Intravascular ultrasound (IVUS), fractional flow reserve (FFR) and optical coherence tomography (OCT) are tools that may be used in a complementary manner and could enhance PCI and patient outcomes. Yet, penetration remains spotty, even in larger facilities.
PROSPECTs of IVUS & FFR
The groundbreaking PROSPECT trial in 2009 found that IVUS, compared with catheter angiography, identified invasive markers of plaque characteristics that may predict future cardiovascular events in patients with acute coronary syndrome (New Engl J Med 2011;364:226-235). Within PROSPECT, researchers evaluated the use of virtual histology (VH)-IVUS imaging, a tool that uses an algorithm to create a colorized picture of plaque to help classify and detect fibrous plaque, fibrofatty plaque, necrotic core and dense calcium.
Lesions identified by VH-IVUS, particularly thin-cap fibroatheromas, were significant predictors of major adverse cardiovascular events. "These plaques would have looked equal on the angiogram and we now have learned that virtual histology is a very positive predictive tool," says Michael C. Foster, MD, a clinical assistant professor of medicine at the University of South Carolina School of Medicine in Columbia, S.C.
|Optical Coherence Tomography (OCT) Helps with Stent Implantation|
Other studies have shown that IVUS can help provide better stent selection, better visualization of plaque and a more accurate determination of occluded vessels compared with angiography. It also can help reduce restenosis rates by providing a more accurate measurement of lumen diameter, plaque area and volume and can ensure proper stent implantation and expansion, says Foster.
But the tool does have confines. "While IVUS is used to assess vessel dimensions and stent implantation, as well as anatomical complications of PCI, it should not be used for lesion assessment in advance of decision making. That is where FFR is needed," says Morton J. Kern, MD, chief of cardiology at the Long Beach VA Healthcare System in Long Beach, Calif.
FFR is used "for any decision point prior to stent implantation in which the operator is uncertain about the significance of a lesion. This applies to all patients with coronary artery disease, post-CABG and post-MI in acute coronary syndromes after stabilization," says Kern.
When Nam et al compared the use of FFR with IVUS to assess intermediate lesions prior to PCI, they found that interventionalists performed fewer PCIs in the FFR arm compared with the IVUS arm (33.7 vs. 91.5 percent) (J Am Coll Cardiol Intv 2010;3:812-17).
Additionally, FAME investigators reported lower rates of death, MI, CABG or repeat-PCI at one year in the FFR group compared with the angiography-guided group (13.2 vs. 18.4 percent). Length of stay and average cost also were lower in the FFR group (3.7 vs. 3.4 days and $5,332 vs. $6,007).
OCT enters the stage
While FFR assesses a lesion's hemodynamic significance and IVUS enhances stent placement, what is OCT's role in the imaging mix? Marco Costa, MD, PhD, director of the Heart & Vascular Institute at University Hospitals Case Medical Center in Cleveland, argues that OCT, with more data, could surpass the use of IVUS in the cath lab.
In fact, a September 2010 report put forth by the Millennium Research Group speculated that as data accumulate and physician adoption increases, the OCT market could grow at an annual rate of almost 60 percent through 2015.
OCT provides a resolution that is greater than IVUS—10 to 15 µm axial resolution and 20 to 25 µm lateral and out-of-plane resolutions—and uses near-infrared light rather than sound to obtain images in only three to five seconds. In comparison, IVUS images are acquired within two to four minutes, says Costa. And, similar to IVUS, OCT is used during a procedure to guide stent selection and can be used post-stenting to evaluate the position and deployment of a stent.
A 2002 study by Jang et al compared the ability of OCT and IVUS to assess coronary plaques, and showed that OCT identified most of the architectural features detected by IVUS and also identified fibrous caps, which can determine plaque vulnerability in lipid-rich plaques (J