVR in BAV patients4.In the experimental study,the tissue of ascending aorta was collected from BAV(n =12),TAV(n = 5)and control(n = 5).BAV patients were divided into type 1 R-N(n = 3),type1 L-R(n = 4),type 0 Lat(n = 3)and type 0 Ap(n = 3).5.HE,EVG and Masson staining showed that no obvious inflammatory cell existed and the elastin and collagen were complete and orderly in the middle layer of the aortic wall in control.However,inflammatory cells could be seen in BAV.And the rupture of elastin and collagen was more serious in BAV compared with TAV and control.6.Among different types of BAV patients,most fragments of elastin and collagen could be detected and the content of those was the least in type 1 L-R group.7.Immunofluorescence and Western blot showed that the overall expression levels of MMPs and TIMPs in BAV were significantly higher than those in control and were different from those in TAV.8.The expression levels of MMPs and TIMPs in type 0 Lat group and type 0 Ap group were highest.In type 1 L-R group,the expression levels of MMPs were relatively high,but the expression levels of TIMPs were relatively low.Conclusion:1.During the median follow-up period of 45 months,BAV(ascending aorta diameter between 35-50mm)are more likely to develop continued dilatation of ascending aorta after AVR than TAV.2.In BAV patients,type 1,smoking history and aortic regurgitation were independent risk factors for ascending aorta dilation after AVR.Therefore,for BAV patients with the above risk factors and the diameter of ascending aorta between 35-50 mm,we should take a positive attitude to the ascending aorta during AVR operation,such as ascending aortic angioplasty,ascending aortic wrapping,Bentall operation,etc.,so as to reduce the risk of long-term expansion or dissection of the ascending aorta.3.Compared with control group,TAV and other BAV types,the ascending aorta in type 1L-R has the most severe extracellular matrix degradation,which makes this type of aorta show the weakest supporting ability.Therefore,this classification is more prone to aortic aneurysm and even dissection.