INOTROPIC AND LUSITROPIC DYSFUNCTION IN MYOCARDIUM FROM PATIENTS WITH DILATED CARDIOMYOPATHY

Isometric force of contraction (DT), peak rate of tension increase (+T), peak rate of tension decrease (-T), time to peak tension (TPT), and time to half-relaxation (T1/2T) were measured in electrically driven human papillary muscle strips (New York Heart Association [NYHA] class IV heart transplants, dilated cardiomyopathy; nonfailing (NF) donor hearts, brain dead) (1 Hz, 37-degrees-C) under basal conditions (1.8 mmol/L Ca2+) and after stimulation with isoprenaline, ouabain, and Ca2+. There was no difference in the isometric contraction (+T, -T, TPT, and T1/2T) between NYHA IV hearts and NF hearts under basal conditions. Inotropic stimulation above 300% of basal DT increased -T significantly more in NF hearts (p < 0.05) compared with NYHA IV hearts. The effectiveness of ouabain and Ca2+ to increase DT was not significantly changed in NYHA IV hearts compared with NF hearts. The isoprenaline-mediated increase in DT was reduced (P < 0.05) in NYHA IV hearts to a similar extent (70%) as beta-adrenoceptors were downregulated. When the rate of stimulation was increased to 3 Hz (force-frequency relationship), force of contraction increased only in NF preparations, whereas it decreased in NYHA IV myocardium (p < 0.05). It was concluded that the contractile apparatus in terminally failing human myocardium is sufficient to maximally increase DT. During inotropic stimulation, abnormalities in diastolic rather than systolic contraction become evident. This may indicate abnormal intracellular Ca2+ handling.