EP maneuvers to differentiate wide QRS tachycardia

EP maneuvers to differentiate wide QRS tachycardia

The only VT in which H precedes V is bundle branch reentrant tachycardia. It is worthwhile looking at the sinus rhythm ECG to see whether it is wide or narrow QRS. If it is narrow QRS, the first thing to do is atrial pacing. If the atrial pacing shows narrow QRS, the clinical tachycardia is likely to be VT.

But it is necessary to pace both atria. Sometimes wide QRS can occur while pacing from right atrial free wall region due to entry into a Mahaim pathway, which may not be picked up by a coronary sinus pacing. While pacing the atria, if wide QRS occurs and the His precedes the V, it is likely to be SVT with aberrant conduction, especially if there is a 12/12 match with the clinical tachycardia. If the His buried within the V, it is likely to be Mahaim fibre pre-excitation. If the sinus rhythm ECG shows wide QRS with 12/12 match with the clinical tachycardia, it favours SVT with aberrancy.

Mode of initiation and tachycardia origin: If atrial pacing induces the tachycardia, it is most likely SVT or pre-excitation, though very rarely a VT may be initiated by atrial pacing.

LBBB pattern with left axis deviation in wide QRS tachycardia should make us suspect Mahaim fibre tachycardia or bundle branch reentrant tachycardia. The sinus rhythm ECG will be normal in Mahaim fibre tachycardia while some bundle branch block pattern is likely in bundle branch re-entry in sinus rhythm ECG. Another possibility which has to be thought of is ARVD. Careful inspection of sinus rhythm ECG for epsilon waves may be useful in this case.