You are evaluating a 48-year-old man with crushing substernal chest pain. The patient is pale, diaphoretic, cool to the touch, and slow to respond to your questions. The blood pressure is 58/32 mm Hg, the heart rate is 190/min, the respiratory rate is 18 breaths/min, and the pulse oximeter is unable to obtain a reading because there is no radial pulse. The lead II ECG displays a regular wide-complex tachycardia. What intervention should you perform next?