A 65 year old male with a history of hypertension, stage IV kidney disease on dialysis presents to the emergency department with dizziness and palpitations for 1 hour. He denies chest pains. His temperature is 37.0 C, blood pressure 80/40, heart rate 150, respirations 24, and oxygen saturation 85% on room air. Physical examination reveals pulmonary rales throughout his lung fields, elevated jugular venous pressure, a regular tachycardic rhythm without murmurs, and trace lower extremity pitting edema. Laboratory studies are normal. His ECG is below. Which of the following is the most appropriate initial therapy?