Beta-adrenergic blockade in the management of acute thyrotoxic crisis, tachycardia and arrhythmias.

TACHYCARDIA is a characteristic feature of thyrotoxicosis at all ages, but the older the patient the more frequent the occurrence of atrial fibrillation. Treatment of thyrotoxicosis is followed by slowing of heart rate and more than half of the thyrotoxic patients with atrial fibrillation, who are treated with anti-thyroid drugs or surgery (Sandler & Wilson, 1959) or radioactive iodine therapy (Staffurth, Gibberd & Hilton, 1965) revert to sinus rhythm. Until thyrotoxicosis is controlled the tachycardia is resistant to digitalis therapy unless a larger dose is employed (McMichael, 1963) and this feature may itself indicate the diagnosis of occult thyrotoxicosis (Cookson, 1959). Even shifts in the protein-binding of thyroxine may play a part in supraventricular tachycardias (Schatz, 1967). The circulatory features of thyrotoxicosis are usually a marked feature of the thyrotoxic crisis or storm, when tachycardia is associated with hyperpyrexia, diarrhoea, psychiatric disturbance, muscle weakness and profuse sweating (Ingbar, 1966). Urgent control of the tachycardia, cardiac arrhythmias and the hypermetabolic state are occasionally required, notably when a fully established crisis develops. In this situation blockade of the sympathetic nervous system or depletion of tissue stores of catecholamines may be of value. The first reports of a striking improvement in patients with thyrotoxic crisis were those treated by epidural block (Crile, 1929) and later using spinal anaesthesia (Knight, 1945). It was suggested that the circulatory changes were due to increased peripheral responsiveness to catecholamines (Brewster et al., 1956), no evidence being found for an absolute increase in their output (Wisewell et al., 1963). Reserpine was found to be effective in controlling thyrotoxic symptoms (Canary et al., 1959) and sympathetic blockade by guanethidine has been used increasingly (Degroot et al., 1961; Leak, 1963; Waldstein et al., 1964) with similar success. Recently propranolol has been tried in thyrotoxic tachycardia,