When the temperature falls, the heart can be put under greater stress and the probability of sudden cardiac death surges among those in mid-life. Excessive drinking, excessive smoking and chronic fatigue in day-to-day life may lead to the onset of sudden chest pain followed by cardiac arrest and death.

Sudden death refers to an unexpected natural death caused within one hour of the onset of symptoms. Most cases of sudden death are the result of heart disorder. Therefore, sudden death is normally considered equivalent to cardiac arrest. The cause of 80 to 90 percent of sudden cardiac death is coronary artery disease (the difficulty of supplying the myocardium with blood due to the buildup of plaque inside the coronary arteries).

About 100-200 of every 100,000 people (0.1-0.2 percent of the entire population) in Korea die as a result of sudden cardiac death each year. Though the frequency is relatively low compared to that in western countries, it is steadily growing each year. Sudden cardiac death sometimes hits adults in their late 30s to early 40s. It predominantly affects men across all age groups, with the frequency in men four times higher than in women. This is true because men are exposed to more risk factors leading to sudden death due to the social environment. 

Sudden death can be likened to the explosion of a powder keg. When a powder keg is filled with enough gunpowder, the right spark sets it off. The structural defects of the blood vessels are like the gunpowder, while internal and external stress factors are like the spark. High blood pressure, diabetes, hyperlipidemia and smoking can damage the walls of blood vessels, and such damage develops into inflammation of the heart muscle resulting in mild arteriosclerosis, blood clots and constricted coronary arteries. For younger generations, smoking is the biggest risk factor.

The final event leading to sudden death is fatal arrhythmia (abnormal heart rhythms), which can be compared to the explosion itself. When fatal arrhythmia occurs, the heart fails to pump and circulate blood, eventually triggering death. Many sudden deaths are known to have taken place when the stomach is filled with food. Therefore, those suffering from heart disease should refrain from overeating.

It has been a well-known fact that the probability of a heart attack increases upon waking up in the morning, but the mechanism was only recently explained. When the body awakens from sleep, mental stress begins to escalate, both consciously and subconsciously, in anticipation of the day ahead. As the body is raised from a supine position to the feet before it is fully loosened up, the rigidity of the parasympathetic nerves during sleep leads to the stimulation of the sympathetic nervous system.

The stimulated sympathetic nervous system causes an increase in the secretion of the stress hormone, constricts blood vessels, increases platelet aggregation and subsequent blood clot formation and heightens the risk for vulnerable plaque rupture cardiac gating. At the same time, blood pressure escalates along with the pulse, putting greater pressure on the heart. This combination of symptoms results in oxygen deficiency in the myocardium and eventually fatal arrhythmia.

Excessive exercise and sexual intercourse are also likely to raise the risk of sudden death by causing excessive activity of the sympathetic nervous system, constricted blood vessels due to the increase in the stress hormone, a rise in blood clots from activated platelets and an increase in the probability of plaque ruptures in the wall of coronary arteries. As is well-known, mental stress causes myocardial ischemia (oxygen deficiency of the cardiac muscle) in patients with heart disease, and this can ignite sudden death. In particular, intense negative emotions such as anger, hostility and depression can cause a higher incidence of coronary artery disease and sudden death. Negative emotions can trigger myocardial ischemia and lead to arrhythmia. Roughly 12-15 percent of all cases of cardiac death occur during sleep, because the probability of heart failure increases with the sleep-induced excessive activity of the sympathetic nervous system. In fact, blood vessels are found to be most constricted around dawn.

It is most important to resuscitate the person whose heart has stopped beating unexpectedly and immediately transport the patient to the hospital. As soon as a case of sudden death is identified, a request for rescue should be made and CPR performed as instructed by the guidelines, using the techniques of chest compressions and mouth-to-mouth breathing. The main purpose of such basic life support is to sustain life without the help of medical devices or medications until advanced life support providers arrive at the scene.

The presence of a lay public competent in performing CPR and providing basic life support is crucial in treating sudden death. For this reason, medically advanced countries closely focus on training lay individuals on performing basic life support, while also fostering experienced advanced life support specialists. Advanced life support aims to increase the resuscitation rate by employing different medical devices such as the defibrillator (an electronic device that terminates fatal arrhythmia through the application of electrical therapy and allows the heart to reestablish its normal rhythm), the artificial respirator and medications that help circulate oxygen and blood as well as normalizing blood pressure.

For defibrillation and CPR to be effective, they have to be administered as soon as sudden cardiac death begins. If treatment occurs within one minute of the onset of fatal arrhythmia, the resuscitation rate surpasses 80 percent. However, the resuscitation rate falls to less than 10 percent if 10 minutes or more have elapsed. In general, the average resuscitation rate reaches 20-30 percent if an advanced life support team can arrive at the scene within the shortest period of time, though the differences in the condition of the patient and the skills of the life support team members are also variables to some extent. The resuscitation rate drops notably if the life support team in charge lacks sufficient training or teamwork or if the incidence occurs at hard-to-access locations.

By Park Jeong-euy

The author is a professor of internal medicine at Sungkyunkwan University School of Medicine. ― Ed.