Retrograde Block in Ventricular Tachycardia

Report:

Ventricular tachycardia 118/min

1:1 retrograde conduction (top)

Ventricular tachycardia 180/min

2:1 retrograde block (middle)

Comment:

The retrograde atrial waves are seen as typical sharp upright deflections in MCL1 or V1 (Marriott lead).

The proximate cause for the change in the morphology and rate of the VT in the top strip is unknown. Possibly, the initial, slower, VT is the same rhythm with 2:1 exit block (the rate does not exactly double, but it does not have to, exactly).

The bottom strip shows both 1:1 and 1:2 conduction, not to mention 2:1 exit block that can be presumed at the beginning of the strip.

The 12-lead ECG during the slower VT is shown below (Fig 43a). This (LBBB) morphology is often seen arising from the RV outflow tract in normal hearts; the patient’s silent coronary artery disease may be coincidental. The slurred descent of the S wave in lead V1 is a clue that the complexes are not supraventricular ones with LBBB, but ectopic ventricular in origin. But the main theme here is the presence of 2:1 retrograde block in the strips: it is not a feature of aberrantly conducted junctional rhythms5. There was only one example I have seen in the last 30 years , now in Volume 14-986 – and the aberrancy was there just for a few beats45.

WPW was mentioned (i) because the analogy is interesting in its own right and (ii) to confuse those who favour the obscurum per obscurius. The ECG in sinus rhythm is shown in Fig 43b.