2012 update on transcatheter aortic valve insertion
Approximately one-third of individuals with symptomatic aortic stenosis are not candidates for open surgical replacement because of advanced age, the presence of comorbid conditions or both. Transcatheter aortic valve replacement (TAVR) has been available as an option for select patients since 2008.
The many developments in the past year related to transcatheter aortic valve implantation (TAVI) include publication of two-year outcome data of the Placement of AoRTic TraNscathetER Valve (PARTNER) trial cohorts and approval by the Food and Drug Administration (FDA) of the Edwards Sapien prosthetic aortic valve (Edwards Lifesciences, Irvine, Calif.) for inoperable patients. The development of paravalvular aortic valve regurgitation is a new concern that has been identified in patients receiving these valves.
On Nov. 2, 2011, the FDA approved the Sapien valve for patients with senile aortic valve stenosis, but use is restricted to those considered inoperable by conventional standards for severe, symptomatic aortic stenosis. "The FDA approved the valve for all transarterial avenues, and in general, suitable vascular access can be identified in almost all patients," says Rakesh M. Suri, M.D., D.Phil., a cardiovascular surgeon at Mayo Clinic in Rochester, Minn.
In the PARTNER trial, 699 patients in cohort A were randomly assigned to TAVI (348 patients) or standard operative valve replacement (351 patients). Of the TAVI patients, those with inadequate peripheral vascular access had transaortic valve implantation (104 patients).
The two-year survival data of high-risk patients (those who were otherwise operable) in the PARTNER trial, published in the May 3, 2012, issue of New England Journal of Medicine, support TAVI as an alternative to surgery in high-risk patients. Mortality from any cause was similar in the TAVI and standard aortic valve replacement groups (P = 0.41). At two years, mortality was 34 percent in the transcatheter group and 35 percent in the standard surgery group (P = 0.78).
Encouragingly, the risk of stroke associated with TAVI appears to level off after the initial spike associated with valve insertion:
- The original PARTNER high-risk TAVI cohort experienced an increased rate of stroke at 30 days compared with patients treated with standard aortic valve insertion (5.5 percent vs. 2.4 percent; P = 0.04).
- This difference persisted at one year (8.3 percent vs. 4.3 percent; P = 0.04).
- At two-year follow-up, however, the frequency of all strokes did not differ significantly between the 2 groups (P = 0.52).
It appears that the constant hazard of late stroke is unrelated to the mode of valve replacement. Current efforts are directed at reducing the perioperative risk of stroke with use of embolic protection devices, thereby making the procedure safer. Earlier this year, a procedural stroke incidence of only 2 percent was reported in the PARTNER 1A transapical continuing access registry.
"Paravalvular regurgitation has emerged as a major concern associated with TAVI," according to Verghese Mathew, M.D., an interventional cardiologist at Mayo Clinic in Minnesota. The first reports of this procedure acknowledged that approximately 77 percent of patients had some degree of paravalvular regurgitation at 30 days. Recent data indicate that at two-year follow-up, paravalvular regurgitation was unchanged in 46 percent and worse in 22 percent.
The presence of paravalvular aortic valve regurgitation was associated with increased late mortality (P < 0.001). The effect of aortic valve regurgitation on mortality was proportional to the severity of the regurgitation, but even mild aortic valve regurgitation was associated with an increased rate of late deaths.
"It is unclear whether paravalvular aortic valve regurgitation causes late mortality or is simply associated with other causative factors," says Kevin L. Greason, M.D., a cardiovascular surgeon at Mayo Clinic in Minnesota.
There are three reasons why patients develop paravalvular aortic valve regurgitation after TAVI:
- Asymmetric or excessive calcification of the aortic valve annulus
- Improper assessment of the aortic valve annulus size
- Valve design
Mayo Clinic investigators are evaluating the first two causes with 3-D transesophageal echocardiography and multidetector computerized tomography. A better understanding of the dynamic, 3-D structure of the aortic valve annulus throughout the cardiac cycle and how it relates to the emergence of paravalvular regurgitation may improve patient selection. "It is likely that not all patients will have the right valve or annulus size to safely undergo transcatheter valve insertion," according to Dr. Greason. Technological advances in the current generation of valve prostheses may better address the problem.
As much as the transcatheter technology has enhanced patient care, more important is the creation of the multidisciplinary heart team to deliver the technology. Cardiologists and cardiac surgeons have combined their talents with remarkable results. When patients are evaluated by the team, the best technology, the best access and the best technique for aortic valve replacement are identified for the individual patient. "One size does not fit all," says Dr. Greason.