Myocardial contractility in relation to hypertrophy and failure in myopathic Syrian hamsters

Myocardial contractility of left ventricular papillary muscles from normal Syrian hamsters and those with hereditary cardiomyopathy has been studied. The animals were divided into five groups corresponding to different pathological stages and the mechanical parameters correlated with these stages. Developed force and dF dt corrected for cross-sectional area were depressed in all myopathic groups. However, developed force and dF dt, uncorrected for cross-sectional area, were restored to normal in the hypertrophied muscles in the myopathic animals at 220 and 320 days of age in the absence of congestive failure (i.e. without edema). In the early myolytic and healing stage and in the terminal edematous stages of the myopathy, force-velocity curves were depressed at all loads. However in hypertrophied and compensated hearts at 220 to 320 days, the force velocity curves were similar to controls when load was expressed as a fraction of P₀. Assuming developed force to reflect the number of contractile sites in parallel, it was concluded that the number of normally active contractile sites per unit area was reduced at all stages of the disease. In the hypertrophied, compensated phase, it was postulated that the qualitative nature of these sites remain normal despite their quantitative reduction.