ECG Review: Too Irregular for VT?

By Ken Grauer, MD, Professor, Assistant Director, Family Practice Residency Program, University of Florida, and Associate Editor, Internal Medicine Alert

Figure. Lead II rhythm strip from a patient with ischemic cardioyopathy.

Clinical Scenario: The lead II rhythm strip shown in the Figure was obtained from an older man with ischemic cardiomyopathy. This asymptomatic 10-beat run of anomalous complexes was felt to be too irregular for VT (ventricular tachycardia). Do you agree?

Interpretation/Answer: The underlying rhythm in this tracing appears to be sinus, based on the presence of three consecutive similar-appearing upright P waves at the end of the tracing. A P wave of similar sinus morphology immediately precedes the tachycardia (beat #3). However, the first two QRS complexes in the tracing (beats #1 and 2) are preceded by different appearing P waves.

The 10-beat run of anomalous (widened) QRS complexes is clearly irregular. Despite this irregularity, it is highly unlikely that this represents a run of atrial fibrillation with QRS widening from aberrant conduction. The WCT (wide-concept tachycardia) begins late in the cycle after beat #3. Its onset is not preceded by a premature P wave, and the WCT occurs at a time in the cycle (ie, well after the T wave of beat #3) when there should not be any reason for aberrant conduction. QRS morphology during the tachycardia is markedly widened and dramatically different from that of the supraventricular complexes seen on this tracing. The clinical setting (older patient, history of ischemic cardiomyopathy) is consistent with VT, and statistically VT is a much more common cause of new-onset tachycardia than atrial fibrillation with aberrant conduction.

Although VT is usually a regular or at least fairly irregular rhythm, it may be irregular as shown here. At times, sustained VT manifests either a “warm up” or “cool down” period prior to establishment of a near regular rhythm. Gradual acceleration and regularity of the last few beats of the WCT seen here may represent such a “warm up” phenomenon. We suspect there is ongoing AV dissociation during the WCT shown here, as part of a sinus P wave appears to be present under the arrow at the midpoint of the tachycardia. The hint of deformity in various parts of other wide QRS complexes before and after this arrow at a rate that approximates the sinus rate suggests possible ongoing atrial activity, but the fact that underlying sinus rhythm was not consistently present before the tachycardia and the indistinct nature of the above noted deformities make our hypothesis of ongoing atrial activity with AV dissociation difficult to prove. Regardless, the irregular WCT seen here is almost certainly a 10-beat run of VT.