A 72-year-old man with hypertension and type 2 diabetes mellitus presents to the emergency department complaining of acute onset palpitations and shortness of breath. His wife reports he became symptomatic 30 minutes ago while watching television. Vital signs: heart rate 148 bpm, blood pressure 82/48 mmHg, respiratory rate 24/min, oxygen saturation 91% on room air. Physical examination reveals an anxious, diaphoretic patient with diminished air entry bilaterally. Cardiac auscultation demonstrates a regular tachycardia with no audible murmurs. A 12-lead ECG is obtained and shows a regular, narrow-complex tachycardia at 148 bpm with P waves not clearly visible. Troponin I is normal. Chest radiograph shows mild pulmonary edema. Which of the following is the most appropriate initial management?

1. A)Intravenous adenosine 6 mg rapid push followed by saline flush
2. B)Oral metoprolol 25 mg with observation for 2 hours
3. C)Synchronized electrical cardioversion at 100 joulesGABARITO
4. D)Continuous cardiac monitoring without intervention pending cardiology consultation
5. E)Intravenous amiodarone 150 mg over 10 minutes