Cardiac Amyloidosis Mimicking Hypertrophic Cardiomyopathy With Obstruction: Treatment With Disopyramide

A 71-year old-man presented with 4 posturally related syncopal episodes. He carried a diagnosis of asymptomatic hypertrophic cardiomyopathy (HCM) without obstruction based on an echocardiogram 7 years earlier. Echocardiography at the time of syncope evaluation demonstrated a hyperdynamic left ventricle with a septal thickness of ≈20 mm (an increase of 4 mm from an earlier echocardiogram), newly present systolic anterior motion of the mitral valve, and a peak left ventricular (LV) outflow tract gradient of 42 mm Hg at rest and 120 mm Hg with Valsalva maneuver (Figure 1). He was referred for septal myectomy, and cardiac catheterization demonstrated nonobstructive coronary artery disease. An ECG showed low-voltage limb leads, unusual in HCM (Figure 2), and cardiac magnetic resonance imaging (MRI) revealed delayed gadolinium enhancement in the papillary muscles, transmural enhancement involving the basal lateral walls, and subendocardial enhancement of the basal, mid, and distal anterior walls. There was also extensive gadolinium uptake in the atrial walls (Figure 3). Because the cardiac MRI suggested an infiltrative process, a cardiac biopsy was performed. This demonstrated extensive amyloid infiltration (Figure 4). Immunohistochemistry was positive for transthyretin, but negative for amyloid A and κ/λ light chains. Genetic testing for common mutations associated with HCM was negative, and no transthyretin mutations were detected. A diagnosis …