SVT or Verapamil-Responsive VT?

Report:

SVT or VT 156/min.

Right bundle branch block.

Left anterior hemiblock.

Comment:

The tachycardia has a typical RBBB/LAHB morphology consistent with aberrantly conducted SVT. The rate varies slightly; this has no diagnostic significance.

The problem are the two narrow complexes (the 9th QRS in the rhythm strip and the 3rd QRS in leads V4-6) which may represent either a transient loss of aberrancy or supraventricular capture beats during a VT with slightly variable rate. They are not early, and an element of fusion is possible. In short, the broad complexes could be of ventricular origin. Conversely, VEBs during the aberrant SVT could produce narrow fusion beats.

Fortunately, a form of ventricular tachycardia with RBBB/LAHB morphology, sensitive to verapamil, has recently been described81, 82. This is therefore one situation where administration of verapamil for possible VT appears justified.

Anything is sometimes possible. Even a VT with morphology identical to that of conducted sinus rhythm or AF has been described, as a "wolf in sheep's clothing"83!

81a. The two normal beats during the VT can be recognised here in their respective leads. 82. Pre-syncopal 15 year old boy with morphologically normal heart. This rhythm slowed down with verapamil IV, but persisted until DC countershock the following day.