Monthly Case from the Department Of Medicine: Around The Block

Submitted by:
Dina Adimora-Onwuka, MD 
Assistant Professor of Medicine
Division of Hospital Medicine
Department of Medicine
Emory University School of Medicine

Edited by:
Maha Sulieman, MBBS Division of Hospital Medicine

Story and Case:

An 86-year-old man with inflammatory bowel disease, dementia, hypertension, dyslipidemia and hypothyroidism was found to be bradycardic (with heart rate in the 40s) without symptoms during a routine vitals check in his assisted living facility. His carvedilol was held, but bradycardia persisted, and he was sent to the emergency department for further evaluation.

He had nausea, vomiting and diarrhea on presentation with a pulse of 46 beats per minute (bpm) and blood pressure of 181/64. Initial electrocardiogram (EKG) showed sinus bradycardia with right bundle branch block (RBBB), Figure 1. Repeat EKG hours later showed a pulse of 48 bpm, now with a left bundle branch block (LBBB), Figure 2. He continued to deny other symptoms associated with bradycardia. High sensitivity troponin and thyroid studies were normal.

Figure 1: 3/4/2022
Sinus Bradycardia with RBBB

Figure 2: 3/5/2022
EKG now with LBBB

What’s the Diagnosis?

Alternating Bundle Branch Block (BBB)

In light of the alternating BBB—RBBB followed by LBBB along with progressing bradycardia, there was a concern for acute deterioration to complete heart block and sudden cardiac death. This prompted the patient’s transfer to the intensive care unit where a temporary pacemaker was placed. Thereafter, he had a left heart catheterization and placement of a permanent dual chamber pacemaker. He was eventually discharged with a cardiology clinic follow up appointment and there, reported feeling well.

Discussion:

Alternating BBB is a unique finding that must be recognized by the clinician, as it can be associated with sudden death. Commonly, when clinicians encounter a BBB, they first classify the abnormality as acute or chronic by comparing serial EKGs. Identifying alternating BBB requires an additional step: it is diagnosed when there are conducted periods of RBBB and LBBB in different leads of the same EKG or different BBB patterns on successive EKGs. This abnormality results from conduction delay in the His-Purkinje system. Acute deterioration to complete heart block may thus occur without warning, leading to sudden cardiac death, in contrast to other conduction abnormalities, such as that of the atrioventricular node, where gradual EKG findings warn of impending deterioration. Alternating BBB portends complete heart block and is associated with increased morbidity and mortality; thus, the American Heart Association identifies it as an indication for permanent pacemaker placement.

Citations:

Bhatt A, Rao S, Infeld M, et al. Alternating Bundle Branch Block: Clinical Considerations. J Am Coll Cardiol. 2017 Mar, 69 (11_Supplement) 2330. h ttps://doi.org/10.1016/S0735-1097(17)35719-4

Saini, A., Padala, S. K., Koneru, J. N., & Ellenbogen, K. A. (2018). Alternating bundle-branch block: what is the mechanism?. Circulation, 137(11), 1192-1194.

Sauer, W. H. (2018). Right bundle branch block. UpToDate. Sauer, W. H. (2018). Left bundle branch block. UpToDate.