Question

A $66$-year-old male comes to the clinic for follow-up of recent fatigue, severe heat intolerance, and an unintentional weight loss of $4.5\text{ kg}$ ($10\text{ lb}$) over the last month. His medical history is significant for ischemic cardiomyopathy with a reduced ejection fraction and recurrent sustained ventricular tachycardia. His medications include sacubitril-valsartan, metoprolol succinate, spironolactone, and amiodarone, which he has taken for two years. Vital signs show a temperature of $37.2^\circ\text{C}$ ($99.0^\circ\text{F}$), a blood pressure of $118/76\text{ mmHg}$, and an irregular pulse of $112/\text{min}$. Physical examination reveals warm, moist skin and a fine bilateral hand tremor. No goiter or exophthalmos is noted.

Laboratory results are as follows:
Thyroid-stimulating hormone (TSH): $<0.01\text{ }\mu\text{U/mL}$ (Normal: $0.4-4.0\text{ }\mu\text{U/mL}$)
Free T4: $4.1\text{ ng/dL}$ (Normal: $0.8-1.8\text{ ng/dL}$)
Free T3: $2.8\text{ pg/mL}$ (Normal: $2.3-4.2\text{ pg/mL}$)

Color flow Doppler ultrasonography of the thyroid gland demonstrates severely decreased vascularity.

Which of the following is the most appropriate next step in the management of this patient's thyroid dysfunction?