In Memory of Tachycardia: A wide complex tachycardia in a young male

EP RoundsA 24-year-old male with no past medical history presents to an urgent care center with palpitations. Four days prior he noticed that his heart rate was elevated and sometimes irregular which he recorded on his fitness watch. He had associated intermittent diaphoresis and dyspnea with exertion. Initial ECG obtained is shown in Figure 1A. He was instructed to follow up with a cardiologist. Transthoracic echocardiogram (TTE) obtained in the office demonstrated global left ventricular (LV) dysfunction with an ejection fraction (EF) of 35%. After being sent to the hospital, administration of intravenous amiodarone terminated the patient’s tachycardia and a subsequent ECG was obtained (Figure 1B). Repeat TTE showed normalization of the EF to 55% and cardiac magnetic resonance imaging (cMRI) demonstrated a normal LV without evidence of myocardial pathology. What is the most likely diagnosis of the tachycardia? What is the etiology of the abnormalities seen in the patient’s ECG as shown in Figure 1A? What is the appropriate management for this patient?