Ventricular fibrillation is reduced in hypothyroid rats with enhanced myocardial α‐adrenoceptor responsiveness

Abstract

1The severity of ventricular arrhythmias induced by coronary artery occlusion and reperfusion has been examined in control rats and animals made hypothyroid by pretreatment with 6-propylthiouracil (PTU). The maximal driving frequency and sensitivity of isolated left atria and papillary muscles to isoprenaline and to phenylephrine in the presence of propranolol, were also examined in tissues from control and hypothyroid animals. 2 Pretreatment with PTU resulted in a potentiation of responses to the a-adrenoceptor agonist phenylephrine in both left atria and papillary muscles, while responses to isoprenaline were depressed in left atria but unaltered in papillary muscles from hypothyroid animals.3 In rats subject to coronary artery occlusion, PTU pretreatment reduced the incidence of ventricular fibrillation during acute myocardial ischaemia and abolished reperfusion-induced ventricular fibrillation. Mortality during myocardial ischaemia and reperfusion was also abolished. Diastolic blood pressure was similar in hypothyroid and control animals, but there was a small reduction in systolic blood pressure and a marked decrease in heart rate in PTU pretreated animals. 4 These results demonstrate that PTU-induced hypothyroidism represents a condition where cardiac a-adrenoceptor-mediated responses are enhanced but the severity of ischaemia-and reperfusion-induced arrhythmias is reduced.

Normalization of peripheral thyroid hormone metabolism induced by successful chronic amiodarone treatment in patients with ventricular arrhythmias

“…That the beneficial effect of amiodarone in cardiac arrhythmias may be related to its thyroid hormone antagonistic action is not new information, like its well-known thyroid-related side effects: other authors [5] have suggested that amiodarone exerts its antiarrhythmic action inducing a selective hypothyroid state in the myocardium, on the basis of the molecular characteristics of the drug, of the similarity between the myocardial electrophysiological effects of amiodarone and those characteristic of hypothyroidism [1,3], and of the protective effect against lethal ventricular arrhythmias exerted by experimentally induced hypothyroidism in some models of sudden death [5,17].…”

Thyroid Hormone Plays an Important Role in Cardiac Function: From Bench to Bedside

“…For patients with hypothyroidism, it is necessary to monitor the effectiveness of amiodarone for the prevention of ventricular arrhythmic recurrence. It has been reported that lidocaine (class IB antiarrhythmic drug) or bretylium tosylate (class III antiarrhythmic drug) might be useful to prevent these paroxysmal ventricular tachycardias and endocavitary electrode stimulation, in place of amiodarone ( Chess-Williams and Coker, 1989 ).…”