• broad complex tachycardia
• narrow complex tachycardia
• ventricular tachycardia
• verapamil

Broad complex tachycardias present a diagnostic and therapeutic challenge to the emergency physician. The majority of cases are ventricular tachycardias (VT) resulting from underlying ischaemic heart disease.^1,2 Broad complex tachycardias may also occur as a result of a supraventricular tachycardia (SVT) in the presence of aberrant conduction. Differentiation has important implications in terms of management and prognosis. If VT is mistakenly diagnosed as SVT with aberrant conduction and treated with calcium channel blockers, the patient is likely to become haemodynamically unstable.³ Some clinicians therefore advocate assumption that all cases of broad complex tachycardia are VT.⁴

Fascicular tachycardia is a distinct subgroup of idiopathic VT that may be confused with either typical VT or SVT.^5,6 Although well recognised by cardiologists, there is only a single report in the emergency medicine literature.⁷ It is characterised by the absence of structural heart disease and classic electrocardiographic and electrophysiological features.^5,8,9 Vagal manoeuvres and adenosine are ineffective in suppressing fascicular tachycardia.^5,8,10 It is also unresponsive to the standard pharmacological treatments, such as lignocaine (lidocaine), used for VT associated with coronary artery disease.^5,8 In contrast, it …