Carotid vasa vasorum imaging can show preclinical atherosclerosis risk

Noninvasive contrast ultrasound imaging of the carotid arteries can help physicians spot atherosclerosis in its early stages and lead to aggressive therapy to prevent myocardial infarctions and strokes.

“Contrast ultrasound carotid imaging is a relatively simple, safe and reliable means of assessing the progression or regression of atherosclerosis, monitoring the effectiveness of therapy, and possibly obviating the need for more invasive testing,” according to Steven B. Feinstein, MD, director of echocardiography at Rush University Medical Center in Chicago. Feinstein spoke at the American Society of Echocardiography 16th Annual Scientific Sessions.

Feinstein uses contrast ultrasound to image the carotid arteries for insights into the mechanisms at work in the development of atherosclerosis and strategies for treatment.

“One night, I was reviewing a videotape of a contrast ultrasound examination of a patient’s carotid artery,” he said. “Not only was blood flowing through the artery, it was also flowing into the carotid plaque from outside the artery walls via an external network of tiny blood vessels known as vasa vasorum.”

Feinstein said the external vasa vasorum appear to nourish the plaque, and as the microvessels within the plaque become engorged with blood they may become increasingly unstable and likely to burst, causing a clot that may trigger an MI or stroke. Accordingly, an abundance of vasa vasorum may be considered a surrogate marker of atherosclerosis.

Contrast-enhanced image of a patient undergoing a routine carotid ultrasound examination. The arrow on right outlines the carotid lumen, which appears white due to the presence of an intravenous contrast agent (Optison Tm, GE). The second arrow points to the carotid plaque, located on the near wall of the carotid artery lumen. Direct visualization of the plaque neovacularization can be identified within the plaque structure.

“Cardiologists traditionally believed that atherosclerosis is the result of fatty deposits that build up within the blood vessel,” Feinstein said. “Although pathologists had observed vasa vasorum surrounding plaque, they could only speculate about what was actually happening.

“We can now use ultrasound contrast agents to literally see blood flowing outside-in, from vasa vasorum through the artery walls and into the plaque. We can see that these blood vessels are feeding the plaque.”

Ultrasound contrast agents produce clear, real-time images of the carotid vasa vasorum. “Carotid artery imaging is a valuable tool for assessing cardiovascular risk, because atherosclerosis is a systemic disease that is not confined to any single blood vessel, and carotid arteries are easily imaged with ultrasound,” he said.

Feinstein also said that the process of nourishing atherosclerotic plaques appears to be similar to the process by which external blood vessels nourish tumors. Feinstein is the inventor of Optison, one of the commercially-available contrast agents currently used by physicians.

Studies suggest that statins can function as an antiangiogenesis agent and significantly reduce the amount of vasa vasorum, said Feinstein.

“In one pig study, CT scans showed dramatically reduced vasa vasorum in pigs that received 20 mg of simvastatin (Zocor, Merck), irrespective of their cholesterol,” he said.

Feinstein has also seen similar patterns among patients who took statins and had fewer vasa vasorum than patients who did not take statins.

For more information:

• Feinstein SB. Carotid plaque and vasa vasorum. Presented at the American Society of Echocardiography 16th Annual Scientific Sessions. June 15-18, 2005. Boston.