VENTRICULAR DYSRHYTHMIA
RATIONALE: can be either completely benign or fatal depending on the type of dysrhythmia and the clinical situation.
Ventricular dysrhythmia, defined as those rhythm disturbances that originate distal to the bifurcation of the bundle of His, can be either completely benign or fatal depending on the type of dysrhythmia and the clinical situation. A PVC in a child may be recognized electrocardiographically by the following criteria: 1) the QRS complex is premature (more than 0.08 seconds before the next expected QRS), 2) the QRS complex has a prolonged duration (a duration more than 0.08 seconds in an infant or more than 0.09 seconds in a child), 3) the morphology of the QRS complex is different from that of a regular QRS, 4) there are marked ST- segment and T- wave abnormalities with the direction of the T- wave usually opposite to that of the QRS complex, and 5) there is no premature atrial depolarization.
Ventricular tachycardia is a series of 3 or more repetitive excitations that originate from the ventricle. Points favoring a ventricular origin are: 1) AV dissociation. If AV dissociation is present with a wide QRS tachycardia it is helpful, if AV dissociation is absent it is not helpful because ventricular tachycardia in children may occur with 1 - 1 retrograde capture of the atria. 2) intermittent fusion or sinus capture beats, and 3) morphology of ventricular tachycardia similar to single PVC's.
PVC's may be detected on a routine resting EKG in 0.8 to 2.2% of children with an otherwise normal heart. On 24 hour EKG single uniform PVC's can be detected in up to 10% of normal teenagers and 5% of normal infants. Children with asymptomatic unifocal PVC's should have a careful clinical examination, EKG, and treadmill exercise test. If there is no associated heart disease and the PVC's disappear with exercise the dysrhythmia is probably innocuous and no further cardiovascular work- up is necessary. Multifocal PVC's are much rarer in children and may have a poor prognosis.
Ventricular tachycardia in children is rare. Approximately 25% of children reported with ventricular tachycardia have a normal heart. Most of these children are asymptomatic. In those patients who have symptoms the presentation is similar to that of supraventricular tachycardia with pallor, irritability, and poor appetite. Syncope or presyncope is uncommon. In children with a normal heart, degeneration to ventricular fibrillation is exceedingly rare.
Children with abnormal hearts are clearly a greater risk for PVC's and ventricular dysrhythmia. In particular patients with intracardiac repair of tetralogy of Fallot, prolonged QT- interval syndrome, sick sinus syndrome, sinus bradycardia, complete AV block, chronic cardiomyopathy or other congenital heart disease are obviously at increased risk for ventricular dysrhythmia.
Since there is a difference in prognosis for ventricular dysrhythmia in children with normal and abnormal hearts, it is important to determine the presence of any acute or chronic causative factors. Clues may be apparent from the history, which should include questions about drugs, especially caffeine and decongestants, old myocarditis, or predisposition to electrolyte imbalance. Physical examination may show mitral valve prolapse or evidence of unsuspected congenital or acquired cardiac disease. Work- up should also include a chest x- ray, routine resting EKG, echocardiogram, exercise testing and 24 hour Holter monitor.
The indications for intracardiac electrophysiologic study are: 1) to confirm the diagnosis in a patient with a wide QRS tachycardia, 2) to characterize known ventricular tachycardia in terms of mechanism and location, 3) to induce a dysrhythmia in a patient with a high risk of sudden death or with a history of syncope, and 4) to determine the efficacy of treatment in preventing ventricular tachycardia.
The prognosis for a child with chronic ventricular dysrhythmia depends to a large extent on whether the patient's heart is normal or abnormal. If the above studies disclose no hemodynamic or angiographic abnormalities, treatment may be withheld unless the patient is symptomatic. All patients with an abnormal heart should undergo treatment. Treatment includes drug therapy, surgery, and pacemaker placement. Drugs commonly used include dilantin, propranolol, quinidine, and disopyramide. Dosages for these drugs are listed in Table 2. Dilantin is recommended as the drug of choice for patients with an abnormal heart and chronic ventricular dysrhythmia.
In patients with a prolonged QT interval and in patients with a normal heart propranolol is the drug of choice. Propranolol should be used cautiously in patients with sick sinus syndrome, AV block or abnormal hemodynamics. Quinidine and disopyramide are generally avoided because of their potential negative inotropic effects. In fact ventricular dysrhythmia may actually worsen when patients are initially started on quinidine. In any child with recurrent ventricular dysrhythmia unresponsive to drugs who has severe symptomatology, incision, encircling ventriculotomy, or cryothermy should be considered.
REFERENCES
Garson, A. Evaluation and treatment of chronic ventricular dysrhythmia in the young. Cardiovascular Reviews & Reports 2 (11): 1164- 1194, 1981.
Pratt, C. Ventricular antiarrhythmic effects of beta- adrenergic blocking drugs: A review of mechanism and clinical studies. J. Clin. Pharm. 22: 335- 347, 1982.
Jacobsen, J. Premature ventricular contractions in normal children. J. Peds. 92 (1): 36- 38, 1978.
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