A man in his 80s with recurrent syncope was admitted to the emergency department. The patient previously underwent an electrophysiological study (the exact procedure was unknown) in another hospital because of syncope, and the result did not suggest the need for pacemaker implantation. He denied a recent medical history of chest pain or dyspnea on exertion. On examination, his oxygen saturation while breathing room air was 98%, and his blood pressure was 120/76 mm Hg. The result of cardiopulmonary examination was unremarkable. Echocardiogram findings revealed a left ventricular ejection fraction of 54% with normal ventricular wall motion. Blood laboratory data, including serial high-sensitivity troponin, D-dimer, renal function, electrolytes, and blood glucose, were unremarkable. The results of the electrocardiogram (ECG) that was performed at admission was recorded (Figure, A).
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Bifascicular block is a conduction disorder that has a reported prevalence of 1% to 1.5%, including complete left bundle branch block or RBBB with either LAFB or left posterior fascicular block.1 Bifasicular block may be accompanied by residual functional bundle lesions, and there is a risk of progression to complete AV block.2 In this case, the elderly patient's baseline ECG showed bifascicular block (RBBB and LAFB) and left posterior fascicle (the residual) working (was functional). The incidence of bifascicular block progressing to complete AV block is 1% to 6% each year.3 A study4 showed that 10% to 15% of patients with bifasicular block may experience syncope within 3 years. The potential causes of syncope are heterogeneous, but intermittent complete AV block is a frequent cause.1,5 In this case, complete AV block was recorded when the elderly patient with bifasicular block experienced syncope again in the emergency department. The patient did not develop any episodes of syncope after dual-chamber pacemaker implantation, confirming that syncope was associated with intermittent complete AV block.
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Corresponding Author: Hao-Yu Wu, MD, PhD, Department of Cardiology, Shaanxi Provincial People's Hospital, No. 256 West Youyi Rd, Shaanxi Province, Xi'an 710068, China (email@example.com).
Published Online: June 13, 2022. doi:10.1001/jamainternmed.2022.2016
Conflict of Interest Disclosures: None reported.
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