Abstract 4139584: Serendipitously Discovered Wild-Type Transthyretin Cardiac Amyloidosis in the Setting of Familial Hypertrophic Obstructive Cardiomyopathy

Introduction: We present a case of hypertrophic obstructive cardiomyopathy (HOCM) with incidental wild-type transthyretin cardiac amyloidosis (ATTRwt-CA) discovered after septal myectomy. Case presentation: A 62-year-old male with a history of bilateral carpal tunnel syndrome as well as a family history of sudden cardiac death consistent with HOCM on autopsy (patient's father) presented to the clinic with symptoms of exertional shortness of breath, hypotension, and pre-syncope. An external monitor revealed one episode of non-sustained supraventricular tachycardia, otherwise was unremarkable. He experienced worsening symptoms for which emergency department evaluation revealed anterior lead T-wave inversions on EKG. Cardiac catheterization revealed non-obstructive coronary artery disease. Shortly thereafter, a cardiac MRI was significant for probable HOCM based on septal hypertrophy, late gadolinium enhancement (LGE) with mid-wall fibrosis in the basal/mid inferolateral segments, and systolic anterior motion (SAM) of the mitral valve. Pre-stress echocardiogram revealed a sigmoid septum with septal wall thickness of 1.6 cm and no left ventricular outflow tract (LVOT) gradient. Post-stress echocardiogram revealed severe SAM with septal contact, LVOT gradient of 70 mmHg, as well as hypotension. Genetic testing was negative, and the patient underwent successful septal myectomy with papillary muscle reorientation and resection of secondary chordae. The pathology of the myocardium obtained during surgery resulted with histological features suggestive of HOCM in addition to confirmed ATTRwt-CA for which tafamidis was initiated. Discussion: Literature reporting HOCM and ATTRwt-CA within the same patient is rare. Both conditions cause increased myocardial thickness which can present phenotypically similar, making diagnosis difficult. Utilization of modern imaging modalities such as cardiac MRI and echocardiography should provide valuable information for differentiation, but as in our case, direct tissue visualization can be required for diagnosis. Each diagnosis has unique imaging characteristics that help define them such as asymmetric septal hypertrophy with dynamic LVOT obstruction, SAM of the mitral valve, and fibrotic areas on LGE in the setting of HOCM compared to diffuse and symmetric global subendocardial LGE and concentric hypertrophy with ATTRwt-CA. Conclusion: Our case reveals the importance of avoiding anchoring bias as concomitant diagnoses can present.