A Burst of VT?
By Ken Grauer, MD, Professor, Department of Community Health and Family Medicine, University of Florida. Dr. Grauer is the sole proprietor of KG-EKG Press, and publisher of an ECG pocket brain book.
Scenario: The ECG shown above was obtained from an older man with palpitations. He was hemodynamically stable with a systolic BP of 140 mm Hg at the time this tracing was recorded. How do you interpret the rhythm? What are your initial priorities?
Interpretation: The first priority in evaluation and management of any tachycardia has already been accomplished namely, ensuring that the patient is hemodynamically stable. If the patient were unstable (i.e., hypotensive, unresponsive, with severe chest pain or shortness of breath), then synchronized cardioversion would be immediately indicated. This is not the case here. Even patients in sustained ventricular tachycardia (VT) may sometimes remain in this rhythm for hours or longer.
The key to interpreting this tracing lies with the lead II rhythm strip above. Careful observation reveals that in addition to being extremely rapid, the rhythm is irregular. Lack of atrial activity confirms the rhythm to be atrial fibrillation with a very rapid ventricular response. Of note is a 10-11 beat run of a wide tachycardia (encompassing the last 4-5 beats in leads V1,V2,V3 and the first 6 beats in V4,V5,V6. As per the title of this ECG Review, the question is whether this represents a burst of VT. Our answer is probably not. Instead, we suspect that the underlying rhythm of atrial fibrillation continues throughout with the period of QRS widening being due to LBBB aberration. Factors in favor of this include: 1) the rhythm during the run maintains the same irregularity as the underlying atrial fibrillation; 2) the wide tachycardia starts and stops without disturbing the underlying rhythm (VT often manifests a post-ectopic pause); and 3) the QRS morphology in the three key leads (I,V1,V6) is consistent with LBBB.
We acknowledge that we cannot be sure this is not VT. That said, the key to management is to slow the rate. Regardless of the true etiology, the wide tachycardia will probably resolve once the heart rate slows.