Identifying patients with non-valvular atrial fibrillation & poorly controlled INR on warfarin who are suitable to be switched to NOACs

Abstract

There are quite a significant number of patients of non valvular Atrial Fibrillation (AF) who are on Warfarin for stroke prevention but fail to achieve stable INR control and hence remain at risk. In recent years at least three different New Oral Anticoagulants (NOACs) have been shown to be effective as well as non inferior to Warfarin for stroke prevention in AF. These drugs despite not having effective antidotes yet are considered to have lesser risk of serious bleeding than Warfarin. Although work may be in progress, no clear guidelines have yet been established to decide which patients require switching to NOACs and when. We decided to address this in the form of an audit of Percent time in therapeutic INR range (TTR) amongst AF patients attending our Warfarin Dosing Service. Using our electronic patient records a total of 797 patients were identified as non-valvular AF patients on Warfarin at our dosing service. We found that 79% of these patients had a TTR of more than 60% and 53% above 70%. The 21% patients who did not meet the TTR target were arguably still at a higher risk of stroke. Moreover the fluctuation in their INRs also put them at a higher risk of bleeding. We went on to check the records for abnormalities of renal (eGFR) and liver blood tests (LFTs) in this cohort. Our results showed that 94% of these patients had normal LFTs, 97% had eGFRs of >30 and 59% had eGFRs of >60. Thus majority of the patients in this cohort were eligible for switching to NOACs. Although our data is limited to a single center, it suggests that approximately 20% of the AF patients on Warfarin may require switching to a NOAC due to poor INR control.