Role of Mahaim fibers in cardiac arrhythmias in man.

Abstract

SUMMARY Twelve patients with evidence of Mahaim fibers are reported, six with nodoventricular (NV) fibers and six with fasciculoventricular (FV) fibers. All patients with NV fibers had left bundle branch block morphology, and a sustained reentrant tachycardia with this morphology was proved in each case. In three of the six, ventriculoatrial dissociation occurred during tachycardia. We postulate that the mechanism of this tachycardia is a macroreentry circuit using the NV fiber for the antegrade limb and the His-Purkinje system with a portion of the atrioventricular node for the retrograde limb. ECGs of patients with FV fibers were varied, suggesting a functional relation to the right or left side of the septum. No direct relationship of FV fibers to observed arrhythmias could be found.THE ROLE of Mahaim fibers in the genesis of cardiac arrhythmias in man has been controversial since they were first described.' The initial report was limited to fibers connecting the His bundle to the septum, but this was soon broadened to include fibers connecting the atrioventricular (AV) Received March 25, 1980; revision accepted November 14, 1980. Circulation 64, No. 1, 1981. All patients were admitted to the hospital and placed on continuous telemetry; all cardioactive medications were discontinued. Before cardiac catheterization, all had history and physical examination, routine blood work, ECG, chest x-ray, and twodimensional echocardiography using a microcavitation technique. All patients gave informed consent before catheterization. Electrophysiologic StudyAll patients were studied in the postabsorptive, nonsedated state using techniques previously described.15' 60, 58, '9 Multiple electrode catheters were used to record and pace from the right atrium, the left atrium via the coronary sinus, and the right ventricle. Observations were made during overdrive pacing and refractory period determination from all three locations, during tachycardia and after deliberate induction of atrial fibrillation. TerminologyRecently, Anderson et al.'5 suggested that there are two main anatomic types of Mahaim fibers -nodoventricular (NV) fibers, which arise from the AV node, and fasciculoventricular (FV) fibers, which arise from the His bundle and bundle branches. Because the functional consequences are significant, we have found it useful to consider the two groups separately according to an anatomic and functional classification ( fig. 1). Anderson et al. proposed two varieties of NV fibers -those which arise from the transitional zone of the AV junction and those which arise from the deep, compact nodal portion of the AV junction. NV fibers, depending on level of takeoff relative to the area of physiologic delay, can be associated with either a short or normal PR interval. Ventricular activation in this case results from fusion of impulse propagation via the NV fiber and the normal conduction system, resulting in QRS complexes with varying degrees of anomalous conduction. The PR interval should be normal with isolated FV fibers...

Right ventricular tachycardia: clinical and electrophysiologic characteristics.

“…In fact, this group of patients represents 75% of the nonischemiarelated exercise-induced ventricular tachycardias observed at our institution. * Another common characteristic of this group of patients was the presentation with frequent, often incessant, repetitive bursts of monomorphic ventricular tachycardias.1418 The 20 patients in the present study who presented with this condition represent 80% of patients with repetitive monomorphic ventricular tachycardia studied at our institution. * Although only a third of these patients had tachycardias induced by programmed stimulation, induction of tachycardia by atrial or ventricular pacing was more common than induction by extrastimuli.…”

Conundrum of Sudden Cardiac Death

“…Indeed, only 4 associated cases exist in the literature. 9,10 Although our patient demonstrated a relatively short refractory period of the AP, the significance of this finding has to be understood in its larger context (the pathway was decremental, adenosine-sensitive, and blocked during atrial pacing at a cycle length of 410 ms). Therefore, in the absence of compelling data linking Mahaim-like pathways to SCD, it remains imperative to still seek alternative causes to minimize the risk of future arrhythmia recurrences and enable appropriate evaluation of family members who may be at risk of an inheritable disorder.…”

AV nodal reentrant tachycardia with mahaim fiber conduction.

“…Heart J. N ovember 1989 Mahaim fiber conduction and AV nodal reentrance is particularly rare. In patients with Mahaim fiber conduction, participation of Mahaim fibers within a tachycardia circuit is difficult to prove.12), 13) We cannot exclude the possibility that the impulses were conducted via Mahaim fibers anterogradely and then conducted retrogradely via the His bundle and the AV node. Wellens et al reported a case of Mahaim fiber conduction associated with dual AV nodal pathways.…”