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Dual Conduction in a Mahaim Fiber EDUARDO BACK STERNICK, M.D., EDUARDO A. SOSA, M.D.,∗ MAUR´ICIO I. SCANAVACCA, M.D.,∗ and HEIN J.J. WELLENS, M.D.† From the Department of Arrhythmia and Electrophysiology of BIOCOR Instituto, Nova Lima, Brazil; ∗ Arrhythmia Unit, Instituto do Cora¸ca˜ o, Universidade de S˜ao Paulo, S˜ao Paulo, Brazil; and †Cardiovascular Research Institute, Maastricht, The Netherlands
Dual Conduction in a Mahaim Fiber. The case of an 8-year-old girl with incessant nonsustained left bundle branch block-like tachycardia refractory to antiarrhythmic drug therapy is reported. Electrophysiologic study revealed the presence of a right-sided accessory atriofascicular pathway. Episodes of nonsustained tachycardia were found to be based upon a dual response in AV conduction over the Mahaim fiber to one P wave. No reentrant tachycardia could be induced. The arrhythmia was cured by catheter ablation targeting a Mahaim potential at the right lateral tricuspid annulus. The findings can be explained by longitudinal dissociation in a single Mahaim fiber, a fiber distally diverging into two fibers with different conduction times, or (less likely) two closely located Mahaim fibers with different conduction times. (J Cardiovasc Electrophysiol, Vol. 15, pp. 1212-1215, October 2004) Mahaim fiber, dual pathways, tachycardia Introduction In the presence of two connections between the atrium and the ventricle or dual AV nodal pathways, two QRS complexes can occur after one sinus P wave.1-11 Mahaim fibers, which are accessory AV pathways with long conduction times and decremental properties, are composed of accessory AV nodal tissue.12-16 We describe the case of a patient with a Mahaim fiber showing two QRS complexes after one sinus P wave. Case Report An 8-year-old girl was referred for an almost incessant tachycardia of 2 years’ duration. Onset of tachycardia was associated with palpitations but was not related to specific factors. Echocardiography revealed no abnormalities. Twelve-lead ECG (Fig. 1, left panel) showed episodes of nonsustained wide complex tachycardia with a left bundle branch block-like configuration. During tachycardia, a 1:2 relationship between the P waves and the QRS complexes was present. In the absence of tachycardia, sinus beats showed a normal PR interval (0.12 s), with a minimally preexcited QRS complex having an rS pattern in lead III (Fig. 2) and absence of septal q waves in the left leads. Twentyfour-hour Holter monitoring showed repetitive bursts of tachycardia occurring throughout the day. The number of episodes and beats per run decreased overnight. Pharmacologic therapy was unsuccessful. Antiarrhythmic drugs such as verapamil, propranolol, and amiodarone did not alter symptoms or reduce the occurrence of tachycardia runs. Methods and Results During electrophysiologic study, measurements during sinus rhythm revealed AH interval 80 ms, HV interval 25 to 30 ms, His-right bundle branch (RBB) interval 20 ms, and QRS width 90 ms. High right atrial pacing at increasing rates showed findings typical of an accessory pathway with long conduction times
Address for correspondence: Eduardo Back Sternick, M.D., Rua Correias 281/301, zip 30315-340, Belo Horizonte, Minas Gerais, Brazil. Fax: 55213132895273; E-mail:
[email protected] Manuscript received 23 January 2004; Revised Manuscript received 5 March 2004; Accepted for publication 11 March 2004. doi: 10.1046/j.1540-8167.2004.04036.x
and decremental properties, seen as progressive AH delay, reversal of His bundle-right bundle depolarization, HV shortening, and increasing preexcitation. Wenckebach block in the accessory pathway occurred with high right atrial pacing at 260 ms. Maximal increase in the anterograde conduction time of the atriofascicular pathway was 140 ms. A proximal Mahaim (M) potential was recorded at the right lateral annulus with an atrium-to-Mahaim (AM) interval of 50 ms. A distal Mahaim potential in the right anteroapical region was recorded (Fig. 2). A 1:2 ratio of P wave to QRS complex was observed when the sinus cycle length was
