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A 35 year old woman was followed up regularly from the age of 8 months, when she was diagnosed with dilated cardiomyopathy secondary to neonatal chickenpox. Aged 5 years, Wolff-Parkinson-White syndrome was recognised based on the presence of a persistent pre-excitation pattern and the occurrence of paroxysmal self limited orthodromic re-entrant tachycardia. During follow up, the degree of the pre-excitation increased progressively. The delta–QRS duration lengthened from 130 ms to 280 ms as the cardiothoracic ratio increased from 0.57 aged 5 years (top) to 0.64 aged 35 (bottom).
In patients with Wolff-Parkinson-White syndrome, the typical QRS pattern with a slurred initial upstroke is the consequence of the fusion between an earlier activation of some part of the ventricular muscle through the bypass tract (expressed by the typical delta wave) and others normally activated by the normal atrioventricular (AV) conduction system.
In our case, the progression of the cardiomyopathy, unquestionably related to increasing myocardial fibrosis, resulted in delayed conduction down the normal route. Thus, a greater part of the ventricles was activated through the anomalous bundle. Consequently, the progressive increase in the degree of the pre-excitation in a damaged muscle devoid of Purkinje fibres, as normally occurs in the basal portions of the ventricles, explains the widening and bizarre configuration of the delta−QRS complex.
The appearance of the relatively narrow QRS (140 ms) during the tachycardia gives indirect support to the interpretation that the amount of pre-excited muscle determines the broad and distorted ventricular complex.