Diagnosis of ventricular tachycardia: a clinical algorithm.

Differentiating ventricular tachycardia from other broad complex tachycardias is important both for the management of the acute arrhythmia and for long term treatment to prevent its recurrence. In our experience ventricular tachycardia is often mistaken for supraventricular tachycardia, and clinical bias in favour of supraventricular tachycardia is strong. Ia Several arrhythmias may give rise to broad complex tachycardias -ventricular tachycardia, supraventricular tachycardia with rate related aberrant conduction (including nodal tachycardia, atrial tachycardia, and reciprocating tachycardia associated with an accessory pathway), and any supraventricular tachycardia in a patient with pre-existing bundle branch block or pre-excitation. Clinically the most important of these is ventricular tachycardia as it has a worse prognosis,' and its acute management is different from that of supraventricular tachycardias-for example, verapamil may cause life threatening hypotension without terminating ventricular tachycardia.2 The algorithm is therefore designed to distinguish ventricular tachycardia from other broad complex tachycardias. We recognise that in some cases arrhythmias cannot be diagnosed using the 12 lead electrocardiogram, and in these circumstances we suggest further, more specialised investigations. Furthermore, where the algorithm indicates ventricular tachycardia this implies only that the arrhythmia is highly likely to be ventricular tachycardia. A bewildering number of features have been described as being valuable for differentiating broad complex tachycardias, and the algorithm is designed to bring together the most important of these features in a coordinated whole. We estimate that 95% of all cases of ventricular tachycardia can be correctly diagnosed by following this scheme. The factors that are useful in distinguishing ventricular tachycardia from other forms of broad complex tachycardia are summarised in the figure. Apart from the specific features, described in more detail below, the patient may have an underlying cardiac disease of which the arrhythmia is an expression. Patients with ischaemic heart disease, especially those with left ventricular aneurysms, may be more likely to develop ventricular arrhythmias. Patients with thyrotoxicosis tend to suffer from atrial arrhythmias. Profound haemodynamic collapse is unusual in supraventricular tachycardia,3 although in all other respects the symptoms of supraventricular and ventricular tachycardia are similar. Clinical features may show atrioventricular dissociation (the venous pulse rate may be less than the ventricular rate, or there may be variable intensity of the first heart sound). Although ventricular tachycardia may sometimes be diagnosed on purely clinical grounds, it is important to obtain an electrocardiographic tracing for confirmation. Unfortunately, in the excitement of treating