We have already described the use of ultrasound to measure the thickness of carotid artery walls, and its value in identifying elderly people at risk of a heart attack (myocardial infarction or MI) and stroke this link . Another recent study, summarized here, looks at the possible connection between the thickness of the inner lining of the carotid artery wall and positive results on treadmill exercise testing ¹ . The results suggest that this measurement can help identify those people without symptoms who may however be at risk for coronary artery disease (CAD), without subjecting them to a stress test.

Just over 500 participants were chosen from the Baltimore Longitudinal Study of Aging. They underwent treadmill exercise testing (which included a thallium scan in some cases ) and ultrasound examination of their common carotid arteries at roughly 2-year intervals. Based on the results, they were classified into 3 categories: "no CAD", "possible CAD" (specific changes in the ECG on exercise), and "definite CAD" (these patients did not undergo exercise testing).

As might be expected, "definite CAD" subjects were older, more often male, had higher systolic pressures and higher blood glucose levels than "no CAD" subjects, with "possible CAD" subjects midway between the two.

A progressive increase in average carotid artery wall thickness was found across these groups - "no CAD": 0.52 mm, "possible CAD": 0.64 mm, and "definite CAD": 0.75 mm.

Further analyses confirmed that the artery wall thickness increased with age, blood pressure level, blood sugar and cholesterol levels - all "indicators" or risk factors for arterial disease. The most influential factors responsible for increased thickness were, in order, increasing age (strongest), "definite CAD", "possible CAD", raised blood pressure, and cholesterol levels (weakest).

The participants with a positive exercise ECG test - the "possible CAD" subjects - were divided further into two subgroups, according to whether they had a positive thallium scan or not. Increasing age was associated with increased artery wall thickness in both these subgroups, but when the readings were corrected to allow for the subjects' different ages, there were increases in average wall thickness in subjects from the different groups, as shown below:

It was interesting to see that the subjects with no symptoms but a positive exercise test together with a positive thallium scan had increased thickness of their carotid arteries to the same extent as those with obvious coronary heart disease.

The same investigators who conducted this study have previously shown that patients without symptoms of coronary disease but with a positive ECG and thallium scan have an equal risk of having a heart attack as those with obvious coronary heart disease. The results summarized here show a progressive increase in carotid artery wall thickness from "no CAD" through two grades of "possible CAD" to "definite CAD". Therefore, we can conclude that ultrasound of the carotid artery can help predict CAD. The examination is less stressful than other ways of assessing the likelihood of coronary disease, and can be used to monitor the effectiveness of steps taken to improve cardiovascular health - correct nutrition, physical exercise and appropriate medication.

Source

Increased carotid artery intima-medial thickness in asymptomatic older subjects with exercise-induced myocardial ischemia
Y. Nagai, EJ. Metter, CJ. Earley, Circulation, 1998, vol. 98, pp. 1504--1509

Footnotes

1.

Increased carotid artery intima-medial thickness in asymptomatic
older subjects with exercise-induced myocardial ischemia.
Y. Nagai, EJ. Metter, CJ. Earley,  et al., Circulation, 1998, vol. 98, pp. 1504--1509