Right ventricular support for off-pump coronary artery bypass grafting studied with bi-ventricular pressure-volume loops in sheep

Objectives: Tilting the heart during off-pump coronary artery bypass grafti ng (OPCABG) causes a strong decrease in cardiac output. It is hypothesized that this decrease is caused by reduced right ventricular filling and that right ventricular support is thus the best way to restore cardiac output. S imultaneous left and right ventricular pressure-volume loops were used to t est this hypothesis. Methods: In seven sheep, the heart was tilted with the use of an Octopus device. After unsupported tilting, a novel right ventric ular support, the Enabler: was activated at a pulsatile flow of 1.6 l/min. Pressure-volume loops of both ventricles were obtained using conductance ca theters, and cardiac output was monitored with an aortic flow probe. Result s: Tilting reduced cardiac output by 31% (4.4-3.1 l/min, P = 0.001) and rig ht ventricular end-diastolic volume by 34% (86-51 mi, P = 0.005), while rig ht ventricular end-diastolic pressure did not decrease. Left ventricular sy stolic pressure was not significantly reduced upon tilting and even increas ed in two animals. During Enabler right ventricular support, the cardiac ou tput remained 23% lower than pre-tilting values (3.4 vs. 4.4 l/min, P = 0.0 01). Conclusions: Restricted right ventricular filling is the primary cause of the strong decrease in cardiac output during tilting. The Enabler right ventricular support can currently not restore cardiac output to pre-tiltin g values, mainly caused by its limited output and a decrease in right ventr icular output upon Enabler activation. Constant monitoring of cardiac outpu t is crucial during (unsupported or supported) tilting as blood pressure al one may not reflect the extent of the reduction in cardiac function. (C) 20 01 Elsevier Science B.V. All rights reserved.