A RARE PRESENTATION OF SYMPTOMATIC COMPLETE HEART BLOCK IN A MILDLY HYPERTHYROID PATIENT

Abstract

INTRODUCTION/BACKGROUND
Hyperthyroidism mainly causes sinus tachycardia and atrial fibrillation. Complete heart block is an extremely rare complication of hyperthyroidism with very few cases reported, mainly in association with acute inflammatory disease, hypercalcemia, administration of drugs, or structural heart disease.

CASE
Here, we report a case of a 62-year-old male with underlying DM, hypertension and cerebrovascular accident. He was brought in for syncopal attack with lethargy, profuse sweating, and dizziness. He denied any history of fever or anginal chest pain. Upon arrival BP was 151/49 mmHg, with heart rate of 27-34 bpm. Systemic examination was unremarkable; there was no goitre or thyroid eye sign present. Serial ECG revealed complete heart block and he was initially managed with intra- venous infusion (IVI) of adrenaline and dopamine, IV atropine boluses and followed by transvenous pacemaker (TPM) insertion. Laboratory investigation including FBC, RP, electrolytes, liver enzymes, and cardiac enzymes were all within normal range. However, thyroid function test showed mild hyperthyroidism with free T4 of 16.4 pmol/l (7.86-14.41), and TSH 0.115 mIU/L (0.38-5.33). TSH receptor antibody was negative. Echocardiography demonstrated good left ventricular systolic function with ejection fraction of 55%, and no regional wall motion abnormalities which made an ischemic aetiology as unlikely. We commenced carbimazole at a dose of 10 mg daily. Subsequently permanent pacemaker was inserted due to dependency on TPM. He had an uneventful recovery and was discharged well.

CONCLUSION
The exact mechanism of complete atrioventricular (AV) block remains unclear. Few reports postulated that interstitial inflammation of the AV node and His-bundle or focal myocarditis around the AV node could have led to cumulative damage to the cardiac conduction system. This case reiterates the importance of recognizing the association between complete AV block and hyperthyroidism due to the rarity of this condition. There is still insufficient information regarding the optimal management of this condition.