Why INR is outside the therapeutic range in patients with acuteischemic stroke and atrial fibrillation

Warfarin is still the primary drug used to prevent vascular events in patients with atrial fibrillation (AF), especially in low-income countries. Therapeutic failure and non-adherence are common causes of recurrent embolic events. The aim of this study was to investigate possible reasons why INR was outside the therapeutic range in patients presenting with acute ischemic stroke and AF.

This prospective study was performed over a ten-month period and all patients admitted with acute ischemic stroke were enrolled. Patients with AF who did not have INR within the therapeutic range (INR=2-3) at the time of admission were identified. During a face-to-face interview, the reasons for INR being outside the therapeutic range were assessed based on a prepared checklist.

During the study period, 810 patients had an acute ischemic stroke, of which 177 had AF heart rhythm (22%). The median age was 76 (IQR: 71-83), and 87 (52%) were male. Of these 177 patients, 44 (25%) had a previous history of AF (“previous AF” group) and 133 (75%) were diagnosed with AF during the current hospital admission (“new AF” group). Among patients on warfarin but with INR outside the therapeutic range (29 in all), 20 (69%) did not see a physician regularly and/or did not take medication according to the physician’s instructions.

The most common reason for INR being outside the therapeutic range was patients lack of awareness of their heart disease (unrecognized AF). Other reasons included irregular visits to the physician and drug non-adherence.