THERAPY AND PREVENTION ARRHIYTHMIAS Effects of procainamide on intra-arterial electrograms during atrial fibrillation: implication for detection algorithms

The effects of antiarrhythmic drugs on electrograms have implications for arrhythmiadetection algorithms in implantable antitachycardia devices. Filtered and unfiltered intra-atrial electrograms were analyzed in eight patients who received procainamide (50 mg/min iv, up to 1000 mg) during 11 episodes of atrial fibrillation. Continuous recordings were made before, during, and after the infusion. The recordings were digitized, divided into 4.27 sec segments, and analyzed for atrial rate, median frequency and amplitude probability density function. Significant differences were noted before and after infusion of procainamide for atrial rate (498 + 97 vs 356 + 146 beats/min; p < .005), median frequency (5.50 + 1.22 vs 4.24 0.99 Hz; p < .0005), and density (58.3 + 13.9% vs 69.1 + 15.0%; p < .005). Preand postprocainamide values were compared with published criteria for detection of atrial fibrillation. Before procainamide, only 2.3%, 5.7%, and 3.4% of the data segments failed to meet criteria for atrial fibrillation by rate, frequency content, and density, respectively. In contrast, after procainamide, 50%, 36.4%, and 28.4% of the data segments failed to meet these same criteria, despite electrograms still meeting morphologic criteria for atrial fibrillation. Thus procainamide resulted in changes sufficient to cause failure ofpublished criteria for detection of atrial fibrillation. These findings have broad implications for the function of antitachycardia devices in patients receiving antiarrhythmic drug therapy. Circulation 77, No. 5, 1047-1054, 1988. WHEN COMPUTER algorithms are designed to detect arrhythmias, an assumption is made that the signal characteristics of the arrhythmia are constant under variable clinical conditions. However, a number of clinical variables may alter these signal characteristics, such as changes in ventricular electrogram characteristics in relation to the time after onset of ventricular fibrillation,1 changes in atrial electrogram amplitude during exercise,2 and changes in electrogram amplitude and rate caused by lead maturation.3 We hypothesized that antiarrhythmic drugs might also change electrogram characteristics. If such changes were to occur, algorithms would have to be robust enough to accommodate these changes and still provide adequate detection. We chose to examine the From the Departments of Biomedical and Electrical Engineering, Northwestern University, and the Division of Cardiology, Department of Medicine, Evanston Hospital, Evanston, IL, and Northwestern University Medical School, Chicago. These findings are based on work supported under a National Science Foundation Graduate Fellowship. Address for correspondence: Steven Swiryn, M.D., Cardiac Electrophysiology, Evanston Hospital, 2650 Ridge Ave., Evanston, IL 60201. Received Oct. 16, 1987; revision accepted Feb. 4, 1988. Vol. 77, No. 5, May 1988 effects of one antiarrhythmic drug, procainamide, on intra-atrial electrogram characteristics during atrial fibrillation. Recently, our laboratory has reported success with an algorithm that utilizes rate, amplitude probability density, and power spectrum measurements to differentiate atrial electrograms during atrial fibrillation and regular tachycardias. In the present study we examined changes in these electrogram characteristics during intravenous infusion of procainamide. To our knowledge, this is the first formal study of the effects of a changing antiarrhythmic drug milieu on the reliability of arrhythmia detection algorithms.