Time of day affects heart attack severity

The severity of a heart heart -- and subsequent recovery -- depends on what time of day the heart attack occurs, U.S. researchers say. Dr. Jay H. Traverse, a cardiologist at the Minneapolis Heart Institute at Abbott Northwestern Hospital in Minneapolis and physician researcher with Minneapolis Heart Institute Foundation who was the study's senior author, and colleagues conducted an analysis of 1,031 patients who had acute heart attacks. The researchers identified 165 patients with their first heart attack who had blocked arteries without evidence of pre-attack chest pain or collateral blood flow. All 165 patients had well-defined ischemic times and the data were supported by a subgroup with cardiac magnetic resonance imaging measurements of the size of heart attack and area-at-risk. The study found the extent of the heart attack size was significantly associated with when the attack occurred. The greatest heart tissue injury occurred with 1 a.m. onset of ischemia -- shortage of the blood supply to the heart -- and 5 a.m. onset of reperfusion -- tissue damage caused when the blood supply returns to the tissue after a period of ischemia or lack of oxygen. The peak injury was detected to be 82 percent higher than that recorded at lowest time of injury. "We were trying to ascertain whether the time of day of when a heart attack occurs influences the amount of damage that the heart sustains, or was this just a phenomenon exhibited in rodents," Traverse said in a statement. The study was published in the journal Circulation Research.