Association of skeletal muscle index and intermuscular adipose tissue index measured by non-contrast chest CT with major adverse cardiovascular events in patients with coronary artery disease: a nested case-control study in a Chinese population

Objective To investigate the association between chest CT-derived body composition indices and major adverse cardiovascular events (MACE) in coronary artery disease (CAD) patients, and to evaluate their utility for risk stratification. Materials and methods This nested case-control study was drawn from a consecutive cohort of 2,226 patients with CAD diagnosed by coronary CT angiography (CCTA) between January 2019 and March 2021. During follow-up, 275 patients developed MACE and were included as cases. From the remaining non-MACE cohort members, 275 controls were selected by simple random sampling, yielding a total of 550 patients. Areas of subcutaneous adipose tissue (SAT), skeletal muscle (SM), intermuscular adipose tissue (IMAT) and visceral adipose tissue (VAT) at the T8 level were segmented on non-contrast chest CT with 3D Slicer, and the corresponding indices and the muscle-to-fat ratio (MSFR) were derived. Associations with MACE were assessed with an inverse-probability-of-sampling weighted Cox proportional-hazards model (robust variance) with pre-specified confounder adjustment, testing of the proportional-hazards assumption, subgroup and interaction analyses, and restricted cubic spline (RCS) analysis. Results A total of 550 patients with CAD were enrolled (275 per group). During a median follow-up of 18 months, 275 MACE events occurred. The MACE group had significantly lower skeletal muscle index (SMI) (37.99 vs. 41.27 cm²/m², P = 0.003) and MSFR, and higher IMAT index (IMATI) (7.47 vs. 6.21 cm²/m², P < 0.001) than the non-MACE group. Higher SMI (HR = 0.636, P < 0.001) was independently associated with lower MACE risk, while higher IMATI (HR = 1.994, P < 0.001) was independently associated with higher risk. Adding SMI and IMATI to traditional risk factors improved reclassification (IDI = 0.044; NRI = 0.502). Restricted cubic spline analysis showed a non-linear inverse association between SMI and MACE risk, and a non-linear positive association between IMATI and MACE risk. Conclusion Higher SMI was independently associated with a lower risk of MACE, whereas higher IMATI was independently associated with a higher risk. Skeletal muscle mass and intramuscular fat infiltration derived from non-contrast chest CT may serve as supplementary indicators for cardiovascular risk stratification in patients with CAD.