Background Among patients with acquired cardiovascular disease taking oral vitamin K antagonist medications, time within therapeutic range (TTR) is considered poor when below 60%. To date, however, there are no data about anticoagulation control in adults with congenital heart disease (CHD). This is concerning given that they represent an emerging and growing population of cardiac patients with specific management considerations.

Objectives In a sample of adults with CHD taking oral vitamin K antagonist medications, we investigated (i) TTR and (ii) socio-demographic and medical factors associated with lower anticoagulation control.

Methods In this retrospective study, the following were study inclusion criteria: age ≥ 18 years, diagnosis of CHD, prescribed oral vitamin K antagonist medication, followed in the thrombosis clinic at least once between January 2005 and December 2010, and adequate frequency of recording of INR values. We documented medical and socio-demographic background, indication for anticoagulation therapy, international normalised ratio (INR) values, and TTR; data were recorded through December 2013.

Results We identified 119 eligible patients (49% male; mean age = 39 ± 17 years; mean follow up duration = 4 ± 2.3 years). Defect complexity was categorised as simple (n = 29; 24%), moderate (n = 46, 39%) or great (n = 44; 37%). Specific indications for oral anticoagulation were cardiac arrhythmias (n = 60; 51%), prior thrombus/emboli event (n = 30; 25%), mechanical valves (n = 24; 20%), and other (n = 5; 4%). Twenty-three patients (19%) had a documented psychiatric disorder and 21 patients (18%) had a history of medication non-adherence. Of 71 patients with known educational attainment, 45 (38%) had earned college or university degrees. Of 119 study patients, the mean TTR was 49 ± 19% (range: 0–89%); 82 patients (69%) had poor anticoagulation control (TTR < 60%). TTR varied significantly by disease complexity (p < 0.05); TTR was lowest among patients with CHD of moderate complexity (44%) and highest among patients with CHD of simple complexity (55%). TTR was also significantly lower among patients with mechanical valves vs. those with other indications for anticoagulation (41% vs. 50%, p < 0.05); 79% of patients with mechanical valves had poor anticoagulation control. TTR was significantly lower for patients for whom non-adherence was documented in the medical chart (32% vs. 52%; p < 0.001). TTR did not vary as a function of age, sex, presence of psychiatric disorder, or educational attainment.

Conclusions Among our study cohort of adults with CHD, patients were within therapeutic INR range only half of the time and more than two-thirds of patients had poor anticoagulation control. Poorer anticoagulation control was observed in patients with moderate defect complexity, with mechanical valves, and with a documented history of medication non-adherence. Future investigation into the clinical outcomes of sub-optimal INR control as well as the potential role of novel oral anticoagulant agents is encouraged.