Diagnosis of ventricular tachycardia: a clinical algorithm.
Authors: M Dancy, D Ward
Journal: BMJ (1985)

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 supra ventricular tachycardia, and clinical bias in favour of supra ventricular tachycardia is strong.13 Several arrhythmias may give rise to broad complex tachycardias ?ventricular tachycardia, supra ventricular tachycardia with rate related aberrant conduction (including nodal tachycardia, atrial tachycardia, and reciprocating tachycardia associated with an accessory pathway), and any supra ventricular 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,1 and its acute management is different from that of supra ventricular 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 tachy? cardia. 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 tachy? cardia from other forms of broad complex tachycardia are sum? marised 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 patients with tachycardia sometimes no record is made of the tachycardia or only a short rhythm strip is recorded. This results in a serious loss of valuable information. Unless the patient is pro? foundly unwell a 12 lead electrocardiogram should be recorded in all cases of tachycardia and if possible it should be recorded continuously or brief strips taken every 30 seconds while any pharmacological intervention is undertaken. A rhythm strip can, however, give valuable information about the regularity of the rhythm and the atrioventricular relation (particularly if the lead with the largest P wave deflection is recorded). The R-R interval during ventricular tachycardia seldom varies more than 40 ms, and if there is greater irregularity than this the rhythm is likely to be supra ventricular, possibly atrial fibrillation with bundle branch block or pre-excitation. There are four main groups of electro cardiographic features that may be helpful (see figure).