ECG Library


All ECG 100

  1. Normal sinus rhythm
  2. Right bundle branch block
  3. SVT with aberrancy - rate dependent left bundle branch block

This ECG is challenging. The rhythm starts as normal sinus rhythm with a right bundle branch block, then a wide-complex tachycardia develops in a left bundle branch block pattern. The important thing to determine is the etiology of the wide complex. The rhythm is either ventricular tachycardia or supraventricular tachycardia with aberrancy. In the acute clinical setting, any wide-complex tachycardia should be treated like ventricular tachycardia until proven otherwise.

Using the Brugada criteria, we see that there is no concordance (QRS complex down in V1 and up in V6), the R to S interval is not greater than 100 ms and there is no AV dissociation that is obvious. We then examine the morphology criteria when the pattern is that of a left bundle. There is no identifiable Q wave or QS in lead V6 which would have favored VT. The is no wide R wave that is 40 ms or greater in V1 or V2 which would have favored VT. There is no slur or notch in the downstroke of the S wave in lead V1 or V2. Lastly, the duration of the onset of the QRS complex to the peak of the S wave is not > 60 ms.

Adenosine was given to this patient and flutter waves were present indicated atrial flutter as the etiology. This is not obvious on the 12-lead ECG tracing, although the heart rate during the tachycardia is almost exactly 150 beats per minute which is typical for atrial flutter.

Related Topic Reviews: Right Bundle Branch Block, Left Bundle Branch Block, Ventricular Tachycardia