Featured arrhythmia| Volume 4, ISSUE 5, P679-680, May 2007

Alternating left bundle branch block and right bundle branch block during tachycardia: What is the mechanism?

Published:October 17, 2006DOI:
      A 68-year-old woman with a history of paroxysmal atrial fibrillation was referred for pulmonary vein isolation. After the pulmonary veins were isolated, burst atrial pacing during infusion of intravenous isoproterenol induced atrial flutter at a cycle length of 230 ms, with variable but rapid AV conduction. An alternating pattern of left bundle branch block (LBBB) and right bundle branch block (RBBB) was observed during the tachycardia (Figure 1). What is the mechanism of the alternating bundle branch block?
      Figure thumbnail gr1
      Figure 1ECG leads V1–V3 showing alternating left bundle branch block with right bundle branch block during atrial flutter with rapid AV conduction.


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