Appraisal of “Mahaim” Automatic Tachycardia

Abstract

A series of four patients with right-sided accessory pathways with long conducting times and decremental properties is reported. All patients underwent radiofrequency catheter ablation, and target areas were guided by a discrete "Mahaim" potential recorded at the lateral aspect of the tricuspid valve. A slow automatic and irregular rhythm with a QRS morphology similar to that of a fully preexcited QRS complex occurred during radiofrequency current delivery. The occurrence of so-called "Mahaim" automatic tachycardia heralded successful elimination of the accessory pathway in a manner similar to that of junctional automatic rhythm during slow pathway ablation in patients with AV nodal reentrant tachycardia. The observation of an automatic rhythm brought about during radiofrequency current ablation of a Mahaim-like accessory pathway is electrophysiologic evidence of the accessory AV nodal behavior of this structure.

The electrocardiogram during sinus rhythm and tachycardia in patients with Mahaim fibers

“…Accessory pathways with long and decremental anterograde conduction have been the subject of extensive debate about their anatomic structure (1)(2)(3)(4), location (5)(6)(7), related arrhythmias (8,9), electrophysiologic properties (10 -12), ablative techniques (13,14), and automaticity (15). Less attention has been given to the 12-lead electrocardiogram (ECG), especially to the ECG during sinus rhythm.…”

Development of the Right Ventricular Inflow Tract and Moderator Band

“…Mahaim-fibers, mostly atriofascicular fibers, connect proximally to the lateral right atrium or right AV junction and insert distally in the right bundle branch or right ventricular free wall. 1,15 As mentioned, the conduction properties of these fibers have been attributed to AV node-like specific conduction tissue in the proximal part of these fibers, whereas the distal part inserts in the right bundle branch. 5,15 Thus far, no developmental model of the cardiac conduction system has been able to demonstrate the presence of a connection of the right bundle branch with the right AV ring.…”

“…1,15 As mentioned, the conduction properties of these fibers have been attributed to AV node-like specific conduction tissue in the proximal part of these fibers, whereas the distal part inserts in the right bundle branch. 5,15 Thus far, no developmental model of the cardiac conduction system has been able to demonstrate the presence of a connection of the right bundle branch with the right AV ring. The explanation of the presence of a lacZ-positive moderator band as a primary fold-derived structure requires understanding of formation of the right ventricular inflow tract.…”

Wide QRS tachycardia changing to a narrow QRS tachycardia. What is the mechanism?

“…[1][2][3][4] However, switch of an anterograde conducting atriofascicular bypass tract tachycardia by a late atrial ectopic to a typical AVNRT has not been described and hence represents a rare cause of a switch from a broad QRS tachycardia to a narrow complex tachycardia.…”