Preexcitation in infancy and childhood

Abstract

A 12-year-old child was admitted to the emergency department (ED) for recurrent palpitations with no evidence of organic heart disease. This symptom, which the patient had complained about since childhood, had never been eleetrocardiographically documented before. On arrival, his electrocardiogram (Figure 1) showed: (1) sinus beats with normal PR interval and no evidence of delta wave; (2) spontaneous onset and termination of tachycardia with narrow complexes of approximately 170 beats/rain; (3) initiation of tachycardia related to a critical shortening of the atrial cycle length (PP), without PR prolongation; (4) during the tachycardia there was a 1:1 atrioventricular relation with a retrograde P wave, negative in leads II and III and positive in I, and an RP interval longer than the PR interval (the P wave in fact was nearer to the following QRS than to the previous one); and (5) the tachycardia terminated by the QRS complex was not followed by a retrograde P wave) The tachycardia was almost incessant and unresponsive to pharmacologic treatment. This arrhythmia is the most common form of incessant supraventricular tachycardia in children. 4 Two mechanisms often have to be considered: (1) reentrant tachycardia using a fast atrioventrieular nodal pathway for anterograde conduction and a slow atrioventricular nodal pathway for retrograde conduction; and (2) orthodromie reciprocating tachycardia using the atrioventricular node-HisPurkinje system for anterograde conduction and a concealed accessory pathway for long retrograde conduction time (concealed preexcitation). In the electrocardiogram shown in Figure 1, the frontal P wave axis (retrograde negative P wave in leads II and III) cannot help to discriminate the arrhythmia, being common to both reentrant and reciprocating tachycardia; the horizontal axis (retrograde P wave positive in lead I), however, with earliest activation of the right atrial free wall, may exclude an atrioventricular nodal reentry, 5