Unusual variants of pre-excitation: From anatomy to ablation: Part I-Understanding the anatomy of the variants of ventricular pre-excitation.

The famous quotation of Winston Churchill, made in his radio broadcast of 1939 regarding Russia's next move, specifically "A riddle wrapped up in a mystery, inside an enigma," perfectly fits the current understanding of unusual accessory atrioventricular pathways, including the variants producing ventricular pre-excitation. It was many decades after their original descriptions that we came better to begin to understand most of their structure-function relationships. Their mysterious pathophysiology was sometimes unveiled after invasive treatments, such as surgical ablation of the atrioventricular conduction axis instead of the accessory pathway itself. Speculations made on this basis have largely been validated by subsequent clinical experience. Most of the names suggested for description of the pathways have stood well the test of time. For some of them, however, this is not the case, with the initial names becoming confusing. In a series of reviews, we re-visit those accessory pathways producing ventricular pre-excitation other than classical Wolff-Parkinson-White syndrome. To set the scene, in this initial review, we describe the development and anatomy of the normal atrioventricular conduction axis, along with the insulating tissues of the atrioventricular junctions. We have sought to illustrate our explanations by using virtual dissection of computerized tomographic datasets, since they retain the intact heart within the setting of the body. These images illustrate well the value of attitudinally appropriate terminology. Thereafter, we discuss the electrophysiological manifestations of the abnormal anatomical pathways which provide the potential for both accessory atrioventricular and intraventricular conduction.