ECG Review

Just Before the Run

By Ken Grauer, MD, Professor, Assistant Director, Family Practice Program, University of Florida. Dr. Grauer reports no financial relationship to this field of study.

Figure.  Non-sequential rhythm strips. There appear to be frequent PVCs and runs of VT.

Clinical Scenario: The two non-sequential tracings in the Figure were interpreted as showing sinus tachycardia interrupted by runs of VT (ventricular tachycardia). Do you agree?

Interpretation/Answer: Although at first glance, the underlying sinus tachycardia seen in this tracing appears to be interrupted by runs of VT, this is not what is occurring. The clue to the real etiology of the runs of widened beats in these two tracings lies in appreciating what occurs "just before" the runs. Note in the top tracing after the initial two sinus beats, that a slightly widened complex is seen (beat #3). Careful inspection of the T wave preceding beat #3 identifies a small amplitude but definitely present upright deflection that is not seen in any of the normally conducted sinus beats (ie, not seen in the T wave of beats #1, 4, 5, 13, 14, 15). This small, upright deflection in the T wave preceding beat #3 in the top tracing is therefore a premature P wave, and the different-looking QRS appearance of beat #3 is the result of aberrant conduction of this PAC. The same phenomenon is seen for the aberrantly conducted PAC at the end of the top tracing (beat #17). Similarly, the run in the middle of the top tracing (beats #7 through 12) is initiated by a PAC (beat #7), and suggests that this slightly irregular WCT (wide-complex tachycardia) is really supraventricular (with aberrant conduction accounting for the QRS widening) — and not VT. Support in favor of this conclusion is found in the lower tracing, where once again each widened complex (or run of widened beats) is initiated by a PAC with aberrant conduction. There is no VT in these tracings.