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With the recent publication of the PARTNER 3 trial (Placement of Aortic Transcatheter Valves 3) and the Evolut Low Risk trial (Evolut Surgical Replacement and Transcatheter Aortic Valve Implantation in Low Risk Patients) last year, physicians are extending the use of transcatheter heart valves to low risk patients with severe aortic stenosis (AS). In addition are the established data supporting the use of transcatheter heart valves in patients who are deemed inoperable or at high or intermediate risk for surgical aortic valve replacement. The pendulum of therapy for degenerative severe AS seems to have swung. Transcatheter heart valve implantation is emerging to become default therapy for patients with severe symptomatic AS who fit the profile of patients enrolled in these landmark trials.

Therefore, it is important to review whom this population includes. Generally, these were elderly patients (>70 years old) who had symptomatic severe AS (high-gradient AS), who were suitable for a transfemoral approach, who had a low risk for coronary obstruction, and who either had no coronary artery disease or disease suitable for percutaneous revascularization with a low SYNTAX score (Evolut Low Risk) or a low/intermediate SYNTAX Score (PARTNER 3). It is also important to point out that patients with bicuspid aortic valves, severe left ventricular outflow tract calcification, severe left ventricular dysfunction, and severe renal dysfunction were not included in the low-risk trials.

We need to be mindful of the following as more patients receive transcatheter heart valves for severe AS and as younger patients get offered this type of therapy, as will undoubtedly happen. Durability data for transcatheter heart valves are very limited, especially beyond 5 years. A study of the SAPIEN XT valve (Edwards Lifesciences; Irvine, CA) compared with the SAPIEN 3 transcatheter heart valve (Edwards Lifesciences; Irvine, CA) within the PARTNER 3 trial showed greater structural valve deterioration of the SAPIEN XT compared with surgically implanted valves. This was not seen with the SAPIEN 3 valve.

Before we consider implantation in younger patients, we need to be mindful of the potential impact of permanent pacemaker implantation post transcatheter aortic valve replacement as well as the potential long-term impact that mild peri-valvular regurgitation might have on long-term follow-up. Recently, a propensity-matched comparison of balloon expandable versus self-expanding transcatheter heart valves from a very large FRANCE-TAVI (Registry of Aortic Valve Bioprostheses Established by Catheter) registry was published that concluded use of self-expanding transcatheter heart valves is associated with a higher risk of peri-valvular regurgitation and 2-year mortality compared with balloon expandable transcatheter heart valves.¹

Another consideration in younger patients is coronary access for future treatment of coronary artery disease. This may impact the initial choice of transcatheter heart valves offered (annular versus supra-annular designs). In addition, more physiological initial deployment techniques that result in optimal commissural alignment need to be developed and adopted.

Finally, as these valves get implanted in lower-risk patients with less comorbidity who may also be younger—and therefore have a longer projected life expectancy—we need to design algorithms or strategies that address inevitable bioprosthetic valve failure and the need for a second or even third transcatheter heart valve, keeping in mind issues such as coronary obstruction/access and residual gradients that may arise from valve/patient mismatch.