Sudden cardiac death is a leading cause of death in the United States, taking more than 400,000 lives each year.

"This finding is revolutionary," said lead researcher Dr. Robert E. Eckart, a cardiologist from Brooke Army Medical Center in San Antonio, Texas. "Previously, it was thought the leading cause of sudden cardiac death in younger people was abnormal muscle thickening of the heart."

Eckart said the cause of sudden cardiac death varies by country. In Italy, for example, the main cause is a unique type of heart muscle problem. "We thought it would be important to look at a population that would be more representative of the U.S. as a whole," he said.

In their study, Eckart and his team collected data on 6.3 million military recruits spanning 25 years, from 1977 to 2002. During this period, there were 127 sudden cardiac deaths, according to the data presented Thursday at the Heart Rhythm 2004 meeting in San Francisco.

"We found that the leading cause of sudden cardiac death was a coronary artery problem," Eckart said. "This anomaly is when one of the coronary arteries takes off from the aorta in an abnormal fashion."

The second leading cause of sudden cardiac death in people with seemingly healthy hearts was the development of a deadly heart rhythm, known as an arrhythmia. Eckart believes this problem is genetic.

Given these findings, Eckart said he has changed his approach to treating young people who complain of chest pain. Before, he screened these patients with an echocardiogram, which is an ultrasound of the heart, to look for abnormal heart muscle.

But now he does an electrocardiogram (EKG) to look for abnormal electrical activity in the heart. Eckart also looks at the condition of the coronary arteries to see if there is any abnormality.

"By doing those two simple things, we are going to make a larger impact on sudden cardiac death in this young population," Eckart said. More research is needed to identify people with a genetic susceptibility to deadly heart rhythms, he added.

Eckart strongly recommends that young patients with a family history of premature sudden cardiac death have an EKG to look for the problems that can cause these deadly heart rhythms.

Dr. Ramon Brugada is a cardiologist and director of molecular genetics at the Masonic Medical Research Laboratory in Utica, N.Y. He said, "This study points out the importance of screening young people with EKGs."

However, many of these conditions can appear normal on an EKG, he cautioned. "You have to catch it at the right time," he said.

"If you have a family history of sudden death, if someone in the family died at 20 or 25 with no previous medical problems, that should raise a red flag that there is some inherited disease. Other family members should have an EKG screening," Brugada advised.

More information

The American Heart Association (news - web sites) can tell you about sudden cardiac death, and the National Heart, Lung, and Blood Institute has a section on heart disease.