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Cardiothoracic Anesthesiology, Montefiore Medical Center, 111 E 210 St, Bronx, NY 10467
(Email: lshore{at}montefiore.org).
Paparella and colleagues [1] have found no differences in coagulation indices when comparing two different heparin doses in off-pump coronary artery bypass grafting (OPCAB) operations. It is interesting that the authors have chosen to pursue this question in OPCAB patients, for we do not even know the answer to this question in patients undergoing cardiopulmonary bypass (CPB), where contact activation and inflammation are at a maximum. The effects of inadequate doses [2] or excessive doses [3] of heparin in the setting of coated surfaces [4] are likely to have greater consequences in CPB than in OPCAB patients. The literature confirms that practice varies greatly and depends on institutional preferences rather than evidence-based medicine.
Studies have shown that OPCAB patients have less activation of coagulation and fibrinolysis than CPB patients, despite lower doses of heparin [5]. Coagulation is still activated but occurs later in the postoperative period, which is not measured in the current study [6, 7]. Paparella and colleagues' thrombin-activatable fibrinolytic inhibitor (TAFI) data support that coagulation activation occurs and is not affected by the heparin dose. This finding repeats itself throughout the literature: Thrombin inhibition must be achieved to minimize activation of cascades, and thrombin inhibition is not complete with heparin alone. Anticoagulation with the direct thrombin inhibitors has proven more complete and perhaps more protective against ischemic events [8, 9].
Surveys reveal a full range of heparin and protamine management strategies in OPCAB [10, 11]. Although the current study is small, it seems unlikely that OPCAB outcomes will be related to a consistent heparin dosing strategy. We may be barking up the wrong tree in trying to identify an optimal anticoagulation protocol using heparin as the anticoagulant. Because of the incomplete inhibition of thrombin rendered by heparin, it may be more productive to study the direct thrombin inhibitors or combination therapy for more maximal suppression of thrombin activation. This is not an insignificant goal, because the long-term patency [12] of OPCAB vein grafts is still not fully elucidated.
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