Stress Test Still First Choice in Detecting Heart Disease Risks

When a celebrity falls ill, it often triggers a wave of concern from those who fear they suffer the same ailment. Thus, when former President Bill Clinton was hospitalized for heart surgery just before Labor Day, hospitals around the country reported receiving a surge in calls from middle-aged people, primarily men, worried that they, too, might be cardiological time bombs.

Clinton - relatively young, generally healthy, physically active and recently slimmed-down - experienced the classic coronary symptoms of chest pressure, which he initially thought were due to heartburn. When the pain persisted, however, he went to the hospital. Tests confirmed that four of the arteries leading to his heart were dangerously clogged, putting him at risk for an imminent heart attack. Within a few days he underwent a quadruple bypass - surgery that replaces the clogged coronary arteries with healthy blood vessels harvested from elsewhere in the body.

Clinton's experience became "a teaching point" about the options for preventing coronary artery disease, or CAD, and the tests for detecting patients' risks, says Michael P. Cinquegrani, MD, Professor and Associate Chief of Cardiovascular Medicine at the Medical College of Wisconsin. "Patients who think they might be at risk for developing heart disease should be checked out," he says.

As President, Clinton had had regular physical exams, including blood tests that found he had elevated cholesterol levels. To normalize his cholesterol, he was prescribed a type of cholesterol-lowering drug called a statin, and advised to lose some weight. He admitted he took the prescription medicine for a while, but had discontinued the drug after he changed to a more healthful diet following years of eating high-fat, fast-food meals like cheeseburgers and french fries. From his hospital bed while awaiting surgery, Clinton told an interviewer that he had always "aced" the cardiac stress tests that were part of his regular physicals.

An Unpredictable Disease
"That's not unusual," Dr. Cinquegrani says. "Coronary artery disease can be highly unpredictable. Some patients might have arterial plaque that is not yet blocking blood flow." With CAD, the coronary arteries - the blood vessels that supply oxygen-rich blood to the heart muscle - develop a build-up of cholesterol (called plaque), and other fatty deposits. This condition is called atherosclerosis, sometimes referred to as "hardening of the arteries."

"If plaque ruptures, a blood clot can form, which obstructs the blood vessel," says Dr. Cinquegrani. "It could cause a heart attack or stroke. "A stress test is a snapshot," he explains. "It shows the condition of the patient when the test is performed. Many patients have plaque that is not yet blocking blood flow. That can change overnight if the plaque breaks open and blocks the artery."

When a Stress Test Is Ordered
Who's at increased risk for heart disease? "One risk factor is a genetic predisposition," says Dr. Cinquegrani. "If it runs in the family, you are at higher risk than the overall population. And the risk increases with age. Obviously, you can't change your genetic heritage or your age, but you can greatly lessen your risk by modifying other major risk factors. You can stop smoking. If tests show you have high blood pressure or high cholesterol, you can take prescribed medications. If you are overweight (and many Americans are), you can lose weight. By losing weight you can reduce the severity of high blood pressure, diabetes and high cholesterol. It could save your life."

"If a patient experiences typical symptoms like chest discomfort or finds himself or herself short of breath or unable to do daily activities without breathing heavily, that patient is a good candidate for a stress test," Dr. Cinquegrani says. Stress tests are the standard test for detecting the presence of blockages in the coronary arteries. They might also be ordered for patients thought to be at risk for heart disease before they embark on an exercise regimen.

Treadmill Test Most Common
In the most common and least expensive type of stress test, the patient walks on a treadmill or pedals a stationary bicycle while attached to an electrocardiograph (ECG) machine, and a blood pressure cuff is placed on one arm. Sometimes a finger sensor is also used to measure the amount of oxygen in the blood. This type of test may be routinely used as part of an annual physical examination.

After a baseline ECG is obtained, the patient begins to perform a low level of exercise. Then, every few minutes, the level of exercise is increased. At each stage of exercise, the pulse, blood pressure and ECG are recorded, along with any symptoms the patient may be experiencing.

An exercise stress test on a treadmill can reveal considerable information and is less expensive than other tests, Dr. Cinquegrani says. In a patient with risk factors for CAD, an abnormal stress test can predict whether significant CAD is present. In a low-risk patient, a normal stress test result can indicate the absence of significant CAD.

Other Types of Stress Tests
When the doctor determines that the results do not accurately reflect the presence or absence of significant CAD, however, other types of tests might be ordered - selectively, Dr. Cinquegrani says. These include an ultrasound of the heart (stress echocardiography) and stress tests in which a radioactive isotope is injected into a vein during exercise.

In stress echocardiography, sound waves produce enhanced images of the heart and its major pumping chamber at rest and at the peak of exercise. This test can exclude the presence of significant CAD in patients suspected of having a "false-positive" result.

In the stress test using a radioactive isotope, the injected material collects in the parts of the heart with good blood flow, which are scanned with nuclear imaging. The resulting pictures can show which portions of the heart might be deprived of optimum blood flow. The entire procedure can take several hours.

For patients who have difficulty walking or riding a bike, a medication can be given to stimulate the heart to work as if the patient were exercising, and results are viewed on an echocardiogram while the patient is lying down. One of these medications is dobutamine, which is similar to adrenaline. Dobutamine is carefully administered to gradually increase the heart rate and strength of the contractions of the heart muscle. Alternatively, a medicine called adenosine is administered, which simulates coronary artery circulation during exercise. With adenosine, nuclear isotope imaging is used.

Many doctors commonly order this type of stress testing for patients who are scheduled for major non-cardiac surgical procedures and are thought to be at high risk for significant CAD, Dr. Cinquegrani says.

Cardiac Catheterization or Angiogram
A test long considered the "gold standard" for detecting CAD is the cardiac catheterization, or angiogram. This diagnostic test is expensive and invasive. The patient is lightly sedated and a catheter inserted into the groin. An X-ray machine is used to help the cardiologist guide the catheter into proper position. Dye is injected through the catheter, and pictures are taken as the dye travels through the arteries to the coronary arteries. Images are projected onto a TV or video screen so that the doctor can view the heart and its arteries during the test.

In some cases, if a blockage is detected, it can be corrected during the exam with a procedure called an angioplasty, in which a balloon catheter is inserted to clear the blockage. A coronary stent is often placed during the same procedure. In other cases with more extensive blockages, the patient is advised to undergo bypass surgery, as Clinton was.

In recent years, other tests have come into vogue, such as ultrafast CT scans of the heart. Such tests may be useful in some patients, Dr. Cinquegrani says.

"While there are many tests that can be done, the most important evaluation is a careful history taken by a physician. The bottom line is, patients should consult their physicians if they have concerns about their coronary arteries. Early diagnosis and treatment may prevent a life-threatening heart attack," he adds.

Barbara Abel
HealthLink Contributing Writer

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.