Time in Therapeutic Range With Vitamin K Antagonists in Congenital Heart Disease: A Multicentre Study

Background: Vitamin K antagonists (VKAs) are frequently prescribed to patients with congenital heart disease (CHD) for atrial arrhythmias or Fontan palliation, but there is a paucity of data regarding time spent in the therapeutic range (TTR). We sought to determine the TTR in patients with CHD and atrial arrhythmias or Fontan palliation prescribed VKAs and explore associations with thromboembolic and bleeding events. Methods: A multicentre North American cohort study was conducted on patients with CHD who received VKAs for sustained atrial arrhythmia or Fontan palliation. TTR was calculated using the Rosendaal linear interpolation method. Generalized estimating equations were used to explore factors associated with time outside the therapeutic range. Results: A total of 567 patients, aged 33 ± 17 years, 56% female, received VKAs for 11.5 ± 8.4 years for atrial arrhythmias (63.0%) or Fontan palliation (58.0%). CHD was simple, moderate, and complex in 10.8%, 20.3%, and 69.0%, respectively. Site investigators perceived good control over international normalized ratio (INR) levels in most patients (75.3%), with no or minor compliance or adherence issues (85.6%). The mean TTR was 41.9% (95% confidence interval [CI], 39.0%-44.8%). Forty-seven (8.3%) and 34 (6.0%) patients had thromboembolic and bleeding events, respectively. Thromboembolic events were associated with a higher proportion of time below the therapeutic range (31.3% vs 19.1%, P = 0.003) and bleeding complications with a higher proportion of time above the therapeutic range (32.5% vs 19.5%, P = 0.006). Conclusions: Patients with CHD who receive VKAs spend < 42% of their time with INR levels in the therapeutic range, with repercussions regarding thromboembolic and bleeding complications.