February 1, 2006 Unless a patient with chest pain is checked out right away, it can be difficult to diagnose a heart condition, as opposed to less life-threatening causes such as heartburn. A new stress test can spot signs of a heart attack up to 30 hours later. Cardiologists inject patients with a radioactive fluid, which helps doctors reveal reduced blood flow to the heart using a CT scan.
BALTIMORE--You have a 50-percent chance of suffering from a heart problem, but how do you know the pain you're feeling is the real thing? Now, a new technique may help save lives and explain unexplainable chest pain, long after the pain is gone away.
Michele Lawson hopes her steady pace during a stress test will reveal why recent chest pain has gone from bad to worse. "It's been radiating down in my arm and into my hands," she tells DBIS.
The best time for diagnosing chest pain is usually right after it happens. Today, however, time is on Michele's side. A new stress test tells doctors the cause of chest pain up to 30 hours after it happens.
Vasken Dilsizian, a cardiologist at the University of Maryland Medical Center in Baltimore, says, "It opens up the window of opportunity of imaging these patients way after the chest pain has disappeared."
After the heart rate is increased, patients are injected with a new, radioactive imaging tracer. It remembers and reveals any reduced blood flow to the heart. "The whole idea of assessing these patients is to predict those who are going to have a heart attack and hopefully intervene before the heart attack occurs," Dr. Dilsizian says.
Cardiologists then use a SPECT, or single-photon emission computed tomography scan to see the tracer. The tracer helps determine non-life threatening causes of chest pain, like indigestion, while catching patients who may be in real danger.
"We don't have to guess anymore whether the chest pain the patient is experiencing is, indeed, related to the heart or not," Dr. Dilsizian says. Michele's not guessing; her scan results revealed a healthy heart.
The new imaging tracer is not yet FDA approved, but is in on-going, multi-center clinical trials for further testing.
BACKGROUND: A team of researchers has demonstrated for the first time that an experimental radioactive compound can show images of heart damage up to 30 hours after a brief interruption of blood flow and oxygen. The discovery may help ER physicians and private doctors determine whether a patient's chest pain -- which may have subsided hours earlier -- is related to heart disease or to a less serious condition, such as indigestion.
HOW IT WORKS: Nuclear medicine combines computers, detectors and radioactive substances called radioisotopes to produce images of blood flow and biochemical functions in the heart and other organs. The radioactive tracer used in this study links a fatty acid to a radioisotope that is injected into the patient. The heart normally uses fatty acid as its primary fuel source for energy. But when arteries narrow or become clogged, or when the heart works harder during strenuous exercise, less blood can flow to the heart. That can slow down or halt the way the body uses fatty acid. This condition is called myocardial ischemia and is a common cause of chest pain. The heart switches from fatty acid to glucose as an energy source in response. The new tracer test targets the signs of this disturbance and apparently remembers the imprint of an episode of reduced blood flow long after it occurs.
ABOUT RADIOISOTOPES: An isotope is a subset of a chemical element that has the same number of protons in the atomic nucleus, but a different number of neutrons. Certain combinations of protons and neutrons make the atoms unstable; these are called radioisotopes. The atoms will become stable over time by emitting gamma radiation -- a process known as radioactive decay. Certain short-lived isotopes are useful for nuclear diagnostic imaging because they can be linked to chemical compounds associated with specific physiological processes in the body. These radioactive tracers emit gamma rays from within the body, which can then be detected by a special gamma ray camera. A computer turns those signals into an image that can be viewed by a physician on a monitor to search for signs of an abnormal condition.
REDUCE YOUR RISK: Causes of chest pain can vary, from heartburn and stress, to more serious heart conditions. You can reduce your risk of the latter by following these tips. Don't smoke. Maintain a healthy weight. Eat foods low in salt and fat, but high in fiber. These include vegetables, whole grains and fruits. Exercise three or more times a week. Find ways to reduce and control stress in your life.
The American Association of Physicists in Medicine contributed to the information contained in the TV portion of this report.
Editor's Note: This article is not intended to provide medical advice, diagnosis or treatment.