867

Abstract

Introduction: Thrombus formation has been linked to adverse outcomes following the Fontan operation. No data exist to describe the effect of warfarin on INR values when the drug is initiated during the early post-operative (PO) period. Hypothesis: Patients will be more likely to achieve a supratherapeutic (ST) INR if their baseline INR was > 1.3 or if warfarin was started early in the PO period. Methods: This retrospective study describes the incidence of ST (> 2.5) INR values after the Fontan procedure at our institution between April, 2009 and January, 2012. Patients met inclusion criteria if the surgical procedure involved the initial conversion to a Fontan circuit and were initiated on warfarin during the immediate PO hospital stay. Excluded patients were those without a documented INR within 24 hours before warfarin initiation or those with < 2 INR values after initiating therapy. Data were analyzed with the Fisher’s exact test, Student’s t-test or Mann-Whitney Rank Sum test, as appropriate. Statistical significance was taken at p < 0.05. Results: A total of 32 patients met inclusion criteria: female (59.4%), systemic right ventricle (61.3%), under 3 y of age (81.3%), lateral caval tunnel Fontan (96.9%), with fenestration (93.8%). The median length of stay was 10 days. ST INR values after warfarin initiation occurred in 12.5 % of patients with an additional 6.3 % requiring dose adjustments due to a rapidly increasing INR. Patients with a ST INR were started on warfarin earlier compared to those in the non-ST group (POD 5 vs POD 2, p=0.037, respectively). Baseline INR values or initial warfarin doses were not significantly different between the groups. There were no reported thrombi or thromboembolic events and the only clinically significant bleeding event occurred while the INR value was subtherapeutic. Conclusions: Patients undergoing the Fontan procedure may require lower doses to achieve similar target INR values when warfarin is initiated closer to the surgical procedure date. Despite this observation, warfarin appears to be a safe agent in the early Fontan PO period when INR is monitored closely. One should use caution and consider dose reduction when initiating warfarin before PO day 3 after a Fontan operation.