Quality of Oral Anticoagulation with Vitamin K Antagonists in 'Real-World' Patients: Lessons from a Six Years Audit Study

Introduction: Among patients receiving vitamin K antagonists (VKA) therapy, maintenance of an international normalized ratio (INR) in the therapeutic range is essential for treatment efficacy and safety. This requires regular monitoring and appropriate dose adjustment. It has been reported that anticoagulation clinics should aim for a time in therapeutic range (TTR) between 70-80% to optimize benefit and minimize the risk of adverse events. Previously (in a study between September 2006 and June 2012), we have reported that patients with longer INR recall interval (4-8 weeks) showed no decrease of monitoring quality and that it would be safe to increase time between measurements.

Aim: Since actual recommendations for improving TTR include shortening INR recall interval (Lip et al. 2018) we aimed to evaluate the quality of anticoagulation monitoring after having increased time between measurements beyond the 4-8 weeks recall interval.

Methodology: We retrospectively analyzed 37931 appointments of 6 consecutive years (July 2012 to July 2018) corresponding to 1587 patients that are regularly followed up at an outpatient Anticoagulation Clinic of a central hospital under anticoagulation for at least 8 weeks, using TTR determined by Rosendaal method. Patients were divided according to target INR in three groups: Group 1 with target INR 2-3, including 1430 patients corresponding to 30743 appointments with mean age 69±15 years (mean±SD), majority (46.4%) with atrial fibrillation (AF); Group 2 with target INR 2.5-3.5, including 125 patients corresponding to 5439 appointments with mean age 67±12 years, majority (85.6%) with mechanical heart valves; Group 3 with target INR 3-4, including 32 patients corresponding to 1749 appointments with mean age 62±14 years, majority (62.5%) with antiphospholipid syndrome. Descriptive statistics (mean, standard deviation, minimum, maximum, chi-square), inferential statistics (t-test, A-Nova and effect sizes) tests and correlations were performed.

Results: The 1587 patient population, 50.5% male, mean age of 68±17 years and 90.1% in Group 1, showed a mortality of 18%. A point-biserial correlation was run to determine the relationship between mortality and gender, age, INR group and diagnostic. Mortality was correlated with diagnosis (57.2% with AF) (r_pb = -.071, n = 1587, p = .004), male gender (60%) (r_pb = -.089, n = 1587, p <.001) and age (75±12) (r_pb = .175, n= 1587, p<.001) but not with INR group (r_pb = -.017, n = 1587, p = .499). Indeed, between groups mortality was not different [Χ²(2)=.492; p=.782; φ=.018] nor mean age [F(2, 1584)=2.588; p=.078; η²=.003], but gender distribution was unequal [Χ²(2)= 10.815; p=.004; φ=.083] with male predominating in Group 1 (51.9%) and female in Group 2 (60.8%) and 3 (65.6%). Patients in Group 1, corresponding to 90.1% of the total population, had TTR of 72%, patients in Group 2 had TTR of 69% and patients in Group 3 had TTR of 60%. Comparatively to the previous study (2006-2012), we noticed a significant decrease in patient population / appointments size (2087/ 61988) (p <.001) with a decrease of TTR in Group 1 (1927 patients) (83%) and Group 2 (120 patients) (74%) but a TTR increase in Group 3 (40 patients) (54%) (p <.001).

Conclusions and Discussion: More than 90% of the population under VKA treatment showed effective TTR which may infer safety in increasing INR recall interval. The TTR decrease with a smaller population may be explained by the introduction of direct oral anticoagulants in patients with less comorbidities. The increase of TTR in patients with higher INR target suggests a better management of patients under VKA therapy that is actually the only choice for challenging patients.