Background: Heparin resistance (HR) is often encountered during cardiovascular operations that require cardiopulmonary bypass. Clinical risk factors and the mechanism underlying heparin resistance are yet to be determined. The aim of this study was to elucidate the clinically valid preoperative predictors related to HR. Methods: The study evaluated 489 patients undergoing cardiovascular operations. Of these, 25 patients presented with HR and received antithrombin III for the initiation of cardiopulmonary bypass with an effective activated coagulation time. The remaining 464 patients, who did not receive antithrombin III, served as controls (NHR). Preoperative patient demographic and laboratory data were analyzed to identify risk factors for HR. Results: The preoperative laboratory data showed platelet count, fibrinogen, D-dimer, creatinine, and C-reactive protein were significantly higher in the HR group than in the NHR group. As expected, the antithrombin III level was significantly lower overall in the HR group (86.0% vs 95.5%, p = 0.009)
however, 80% of the patients in the HR group showed normal antithrombin III levels preoperatively. Multivariable logistic regression analysis identified chronic aortic dissection, chronic obstructive pulmonary disease, smoking, and elevated fibrinogen levels as independent predictors for HR. Conclusions: HR was shown to be associated with preoperative high fibrinogen levels, a smoking habit, and a preoperative diagnosis of chronic, but not acute, aortic dissection, with chronic obstructive pulmonary disease as comorbidity. Administration of antithrombin III resolved HR in all of the affected patients, even when their preoperative antithrombin III level was within the normal limit.