NEW YORK (Reuters Health) - The blood pressure, nerve, and hormonal changes wrought by obstructive sleep apnea (OSA) may increase the risk of heart attack during the night, new research suggests.

OSA is a common problem in which tissues in the back of the throat temporarily collapse during sleep causing numerous, brief episodes of interrupted breathing. The condition, which can cause extreme daytime sleepiness, can be effectively treated with a special breathing device that alleviates the blockage by pushing air into throat.

The body changes that occur with OSA may lead to blockage of the coronary arteries and heart attack, Dr. Virend K. Somers and associates explain in the Journal of the American College of Cardiology. If OSA is a trigger for a heart attack, a peak of heart attack symptoms would be expected during the night.

To investigate this premise, Somers at the Mayo Clinic in Rochester, Minnesota, and colleagues studied 92 heart attack patients in whom the time the chest pain began could be documented. The patients underwent overnight sleep tests 2 to 3 weeks after their heart attack.

OSA was identified in 64 patients (70 percent). Those with and without OSA were generally similar in terms of their health background and current medications.

From midnight to 6 am, the frequency of heart attack was higher in OSA patients, whereas from 6 am to noon, it was higher in patients without OSA. All told, patients with OSA were 6-times more likely to have to have a heart attack at night compared with patients without OSA.

These findings suggest that nighttime heart attacks may contribute to the increased likelihood of nighttime sudden death that has been reported in OSA patients, Somers' group concludes.

The researchers recommend that patients with a heart attack at night be evaluated for OSA.

SOURCE: Journal of the American College of Cardiology, July 2008.