Arq. Bras. Cardiol. 2023; 120(1): e20220864
The Rare Alternans Pre-Excitation Pattern: Is It a Genuinely Benign Phenomenon?
Mirella Facin
, Nelson Samesima
This Short Editorial is referred by the Research article "Wolff-Parkinson-White Presenting as QRS Alternans and Other Differential Diagnoses in a Large Pre-Participation ECG Screening Cohort".
The conduction system is a specialized myocardial cell arrangement that neatly generates and transmits electrical stimuli, leading to sequentially coordinated contractions in each cardiac cycle. A thick layer of fibrous tissue, the annulus fibrosus, almost entirely insulates the atrial from the ventricular myocardia, except in the region of the atrioventricular (AV) node and His-Purkinje system, which, in normal hearts, stands as the single electric pathway between the upper and lower chambers. ,
In some individuals, however, threads of myocardial tissue directly connecting atria to ventricles remain from previous developmental stages and endure after childbirth. The presence of additional atrioventricular conduits or accessory pathways (AP) allows the electrical stimuli to bypass the AV node, resulting in earlier activation of the ventricles or pre-excitation. Bypass tracts may cross the atrioventricular groove wherever atrial and ventricular myocardium are juxtaposed. Most are capable of bidirectional and non-decremental conduction and may serve as a limb to reentrant orthodromic/antidromic circuits or fast lanes for impulse transmission during other supraventricular tachycardias, such as atrial fibrillation (AF).
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