Sudden cardiac death is sudden, unexpected death from an electrical problem in the heart. The most common cause is a rapid heart rhythm, called ventricular tachycardia.

Abnormal electrical signals cause the lower chambers of the heart (the main pumping chambers) to beat too fast. If normal rhythm isn't restored, the lower chambers eventually become unable to pump blood.

The heart muscle simply quivers, instead of contracting. This is called ventricular fibrillation. The heart can't pump oxygenated blood to the body and the patient quickly loses consciousness. Death can occur within minutes. More than 70 percent of patients in sudden cardiac death die before reaching the hospital.

Researchers estimate sudden cardiac death causes 300,000 deaths every year in the U.S. It is more common in men than in women and in people over 35. The two most important risk factors for the condition are blockages in the coronary arteries (coronary artery disease) and scarring of the heart muscle from a prior heart attack. Congenital heart disease or malformations can also lead to sudden cardiac death, especially in younger people.

Exercise and Heart Risks

Generally, athletes are in top physical health. However, even well conditioned athletes may be at risk for sudden cardiac death. In 1993, pro-basketball player Reggie Lewis collapsed and died during an off-season practice. He was only 27. In 1995, Olympic gold medalist Sergei Grinkov died. The Russian skater was 28.

Sudden cardiac death in professional athletes is still a relatively rare occurrence. However, health experts worry that many "weekend" athletes may be unknowingly at risk. Researchers estimate one out of every 15,000 to 18,000 joggers or vigorous exercisers 35 and older die of sudden cardiac death. Most people are unaware they are at risk for the condition.

Screening for Heart Risks

Doctors urge health screening for all marathon runners. Younger runners may have congenital heart problems that put them at risk for sudden cardiac death. Runners over 35 may have early signs of coronary artery disease. Often, they are unaware of their risk because they have no symptoms. Screening may also be recommended for those who participate in vigorous exercise and have risk factors for heart disease or sudden cardiac death (like being male, middle-aged or having a family history of heart problems).

Three types of screening tests are recommended. The first is an ultra fast CT scan (also known as the electron beam CT scan or a coronary calcium scorer). This test measures the amount of calcification in the coronary arteries. The more calcification, the more plaque and the greater the likelihood of a heart problem at some point in the future. Plaque can build and block the flow of blood through an artery. In other cases, some of the plaque can break loose. When that happens, the body may sense an "injury" to the wall of the artery and initiate clots to "heal the wound." The clots that develop in the area can block blood flow. Ultrafast CT scans are good for detecting calcium in patients who have no symptoms or risk factors for heart disease. However, the tests can be expensive and are not covered under all health insurance programs.

The second type of screening is the standard stress test. Stress tests are most useful to determine if a patient's symptoms (like shortness of breath or chest pain) are associated with coronary artery blockages. The test is not always an ideal screening tool because it usually only picks up serious blockages (usually those blocking an artery by 70 percent or more). Patients with less severe blockage may still have a normal stress test and can be at risk of a heart attack or sudden cardiac death.

If doctors still have any suspicion of heart problems after the first two tests, a coronary angiogram may be recommended. In this procedure a special dye is injected into the arteries and X-rays are taken of the heart. The X-rays detect the dye as it flows through the heart and allows doctors to determine if there are any areas of blockage in the arteries. If blockages are found, doctors may perform angioplasty (opening the blockage by inflating a balloon inside the artery to compress the plaque).

SOURCES

Heart Rhythm Society, http://www.hrspatients.org