R. H. Hollis1,2, J. T. McMurtrie1,2, L. A. Graham1,2, J. S. Richman1,2, T. M. Maddox4, K. M. Itani3, M. T. Hawn1,2 1Birmingham Veterans Administration Hospital,Center For Surgical, Medical Acute Care Research And Transitions (C-SMART),Birmingham, AL, USA 2University Of Alabama At Birmingham,Section Of Gastrointestinal Surgery, Department Of Surgery,Birmingham, AL, USA 3Boston University And Harvard Medical School,Department Of Surgery, VA Boston Health Care System,Boston, MA, USA 4University Of Colorado School Of Medicine,VA Eastern Colorado Health Care System,Denver, CO, USA
Introduction: Patients with cardiac risk factors undergoing surgery are not only at increased risk of myocardial infarction (MI) but are often exposed to an increased risk of bleeding from perioperative antiplatelet therapy or from the need for therapeutic anticoagulation. Patients who receive blood transfusions in the setting of MI are associated with worse outcomes. However, the temporal relationship and related risk of postoperative myocardial infarction and blood transfusions are not well established.
Methods: We matched patients with coronary stents who underwent inpatient non-cardiac surgery within two years of stent placement to two patients with similar cardiac risk and surgical procedures without coronary stents. Our independent variable of interest was peri-operative transfusion and patients receiving preoperative transfusions were excluded. Our outcome variables were MI and death at thirty-days post-operatively. The relationship between timing of MI and transfusion was assessed. MI time was determined by postoperative time to first troponin lab value meeting threshold 0.04 ng/ml. Time to transfusion was defined as time to receipt of first blood transfusion, with time zero assigned to intraoperative transfusions. GEE model was employed to adjust for risk factors for mortality and to determine predictors of MI. Statistical analysis was performed by chi-square test and Wilcox t-test.
Results: We identified16,807 patients with cardiac risk factors undergoing inpatient non-cardiac surgery, of which 327 (1.9%) experienced postop MI. Of those patients with MI, 50% received a blood transfusion. The overall median postoperative time to transfusion was sooner than MI (1 vs. 36 hrs). Mortality was higher following MI compared to transfusion or no MI or transfusion (17.7% vs. 5.3% vs. 1.5%; P < 0.001). Of patients with both outcomes of MI and transfusion, 57% (97/169) received a transfusion prior to MI and were at increased mortality compared to patients with first transfusion after MI on unadjusted (22.7 and 11.1%; P <0.05) and adjusted analysis(OR=2.4, 95% CI 0.9-6.2). Of all patients with a perioperative transfusion, only a history of a cardiac stent was significantly associated with MI (OR=1.8, 95% CI 1.4-2.5).
Conclusion: The occurrence of a transfusion prior to MI is associated with increased mortality. Cardiac stent placement is a predictor of MI in patients receiving a blood transfusion, suggesting that peri-operative bleeding may be in the causal pathway for post-operative MI in this patient population.
