Heart disease can be a silent killer. For hundreds of thousands of people every year, the first sign is a sudden heart attack or even death.
This dismal statistic has spurred the search for more reliable ways to identify heart disease earlier. Proponents of a relatively new cardiac scan, which has been widely touted in television and radio spots, say it can be an accurate forecaster of whether someone is headed for a heart attack.
The scan, officially known as electron beam computerized tomography, is an ultra-fast imaging procedure (similar to a CT scan) that measures calcium deposits in the arteries of the heart.
Calcium deposits are an early indicator that fatty plaque is building up in arterial walls; such plaque restricts blood flow and can break loose, causing a heart attack or stroke. Although the presence of fatty plaque doesn't guarantee a heart attack, "each step up in calcium is associated with an increased mortality rate," says Dr. Daniel S. Berman, a cardiologist at Cedars-Sinai Medical Center in Los Angeles.
"Since most people with coronary artery disease don't have heart attacks, you have to follow a large group of patients for several years before you can demonstrate that calcium is bad for you," adds Berman, who is studying the effectiveness of the scans.
Although many doctors doubt the scans can accurately spot heart disease, much less save the thousands of lives supporters claim, some research indicates they may work.
The need for accurate screening tests is crucial. Heart disease kills more than 500,000 Americans each year, but a third of people with heart disease don't have any of the traditional risk factors, such as diabetes, high blood pressure, high cholesterol, a smoking habit or a family history of heart disease.
"We don't know the precise reasons why an individual patient gets blocked arteries," says Dr. P.K. Shah, director of cardiology at Cedars-Sinai. "We know risk factors predispose people. But some people who have them will get heart disease, while others won't. So how do we better identify the people who are going to get into trouble?"
In one 2003 study, 10,377 people at above-average risk for heart disease but who had no symptoms were tested for calcium in their arteries. Despite the presence of such known cardiac risk factors, "the strongest predictor of death was the coronary artery calcium," says Berman, a study coauthor.
In another 2003 study conducted at the University of Illinois College of Medicine in Chicago, 5,635 men and women with no symptoms of heart disease were given the scans. Three-and-a-half years later, 224 of the volunteers had required bypass surgery or angioplasty to open up clogged heart arteries, had suffered a heart attack or had died. High amounts of calcium deposits had been detected in 95% of those who had such an event; low amounts of calcium had been detected in 67% of those who did not. The more calcium, the greater the risk, and the worst the prognosis, according to the researchers.
Because these patients had cardiac risk factors, however, the results may not be representative of the general population. A study underway at Cedars-Sinai may help determine not only whether the scans are useful for everyone but also whether the results can improve patient compliance to preventive measures. Anecdotally, doctors have found that scans often motivate people to alter diets, exercise more and take cholesterol-lowering drugs. "When a scan shows they have extensive calcification, many recalcitrant patients get religion immediately," says Shah.
The study, which began in 2001 and is scheduled to run two more years, involves 2,250 men ages 45 to 80 and women ages 55 to 80 with no cardiac symptoms or evidence of heart disease. Volunteers are given a scan, and counseling on how to reduce risk factors.
"We have such great therapies now that we can reduce heart attacks and strokes by 75%," says Berman, the lead investigator for this study. "And the earlier we can pick up the disease, the better we're able to treat it."
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Several tests are used to detect heart disease, but none of them is foolproof and they're usually given only to people with known risk factors.
The most common is the electrocardiogram, or ECG, in which electrodes are attached to the patient's arms, legs and chest to measure the electrical impulses generated by the heart. An ECG can determine whether there is coronary artery disease, whether the heart muscle has become abnormally thickened, or whether there are problems with how these electrical impulses are controlling the heart rate or heart rhythm.
Because some forms of cardiac disease can be missed when a patient is resting, doctors can perform a test in which a patient's heart is stressed by exercise -- either by walking on a treadmill or pedaling a stationary bike. If the arteries are partially blocked, the increased exertion will reduce the blood supply to the heart muscle, often triggering chest pain and changes in the heart rhythm or blood pressure.
An echocardiogram, which can detect changes in the heart muscle during exercise, also may be performed in conjunction with a stress test.