Body Mass Index as a Continuous Predictor of Survival after Heart Transplantation

Abstract

<h3>Purpose</h3> Both underweight and overweight recipients have poor outcomes after heart transplant (HT). However, the precise threshold of body mass index (BMI) as a predictor of heightened risk is unclear. We, therefore, examined the effect of BMI on short term survival as a continuous metric. <h3>Methods</h3> We identified adult patients listed for HT between 2000 and 2018 in the Scientific Registry of Transplant Recipients with recorded BMI at the time of listing. We calculated survival at 30 days and one year after HT and constructed Cox proportional hazards regression models adjusted for known recipient and donor risks. Recipient BMI was modeled using a restricted cubic spline with knots at 18, 25, 30, and 35 kg/m² with a value of 22 used as a referent. <h3>Results</h3> 37,068 adult HT recipients were included: median (25th, 75th percentile) BMI of 27 (23, 30) kg/m², recipient age 55 (46, 62) years, 27,668 (74.6%) men, and 9,683 (26.1%) with diabetes. After risk-adjustment, Cox proportional hazards regression showed a 3% increase in both 30-day (HR 1.031, 95% CI 1.024-1.037; p<0.0001) and 1-year mortality for every unit increase in recipient BMI (HR 1.025, 95% CI 1.022-1.033; p<0.0001). When modeled as a cubic spline, BMIs below 22 kg/m² had a neutral effect on both 30-day and 1-year mortality (although with wide confidence bars), with mortality risk steadily increasing in a non-linear fashion (Figure). <h3>Conclusion</h3> Increases in recipient BMI was associated with an incremental risk of 30-days and 1-year mortality following HT.