• Mohammad Shenasa, Mark E Josephson, and Andrew L Wit.
• Heart & Rhythm Medical Group, San Jose, CA, USA.
• Pacing Clin Electrophysiol. 2017 Nov 1; 40 (11): 1234-1241.

BackgroundParoxysmal atrioventricular (A-V) block is relatively rare, and due to its transient nature, it is often under recognized. It is often triggered by atrial, junctional, or ventricular premature beats, and occurs in the presence of a diseased His-Purkinje system (HPS). Here, we present a 45-year-old white male who was admitted for observation due to recurrent syncope and near-syncope, who had paroxysmal A-V block. The likely cellular electrophysiological mechanisms(s) of paroxysmal A-V block and its differential diagnosis and management are discussed.MethodsContinuous electrocardiographic monitoring was done while the patient was in the cardiac unit.ResultsMultiple episodes of paroxysmal A-V block were documented in this case. All episodes were initiated and terminated with atrial/junctional premature beats. The patient underwent permanent pacemaker implantation and has remained asymptomatic since then.ConclusionsParoxysmal A-V block is rare and often causes syncope or near-syncope. Permanent pacemaker implantation is indicated according to the current guidelines. Paroxysmal A-V block occurs in the setting of diseased HPS and is bradycardia-dependent. The detailed electrophysiological mechanisms, which involve phase 4 diastolic depolarization, and differential diagnosis are discussed.© 2017 Wiley Periodicals, Inc.

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