Part II—Clinical presentation, electrophysiologic characteristics, and when and how to ablate atriofascicular pathways and long and short decrementally conducting accessory pathways

Abstract

Recognition of the presence, location, and properties of unusual accessory pathways for atrioventricular conduction is an exciting, frequently difficult, challenge for the clinical cardiac arrhythmologist. In this second part of our series of reviews relative to this topic, we discuss the steps required to achieve the correct diagnosis and appropriate management in patients with the so‐called “Mahaim” variants of pre‐excitation. We indicate that, nowadays, it is recognized that these abnormal rhythms are manifest because of the presence of atriofascicular pathways. These anatomical substrates, however, need to be distinguished from the other long and short accessory pathways which produce decremental atrioventricular conduction. The atriofascicular pathways, along with the long decrementally conducting pathways, have their atrial components located within the vestibule of the tricuspid valve. The short decremental pathways, in contrast, can originate in the vestibules of either the mitral or tricuspid valves. As a starting point, careful analysis of the 12‐lead electrocardiogram, taken during both sinus rhythm and tachycardias, should precede any investigation in the catheterization room. When assessing the patient in the electrophysiological laboratory, the use of programmed electrical stimulation from different intracardiac locations, combined with entrainment technique and activation mapping, should permit the establishment of the properties of the accessory pathways, and localization of its proximal and distal ends. This should provide the answer to the question “is the pathway incorporated into the circuit underlying the clinical tachycardia”. That information is essential for decision‐making with regard to need, and localization of the proper site, for catheter ablation.

High density mapping of atrial insertion of retrograde decremental accessory pathway 3D-illustration of accessory atrio-ventricular conduction network

“…Atrial component of decremental accessory pathways, found in the vestibule of the tricuspid valve, could harbor remnants of the tissues that give rise to the normal AV node (4). Localization of the area of recording of a specific potential in our case was consistant with the location of the vestibule of the tricuspid valve (4) and thus could appear to be a 3D representation of what has been described in autopsies (3,4). The relative wide area of recording was not indicative of common accessory pathway potentials, neither the long VA interval was evocative of conduction through an usual accessory pathway where local ventricular and atrial events are commonly fused.…”

“…Thus, it seems to be the first report of orthodromic reciprocating tachycardia using a purely concealed decremental accessory pathway with findings compatible with an accessory AV node. Some more common by-pass tracts however may also have decremental properties without being categorized as Mahaim fibers : these short decrementally conducting AV pathways may simply be due to alteration of conduction properties or tortuosity (4,11). However they usually do not present with retrograde conduction (2,12) and large areas of specific potentials are not described in this setting.…”

Adenosine—A drug with myriad utility in the diagnosis and treatment of arrhythmias

“…Adenosine also terminates APs with decremental conduction properties such as atriofascicular tachycardia and PJRT. 19…”

“…Adenosine creates a conduction block in the slow pathway in AVNRT and in the AV node in AVRT. Adenosine also terminates APs with decremental conduction properties such as atriofascicular tachycardia and PJRT 19 …”

“…However, adenosine can block conduction in the APs, which have long conduction time (decrementally conducting) such as atriofascicular pathways and permanent junctional reciprocating tachycardia (PJRT). 19 Atriofascicular pathways contain AV nodal tissue, they are also expected to slow down with verapamil. 20 However, in a detailed case study, there was no acute response to verapamil.…”