A 68-year-old woman presents to your office complaining of shortness of breath. She reports that over the last two months, she has become progressively short of breath with activity. She feels dizzy when she walks faster; her abdomen feels distended; and her legs feel swollen. Her temperature is 98 °F, heart rate is 56 beats/min, blood pressure is 110/84 mm Hg, respirations are 19 breaths/min, and oxygen saturation is 94% on room air. Physical examination is notable for bilateral crackles in the lung fields and pitting edema in bilateral lower extremities. You ordered an ECG, which shows the right bundle branch block with low voltage QRS complexes. Later your order an echocardiogram which revealed a concentric thickening of the left ventricle; relative apical-sparing or “cherry-on-top” pattern on a longitudinal strain bull’s eye display with bright myocardium. Laboratory tests revealed elevated troponin. Abdominal fat biopsy shows apple-green birefringence with Congo red staining. Of the following, which is the most likely diagnosis in this patient?
