Cardiac MRI Pectoralis Muscle Thickness as a Measure of Sarcopenia: Prognostic Significance, Interreader Agreement, and Physiologic Correlation

Purpose To evaluate pectoralis muscle thickness at routine cardiac MRI as a marker of sarcopenia, including prognostic significance for major adverse cardiac events (MACE), interobserver agreement, and correlation with physiologic parameters. Materials and Methods This retrospective cohort study included adult patients undergoing cardiac MRI for assessment of suspected cardiomyopathy between October 2018 and February 2020. Measurements of maximum pectoralis major thickness were performed by two experienced radiologists using axial images at the level of the carina. A random subset of 50 patients were re-evaluated to assess intra- and interobserver agreement. The primary end point was MACE, defined as a composite of cardiac death, resuscitated sudden cardiac death, appropriate implantable cardioverter defibrillator discharge, or hospitalization for heart failure. Prognostic significance of pectoralis major thickness measurements for MACE was assessed using Cox proportional hazard models, and correlation between muscle thickness measurements and cardiopulmonary exercise testing (CPET), performed within 1 year of MRI, was assessed using Spearman correlation. Results The study included 1045 patients (mean age, 50 years ± 17 [SD]; 642 male, 403 female). After median follow-up of 3.3 years (IQR: 2.3-3.9 years), MACE occurred in 66 patients. In multivariable models adjusted for patient age, left ventricular ejection fraction, late gadolinium enhancement, and cardiomyopathy cause, pectoralis major muscle thickness was predictive of MACE in both male (hazard ratio [HR], 0.89 [95% CI: 0.85, 0.94]; <i>P</i> < .001) and female patients (HR, 0.85 [95% CI: 0.76, 0.96]; <i>P</i> = .008), with improved model fit in nested models. Pectoralis muscle thickness measurements had excellent intra- and interobserver agreement (intraclass correlation coefficient, 0.99 and 0.95, respectively) and correlated with absolute peak oxygen uptake (<i>r</i> = 0.65, <i>P</i> < .0001) and oxygen uptake efficiency slope (<i>r</i> = 0.61, <i>P</i> < .001) in the subset who underwent CPET within 1 year of MRI (<i>n</i> = 258). Conclusion Pectoralis major muscle thickness at routine cardiac MRI is a simple, reproducible measure of sarcopenia that was associated with MACE occurrence in male and female patients and correlated with CPET parameters. <b>Keywords:</b> Cardiac, Cardiomyopathies, MR Imaging <i>Supplemental material is available for this article.</i> © RSNA, 2024.