Thoracic Intermuscular Adiposity, Coronary Microvascular Dysfunction, and Prognosis After Cardiac Surgery

Body mass index is a widely-used yet imprecise measure of adiposity. Thoracic intermuscular adiposity is reported to be related with coronary microvascular dysfunction (CMD), but their prognostic implications after cardiac surgery are not clear. This study aimed to investigate whether computed tomography-derived thoracic intermuscular adiposity and CMD provide better prognostic information than body mass index in patients undergoing cardiac surgery.

This study consecutively enrolled 666 patients undergoing elective surgery from 3 centers. Using computed tomography at the T12 vertebral level, we quantified the cross-sectional areas (cm²) of skeletal muscle, subcutaneous adipose tissue, and intermuscular adipose tissue. Intermuscular fat fraction was calculated as intermuscular adipose tissue/(intermuscular adipose tissue+skeletal muscle)×100%. CMD was defined by a coronary angiography-derived index of microcirculatory resistance >25. The primary end point was major adverse cardiovascular events (MACE), a composite of all-cause mortality, myocardial infarction, and rehospitalization for heart failure.

A total of 63 MACEs (9.5%) occurred during a median 17-month follow-up. Obesity defined by body mass index (10.7% of patients) was not associated with MACE (P=0.187). Each 1% increase in intermuscular fat fraction was significantly associated with CMD (adjusted odds ratio, 1.22 [95% CI, 1.14-1.31]; P<0.001), whereas body mass index showed no such correlation (P=0.964). CMD independently predicted MACE (adjusted hazard ratio, 2.03; [95% CI: 1.15-3.61]; P = 0.015), whereas intermuscular fat fraction did not (P=0.516). The annualized MACE rate was significantly higher in patients with CMD (11.0% versus 5.2%, P=0.004).

Computed tomography-derived intermuscular adiposity correlated strongly with CMD, and preprocedural CMD was associated with a higher risk of MACE after cardiac surgery. External validation and prospective studies are warranted.