Asynchronous Electrical Activation Induces Asymmetrical Hypertrophy of the Left Ventricular Wall

TLDR: LV pressure-volume analysis showed that ventricular pacing reduced LV function to a similar extent after 15 minutes and 6 months of pacing, and local cardiac load regulates local cardiac mass of both myocytes and collagen.

Abstract: Background—Asynchronous electrical activation, induced by ventricular pacing, causes regional differences in workload, which is lower in early- than in late-activated regions. Because the myocardium usually adapts its mass and structure to altered workload, we investigated whether ventricular pacing leads to inhomogeneous hypertrophy and whether such adaptation, if any, affects global left ventricular (LV) pump function. Methods and Results—Eight dogs were paced at physiological heart rate for 6 months (AV sequential, AV interval 25 ms, ventricular electrode at the base of the LV free wall). Five dogs were sham operated and served as controls. Ventricular pacing increased QRS duration from 47.2±10.6 to 113±16.5 ms acutely and to 133.8±25.2 ms after 6 months. Two-dimensional echocardiographic measurements showed that LV cavity and wall volume increased significantly by 27±15% and 15±17%, respectively. The early-activated LV free wall became significantly (17±17%) thinner, whereas the late-activated septum ...