Transcatheter Aortic Valve Implantation vs Surgical AVR for Severe Aortic Stenosis

Abstract & Commentary

By Andrew J. Boyle, MBBS, PhD, Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco. Dr. Boyle reports no financial relationship relevant to this field of study.

Source: Smith C, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011;364:2187-2198.

Percutaneous transcatheter aortic valve implantation (TAVI) is an emerging technique for the treatment of aortic stenosis (AS). By this method, a bioprosthetic valve (bovine pericardium) attached to a stent can be deployed in the aortic valve position via a catheter delivery system inserted through either the femoral artery or via the apex of the left ventricle. This technique is available in Europe and is being considered by the FDA for release in the United States. The previously presented Partner Trial Cohort B demonstrated a 20% reduction in mortality with TAVI compared to medical therapy in patients with inoperable severe AS. However, in patients who are still candidates for surgical aortic valve replacement (AVR), it is not known whether TAVI is a reasonable alternative. The Partner Trial Cohort A, presented here by Smith et al, is a randomized, multicenter trial comparing TAVI vs AVR in high-risk patients with severe symptomatic AS. The study was designed to demonstrate noninferiority of TAVI compared to AVR and the primary endpoint was all-cause mortality at 1 year.

The study was performed in 25 centers in three countries, but predominantly in the United States. The authors enrolled 699 patients with severe AS (defined as aortic valve area < 0.8 cm2 plus either a mean gradient ≥ 40 mmHg or a peak velocity of at least 4.0 m/sec) and randomized them to surgical AVR (n = 351) vs TAVI (n = 348). All patients were deemed to be at high risk by the regional surgeon, guided by an estimated post-operative mortality of at least 10% by the STS (Society of Thoracic Surgeons) scoring system. Exclusion criteria were a bicuspid or non-calcified valve, coronary artery disease requiring revascularization, a left ventricular ejection fraction of less than 20%, an aortic annulus diameter of < 18 mm or > 25 mm, severe (4+) mitral or aortic regurgitation, a recent neurologic event, and severe renal insufficiency. Patients assigned to TAVI underwent transfemoral placement (n = 248), unless there was significant peripheral arterial disease (PAD) that precluded large sheath placement in which case they underwent a trans-apical procedure (n = 103). All patients received heparin during the procedure and dual antiplatelet therapy for 6 months post-procedure.

This study enrolled high-risk patients but there were no differences between groups at baseline. The mean age was an astonishing 84 years and the mean STS score was 11.8%. Ninety-four percent of patients were in NYHA class III or IV. After randomization, 42 patients did not undergo the assigned procedure (4 in the TAVI group and 38 in the surgical AVR group). The TAVI procedure was aborted or converted to an open procedure in 16 of 348 patients (4.6%) and surgical AVR was converted to TAVI in one case.

At 1 year, there was no difference in mortality following TAVI vs surgical AVR. The all-cause mortality rate was 24.2% in the TAVI group and 26.8% in the surgical AVR group (P = 0.44), an absolute reduction of 2.6% in the TAVI group. This was within the authors' predefined margin of 7.5% for noninferiority (P = 0.001 for noninferiority). The rates of major stroke were 3.8% in the TAVI group and 2.1% in the surgical AVR group at 30 days (P = 0.20) and 5.1% and 2.4%, respectively, at 1 year (P = 0.07). At 30 days, major vascular complications were significantly more frequent with TAVI (11.0% vs 3.2%; P < 0.001); adverse events that were more frequent after surgical replacement included major bleeding (9.3% vs 19.5%; P < 0.001) and new-onset atrial fibrillation (8.6% vs 16.0%; P < 0.01). More patients undergoing TAVI had an improvement in symptoms at 30 days, but by 1 year, there was not a significant between-group difference.

At 1 year, TAVI was slightly superior to surgical replacement with respect to the mean aortic-valve gradient (10.2 ± 4.3 mmHg vs 11.5 ± 5.4 mm Hg; P = 0.008) and mean valve area (1.59 ± 0.48 cm2 vs 1.44 ± 0.47 cm2; P = 0.002), although the clinical significance of such small differences remains unknown. Moderate or severe paravalvular regurgitation was more frequent in the TAVI group than in the surgical group at 30 days (12.2% vs 0.9%; P < 0.001) and at 1 year (6.8% vs 1.9%; P < 0.001). The authors conclude that in high-risk patients with severe AS, TAVI, and surgical AVR were associated with similar rates of survival at 1 year, although there were important differences in periprocedural risks.

Commentary

This landmark trial demonstrates that percutaneous TAVI is a realistic alternative to surgical AVR in high-risk patients with severe symptomatic AS. It is worth noting that the predicted 30-day surgical mortality was 11.8%, but the observed mortality was 8.0% in those who underwent surgical AVR. This suggests that the surgeons involved in this trial were very skilled, and yet TAVI still performed well compared to such skilled surgery.

There are important periprocedural complications that warrant mention. Vascular access complications are more common with TAVI than with surgical AVR. Although these may sound like minor complications, they can be more severe than most cardiac catheterization-related access site complications due to the large sheath sizes. As experience with the procedure has grown, and the devices are becoming smaller, access site complications are becoming less frequent, and we can expect the rates to continue falling as devices and techniques continue to evolve. Furthermore, there was a numerically higher rate (double) of stroke in the TAVI group. The rates were higher in both the transfemoral and the transapical groups. Hopefully this rate declines as the devices become lower in profile and with newer embolic protection devices that are being developed. Further research is needed to reduce this stroke risk if TAVI is to become a permanent part of the treatment landscape for AS. We look forward to further data from this trial that will involve cost-effectiveness analyses.

The future for percutaneous aortic valve therapies looks bright. The FDA is currently considering approval for this device, and another percutaneous aortic valve is in phase 3 clinical trials. Numerous iterations of devices are in early-phase testing and, in the years to come, there will likely be significant improvements over the generation of devices currently used in Europe. However, for now, surgical AVR remains the standard of care for patients in the United States with severe AS.