BMI affects survival in patients undergoing aortic valve replacement
MedWire News: Results of a US study suggest that body mass index (BMI) has a significant effect on survival in patients undergoing aortic valve replacement (AVR) for aortic stenosis (AS).
"Better survival was observed in patients with BMIs in the low 30s compared to patients with BMIs in the mid 20s and >40 kg/m2," report William Roberts (Baylor University Medical Centre, Dallas, Texas) and co-investigators in the American Journal of Cardiology.
The team investigated the effect of BMI on 30-day and late outcomes in 865 patients with AS who were undergoing AVR from January 2002 through June 2010. For all patients, the AVR procedure was their first cardiac operation, with or without a first simultaneous coronary artery bypass graft.
Roberts et al assigned the study cohort into four BMI categories: ≤25, 25-30, 31-40, and ≥40 kg/m2, and then modeled BMI using cubic splines in order to "avoid bias inference regarding BMI and mortality."
Propensity-adjusted analysis indicated a strong and significant association between BMI and 30-day and long-term (9-year follow-up) mortality.
They report that patients with a BMI in the low thirties had a significantly lower risk for 30-day and long-term mortality compared with patients whose BMI was in the mid twenties or over 40 kg/m2.
Specifically, the propensity-adjusted risk for mortality at 30 days was approximately 20% for patients with a BMI of 30 kg/m2. This compared with a 30% risk for patients with a BMI of 20 kg/m2 and a near 40% risk for those with a BMI of 40 kg/m2 or more.
The probability of survival at 7.5 years was approximately 0.5 for those with a BMI of 20 kg/m2 and between 0.5 and 0.6 for those with a BMI of 40 kg/m2 or more. This compared with a probability of 0.65 for those with a BMI of 30 kg/m2.
The authors say that most previous reports have found the two extremes of BMI (severe under and overweight) to have deleterious effects on early and/or late mortality.
The present study adds to these findings, they say, by suggesting that patients with a BMI in the early thirties had a reduced risk for mortality compared with severely under- and overweight patients.
Furthermore, the researchers note that "a major strength of the present study is that BMI was modeled using restricted cubic splines to avoid grouping it into arbitrary categories and/or assuming linear (or other shaped) associations between BMI and study outcomes," which they say is an "inherent" problem with BMI categorization.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
By Nikki Withers