Achieving target international normalization ratio in haemodialysis patients with atrial fibrillation: is it feasible?

Abstract

Sir, Atrial fibrillation (AF), the commonest sustained arrhythmia in clinical practice, is associated with increased mortality and cardiovascular morbidity both in non-uraemic and (recently) dialysis patients. Standard treatment for permanent AF consists of oral anticoagulation and ventricular rate control. In the general population (patients with nonvalvular AF), it has been well recognized that treatment with anticoagulants significantly reduces the risk for embolic phenomena, especially stroke [1–4]. The use of oral anticoagulation with warfarin in haemodialysis (HD) patients has been debated mainly for the following reasons: (i) increased risk of haemorrhagic phenomena due to difficulties in controlling international normalization ratio (INR), bleeding tendency secondary to severe chronic kidney disease, concomitant use of low molecular weight heparin for anticoagulation during dialysis sessions and (ii) absence of definitive guidelines for the prevention of embolic events in HD patients with AF. For the above-mentioned reasons, a significant number of high-risk HD patients for embolic events are often deprived of this life-saving (for the general population) treatment. Recently, we have shown that in a high-risk group (CHADS score ≥ 2) of HD patients with AF, only 25.5% received warfarin, 23.4% received antiplatelet agents and 51.1% received no prophylaxis at all [5]. Undoubtedly, difficulties in achieving constantly INR targets in this population group make certain nephrologists reluctant to use warfarin. We evaluated the INRs in a group of 20 HD patients (from five HD units) receiving warfarin anticoagulation for AF for >1 year. Prothrombin time and INR were measured once weekly in all patients just before the beginning of the dialysis session. Overall, 1040 measurements (>1 year) were analyzed. We calculated the percentages of on target, above target and below target INRs and the percentage of INRs >5 and/or those accompanied by a haemorrhagic event necessitating the temporary discontinuation of warfarin therapy. According to our results, the target INR [2, 3] was achieved in 30.3% (315/1040) of measurements; the percentages for above and below target INRs were 15.0% (156/1040) and 54.7% (569/1040), respectively. Only 6.2% (65/1040) of measurements revealed an INR >5 ± a haemorrhagic event. Our results indicate that achieving the target INR in HD patients (even when a frequent supervision policy is followed) is a difficult task. It is worth noting that almost 70% of measurements during the 12-month observation period were not in the target INR range and 54.7% (>1 in 2) were below the target; the interpretation of this finding is staggering: HD patients with AF receiving warfarin were not adequately protected from embolic phenomena and were also exposed to increased bleeding risk for >50 and 15% of the observation period, respectively. This is of course a small pilot observational study aiming at revealing the difficulties in achieving the target INR in HD patients with AF and therefore definitive conclusions cannot be drawn. Nevertheless, our observations highlight the particularities of the HD population even when addressing a relatively common medical condition.