Ventricular tachycardia (VT) is defined as three or more repetitive excitations arising from the ventricles with a rate more than 120 bpm or 25% faster than the sinus rate. The QRS complexes are different from the sinus QRS complexes and are typically wide, except in young infants in whom minimal QRS prolongation (0.08 to 0.09 seconds) may be seen. VT may be extremely rapid, up to 500 bpm, and slightly irregular because of intermittent sinus capture beats. The differential diagnosis includes SVT with persistent aberrancy (see Figure 164-4) and SVT with antegrade conduction across an accessory pathway (see Figure 164-3), both of which are relatively uncommon. Safety dictates that all wide QRS tachycardias be considered VT until proven otherwise. The presence of similar but isolated PVCs and fusion beats in sinus rhythm assists in establishing the diagnosis, but VT is confirmed by the presence of atrioventricular dissociation.

VT in the newborn and young infant is rare, but if it is drug resistant and incessant, then a ventricular tumor may be present. Mitochondrial fatty acid β-oxidation disorders may also cause VT in neonates.[7] Predisposing factors in older children and adolescents include myocarditis, repaired and unrepaired congenital cardiac lesions, cardiomyopathies, long QT syndrome, catecholamine- or exercise-induced VT, marked electrolyte imbalances, and use of street drugs (eg, cocaine). In general, VT is a marker for myocardial disease.

Acute management depends on the patient's clinical status, which is determined by the rate and duration of VT and the presence of structural cardiac lesions or prior myocardial dysfunction. Hemodynamic compromise dictates electrical cardioversion with 1 to 2 watt-seconds/kg. If reasonable clinical stability is present, then intravenous lidocaine, procainamide, magnesium, or amiodarone can be administered.

Chronic suppressive therapy is predicated on the risk of recurrence, the morbidity and mortality of the type of VT, and the risk-benefit ratio of treatment. Beta-blockers, sotalol, and amiodarone are commonly used antiarrhythmic agents to prevent VT recurrences. Other treatments include implantation of an automatic cardioverter-defibrillator and VT ablation. One form of VT, accelerated ventricular rhythm, is characterized by a rate of 120 bpm or less. This is less than 25% faster than the basic sinus rate and is benign, requiring observation only (Figure 164-7). Relatively benign forms include right ventricular outflow tract and idiopathic left VT. These entities occur in structurally normal hearts and have a substantial incidence of spontaneous resolution in childhood.

Figure 164-7 Accelerated ventricular rhythm with a ventricular rate of 110 bpm in a healthy 7-year-old girl. First-degree block is present in the sinus beats.