Last reviewed 01/2018

It may be difficult to distinguish the following disorders:

  • ventricular tachycardia
  • SVT with aberrant ventricular conduction (fixed or rate related)

Distinguishing features include:

  • in SVT, and not in VT, P waves are associated with specific QRS complexes, i.e. ventricular contraction is preceeded by atrial contraction
  • in SVT-with-aberrant-conduction, the QRS complex shows left bundle branch or right bundle branch block, i.e. an M pattern in V6 or V1 respectively
  • an SVT maintains the same QRS complex seen in sinus rhythm
  • an SVT maintains the cardiac axis seen in sinus rhythm whereas VT often has left axis deviation
  • fusion or capture beats on the ECG are characteristic of VT
  • a broad complex tachycardia is likely to be ventricular in origin if the QRS duration is greater than 140 ms


  • (1) Hampton J. Interpreting the ECG. Medicine International (1993), 21, 318-24.