OBJECTIVE: Although it is widely believed that off-pump coronary artery bypass graft surgery (OPCAB) leads to hypercoagulability, efforts to document such a state have been unrevealing. We hypothesized that the preservation of coagulation after OPCAB increases the risk of developing a regional hypercoagulable state within saphenous vein grafts (SVG) that is detectable using coronary sinus analyses.
METHODS: Systemic (arterial) blood samples were obtained preoperatively and 15 minutes after protamine administration in patients undergoing OPCAB (N=60) or on-pump CABG (N=31). Regional (coronary sinus, CS) blood samples were obtained in a subset of patients (N=34 OPCAB, N=10 on-pump CABG) to perform transcardiac analyses. Each sample was analyzed by ELISA for thrombin generation (F1.2) and myocardial injury (myoglobin) and by whole blood aggregometry (impedance change in response to 1 μg/mL collagen) to define platelet function. Graft flow was measured intraoperatively using transit-time ultrasound. Percent luminal endothelial integrity (EI) was assessed in SVG biopsies using CD31-directed immunohistochemistry.
RESULTS: Systemic analyses showed that OPCAB led to less perioperative increase in F1.2 compared to on-pump CABG (300±59 vs. 830±217%, p<0.03). In contrast, regional (i.e., CS) analyses showed that OPCAB provoked significantly more transcardiac thrombin generation (203±77 vs. 20±25% increase in F1.2, p<0.03), and exhibited a trend towards increased platelet function (6.8±1.5 vs. 4.2±0.9 ohms, p=0.15). SVG flow rates were significantly reduced in OPCAB compared to on-pump CABG (39.4 vs. 66.5 mL/min, p=0.0002), but EI (28.7±3.6 vs. 31.1±3.2%) and transcardiac myoglobin release (83.2±24.1 vs. 82.5±59.3%) were equivalent.
CONCLUSIONS: Despite similar myocardial injury and equal SVG quality, OPCAB was associated with a regional burst in thrombin formation after protamine administration that did not occur during on-pump CABG. This regional hypercoagulable state may be influenced by decreased SVG flow rates and preserved platelet function compared to on-pump CABG. Alternate antithrombotic strategies are indicated for OPCAB.