Abstract 2129: Delayed Enhancement on Cardiac MRI Demonstrates the Spatial Significance of QT Dispersion Correlating with the Maximal Monophasic Action Potential Duration in Hypertrophic Cardiomyopathy
[Delayed enhancement (DE) on cardiac MRI (CMR) represents myocardial scar that produces abnormal depolarization. However, it is unclear whether DE expansion also affects the myocardial repolarization properties. Since QT dispersion (QTd) reflects the differences in action potential duration in the ventricle, it must be clarified whether the DE distribution correlates with the transmural dispersion of QT interval or monophasic action potential duration (MAPd). To elucidate the relationships between DE depth, localization of the longest QT lead (LQT-lead), longest MAPd site (LMAP-site) and QTd on ECG in patients with hypertrophic cardiomyopathy (HCM). A CMR and 12-lead ECG recording were performed in 50 patients with HCM. Monophasic action potential (MAP) was also recorded during the electrophysiologic study. The DE and MAP sites were classified into 12 left ventricular segments (Basal - Middle -Apical × Anterior - Septal - Inferior - Lateral). At each segment, the DE depth was scored into 1 to 4 from endocardial to epicardial sites, and the MAPd measured at 90% repolarization (APD90) was analyzed. The corresponding ECG lead groups were defined as V3–5 for Anterior, V1–2 for Septal, II, III, aVF for Inferior and I, aVL, V5– 6 for Lateral. The coincidence between the highest score segment, LQT-lead and LMAP-site, and correlation between the sum of DE scores (total DE) and QTd were investigated. The highest DE score segment had a good coincidence with not only the LQT-lead (90%) but also the LMAP-site (80%) in the HCM patients. The total DE score was significantly and positively correlated with the QTd (r=0.72, p<0.001). Furthermore, the total DE was significantly greater in the patients who had episodes of ventricular tachycardia (VT) (n=28) than in those not (23.7±8.1 vs. 12.3±8.0, p<0.001). The QTd in the patients with VT was significantly greater than that in those without (48.9±7.6 ms vs. 39.9±7.9 ms, p<0.001). The distribution of DE was significantly correlated with QTd and MAPd. A longer QTd and MAPd were associated with a higher DE score. The transmural distribution of DE represents the myocardial repolarization abnormalities, and may represent fibrotic areas which lead to VT foci in HCM.