Impact of body mass index on outcomes following mitral surgery: does an obesity paradox exist?

OBJECTIVES

This study was conducted to clarify the relationship between body mass index and mitral valve (MV) surgery and to determine whether an 'obesity paradox' exists in the context of surgery for degenerative MV disease.

METHODS

In this retrospective single-centre study, we analysed data from 715 patients who underwent mitral surgery for degenerative disease from 2000 to 2015. Patients were classified according to body mass index: underweight (<20 kg/m2), normal weight (20-24.99 kg/m2), overweight (25-29.99 kg/m2) and obese (≥30 kg/m2). Early and long-term results were investigated. Multivariable analysis was conducted to identify risk factors for long-term mortality.

RESULTS

Mean follow-up was 67 ± 44 months (range 0-190 months). There were no differences between groups regarding 30-day mortality (P = 0.35), stroke (P = 0.45), reoperation for bleeding (P = 0.9) and length of hospital stay (P = 0.31). Obese patients were at increased risk of acute kidney injury when compared with normal weight patients (17% vs 5%; P = 0.03) but not when compared with the other groups; this was confirmed within the subgroup with depressed ejection fraction (42% vs 10%, P = 0.02). No differences in long-term survival were found across groups for all patients (P = 0.62) and for patients with depressed ejection fraction (P = 0.6), with a trend towards worse survival in obese patients undergoing MV repair (P = 0.06). Survival in obese patients undergoing repair was significantly worse than that in obese patients undergoing replacement (P = 0.04).

CONCLUSIONS

An 'obesity paradox' was not demonstrated after surgery for degenerative MV disease. Obese patients are more prone to acute kidney injury and have worse late survival after MV repair.