Hospital volume independently predicts AVR mortality

High-risk patients who need aortic valve replacements (AVR) with or without CABG may benefit from hospitals that perform a high volume of these procedures, according to a study published in the November issue of Annals of Thoracic Surgery.

An analysis of outcomes from a Michigan database of more than 6,000 cardiothoracic surgical procedures found that hospital volume was among the independent predictors of mortality from AVR or AVR/CABG. Hospital volume was also a predictor of 30-day readmission rates and prolonged ventilation.

“The recent advent of transcatheter aortic valve replacement (TAVR) as a viable alternative to conventional AVR for certain patient groups has thrust the discussion of volume-outcome relationships for valvular heart disease into the forefront,” wrote the authors, led by Himanshu J. Patel, MD, of the University of Michigan Medical Center in Ann Arbor.

Because of the recent changes in the healthcare landscape, they explained, there is also a focus on surgeon and hospital volume to measure institution of TAVR programs at hospitals.

“This suggests that a population-based study using a robust clinical database evaluating AVR and exploring volume-outcome relationships is timely and warranted,” the authors wrote.

The patients whose data were included in the analysis were part of the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative, a group of 33 hospitals that perform heart surgery throughout the state. They used data from between 2008 and 2011 and included the total volume of AVR with or without CABG, ascending aorta or other valve procedures and aortic root replacements to account for the effects of the experience of the hospitals and the surgeons. The primary outcome was operative mortality both in the hospital and at 30 days after discharge.

Hospital volume, along with age and female sex, independently predicted early mortality, “with a hinge point of a 4-year volume of 390 procedures (high-volume hospital [HVH], 2.41 percent vs. low-volume hospital [LVH], 4.34 percent).”

Multivariate analysis that controlled for a number of comorbidities and demographics found HVHs had a reduced risk-adjusted mortality (odds ratio [OR] 0.54) compared with LVHs. Risk of prolonged ventilation was also lower among HVHs (OR 0.66), but not in 30-day readmission rates.

Only high-risk patients (those with a predicted risk of mortality greater than or equal to 4.7 percent) seemed to gain from the higher procedure volumes.

“This supports that volume-outcome hypothesis, in which processes of care necessary to treat high-risk complex patients may exist inherently in larger hospitals,” the authors argued.

The next steps, they added, should be to determine the specific processes in place at both HVHs and LVHs.