Wide complex tachycardia (WCT) is an abnormally fast heart rate, demonstrating a widened QRS complex. In the adult patient, the ventricular rate is usually over 120 bpm and the QRS complex is prolonged to greater than 0.12 second in duration or width. In the infant and young child, the clinician should use age‐specific norms for rates when interpreting the electrocardiogram (ECG). The wide QRS complex is caused by abnormal depolarization of the ventricles because of one of three mechanisms – ectopic ventricular foci (i.e. premature ventricular contraction [PVCs] and/or ventricular tachycardia [VT]), aberrant conduction (i.e. supraventricular tachycardia [SVT] with aberrant conduction), or ventricular preexcitation (i.e. Wolff–Parkinson–White [WPW] syndrome). Thus, the differential diagnosis for WCT (Table 23.1) includes VT, SVT with aberrant conduction, and ventricular preexcitation syndrome‐related tachycardia. WCTs may be either regular or irregular. See Clinical Presentation Box 23.1.

See Management Box 23.1.

Ventricular Tachycardia

VT almost always presents with a widened QRS complex. In the adult, the QRS complex is most often greater than 0.12 second in width; in infants and very young children, the QRS complex may not appear “wide” by adult standards when, in fact, it is. In VT, the QRS complex can be described as monomorphic (i.e. one predominant shape for the QRS complexes; Figure 23.1) or polymorphic (more than one shape for the QRS complexes; Figure 23.2). The focus of VT is found most often in the ventricular myocardium. The very rare form of fascicular tachycardia is a form of VT with a narrow QRS complex; the QRS complex is narrow in this instance because of the rhythm focus being in the intraventricular conduction system. Monomorphic VT demonstrates QRS complexes that are uniform in appearance (i.e. all appear the same or very similar). This rhythm is often seen in patients with ischemic heart disease or in the setting of an active myocardial infarction. The wide complex is caused by depolarization occurring at an ectopic ventricular focus, outside the normal conducting system. Monomorphic VT is always regular (Figure 23.1).

Polymorphic VT is a form of VT in which the morphology of the QRS complexes varies from beat to beat (Figure 23.2). The variation in the QRS complexes can be minimal or maximal. One subtype of polymorphic VT is Torsades de Pointes (TdP) in which the QRS complexes appear to be twisting around an electrical baseline (Figure 23.2b and c). If the patient’s cardiac rhythm can be viewed in a supraventricular setting either before or after the TdP occurs, the QTc interval is usually prolonged. Polymorphic VT, including TdP, is generally irregular. This rhythm is seen in a range of settings, including acute coronary syndrome, toxicologic presentations, and early in cardiac arrest.