Prompt Thyroid Hormone Replacement Reversing Severe Bradycardia & Syncope

Thyroid disease, particularly hypothyroidism, can significantly affect the cardiovascular system, leading to structural, functional, and conduction abnormalities. Hypothyroidism decreases inotropy and chronotropy and may cause bradycardia or conduction defects. Although these changes are typically reversible with thyroid hormone replacement, severe cases may necessitate pacemaker placement. This case describes an 82-year-old female with hypothyroidism, atrial fibrillation, and left bundle branch block (LBBB) who presented with recurrent syncope due to hypothyroidism-induced bradycardia with sinus pauses. Her symptoms resolved with thyroid hormone optimization, highlighting the importance of prompt recognition and treatment of hypothyroidism-related cardiac manifestations to prevent unnecessary pacemaker implantation.