Relationship of mechanical dyssynchrony to QT interval prolongation in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is usually associated with electrocardiographic (ECG) abnormalities. QT interval and its dispersion can be clinical markers of electrophysiological instability and ventricular arrhythmias. We aimed to clarify the relation of QT variables to mechanical dyssynchrony and myocardial function in HCM.

The study population comprised 82 HCM patients, 28 healthy subjects as control. We assessed regional deformation indexes using vector velocity imaging in 12 myocardial segments. Peak systolic strain (ε(sys)), strain rate (SR(sys)), and post-systolic strain (PSS) were measured. Contraction time (CT) was measured from regional strain curves for each segment, as the time from the beginning of the Q-wave to the time-to-peak ε(sys) (TPS), mechanical dyssynchrony was estimated as TPS-SD. From 12-lead surface ECG, QT interval, QT dispersion, and its corrected values were measured. According to QT(c) (QT(c) ≥ 440 or <440 ms), patients were categorized into two groups: long QT and normal QT HCM. In the long QT group, QT(cd) and CT in all left ventricular (LV) segments were significantly prolonged; ε(sys) and SR(sys) were markedly attenuated compared with the other two groups (P<0.001). LV dyssynchrony was significantly greater (P<0.001) and PSS was more frequent in long QT HCM compared with the other two groups (P<0.001). TPS-SD was correlated positively with QT(c) (r=0.38, P<0.01) and QT(cd) (r=0.45, P<0.001). QT(c) ≥ 440 ms identified LV mechanical dyssynchrony with 70% sensitivity, 100% specificity, and positive predictive value.

QT interval prolongation on surface ECG shows significant association with mechanical dyssynchrony and LV dysfunction in HCM. This may add pathophysiological insight into understanding ECG changes in such myocardial disease.