Transcatheter aortic valve replacement for bicuspid aortic valve stenosis
SIZING OF THE PROSTHESIS
Sizing of the prosthesis in patients with bicuspid aortic valve stenosis remains a challenge: some experts advocate the usual practice of measuring the perimeter and area at the level of the annulus, while others advocate measuring at the level of the commissures, 4 to 8 mm above the annulus. Balloon valvuloplasty may be a useful sizing tool, though it carries the hazards of severe aortic regurgitation and periprocedural stroke.
Angiography of the ascending aorta during balloon valvuloplasty can help verify whether an adequate seal is achievable and aid in selecting an appropriately sized prosthesis. Liu et al10 performed sequential balloon aortic valvuloplasty before TAVR with a self-expanding valve in 12 patients. Of these, 11 (91.7%) received a smaller device than they would have with multidetector computed tomography-guided annulus measurement.
Given that a larger valve may increase the risk of annular rupture, implantation of a smaller valve is always reasonable in bicuspid aortic valve as long as it achieves appropriate sealing with no paravalvular leak.
THE NEED FOR A PACEMAKER
After undergoing TAVR, more patients who have a bicuspid aortic valve need a permanent pacemaker than those who have a tricuspid aortic valve. This group appears to be more vulnerable to conduction abnormalities after TAVR, and rates of new pacemaker implantation as high as 25% have been reported with the newer-generation devices. Perlman et al8 observed that even when the Sapien 3 valve was implanted high in the left ventricular outflow tract, nearly 10% of patients needed a new pacemaker.
This is an important issue, as most patients with bicuspid aortic valve with severe aortic stenosis are relatively young and may endure deleterious effects from long-term pacing.
LONG-TERM OUTCOMES
The data on long-term outcomes of patients with bicuspid aortic valve who undergo TAVR are limited, and the available studies were small, with relatively short-term follow-up. However, Yoon et al compared TAVR outcomes between bicuspid and tricuspid aortic stenosis patients using propensity-score matching and demonstrated comparable all-cause mortality rates at 2 years (17.2% vs 19.4%, P = .28).6
Given the relatively long life expectancy of patients with bicuspid aortic valve undergoing TAVR, who tend to be younger than those with tricuspid aortic valve stenosis, longer-term data are needed to draw meaningful conclusions about the durability of transcatheter valves in this population. The bicuspid aortic valve is asymmetric, so that during TAVR the stent may not expand completely, and this in theory may result in more strain on the prosthesis and accelerate its structural deterioration.
In a recent meta-analysis, Reddy et al11 analyzed 13 observational studies in 758 patients with severe bicuspid aortic valve stenosis undergoing TAVR with older and newer devices. The mean Society of Thoracic Surgeons Predicted Risk of Mortality score, which predicts the risk of death within 30 days, was 5.0%, but the actual rate was 3.7% (95% confidence interval [CI] 2.1%–5.6%). A high procedural success rate of 95% (95% CI 90.2%–98.5%] was also noted, but the rates of new permanent pacemaker implantation (17.9%, 95% CI 14.2%–22%) and severe perivalvular leak (12.2%, 95% CI 3.1%–24.8%) were somewhat elevated.11
NOT FOR ALL, BUT AN EMERGING, VIABLE OPTION
As implanted prostheses and TAVR techniques undergo continuous improvement and as the experience of operators and institutions advances, procedural outcomes will likely improve.
The available data suggest that TAVR with the newer devices, when performed by experienced hands, is a viable option across most of the risk spectrum in patients with severe tricuspid aortic stenosis, including low-risk patients,12 and selectively in patients with bicuspid aortic valve stenosis. However, for patients with bicuspid aortic valve with severe aortic stenosis and associated aortopathy, surgery remains the standard of care.
More study is needed to identify patients with bicuspid aortic valve who can be safely and effectively treated with TAVR.
