Asymptomatic High-Grade Atrioventricular Block in a Serviceman: A Case Report

Background. High-grade atrioventricular (AV) conduction disorders are associated with an increased risk of syncope, severe hemodynamic compromise, and sudden cardiac death. Although these disorders usually manifest with clinically significant symptoms, some patients may remain asymptomatic despite advanced conduction abnormalities, making timely diagnosis and appropriate treatment particularly challenging. Such cases are of special clinical importance in individuals whose professional activities require a high level of physical fitness and constant readiness, including military personnel.Aim. To present a clinical case of asymptomatic severe bradyarrhythmia with transient high-grade atrioventricular block in a serviceman, to describe the diagnostic approach, and to demonstrate the effectiveness of permanent dual-chamber pacemaker implantation.Case Report. A serviceman underwent a routine medical examination without any cardiovascular complaints, including syncope, dizziness, dyspnea, or palpitations. Standard electrocardiography revealed severe bradycardia and second-degree AV block (Mobitz II) with 2:1 conduction. Twenty-four-hour Holter ECG monitoring demonstrated marked sinus bradycardia with an average heart rate of 40 beats/min, a minimum heart rate of 19 beats/min, numerous episodes of first- and second-degree AV block, recurrent episodes of high-grade AV block with 3:1 conduction, transient complete third-degree AV block, and RR pauses exceeding 3.4 seconds. More than 12.000 pauses longer than two seconds were recorded, predominantly during the nighttime. Echocardiography showed mildly reduced left ventricular systolic function with an ejection fraction of 49 %. Based on current clinical recommendations and the documented advanced conduction abnormalities, the patient underwent successful implantation of a dual-chamber rate-responsive pacemaker.Results. The patient underwent successful implantation of a dual-chamber rate-responsive pacemaker. Follow-up Holter ECG monitoring demonstrated stable cardiac rhythm with effective pacing, no clinically significant arrhythmias, and no pauses exceeding two seconds. The patient remained clinically stable during the postoperative period.Conclusions. This case highlights that severe atrioventricular conduction disorders may remain clinically silent despite pronounced electrophysiological abnormalities. Routine electrocardiographic screening followed by comprehensive Holter ECG monitoring plays a crucial role in detecting occult high-grade AV block and identifying patients at risk of potentially life-threatening complications. Timely implantation of a permanent dual-chamber pacemaker provides effective rhythm stabilization and represents the treatment of choice in patients with advanced AV conduction disturbances, even in the absence of clinical symptoms.