Bigeminal Ventricular Tachycardia

Report:

Monomorphic ventricular tachycardia 90 – 110/min

Alternating cycle length, with bigeminy

Retrograde conduction, 1:1

Probable old anterior infarction

Comment:

Most of the rate variation is in the long cycles. The basic mechanism is probably 3:2 conduction from the ectopic focus to the ventricles; the long cycles contain the blocked beats. The exit block appears to be Möbitz 1 in type: the long cycles are less than the sum of two short ones. An alternative theory (to exit block) is alternation of exit times from the site of the automatic pacemaker. A complex model postulates self-entrainment of a parasystolic VT101.

The bizarre Qrs morphology in V2 suggests an old anterior infarction. In general, VEB QR and QRS patterns indicate an underlying infarction, while QS ones are common and lack specificity. At times, previous infarction is only seen in VEBs or VT, while the supraventricular rhythm’s QRS is normal or non-diagnostic. This was one of these times (below).

One of the lines of evidence for ventricular ectopic origin of a broad-complex tachycardia is the occurrence of single VEBs of identical morphology. The trace below (Fig 113a), taken after (spontaneous) reversion to sinus rhythm, shows VEBs of the same morphology as the tachycardia. Retrograde VA conduction is also present, perhaps making the sinus rate slower than it would have been otherwise.