Obesity and cardiac risk after kidney transplantation: experience at one center and comprehensive literature review

Abstract

Background: The cardiac implications of obesity in kidney transplant recipients are not well-described.

Methods: We examined associations of body mass index (BMI) at transplant with posttransplant cardiac risk among 1102 renal allograft recipients at a single center in 1991 to 2004. Cumulative posttransplant incidences of congestive heart failure (CHF), atrial fibrillation (AF), myocardial infarction, and a composite of these cardiac diagnoses were estimated by the Kaplan-Meier method. Bivariate (hazards ratio) and covariate (adjusted hazards ratio) relationships of BMI increments with cardiac risk were modeled by Cox's regression. We also systematically reviewed the literature on BMI and cardiac events after transplant.

Results: In the local data, 5-year cumulative incidence of any cardiac diagnosis rose from 8.67% to 29.35% across the lowest to highest BMI quartiles (P=0.02), driven primarily by increases in CHF and AF. In contrast, the rate of myocardial infarction did not differ by BMI quartile (P=0.56). Each 5 U BMI increase predicted 25% higher risk of the cardiac composite (hazards ratio 1.25, 95% CI 1.07-1.47, P=0.005), a relationship that persisted with significance after covariate adjustment (adjusted hazards ratio 1.19, 95% CI 1.00-1.43, P=0.049). BMI independently predicted cardiac risk in subcohorts with pretransplant heart disease and with nondiabetic renal failure. Data from 26 original articles support BMI as a risk factor for posttransplant CHF and AF, whereas findings for coronary/ischemic outcomes are inconsistent and predominantly negative.

Conclusions: High BMI at transplant predicts increased cardiac risk, especially of CHF and AF. Further research should examine whether obesity treatment modifies cardiac risk after kidney transplantation.

Figure 1

Five-year cumulative incidence estimates of cardiac events in the single-center sample, by BMI rank and baseline comorbidity

Figure 2

Adjusted BMI-related cardiac risk per 5 unit BMI increase within the full sample and subgroups from the single center*. *Stepwise Cox's regression in the full sample was performed to adjust for the following potentially confounding variables: recipient age, race, gender, ESRD etiology, pre-transplant dialysis duration, pre-transplant cardiac history; donor type (living, standard criteria deceased, or expanded criteria deceased); use of induction and maintenance immunosuppresion at discharge; and transplant year. All variables except the subgroup classification factor were included in stepwise regression in the subgroup analyses.