Use of inotropic agents in open heart surgery
Inotropic drugs, particularly sympathomimetic agents, which are primarily used in the management of sudden pump failure, increase the velocity and force of ventricular contraction. This action is observed in isolated cardiac muscle preparations, in intact animal studies, and by measuring various indices of contractility in man. For example, careful measurement of ventricular dimensions during infusion of dopamine reveals a reduced end-diastolic volume, increased velocity of wall movement during systole, and a decreased end-systolic volume.
All inotropic drugs exert some peripheral vascular actions that make it difficult to evaluate the effects of a pure inotropic intervention. Even if pure inotropic agents were available it would be difficult to isolate their inotropic effects from reflex circulatory effects that may occur. For example, any increase in stroke volume generated by more forceful ventricular contraction would lead to a change in arterial blood pressure, which in awake or lightly anesthetized man, secondarily leads to reflex changes in cardiac performance and a decrease in peripheral resistance due to stimulation of baroreceptors.
Inotropic drugs in normal man increase coronary blood flow in proportion to the increase in myocardial oxygen consumption associated with increased contractility, increased cardiac work, increased heart rate, and increased metabolic rate associated with the use of these agents. In patients with acute coronary artery occlusion and myocardial infarction, the use of inotropic agents to support acute heart failure is associated with increased risk of extension of the size of infarction because of increased myocardial oxygen demands. The rationale for their use is based . . .