Initial learning curve, annual case volume key in TAVR outcomes

A learning curve of at least 225 procedures is required for hospitals to perform transcatheter aortic valve replacements (TAVRs) with the lowest mortality rates, suggests a study of 16 centers participating in an international registry.

The findings, published online in JACC: Cardiovascular Interventions, also point to annual institutional case volume as an important predictor of procedural safety and 30-day patient mortality.

Anthony W.A. Wassef, MD, and colleagues studied procedural and clinical outcomes for 3,403 patients who underwent TAVR at 16 different facilities in Europe, North America and South America. The centers contributed to an international TAVR registry from the start of their programs, allowing the researchers to analyze whether an initial learning curve and annual case volumes were associated with clinical outcomes.

Patients who were among the first 75 to receive TAVR at a given institution were almost four times more likely to die within 30 days after multivariable adjustment versus those who underwent the operation at a center with at least 300 cases under its belt. Compared to centers with at least 300 procedures, those with 76 to 225 cases’ experience demonstrated about a 2.5-fold risk of mortality. Unadjusted 30-day mortality rates dropped incrementally from 9.6 percent for the least experienced centers to 3.3 percent for the most experienced.

“In addition to a comprehensive pre-procedural patient assessment by a dedicated heart team, the TAVR requires a unique skillset and expertise for implantation and expeditiously (managing) unexpected complications,” Wassef et al. wrote. “Therefore, adequate training and experience play a critical role in improving procedural safety and clinical success.”

The study is particularly timely given CMS’s plan to release a new National Coverage Determination (NCD) for TAVR by June 25, 2019. The Medicare Evidence Development and Coverage Advisory met in July to vote on questions dealing with the importance of volume requirements for centers to start and maintain a TAVR program. On a question about how confident panelists were that the benefits of meeting procedural volume requirements outweigh the harms of limiting TAVR to only those hospitals, the results were almost split down the middle with an average score of 3.11 on a scale of 1 to 5.

“Results from the study report here by Wassef et al. suggest that there is a danger of lowering TAVR quality of care by doing away or relaxing volume requirements,” wrote John D. Carroll, MD, a cardiologist with the University of Colorado School of Medicine, in an accompanying editorial.

“This would create many new centers starting a new learning curve, result in more low-volume centers, and potentially diluting the case volume and advanced skills of established and high-volume centers.”

In addition to the differences in mortality, Wassef and colleagues found major vascular complications were significantly reduced for patients receiving TAVR in the most experienced centers.

And for annual procedural volumes, the authors noted the lowest-volume centers—with less than 50 cases per year—carried 2.7 times the risk of all-cause mortality compared to centers above that threshold. In addition, their patients were 60 percent more likely to meet the prespecified early safety endpoint, defined as a 30-day composite of death, stroke, major bleeding, vascular complications, surgical conversion and renal failure.

There were no significant differences in clinical outcomes for centers performing 50 to 100 TAVRs per year versus those performing more than 100.

“There are many low volume centers performing (fewer than) 50 procedures a year both in the United States and internationally,” Wassef and coauthors noted. “This trend is likely to continue with potential utilization of this technology in lower risk patients. The findings from the present study suggest a minimum annual volume threshold to provide the best clinical outcomes for patients undergoing TAVR procedures and can serve as a guide for optimal distribution of resources and technology.”

The researchers acknowledged their study only assessed the learning curve and annual volume of TAVR centers, not individual operators. However, they said most centers rely on a two-member TAVR team and previous data from coronary interventions suggest center volume is a stronger predictor of outcome than individual operator volume.

“Further research is required to determine whether newer TAVR technology, focused training, and proctoring can abbreviate the TAVR learning curve,” Wassef et al. wrote.

Access to care for rural patients and other underserved populations is one popular argument against imposing strict volume thresholds on TAVR centers. But Carroll said until access to care is proven to be a bigger problem than procedural quality, policymakers would be wise to limit TAVR to experienced centers.

“Until a definitive study shows access is a major problem in the United States, as well as other countries, we must emphasize quality of care with reasonable access rather than taking the McDonald’s strategy of saturation of markets for business reasons,” he wrote. “Our patients deserve better.”