Intended for healthcare professionals

Clinical Review ABC of clinical electrocardiography

Broad complex tachycardia—Part I

BMJ 2002; 324 doi: (Published 23 March 2002) Cite this as: BMJ 2002;324:719
  1. June Edhouse
  1. Francis Morris.

    Broad complex tachycardias occur by various mechanisms and may be ventricular or supraventricular in origin. In the emergency setting most broad complex tachycardias have a ventricular origin. However, an arrhythmia arising from the atria or the atrioventricular junction will produce a broad complex if associated with ventricular pre-excitation or bundle branch block. The causes of ventricular and supraventricular tachycardias are generally quite different, with widely differing prognoses. Most importantly, the treatment of a broad complex tachycardia depends on the origin of the tachycardia. This article describes monomorphic ventricular tachycardias; other ventricular tachycardias and supraventricular tachycardias will be described in the next article.

    Varieties of broad complex tachycardia

    • Monomorphic ventricular tachycardia

    • Fascicular tachycardia

    • Right ventricular outflow tract tachycardia

    • Torsades de pointes tachycardia

    • Polymorphic ventricular tachycardia

    • Bundle branch block with aberrant conduction

    • Atrial tachycardia with pre-excitation

    Non-sustained ventricular tachycardia (top) and accelerated idioventricular rhythm (bottom)


    Ventricular tachycardia is defined as three or more ventricular extrasystoles in succession at a rate of more than 120 beats/min. The tachycardia may be self terminating but is described as “sustained” if it lasts longer than 30 seconds. The term “accelerated idioventricular rhythm” refers to ventricular rhythms with rates of 100-120 beats/min.

    Ventricular tachycardia is described as “monomorphic” when the QRS complexes have the same general appearance, and “polymorphic” if there is wide beat to beat variation in QRS morphology. Monomorphic ventricular tachycardia is the commonest form of sustained ventricular tachycardia

    Monomorphic and polymorphic ventricular tachycardia

    The electrophysiology of a re-entry circuit was described in last week's article

    Mechanisms of ventricular arrhythmias

    The mechanisms responsible for ventricular tachycardia include re-entry or increased myocardial automaticity. The tachycardia is usually initiated by an extrasystole and involves two pathways of conduction with differing electrical properties. The re-entry circuits that support ventricular tachycardia …

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