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ECG Findings

  • Wide complex, regular tachycardia (usually > 140 bpm)

  • QRS morphology consistent with one of the bundle branch block patterns


  1. The rapid rate of an SVT may “outrun” the ventricular conducting system’s ability to repolarize quickly, producing a rate-related bundle branch block. The signal then must propagate cell to cell, producing a wide-complex tachycardia. A typical bundle branch pattern usually results.

  2. When a person with a chronic wide-complex (aberrant) bundle branch block enters an SVT, the ECG will display a wide-complex, regular tachycardia. However, when the patient does not have prior ECGs, it can be difficult to distinguish SVT with aberrancy from a ventricular tachycardia (VT). Many different criteria have been proposed to distinguish the two, but unfortunately, most are neither extremely sensitive nor specific. When in doubt, treat as a VT, as many of the typical SVT pharmacologic agents are detrimental in patients with VT and can lead to ventricular fibrillation and death.


Supraventricular Tachycardia with Aberrant Conduction, Underlying RBBB. (ECG contributor: Walter Clair, MD.)


Wide-complex tachycardia with a rate of 188 bpm. This patient has sudden onset of SVT with a known underlying RBBB. QRS complexes are wide (lower double arrows) and R-R intervals are regular (upper double arrows).


Wide-complex tachycardia at approximately 150 bpm. The R-R interval is regular, except for one pause, when characteristic atrial flutter waves are apparent (arrowhead).


Irregularity in the R-R interval, as seen most easily in the baseline (double arrows), strongly suggests the presence of rapidly conducted atrial fibrillation with aberrancy.

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