Abbreviations and Acronyms

AS

aortic stenosis

CT

computed tomography

TAVR

transcatheter aortic valve replacement

Introduction

The 2020 American College of Cardiology/American Heart Association guidelines¹ for managing valvular heart disease changed the focus of aortic stenosis (AS) treatment from the determination of risk stratification and feasibility to shared decision-making with the patient regarding recovery goals and the potential need for valve reoperation. In the United States, patients older than 65 years of age with symptomatic, severe AS have the option of transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement. The European guidelines employ an age cutoff of 75 years,² which is more aligned with patients in the low-risk randomized controlled trials and the median age of low-risk patients in the Society of Thoracic Surgeons national database.³ Currently, patients younger than 65 years of age with AS are the fastest-growing TAVR demographic in the Vizient Clinical Database, with 47.5% having undergone TAVR in 2021.⁴ Given their young age and longer life expectancy, many patients will require a second valve in their lifetime. The patient's desire for a faster operation and quicker recovery must be balanced against the long-term objectives of the lifetime management of valvular heart disease.

For older patients, a single prosthetic valve may be all that is needed, but for patients in their 60s with an initial bioprosthetic valve, a second valve is likely to be needed, and for patients in their 50s, 3 valves could be required. Although there are many considerations when discussing the “best” first valve for a specific patient, such as age, comorbidities, aortic root anatomy, concomitant valve disease, and coronary reaccess, the feasibility of a second valve must be considered at the preplanning stage for the first valve, especially in the younger patient population.

Current Limitations

The treatment options for failed bioprosthetic valves are surgical removal, placing a prosthetic valve within the failed surgical valve (valve in valve), or redo TAVR. For redo surgical aortic valve replacement, 30-day mortality has ranged from 2.5% to 9%.^5,6 Surgical removal of a prosthetic valve has been associated with much higher risks, including an in-hospital mortality rate of 11.9%, a 30-day mortality of 13.1%, and a 1-year mortality rate of 28.5% in the EXPLANT-TAVR registry.⁷ Importantly, 26.8% of patients presenting with failed prosthetic valves were not candidates for redo TAVR because of unfavorable anatomy. For redo TAVR, 30-day mortality rates of 0.7% to 4.6% have been reported.^6,8

The challenge with redo TAVR is the creation of a continuous leaflet neoskirt, which acts like a covered stent and can directly occlude the coronary ostia or reach the level of the sinotubular junction. The neoskirt can compromise coronary flow, prevent access to the coronary arteries, or completely sequester the sinus. Coronary obstruction after valve-in-valve surgery was associated with more than 50% mortality in the VIVID registry.⁹

For well-selected patients, redo TAVR is associated with good short-term outcomes. The redo TAVR registry identified 212 consecutive redo TAVRs, with device success using Valve Academic Research Consortium–2 criteria being achieved in 180 patients (85.1%). Failures were the result of a residual high-gradient pressures of 20 mm Hg or greater (14.1%); valvular regurgitation (8.9%); and, in only 2 cases, coronary artery obstruction (0.9%).⁸ What is unknown is how many patients were not selected to undergo redo TAVR because of an anticipated high risk of coronary artery obstruction resulting from unfavorable anatomy.

Recent Developments

The neoskirt height is unique to each valve manufacturer and valve size. Extensive benchtop research has delineated the heights of the fully pinned valve leaflets.^10,11 Redo TAVR feasibility can be assessed using computed tomography (CT) scanning on the basis of pinned leaflet height and root measurements. Table I details the steps to determine redo TAVR feasibility—most importantly, confirming that the valve-to–coronary artery distance is at least 4 mm and that the valve-to–sinotubular junction measurement is at least 2 mm, as demonstrated in Figure 1.

TABLE I. Measurements to Define Redo TAVR Feasibility

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Because of the potential increased risk of encountering unfavorable aortic root anatomy with failed supraannular valves, a CT simulation study was completed using the existing post-TAVR CT images from the Evolut Low Risk Trial (Medtronic).¹² The series evaluated the placement of a SAPIEN 3 valve (Edwards Lifesciences) within an Evolut valve at 4 locations, defined by the node level on the initial valve, as well as an Evolut-in-Evolut valve. Generally, the SAPIEN 3 valve was downsized by 1 size from the Evolut valve, confirmed using CT measurements according to the SAPIEN 3 valve indications for use. The new Evolut valve was size-matched to the initial implant. The neoskirt height was defined by the inflow edge of the index valve to the outflow edge of the SAPIEN 3 valve or the fully pinned leaflet heights for the Evolut-in-Evolut valve. Redo TAVR was deemed to have low risk of coronary artery flow obstruction and coronary artery inaccessibility if the neoskirt was below the coronary ostia midpoint. Considering a valve-to–coronary artery distance of at least 4 mm, a valve-to–sinotubular junction measurement of at least 2 mm, and an additional measurement of valve-to-aorta distance (leaflets pinned at the aorta) of at least 2 mm for the Evolut-in-Evolut valve, redo TAVR in a failed Evolut valve was most feasible (80% of cases) if the SAPIEN 3 valve was placed with outflow at node 4. Notably, even with this optimized scheme, only 68% of patients were deemed to have easy coronary artery accessibility.

Beyond the specific anatomic root measurements (Table I), the implantation depth of the initial valve at the noncoronary cusp determined the feasibility of a redo TAVR; the higher the index valve, the greater the risk of not being able to place a second valve. This finding raises concerns because placing implants higher in the aortic annulus is preferred to avoid conduction disturbances and pacemakers. Per the Optimize PRO protocol, the target Evolut implant depth was 1 to 5 mm, with a mean depth of 3 mm.¹³

Future Directions

Transcatheter aortic valve replacement is now an acceptable treatment across all risk levels, and younger patients are receiving implants with the anticipation that during their lifetime, their valve will fail. More and more patients are presenting with failed prosthetic valves. With the possibility of an exponential increase in cases, the criteria for who can undergo redo TAVR and the optimal prosthetic valve implantation technique are poorly understood. Leaflet modification strategies may not be useful because leaflets trapped between the 2 prosthetic valve frames do not adequately splay to facilitate unobstructed blood flow to the coronary arteries. Although the current focus is on redo TAVR feasibility after failed TAVR, future patients will require a much more complex decision-making process whereby selecting and properly placing the first valve will facilitate the placement of the second valve. Computer simulation and artificial intelligence may ultimately guide these decisions, and active research is underway to develop guidance for the lifetime treatment of patients with AS.