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SUMMARY The electrophysiological effects of flecainide acetate (2 mg/kg as an intravenous infusion over five minutes) were assessed in 47 patients undergoing electrophysiological study. Seven patients had normal electrophysiology, 16 had a direct accessory atrioventricular pathway, 12 had dual atrioventricular nodal (AH) pathways, five had paroxysmal ventricular tachycardia, six had conduction system disease, and one patient had a left atrial tachycardia.No significant change occurred in sinus cycle length. The PA interval, AH interval, and HV interval were all significantly prolonged. The QRS complex duration increased significantly. The QT interval showed slight prolongation due entirely to the increase in QRS duration.Refractoriness of the atrial and ventricular myocardium was slightly prolonged, but was significant only at ventricular level. No significant change occurred in refractoriness of the norma atrioventricular node. Pronounced prolongation of retrograde "fast" AH pathway refractoriness was observed in those patients with dual AH pathways. Anterograde and retrograde accessory pathway refractoriness were both greatly increased.These electrophysiological properties strongly suggest that flecainide will be useful in the management of a wide variety of cardiac arrhythmias. It should be administered, however, with caution to patients with pre-existing conduction system disease. Because repolarisation is not delayed flecainide is unlikely to induce ventricular arrhythmias related to prolongation of the QT interval.Flecainide acetate4 (N-(2-piperidylmethyl)-2,5-bis (2,2,2-trifluoroethoxy) benzaamide acetate) belongs to a unique series of trifluoroethoxybenzamides' 2 which have proven antiarrhythmic activity against a variety of experimentally induced arrhythmias. [3][4][5] Human pharmacokinetic studies have shown that flecainide is almost completely absorbed after oral administration, undergoes minimal hepatic biotransformation, and has a long plasma elimination half-life ranging from 11 to 22 hours,67 properties that are highly desirable for the long term use of antiarrhythmic agents.This study was undertaken to investigate the acute electrophysiological effects of intravenous flecainide on cardiac conduction and refractoriness in man.

To determine the effect of flecainide acetate, a Class IC antiarrhythmic drug, The medication was given to 28 patients with ventricular pacing electrodes. Eleven patients with temporary pacing electrodes (Group I) received intravenous flecainide (2 mg/kg over 10 minutes). Ten patients with chronic permanent electrodes (Group II) were given the same dose at the time of elective pulse generator change. Seven, with implanted multiprogrammable pacemakers capable of threshold analysis (Group III), were given intravenous flecainide and 5 of these were then given the drug orally for up to 3 weeks (100 mg/day increasing to 400 mg/day). In Group I the threshold measured at a pulse width of 0.5 ms rose from a control value of 0.66 to 1.44 volts after 10 minutes (p less than 0.01). In Group II the threshold rose from 1.73 to 2.13 volts (p less than 0.01) and 2 patients had total suppression of their ventricular escape rhythm for approximately one hour. In Group III patients, intravenous flecainide resulted in a rise escape rhythm for approximately one hour. In Group III patients, intravenous flecainide resulted in a rise of the pulse width threshold measured at 2.7 volts from 0.14 to 0.22 ms (p less than 0.02) and at 4.9 volts from 0.06 to 0.11 ms (p less than 0.05) after 10 minutes. After 3 weeks of oral therapy the threshold at 2.7 volts had risen to 0.11 ms /ms (p less than 0.05 after 10 minutes. After 3 weeks of oral therapy the threshold at 2.7 volts had risen from 0.09 to 0.28 ms (p less than 0.02) and at 4.9 volts from 0.06 to 0.16 ms (p less than 0.05) Flecainide significantly increased both acute and chronic thresholds and the most marked rise (greater than 200%) occurred during chronic oral therapy. Both intravenous and oral flecainide should be used with care in patients with either temporary or permanent pacing systems.

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