Secondary and primary repolarization changes in left ventricular hypertrophy: a model study

The contributions of reduced conduction velocity (CV) and prolonged action potential duration (APD) to QT interval prolongation and T wave and T vector loop morphology in left ventricular hypertrophy (LVH) were studied using an analytical computer model. Three types of anatomic LVH were simulated: concentric and eccentric hypertrophy, and left ventricular dilatation. In each LVH type, depolarization changes were simulated by CV slowing and primary repolarization changes by APD prolongation. Both CV slowing and APD prolongation prolonged the QT interval; however, the secondary and primary repolarization changes differed in additional electrocardiogram (ECG) characteristics creating specific vectorcardiographic/ECG patterns. The secondary repolarization changes were characterized by prolonged QT interval, accompanied by pronounced QRS changes, including increased maximum spatial QRS vector magnitude, prolonged QRS duration, QRS morphology consistent with intraventricular conduction delay, lower values of the T/QRS duration ratio, increased maximum spatial T vector magnitude, narrow and prolonged discordant T vector loops, and discordant tall T waves creating a pattern of ST strain in the precordial ECG leads. QT prolongation in primary repolarization changes was accompanied with inconsiderable changes of QRS amplitude and duration, higher values of the T/QRS duration ratio, widened rounded T loops, and notched or bifid T waves in left precordial leads of the 12-lead ECG. These simulation data are consistent with the accumulated evidence suggesting that LVH induces changes in CV and APD. Our results emphasize the need for simultaneous consideration of morphologic QRS and T wave patterns together with QT prolongation in clinical evaluation of LVH.