Seeking to Prevent Sudden Cardiac Death - Brief Article

Most of us take a steady heartbeat--about 100,000 beats per day in near-perfect rhythm--for granted. Some people, though, may suddenly develop a dangerous and irregular rhythm that could cause the heart to beat wildly out of control. Identifying people with this electrical glitch that puts them at risk could allow them to receive implantable defibrillators, possibly saving thousands of lives each year.

Joseph M. Smith, associate professor of medicine and biomedical engineering, Washington University School of Medicine in St. Louis (Mo.), has invented a noninvasive test that identifies this glitch in advance of a patient's first rhythm problem. The test measures a tiny fluctuation in heartbeat called the T-wave alternans.

Most cardiac patients undergo a stress test to evaluate problems associated with insufficient blood supply to the heart--a plumbing problem. Such tests are of little value in detecting the electrical malfunctions responsible for sudden death. Studying the electrical system of the heart typically requires an invasive test in which electrode catheters are placed inside it. Just a small minority of patients with plumbing problems who also are suspected of having electrical problems go on to receive the invasive test. As a result, some people go about their daily lives without knowing they might suddenly die. In fact, one in three people who develop fatal arrhythmias have had no previous arrhythmia or symptoms of known heart conditions.

Some individuals with other types of heart disease, such as cardiomyopathy, also die suddenly, and doctors are frustrated by their inability to identify and treat such people before a first life-threatening event occurs. "Because sudden cardiac death continues to claim 250,000 people each year in the United States alone, more people at risk need to be identified and treated, especially now that we have such compelling data on the efficacy of internal defibrillators in preventing these sudden deaths," Smith notes. Automatic internal defibrillators are small devices that resemble pacemakers. They are implanted under the skin in same-day surgical procedures and correct the heart-rhythm abnormalities that otherwise would cause sudden death.

Taking the alternans test is similar to getting the standard stress test except that a patient is hooked up to a few extra leads. These additional leads help pick up subtle beat-by-beat abnormalities that are detected through computer analysis, much like a microscope picks up details that can't be seen by the naked eye. By examining the relationship between the presence of these tiny signals and a patient's heart rate, doctors can identify people at risk of developing life-threatening arrhythmias. The cost of the alternans test is similar to that of a regular stress' test.

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