ABSTRACT
The authors review the state-of-the-art on ventricular pre-excitation in medical and arrhythmological literature in order to facilitate the recognition of the various clinical forms, like classic and occult Wolff Parkinson withe syndrome and Lown Ganong Levine syndrome. A historical introduction reviews our electrophysiopathological knowledge of the electrical activation and conduction of ventricular pre-excitation compared to normal, starting from the anatomic discovery of conduction pathways to the possible use of transesophageal electrostimulation and endocavity mapping to study electric potentials. Avantgarde technologies have also been developed to eliminate anomalous pathways firstly by using a direct current dirscharge and secondly radiofrequency. Atrioventricular electric activation has been widely illustrated in normal subjects in order to create a model for comparison with pathological ventricular pre-excitation: the upper left portion of the septum is no longer the first zone to trigger the kinetic mechanism compared to the early fascicular fraying of the homonymous branch. Instead the upper right part of the septum is activated earlier owing to the anomalous fascia connected on this side to the right branch through their septal arborisations. As a result, this new conduction pathway activates the ventricular masses earlier through an anomalous route, given that there is no further contact with the atrioventricular nodes which act as a control. A similar situation is found in the left branch block where the ventriculogram is late with a normal PR, unlike pre-excitation when an early delta wave is present with a short PR. Electric conduction is also illustrated based on new knowledge of the circuit structures and the rings theory. Orthodromic tachycardia is distinguished from the antidromic form, double accessory pathway tachycardia, ectopic reciprocant atrial fibrillation tachycardia and occult bundle tachycardia which is studied using transesophageal stimulation with a time threshold of 70 ms for ventricular-atrial retrograde activation. The stimulation techniques using single or repeated extrastimulus are explained for this purpose, as well as those with serial extrastimulation and the physical characteristics of the circuit based on the ratio between voltage and resistance. The authors also report the practical aims of electrostimulation for determining the electric threshold of the anomalous circuit in terms of refractoriness, electric atrial stability, reciprocity and the occurrence of the macro re-entry. Lastly, the authors describe electric conduction by anomalous pathways based on the criterion of conduction and activation, both of which are analysed and compared on the basis of the intrinsicoid deflection morphology on the surface ECG: the aberrant qRs usually suggests an antidromic ventricular activation and retrograde conduction between atrium and ventricle, while normal intrinsicoid deflection demonstrates that the activation is orthodromic and the conduction anterograde, namely ventricle-atrial. Having been reproduced in a synoptic synthesis, these manifestations show a regular electrophysiological pattern because they are dissimilar from the behaviour of the monophasic bioelectric potential of the cardiac cells specialised in the conduction of the stimulus, whether they represent a normal or pathological electric pathway. The study is rounded off by the analysis of the reciprocant tachycardias and their re-entry varieties related to the type of the anomalous bundles. A number of types of re-entry can be identified: sinusal re-entry (micro re-entry), atrial re-entry, re-entry in the atrio-ventricular node, re-entry tachycardia and the so-called triggered type. The discussion of the electrophysiopathological aspects of pre-excitation is followed by the clinical forms of ventricular pre-excitation that can be divided into 3 main types. The different ECG clinical pictures are set out in the summary table, together with the type of shunt and activation and possible variants, following Rosenbaum s classic paint: the common type B, the rare type A and a last variant, the C type. This section also describes the positional peculiarities of the Kent-Paladino bundle, the left ventricular, septal (anterior and posterior) and the multiple-bundle ones. The authors also illustrate the criterion and meaning of endocavity mapping in the search for anomalous bioelectric potentials that identify the pathway or the location of the endocardiac bundle and/or foci to be eliminated. A new echocardiographic technique is described with a conventional M mode, digitalised 2D and tissular Doppler which has a comparable ability to identify the anomalous pathways of electric conduction using a non-invasive method. (ABSTRACT TRUNCATED)
