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Centers doing a higher volume of transcatheter aortic valve replacement (TAVR) started performing fewer isolated surgical procedures over time -- and when they did, it was on patients who tended to have a lower risk profile than before, a Medicare database study showed.

Those in the top two quartiles by TAVR volume showed a shrinking volume of isolated surgical aortic valve replacement (SAVR) from 2011 to 2014 (third quartile 1,557 to 1,391 and fourth quartile 2,607 to 1,791), whereas other hospitals appeared to be taking on slightly more SAVR cases, according to Robert Yeh, MD, MSc, of Beth Israel Deaconess Medical Center in Boston, and colleagues. Their study was published online in .

"The volume of TAVR has increased rapidly since its approval and now exceeds that of isolated SAVR in the United States. Despite this, SAVR volume has not decreased after the advent of TAVR in the United States and Europe, suggesting that TAVR has broadened eligibility for aortic valve replacement rather than displacing SAVR as an alternative treatment," the investigators commented.

A change in patient case mix also led hospitals performing the most TAVR to perform SAVR in patients with fewer comorbidities from 2011 to 2014. This was accompanied by falling rates of 30-day and 1-year mortality after surgery.

"The decline in SAVR volume in the larger volume TAVR centers, together with a lower risk profile of the SAVR population, implies that higher risk patients are most likely appropriately undergoing TAVR rather than SAVR," said one group led by Vinod Thourani, MD, of MedStar Heart and Vascular Institute and Georgetown University in Washington, D.C., in an accompanying editorial.

However, SAVR mortality declined even in hospitals not performing TAVR, so the data may also reflect an overall trend of decreasing mortality following these procedures, according to Yeh's group.

Their study included adult patients with severe aortic valve disease who were recorded in the Medicare Provider Analysis and Review database as getting isolated SAVR procedures during the study period (n=37,705).

Finding that lower-quartile TAVR- and non-TAVR centers kept up their SAVR volumes suggests that some patients don't have access to TAVR, wrote Thourani and colleagues, who pointed out that many hospitals were excluded from the analysis because they performed too few of either operation.

Out of 1,165 U.S. hospitals, only 85 performed more than one each of SAVR and TAVR per year in 2011-2014. Each hospital averaged 60.4 isolated SAVRs annually.

Recently, a panel was split on whether procedural volume should continue to be the main stipulation for TAVR reimbursement by Centers for Medicare and Medicaid Services. Panelists expressed confidence that a certain threshold should exist before a hospital starts a TAVR program, though some noted that such volume requirements keep the procedure out of reach for smaller, rural, and underserved area hospitals.

A new National Coverage Determination for TAVR is due out by June 25, 2019.

"The ideal aortic valve disease program requires cardiology and cardiac surgical expertise, together with a support network that includes anesthesia, intensive care, specialist surgical and medical services (neurology and aged-care medicine), nursing and allied health. This is most likely to be found in a high-volume center and lead to the best results, especially in high-risk patients," the editorialists said.

"Striking a balance between patient conveniences with a large number of low-volume centers versus improved clinical outcomes with regionalization of services should be guided with evidence," the group urged, highlighting the importance of large population registries such as the STS/ACC Transcatheter Valve Therapy registry in monitoring TAVR outcomes.

The potential for unmeasured confounding and miscoded records was a major limitation of the retrospective analysis, the authors acknowledged. In addition, surgical risk scores were not available in their dataset.