Smartwatch bradycardia alarms leading to a diagnosis of lamin A/C cardiomyopathy: a case report.

Background: Genetic aetiologies of early-onset arrhythmias and cardiomyopathy (CM) are common, but timely diagnosis requires a high index of suspicion. Case summary: An asymptomatic 47-year-old man presented to cardiology clinic for smartwatch low-rate alarms. His brother had exertional syncope and died in his 20s from heart failure. Transthoracic echocardiogram showed reduced left ventricular ejection fraction (35%). A Holter monitor showed third-degree atrioventricular block and frequent pauses (longest 4.9 s). He was admitted to the hospital and following a cardiac magnetic resonance imaging with late gadolinium enhancement a cardiac resynchronization therapy-defibrillator was placed. Genetic testing identified a pathogenic variant in the lamins protein A and C (LMNA) gene. Discussion: Left ventricular dysfunction with or without arrhythmias should raise concern for familial CM and warrants further evaluation. Lamin A/C cardiomyopathy is the second most prevalent cause of familial dilated CM and is notable for an indolent course with conduction disturbances that frequently precede left ventricular dysfunction. Smartwatch alarms can potentially help with the early identification of patients with risk factors for familial CM before the development of overt symptoms.