A randomized clinical trial investigating the relationship between aprotinin and hypercoagulability in off-pump coronary surgery

Abstract

Background: Off-pump coronary artery bypass (OPCAB) surgery is associated with a hypercoagulable state in which the platelet thrombin receptor, protease-activated receptor-1 (PAR-1), helps propagate a thrombin burst within saphenous vein grafts. Aprotinin, used in cardiothoracic surgery mainly for its antifibrinolytic properties, also spares platelet PAR-1 activation due to thrombin. We hypothesized that this PAR-1 antagonistic property provides an antithrombotic benefit during OPCAB surgery.

Methods: Patients were randomly assigned to receive saline (n = 38) or a modified full-dose regimen of aprotinin (n = 37) IV during OPCAB surgery. Blood sampled perioperatively from the coronary sinus, skin wounds, and systemic circulation was analyzed to test coagulation and platelet function. Major adverse cardiovascular events were monitored by obtaining troponin I at 24 h (myocardial infarction), predischarge computed tomography angiography (vein graft thrombosis), and by clinical examination for stroke.

Results: Coronary sinus blood obtained immediately after OPCAB surgery showed significantly less activation in the aprotinin group, as judged by reduced formation of platelet-leukocyte conjugates (P < 0.02) and platelet-derived microparticles (P < 0.05). The aprotinin group showed inhibition of platelet aggregation induced by thrombin (P = 0.007) but not adenosine diphosphate. Thrombin generation, defined by F1.2 levels, was significantly reduced by aprotinin in the coronary sinus but not in skin wound incisions. Major adverse cardiovascular events were significantly reduced in aprotinin-treated patients (5.4% vs 29.7%, P < 0.05). Aprotinin also demonstrated antifibrinolytic properties through diminished red blood cell transfusion (P < 0.04) and reduced blood loss postoperatively (603 +/- 330 vs 810 +/- 415 mL, P < 0.004).

Conclusion: This study demonstrates that aprotinin protects patients undergoing OPCAB surgery from a hypercoagulable state by diminishing thrombin-induced platelet activation and thrombin generation within saphenous vein grafts, while maintaining systemic hemostatic and antifibrinolytic benefits. These results support further investigation of aprotinin and other PAR-1 antagonists in OPCAB surgery.

Figure 1

Histograms from flow cytometric analyses of coronary sinus blood obtained from a representative patient from the aprotinin and placebo group. Three CD41a+ populations were found based on forward scatter characteristics (FSCs): microparticles (CD41⁺, FSC^low), single platelets, and platelet conjugates (CD41⁺, FSC^high) (A). Platelet-derived microparticles were defined as CD41⁺, annexin V⁺ events from the overall microparticle population, and quantified by the M1 gate shown (B). The aprotinin group (thin line) showed significantly less platelet-derived microparticles in coronary sinus blood after off-pump coronary artery bypass (OPCAB) surgery versus the placebo group (thick line). Side-scattering characteristics (SSCs) were used to stratify the platelet conjugate population into a subset with higher granularity (arrow). This CD41⁺, FSC^high, SSC^high population, representing platelet-granulocyte conjugates, was significantly reduced by aprotinin (black area) versus placebo (gray area).

Figure 2

Ex vivo analysis of blood samples by whole blood aggregometry was used to define platelet responsiveness to thrombin at doses ranging from 0.25 to 1.0 U/mL in both groups before and immediately after off-pump coronary artery bypass (OPCAB) surgery. A slight reduction in the thrombin dose-response relationship was seen in the placebo group after OPCAB surgery compared with baseline (A). In contrast, the aprotinin group showed a significantly greater change in postoperative platelet responsiveness that was specific to thrombin and not seen with other agonists, collagen, and adenosine diphosphate (B).

Figure 3

Blood emanating from a standardized skin wound was collected and analyzed for F1.2 to define the physiological role of thrombin formation in response to microvascular injury. Patients from both the aprotinin and placebo groups showed lower F1.2 levels in these blood droplets after surgery (30 min after protamine administration) compared with baseline. However, this decrease occurred in both groups with no difference noted in the postoperative wound F1.2 levels.

Figure 4

Blood was simultaneously obtained from the coronary sinus and aorta after the administration of protamine and analyzed for prothrombin fragment F1.2 and fibrinopeptide A (FPA), markers of the formation, and enzymatic activity of thrombin, respectively. The percent transcardiac change in these markers was calculated as a means of defining regional hypercoagulability, an assay previously shown by our group to predict the risk for saphenous vein graft thrombosis. The postoperative gradient for F1.2 was significantly reduced in the aprotinin versus placebo group but no difference was noted for FPA.