Endocrine Abstracts

Introduction: Thyroid hormones play an important role in the normal functioning of cardiac and vascular physiology, therefore hypothyroidism results in profound cardiovascular effects. Arrhythmia in patients with hypothyroidism seems rare and not well recognized.

Observation: Our first patient was a non-smoker 61-year-old woman, followed-up in the cardiology department for hypertension and dyslipidemia during the previous 5 years. She was treated with ACE inhibitors and a statin. Her sister had a dysthyroidism. The history was marked by the appearance of palpitations over the past 2years. Physical examination showed a palpable thyroid of normal size. The chest X-ray didn’t show any anomaly. Sinus tachycardia was found on ECG. Renal and lipid balance was correct. The thyroid investigation showed a subclinical hypothyroidism with a sensitive thyroid stimulating hormone: (TSH) = 6,05 mU/l and Free T4=14,8 pmol/l. One year later, the patient showed symptoms of weight gain and asthenia. A check-up was done: TSH=7,2 mU/l; FT4=14 pmol/l; AntiTPO antibodies were negative (=4,9), Cholesterol=6,5mmol, TG=3mmol inciting to treat her with appropriate thyroxin replacement with a regular follow-up. The patient no longer reported tachycardia. Our second case was about a 57- year-old female patient, with a history of hypertension for 5 years. She was treated with ACE inhibitors. The patient was admitted to the cardiology department for junctional tachycardia and treated with beta blockers and digoxin. There was no infectious syndrome associated during her hospitalization, she was found to have subclinical primary hypothyroidism (TSH=12.8 mU/l/FT4=12.5 pmol/l), her anti TPO antibodies were negative. The initial cervical ultrasound noted a 5.5 mm right lobar nodule classified as TIRADS4B (EU-Tirads5) with an ultrasound aspect of thyroiditis for the rest of the parenchyma. Three months later, the thyroid assessment was checked and was normal (TSH=3.7 mU/l) and the control cervical ultrasound showed multiple micro cysts in both lobes Eu-TIRADS2. The cardiac rhythm disorder was resolved at that time. The ultrasound follow-up two years later showed a heterogeneous hypo echoic thyroid gland with no thyroid nodule.

Conclusion: Hypothyroidism can result in decreased cardiac output, increased systemic vascular resistance and atherosclerosis with ischemic heart disease risk. Cases of arrhythmia are rarely reported in hypothyroidism and could be due to alteration of myocyte-specific gene expression, interstitial oedema, myofibril swelling with loss of striation, endothelial dysfunction, disturbances of the sympathetic-vagal tone, increased arterial stiffness… Replacement with thyroxin could help and should be initiated cautiously.