Endocrine Abstracts

Introduction:Hypothyroidism may be associated with bradycardia, low voltage complexes,ST-T wave changes, atrioventricular and intraventricular conduction disturbances. Extrasystoles and tachyarrhythmias of both atrial and ventricular origins have been described in hypothyroidism with the ventricular tachyarrhythmias associated with prolonged QT interval.

Aims: To ascertain the prevalence of cardiac arrhythmias in primary hypothyroidism.

Methods:Twenty hypothyroid patients (two males,mean age of 33.1 years, range 16-52) were prospectively studied before and after three months of thyroxine treatment and compared with ten matched controls (two males,mean age 35.1 years, range 28-50).Following ethical approval, all subjects underwent routine blood tests including thyroid function tests, electrocardiograph, and holter monitoring.

Results:Average heart rate was significantly lower in hypothyroid patients at presentation( 58 plus /minus 11 versus 71 plus/minus 9 beats per minute post thyroxine treatment, p= .0004) and 74 plus/minus 12 beats per minute in the control group. Frequent ventricular ectopics were present in three patients ( 15 percent) at baseline, four patients ( 20 percent) following thyroxine supplementation compared with two(20 percent) controls.One patient had an episode of ventricular tachycardia associated with long QT interval which normalised with thyroxine treatment, with no recurrence of ventricular tachycardia thereafter. Supraventricular ectopics were present in ten ( 50 percent) patients both at baseline and after thyroxine treatment compared with five(50 percent)controls.Three patients(15 percent) had low voltage QRS complexes and one (10 percent) patient had non-specific T wave changes which reverted to normal following thyroxine replacement.

Conclusion: Hypothyroidism can lead to various electrocardiographic changes including low voltage QRS complexes and T wave inversion. It can also lead to bradyarrhythmias, mainly sinus bradycardia, which settles with thyroxine replacement. Ventricular tachycardia with prolonged QT interval attributable to the hypothyroid state occurred in one patient, with the QT interval normalising with thyroxine replacement therapy.