Do coronary bypass graft flows differ between on-pump and off-pump operations?

Background: The aim of this study is to compare hemodynamic factors in coronary bypass grafts on-pump and off-pump.

Methods: Two propensity score-matched groups of 89 patients each including 408 dual beam Doppler flow measurements were compared. The study included only patent and single terminolateral bypass grafts.

Results: Flow was 64.9 +/- 37.3 mL/min in the on-pump group versus 58.6 +/- 35.0 mL/min in the off-pump group (p = 0.063); velocity was 23.8 +/- 10.5 versus 20.5 +/- 10.4 cm/s (p = 0.004); resistance measured as mm Hg/(mL/min(-1)) was 1.50 +/- 1.09 versus 1.76 +/- 1.14 (p = 0.020); pulsatility index was 1.98 +/- 1.52 versus 2.44 +/- 1.62 (p = 0.004). The hematocrit was 23.5 +/- 3.8% in the on-pump and 32.9 +/- 4.1% in the off-pump groups (p < 0 0.001). Multivariate analysis showed that hematocrit was the most significant factor influencing flow (p < 0.001) and velocity (p < 0.001), along with resistance (p = 0.004) and pulsatility index (p < 0.001). In a subset of 50 hemodynamic measurements made on left internal thoracic arteries implanted onto left anterior descending arteries and matched for hematocrit, there were no differences between on-pump and off-pump groups regarding flow, velocity, resistance, or pulsatility index.

Conclusions: Off-pump compared with on-pump bypass surgery is associated with lower velocity and higher resistance in the grafts, mainly caused by changes in hematocrit and viscosity related to hemodilution.