Irregular Monomorphic Ventricular Tachycardia

Report:

Ventricular tachycardia 128-170/min.[! !][! XE "Ventricular tachycardia:uniform" \t "See monomorphic" !]

Periods of bigeminy

Comment:

It is uncommon for monomorphic VT to be irregular. The irregularity, however, is confined to long-short cycle alternation at the beginning and the end of the recording. It is consistent with exit block from the ectopic focus (or circuit).

In the left precordial leads there is also an obvious alternation in the QRS size. This is not an electrical alternans which, by definition, requires fixed cycle length and conduction.

The diagnosis of VT in this case rests with QRS duration over 0.16” in V1 and the broad R wave in the same lead, causing the nadir of the S wave to be reached quite late, 0.10” after the QRS onset1. The left axis deviation in the frontal leads, once held to contribute to the diagnosis of VT, is now deemed insignificant. Approximately 50% of left bundle branch blocks also have left axis deviation.

In the inferior leads the QRS is terminated by a sharp negative notch, with corresponding wrinkles of different polarities in other leads. It may well be a retrograde P wave, but distinction from it being part of QRS complex is not possible in this trace. If there was other, independent (dissociated) atrial activity, this terminal notch could confidently be assigned to the QRS complex.

Below (Fig 2a) is another trace, taken an hour earlier. It is regular at approximately 138/min, but otherwise identical to the trace discussed above.