Response to thyrotrophin-releasing hormone in atrial dysrhythmias

Thyroid disorders in the elderly. Difficulties in diagnosis and treatment

The diagnosis and management of disorders of thyroid function in the elderly present particular problems. The diagnosis may be missed because of the insidious onset of the disorder and the tendency to attribute many of the complications of hypo- or hyperthyroidism to other causes. Hyperthyroidism presenting as 'apathetic thyrotoxicosis' is seen much more commonly in elderly subjects than in the young, and unless the clinician is familiar with the clinical presentation, the diagnosis may not be considered. Both disease and concomitantly administered drugs may alter thyroid function tests, and abnormal tests do not necessarily mean hyper-or hypothyroidism. Euthyroid hyperthyroxinaemia is often difficult to distinguish from hyperthyroidism. Hyperthyroidism is usually controlled initially by antithyroid drugs, such as carbimazole, which interfere with the synthesis of thyroid hormone. The patient may start to feel better in 1 to 2 weeks and show objective signs of improvement in 3 to 6 weeks. Propranolol may provide earlier symptomatic relief, but must be used cautiously in older people due to its potential adverse effect on cardiac function. Thyroxine should be introduced slowly in those with hypothyroidism; the initial dose is 0.025 to 0.05 mg daily. Because of the long half-life of thyroxine, the dose is increased every 4 to 6 weeks until the patient is clinically euthyroid and the thyroid stimulating hormone level returns to normal. In elderly people the early treatment of subclinical hypothyroidism is justified.

Management of atrial fibrillation in the post-thyrotoxic state

This study was designed to investigate the appropriate timing for cardioversion in patients with chronic atrial fibrillation who had been rendered euthyroid from a thyrotoxic state. We carried out a retrospective study of 163 patients with thyrotoxic atrial fibrillation, with a mean follow-up of 34 months. With control of thyroid function alone, 101 patients had spontaneous reversion of atrial fibrillation to sinus rhythm and 62 patients had persistent atrial fibrillation. In those with spontaneous reversion, the longest duration of atrial fibrillation prior to the euthyroid state was 13 months. In those with persistent fibrillation, the shortest duration of atrial fibrillation prior to the euthyroid state was eight months. Almost three-quarters of those with spontaneous reversion had conversion to sinus rhythm within three weeks of becoming euthyroid. No spontaneous reversion occurred if atrial fibrillation was still present after the patients had been in a euthyroid state for four months. This study suggests that spontaneous reversion of atrial fibrillation to sinus rhythm is highly unlikely if the duration of atrial fibrillation before the euthyroid state is achieved exceeds 13 months, or if it is still present after the patient has been in a euthyroid state for four months, Cardioversion should be performed at about the 16th week after the euthyroid state is achieved.