Sounding Out Vascular Ultrasound
Although vascular disease may be a new frontier for echocardiographers, it wasn’t so long ago that cardiologists and the echo lab didn’t put too much focus on the vascular system, says Emile Mohler III, MD, director of vascular medicine at the University of Pennsylvania Health System in Philadelphia and chairman of the ASE’s recently-formed Vascular Ultrasound Council. Instead, he says, they tended to focus on the heart.
A focus on the vascular system, says Mohler, was found “in vascular surgery labs in the past. But, more recently it has changed—cardiologists have expanded from the heart out to look at the carotids and even the kidney and intestinal arteries.”
This has been accompanied by new, and renewed, interest in techniques such as 3D ultrasound and contrast ultrasound. Three-dimensional ultrasound is a “sexy” technique that, according to Mohler, could be very useful in noninvasively imaging plaque carotid artery plaque.
While ultrasound contrast agents, on the other hand, have been around since the early 1990s, only recently has the technique taken on a higher profile—namely to improve the accuracy and quality of scans.
Stephen Feinstein, professor of medicine and director of echocardiography at Rush University Medical Center in Chicago, is bullish on the role contrast can play in carotid ultrasound. According to Feinstein, it is helpful in monitoring carotid plaque and preventing cardiovascular disease, heart attack, and stroke, particularly when it comes to delineating intimal medial thickness—a measurement of the thickness of the artery walls that can help detect and measure the progression of atherosclerosis—and identifying the structure and composition of plaque.
So, like many in the field of echocardiography, Feinstein was dismayed when, in 2007, the U.S. FDA required the makers of ultrasound contrast agents to include a black box warning on the products’ labels following reports of deaths after the use of ultrasound contrast agents.
Although the FDA’s action “certainly had a chilling effect” on the contrast ultrasound, says Feinstein, there has been “a tremendous grassroots response,” in defense of the technique.
“A polyglot of papers has come out,” says Feinstein, specifically pointing to a study by Mustafa Kurt, MD, and his colleagues at the Methodist DeBakey Heart & Vascular Center Imaging Institute in Houston (Journal of the American College of Cardiology, March 2009, Vol. 53, pp. 802-810). The researchers concluded that the appropriate use of contrast ultrasound results in improved endocardial visualization, which positively affects diagnostic efficiency, resource utilization and can result in critical changes in patient management.
“It is spectacular,” says Feinstein, referring to the JACC study. “The data show that contrast ultrasound improves image quality, and that the failure to use it may cause patients more harm through receiving an incorrect diagnosis, undergoing more tests, and experiencing worse outcomes.”
Although the FDA modified its black box warning in 2008, several contraindications remain, such as those related to the use of contrast ultrasound on patients with pulmonary hypertension or unstable cardiopulmonary conditions. And Feinstein and his
colleagues, whether through research papers or forums such as the International Contrast Ultrasound Society, are continuing their lobbying efforts for a technique that, he says, “saves money, reduces risk, and makes a better diagnosis.”
And while he could have done without the controversy, he does see something positive coming out of the FDA’s action.
“You know, it actually makes for a pretty nice story,” says Feinstein. “When all this occurred, there wasn’t too much of a focus on contrast ultrasound. It was a smaller market, people really didn’t understand contrast ultrasound, and there were only two companies marketing it. So maybe in some way this [action by the FDA] was a little fortuitous. We now have attention focused on our work, and we have the ability to put forward our data.”
Another area in which ultrasound has taken on a high profile role in carotid artery evaluation is in the detection of some lesser known diseases of the carotids, such as fibromuscular dysplasia (FMD).
FMD is a condition in which an artery has an abnormal cluster of cells growing on its wall, causing the artery to narrow. While it most commonly affects the renal arteries, the second most commonly affected artery is the carotid. FMD causes stroke, heart attack, ruptured aneurysms and is, says Moeller, “the most unknown dangerous disease of the carotids.”
Though commonly considered a rare condition, FMD is “not as rare of a disease as people think,” says Jeffrey W. Olin, DO, director of vascular medicine and a professor at The Mount Sinai School of Medicine in New York City.
The problem with diagnosis, according to Olin, is that FMD is frequently missed, “even by vascular specialists. And it’s almost uniformly missed by people performing carotid ultrasounds who don’t have extensive experience in that particular technique—they don’t even look in the area of the carotid artery that affects FMD.”
Olin says there’s a “mistaken belief” that the only area of the carotid artery that needs to be imaged is the carotid bifurcation—the area where the common carotid artery divides into the internal and the external carotid. “That’s the location where atherosclerosis occurs, and that’s quite common,” says Olin. “So many people imaging the carotid artery don’t look distally enough—in the artery closest to the brain—and that’s where FMD occurs.” An echocardiographer who only looks at the bifurcation is going to miss conditions—like FMD—that occur elsewhere in the carotids.
Ultrasound can be used to diagnose the condition, but the technology isn’t going to be of much use unless, Olin says, an echocardiographer is trained in the proper technique.
“But many [echocardiographers] have never been thoroughly trained in carotid ultrasound,” he says, “and they are trying to pick this up through post-graduate courses, and those courses almost uniformly talk about the most common things they’ll see. So they won’t talk about something like FMD.”
There are other conditions of the carotid that a well-trained echocardiographer should be able to detect as well, says Olin, such as Takayasu arteritis, giant cell arteritis, and carotid dissection.
“Splaying of the internal and external carotid artery may not be picked up if the clinician isn’t familiar with the disease,” says Olin. “Carotid dissection can be very subtle and needs a lot of expertise to pick up.” So, as far as diagnosing these conditions of the carotids is concerned, Olin believes, a lot has to do with training, and much has to do with the kinds of conditions clinicians are exposed to.
“I tell all my fellows that it’s just not good enough that they can image all portions of an artery,” says Olin. “They also have to know what diseases are affected within those portions. If a clinician isn’t familiar with the disease, then the often subtle findings you would see on an ultrasound will be missed.”