Alternating bundle branch block refers to the occurrence of Right bundle branch block (RBBB) and Left bundle branch block (LBBB) in the same patient at different times. Alternating bundle branch block is a rare ECG pattern and has a high risk of progression to complete atrio-ventricular block.
This phenomenon denotes likely severe disease in the infra-Hisian conduction system involving both bundle branches, with a propensity for developing complete atrioventricular (AV) block. The likelihood of complete AV block is higher in those who develop alternating bundle branch block.
ESC (1) and ACC/AHA/HRS (2) guidelines recommend Pacemaker implantation (Class I) in alternating bundle branch block.
References:
1/ 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. European Heart Journal, Volume 42, Issue 35, 14 September 2021, Pages 3427–3520.
2/ 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Circulation Vol.140, No.8, 2018.