Electrophysiologic studies in a child with concealed preexcitation syndrome

Supraventricular tachyarrhythmias may be due to an ectopic atrial focus or to a reentry circuit associated with Wolff-Parkinson-White syndrome. The distinction between these two etiologic factors, especially when preexcitation is concealed, has important therapeutic implications. Tachyarrhythmias resistant to medical management and due to a reentry circuit are amenable to surgical intervention, whereas those related to ectopic atrial foci are not. Although it can be difficult to differentiate these two mechanisms using the surface ECG, particularly in concealed preexcitation where the ECG is atypical, His bundle electrograms with atrial pacing have proved helpful in making the distinction. A nine-year-old boy with concealed preexcitation syndrome is presented and the mechanisms of tachyarrhythmias associated with preexcitation syndrome are reviewed.