Thousands of high-school and college athletes compete every year without incident, and indeed, they’re considered in the peak of health. That’s why it’s a shock to the public when a young player collapses and dies during a competition.

When this tragedy does happen, especially in football and basketball, it’s usually because there was an undiagnosed cardiac irregularity: Competitive sports put great stress on the heart. The case of Reggie Lewis, of the Boston Celtics, for example, who collapsed during an off-season practice in 1993 and died of cardiac arrest, is widely remembered as a sad example of this.

In Florida, about a half-dozen athletes each year are stricken; nationwide, the numbers are disputed, perhaps in the 800-900 range. But less important than the actual numbers, however, are the implications, says Dr. Robert J. Myerburg, a professor of cardiology at University of Miami’s School of Medicine, who has been researching the issue of sudden cardiac death for years. “There’s a lot to be gained in terms of the years ahead for young athletes,’’ he says.

Indeed, “the possibility of finding an irregularity is rare, but if it is not detected, the consequences can be catastrophic,” said Dr. Theodore Abraham, associate professor at the Johns Hopkins University School of Medicine’s Heart and Vascular Institute, after a study done in 2009.

Myerburg and others emphasize the need for prevention – especially in athletes ages 13-18, who are at even higher risk than the more mature 18-25-year-olds. That’s because with age, the higher risk kids disappear from the numbers who are screened.

Screening and tests such as electrocardiograms (EKGs) are often performed for athletes at the college level, he says, “but I believe they are more important starting in high school, since the type of genetic condition that causes sudden cardiac death worsens after puberty.” A little more than a third sudden cardiac deaths in athletes are caused by a genetic condition known as hypertrophic cardiomyopathy, a disease in which the muscle of the heart is thickened without any obvious cause.

“There are medications that can improve the condition,” says Myerburg, “but these persons must not participate in competitive sports.” There are other conditions that may also contribute to an athlete’s sudden death – coronary artery anomalies (or malformation of coronary vessels), for example, which are congenital abnormalities in the anatomy of the heart. They are sometimes found in combination with other congenital heart defects.

He notes it’s customary for students interested in taking part in a competive sport to submit to a physical exam, and to fill out a medical form that might turn up signs of cardiac trouble. Questions typically asked are whether a player has had chest pain, dizziness or breathing troubles while exercising. Medical professionals also consider an athlete’s family history when assessing risk factors, especially if someone closely related has died prematurely of a heart condition, or while exercising.

If a student has any of these factors, answers yes to any of these, a red flag is raised and an EKG would be justified, says Myerburg.

In addition, Myerburg favors increased use of the EKG, and in some non-routine cases, an echocardiogram (ECHO) or a stress test. . He especially recommends them for anyone interested in playing football and basketball; for reasons not fully understood, most cases of sudden cardiac deaths occur in those two sports.

Myerburg notes that the International Olympic Committee, Japan and much of Europe require pre-participation screening. But in the United States, “these tests are not mandatory, perhaps for economic reasons.’’

On the playing fields, it’s common to have an automated external defibrillator or AED, on hand; it’s a portable electronic device that diagnoses the potentially life threatening cardiac arrhythmias of ventricular fibrillation and ventricular tachycardia in a patient. Defibrillation – the application of electrical therapy that stops the arrhythmia – allows the heart to reestablish an effective rhythm.

“But help must arrive three or four minutes after the episode, in addition to the AED, or the person can die,” Myerburg says, emphasizing the need to apply preventive measures.