Transcatheter aortic valve replacement or surgical aortic valve replacement: Establishing a middle ground

Abstract

Transcatheter aortic valve replacement (TAVR) has emerged as an established standard of care for patients with severe aortic stenosis (AS), irrespective of their surgical risk. However, despite the continuous advancements over last two decades, there are still significant challenges in field in terms of appropriate selection of patients as well as the valves. While there is no doubt that TAVR has now become the leading mode of treatment for severe AS patients, surgical aortic valve replacement (SAVR) still holds its value for the selective group of patients who are not ideal candidate for the minimally invasive procedure: TAVR. The dilemma is palpable in the clinical field that warrants best approach focusing on the lifetime management of these patients. In the recent metanalysis by Moradi et al, the authors provide a comprehensive insight into TAVR vs SAVR in terms of mortality, procedural complications, and post-procedure adverse events. In this editorial, we shed light on comparative analysis of both modalities to establish a middle ground.

Key Words: Transcatheter aortic valve replacement; Surgical aortic valve replacement Pacemaker implantation; Aortic stenosis; Transcatheter heart valves

Core Tip: In the last few years, transcatheter aortic valve replacement (TAVR) has emerged as a formidable and preferred alternative to surgical aortic valve replacement (SAVR) for the treatment of symptomatic patients with severe aortic stenosis across all risk strata owing to the results of large randomized controlled trials (RCTs). Moradi et al in their metanalysis of RCTs provide a comprehensive insight into TAVR vs SAVR in terms of mortality, procedural complications, and post-procedure adverse events. In this editorial, we discuss the current status of TAVR vs SAVR and shed light on comparative analysis of both modalities to establish a middle ground.

INTRODUCTION

The first transcatheter delivery of an aortic valve prosthesis was performed by Cribier et al[1] in April 2002. Since then, based on supporting data from randomized clinical trials (RCT), TAVR has emerged as a reasonable alternative to surgical aortic valve replacement (SAVR) for the treatment of symptomatic patients with severe aortic stenosis (AS) across all risk strata. Last two decades have witnessed substantial growth and improvement in transcatheter heart valve (THV) systems and transcatheter aortic valve replacement (TAVR) techniques. While the number of patients treated with minimally invasive TAVR has been noted to surpass SAVR lately, yet new challenges have endured over time and there is further demand to optimize risk reduction for better outcomes[2]. In this issue of World Journal of Cardiology, Moradi et al[3], in their systematic review and meta-analysis of RCTs, provide a comparative comprehensive insight into TAVR and SAVR in terms of mortality, procedural complications, and post-procedure adverse events. The authors included 10 RCTs and affirmed that TAVR was associated with lower rates of acute renal injury [Risk ratio (RR): 0.33; 95%CI: 0.25–0.44], major bleeding (RR: 0.37; 95%CI: 0.30–0.46), and new onset atrial fibrillation (RR: 0.44; 95%CI: 0.34–0.57), while the rates of permanent pacemaker implantation (RR: 3.49; 95%CI: 2.77–4.39), major vascular complications (RR: 2.47; 95%CI: 1.91–3.21), paravalvular leaks (PVL) (RR: 4.15; 95%CI: 3.14–5.48) were higher compared to SAVR. The stroke and myocardial infarction rates were similar among two groups. Mortality was noted lower at 1-year in TAVR (8 studies) and higher at 5-year (5 studies).

TAVR VS SAVR

The authors should be commended for providing the comprehensive comparison of TAVR vs SAVR, however, it should be emphasized that these results comprised of all cohorts irrespective of their surgical risk and should be extrapolated with caution when comparing the individual risk-cohort. Lower mortality at 1-year in TAVR cohort is possibly due to inclusion of more low-risk trials in the analysis at 1-year, compared to 5-year. As an example, at 1-year, the results of both low-risk trials, Placement of Aortic Transcatheter Valves (PARTNER)-3, and evolut low risk were included, but at 5-year, only PARTNER-3 was included in the meta-analysis. The initial landmark RCT comparing the two modalities, PARTNER-1, enrolled high-risk patients, with TAVR demonstrating non-inferiority with comparable outcomes to SAVR in terms of all-cause mortality but with higher proportions of major vascular complications and lower risk of major bleeding[4,5]. While the risk of stroke was initially higher in the TAVR group at 30 days and 1 year, this difference disappeared over 5 years. Then, the PARTNER-2[6] and Surgical Replacement and Transcatheter Aortic Valve Implantation[7] trials in the intermediate-risk cohort, again exhibited non-inferiority of TAVR for mortality and stroke, with continued concerns regarding higher incidences of major vascular complications vs SAVR, however, the rates of major bleeding and acute renal failure were lower than SAVR. These studies also found higher rates of PVL and pacemaker implantation in TAVR cohort[6,7]. There is no doubt that the presence of calcified and tortuous iliofemoral vessels is expected to increase the risk of vascular complications in intermediate to high-risk cohorts with burden of other comorbidities, particularly when obtaining large bore transfemoral access for TAVR. In contrast, the risk appears to be mitigated and comparable in low-surgical risk patients with favorable vascular anatomy[8]. Subsequently, low-risk trials including PARTNER-3[9] and evolut low-risk[8] demonstrated similar all-cause mortality and stroke rates among two groups, although the risk of atrial fibrillation and major bleeding were again noted higher in SAVR group, however, the evolut low-risk trial did raise the concerns of higher pacemaker implantation need with self-expandable valves (SEV)[10]. Therefore, altogether, the findings of current meta-analysis do resonate with the results of prior RCTs.

The unequivocal question remains; would TAVR predominantly replace SAVR across all risk strata? We must acknowledge the fact that despite continuous refinement in the technology and availability of newer THV systems, the limitations with TAVR prevails, including higher rates of permanent pacemaker than SAVR, even in low-risk cohort. While the operator dependent elements such as depth of implantation can be expertise, the presence of baseline conduction abnormalities such as right bundle branch block does pose higher risk of pacemaker implant post-TAVR[11]. Furthermore, SEV has higher rates than balloon-expandable valves, again documented in the recent 4-year data of evolut low-risk[12]. Newer techniques such as shallow depth implantation and cusp overlap have shown some promise in mitigating the risk of pacemaker implantation[13]. Additionally, the presence of moderate to severe PVL post-TAVR is found to be associated with long-term increased risk of mortality[14]. Although, the improvement in the device design and better sealing mechanisms of CoreValve Evolut PRO/PRO+/FX systems have led to reduction in PVL[15,16], factors including valve under-sizing, malpositioning, left ventricular outflow tract (LVOT) calcification, incomplete passive expansion of SEV appears to contribute to PVL. Finally, we should also recollect that the landmark RCTs comparing two modalities did exclude patients with unfavorable anatomies such as bicuspid aortic valve, short or large annulus diameters, severe LVOT calcification, concomitant severe valvular or coronary disease, associated aortopathy, and poor transfemoral access. Consequently, this rare group of patients in real world scenarios, would continue to challenge both modalities, particularly TAVR.

The key limitation of bioprosthetic valves is their susceptibility to degeneration, which is of the utmost importance when considering the lifetime management of young patients. The current evidence reports promising results for durability of TAVR valves beyond 5 years and freedom from structural valve deterioration (SVD) from 6 and 9 years of duration[17-19]. The longest reported follow up of TAVR comes from Nordic Aortic Valve Intervention Trial, where at 10 years, the risk of SVD was lower after TAVR than after SAVR, while the risk of bioprosthetic valve failure was similar among them at 8 years[20]. In contrast, the contemporary studies of surgical valves have demonstrated excellent durability exceeding 17 years on protocolized follow-up[21]. Therefore, when considering lifelong management, the latest guidelines endorse TAVR over SAVR for patients with severe AS with age > 80 years or younger patients with life expectancy < 10 years (Class I recommendation)[22]. On the contrary, young patients < 50 years of age, SAVR with mechanical prosthesis is reasonable if no contraindication to anticoagulation (Class IIa recommendation)[22]. For the age group of 50 to 65 years, the choice of valve (mechanical or prosthetic) and procedure (TAVR or SAVR) should be considered after evaluating individual patient factors and shared-decision making[22]. Lastly, patients more than 65 years of age, guideline suggests it is reasonable to choose bioprosthetic valve (TAVR or SAVR) over mechanical prosthesis. The specific longevity of valve can vary based on individual factors and the type of valve used, and currently there is no precise tool for prediction.

Therefore, keeping this in mind, the next generation valve system should not only alleviate the limitations of earlier generation valves; should also offers long-term durability. The latest generation Evolut FX + transcatheter valve system is designed to enable lifetime management solutions such as coronary access, and studies are eagerly awaited. The fifth-generation SAPIEN 3 Ultra Resilia valve in a recent study demonstrated lower mean gradients and lower rates of PVL than earlier generations of balloon expandable THV platforms[23]. In latest study, the ALIGN-AR trial, the Trilogy THV (JenaValve Technology, Irvine, CA, United States) demonstrated the safety and effectiveness of treating native moderate to severe or severe aortic regurgitation in high surgical risk cohort at 1-year[24]. Therefore, with continuous refinement in technology over last two decades, TAVR has also emerged as an economically dominant strategy, with studies suggesting while TAVR procedures initially seems expensive due to higher valve prices, though this is often offset by shorter hospital stay and lower long-term costs[25].

CONCLUSION

Undoubtedly, TAVR has emerged as a feasible treatment for inoperable or high-surgical risk patients, but ambiguity remains in the selection of appropriate modality in the low- and may be intermediate-risk cohorts. While there is no straightforward answer, factors such has patient age, lifetime management, individual risk profiles, congenital anomalies, associated comorbidities should be taken into account by the institutional heart teams, while establishing a reasonable middle ground among two modalities with a sole purpose of improving long-term patient outcomes. The future generation valve systems should focus on alleviating the limitations of earlier generation valves and resilience to SVD offering long-term durability.