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J Thorac Cardiovasc Surg 2006;132:733-734
© 2006 The American Association for Thoracic Surgery
Letter to the Editor |
a Division of Cardiovascular Anesthesia and Intensive Care, Policlinico di Monza, via Amati 111, Monza 20052, Italy
b Division of Cardiac Surgery, Policlinico di Monza, via Amati 111, Monza 20052, Italy
c Coagulation Service and Thrombosis Research Unit, Ospedale San Raffaele, Milano, Italy
(Email: valter.casati{at}policlinicodimonza.it).
The results of the study by Paparella and colleagues1
recently published in the Journal confirm part of the observations described in previous reports addressing the activation of coagulation and fibrinolysis in coronary surgery performed with (ONCAB) or without (OPCAB) cardiopulmonary bypass (CPB). However, some of the statements contained in their "Discussion" section deserve critical consideration. Because no difference in tissue factor (TF) "production" was observed in the 2 groups of patients while prothrombin fragment 1.2 levels were higher in patients undergoing ONCAB, the authors state that the extrinsic pathway of coagulation should not be considered the only trigger for thrombin formation during CPB. Although the intrinsic pathway might also play a role in thrombin formation during CPB, the observation of circulating levels of TF that are not significantly different does not per se demonstrate a similar activation of the extrinsic pathway of coagulation in the 2 groups of patients. TF is a transmembrane protein expressed by white blood cells under conditions of activation, and deposition of such cells in the CPB circuit has been shown before.2 Therefore plasma levels of TF might not reflect the true "exposure" of TF to circulating blood. The authors state that in patients undergoing OPCAB, administration of a heparin dose similar to the one used during CPB (300 U/kg) eliminates the production of thrombin during the time of the operation. "Elimination" of thrombin production would lead to severe bleeding, which cannot obviously be the aim of heparin administration. The authors also state that platelet function, as analyzed by using an in vitro bleeding test (PFA-100), is better preserved during OPCAB surgery than during CPB and that the lack of CPB and cardiotomy suction, together with the reduced formation of thrombin, might explain why platelet function is preserved in patients undergoing OPCAB. The PFA-100 is influenced by the platelet count and the hematocrit level, which are both obviously higher in patients undergoing OPCAB, and by von Willebrand factor levels, which are known to increase postoperatively. Thus the PFA-100 can hardly be considered validated in evaluating platelet function in the setting of cardiac surgery. Despite the observation of a similar postoperative "hypercoagulable" pattern in the 2 groups of patients, the authors also emphasize that D-dimer levels are lower in patients undergoing OPCAB, advising against the use of antifibrinolytic drugs, which might increase the risk of vein graft occlusion in this surgical setting. These conclusions are in disagreement with the results previously reported by our group3 and with the clinical observations of the authors. A similar, although not negligible, 24-hour postoperative bleeding value was recorded in the 2 groups (total blood loss: ONCAB, 861.2 ± 340.3 mL; OPCAB, 933.7 ± 382.6 mL). In a pilot study carried out in patients not receiving antifibrinolytic drugs, we recorded an average total blood loss of 850 mL in patients undergoing ONCAB and 750 mL in patients undergoing OPCAB.3 In a larger study powered to detect differences in bleeding between patients undergoing ONCAB and patients undergoing OPCAB randomized to receive tranexamic acid or placebo, the average total blood loss was 754 mL and 552 mL in patients undergoing ONCAB off or on tranexamic acid treatment and 654 and 375 mL in patients undergoing OPCAB off or on tranexamic acid treatment, respectively, with a significant reduction in bleeding for both groups in the tranexamic acid arm (P < .006).4 In both studies the difference in total bleeding observed between patients undergoing ONCAB and patients undergoing OPCAB was obviously affected by the different amount of heparin infused in the 2 groups (3 times higher in patients undergoing ONCAB). Moreover, in the same study we found that tranexamic acid administration not only significantly reduces perioperative bleeding and the need for allogeneic transfusions both in patients undergoing ONCAB and patients undergoing OPCAB but also modulates inflammation, particularly in OPCAB surgery.4 In view of these certain advantages of antifibrinolytic drugs and of a procoagulant postoperative state of uncertain significance,5,6 the advice against the use of antifibrinolytic agents is, in our opinion, at least debatable.
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