Body mass index and risk of adverse cardiac events in elderly patients with hip fracture: a population-based study.

OBJECTIVES: To determine whether obesity affects cardiac complications after hip fracture repair.
DESIGN: A population-based historical study using data from the Rochester Epidemiology Project.
SETTING: Olmsted County, Minnesota. PARTICIPANTS: All urgent hip fracture repairs between 1988 and 2002. MEASUREMENTS: Body mass index (BMI) was categorized as underweight (<18.5 kg/m(2)), normal-weight (18.5-24.9 kg/m(2)), overweight (25.0-29.9 kg/m(2)), and obese (>or=30 kg/m(2)). Postoperative cardiac complications were defined as myocardial infarction, angina pectoris, congestive heart failure, or new-onset arrhythmias within 1-year of surgery. Incidence rates were estimated for each outcome, and overall cardiac complications were assessed using Cox proportional hazards models adjusted for age, sex, year of surgery, use of beta-blockers, and the Revised Cardiac Risk Index.
RESULTS: Hip fracture repairs were performed in 184 (15.6%) underweight, 640 (54.2%) normal-weight, 251 (21.3%) overweight, and 105 (8.9%) obese subjects (mean age 84.2 +/- 7.5; 80% female). Baseline American Society of Anesthesiologists (ASA) status was similar in all groups (ASA I/II vs III-V, P=.14). Underweight patients had a significantly higher risk of developing myocardial infarction (odds ratio (OR) 1.44, 95% confidence interval (CI)=1.0-2.1; P=.05) and arrhythmias (OR=1.59, 95% CI=1.0-2.4; P=.04) than normal-weight patients. Multivariate analysis demonstrated that underweight patients had a higher risk of developing an adverse cardiac event of any type (OR=1.56, 95% CI=1.22-1.98; P<.001). Overweight and obese patients with hip fracture had no excess risk of any cardiac complication.
CONCLUSION: The obesity paradox and low functional reserve in underweight patients may influence the development of postoperative cardiac events in elderly people with hip fracture.