|Image Source: Boston Scientific|
Washington, DC—Intravascular ultrasound (IVUS) could help physicians make treatment decisions with complex lesions that fall within the intermediate SYNTAX score range, between 23 and 32, according to Peter J. Fitzgerald, MD, who spoke here last week at the Cardiovascular Research Technologies (CRT) 2009 conference.
“We need to use imaging to look at anatomy and physiology to figure out which lesions have to be treated today and then to assess the use of those imaging tools,” said Fitzgerald, who is director of the Center for Cardiovascular Technology at Stanford University.
In Japan, where IVUS reimbursement is less restricted, the imaging technique is used in approximately 88 percent of all PCI procedures, compared to only 18 percent in the U.S., where reimbursement is minimal.
The scant use of IVUS in the U.S. is particularly troublesome because evidence shows two things: a stent that is not properly implanted or expanded leads to neointimal hyperplasia or slow healing and IVUS can help interventionalists better implant stents.
Fitzgerald said interventionalists sometimes do not optimally expand drug-eluting stents (DES) to the full size of the true luminal diameter because they think the drug will mitigate that issue. “I would argue that it won’t,” he said.
There are data beginning to emerge, he said, that correlate the long-term efficacy and safety of DES to them being well expanded and well apposed into the vessel wall. DES that do not have the full maturity of endothelial coverage are particularly vulnerable for adverse events and “necessitate the long-term duration of dual-antiplatelet therapy.”
Fitzgerald showed images that demonstrated how angiography does not always clearly depict incomplete apposition, while IVUS imaging has no difficulty in this respect. Studies show that 30 percent of patients leave cath labs with incomplete stent apposition.
“These stents that are supposed to deliver a drug to the vessel wall are not well positioned and are potentially vulnerable to safety and efficacy issues,” he said.
Grayscale or chromo-flow IVUS can quickly identify the gap between the stent and the vessel wall during PCI. Interventionalists can correct the problem by using a larger balloon to expand the stent or by using a balloon with appropriate pressure, he said.
Fitzgerald also touted the benefits of optical coherence tomography (OCT) during PCI, which allows physicians to identify plaque composition such as lipids or fibrous tissue, important indicators of vulnerable plaque. “With IVUS, plaque composition is something we postulate, but with OCT we can actually measure it,” he said.
Fourier domain OCT, which relies on a different algorithm than conventional OCT, is faster, among other improvements and minimizes the amount of flushing required during OCT imaging to reduce interference from blood. He said this technology may be particularly helpful with percutaneous structural heart treatment, such as atrial fibrillation ablations and mitral valve repair or replacement.
“We don’t have good synchronous imaging for these percutaneous procedures and it would help to have this technology on our catheters,” Fitzgerald said.