Table 1 Causes of wide complex tachycardias (WCTs) in patients without structural heart disease.

Monomorphic configuration

Supraventricular tachycardia (SVT)

• Bundle branch block (figs 1, 2)

- functional (RBBB more often than LBBB)

- pre‐existing

- rate related

• Antidromic (i.e. retrograde conduction over AV node; figs 3, 4)

• Non‐specific conduction delay

- class I or class III antiarrhythmic drugs

- electrolyte imbalance

Ventricular tachycardia (VT)

• LBBB, inferior axis (fig 7): idiopathic right ventricular VT

• RBBB, superior axis (fig 8): idiopathic left ventricular VT

• Pacemaker mediated VT

Polymorphic configuration

Supraventricular tachycardia

• Atrial fibrillation with pre‐excitation (fig 3)

Ventricular tachycardia

• Torsade de pointes (long QT syndrome) (fig 9)

• Brugada syndrome

• Catecholaminergic polymorphic VT (fig 10)

• Short QT syndrome

All WCTs should be treated as if the rhythm was VT until proven otherwise.

AV, atrioventricular; LBBB, left bundle branch block; RBBB, right bundle branch block.