Supraventricular Tachycardia Beyond the Heart: A Case of Undiagnosed Graves' Thyrotoxicosis Presenting as an Episode of Supraventricular Tachycardia.

Thyrotoxicosis is a hypermetabolic condition defined by elevated levels of triiodothyronine (T3) and/or thyroxine (T4) in the serum. While irregular heart rhythms like atrial fibrillation are commonly linked to this condition, other types such as supraventricular tachycardia (SVT) characterized by sudden onset, narrow QRS complexes, and regular RR intervals in the absence of structural heart disease are much less frequently reported and often overlooked.  We present a compelling case of Graves' thyrotoxicosis in a middle-aged male patient, whose only presenting symptom was SVT, in the absence of typical systemic signs of hyperthyroidism or structural cardiac abnormalities. This case challenges the conventional diagnostic trajectory of thyrotoxicosis, emphasizing the importance of including thyroid function testing in the diagnostic workup of unexplained arrhythmias. Early recognition of such atypical presentations is crucial, as appropriate treatment of the underlying thyrotoxicosis can lead to resolution of the arrhythmia and improved clinical outcomes.