Download this article's Factoid (PDF & PPT for Gold Subscribers)

In high-risk patients with severe aortic stenosis, prosthesis-patient mismatch is more common following surgical aortic valve replacement (SAVR) than transcatheter aortic valve replacement (TAVR). Moreover, SAVR patients with severe mismatch have impaired regression of left ventricular (LV) mass and reduced long-term survival. TAVR patients with severe mismatch also face increased mortality in the absence of residual aortic regurgitation.

In light of the findings, the authors suggest that TAVR may be the preferred therapy for patients with a small aortic annulus, who are especially susceptible to prosthesis-patient mismatch.

The core data were originally presented at the American College of Cardiology/i2 Scientific Session and the American Society of Echocardiography 24^th Annual Scientific Sessions, both in 2013.

Mismatch Higher After Surgery

The overall incidence of patient-prosthesis mismatch was lower among TAVR patients than SAVR patients in the randomized trial (46.4% vs 60.0%; P < .001), as were rates of moderate (26.6% vs 31.9%) and severe (19.7% vs 28.1%) mismatch. Severe mismatch was also lower with TAVR compared with SAVR, particularly among patients with an aortic annulus diameter < 20 mm (19.0% vs 33.7%; P = .002). 

After the procedure, TAVR patients had a higher indexed aortic valve area and lower gradient compared with SAVR patients (P = .0004 for both).

Rates of overall, moderate, and severe mismatch in the TAVR registry (43.8%, 30.2%, and 13.6%, respectively) were similar to those in the randomized TAVR arm. In addition, TAVR registry patients who underwent postdilation had less mismatch compared with those who did not (30.6% vs 45.8%; P < .001).

At 1 year, LV mass had regressed less in patients with vs without mismatch in the SAVR arm but not the randomized TAVR arm; mismatch patients in the TAVR nonrandomized cohort showed a trend toward less regression (table 1).

Table 1. Percent Change in LV Mass From Baseline to 1 Year

Abbreviation: RCT, randomized controlled trial.

On multivariable analysis, severe mismatch predicted 2-year mortality in the SAVR arm (HR 1.78; 95% CI 1.02-3.11), though not in the randomized TAVR arm. Among nonrandomized TAVR patients, severe mismatch was associated with 1-year mortality in patients with no postprocedural aortic regurgitation (HR 1.88; 95% CI 1.09-3.22). 

Mismatch Due in Part to Surgical Valve Design

According to the study authors, the lower incidence of prosthesis-patient mismatch with TAVR may be due to the superior hemodynamic performance of transcatheter valves. “Although the transcatheter valves are stented valves, the stent is thinner and no sewing ring occupies the annular space, which causes less obstruction to blood flow,” they observe.

In a telephone interview with TCTMD, study coauthor Josep Rodés-Cabau, MD, also of the Québec Heart and Lung Institute, suggested that valve postdilation and valve oversizing relative to the annulus probably also play a role in better TAVR results. In fact, he said, the best way to minimize mismatch is to size the aortic valve accurately using computed tomography or 3D echocardiography.  In the future, it will be important to compare the hemodynamic performance of various TAVR devices, he added, particularly in patients with a small annulus.

The increased mortality associated with mismatch may be due to the negative effect of persistent residual LV afterload and hypertrophy on normalization of coronary flow reserve, the investigators suggest. 

They offer a number of possible explanations for the discrepant impact of mismatch on SAVR vs TAVR patients. First, in the randomized TAVR arm, patients with mismatch were younger and had higher BMI and higher prevalence of obesity than those without mismatch—all of which could have contributed to better survival. In addition, mismatch severity may have been overestimated in obese patients, they say.

Second, several studies have linked moderate-to-severe aortic regurgitation to increased mortality risk. In both TAVR cohorts, patients with mismatch had less postprocedural regurgitation than those without mismatch, and paravalvular regurgitation was rare in the SAVR arm regardless of mismatch status. “Thus, paravalvular regurgitation may have confounded or masked the effect of [prosthesis-patient mismatch] on LV mass regression and survival in TAVR,” the study authors say.

SAVR-TAVR Mismatch Difference May Decline

Dr. Rodés-Cabau acknowledged that the difference in the incidence of mismatch between SAVR and TAVR may have been exaggerated by the PARTNER protocol, in which the vast majority of surgeons used an Edwards bioprosthesis and were discouraged from performing root enlargement in patients with a smaller annulus to avoid mismatch. Moreover, recent years have seen advances in surgical devices, including stemless valves, that might yield lower rates of mismatch, he added.

Still, he said, in patients with a small annulus—including older, frail women—surgery often provides only marginal improvement in hemodynamics, making TAVR a very good option in this group. 

In an accompanying editorial, Jeffrey J. Popma, MD, and Kamal Khabbaz, MD, both of Beth Israel Deaconess Medical Center (Boston, MA), say the study data “suggest the untoward effects of [prosthesis-patient mismatch] after surgery in patients with a smaller aortic annulus are offset by more frequent moderate-severe paravalvular regurgitation after TAVR, resulting in similar 2-year mortality rates in the 2 groups.” However, efforts to reduce such regurgitation with next-generation TAVR devices and improved valve sizing and implantation techniques “may tip this mortality balance more favorably toward TAVR,” they add.

Note: Two study coauthors are faculty members of the Cardiovascular Research Foundation, which owns and operates TCTMD.

1. Pibarot P, Weissman NJ, Stewart WJ, et al. Incidence and sequelae of prosthesis-patient mismatch in transcatheter versus surgical valve replacement in high-risk patients with severe aortic stenosis: a PARTNER trial cohort-A analysis. J Am Coll Cardiol. 2014;64:1323-1334.
2. Popma JJ, Khabbaz K. Prosthesis-patient mismatch after “high-risk” aortic valve replacement [editorial]. J Am Coll Cardiol. 2014;64:1335-1338.

Related Stories:

• Studies Zero in on Baseline Factors That Influence TAVR Outcome
• Patient-Prosthesis Mismatch May Diminish Transcatheter Valve Benefit
• CT Measurements of Aorta Underscore Shortcomings of Valve Sizing Guidelines