Arrhythmias Involving Variants of Accessory Pathways

摘要

Differently from the common fast-conducting atrioventricular accessory pathways (APs), known as Kent bundles, some AP variants show atypical electrophysiologic properties or connections with the normal atrioventricular (AV) conduction system (Fig. 1). These forms are known as variants of APs and may, as well, originate variants of ventricular preexcitation (VPE) on surface electrocardiogram (ECG). Apart from the interesting pathophysiologic considerations on their ability or in some cases inability to sustain macro-reentrant supraventricular arrhythmias, these AP variants can pose challenges for correct diagnosis and treatment during invasive electrophysiology procedures. For historic reasons, AP variants are often named under ep-onyms, among which "Mahaim" is more frequently used and declined in "pseudo-Mahaim" or "Mahaimlike" and "true Mahaim" to identify atrio-fascicular (AFs) or AV APs capable of slow and decremental conduction and fasciculo-ventricular (FV) fibers, respectively. To avoid confounding terminology, terms reflecting anatomic and functional characteristics are preferable. Box 1 reports the different forms of AP variants, subclassified according to their capability of sustaining macro-reentrant supraventricular arrhythmias. In this regard, under certain circumstances, AV, AFs, and, very rarely, nodo-ventricular (NV) fibers can be responsible for reentrant supraventricular tachycardias with a peculiar ECG pattern, which become incessant in case of concealed slow-conducting APs, as in the so-called "Coumel tachycardia."