Graft Flow Evaluation with Intraoperative Transit-Time Flow Measurement in Off-Pump versus On-Pump CABG

Introduction: Quality control during coronary artery bypass surgery is imperative for early detection of technical issues. The most frequently used method for intraoperative graft assessment is transit-time flow measurement (TTFM). Based on clinical observation that notes an increased mean graft flow (MGF) in on-pump (ONCABG) procedures, we attempted to find a change in MGF between ONCABG and OPCAB procedures.

Metirials and Methods: The database of the multicenter REQUEST study was retrospectively reviewed to quantify the average change between on and off pump procedures for different grafts and coronary artery targets. The target population was divided into an OPCAB group and an ONCABG group. Patients in the two groups were matched according to the type of graft(s) received. Primary endpoints were MGF, pulsatility index (PI) and diastolic filling (DF) variations for each between-group comparison.

Results and Disscusion: The original REQUEST study enrolled 1046 patients undergoing coronary artery bypass grafting, 30 of which were excluded based on predetermined criteria. 40.1% (407/1016) of the procedures were performed off-pump with a total of 1494 ONCABG grafts and 994 OPCAB grafts. There was no statistically significant difference in in-hospital mortality between the groups. MGF was higher for ONCABG vs. OPCAB (33ml/min vs. 27ml/min, respectively, for all grafts, P<0.001). This difference was more pronounced in venous than in arterial grafts (41ml/min vs 30ml/min, P<0.001, and 28ml/min vs 26ml/min, P=0.001, respectively).

Conclusion: In this large, multicenter cohort, ONCABG MGF was higher than OPCAB MGF and ONCABG PI was lower than OPCAB PI. One reason ONCABG MGF may be higher is due to coronary vasodilation caused by global myocardial ischemia during cardioplegic arrest. This data may have clinical implication when considering surgical technique in different clinical scenarios. Further investigation is needed to correlate off and on pump MGF with graft patency and make specific cut-off values.