Fluctuations in warfarin dose response after heart valve surgery: implications for cardiac rehabilitation

In patients undergoing heart valve surgery (HVS) who require warfarin therapy, the maintenance of low variability in the level of anticoagulation early after operation is generally difficult. Aim of this study was to evaluate the time in therapeutic range (TTR) in HVS patients receiving oral anticoagulation therapy (OAT) during phase I-II of cardiac rehabilitation (CR), and, secondly, to identify clinical variables associated with inadequate anticoagulation. Methods: Observational study of consecutive in-hospital patients directly tracked from a cardiac surgery unit to a CR facility. OAT was monitored both in terms of administered warfarin doses and resulted INR values, from day 1 to day 15 after operation. Clinical variables were tested in a logistic regression model for the prediction of inadequate anticoagulation, defined as the presence of nontherapeutic INRs for ≥5 days between day 8 and 15. Results: Eighty-one patients (males 56%, age 62±19 yrs.), following valvuloplasty (37%), mechanical (17%), and bioprosthetic (45%) valve replacement were considered. The prescribed warfarin dosages were significantly higher from day 1 to day 7 than from day 8 to day 15 (4.6±3.6 and 3.0±1.1 mg respectively, p< 0.001). Overall, TTR was 6±3 days, while time with elevated and lower INRs accounted for 1.3±1.6 and 8.0±3.5 days respectively. At day 7, only 25% of patients (n= 20) showed a therapeutic INR value. Inadequate anticoagulation between postoperative day 8 and 15 was displayed in 41 (51%) patients, with hypertension as the only independent predictor (p< 0.001) at multivariate analysis. Conclusions: Despite intensive monitoring, half of patients have nontherapeutic INR values (mainly subtherapeutic) in the first two weeks after HVS while on warfarin. Giving the high risk of completing the hospitalization phase without a stable OAT in many patients, both cardiac surgeons and cardiologists should not miss the opportunity to improve patients education, and consider a direct track to anticoagulation management services after discharge.