time in therapeutic range as a marker for thrombotic and bleeding outcomes in fontan patients

Fontan patients managed with warfarin are at risk not only for thrombotic events, but also for bleeding episodes as a consequence of anticoagulation treatment. the aim of this study was to determine whether time spent in patient specified therapeutic range (ttr), when managed in a cardiology-based pharmacist managed anticoagulation clinic (pmac), is a useful target metric for monitoring, as well as improving outcomes. a single center retrospective review was conducted evaluating ttr of all fontan patients (n = 45) on warfarin managed in our outpatient cardiology pharmacist managed anticoagulation clinic (pmac) during a 19 month time frame. the primary outcome was time spent within, above, and below therapeutic range. secondary outcomes were thrombotic event (te) incidence pre- and post pmac enrollment and bleeding event incidence during pmac management. of the fontan patients included, 55.6% were male and the median age at latest anticoagulation clinic follow-up was 19 years (iqr 13, 29). a composite 52.9 patient years of warfarin therapy was evaluated during the study time frame. the mean ttr for patients was 84.1 ± 5.2%. the most frequent reasons for non-therapeutic inrs were diet changes (42.8%), medication non-compliance (13.7%), and drug interactions (8.8%). only one te occurred during the study time frame. the incidence of te in this population was decreased after pmac enrollment (1 per 52.9 patient year versus 1 event per 17.4 patient year; p < 0.0002). two major bleeds that required emergency department visit occurred during this time, none were cerebral or gastrointestinal. in fontan patients anticoagulated with warfarin, a greater than 80% ttr can be achieved in a pmac. such high time in therapeutic range was associated with excellent outcomes, despite the obvious complexity of this population.