Pulseless Electrical Activity

A 66-year-old woman with metastatic lung adenocarcinoma presents with sudden dyspnea, pleuritic chest pain, and presyncope. She becomes unresponsive with absent central pulses. High-quality chest compressions are initiated at 100–120/min. The cardiac monitor demonstrates the rhythm marked **A**: an organized narrow-complex rhythm at 65 bpm with visible P waves, QRS complexes, and T waves, but NO palpable central pulse. Which of the following is the MOST appropriate immediate management step for this rhythm?