UAB cardiologists are the first in the United States to perform a post-market study of a new high-definition intravascular ultrasound (HD-IVUS) used for stenting cardiac arteries. IVUS has been an option for cardiologists for almost 30 years, but many physicians still routinely use angiography for placing heart stents. The new 60 MHz HD-IVUS provides higher image resolution than the conventional 40 MHz model, and UAB researchers believe it will improve outcomes for heart patients.
"This next-generation IVUS gives us the ability to assess the entire vessel wall structure, which allows us to better assess the patient's situation and to make good decisions for their care that will give us optimal results," says UAB Cardiologist Massoud Leesar, MD.
When making the decision to put a drug eluting stent in a vessel wall, a physician must measure the size of the stent needed for the procedure. "If you can see a clear image of the vessel wall, you can be more accurate in the placement of the stent. Precise implantation of coronary stents is important to prevent adverse outcomes. Under-expansion and strut malposition of a coronary stent is associated with higher incidence of restenosis and stent thrombosis," Leesar says. "Recent randomized trials of IVUS with drug eluting stents showed that IVUS-guided stenting significantly reduced the incidence of stent restenosis."
The HD-IVUS has transducers that are miniaturized to less than four-hundredths of an inch and placed on the tip of a catheter. The catheter can be slipped into the coronary arteries over the same guide wire that is used to position angioplasty balloons or stents. It becomes, in effect, a tiny camera that gives a cross-sectional view of the artery.
The other end of the catheter connects to a computer workstation that converts the sound waves from the transducer into real-time images on a monitor. IVUS uses high-frequency sound waves to provide images from inside the blood vessels. Sound waves sent from the transducer bounce off of the walls of the artery and return to the transducer as echoes. A computer converts these echoes into images on the monitor to produce pictures of the coronary arteries or other blood vessels.
The HD-IVUS provides a higher image acquisition rate and enables high-speed pullback imaging at up to 10 millimeters per second, compared to the 0.5 millimeter-per-second 40 MHz IVUS. "This new model also has the technical advantage of improved detection of lumen and vessel borders due to higher blood speckling and lower signal penetration depth within the tissue, and it can distinctly differentiate three levels of the vessel wall - the intima, media and adventitia," Leesar says. "This will allow better assessment of the vessel pathology and assessment of the stent expansion."
UAB researchers are the first to develop a protocol for using the HD-IVUS to determine which technique is best. They already know that HD-IVUS provides better image quality and can better determine the size of the stent, but they want to make sure they are using the right technique in these patients.
"We have used a special technique in some patients who receive drug eluting stents, but it is not finalized," Lessar says. "Generally, each physician chooses a technique based on intuition. That's why we are studying each technique used at UAB for placing stents. It is simple and can be done, but it has not been systematically studied."
Currently approximately 55 percent of patients are archiving an optimal stent expansion by using IVUS. On the other hand, using the new technique of stent expansion by HD-IVUS, the percentage of optimal stent expansion can be achieved in 80 to 90 percent of patients.
Leesar says this study is the first step to explore this technology and to attain approval to use it. "I'm sure other hospitals have this technology, but our aim is to take advantage of it and to use the special technique to attain optimal results," he says. "We will be able to expand this technology to improve outcomes of stenting, which is our primary goal.