Pharmacodynamic Response to Warfarin After Conversion of Atrial Fibrillation or Flutter to Sinus Rhythm

Melissa C. Staats; Michael E. Ernst


Am J Health Syst Pharm. 2012;69(13):1158-1161. 

In This Article


A waiver of consent was obtained from the institutional review board at our facility to perform this retrospective chart review. A computerized search of the electronic medical record (EMR) system was performed to identify individuals with atrial fibrillation or flutter who were followed by the anticoagulation management service (ACMS) and whose records indicated a Current Procedural Terminology code for elective cardioversion or ablation between May 1, 2009 (the "go-live" date for the EMR system), and August 1, 2011. Among the 85 such cases identified, 16 were excluded from the study because the atrial fibrillation or flutter spontaneously converted to sinus rhythm, warfarin therapy was not administered before a conversion procedure, or pacemaker placement was performed. Of the remaining 69 patients, 48 had undergone cardioversion and 14 had undergone ablation procedures; of those patients, 16 were excluded because their cardioversion or ablation procedure was unsuccessful. A procedure was considered unsuccessful if conversion to sinus rhythm did not occur during the procedure or if the rhythm reverted to atrial fibrillation or flutter before a postprocedure INR determination. After those exclusions, the evaluable study population consisted of 46 patients.

Patient charts were abstracted for demographic data pertaining to sex, age, diagnosis, and type of procedure. Antiarrhythmic and rate control medications, blood pressure, and heart rate were also obtained for four-week periods before and after the procedure. Each INR measured in the three months leading up to and after the procedure was recorded and matched to a corresponding weekly warfarin dose, as recorded in ACMS notes. From this information, average preprocedure and postprocedure weekly doses for periods of up to four weeks and for an expanded time period (more than four weeks to three months) were calculated.

Paired t tests were performed using SPSS, version 19.0 (IBM Corporation, Armonk, NY), to compare within-individual continuous data such as the calculated mean weekly warfarin dose before and after cardioversion procedures, blood pressure, and heart rate. Additionally, the percentage of patients who had a warfarin dosage change of ≥10% (in either direction) between the preprocedure and postprocedure periods was determined.


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