Subclinical hyperthyroidism increases risk of AF

SUBCLINICAL hyperthyroidism (SCH) is associated with a raised risk of incident atrial fibrillation (AF) and with death from coronary heart disease (CHD), a study suggests.

Swiss researchers analysed data from 10 prospective cohorts totalling 52,000 people (58% women) with a median age of 59 years. SCH, defined as thyroid stimulating hormone (TSH) lower than 0.45mIU/L with normal free thyroxine, was associated with a 68% increased risk of incident AF, 29% increased risk of CHD mortality and 24% increased risk of total mortality over nearly nine years of follow-up. The highest risks of events and death occurred when TSH was lower than 0.10mIU/L.

A leading US endocrinologist commented in an accompanying editorial that the findings provided “sufficient evidence to consider treatment” of SCH, “especially in elderly patients with cardiac risk, hyperthyroid symptoms or osteoporosis”.

Dr Jennifer Wong, consultant endocrinologist with Jean Hailes for Women’s Health, said SCH may be picked up by GPs on screening for osteoporosis or routine blood tests but she did not advocate more testing. Treatment would depend on the underlying cause of SCH, she said.

Meanwhile, a separate study conducted over eight years of subclinical hypothyroidism in UK general practice patients found treating the condition reduced ischaemic heart disease events and all-cause mortality in people aged 40–70 years, but not older patients.

Arch Intern Med 2012, online 23 April