Role of Subclinical Iatrogenic Hyperthyroidism in the Setting of Heart Disease and Arrhythmic Burden

Background: Subclinical hyperthyroidism is defined by a subnormal serum thyroidstimulating hormone (TSH) level with normal free thyroxine (FT4) and free triiodothyronine (FT3) levels. Its prevalence varies from 0.6% to 16% in the elderly and can increase to 20% in patients receiving thyroid hormone replacement therapy. Thyroid disease and/or replacement therapy are frequently associated with cardiovascular involvement. Cases Presentation: We report three clinical cases of patients with initial subclinical hyperthyroidism and cardiological manifestations, including supraventricular and ventricular extrasystoles, prolapse of the mitral valve with severe regurgitation, higher mean heart rate and deterioration of the arrhythmias on arrhythmogenic dysplasia substrate. Conclusion: We discuss the role of appropriate and early correction of thyroid dysfunction in improving cardiological manifestations.