Surgical aortic valve replacement (SAVR) has long been the standard of care for patients with symptomatic severe aortic stenosis (AS). However, over the last decade, the emergence of transcatheter aortic valve replacement (TAVR) has shifted the treatment paradigm for extreme- and high-risk patients.^1-4 As indications for TAVR expand to include younger and healthier patients who are expected to outlive their initial bioprosthesis, understanding the long-term implications of the initial intervention is paramount.^5-8 Patients undergoing SAVR may receive a mechanical or bioprosthetic aortic valve, with the former offering a more durable treatment solution at the cost of lifelong anticoagulation.⁹ Fortunately, advances in TAVR have been paralleled in part by development of new surgical bioprostheses, which have improved hemodynamics and potentially better leaflet anticalcification treatment in the hopes of reducing rates of structural valve deterioration (SVD), thus increasing durability without the need for anticoagulation.¹⁰ Younger patients must have the realistic expectation of the need for re-intervention and the implications of initial intervention.

Since the turn of the century, there has been a dramatic shift towards bioprosthetic valve implantation in SAVR owing to preference in younger patients and the risk of bleeding associated with long-term anticoagulation in older patients.¹¹ In older patients with short life expectancy attributed to additional co-morbidities, valve durability is less of a concern, with TAVR being the preferred treatment.¹² For younger patients, this fully percutaneous alternative to surgery is an attractive short-term option with lower procedural risk and the possibility to return to work and a normal active life earlier relative to SAVR. However, the risk of permanent pacemaker implantation, the surgical risk of TAVR explantation, and paravalvular leak post-TAVR must be considered in younger patients. These complications may be fairly well tolerated in older patients, but it is less clear what the long-term effects may be in younger patients. Additionally, younger patients with aortic stenosis are more likely to have bicuspid aortic valves (BAV). BAV patients may have more bulky calcified leaflets or a heavily calcified raphe which can limit transcatheter heart valve (THV) expansion and may affect durability. This predisposes to paravalvular leak which results in increased volume load that may not be tolerated over the lifetime of the THV. Despite these considerations, studies have shown that TAVR can effectively treat AS associated with BAV in appropriately chosen patients.

The long-term implications of a TAVR-first strategy for young patients remain unknown. The NOTION (NOrdic aortic valve intervenTION) trial is the first trial to randomize low-risk patients to SAVR versus TAVR and the only one with available long-term data.¹³ At 8 years follow-up, there were no significant differences in mortality, stroke, myocardial infarction or bioprosthetic valve failure.¹³ In fact, there was a statistically significant difference in hemodynamic performance of the valves favoring TAVR, based on effective orifice area and mean transvalvular gradient. This may reflect the ability of TAVR to expand into a range of annular sizes, whereas surgical valves are sized in fixed increments, although the long-term effects of these differences remain undefined. This is encouraging data given the gradual improvements in THVs over the last decade. With trends over the last 5five years to begin intervening on AS sooner in the disease course, data comparing initial SAVR versus TAVR will be critical. Data from the pivotal low-risk TAVR trials in the United States will shed additional light on the durability of contemporary THVs.^7,8 Until then, SAVR remains the standard of care for younger patients with longer life expectancy, offering several feasible options in the event of bioprosthetic valve failure¹² although patients are increasingly requesting TAVR.

Bioprosthetic failure following SAVR or TAVR may be treated with re-do surgery or valve-in-valve (ViV) TAVR. Registry data suggests that both offer similar short-term outcomes.¹⁴ However, given the marked differences in hazard functions between the two treatment options, a properly designed randomized trial is required to guide clinical decision making when selecting reintervention following SAVR. Unfortunately, this is unlikely to occur given the challenges of randomizing patients to surgery. The same can be said regarding bioprosthetic failure following TAVR. Given the relatively recent emergence of TAVR and the fact that most initial patients were older with multiple comorbidities, the collective experience with failing THVs remains insufficient. Late surgical explantation following TAVR may require aortic root repair and/or reconstruction and is associated with increased morbidity and mortality relative to redo SAVR after SAVR.^15,16 This occurs due to the incorporation of the THV stent frame into the aortic wall over time and often requires extensive dissection to explant. For patients in whom this increased risk is not tolerable, ViV TAVR is an attractive alternative to surgery and, in carefully selected patients, appears to be safe.¹⁷ Unfortunately, a larger than expected percentage of patients with failing THV may not be candidates for ViV TAVR due to anatomic and hemodynamic considerations. In ViV TAVR the leaflets of the initial bioprosthesis (SAVR or TAVR) are pinned in the open position by the ViV TAVR, which for patients with low coronary heights or inadequate sinuses can result in sinus sequestration or direct obstruction at the coronary ostium.^18-20 Recent trends of higher THV implantation relative to the aortic valve annulus in order to guard against risk of complete heart block may specifically limit the anatomic feasibility of TAVR-in-TAVR.

For patients with prior bioprosthetic SAVR, this problem can be ameliorated through the BASILICA (Bioprosthetic or native Aortic Scallop Intentional Laceration to prevent Iatrogenic Coronary Artery obstruction) procedure in which the operator uses an electrified wire to split the bioprosthetic leaflets to prevent coronary occlusion.²¹ A modified balloon-assisted BASILICA procedure has been described which allow for more effective leaflet modification in patients previously thought to be ineligible for TAVR-in-TAVR.²²

Additionally, VIV after SAVR or TAVR may result in unacceptably high rates of patient prosthesis mismatch (PPM). Severe PPM as defined by indexed valve area is associated with increased risk of death and heart failure exacerbation.²³ The ViV TAVR must be appropriately sized to fit within the previous prosthesis to facilitate full expansion; this often requires downsizing relative to the prior implant and will result in increased transvalvular gradients and decreased effective orifice area. In older or more sedentary patients, this may be tolerated, but will be of concern when younger, more active patients require aortic valve reintervention.

At the time of initial SAVR, younger patients who have small aortic annuli (i.e., less than 23 mm) may benefit from an aortic root enlargement to have a larger prosthesis placed. This will facilitate future transcatheter reintervention but comes at the expense of slightly higher perioperative risk and higher risk of pacemaker implantation.

When preoperative ViV TAVR sizing suggests the possibility of moderate to severe PPM, it is possible to "crack" the frame of the previous prosthesis using an endovascular balloon. This may increase the valve annulus size by 1-2 mm and facilitate the implantation of a larger THV, reducing transvalvular gradients. Risks of cracking include recognizing the utility of cracking; some newer prostheses have frames designed to allow the frame to expand more easily.

Given the durability ambiguity of current THVs, a comprehensive heart team discussion including both SAVR and TAVR should occur with younger patients with symptomatic severe AS. Currently, there is no single sequence that can be applied to all patients, as individual anatomy, lifestyle, and preferences must be considered. Choice of initial intervention has major implications over a patient's lifespan and should consider overall and not just current risk. Ultimately, planning a series of interventions is complicated and additional data from the pivotal TAVR trials regarding THV durability, structural valve deterioration, TAVR explantation, and THV thrombosis are likely to impact the decision-making for initial intervention in young patients with severe AS.

References

1. Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med 2010;363:1597-607.
2. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011;364:2187-98.
3. Adams DH, Popma JJ, Reardon MJ, et al. Transcatheter aortic-valve replacement with a self-expanding prosthesis. N Engl J Med 2014;370:1790-98.
4. Popma JJ, Adams DH, Reardon MJ, et al. Transcatheter aortic valve replacement using a self-expanding bioprosthesis in patients with severe aortic stenosis at extreme risk for surgery. J Am Coll Cardiol 2014;63:1972-81.
5. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med 2016;374:1609-20.
6. Reardon MJ, Van Mieghem NM, Popma JJ, et al. Surgical or transcatheter aortic-valve replacement in intermediate-risk patients. N Engl J Med 2017;376:1321-31.
7. Mack MJ, Leon MB, Thourani VH, et al. Transcatheter aortic-valve replacement with a balloon-expandable valve in low-risk patients. N Engl J Med 2019;380:1695-705.
8. Popma JJ, Deeb GM, Yakubov SJ, et al. Transcatheter aortic-valve replacement with a self-expanding valve in low-risk patients. N Engl J Med 2019;380:1706-15.
9. Zhao DF, Seco M, Wu JJ, et al. Mechanical versus bioprosthetic aortic valve replacement in middle-aged adults: a systematic review and meta-analysis. Ann Thorac Surg 2016;102:315-27.
10. Rodriguez-Gabella T, Voisine P, Puri R, Pibarot P, Rodes-Cabau J. Aortic bioprosthetic valve durability: incidence, mechanisms, predictors, and management of surgical and transcatheter valve degeneration. J Am Coll Cardiol 2017;70:1013-28.
11. Head SJ, Celik M, Kappetein AP. Mechanical versus bioprosthetic aortic valve replacement. Eur Heart J 2017;38:2183-91.
12. Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA guideline for the management of patients with valvular heart disease: executive summary: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. J Am Coll Cardiol 2021;143:e35-e71.
13. Jorgensen TH, Thyregod HGH, Ihlemann N, et al. Eight-year outcomes for patients with aortic valve stenosis at low surgical risk randomized to transcatheter vs. surgical aortic valve replacement. Eur Heart J 2021;42:2912-19.
14. Deharo P, Bisson A, Herbert J, et al. Transcatheter valve-in-valve aortic valve replacement as an alternative to surgical re-replacement. J Am Coll Cardiol 2020;76:489-99.
15. Fukuhara S, Brescia AA, Shiomi S, et al. Surgical explantation of transcatheter aortic bioprostheses: results and clinical implications. J Thorac Cardiovasc Surg 2021;162:539-47.e1.
16. Hirji SA, Percy ED, McGurk S, et al. Incidence, characteristics, predictors, and outcomes of surgical explantation after transcatheter aortic valve replacement. J Am Coll Cardiol 2020;76:1848-59.
17. Landes U, Webb JG, De Backer O, et al. Repeat transcatheter aortic valve replacement for transcatheter prosthesis dysfunction. J Am Coll Cardiol 2020;75:1882-93.
18. Rogers T, Greenspun BC, Weissman G,et al. Feasibility of coronary access and aortic valve reintervention in low-risk TAVR patients. JACC Cardiovasc Interv 2020;13:726-35.
19. Forrestal BJ, Case BC, Yerasi C, et al. Risk of coronary obstruction and feasibility of coronary access after repeat transcatheter aortic valve replacement with the self-expanding evolut valve: a computed tomography simulation study. Circ Cardiovasc Interv 2020;13:e009496.
20. Ribeiro HB, Rodes-Cabau J, Blanke P, et al. Incidence, predictors, and clinical outcomes of coronary obstruction following transcatheter aortic valve replacement for degenerative bioprosthetic surgical valves: insights from the VIVID registry. Eur Heart J 2018;39:687-95.
21. Khan JM, Greenbaum AB, Babaliaros VC, et al. The BASILICA trial: prospective multicenter investigation of intentional leaflet laceration to prevent TAVR coronary obstruction. JACC Cardiovasc Interv 2019;12:1240-52.
22. Greenbaum AB, Kamioka N, Vavalle JP, et al. Balloon-assisted BASILICA to Facilitate Redo TAVR. JACC Cardiovasc Interv 2021;14:578-80.
23. Herrmann HC, Daneshvar SA, Fonarow GC, et al. Prosthesis–patient mismatch in patients undergoing transcatheter aortic valve replacement: from the STS/ACC TVT registry. J Am Coll Cardiol 2018;72:2701-11.

Clinical Topics: Anticoagulation Management, Arrhythmias and Clinical EP, Cardiac Surgery, Cardiovascular Care Team, Congenital Heart Disease and Pediatric Cardiology, Diabetes and Cardiometabolic Disease, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Valvular Heart Disease, Implantable Devices, Aortic Surgery, Cardiac Surgery and Arrhythmias, Cardiac Surgery and CHD and Pediatrics, Cardiac Surgery and Heart Failure, Cardiac Surgery and VHD, Congenital Heart Disease, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Interventions, CHD and Pediatrics and Prevention, CHD and Pediatrics and Quality Improvement, Acute Heart Failure, Interventions and Structural Heart Disease

Keywords: Transcatheter Aortic Valve Replacement, Bioprosthesis, Aortic Valve, Follow-Up Studies, Bicuspid Aortic Valve Disease, Coronary Occlusion, Coronary Vessels, Feasibility Studies, Lacerations, Motivation, Return to Work, Sedentary Behavior, Standard of Care, Aortic Valve Stenosis, Registries, Clinical Decision-Making, Myocardial Infarction, Life Expectancy, Anticoagulants, Surgical Instruments, Heart Failure, Heart Block, Hemodynamics, Dissection, Morbidity, Iatrogenic Disease, Pacemaker, Artificial, Thrombosis, Pectinidae, Stents, Stroke

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