Monday, September 29, 2008

Most Heart Attacks Happen at THIS Time

Although heart attacks can and do happen any time of the day or night, the most dangerous time for a cardiovascular emergency, which includes not only sudden cardiac death, rupture or aneurysm of the aorta, but also pulmonary embolism and stroke, is during the last phase of sleep and right after you wake up.

Roberto Manfredini, professor of internal medicine at the University of Ferrara in Italy told TIME magazine that the risk was specifically estimated by a group of Harvard University researchers, who concluded that, on average, the extra risk of having a heart attack between 6 a.m. and noon is 40 percent. If you count only the first three hours after waking up, the relative risk is threefold!

Why? Blame it on circadian rhythms, those physiological changes that repeat at about 24-hour intervals. Most of our cardiovascular functions exhibit circadian changes. A heart attack happens when there is an imbalance between a greater need for oxygen in the heart and a decreased supply of oxygen to the heart--or both. When we wake up, we need more oxygen support to our heart as we begin physical activities and our blood pressure and blood sugar levels rise. "All those factors lead to an increase of oxygen consumption but at the same time contribute to the constriction of vessels. So you have reduced vessel size and reduced blood flow to the coronary vessels," Manfredini tells TIME. Basically, the one time you need the most blood flow, you actually have less.

Healthy people can adjust to this just fine. If you have plaque in the coronary vessel and these changes occur at the same time and then peak at the same time, you have a far higher risk of having a heart attack during the first three hours after waking up. The risk is also high just before waking up in the last stage of sleep, called REM, or rapid eye movement, sleep. "...When you dream, you have a dramatic increase of activity of the autonomic nervous system--even more than when you are awake," Manfredini told TIME. "Probably each of us can remember waking up in the morning sometimes feeling very tired. That's because during that stage of dreams, we were running or facing some danger. Your heart was running, so it was consuming oxygen. And for similar reasons to those when you're awake, that activity is risky if you don't have a good vessel system."

You can't minimize the effect by just waking up later. The pattern holds no matter the exact time you awaken because the risk is linked to activities.

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