Normal Contractile State of Hypertrophied Myocardium after Pulmonary Artery Constriction in the Cat

The contractile function of right ventricular papillary muscles from normal cats and cats in which the pulmonary artery had been constricted for 6 or 24 wk was examined. Acute pulmonary artery constriction reduced cross-sectional area by an average of 70%, resulting in a 30% mortality from congestive heart failure, all such deaths occurring within the first 3 wk after banding. The increase in right ventricular mass in animals surviving for 6 or 24 wk was similar, averaging 70%. No banded animals had evidence of congestive heart failure at the time of sacrifice, and cardiac output and right atrial pressures were similar to those in control animals.6 wk after banding, the active length-tension curve, maximal rate of rise of isometric force, force-velocity relations, and isometric force with paired stimulation and norepinephrine were all significantly depressed when compared to their respective values in control animals. In contrast, none of these variables was significantly different from control values in animals banded for 24 wk. These observations indicate that depressed contractile state is not a fundamental characteristic of pressure-induced hypertrophied myocardium and reemphasize the important temporal relationship between contractile state and the imposition of sudden sustained loads.