Abstract Body (Do not enter title and authors here): Introduction: New innovations in AI allow opportunistic detection of non-coronary features on coronary artery calcium (CAC) scans, enabling screening for a range of conditions, and improved cardiovascular disease (CVD) prediction. Myosteatosis, excessive fat infiltration into skeletal muscle, is increasingly recognized as a marker of systemic metabolic dysfunction and can be quantified in CT using the mean attenuation of skeletal muscle. We evaluated AI-measured myosteatosis in thoracic skeletal muscle for predicting future atrial fibrillation (AF), heart failure (HF), and total CVD.
Methods: We used baseline CAC scans and 15-year follow-up data from 5,489 asymptomatic participants (47.8% male) in the Multi-Ethnic Study of Atherosclerosis (MESA). Myosteatosis was operationally defined as the lowest quartile of thoracic skeletal muscle mean attenuation (males<33 Hounsfield Units (HU) and females<27 HU). Hazard ratios [HR] for bottom vs top quartile of mean muscle CT density were evaluated using proportional hazards regression models adjusted for CVD risk factors, inflammatory markers, and social determinants of health.
Results: Myosteatosis was associated with worse outcomes in both sexes: HRs in males were 4.59 (95% CI, 3.52–5.99) for AF, 8.46 (4.61–15.52) for HF, and 3.56 (2.89–4.37) for total CVD, with corresponding HRs in females of 4.68 (3.48–6.29), 8.01 (3.62–17.72), and 4.37 (3.42–5.57), respectively. After full adjustment, associations remained significant for HF (1.93 [1.31–2.82]), AF (1.78 [1.26–2.50]), and total CVD (1.44 [1.09–1.91]) in males, and for AF (1.69 [1.17–2.45]) and total CVD (1.75 [1.29–2.39]) in females. Individuals in the top quartile of CAC (>89.5 HU) who also had myosteatosis had greater 15-year incidence of AF (45.4%) and HF (21.8%) than those in either group alone (CAC, AF: 29%, HF: 9.5%; myosteatosis, AF: 20.9%, HF: 5.3%).
Conclusion: Thoracic skeletal myosteatosis in CAC scans is an independent predictor of AF, HF, and total CVD over 15 years. Improving clinical outcomes through the detection of myosteatosis, and other opportunistic findings in CAC scans as part of the AI-CVD initiative, merits further investigation.