DALLAS, April 20 -- Thermography, which measures the temperature of the blood vessels, may hold potential as a new tool to identify individuals at risk for an impending heart attack, according to a report in today's Circulation: Journal of the American Heart Association.
In the study, scientists measured the temperature at selected sites on the interior lining of the coronary arteries of 90 people. They used a tiny thermometer attached to the tip of a catheter. Temperature variations were not detected in people free of atherosclerosis, the fat-laden plaque obstructions in the arteries.
Other researchers had previously found temperature elevations in tissue from carotid arteries, which carry blood to the brain, says Christodoulos Stefanadis, M.D., lead author of the study.
"This is the first time, however, that temperature has been measured in the heart or coronary arteries of living humans," says Stefanadis, associate professor of cardiology at the University of Athens and director of the cardiac catheterization laboratory and coronary care unit at Hippokration Hospital in Athens.
Heart attacks most frequently occur when a fat-laden deposit, known as a plaque, ruptures and triggers the formation of blood clots that block the flow of blood to the heart. Similarly, plaque ruptures in the artery that carries blood to the brain can cause strokes.
Because temperature was measured before the heart attacks occurred, the study suggests that increased temperature may precede the rupture.
According to Valentin Fuster, M.D., Ph.D., president of the American Heart Association, "Techniques such as thermography that can identify the vulnerable plaque -- one that may rupture and cause a heart attack -- may be used in the future as a way to help physicians predict which individuals are most likely to have a heart attack. The technology fits into a growing number of methods -- invasive and noninvasive -- being developed that are based on the new knowledge that plaque rupture is one of the major triggers of a heart attack."
Other similar methods are intravascular ultrasound and magnetic resonance imaging.
Measuring the heart's temperature might also prove useful for diagnosing conditions such as myocarditis, an inflammation of the heart muscle, and aortitis, an inflammation of the large artery that carries blood away from the heart, the researchers suggest. The technique also might be useful for predicting which plaque-obstructed arteries, already opened by balloon angioplasty, have a high risk of narrowing again. A heart thermometer could also be used to monitor the effects of antibiotics or other drugs.
The researchers undertook the study because of growing evidence that bacterial infections and inflammation may play a significant role in the development of atherosclerosis. Temperature elevations could provide an easy method to detect infections or inflammation.
"According to the theory of inflammation as a factor in the development of atherosclerosis, local increase of temperature could be detected in plaques," Stefanadis says. "Our finding supports, but does not prove, the theory that bacterial infection is a factor contributing to atherosclerotic plaque development."
The study involved 90 patients who underwent catheter examinations of their heart arteries. Forty-five were examined because of heart-valve problems or chest pain, but were found to be free of atherosclerosis. They served as the study's control group.
Fifteen patients had stable angina, or chest pain caused by the build up of plaques that reduce blood flow to the heart; 15 had unstable angina, in which attacks of chest pain progressively increase in intensity and cannot be reduced by drugs; and 15 had suffered a heart attack and were examined no later than six hours after the onset of chest pain.
Five temperature readings were taken at sites along a section of healthy artery wall. In people with atherosclerotic arteries, the researchers also took five readings at sites on the plaque.
Temperatures were essentially the same wherever measured in the artery walls of people free of heart disease -- an average of 0.65° F above the oral temperature. In patients with stable angina, unstable angina, and an acute heart attack, the temperatures of their plaques were consistently higher than the uniform temperatures of their healthy artery walls.
The temperature differences between healthy and atherosclerotic arteries increased with the seriousness of the diagnosis. The plaques of patients with stable angina averaged 0.190° F above the temperature in their unaffected, healthy arteries. The average temperature increase for those with unstable angina was 1.23° F and 2.65° F for people who had just suffered a heart attack.
Moreover, the plaques themselves showed temperature variations at the five sites measured. The greatest difference in site-to-site plaque temperatures occurred among the heart attack patients, followed by those with unstable angina and those with stable angina.
No correlation was found between the amount of narrowing in the blood vessels and the temperature of the plaques. "This explains the observation that the internal diameter of the blood vessel is not critical -- both wide and narrow blood vessels could lead to acute heart attacks," Stefanadis says. "Therefore, the detection of temperature provides useful information in all areas of the blood vessel."
Levels of C-reactive protein, a strong indication of infection, increased as the plaque temperatures rose. "The correlation between C-reactive protein and increased temperature in coronary plaques supports the theory that temperature is due to acute inflammation," Stefanadis says.
Co-authors are Leonidas Diamantopoulos, M.D.; Charalambos Vlachopoulos, M.D.; Eleftherios Tsiamis, M.D.; John Dernellis, M.D.; Konstantinos Toutouzas, M.D.; Elli Stefanadi, M.S.; and Pavlos Toutouzas, M.D.
Materials provided by American Heart Association. Note: Content may be edited for style and length.
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