Chronic progressive pressure overload of the cat right ventricle

When an abrupt, fixed increase in afterload induces hypertrophy, the myocardium exhibits normal pump function in vivo, depressed muscle function in vitro, and paradoxically increased oxygen consumption. Such abnormalities may be either a transient response to a reversible myocardial injury or instead may be a persistent characteristic of hypertrophy contributing to eventual heart failure. To distinguish between these alternatives, we developed a model of chronic progressive pressure overload. Kittens had either a sham operation or pulmonary banding for 25 (group I) or 60 (group II) weeks. Banding produced a gradually increasing pressure overload with growth, maximum at 16 weeks after operation. The ratio of right ventricular to body weight increase from 0.54 +/- 0.03 to 0.82 +/0.04 g/kg (P less than 0.01) in group I and from 0.50 +/- 0.03 to 0.72 +/- 0.03 (P less than 0.01) in group II. In vivo right ventricular pump function (cardiac output and ejection fraction) was normal in both groups. In vitro contractile function and metabolism were measured in papillary muscles from the same right ventricles. Both experimental groups showed marked contractile abnormalities: preloaded shortening velocity was reduced from 0.80 +/- 0.05 to 0.53 +/- 0.05 muscle length/sec (P less than 0.01) in group I and from 0.84 +/- 0.04 to 0.60 +/- 0.06 (P less than ).01) in group II. Maximum isometric active tension was reduced from 60 +/- 7 to 35 +/- 5 mN/mm2 (P less than 0.01) in group I and from 56 +/- 5 to 27 +/- 4 (P less than 0.01) in group II. Metabolism was normal in both experimental groups. Thus, under conditions relevant to the study of clinical cardiac hypertrophy that are unlikely to cause acute injury, hypertrophy produces persistently abnormal intrinsic contractile function