Diminished anticoagulant response to heparin in patients undergoing coronary artery bypass grafting.

Patients are at risk for a diminished anticoagulant response to heparin during coronary artery bypass graft operations. To answer the question of whether preoperative heparin therapy and intra-aortic balloon counterpulsation are associated with a diminished response in the period before cardiopulmonary bypass, we observed prospectively the baseline and postheparinization activated clotting times in 76 patients undergoing elective coronary artery bypass graft procedures. They included 42 patients who had received preoperative heparin therapy (26 had intra-aortic balloon pumps and 16 did not). Thirty-four comparison patients (controls) were matched for age, sex, race, and heparin lot. Patients receiving preoperative heparin therapy, either with or without intra-aortic balloon pumps, had significantly lower activated clotting times than patients in the control group after a 300 IU/kg dose of porcine intestinal heparin. Total preoperative heparin dose, days of preoperative heparin therapy, and baseline activated clotting times were not predictive of heparin resistance. In conclusion, patients receiving preoperative heparin therapy (with or without intra-aortic balloon pumps) are at increased risk for inadequate heparinization before cardiopulmonary bypass.