Study objective: The aim was to study the nature, magnitude, and time course of left ventricular structural adaptations to evolving heart failure.
Design: 17 male mongrel dogs, weight 24.9(SD 3.7) kg, underwent rapid ventricular pacing (250 beats.min-1) until severe heart failure developed. Two dimensional echocardiographic and Doppler studies were performed at control, then weekly to severe heart failure. Haemodynamic measurements were made at control and severe heart failure. All studies were performed with the animals conscious during temporary sinus rhythm.
Measurements and main results: Left ventricular diastolic volume gradually increased and the left ventricle assumed a more globular shape associated with significant wall thinning. Both the change in diastolic volume after one week of pacing and at the time of severe heart failure correlated with the time to peak heart failure. Mitral regurgitation was mild after one week of pacing, became moderate in most animals at severe heart failure, and lagged temporarily behind the increase in cardiac dimensions. The percentage increase in mitral annular size was significantly less than the increase in left ventricular cross sectional area.
Conclusions: In pacing induced heart failure (1) marked left ventricular remodelling occurs, (2) the extent of left ventricular dilatation, both early and late, correlates directly with the time required for the development of severe heart failure, (3) mitral regurgitation is an epiphenomenon and is most likely to be caused by the increase in left ventricular cross sectional area.