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Heart Disease Screening: Is New Technology Better?
Most of us associate
heart disease
with the symptoms of chest pain, breathing difficulties and an irregular heartbeat. We assume that if our hearts were having difficulty, we’d know it. Yet, 50% of men and 64% of women who die suddenly of coronary heart disease experience no previous symptoms. Current screening for heart disease is targeted towards individuals with symptoms or known risk factors. Recent studies are raising the question of whether alternative heart screening can and should be used to identify those at risk but who show no outward symptoms of the disease.
Traditional Screening
There are many ways to screen for heart disease, from very simple to more complicated methods. Depending on the reason for testing, whether it’s family history, elevated cholesterol levels, blood pressure problems, or particular symptoms, your doctor will decide which method is most appropriate.
The simplest screening method is a physical exam, complete with review of medical history and perhaps an electrocardiogram (EKG) . An EKG is a quick and easy way to look at the functioning of the heart by reading its electrical waves. This test can detect irregular heartbeats, an enlarged heart, and problems with blood flow to the heart. Electrocardiograms are extremely useful for diagnosing heart-related symptoms. They have not shown much, if any, benefit in screening for most common kinds of heart disease.
Stress Tests
For over 50 years, exercise stress tests have been used to assess the heart. This type of test, as its name implies, looks at the heart while under the added stress of exercise. The patient is asked to walk or jog on a treadmill at increasing speeds, and the heart is evaluated using the measurements of EKG, heart rate, blood pressure and breathing. Stress tests are used to diagnose coronary heart disease and to help determine a safe level of exercise for the individual tested.
A thallium stress test, used extensively over the past 30 years, is an exercise stress test that also introduces a radioactive substance called thallium into the bloodstream. As the thallium works its way through the heart, a special camera takes pictures of how well the heart is being supplied with blood. Pictures are taken right after the exercise test, and again after resting. Thallium stress tests are used to diagnose the extent of coronary blockage, causes of chest pain, and how well a patient is doing after a heart attack. In recent years thallium tests have probably been less frequently used than stress echocardiograms. A stress echocardiogram accomplishes the same purpose but does not require an injection. After exercise, sound waves are used to make a photographic record of the pattern and amount of movement of the heart’s walls. This can tell doctors where there are areas that are not properly supplied with blood due to plugged arteries. For persons who cannot exercise, cardiologists have other ways to successfully perform both thallium and echocardiographic stress tests.
CT Scans
More recently, computed tomography (CT) scans have been used to evaluate the heart. The two types used are electron beam CT (EBCT) and multislice spiral CT (MSCT). Both these tests look at how much calcium has accumulated in the coronary arteries. The presence of calcium is important because it indicates that there is plaque along the coronary artery walls. Plaque buildup is dangerous because it decreases blood flow to the heart, so it increases the risk for heart attack and stroke.
While stress tests and CT scans have traditionally been used to assess the heart health of hearts of high risk people—or those with multiple risk factors, new studies have shown surprising test results for those considered low to moderate risk for heart disease.
Calcium Scores
In a study out of Cedars-Sinai Medical Center, Daniel Berman, MD and colleagues studied 1,195 patients who had no known heart disease. All patients went through stress testing and 79 were found to have abnormal blood flow to their hearts. The researchers then used CT scanning on these 79 patients in order to detect the presence of calcium in their arteries. Based on calcium scores, the researchers found that 88% of the group had an increased risk of heart attack, and 68% were considered at the highest risk for heart attack. More revealing, when the researchers scanned the remaining patients– those with normal stress test results—they found that 56% had calcium scores that put them at increased risk, and 31% had scores that placed them at the highest risk for heart attack. The study is noteworthy in that it showed that there are quite a few patients with normal stress tests who may still have extensive blockage in the coronary arteries and still be at risk of heart attack.
Other studies have documented the accuracy of electron beam CT (EBCT) scanning in comparison to other methods. In a study out of the University of Michigan, Lawrence F. Bielak, DDS, MPH and colleagues studied the accuracy of EBCT in detecting coronary artery disease. Two hundred thirteen patients were examined using a combined coronary angiography (an x-ray of the coronary arteries through the placement of a catheter in a vein) and EBCT, while 765 participants were examined using EBCT only. When the researchers looked at the calcium scores, they concluded that the EBCT was highly indicative of the presence of coronary artery disease. Specifically, a calcium score of 200 or greater among those 50 years old or older, and a score of 100 or greater among those younger than 50, showed “strong evidence” of obstructive coronary artery disease.
Another study compared exercise testing and EBCT scanning. David M. Shavelle MD and colleagues studied 97 patients who underwent stress testing with an imaging agent, treadmill EKG testing, and an EBCT scan to evaluate chest pain. The results showed a higher risk for coronary artery disease among those with an abnormal EBCT scan than those with abnormality in other tests. The researchers concluded that EBCT has higher sensitivity in diagnosing heart disease than the stress test or treadmill EKG test. In 2000, the American College of Cardiology and American Heart Association concluded that EBCT might be useful in some settings, but that further studies were needed before EBCT could be endorsed for screening. As of September 2006 this statement had not been revised.
The Future of Heart Disease Screening
The sooner coronary artery disease can be detected and treated, the better the outcome. Studies of EBCT and other scans are promising, yet the jury is still out on who the best candidates are for their use. Some studies suggest that individuals at intermediate risk are best served by EBCT scans. There has been considerable interest in the use of a blood test called “c reactive protein” as part of a blood panel for cardiac risk screening. While useful in some settings, this test too will require further validation before its usefulness can be established. Clearly, further study is warranted, but having one more tool in the fight against heart disease can’t help but benefit us all.
RESOURCES:
American Heart Association
http://www.americanheart.org
National Heart, Lung and Blood Institute
http://www.nhlbi.nih.gov
References:
American Heart Association. Heart Disease and Stroke Statistics, 2004 Update. Available at: http://www.americanheart.org/presenter.jhtml?identifier=1200026 . Accessed September 9, 2004.
Berman DS, Wong ND, Gransar H, et al. Relationship between stress-induced myocardial ischemia and atherosclerosis measured by coronary calcium tomography. Journal of the American College of Cardiology . 2004;44:923-930.
Bielak LF, Rumberger JA, Sheedy PF 2nd et al. Probabilistic model for prediction of angiographically defined obstructive coronary artery disease using electron beam computed tomography calcium score strata.
Circulation.
2000;102:380-385.
Shavelle DM, Budoff MJ, LaMont DH et al. Exercise testing and electron beam computed tomography in the evaluation of coronary artery disease. Journal of the American College of Cardiology . 2000;36:32-38.
Last reviewed February 2006 by Lawrence Frisch, MD, MPH
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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