Is There a Volume-Outcome Relationship With Newer TAVR Valves? Maybe Not, Registry Suggests

Use of newer balloon-expandable valves for TAVR may weaken the relationship between procedural volume and outcomes, according to now-published data from the Society of Thoracic Surgeons/American College of Cardiology TVT Registry.

Looking at all three generations of Edwards Lifesciences’ balloon-expandable valves—Sapien, Sapien XT, and Sapien 3—researchers led by Mark Russo, MD (Robert Wood Johnson University Hospital, New Brunswick, NJ), found a learning curve that lasted for about the first 200 cases in which lower procedural volumes were associated with higher rates of mortality and stroke. After the learning curve, there was no significant relationship between volume and outcomes.

In analyses confined to Sapien 3 (S3), however, neither a learning curve nor a volume-outcome relationship was observed, even at centers with no prior balloon-expandable TAVR experience.

“After the maturation of the TAVR procedure and introduction of enhanced new technology, excellent outcomes should be achievable even early in a center’s experience,” Russo told TCTMD in an email. “The rollout and adoption of TAVR represent a new paradigm for the introduction of device therapies in the modern era. Intensive training, the heart team approach, group learning, and crowd wisdom can mitigate learning curves and volume-outcome relationships.”

These new findings will add fodder for the ongoing debate about the place of procedural volume requirements when assessing the quality of new and existing TAVR programs.

Ongoing Controversy

The study results, initially presented last year at the Structural Heart Disease Summit and now published online ahead of the February 5, 2019, issue of the Journal of the American College of Cardiology, contribute to the ongoing discussion about how best to evaluate new and existing TAVR programs. The US Centers for Medicare & Medicaid Services is currently reevaluating its national coverage determination for TAVR, with a focus on the volume issue.

Studies have largely found some degree of volume-outcome relationship for TAVR—with higher-volume centers achieving better outcomes—but there is some conflicting evidence.

Russo et al delved into this controversial area by examining data from the TVT Registry on balloon-expandable valve implants only. The analysis included 61,949 patients treated for severe aortic stenosis in a native valve across 450 hospitals between November 2011 and January 2017. Of these, 29% received a Sapien valve, 25% a Sapien XT valve, and 46% an S3 valve.

“We hypothesized that refinements and dissemination in procedural techniques, opportunities for group learning, extensive proctoring, and ongoing case support, as well as improvements in device technology, would result in shorter periods of learning for late adopters compared with early adopters; likewise, any volume-outcome relationship would be less strong in more recent experience,” the investigators explain.

And that’s what they found, with no apparent learning curve or volume-outcome relationship seen when TAVR was performed with the S3 valve, at least in terms of mortality and stroke. At centers with no prior balloon-expandable TAVR experience, there was a nonsignificant trend toward more major vascular complications at those performing two or fewer Sapien 3 implantations per month (P = 0.052).

The findings seemingly contrast with a previous look at TVT Registry data by a team led by John Carroll, MD (University of Colorado, Aurora), which showed that increasing experience with TAVR was associated with lower rates of in-hospital mortality, vascular complications, and bleeding. Russo et al note that that study included data up to November 2015, and therefore included relatively little use of S3 and greater use of non-transfemoral access.

“Given that the introduction of S3 commercially coincided with the learning curve termination in this analysis, and the earlier TVT study includes much lower rates of conscious sedation and transfemoral access, this omission of current practices and the most current-generation balloon-expandable device (S3) attenuates this older study’s practical applicability to contemporary circumstances,” the authors say.

Still, Russo added that the two studies might not conflict as much as some people think and actually have similar conclusions. “One, early in the US TAVR experience, there was a clear learning curve and volume-outcomes relationship,” he said. “Two, after adjustment for patient and procedural characteristics, there was no demonstrable volume relationship with mortality or stroke” in analyses confined to transfemoral access only.

Where Does Volume Fit?

Commenting for TCTMD, Saif Anwaruddin, MD (Hospital of the University of Pennsylvania, Philadelphia), said it’s possible that the volume-outcome relationship might be less important with the S3 valve, but he introduced a note of caution. In an analysis stratified by STS score, he pointed out, there remained a significant relationship between higher implant frequency and lower 30-day mortality among patients at intermediate risk (STS score 3 to less than 8).

“As TAVR potentially expands into lower and lower risk cohorts, I think that’s going to be important because if there is that relationship and you do get better outcomes with regards to mortality at higher-volume sites in lower-risk patients, then I think that’s an important signal and consideration,” said Anwaruddin, who co-wrote an accompanying editorial with Matthew Saybolt, MD (Monmouth Cardiology Associates, Eatontown, NJ).

However, the bigger issue deals with how the quality of new and existing TAVR programs should be assessed and how much of a role procedural volume and mortality should play in that process, Anwaruddin said. Mortality following TAVR has continued to decline since the earliest days of the procedure, and while that shows great progress, mortality becomes less useful if used as a major outcome metric.

“It’s still very important, because you don’t want to have a signal for mortality at 30 days in lower-risk patients who shouldn’t be dying from the procedure,” said Anwaruddin. “But I think other things need to be considered beyond mortality, stroke, and vascular complications.” He cited factors like infrastructure, effectiveness, safety, intervention quality, timing, and appropriateness, noting, “They’re not as easily definable as mortality or major vascular complications but they’re still important.”

And while volume will continue to be involved in assessments of the quality of TAVR programs, Anwaruddin said, “I think what we need to do is to move to more sophisticated metrics to measure good-quality care, complete care, for these patients. . . . And this may not be related solely to volume. There may be other components that we need to delve into deeply to figure out what makes a good TAVR program that does good-quality work.”

Russo agreed, saying, “Just like we refine our technologies and practices, we must continue to refine our quality metrics to measure related outcomes. As death and stroke after TAVR become increasingly uncommon, other outcomes, including pacemakers, paravalvular leak, vascular complications, functional status, and quality of life, must be assessed to measure quality. Moreover, in this setting volume is not a surrogate for quality and should not be used alone to restrict TAVR availability in lower-volume, high-quality centers, as well as [in] underserved populations."