Myocardial infarction, cardiac anatomy and ventricular loading.

To see whether the hypertrophic response of the surviving myocardium after infarction leads to a complete reconstitution of ventricular mass, the left coronary artery was ligated in rats and the animals killed one month later. In infarcts affecting an average of 38% of the free wall of the left ventricle, the ratio of wall thickness to chamber radius remained essentially constant. On the other hand, the ratio decreased significantly in the presence of infarcts involving an average of 60% of the ventricular wall. In addition, inadequate growth adaptations were detected in both groups of infarcts with respect to myocyte volume and length and to capillary volume and length. These defects in the regeneration of myocardial structures were associated with elevations in diastolic wall stress which were more prominent in the larger infarct group. The limited growth reaction of the myocyte and vascular compartments may be implicated in the persistence of cardiac dysfunction and failure late after infarction.