Evidence for an inefficient energy utilization in cardiac hypertrophy. Studies on the isolated human ventricular myocardium.

Abstract

Cardiac muscle mechanics and myocardial oxygen consumption were determined in both normal left ventricular wall strips and hypertrophied left ventricular papillary muscle obtained from patients in the process of cardiac surgery (mitral valve replacements, corrections of ventricular septal defects). Isotonic preloaded, isotonic after-loaded and isometric contractions were employed. The oxygen consumption was assessed by gas chromatography. Compared with the normal muscles, cardiac muscle mechanics (shortening, velocity of shortening, cardiac work, cardiac power) were reduced about 40–50 per cent in the hypertrophied muscles. Force-velocity relations were depressed with decreases of both the preload velocity (normal: 0.79±0.08, hypertrophied: 0.38±0.05 muscle lengths/sec,p<0.01) and the maximum isometric tension development (normal: 3.8±0.6, hypertrophied: 2.1±0.48 g/mm2,p<0.01). However, the oxygen consumption per gram/mm2 of developed tension was not depressed, averaging 0.52±0.08 (normal) and 0.92±0.13 µl/mg/beat-10−3 (hypertrophied),p<0.01. At isometric conditions, oxygen consumption was nearly the same in both groups, however, despite a maximum oxygen availability maximum isometric tension development was reduced in the hypertrophied myocardium at about 40–50 per cent. These results demonstrate an inefficient energy utilization in the isolated hypertrophied human ventricular myocardium.