Antelope Valley Hospital has surpassed the national average time limit for treating victims of an especially dangerous type of heart attack a month after the county designated it a special receiving center. The hospital is one of 21 hospitals in L.A. County selected as a receiving center for ST Elevation Myocardial Infarction, or STEMI, heart attacks. The American College of Cardiology and American Heart Association recommends hospitals treating STEMI patients achieve a “door-to-balloon” time, or interval between arrival at the hospital and the opening of a blocked artery with an angioplasty balloon, within 90 minutes. Antelope Valley, which became a STEMI center Feb. 1, had an average door-to-balloon time of 47 minutes, said Receiving Center Director Dr. Anil Kumar, in a statement. “By saving valuable minutes, we are saving the heart muscle,” he said.