An Evaluation of Warfarin Dose Changes after Discharge from Mechanical Circulatory Support Device Implantation

Purpose To determine the chronic warfarin dose trends in mechanical circulatory support (MCS) device patients in the period after discharge from implantation. This may provide practitioners some general guidance when caring for an assortment of outpatient MCS recipients. Methods MCS patients implanted between 9/2013 and 5/2018 with warfarin dosing records during the first year after implant were evaluated. Average warfarin doses per day were tabulated and compared at months 1, 3, 6, and 12 post discharge. Data points were censored if a new significant drug interaction was noted to be influencing the subsequent analysis period. Results The study group totaled 49 patients. It was comprised of 31 Heartware, 12 Heartmate II, 4 total artificial heart, and 2 Heartmate III recipients. All patients were titrated towards an international normalized ratio (INR) goal of 2.0-3.0 initially. Eighty-two percent of the group was Male, the average age was 58.2 years old, and the average length of stay for the implant admission was 34.5 days. During the first year after discharge from receiving a MCS device, 34 patients experienced a net increase in the average warfarin dose per day, while 14 patients saw a net decrease. One patient's warfarin dosage remained the same from discharge until month 12. The mean increase in warfarin dose was 8.8%, 21.0%, 25.1%, and 26.5% at months 1, 3, 6, and 12 respectively. The dose increases were statistically significantly different at months 6 (p=0.023) and 12 (p=0.049) versus the dose increase at month 1. The dose increase comparison between month 1 and 3 were not statistically different (p=0.076). The median warfarin dose at discharge was 4mg per day with an interquartile range of 2.57 mg to 6 mg per day. By month 12, the median daily dose was 4.3 mg per day with an interquartile range of 3.9 mg to 6.4 mg per day derived from weekly totals. Conclusion MCS team members that manage warfarin dosing may expect gradual increases on average during the first year post discharge. This expectation may avert unwanted sub-therapeutic INRs in these MCS patients.