ELECTROPHYSIOLOGIC AND ANTIARRHYTHMIC EFFECTS OF INTRAVENOUS BISOPROLOL IN ATRIOVENTRICULAR NODAL REENTRY TACHYCARDIA

Beta-blockade may be useful in the termination and prevention of atrio ventricular nodal reentry tachycardia (AVNRT), An electrophysiologic s tudy was performed in 9 patients (4 men and 5 women; mean +/- SD age, 56 +/- 16 years) with documented AVNRT before and after the intravenou s administration of 5 mg of bisoprolol, In 5 of the 9 patients, AVNRT was terminated by bisoprolol, and AVNRT could no longer be induced in 6 of the 9 patients, Bisoprolol significantly prolonged the Wenckebach cycle length but did not affect fast pathway refractoriness or atriov entricular (AV) nodal conduction time during sinus rhythm or various p aced cycle lengths up to 430 milliseconds, Conversely, it significantl y prolonged the mean atrium-His bundle (AH) interval during AVNRT from 244 +/- 65 milliseconds to 320 +/- 64 milliseconds, These observation s suggest that the effects of bisoprolol on the AV node, primarily at short cycle lengths, are rate dependent, Due to AH prolongation, mean tachycardia cycle length significantly increased from 313 +/- 58 milli seconds to 378 +/- 50 milliseconds, but there was no difference in the relative amount of prolongation between responders (60.8 +/- 26 ms) a nd nonresponders (64.6 +/- 37 ms), Bisoprolol appears to be useful in the termination and prevention of AVNRT during programmed electrical s timulation studies, Its effects on the AV node are use dependent.