Author + information
- Received February 25, 1985
- Revision received July 16, 1985
- Accepted August 1, 1985
- Published online January 1, 1986.
- Lucia Mangiardi, MD*,a,
- Fiorenzo Gaita, MD*,
- Susanna Brun, MD*,
- Patrizia Presbitero, MD*,
- Koonlawee Nademanee, MD, FACC† and
- Bramah N. Singh, MD, DPhil, FACC†
- ↵aAddress for reprints: Lucia Mangiardi, MD, Department of Cardiology 691/111E, Wadsworth Veterans Administration Hospital, Wilshire and Sawtelle Boulevard, Los Angeles, California 90048.
As a clinical entity atrioventricular (AV) block due to hypothyroidism is rare. Such a case induced by hypothyroidism complicating long-term therapy with amiodarone in a 45 year old woman with pre-excitation is presented. Electrophysiologic data obtained before and during thyroxine replacement therapy showed that hypothyroidism lengthens the effective refractory period of the atria, AV node, bypass tract and His-Purkinje system (that in the ventricle not being measured); this lengthening resembles the effects of long-term administration of amiodarone. These observations suggest that depressed thyroid function may be protective against arrhythmias but a patient with preexisting conduction system disease may develop AV block. The tendency to develop AV block in a patient who is euthyroid was reduced by bypass tract conduction. These findings are significant not only in monitoring amiodarone effects during chronic prophylactic drug therapy but also in providing further insight into the complex interrelation between the action of the drug and the thyroid hormones on cardiac muscle.
- Received February 25, 1985.
- Revision received July 16, 1985.
- Accepted August 1, 1985.
- American College of Cardiology Foundation