Atypical Presentation and Management of Hypertrophic Cardiomyopathy with Atrioventricular Conduction Abnormality

BACKGROUND: Atrioventricular (AV) block is a described but rare complication of hypertrophic non-obstructive cardiomyopathy. When present, marked bradyarrhythmia presents with syncope or presyncopal symptoms. We hypothesize that the bradyarrhythmia in this patient with hypertrophic cardiomyopathy (HCM) led to an imbalance in demand and supply of the large ventricular muscle mass, leading to a troponin leak and angina-like symptoms.
CASE REPORT: We report a case of an 83-year-old female with long-standing hypertension and known stable first degree AV block and bifascicular block who was admitted with left shoulder pain radiating down her left arm that woke her from sleep. During admission, serial electrocardiograms showed marked bradycardia with progression of baseline 1st degree block to 2nd degree AV block. Serial troponin I levels were elevated to 39 ng/mL. A coronary angiogram was performed, which showed mild non-obstructive coronary artery disease. An echocardiogram demonstrated severe concentric biventricular hypertrophy with low normal ejection fraction and no evidence of left ventricular outflow tract (LVOT) obstruction. Over the next 24 hours, telemetry monitoring demonstrated progression to complete heart block with severe bradycardia down to the 30 beats per minute. A dual-chamber pacemaker was implanted to treat complete heart block.
CONCLUSIONS: Many patients with HCM are clinically asymptomatic, but those that are symptomatic can present with chest pain, symptoms related to heart failure, presyncope, syncope, and palpitations. Complete heart block is a rare complication, and AV conduction disturbance requiring permanent pacemaker placement was reported in only 6% of one large cohort of HCM patients. Our case highlights this unusual occurrence.

Keywords: atrioventricular block, Cardiomyopathy, Hypertrophic, Pacemaker, Artificial