New research by UT Southwestern cardiologists counters long-held beliefs that hospitals performing greater numbers of heart valve surgeries have better outcomes.

The JAMA Cardiology journal study involving nearly 700 hospitals found little correlation between the number of several common heart valve procedures—aortic valve replacement and mitral valve replacement or repair—performed and mortality rates during the hospital stay.

“If we used purely volume-based criteria to judge hospitals good or bad, we would misclassify nearly 45% of all hospitals in the U.S.,” said senior author Dr. Dharam Kumbhani, Assistant Professor of Internal Medicine at UT Southwestern Medical Center. “We found that, contrary to many older studies, there was a very weak association of hospital annual volumes with risk-adjusted outcomes for these procedures.”

More than 100,000 heart valve surgeries are performed annually, usually to repair leaky or narrowed valves, which regulate blood flow through the heart.

More than a third of the hospitals with the highest volumes of valve repair surgeries had the highest risk-standardized mortality rates, while roughly 20% of the hospitals with the lowest surgical volumes scored among the best in terms of risk-standardized mortality. The analysis took into account differing patient characteristics and additional illnesses, as well as the hospitals’ different risk-standardized mortality rates.

The study also found that while volumes of aortic and mitral valve surgeries tracked with each other (high-volume hospitals for aortic valve surgery were also high-volume for mitral valve surgery), outcomes for one type of valve surgery did not predict outcomes for the other.

“A center that has the best outcomes for aortic valve surgery does not necessarily have the best outcomes for mitral valve surgery. Patients need to consider outcomes for individual surgeries at hospitals to make a true informed decision prior to valve surgery,” said Dr. Kumbhani, who is part of the Transcatheter Aortic Valve Replacement (TAVR) team at UT Southwestern, which provides aortic valve replacement to patients without open surgery.

The research is important because there is growing interest in designating some hospitals as regional centers of excellence for complex valvular care, and the number of procedures performed may become a criterion for choosing them. In this study, researchers looked at data from 682 hospitals that performed surgical aortic valve replacement and mitral valve replacement and repair between 2007 and 2011, and divided them into three groups based on volume.

“We were really trying to answer an important and very fundamental question: How do you define quality when assessing heart valve surgical programs?” said Dr. Mark Drazner, another researcher on the study and Professor of Internal Medicine, Clinical Chief of Cardiology, and Medical Director of the Heart Failure, Left Ventricular Assist Devices (LVADs), and Cardiac Transplant Program at UT Southwestern, who holds the James M. Wooten Chair in Cardiology. “These data suggest that one needs to move beyond simply counting how many operations are performed annually by a hospital,” he said.