Ventricular tachycardia in infancy: evidence for a reentrant mechanism

Idiopathic ventricular tachycardia and fibrillation

Important data have recently been added to our understanding of sustained ventricular tachyarrhythmias occurring in the absence of demonstrable heart disease. Idiopathic ventricular tachycardia (VT) is usually of monomorphic configuration and can be classified according to its site of origin as either right monomorphic (70% of all idiopathic VTs) or left monomorphic VT. Several physiopathological types of monomorphic VT can be presently individualized, according to their mode of presentation, their relationship to adrenergic stress, or their response to various drugs. The long-term prognosis is usually good. Idiopathic polymorphic VT is a much rarer type of arrhythmia with a less favorable prognosis. Idiopathic ventricular fibrillation may represent an underestimated cause of sudden cardiac death in ostensibly healty patients. A high incidence of inducibility of sustained polymorphic VT with programmed ventricular stimulation has been found by our group, but not by others. Long-term prognosis on Class IA antiarrhythmic medications that are highly effective at electrophysiologic study appears excellent.

Atenolol in children with ventricular arrhythmias

Twenty children and adolescents treated orally with atenolol for chronic paroxysmal ventricular tachycardia (n = 10) or Long QT Syndrome (n = 10) over a 5 year period were retrospectively evaluated to ascertain the efficacy of arrhythmia suppression, the effective dosage, the cardiovascular effects, and the incidence of adverse effects. Patients with paroxysmal ventricular tachycardia were classified by their response to exercise or catecholamines. Atenolol was effective in each patient (n = 5) whose tachycardia was precipitated or exacerbated by exercise or catecholamines when the patient was receiving a dosage of approximately 1.7 mg/kg/day. In those patients (n = 4) in whom exercise or catecholamines either suppressed or had no effect on the tachycardia, none were effectively treated in spite of receiving comparable dosages. Three of these four patients also had structural abnormalities or myocardial dysfunction. Atenolol was effective in treating 4 of 10 patients with long QT syndrome with a dosage of approximately 1.5 mg/kg/day. Six ineffectively treated patients received similar dosages, and four required either additional medication or surgical sympathectomy for persistent syncope. The other two patients died suddenly. Cardiovascular side effects included bradycardia in three patients and hypotension in one. Noncardiovascular effects included mild fatigue (four patients) headache (two), sleep disturbance (two), and difficulty concentrating (one). The medication was discontinued because of side effects in two patients. Atenolol is more likely to be effective in the suppression of paroxysmal ventricular tachycardia in children if the tachycardia is exacerbated by exercise or catecholamines and if the heart is otherwise normal.

Ventricular tachycardia in children without heart disease

To assess the natural history of ventricular tachycardia (VT) in children without heart disease, the clinical course of 26 children, aged 1 day to 15 years at initial detection, was reviewed. Symptoms related to the rhythm were present in 8 children at some time during their course of follow-up. Evaluation included echocardiogram (19 patients), Holter monitoring (22 patients), graded treadmill exercise testing (16 patients) and invasive electrophysiology (4 patients). Exercise induced or exacerbated VT in 9 patients, but suppressed rhythm in 7. Ten patients were never treated. Of the remaining 16 treated patients, therapy was discontinued in 10 on the basis of the electrocardiographic or Holter monitor recordings. Six continued to receive therapy without complications. There were no known deaths over a period of 1 month to 34 years (mean 59 months, median 42 months). Although 2 patients have been lost to follow-up, based on our findings and a review of the reported cases of VT in children to date, after undergoing complete noninvasive cardiac evaluation symptomatic patients should be treated and studied with invasive electrophysiology if antiarrhythmic control is inadequate. The rate of VT or age at onset are not predictive of outcome in asymptomatic patients. As a group, these patients do not appear to benefit from therapy, but warrant follow-up since deaths have been reported in untreated asymptomatic patients.

Advances in the management of cardiac arrhythmias in children

The authors discuss several recent developments in the diagnosis and management of cardiac arrhythmias in the young, focusing on areas in which the greatest progress has been made so that the pediatrician can incorporate these developments into his practice and participate more fully in the management of the patient requiring tertiary care.

Induction of nonsustained atrial flutter by programmed atrial stimulation in children: incidence, mechanisms, and clinical implications

Nonsustained atrial flutter was induced by programmed atrial extrastimulation in 6 (4%) of 137 children with preoperative congenital heart defects, who underwent electrophysiologic evaluation as part of cardiac catheterization. None of these patients had ECG or clinical evidence of arrhythmias. Atrial reentry was induced by programmed atrial extrastimulation in these six patients at coupling intervals slightly longer than the coupling interval at which flutter was induced. The flutter cycle length was similar to the atrial refractory periods. The duration ranged between 0.4 second and 60 seconds. The PA interval and the duration of the P wave were normal in all of the patients. Five of the six had normal PR intervals. It is concluded that nonsustained atrial flutter may be induced by programmed atrial extrastimulation in dysrhythmia-free children. The cycle length is determined by atrial refractoriness and, contrary to adults with clinical atrial flutter, prolonged PA and P wave duration are not predisposing factors.

Role of electrophysiologic testing in the therapy of ventricular arrhythmias

The past decade has witnessed important advances in the understanding of the mechanism underlying ventricular arrhythmias. It has become clear that sustained ventricular arrhythmias can generally be reproduced with programmed ventricular stimulation in the clinical electrophysiology laboratory. False positive results may, however, occur with very vigorous stimulation techniques, particularly in patients without documented arrhythmias. False negative results are not infrequent in victims of cardiac arrest. Ability or inability to initiate ventricular tachycardia during acute and chronic drug testing has predicted clinical failure or success, at least for conventional antiarrhythmics. Patients with sustained ventricular tachycardia and cardiac arrest occurring outside the peri-infarction period are those most likely to benefit from study. Conventional antiarrhythmic agents are successful in about one-third of patients with a high degree of concordance among these drugs. Amiodarone is frequently effective in patients with drug-refractory ventricular arrhythmias. However, its efficacy cannot be predicted by programmed stimulation. This is in striking contrast to Type 1A anti-arrhythmic agents.

Atrial pacing from the esophagus in the diagnosis and management of tachycardia and palpitations

Recent reports have emphasized the usefulness of programmed electrical stimulation of the heart for predicting the effectiveness of pharmacologic therapy of recurrent tachycardias and for determining the basis of recurrent palpitations. We used programmed electrical stimulation of the atrium from the esophagus to study 12 children (ages 1 to 13 years) with either electrocardiographically documented tachycardia (seven patients) or recurrent palpitations (five patients). Atrial stimulation from the esophagus initiated and terminated tachycardia in all seven patients who had a previously documented tachycardia. In five of these patients tachycardia could not be initiated after therapy with quinidine sulfate, and no recurrences have been noted in 12 to 18 months of follow-up. In two patients tachycardia could be reinitiated despite therapeutic quinidine levels, and tachycardia has recurred despite quinidine therapy. Atrial stimulation from the esophagus initiated tachycardia in four of five patients with a history of palpitations. Electrocardiographic documentation of tachycardia was beneficial, because it provided a basis for determining whether therapy for tachycardia was indicated, and in some instances provided an opportunity for patient education to permit-self termination without medication.

Mechanisms of regular, wide QRS tachycardia in infants and children

A regular wide QRS tachycardia was electrocardiographically documented in 32 patients aged 1 month to 18 years. The mechanisms of the tachycardia were evaluated using standard multicatheter electrophysiologic techniques. These mechanisms included (1) orthodromic reciprocating tachycardia with bundle branch aberration (seven patients), (2) antidromic reciprocating tachycardia using single (three patients), or multiple (three patients) atrioventricular connections (Kent bundles), (3) atrial flutter with ventricular preexcitation over accessory connections (eight patients), (4) reciprocating tachycardia using a nodoventricular connection (Mahaim fiber) (five patients), and (5) ventricular tachycardia (six patients). Regular side QRS tachycardias are not rare in pediatric patients. Their mechanisms can be quite complex, and electrocardiographic analysis with respect to QRS configuration, heart rate, or the presence or absence of ventriculoatrial dissociation is not sufficient for diagnostic purposes. Our results show that considerable understanding of the mechanism of regular, wide QRS tachycardias can be obtained by multicatheter electrophysiologic study. Understanding the mechanism is essential in order to make rational use of available therapeutic options.