What is Driving AVr?

It is well stated that AVR with bioprostheses in young adults is associated with high rates of SVD and reintervention; in patients aged between 20 to 40 years, one or more reinterventions during their lifetime are anticipated^[9]. Although early mortality is low, the long-term survival is reduced, with a life expectancy of 60% to 75% of the age- and sex-matched life expectancy of general population. Etnel et al.^[9] have reported that bioprosthetic AVR in young adults is associated with low early mortality (3.30%), but the late mortality is high (2.39%/year), and thus overall life expectancy is impaired compared with the general population. Their study showed that thromboembolism (0.53%/year) and bleeding (0.22%/year) rates are far lower than reported for mechanical AVR in young adults (0.90%/year and 0.85%/year, respectively). Others have also reported that after AVR, thromboembolism and bleeding rates were higher compared to the general population and higher than after the Ross procedure and AVr^[10]. On the other side, AVr is consistently associated with a low risk of late valve-related morbidity, thromboembolism (< 0.7%/patient year), bleeding (< 0.3%/patient year), and infective endocarditis (< 0.2%/patient year)^[7,11]. Overall freedom from reoperation was 95% for tricuspid valves at 10 and 15 years, 89% for bicuspid aortic valves (BAV) at 10 years, and 83% for BAV at 15 years. These results are encouraging for a more widespread use of AVr, but undeniable factors like case selection and institutional case volume make a significant difference in the long-term outcomes.

Why is AVr Challenging?

AV is considered one of the parts of several components of the aortic root functioning unit and to achieve good repair outcomes, the surgeon has to address lesions at multiple levels, e.g., sinotubular junction (STJ), functional aortic annulus (FAA), sinus of Valsalva (SOV), and AV simultaneously (Table 1). In the initial experience, only FAA was in focus, and leaflet issues were remained unaddressed, but as experience grew, surgical groups identified the importance of leaflets, SOV, and the role of valvular pathology, respectively^[12]. Basic concept of good repair is to increase free margin length with maximising coaptation height, and performing all these additional procedures not only increases myocardial ischemic time but also increases chances of repair failure^[13].

In vast majority of the developing nations of southeast Asia, South America, and Africa, rheumatic heart disease (RHD) is still the most common valvular pathology, and mitral valve involvement is the most common finding, followed by multivalvular lesions^[1]. While in the developed Western world, RHD numbers are going down with increase in the degenerative valvular lesions (30-50%), and more often degenerative valves are stenotic lesions. Although the overall incidence of connective tissue disorder and congenital AV disease is stable (25-40%), the numbers of pure aortic regurgitation (AR) are limited, which could be a bottleneck in the learning curve for the surgeons^[14].

Another very important aspect of the reliable AVr is to recognise intraoperative etiopathology comprehensively and to standardise findings for the proper reporting. AR has been classified in three groups to help the pathophysiology of the lesion and decide about type of repair (Figure 1)^[15]. In a retrospective surgical study, pure valvular AR (type 1 lesion) was reported in 46% of the cases, while 54% of the patients had annular or ascending aortic dilatation (types 2 and 3 lesion)^[14]. AVr outcomes are better in types 1 and 2 regurgitant lesions, while type 3 AR had poor outcomes because of poor tissue quality. Normal range of coaptation height is between 4-5 mm, while geometric height and effective height are 5 mm (BAV) and 9 mm, respectively^[15]. All these finer technical points are part of a long learning curve, and if AVr is not performed regularly, then results might be suboptimum.

Anaesthetic experience in the intraoperative transoesophageal echocardiogram (TOE) is pivotal during AVr or aortic root procedures (remodeling or reimplantation) as it can guide towards better functional repair. De Waroux et al. have predicted “repairability” on the TOE and reported high reoperation rates (35% at the four-year follow-up) after AVr in the high-risk valve anatomy (type 3 lesions, type 2 lesion with severe prolapse, moderate calcification, significant leaflet restriction, valve coaptation < 4 mm, coaptation below the annular plane, and need for large pericardial patch extension)^[16].

Does Aortopathy Differs in Caucasian vs. Non-Caucasian Population?

Multiple meta-analysis has demonstrated potential long-term benefit of valve-sparing root replacement in cases of aortopathy in Caucasian patients, but on the contrary, long-term follow-up in Asian population are limited and occasional^[27,28].

The pattern of aortopathy in European and Asian population is significantly different as far as clinical features of the cardiovascular, ocular, and skeletal systems are concerned^[29]. Asian Marfan populations have a higher prevalence of aortic root dilatation and mitral valve prolapse compared with Caucasian Marfan populations. Type 0 BAV was more frequently observed among Europeans compared with Asians (14.5% vs. 6.8%), whereas type 1 BAV with fusion raphe between the right and non-coronary cusps was more frequently observed in the Asian group compared with the European group (19.7% vs. 13.6%). In addition, the European group had higher prevalence of significant AR and diffusely dilated type of bicuspid aortopathy compared with the Asian group^[30].

Another North American study showed that aortic dilatation and severity of BAV were higher in the Caucasian communities compared to the African American patients^[31]. Their findings raise some important issues regarding the role of genetic, ethnic, or other vascular modifiers which need to be studied in the future. Russo et al.^[32] have reported that patients who underwent surgery for type 1 BAV had more fibrosis, medio-necrosis, cystic medial necrosis, smooth muscle cell orientation, elastic fragmentation, and inflammation compared with other configurations in the follow-up.

It would be interesting to report differences in the aortopathy patterns from the different parts of the world and tailor-making surgical options based on those findings.

How Common is Pure AR and How Many Cases Surgeons Need to Keep Competence?

The Global Burden of Disease study group had reported that isolated AS was the third, and pure AR was the fourth most common valve lesion in RHD cases^[33]. Even in the Western world, referral for pure AR is not frequent in the regular cardiothoracic units, and it significantly reduces surgical team’s competency in giving standard expected outcomes.

Malas et al.^[34] have conducted a collaborative study with contribution from two busy AVr centres (one in Canada and another in Belgium) and reported about the learning curve to master the AVr technique. It takes approximately 40-60 cases to bring down complication rates, cardiopulmonary bypass time, aortic cross-clamping time, and to give standard reproducible outcomes. If surgeons are not getting regular referral, then they might take five to six years to perform the required numbers to overcome the steep learning curve.

Standardization of AVr Reporting

Standardization of the reporting can be tedious because of various surgical strategies, different techniques, and variable reporting patterns of the results^[15]. Comparing outcomes with proven technique like AVR can be challenging^[11]. The Aortic Valve Insufficiency and ascending aorta Aneurysm InternATiOnal Registry (AVIATOR) was created in European centres for enrolling patients with this subset of pathology^[35]. The reconstructive surgery includes isolated valve repair in 27%, partial root or tubular aorta replacement plus valve repair in 23%, and valve-sparing root replacements in 50% of the cases. Replacements include isolated valve replacement in 22%, tubular aorta plus AVR in 19%, and root plus valve replacement (Bentall) in 59% of the cases. Most of the expert European centres on AVr are reporting patients in the AVIATOR, while participation from American (9.5%) and Asian countries is low (0.5%), which again reflects on the discord in reporting.

Follow-up and Reoperation

A multivariate analysis of the AVr failure in a series with 10-year follow-up using intraoperative TOE had identified a shorter coaptation length (< 4 mm), eccentric jet, coaptation occurring below the level of the aortic annulus, a larger aortic annulus, and residual AR (central jet > 3mm) at the end of surgery as high-risk factors of repair failure^[36]. Type 3 repairs were especially at risk of AR recurrence because the leaflet tissue is either of not good quality (infective endocarditis, calcification, or rheumatic disease leading to the fibrosis) or insufficient to reconstruct the leaflet and require pericardial patching. Finally, another well reported pathological finding is the extension of native disease process in the residual repaired valve tissues and involves neo-cusp pericardial patch as well, eventually leading to AVr failure.