eComment: Cardiac displacement during off-pump coronary artery bypass grafting surgery: how much displacement is too much?

We read with great interest the article by Atasever et al. [1] on hemodynamic changes during off-pump coronary bypass surgery (OPCAB). Pulse contour analysis was used for cardiac output (CO) monitoring, and among other microcirculatory and tissue oxygenation variables, cerebral tissue oxygenation index was measured by near-infrared spectrophotometry. The authors reported a significant reduction in CO by 48% upon cardiac displacement that is paralleled by a 40% reduction in mean arterial pressure (MAP) to significantly low levels (38±16 mmHg). Not surprisingly, at such low perfusion pressures, cerebral oxygenation is markedly affected. Contrary to the authors' findings, previous studies examining hemodynamic changes during OPCAB have consistently reported minimal reduction of MAP even when CO was markedly reduced, due to a compensatory rise in systemic vascular resistance [2–4]. This picture of a relatively preserved MAP despite a dropping CO was also reported in higher risk patients with compromised left ventricular function [2, 4], rather than the low-risk group that the authors have examined. More importantly, in the face of such hemodynamic changes that are known to be transient in most cases, the authors have failed to define the exact points in time in which these hemodynamic variables were obtained, the duration of these changes, and when any corrective measures were undertaken. The potential contribution of arrhythmias or myocardial ischemia to the reported hemodynamic upsets is another important missing variable in their report. Maintaining hemodynamic and electrical stability of the heart is central to the safety and success of OPCAB. And while the authors conclude that hemodynamic alterations during cardiac displacement in OPCAB reduce cerebral tissue oxygenation; given the relatively exaggerated hemodynamic disturbance in their cohort, generalizing these findings to all OPCAB procedures would be quite questionable.