When Is Heart Attack Most Harmful?

Heart attack, also known as myocardial infarction (MI), is a condition in which interruption of blood supply to heart occurs and causes heart cells to die. This is commonly due to blockage of a coronary artery.

A study recently reported that the size of a heart attack and the harm it can cause depends on what time it strikes. Researchers from the Minneapolis Heart Institute at Abbott Northwestern Hospital found that the greatest injury that a heart attack causes to the heart is when it takes place between 1am and 5am. This is because key restrictions occur in humans' blood supply according to the time of day, according to their findings published online on November 17, 2011 in the medical journal ‘Circulation Research’.

Studies had found that infarct size after ischemia or reperfusion exhibits a circadian dependence on the time of coronary occlusion in rodents. In order to find out whether a similar circadian dependence of infarct size occurs in humans, researchers analyzed 1,031 patients of acute heart attack referred for primary percutaneous coronary intervention with known ischemic times between 1 and 6 hours.

165 patients, who had their first heart attack because of blocked arteries, were identified. They all had well-defined ischemic times and data on size of heart attack, and area-at-risk were recorded. It was observed that the extent of infarct size was significantly associated with time of day onset of infarction.

The ability of heart to protect itself against more severe damage varies over a 24-hour cycle. It is important for scientists to identify those protective changes since this would help pharmaceutical manufacturers develop medications to prevent cardiovascular disease.

Meanwhile, it is known that sleep consists of different phases. Early morning sleep is known as rapid eye movement sleep during which people dream. While the body is asleep, the mind is still awake. The autonomous nervous system is stimulated and releases hormones like adrenaline, noradrenaline and cortisol. These hormones increase the activity of the heart that beats and works harder but the hormones constrict the blood supply to the heart.

One main reason why heart attack are worst at night is that people tend to wait till morning to go and get examination or treatment from doctors. Most people might just think that it was indigestion and simply took some antacids.