Ventriculoarterial coupling influences regional contractility

The purpose of this study was to adjudicate whether concomitant manipulation of inotropic state and arterial elastance influences linear indices of regional contractility. Fifteen autonomically denervated open-chest porcine hearts were instrumented with midmyocardial ultrasonic crystals and aortic and left ventricular chamber microamanometers. Linear left anterior descending coronary artery regional stroke work vs preload relationships (RSW) were generated by 10-sec vena caval occlusion at control and altered contractile states (either dopamine, 5 micrograms/kg/min, or propranolol, 0.2 mg/kg) and following arterial elastance variation (phenylephrine or nitroprusside), effecting an average 30% change in mean arterial pressure (MAP). Global contractility (dP/dt) was doubled (227% of control) by dopamine and halved (35% of control) by propranolol at constant preload (end-diastolic volume, end-diastolic pressure) and afterload (MAP). Regional contractility (RSW slope) was increased from 135 +/- 11 to 211 +/- 28, P less than 0.01, by dopamine, but unchanged with propranolol (106 +/- 10 vs 118 +/- 14, NS). Bidirectional changes in aortic elastance depressed the dopamine-augmented RSW slope (115 +/- 17, nitroprusside; 132 +/- 14, phenylephrine; P less than 0.01 vs dopamine). These differences were attenuated by propranolol infusion (98 +/- 7, nitroprusside; 132 +/- 9, phenylephrine; NS vs propranolol). Thus, optimizing ventriculoarterial coupling should supersede simple afterload manipulation in perioperative cardiac support.