Slide 1: Case 1. You’re called overnight to review tele alarms alerting you to this rhythm. Tele strip shown. What do you see? What is your differential diagnosis?

Slide 2: Case 2. You receive a page. It says, “can you also check out this EKG while you’re here?” EKG shown. Rhythm. Wide complex (QRS greater than 120 ms) and tachycardia (R-R rate is 170 beats per minute). The differential diagnosis includes ventricular tachycardia and supra-ventricular tachycardia with aberrancy. How do you differential supra-ventricular tachycardia with aberrancy from ventricular tachycardia?

Slide 3: Let’s review. Where do these arrhythmias start from? Graphic of the heart with labels showing the SA node, AV node, His-Purkinje system, left bundle branch, and right bundle branch. Ventricular tachycardia originates below the the level of the AV node. Supra-ventricular tachycardias originate at or above (supra-) the level of the AV node (-ventricular).

Slide 4: Ventricular tachycardia. What are some EKG features that confirm this diagnosis? Fusion beats. When a supra-ventricular and ventricular beat coincide to produce a hybrid complex of intermediate morphology. Capture beats. When a supra-ventricular beat gets conducted through the His-purkinje system and captured in the strip. From our first case that tele strip shows AV dissociation. AV dissociation is pathognomonic for ventricular tachycardia. Tele strip shown with arrows pointing to deflections from the atria and ventricle. Some other clues. Typically diseased heart (i.e. prior MI, CHF, etc.). Concordance of precordial leads (V1-6 all positive or all negative). Prominent pulsation on jugular venous exam = cannon A waves (when atria contract against a closed valve signaling AV dissociation). Let’s compare that to supra-ventricular tachycardia with aberrancy. Telemetry strips from LITFL.

Slide 5: Supra-ventricular tachycardia with aberrancy. Typically healthy heart. Sometimes responsive to vagal maneuvers. Wide QRS represents either a pre-existing conduction delay (eg. left bundle branch block) or rapid impulses reaching refractory conduction tissue. If visible, P-waves are usually 1 to 1 ratio with QRS complexes – unless atrial tachycardia or multi-focal atrial tachycardia. Tele strip with arrows showing the 1 to 1 ratio. Don’t forget to look at prior baseline EKGs, specifically QRS morphology. Supra-ventricular tachycardia with aberrancy may have a similar morphology to baseline QRS. From our second case, baseline EKG showed left bundle branch block with wide QRS.

Slide 6: Still stuck? Check aVR? Think back to our July 18th, 2019 post. Suspect ventricular tachycardia if you see anything in aVR other than negative QRS with a sharp downstroke. EKG reading for case 1 and case 2 shown. Patient 2 most likely has supra-ventricular tachycardia!


  • Vereckei A, Duray G, Szénási G, Altemose GT, Miller JM. New algorithm using only lead aVR for differential diagnosis of wide QRS complex tachycardia. Heart Rhythm. 2008 Jan;5(1):89-98. PMID 18180024.

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