Aberrant Conduction?
November 15, 2023
By Ken Grauer, MD
Professor Emeritus in Family Medicine, College of Medicine, University of Florida
How would you interpret the ECG in the figure below? Is this rhythm most likely to be a re-entry supraventricular tachycardia (SVT) with aberrant conduction?
My Thoughts: Unfortunately, no clinical information is available for this case, but we still can arrive at a presumptive diagnosis.
• The rhythm is fast and regular; the rate is ~190 beats per minute to 200 beats per minute.
• The QRS complex is wide.
• Normal sinus P waves are not visible. That said, I cannot rule out the possibility of 1:1 V:A (i.e., retrograde) conduction, considering the negative point at deepest descent of the ST segment in each of the inferior leads.
Impression: The best description of this rhythm is that there is a regular wide complex tachycardia (WCT) at ~190 beats per minute to 200 beats per minute, without a clear sign of atrial activity. The differential diagnosis is between VT vs. some form of SVT, with either pre-existing bundle branch block or aberrant conduction.
• There is a tendency by all too many clinical providers to assume that because QRS morphology in this rhythm resembles right bundle branch block (RBBB) conduction, this rhythm is SV with aberrant conduction. This is the wrong approach, since clinical prudence dictates a need to always assume a regular WCT without clear sign of atrial activity is VT until proven otherwise, not the other way around.
• To emphasize, although QRS morphology in the rhythm manifests several features of RBBB conduction (e.g., an all-positive QRS in right-sided lead V1 and wide terminal S waves in lateral leads I and V6), there are some atypical features. There is a lack of a typical triphasic (rSR’) complex in lead V1, in which the S wave descends below the baseline. There is a lack of the expected qR morphology in each inferior lead, as is typical for left posterior hemiblock conduction. Also, there is a strange similarity in QRS morphology in five of six chest leads, which usually is not seen with simple RBBB conduction.
Bottom Line: While impossible to rule out an SVT with either pre-existing RBBB or aberrant conduction, the atypical features for RBBB conduction in this tracing suggest the clinician should assume fascicular VT until proven otherwise and treat the patient accordingly.
For more information about and further discussion of this case, please click here.
How should one interpret the ECG in the figure? Is the rhythm most likely to be a re-entry supraventricular tachycardia with aberrant conduction?
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