Pharmacodynamic response to warfarin after conversion of atrial fibrillation or flutter to sinus rhythm

The results of an evaluation of the impact of restoring sinus rhythm on warfarin sensitivity are reported.

A retrospective review of the records of all patients (n = 46) with atrial fibrillation or flutter who underwent cardioversion or ablation procedures to restore sinus rhythm at a large medical center during a 27-month period was conducted. Patient data covering the 3-month periods before and after the procedures were reviewed to identify the warfarin doses required to maintain International Normalized Ratio (INR) values in the recommended range of 2.0-3.0. Within-individual preprocedure and postprocedure mean weekly warfarin doses for two periods (zero to four weeks and an expanded period of four weeks-3 months) were compared using paired t tests.

The average weekly warfarin dose during the four-week preprocedure period was not significantly different from the doses during the four-week and expanded postprocedure periods. The average weekly doses during the four-week and expanded postprocedure periods were significantly less than those used in the expanded preprocedure period (p = 0.004 and p = 0.046, respectively).

Warfarin dosages required to maintain a goal INR of 2.0-3.0 were relatively stable in the four weeks before and after procedures to convert atrial fibrillation or flutter to sinus rhythm. Changes in the weekly warfarin dose requirement of ≥10% after the procedures were implemented in a small proportion of patients. The mean weekly warfarin dose was significantly lower in the three months after than in the three months before the procedure.