Among the patients studied, 269 had morning heart attacks, 240 had their attack in the afternoon, 161 had heart attacks between 6 p.m. and midnight and 141 had an attack between midnight and 6 a.m.
In addition, attacks that occurred to the back wall of the heart caused more damage than heart attacks in other locations in the heart, they found.
The findings have important implications, Ibanez said. "From a treatment point of view, when heart attacks happen in the early morning hours a more aggressive management of the case could result in better outcomes," he said.
In addition, knowing that morning heart attacks cause more heart damage might help in developing new drugs that could target the specific causes of these attacks, Ibanez said.
Dr. Gregg Fonarow, associate chief of cardiology at UCLA's David Geffen School of Medicine, said that "there is circadian variation in the incidence of heart attack, with a higher incidence in the sleep-to-wake transition period."
This circadian rhythm may include fluctuations in the nervous system, cortisol levels and other factors that up the risk of heart attack. There may also be circadian differences in how heart cells function, he said.
"However, irrespective of time of day, achieving timely reperfusion of blood with direct coronary intervention or breaking up clots is critical for patients with a myocardial infarction," Fonarow said.
For more information on heart attacks, visit the American Heart Association.
SOURCES: Borja Ibanez, M.D., Ph.D., National Center for Cardiovascular Research, Madrid; Gregg Fonarow, M.D., associate chief, cardiology, David Geffen School of Medicine, University o
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