A 28-year-old male with a 5-year history of duodenal bulb ulcers presents with recurrent melena and intermittent proton pump inhibitor (PPI) use. Four hours ago, he experienced three episodes of hematemesis (total ~600ml) and three episodes of melena (total ~200g), accompanied by significant dizziness, sweating, and palpitations. He had multiple syncopal episodes when changing from lying to sitting position. Despite aggressive resuscitation, his blood pressure (BP) dropped again to 90/60mmHg after initial improvement, requiring daily transfusion of 4U red blood cells (RBCs) to maintain BP at 90/60mmHg. Blood urea nitrogen (BUN) rose to 14.3mmol/L. Gastroscopy under transfusion revealed jet bleeding from an ulcer on the anterior wall of the duodenal bulb. The most effective next step is: