What is the most appropriate next step in management?

An 80-year-old man was referred because of weight gain and low mood but said he was otherwise well. He had a complex cardiac history including a ventricular fibrillation arrest and a permanent pacemaker, but he had been very well for the past 3 years. He was taking amiodarone 100 mg daily, lisinopril 40 mg daily and furosemide 80 mg daily.

On examination, he had a pacemaker in situ and his pulse was 84 beats per minute and regular. He had a 2/6 mid-systolic murmur in the aortic area with no radiation, mild ankle oedema, and scanty basal crackles bilaterally on auscultation of his chest.

Investigations (before attending clinic):

serum thyroid-stimulating hormone19.0 mU/L (0.4C5.0)

serum free T411.0 pmol/L (10.0C22.0)

anti-thyroid peroxidase antibodies300 IU/mL (<50)

What is the most appropriate next step in management?
A . review with repeat thyroid tests in 3 months
B . start levothyroxine 25 micrograms daily
C . start levothyroxine 100 micrograms daily
D . start liothyronine sodium 10 micrograms twice daily
E . stop amiodarone