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Syncope — ABIM Board MCQ

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ModerateCardiovascularSyncopeABIM Board

A 67-year-old man has had three abrupt episodes of syncope without prodrome during the past 9 months. His ECG shows bifascicular block. Echocardiography shows a left ventricular ejection fraction of 58% and no significant valvular disease. Orthostatic vital signs are normal. A 48-hour Holter monitor is unrevealing, and an electrophysiologic study shows no inducible high-grade atrioventricular block or ventricular arrhythmia. Which of the following is the most appropriate next diagnostic study?

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Correct answer: D — Implantable loop recording

The correct answer is D. Abrupt syncope without prodrome and bifascicular block suggest an intermittent bradyarrhythmia, particularly paroxysmal high-grade atrioventricular block. A negative short-term monitor and electrophysiologic study do not exclude an infrequent conduction event. Because episodes occur months apart, an implantable loop recorder offers a substantially longer monitoring period and the best opportunity to establish symptom-rhythm correlation. A 30-day external monitor is less likely to capture these infrequent episodes. Routine EEG and head CT are not indicated without seizure features, persistent altered consciousness, focal neurologic deficits, or head trauma. Carotid duplex ultrasonography evaluates cerebrovascular disease but does not identify the cause of isolated syncope in the absence of focal neurologic findings.

Reference: Shen WK, et al. 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope, Data Supplement, Section 3.2.3: Cardiac Monitoring. 2017. https://jaccjacc.acc.org/Clinical_Document/Syncope_Guideline_Data_Supplement.pdf