How Durable Are Bioprosthetic Surgical Aortic Valves?

Useful comparative evidence for the durability of bioprosthetic aortic valves is lacking because of the wide variability of data collected between various studies and reports. That’s the conclusion of the most comprehensive literature review to date focused on structural valve deterioration (SVD) of surgical bioprosthetic aortic valves. The analysis was published online in JAMA Cardiology December 5 by a team of Cleveland Clinic researchers.

“Our review found vastly different follow-up periods and end points, as well as the use of no fewer than 11 different definitions of structural valve deterioration,” says the study’s corresponding author, Samir Kapadia, MD, Section Head of Invasive and Interventional Cardiology at Cleveland Clinic. “The lack of standard data collection precludes comparisons and meta-analyses.”

Ample data, but it varies widely

Although bioprosthetic aortic valves are less durable than their mechanical counterparts, they are increasingly used because of mechanical valves’ requirement for lifelong anticoagulation with its accompanying risk of bleeding complications. Nevertheless, the durability of the various bioprosthetic valves used clinically is unknown. Although many studies have reported on SVD, comparisons between available devices are difficult to make because of inconsistent data collection among studies.

To better understand the limitations of current evidence, the Cleveland Clinic investigators performed a systematic review of published literature through November 2016 with the goal of capturing all available studies on the durability of surgical bioprosthetic aortic valves. They found and analyzed 167 studies and 12 FDA reports, which collectively included 101,650 patients and 17 different valve types.

Wide variability was found among the studies in multiple parameters:

• Mean follow-up ranged from less than one year to 14 years.
• Completeness of follow-up ranged from 0.1 percent to 95 percent.
• Kaplan-Meier estimates (reported for up to 30 years of follow-up) varied from having 0 percent to 37 percent of patients remaining at risk at maximum follow-up.

Moreover, SVD definitions were inconsistent between studies, with some based on clinical factors (e.g., symptoms of heart failure, echocardiographic parameters or reoperation) and others on morphological deterioration of the valve (e.g., wear, calcification, leaflet tear, stress fracture or stent creep), in varying combinations.

Another surprising finding, according to the authors, was that only 11 studies (6 percent) reported core laboratory data, with the longest core laboratory follow-up being just five years.

“The result of poor data is that it leaves us with no reliable benchmark for valve deterioration,” says cardiothoracic surgeon Lars Svensson, MD, PhD, Chair of Cleveland Clinic’s Miller Family Heart & Vascular Institute and a co-author of the study. “Having a standard is critically important, not only for comparing existing valves but also as a benchmark against which to measure new valves and transcatheter devices as they are developed.”

Moving toward better data

The authors point out the particular importance of collecting long-term follow-up data for evaluating SVD in aortic valves. Multiple studies show that SVD risk decreases with increasing patient age at implantation. As increasing numbers of younger patients opt for a bioprosthetic valve to avoid lifelong anticoagulation therapy, a firm understanding of age-related risk is critical.

Standardizing definitions of SVD for bioprosthetic aortic valves should be another important priority, the authors note, and they identify two recent reports that include proposals for doing so:

• A proposal from the Valve in Valve International Data Group (Circulation. 2018;137:388-399) suggests defining SVD based on a staged system that takes into account the gradual nature of degeneration (e.g., three stages progressing from morphologic valve changes without hemodynamic changes through severe regurgitation or stenosis).
• A proposal from three European cardiovascular societies (Eur Heart J. 2017;38:3382-3390) defines SVD according to either hemodynamic or morphological features.

Finally, the authors of the literature review recommend that long-term core laboratory analysis be standard practice for studies.

“With so many valves in use and more options becoming available all the time, we must have a way to compare them,” concludes Dr. Kapadia. “For physicians to make evidence-based decisions, studies need to adopt an approach with long-term and complete data collection, standardized methodologies and uniform definitions.”

Photo credit: © Russell Lee