Catecholamine Depletion in Thyrotoxicosis

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Abstract
Large doses of guanethidine were given parenterally to 9 patients with untreated thyrotoxicosis. Studies were made before and 1 or 2 days after therapy. Six patients received maximally tolerated amounts of guanethidine. Heart rate; cardiac index; arterial pressure; and left ventricular ejection time, pressure time per minute, and work were significantly lower at rest (-16 to -39%) after therapy. Oxygen consumption was not changed. Cardiac index and stroke volume remained above normal suggesting that either catecholamine depletion was incomplete or that non-adrenergic factors continued to maintain a hyperkinetic circulatory state. Catecholamine depletion did not inhibit normal qualitative response to supine exercise although exercise heart function was lower since resting levels had been reduced by drug. Reduction of left ventricular work and pressure time suggests drug may be useful as short term aid in patients with heart failure and thyrotoxicosis. Caution is suggested since guanethidine may reduce blood flow in some vascular beds more than oxygen demand.