Intermittent High-Grade Atrioventricular Block as a Presenting Sign of Left Ventricular Noncompaction

Left ventricular noncompaction is characterized by excessive trabeculation and is variably associated with heart failure, arrhythmias, thromboembolism, and conduction disease.

A 37-year-old man with palpitations and chest discomfort had intermittent high-grade (Mobitz II) atrioventricular block on event monitoring (3.7-second pause). Cardiac magnetic resonance revealed apicolateral hypertrabeculation with a diastolic noncompacted:compacted ratio of 3.5 without late gadolinium enhancement; transthoracic echocardiography showed preserved ejection fraction (60%). Electrophysiology recommended longitudinal rhythm surveillance with an implantable loop recorder; pacemaker was deferred. Genetic testing was advised but not authorized by insurance.

Intermittent high-grade atrioventricular block can be an initial manifestation of left ventricular noncompaction with preserved systolic function. Recognition of this association supports advanced imaging in unexplained conduction disease in young adults and favors loop-recorder-guided surveillance with multidisciplinary follow-up, including genetics.

Unexplained high-grade atrioventricular block in a young adult should prompt advanced structural evaluation-including cardiac magnetic resonance-to exclude left ventricular noncompaction and other cardiomyopathies. Preserved ejection fraction and absent late gadolinium enhancement can coexist with clinically relevant conduction disease in left ventricular noncompaction. Implantable loop recorder-guided surveillance enables individualized timing of device therapy and complements genetic evaluation and cascade family screening.