Introduction: The non-thyroidal illness syndrome (NTIS) or the sick euthyroid syndrome refers to abnormal changes in circulating thyroid hormones due to systemic illnesses. Thyroid hormones are pivotal in the regulation of normal cardiac functions. However, the effects of the NTIS on the heart in acute coronary syndrome (ACS) are still unclear.
Methods: A 6-month prospective cohort study involving 85 patients admitted with ACS was carried out. TSH, FT4 and FT3 were assessed on days 1, 5 and 42. Antithyroid peroxidase antibodies, antithyroglobulin antibodies, fasting blood sugar, HbA1c and fasting serum lipid were obtained on admission. Mortality, functional status (Killip and New York Heart Association Classifications), arrhythmias and readmission rate were recorded.
Results: The prevalence of NTIS was 53%. It was seen in 48% of unstable angina (UA), 54% of non-ST elevation myocardial infarction (NSTEMI) and 56% of ST elevation myocardial infarction (STEMI) patients. NTIS is associated with cardiovascular mortality, all-cause mortality, severe heart failure and a higher readmission rate. The levels of FT3 correlate with severity of myocardial damage as measured by CK and Troponin T. Lower TSH was seen in the non-survivors and in those with ventricular arrhythmias. The most common presentation of NTIS was low FT3 (43.5%), followed by low TSH (12.9%) and FT4 (4.7%). None of the predisposing factors analysed were associated with the development of NTIS.
Conclusions: NTIS in patients with ACS is associated with increased cardiovascular mortality and morbidity, and affects UA, NSTEMI and STEMI equally.
Keywords: Non-thyroidal illness syndrome (NTIS); acute coronary syndrome.