A 32-year-old female presents to the emergency department with sudden-onset palpitations, shortness of breath, and light-headedness that began an hour ago while she was at work. She describes the palpitations as rapid and regular, and they have not subsided since they started. She denies any chest pain, nausea, or sweating but feels anxious due to the persistent symptoms.

The patient has no significant past medical history, but she mentions experiencing similar episodes of palpitations a few times in the past, which resolved on their own after a few minutes. She does not take any regular medications and leads an active lifestyle with no known triggers for these episodes.

On examination, her vital signs show a heart rate of 170 beats per minute, a blood pressure of 110/75 mmHg, and no signs of respiratory distress. Her heart sounds are rapid and regular, without murmurs. An ECG reveals a narrow complex tachycardia, consistent with supraventricular tachycardia (SVT).

The patient is treated with vagal manoeuvres, which are unsuccessful, followed by intravenous adenosine, resulting in the immediate termination of the arrhythmia. Her heart rate returns to normal, and she reports feeling much better. After a period of observation, she is discharged with advice to avoid potential triggers like excessive caffeine or stress. She is referred to a cardiologist for further evaluation and consideration of long-term management options, including catheter ablation if the episodes recur.