High-risk patients undergoing aortic valve replacement (AVR) experience less morbidity and mortality at the hospitals that perform the most procedures, a population-based study reported.

Mortality at high volume hospitals was 2.41% versus 4.34% at low volume hospitals, wrote Himanshu J. Patel, MD, of the University of Michigan, and his co-authors, in the October 31 issue of Annals of Thoracic Surgery.

The "hinge point" that distinguished a high-volume center was 390 procedures over 4 years.

"At this hinge point, observed to expected ratio (O/E) for operative mortality after AVR was lower in [high-volume hospitals] for patients with a predicted risk of mortality greater than 4.7%," the authors wrote.

Compared with low-volume counterparts, high-volume centers also reported lower rates of prolonged ventilation (24.9% versus 30.9%, P<0.001), postoperative transfusion (46.1% versus 59.0%, P<0.001), pneumonia (6.6% versus 9.0%, P=0.01), and multisystem organ failure (0.7% versus 1.8%, P=0.012).

Other independent predictors of early mortality (all P<0.05) identified by the study "included age, female sex, and predicted risk of mortality," the authors wrote.

The study was based on 6,270 patients undergoing AVR or AVR plus coronary artery bypass grafting (CABG) procedures between 2008 and 2011 and entered in a statewide, audited, cardiothoracic database to which all 33 hospitals that perform adult cardiac surgery in Michigan report.

The median age of the cohort was 72, with 63.1% being male. The median predicted risk of mortality was 2.57%, and the predominant aortic valve disease in the sample was aortic stenosis (87.9%), although 14.4% had severe aortic insufficiency.

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