Another Irregular Monomorphic Ventricular Tachycardia

Report:

Ventricular tachycardia 152/min

Comment:

Marked cycle length irregularity is uncommon in sustained monomorphic VT, especially at faster rates, except at the onset or termination of the paroxysm58. Nevertheless, slight variation in cycle length is sufficiently common to be claimed as one of the differential diagnostic criteria against SVT. It is not a very good criterion.

Two of the cycles are obviously shorter than the others; the rest of the trace is more regular. It is possible to speculate that the real rate of the tachycardia is much faster, but limited in expression by a 2:1 exit block, temporarily lifted for the two short cycles to occur.

The slowly rising R complexes in V1 and the virtually concordant precordial pattern differentiate this trace from aberrantly conducted SVT. Atrial flutter with 2:1 block through a bundle of Kent in WPW type ‘A’ or SVT with 1:1 anomalous conduction cannot be excluded, but are uncommon even in patients with known WPW syndrome, let alone this geriatric patient with no past history of it. Besides, atrial flutter would tend toward 1:1 conduction in WPW syndrome.

A post-cardioversion trace, showing flutter with predominant 2:1 block, incomplete LBBB and old inferior MI is shown below(Fig 61a).