IVUS helpful in stent placement, locating vulnerable plaque in patients
Intravascular ultrasound (IVUS) can play an important part in drug eluting stent placement as well as be a crucial tool in locating vulnerable plaques in heart patients, according to clinical data highlighted by Volcano Corp. at this week’s American Heart Association's Scientific Sessions 2006 in Chicago. The results are a summary of related clinical data which evaluate the role IVUS can play in interventional procedures.

The study looked at current IVUS applications related to optimal drug-eluting stent (DES) sizing and placement, post-DES confirmation of expansion and apposition, and the ability of Volcano's proprietary VH IVUS technology to identify plaque composition, and in turn help identify angiographically silent or intermediate lesions potentially at risk for a future coronary event.

Regarding the role played by IVUS in placement of bare-metal and drug-eluting stents, Scott Huennekens, president and CEO of Volcano Corp. stated that, "Many physicians believe that IVUS can help ensure proper stent expansion and apposition. Furthermore, using angiography alone, it is often impossible to determine where a lesion begins and ends. IVUS provides information regarding lesion morphology and location, helping physicians to more completely cover diseased tissue with stents."

Study data highlighted included:

  • Dr. William Wijns based in Aalst, Belgium, recently presented data showing that 77 percent of DES patients reporting stent thrombosis displayed incomplete stent apposition at the time of thrombosis. This compares to patients without stent thrombosis that only had a 12 percent incidence of incomplete apposition. "Based on the safety concerns of drug eluting stents with early and late stent thrombosis there are three immediate things all interventionalists should do to improve on modifiable risk factors,” Wijns said. “First is case selection that includes individualized evaluation of benefit and risk, second is optimization of implantation technique in order to reduce early stent thrombosis including the use of IVUS, and third is ensure patient compliance with dual, anti-platelet therapy."

  • Dr. Marco Costa from the University of Florida recently presented a double-blinded, prospective multi-center trial of 1,419 patients. The data demonstrate that geographic miss occurs in 66.5 percent of DES procedures using only angiographic guidance, which also correlated with higher target vessel revascularization and myocardial infarction.

  • Dr. Renu Virmani, a cardiovascular pathologist, recently presented autopsy data which identified the five primary causes of late stent thrombosis. These included discontinuation of anti-platelet therapy, stent mal-apposition, stent struts imbedded in necrotic core, hypersensitivity reaction to the implant, and ostial or bifurcation stenting.

  • Dr. Gregg Stone recently presented a clinical update on the initial 250 patients in the landmark PROSPECT natural history trial, including baseline demographic data and imaging examples. PROSPECT is a 700 patient U.S. and European study being sponsored by Abbott Vascular (formerly the vascular business of Guidant Corporation) and Volcano, and is designed to study the progression of plaque in patients suffering from acute coronary syndrome. The initial findings were presented by Stone, and concluded that three-vessel VH IVUS imaging is feasible in a clinical setting. The interim data also showed that on average, 2.5 angiographically visible but "mild" (diameter stenosis < 30 percent) lesions are left untreated, and that 16 percent of these lesions are in fact severe by quantitative coronary angiography (diameter stenosis > 50 percent), and met current guidelines for interventional or surgical intervention. By IVUS, the total number of identified lesions was 2.9 per patient in the proximal and mid-coronary tree, of which 25 percent are classified as severe by IVUS. Using VH IVUS, Stone and colleagues were able to identify lesions with presumed characteristics of vulnerable plaque in 35 percent of patients, which remain untreated as part of the PROSPECT trial design. This data (after follow-up) may allow physicians to more accurately triage intermediate lesions, and be used to assess appropriate interventional or systemic treatment for atherosclerotic disease.

  • Interim Data from the Volcano-sponsored VH Registry was presented as part of six separate abstracts correlating VH IVUS tissue characterization data to baseline patient demographics, clinical presentation, and cardiac risk factors. The initial data presented at TCT 2006 was taken from the first 990 worldwide patients (of the more than 3,000 patients currently enrolled). Some initial findings from this data demonstrated important correlations:
  • Men have more plaque volume than women;
  • Male plaque composition consists of higher fibrous and fibro-fatty content;
  • With age, the amount of dense calcium and necrotic core increases significantly, especially in women post menopause;
  • Patients with prior cardiac history, myocardial infarction, previous coronary bypass and diabetes have an increased amount of both dense calcium and necrotic core;
  • Patients with ischemia do not have an increased plaque burden, but rather a difference in composition of the plaque; and
  • A combination of aspirin and statin therapy correlated with less plaque burden, and less fibrous and fibro-fatty plaque, suggesting the effectiveness of systemic therapy may be measured by both amount and composition of plaque.