Diagnosis of ATTR Cardiac Amyloidosis
A 69-year-old African-American man was referred for evaluation of heart failure (HF). He presented to his primary care provider with 6 months of worsening dyspnea on exertion and lower extremity edema. The patient reported sleeping in a recliner for the week prior. He also noticed that his blood pressure had been lower recently, necessitating reduction of the dose of some of his antihypertensives.
His vital signs today include heart rate 78 bpm and blood pressure 101/68 mm Hg. His body mass index is 23 kg/m2.
Physical examination reveals an irregular heart rhythm without murmur or gallop. He has bibasilar crackles and 3+ pitting edema on the bilateral lower extremities to his upper thigh. Examination of his hands reveals flattening of the thenar eminence and numbness of his thumb, index, and middle finger bilaterally. Electrocardiography shows atrial fibrillation with a rate of 75-80 bpm and left bundle branch block. A transthoracic echocardiogram reveals ejection fraction 60-65% with concentric left ventricular wall thickening (1.7 cm posterior wall, 1.6 cm interventricular septum). There is biatrial enlargement with thickening of the interatrial septum and moderate tricuspid regurgitation.
A pyrophosphate scan shows grade 3 uptake, kappa free light chain 4.02 mg/dL, lambda free light chain 2.01 mg/dL, free light chain ratio 2.0, and an M-spike on serum immunofixation.
Which one of the following is the best next step for the diagnosis of this patient's cardiomyopathy?