Ventricular Tachycardia : Narrower QRS in VT

Report:

Top:

Sinus arrhythmia

Borderline first degree AV block

VEBs

Rate-dependent right bundle branch block

Bottom:

Sinus rhythm

Right bundle branch block

Ventricular tachycardia 148/min

AV dissociation

Comment:

The tachycardia in the bottom strip has more normal QRS morphology than the broad RBBB in sinus rhythm. Its QRS duration is only 0.14” and in most beats it shows a definite rSR’ pattern. On its own morphology alone, it should be aberrant SVT rather than VT. However, the patient has an obvious pre-existing RBBB, and a rate-dependent one at that: it is unlikely that the conduction would partially normalise rather than become even more aberrant at 148/min. It should be remembered that other leads may show broader VT complexes, but it is not essential for the diagnosis. Like single VEBs, VT can be narrower than the sinus rhythm complexes in all the leads. This tends to occur if the ectopic focus is located in the ventricular septum99.

More decisively, there is a dissociation between the sinus P waves and the tachycardia. It favours the diagnosis of VT, but does not prove it: you cannot tell a pacemaker by the company she does not keep!4 This could still be perversely aberrant junctional tachycardia with AV dissociation.

10. 70 year old Chinese man with long history of congestive heart failure.