Background: Subclinical hypothyroidism (SCH) is a risk factor for cardiovascular disease (CVD), particularly myocardial infarction (MI), due to its association with dyslipidemia, inflammation, oxidative stress, and endothelial dysfunction. COVID-19 exacerbates these risks by disrupting thyroid function and the renin-angiotensin system (RAS).

Methodology: This retrospective study included 90 MI patients (45 with and 45 without COVID-19). Thyroid function, lipid profiles, oxidative stress, and inflammatory markers were assessed. Cardiac severity was evaluated using ECG changes, levels of biochemicak markers like troponin I, CK-MB.

Results: SCH patients had elevated TSH (6.2 vs. 4.8 mIU/L, p < 0.05), LDL (157.2 mg/dL), triglycerides (189.6 mg/dL), oxidative stress (MDA: 5.2 nmol/mL), and CRP (12.6 mg/L, p < 0.01). Cardiac injury markers and hospital stays were significantly worse in COVID-19 MI patients.

Conclusion: SCH is an independent risk factor for MI, worsened by COVID-19. Routine thyroid screening in MI patients and further research on thyroid hormone therapy (THRT) are recommended.