When former President Bill Clinton was diagnosed with heart disease and underwent a quadruple bypass operation to clear his blocked heart arteries in 2004, some Americans panicked and opted to undergo all sorts of tests to find out if they, too, had heart disease.
This hysteria -- and call to arms -- has been dubbed the "Bill Clinton Effect." More than two years after he underwent surgery, cardiologists now have even better high-tech tests enabling them to diagnose heart disease earlier -- with pinpoint precision. And more tests are being investigated.
"Ten to 15 years ago, industry and academia alike identified cardiovascular disease [CVD] as a disease to be tackled," says Stanley l. Hazen, MD, PhD. Hazen is section head of preventive cardiology and cardiac rehabilitation at The Cleveland Clinic in Ohio. "The boon of this research has yet to be materialized, but there are an extensive number of compounds and screening methods in the pike that look promising and attractive."
From blood tests to advances in imaging, here are a few highlights in heart disease detection.
When you ask your doctor if you have heart disease, he assesses the likelihood based on risk factors. Some key risk factors are age, smoking, diabetes, being male, high blood pressure, and cholesterol. But studies have shown that almost half of the people who suffer coronary events have only two risk factors: being male and over 65. So it is very exciting when new tests come along that can help identify people before they have an event such as a heart attack.
In terms of blood markers, Hazen says that "the mainstay for assessing heart disease risk is low density lipoprotein ['bad'] cholesterol testing". But while we know that LDL plays a major role in determining heart disease, the relationship between severity and the timing of the disease is "incredibly poor. There is much room for improvement," says Hazen.
Checking for C-Reactive Protein
In terms of blood-based screening tests, doctors are increasingly looking at levels of C-reactive protein (CRP), which is an inflammatory marker found in the blood. Several studies have shown that increased concentrations of CRP appear to be associated with increased risk for coronary heart disease, sudden death, and peripheral arterial disease. Inflammation is increasingly being viewed as a major risk factor for heart disease.
"This test is recommended by the American Heart Association and the federal Centers for Disease Control and Prevention," Hazen says. "If it's used as a routine screen in intermediate-risk subjects, it's an even stronger predictor of cardiovascular disease risk than LDL," he tells WebMD. While CRP levels are not specific to the heart, "in terms of risk prediction, it's equal to or better than cholesterol," he says. "More and more we will be seeing an increase in the use of CRP as an adjunct to risk stratification."
Testing for MPO
Another key blood-based marker that may be available soon is myeloperoxidase (MPO). This is an enzyme in white blood cells that is linked to inflammation and CVD. Research has shown that an elevated blood level of MPO predicts the early risk of heart attack. MPO has been shown to be helpful in deciding if a patient's pain is related to heart disease.
Hazen says that "MPO looks like a great addition to risk screening in people who come to the hospital complaining of chest pain. And it seems to be a marker for vulnerable plaque." Vulnerable plaque refers to areas of thickening in the walls of arteries that are most likely to rupture and cause a heart attack or stroke.
A Glimpse of the Future
But in the future, blood tests may incorporate more than one marker in the hopes of creating a unique fingerprint of individual risk.
Gazing into his crystal ball, Hazen tells WebMD that "there won't be one single test in the future, but a blood-based array or panel to give the individual a snapshot of their long-term and near-term risks as well as which risks need to be worked on to help guide doctors in terms of where to focus risk-reduction efforts."
Aside from blood-based tests, improved imaging devices also hold enormous promise in screening for heart disease.
Traditionally, as with Clinton, doctors would use an angiogram to detect blockages in heart arteries. During a coronary angiogram, a thin, flexible tube called a catheter is inserted in a blood vessel, usually in the groin, and guided toward the heart. Then a dye is injected into the blood vessel to make it more visible on an X-ray. Complications are rare but can include stroke, damage to the arteries, or internal bleeding.
And these are some of the reasons that there is so much enthusiasm for the 64-slice computerized tomography (CT) scan. With this test, doctors can determine if there is calcium buildup in the heart arteries. While older multislice CT scans only allowed visualization of smaller parts of the heart, the 64-slice CT lets doctors visualize more. And computer processing yields a three-dimensional image of the arteries. This procedure eliminates the risk and discomfort associated with traditional angiograms, but there are the usual risks associated with exposure to X-radiation.
"The CT scan provides remarkably sharp images," Hazen says "The use of cardiac CT is going to explode. The images are spectacular."
Hazen isn't alone in his enthusiasm for this test. "The 64-slice CT scan is the most exciting new instrument we have," says Edward B. Diethrich, the founder and medical director of the Arizona Heart Institute in Phoenix. "The results we have seen in patient assessment and care are really fantastic."
Hazen does add that the 64-slice CT is not for everyone, "Data from the CT is acquired between beats so it doesn't provide as good of an image for people who are very large or who have an irregular heart rhythm or large calcifications in their arteries," he says.
Although there is no doubt that the images with the improved CT scanners are very sophisticated, there is still controversy about the significance of calcium measurements in predicting heart disease.
"The CT scan is good, but it is not as specific for heart disease because people sometimes have calcium in blood vessels and no heart disease or vice versa," says cardiologist Gerald Fletcher, MD, of the Mayo Clinic in Jacksonville, Fla. Fletcher is a spokesman for the American Heart Association.
Because of this controversy regarding calcification scores, most insurance companies do not cover the heart CT scan as a screening test. But Flectcher says "the horse is out of the barn and people are paying out of pocket for it, and it has value as a screening technique when taken with precautions."
Richard D. White, MD, the clinical director of the Center for Integrated Non-Invasive Cardiovascular Imaging at the Cleveland Clinic, also urges caution with the use of cardiac CT scans. Cholesterol screens, stress tests, and other traditional risk stratification methods "are still the backbone of understanding the propensity of a patient to develop coronary artery disease," White says. "It would be detrimental if we got so enamored with imaging that we put them completely on the back burner."
White says the CT scan is best used when doctors have a significant concern about a risk for coronary artery disease in patients who are clearly not in need of a catheterization. "A swing vote from cardiac CT would help to decide whether to commit a patient to more testing or therapy" he says.
Another test for which both White and Fletcher see a bigger role in the future is magnetic resonance imaging (MRI) of the heart. According to Fletcher, MRI is more accurate than CT scanning. Although MRI is more difficult to perform and more expensive than CT scanning, he predicts that it will have an even bigger role in the future in detecting heart disease.
Other tests available to doctors include intravascular ultrasound (IVUS), a catheter-based technique, which provides real-time, high-resolution images of the heart and its arteries. "The images are in four distinct colors to tell what kind of plaque is there," Diethrich says. "We think that it is going to be very important because plaques differ a great deal. Some cause trouble and other plaques do not."
IVUS "is very good and accurate," says Fletcher. He also envisions a growing role for magnetic resonance angiogram (MRA). MRA is a noninvasive imaging test that uses a powerful magnet and radio waves to provide detailed images of the coronary arteries in less than one hour. "It's less invasive than catheterization," he tells WebMD.
Fletcher cautions that while the new tests hold tremendous promise, they should not replace the traditional screening tests. "We know that old-fashioned cholesterol and blood pressure are important and the American public is still not properly controlling these basic things to prevent CVD," he says.
"There is no easy way," Fletcher says. "If you have high blood pressure and cholesterol and smoke or are overweight and sedentary, you need to address these risk factors before turning to new technologies," he says. "Start with the basic things and then look for your calcium score or CRP."