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Elevated artery temps may identify patients at risk
A new procedure that measures the temperature of blood vessels may hold potential as a way to identify people at risk for an impending heart attack, a new study found.1
A simple, inexpensive test, thermography may prove useful also for diagnosing conditions such as myocarditis and aortitis, and predicting which plaque-obstructed arteries, already opened by balloon angioplasty, have a high risk of narrowing again. Thermography could also monitor the effects of antibiotics or other drugs.
The investigators used a tiny thermometer attached to the tip of a catheter to measure the temperature at selected sites on the interior lining of the coronary arteries of 90 people, of whom half were without disease and half had atherosclerosis. The researchers divided the heart-disease patients into three groups: 15 with stable angina, 15 with unstable angina, and 15 who had experienced a heart attack.
Five readings were taken at sites along a section of healthy artery wall. Another five were taken at sites on the plaque in the patients with atherosclerotic arteries. Among 45 disease-free people, the temperature was steady throughout the coronary artery — an average of 0.65° C above oral temperature. Among the 45 with hardening of the arteries, plaque temperatures were lowest in the stable-angina group and highest in the heart-attack group.
The temperature difference between plaque and healthy vessel wall was progressively greater in patients with more severe clinical conditions. The average difference was:
— 0.106° C among patients with stable angina;
— 0.683° C among patients with unstable angina;
— 1.472° C among infarction patients.
No correlation was found between the amount of narrowing in blood vessels and plaque temperature. "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," wrote the lead author.
Because it can identify vulnerable plaque — that is, plaque that may rupture and cause a heart attack — thermography can be used to help predict which individuals are most likely to have a heart attack, commented Valentin Fuster, MD, president of the American Heart Association: "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."
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, they reasoned, could provide an easy method to detect infections or inflammation.
Levels of C-reactive protein, a strong indication of infection, increased as the plaque temperatures rose, supporting the theory that temperature elevation is due to acute inflammation.
"According to the theory of inflammation as a factor in the development of atherosclerosis, local increase of temperature could be detected in plaques," the lead author wrote. "Our finding supports, but does not prove, the theory that bacterial infection is a factor contributing to atherosclerotic plaque development."
1. Stefanadis C, Diamantopoulos L, Vlachopoulos C, et al. Thermal heterogeneity within human atherosclerotic coronary arteries detected in vivo: A new method of detection by application of a special thermography catheter. Circulation 1999; 99:1,965-1,971.