Clinical Scenario: The ECG shown in the Figure was obtained from a woman in her 60s with known coronary disease. In view of the fact that ventricular tachycardia (VT) may sometimes be slightly irregular, would you interpret the rhythm in this Figure as probable VT?
Interpretation: The rhythm in the Figure is a fairly regular, wide-complex tachycardia. Whenever this is seen in an older adult with known coronary disease—VT must always be assumed until proven otherwise, especially when QRS morphology looks as bizarre as it does in this tracing. That said—the cause of the wide complex tachycardia in the Figure is not VT. As is often the case—the key clue for interpreting this rhythm lies with "looking for a pause"!
Whereas on initial inspection one might not think any P waves at all are present on this tracing, the brief pause preceding the last beat in lead aVF strongly suggests otherwise. A P wave clearly precedes this last beat in lead aVF with a normal PR interval. Looking again at lead II, it can now be seen that the second QRS complex in this lead is also preceded by a P wave with a similar PR interval as the last beat in lead aVF. The small upright deflection at the midpoint of the R-R interval for the other beats in lead II is therefore not a T wave, but instead represents sinus node activity. Therefore, the rhythm in this tracing is sinus tachycardia with several premature supraventricular beats (PACs or PJCs)—and QRS widening as the result of an unusual form of IVCD (intraventricular conduction delay). We emphasize that without the pauses in the rhythm described above, one would have to assume VT for this tracing.