Optimizing myocardial supply/demand balance with alpha-adrenergic drugs during cardiopulmonary resuscitation

In 14 dogs the determinants of myocardial blood supply and metabolic demands were assessed during cardiopulmonary resuscitation (CPR) and under steady-state conditions in fibrillating hearts on cardiopulmonary bypass. During open chest cardiac massage (nine dogs), coronary diastolic blood pressure and blood flow were low. Vasopressor infusion (methoxamine or epinephrine) raised diastolic pressure from 33 +/- 3 to 55 +/- 3 mm. Hg and increased coronary blood flow (CBF) 124 percent (from 38 +/- 3 to 85 +/- 11 c.c. per 100 Gm. per minute. Comparison of these drugs in fibrillating hearts on cardiopulmonary bypass showed that epinephrine increased the "vigor of fibrillation" (intraventricular balloon pressure rose 24 percent and oxygen uptake increased 42%) but impeded subendocardial flow 53% (endocardial/epicardial flow ratio fell from 0.79 to 0.48). In contrast, methoxamine did not significantly change intraventricular balloon pressure, oxygen uptake, coronary flow, or its distribution. We conclude that augmentation of diastolic pressure with alpha adrenergic drugs during CPR improves coronary perfusion and that inotropic drugs may worsen myocardial ischemia during CPR by raising oxygen demands while simultaneously impeding subendocardial blood supply.