Preexcitation in infancy and childhood

Preexcitation in Infancy and Childhood VINCENZO MARAFIOTI, MD, PIERO ZARDINI, MD Arrhythmic emergencies are fairly unusual during infancy; therefore, when they occur, they present a difficult diagnostic mad therapeutic problem. The supraventricular tachycardias are the most c o m m o n ones in childhood, and the predominant among these is the reciprocating form through an accessory pathway. 1-2

CASE1 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

From the Institute of Cardiology, University of Verona, Italy. Manuscript received September 26, 1996; accepted September 26, 1996. Address reprint requests to Dr Marafioti, Divisione Clinicizzata di Cardiologia, Ospedale Civile Maggiore, Piazzale Stefani 1, 37126 Verona, Italy. Key Words: Preexcitation, reentrant tachycardia, reciprocating tachycardia. Copyright © 1998 by W.B. Saunders Company 0735-6757/98/1602-002358.00/0 188

indicating a reciprocating form through an accessory pathway with slow retrograde conduction. The reciprocating tachycardia, also known as Coumel's tachycardia, is usually identified in childhood and rarely at an adult age (as happens for the reentrant form), and typically shows a "permanent" pattern with only short sinus rhythmic phases (in the atrioventricular nodal reentry, the arrhythmia has a mainly paroxysmic trend). Moreover, the reentrant tachycardia may be combined with organic heart disease, ie, interatrial defect, mitral valve prolapse, or sick sinus syndrome, which does not happen with the reciprocating tachycardia.6 Coumel's tachycardia may be considered a variant form of preexcitation (concealed preexcitation),7 which influences the patient's quality of life because of its permanent pattern and disappointing response to pharmaceutical treatment. If the diagnosis is delayed and surgical treatment is not given, these patients suffer for most of their lives, being in tachycardia longer than in sinusal rhythm. 5

CASE2 A 27-day-old male infant (height 55 cm; weight, 3,910 kg) was brought into the ED for congestive cardiac failure. At physical examination, cyanosis, polypnea, gallop rhythm, and hepatomegalia were observed. Marked cardiac enlargement and congested lung fields were evident on thoracic roentgenogram. Analysis of blood gases showed: Po2, 45.6 mmHg; Pco2, 26.3 mmHg; pH, 7.38; and O2 saturation, 80.5%. On admission, an electrocardiogram (Figure 2) showed a supraventricular tachycardia with narrow complexes of approximately 300 beats/rain. After the conversion to sinus rhythm through atrial pacing from the esophagus, preexcitation was evident (Figure 3). On this electrocardiogram, the delta wave and QRS complex reflect conduction across the left lateral accessory pathway: delta wave and QRS are negative in leads I and aVL, and positive in the anterior precordial leads, III, and aVE The Wolff-Parkinson-White (WPW) syndrome is present in 10% to 50% of infants with supraventricular tachycardia.2 The electrocardiographic diagnosis may be difficult at first in patients in whom a narrow QRS tachycardia appears. The preexcitation often becomes evident only after conversion to normal sinus rhythm. 2 In 32% to 50% of cases, such arrhythmias occur as emergencies, causing acute heart failure, 1 which is attributable to the deceptive modality of the syndrome's first appearance. A newborn child cannot verbally express a symptom such as "palpitation." In the absence of heart disease, a high heart rate can easily be tolerated in early childhood. Moreover, the recognition of arrhythmia outside the hospital becomes possible only belatedly, following the appearance of congestive heart failure signs, as in our small patient. The WPW syndrome, even when it begins as an arrhythmic emergency, naturally resolves itself in 80% to 90% of cases after the first year of life. Moreover, atrial pacing from the esophagus can be safely and reliably accomplished in these patients.8

FIGURE 1. Coumel's tachycardia with spontaneous onset and termination. Note negative retrograde P waves in leads II and III and positive in I, with the RP interval longer than the PR interval.

FIGURE 2. Electrocardiogram showing a supraventricular tachycardia with narrow QRS complexes of approximately 300 beats/rain.

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FIGURE 3. Electrocardiogram after conversion to sinus rhythm with atrial pacing from esophagus: evidence of preexcitation with atrioventricular conduction over a left lateral accessory pathway.

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AMERICAN JOURNAL OF EMERGENCY MEDICINE • Volume 16, Number 2 • March 1998

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reciprocating tachycardia in young patients. J Am Coil Cardiol 1986;8:385-390 5. Marriot HSL, Conover BH: Advanced concepts in arrhythmias. Phoenixville, PA, Mosby c/o John Scott and Company, 1989 6. Yeh SJ, Yamamoto T, Lin FC, Wu D: Atrioventricular block in the atypical form of junctional reciprocating tachycardia: evidence supporting the atrioventricular node as the side of reentry. J Am Coil Cardiol 1990;15:385-392 7. Critelli G, Gallagher J J, Monda V, Coltorti F, et al: Anatomic and electrophysiologic subtrate of the permanent form of junctional reciprocating tachycardia. J Am Coil Cardiol 1984;4:601-610 8. Benson DW, Dunnigan A, Sterba R, et ai: Atrial pacing from the esophagus in diagnosis and management of tachycardia and palpitations. J Pediatr 1983;102:40-46