Identification of clinical factors predicting warfarin sensitivity after cardiac surgery

Objectives: Warfarin is commonly initiated post-cardiac surgery to reduce the risk of intra-cardiac thrombus formation.Studies have found that sensitivity is increased after cardiac surgery and anti-coagulation is subsequently difficult to manage.This study set out to identify clinical markers of increased warfarin sensitivity in patients’post-cardiac surgery, and build a modelthat can predict warfarin sensitivity, and improve safety in this setting.Methods:The study was an observational, retrospective cohort design.Clinical parameters including Left Ventricular Ejection Fraction (LVEF), cross-clamp time, age, serum albumin and C-reactive protein concentrations were collected from consenting patients who had undergone cardiac surgery and prescribed post-operative warfarin. Warfarin Dose Index (WDI) was calculated for each patient from their INR and warfarin dose, as a measure of sensitivity.Results:41 patients were recruited to the study.Logarithmically transformed WDI (log WDI) significantly correlated with LVEF, cardiopulmonary bypass (CPB) time, cross-clamp time, baseline INR and co-administration of amiodarone (p<0.05).When added to a linear regression model, LVEF and cross-clamp time produced a model that accounted for 41% of variance in log WDI (R2=0.41), p=0.0002).Applying a log WDI cut-off value of -0.349 discriminated between patients who develop an INR >4 and those who do not with a sensitivity of 75% and a specificity of 70%.Conclusions:This single centrestudy has highlighted two risk factors for increased warfarin sensitivity post-cardiac surgery.Further research is needed to confirm these findings in a wider, more diverse population, and to validate this model.