The effect of positive inotropes on the failing human myocardium.

Heart failure is associated with pathobiochemical changes that can reduce the responsiveness of the myocardium to positive inotropic agents. We studied the contractile effects of a range of inotropic agents on papillary muscle strips from healthy and failing human hearts. Specimens were obtained from patients with different grades of heart failure. These included individuals undergoing mitral valve replacement (New York Heart Association Class II-III) or receiving heart transplantation (New York Heart Association Class IV). Heart failure was associated with attenuation of myocardial contractile responses to dobutamine, histamine, 3-isobutyl-1-methylxanthine, and the phosphodiesterase inhibitors, milrinone and pimobendan. However, pretreatment of the papillary muscle with isoprenaline augmented the positive inotropic effect observed with the phosphodiesterase inhibitors. The contractile response to ouabain was not influenced by the presence of heart failure. We conclude that, unlike beta-adrenoceptors, cardiac glycoside receptors in the myocardium are not down regulated in the presence of heart failure.