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New IVUS systems give three-dimensional images of the amount of plaque inside an artery. Virtual histology colors the different types on the image to more clearly differentiate them.

Cardiologists around the state are sometimes hesitantly, sometimes enthusiastically beginning to take advantage of newly improved intravascular ultrasound (IVUS) applications in their practices.

“IVUS technology has been around since the early 90s or so,” said Dr. Riley Foreman, a cardiologist with Cooper Clinic in Fort Smith, “but they used to be a lot more cumbersome and less useful.”

He said Cooper Clinic last year purchased a newer IVUS system from Volcano, Inc. Volcano and Boston Scientific are the two primary manufacturers of the technology, Foreman said.

“The technology has really evolved. In the beginning, it required bulky catheters and we had to get an ultrasound expert to run it. Now the system is not only much smaller and faster, it’s also more reliable,” said Foreman.

IVUS works by bouncing high-frequency sound waves off tissue of varying densities inside the blood vessel. A wire inserted in the catheter records the data and makes it immediately available. Mindy Hill, a registered nurse at the Medical Center of South Arkansas in El Dorado who works extensively with IVUS, said the whole process now takes a matter of seconds.

“On every case, we go ahead and program their name and all their information into the system before they get here,” she said. “If they tell us they’re going to IVUS, all we have to do is hook a catheter into the memory and press OK and we’re ready to record. It’s easy to set up, very quick to do. Sometimes it takes us 30 seconds to do a run.”

Foreman said that IVUS can be an excellent supplement to angiography for some patients. “Angiograms are still the gold standard for fixing arterial blockages,” he said. “If an artery looks normal on an angiogram, it probably is normal. IVUS, though, gets a true picture inside the artery.”

He said IVUS is particularly helpful in iffy cases.

“If you’re not sure if a blockage is important or not, the use of IVUS can really tip the scales,” Foreman said.

Dr. Tom Conley of North Little Rock has embraced IVUS wholeheartedly. Not only does he likely use it more than any other cardiologist in the state, he uses it much more than do most cardiologists in the nation.

“The average per case use of IVUS is about 10 percent nationwide. My use is over 100 percent. I do more IVUS than I do interventions,” Conley explained. “I’m IVUSing cases and finding out either a) based on the IVUS data, they don’t need  to be intervened or b) it’s much worse than previously thought and they need a stent or a bypass or something like that.”

One of the main reasons Conley is such a fan of IVUS is a benefit Foreman also cites: the intravascular images it provides give a more accurate picture of the size of the vessel, meaning stents can be sized more appropriately than with angiography alone.

“Typically, angiograms severely underestimate the caliber of the vessel,” Conley said. “You’ll look at an angiogram and estimate angiographically that it’s 2.5-3 mm in diameter, but when you go with an IVUS catheter, you’ll measure it as 4-5 mm in diameter. The very serious impact of that is that those people who don’t use IVUS are putting stents in coronaries that are too small in diameter and too short in length.”

Undersizing stents too often leads to restenosis, Foreman said. “The feedback we get from IVUS on how big to blow the stents up is invaluable,” he said.

“I think the reason that drug-eluding stents got such a bad reputation a few years ago was that we were putting in undersized stents and they were getting subacute stent thrombosis,” Conley said. “Had they used IVUS, they would do what we do and find that the vessel itself is actually quite a bit larger than the angiogram shows.”

Conley disagrees that angiography is still the gold standard, saying there is too much error built into the angiographic system to be used alone. “You don’t appreciate the caliber of the vessel or the extent of the plaque. Those of us who do a bunch of IVUS have learned that there is much more plaque in the artery apparent with IVUS than you’ll ever appreciate angiographically,” he said. “It’s not at all uncommon to see a vessel that you think is angiographically normal, and you get in there with IVUS and it’s 50 percent stenosed. Angiography is not a precise way to measure plaque burden.”

Conley said that the detailed plaque morphology available through IVUS often alters the way cardiologists treat patients. “I do a lot more intracoronary rotational atherectomy with IVUS than I would have done otherwise,” he said. “This is not a replacement for arteriography, but it certainly is in order of magnitude more sophisticated.”

Another advancement in some newer IVUS systems is virtual histology, which, when activated, translates images of the different types of plaque into four distinct colors on the IVUS monitor and printouts. Conley is more dismissive of this capability, calling it “a technology looking for an application,” but Foreman said it can be quite useful.

“Virtual histology gives a better picture of what the cellular tissue looks like,” he said. “The precise morphology can tell you if the patient is more vulnerable to a heart attack, and may end up changing treatment. If there’s a 70 percent lesion with necrotic plaque, for instance, it may make us more likely to operate.”

Moreover, Foreman said it can be an excellent tool for communicating the severity of a blockage to patients. “The visuals can make a big difference in talking with patients. It can change the decision point in some patients, whether to authorize surgery or not,” he said.

Wilkins agreed, saying, “Our patients can see a colored picture, see how big the vessel should be and can see that all this other stuff is plaque. It makes a difference to be able to see inside the vessel.”

Conley said that he proselytizes the benefits of IVUS to his colleagues in the state with limited success.

“We all feel we’re already really good at what we do, but I’ve found IVUS, especially with its recent improvements, can help make us better,” he said. “Even in my own practice, I’ve got partners who for a long time were not using IVUS, and they have become enthusiastic converts. They’re using IVUS a lot now. The data to be gleaned from this is breathtaking and your ability to do things is breathtaking. More importantly, the reassurance that you’ve done the right thing for the patient is just unparalled.”



July 2008

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