Myocardial Disarray and Fibrosis across Hypertrophic Cardiomyopathy Stages Associate with ECG Markers of Arrhythmic Risk

Abstract Background Myocardial disarray, an early feature of hypertrophic cardiomyopathy (HCM) and a substrate for ventricular arrhythmia, is poorly characterised in prehypertrophic sarcomeric variant carriers (SARC+LVH-). Objectives Using diffusion tensor cardiac magnetic resonance (DT-CMR) we assessed myocardial disarray and fibrosis in both SARC+LVH- and HCM patients and evaluated the relationship between microstructural alterations and electrocardiographic (ECG) parameters associated with arrhythmic risk. Methods Sixty-two individuals (24 SARC+LVH-, 24 HCM and 14 matched controls) were evaluated with multiparametric CMR including stimulated echo acquisition mode (STEAM) DT-CMR, and blinded quantitative 12-lead ECG analysis. Results Mean diastolic fractional anisotropy (FA) was reduced in HCM compared to SARC+LVH- and controls (0.49±0.05 vs 0.52±0.04 vs 0.53±0.04, p=0.009), even after adjustment for differences in extracellular volume (ECV) (p=0.038). Both HCM and SARC+LVH- had segments with significantly reduced FA relative to controls (54% vs 25% vs 0%, p=0.002). Multiple repolarization parameters were prolonged in HCM and SARC+LVH-, with corrected JT interval (JTc) being most significant (354±42ms vs 356±26ms vs 314±26ms, p=0.002). Among SARC+LVH-, JTc duration correlated negatively with mean FA (r=-0.6, p=0.002). In HCM, the JTc interval showed a stronger association with ECV (r=0.6 p=0.019) than FA (r=-0.1 p=0.72). JTc discriminated SARC+LVH- from controls (Area-under-the-receiver-operator-curve 0.88, CI 0.76-1.00, p<0.001), and in HCM correlated with the ESC HCM sudden cardiac death risk score (r=0.5, p=0.014). Conclusion Low diastolic FA, suggestive of myocardial disarray, is present in both SARC+LVH- and HCM. Low FA and raised ECV were associated with repolarization prolongation. Myocardial disarray assessment using DT-CMR and repolarization parameters such as the JTc interval demonstrate significant potential as markers of disease activity in HCM.