Monocyte Activation in On-Pump Versus Off-Pump Coronary Artery Bypass Surgery

Objective: Monocyte activation plays a key role in amplifying both inflammatory and coagulopathic sequelae in patients undergoing on-pump coronary artery bypass graft (CABG) surgery. Off-pump CABG diminishes, but does not eliminate, the systemic inflammatory response and its influence on monocyte activation remains unclear. This study was performed to determine if off-pump CABG suppresses all features of monocyte activation. Design: Prospective, controlled, clinical study. Setting: University-affiliated veterans affairs hospital and laboratory. Participants: Twenty-two patients scheduled to undergo primary CABG surgery (11 on-pump and 11 off-pump). Interventions: On-pump and off-pump CABG surgery was performed via median sternotomy. Anticoagulation and heparin reversal were identical. Moderate hypothermia (28°-30°C) was used for on-pump CABG surgery, whereas temperature was maintained above 35.5°C for off-pump CABG. No antifibrinolytic agents were used. Measurements and Main Results: Perioperative monocyte changes were assessed by using cellular (CD11b, monocyte-platelet conjugates) and secreted markers (plasma IL-6, IL-8, and IL-10) measured at 6 time points before, during, and after CABG surgery. Off-pump CABG surgery completely blocked the increases in monocyte CD11b expression (p < 0.001) and monocyte-platelet conjugate formation (p < 0.001) observed in the on-pump group. In contrast, plasma interleukin levels were significantly elevated in both groups, although off-pump CABG surgery resulted in lower levels (p < 0.001) and a delayed time course. Conclusions: Off-pump CABG surgery attenuates monocyte secreted cytokines and completely suppresses activation-dependent monocyte cell-surface changes (CD11b, monocyte-platelet conjugate formation). Whether these pathophysiologic differences in monocyte activation translate into a reduction in adverse events after CABG surgery warrants a larger, randomized, outcomes study.