1. LipiScan IVUS Coronary Imaging System
James A Goldstein MD*, Ryan D Madder MD*, Simon R. Dixon MBChB*, Sean P Madden PhD†, Brian J Gilan MS†, Michael J Hendricks†, James E Muller MD†
*Department of Cardiovascular Medicine, William Beaumont Hospital, 3601 West 13 Mile Road, Royal Oak, Michigan 48073, USA (248) ,
† InfraReDx, Inc., 34 Third Avenue, Burlington, MA 01803, USA
(781) ,
Introduction
Clinical Use
Culprit Lesion Characterization
Implications for stent length, position, and propensity for complication
A novel catheter system combining near-infrared spectroscopy (NIRS) and intravascular ultrasound (IVUS) has recently been FDA cleared and is now commercially available. The NIRS-IVUS catheter imaging system simultaneously acquires co-registered structural and chemical information, enabling an unprecedented ability to characterize coronary artery plaques.
In two initially similar LMCA cases, both patients had moderate to severe stenoses in the proximal LAD (A and D). One had extensive LCP from the LMCA through the bifurcation and into the LAD (A), and the other had little to no LCP in the LMCA and a small LCP more distal in the LAD (D). The first case was treated with a 3.5x13mm Cypher with the proximal end landing in the middle of the large LCP (B, green arrows), and the second was treated with a 4.0x28mm Taxus covering the small LCP with generous margins (E, green arrows).
The LipiScan IVUS Coronary Imaging System consists of a console with a pullback and rotation device (PBR) (right) and a 3.2 Fr monorail NIRS-IVUS catheter (left). The console contains the laser, computer, and dual displays for operator and physician. The PBR contains detection electronics and all provisions for automated pullback at 0.5 mm/s. The catheter incorporates fiber optic light delivery and a 40 MHz ultrasound transducer.
Courtesy: Dr. Simon Dixon
William Beaumont Hospital, Royal Oak, Michigan
Courtesy: Dr. Jeffrey Zimmet
San Francisco VAMC, San Francisco, California
Pre PCI
Pre PCI A B E F A D
Post PCI
Post PCI B
Technology
6 months E
80% LMCA
100% LCX D C G
4+ Months Event Free
Near-infrared spectroscopy (NIRS) is widely used in many disciplines to identify the chemical composition of unknown substances, including lipids. Intravascular NIRS has been rigorously validated versus histology in a prospective, double-blind autopsy study and remains the only technology to obtain an FDA claim for detection of lipid core plaque (LCP) and assessment of lipid core burden index (LCBI) in the coronary arteries. NIRS alone, however, cannot provide structural measurements and must be co-registered to other structural imaging modalities such as IVUS or angiography. IVUS has been used for over 20 years to make structural assessments of the artery walls. While IVUS provides excellent information about plaque structure, the technique is not well-suited for identification of composition, such as distinction of a lipid core. Interpretation of multiple cross-sections of grayscale IVUS, or careful analysis of RF or ultrasound back-scatter can in some cases identify lipid core plaque but the technique is time-consuming, requires expert interpretation and is difficult or impossible to perform in the presence of calcification. Combining NIRS and IVUS provides the opportunity to leverage the unique strengths of both technologies. Simultaneous acquisition of both modalities of data enables a more complete characterization of plaque than would be possible with either modality alone or in sequence.
A 69 year old female presented with an anterior STEMI and underwent emergent coronary angiography demonstrating an occluded proximal LAD (A, blue arrow). After performing aspiration thrombectomy, repeat angiography showed an irregular and hazy culprit-lesion in the proximal vessel (B, yellow arrows). NIRS-IVUS imaging revealed a bulky, positively-remodeled LCP with ulceration (northeast quadrant) at the culprit site (C, yellow arrow). Nearly-circumferential LCP was present at the culprit site on the NIRS chemogram (D, yellow arrow). The proximal and distal edges of the culprit angiographic stenosis are bookmarked on the NIRS chemogram (D, green lines on chemogram) and are co-registered to the angiogram (green arrows). Angiography after stent placement is shown (E). Repeat NIRS-IVUS after intervention revealed no evidence of LCP (F) and excellent stent-strut apposition to the vessel wall (G). C
After PCI, both achieved a similar, excellent angiographic result (B and E). In the first case, a post-PCI NIRS scan was done, showing that the large LCP remained (B, chemogram). Six months later, the patient with the LCP extending into the LMCA returned with total occlusion of the LCX and 80% occlusion of the LMCA. More than four months later the patient without the LMCA LCP has yet to have a known event.
Association with Peri-procedural MI
Summary MI
No MI *
Composition of coronary artery plaques is an important feature of the coronary artery disease state, but prior imaging techniques have not been able to provide accurate, real-time, and easily obtainable plaque composition information. The presence or absence of lipid core is one of the most important composition parameters related to stenting safety and the risk of rupture of a given plaque. IVUS provides valuable information about plaque size, the structural nature of remodeling, and can help optimize stent placement and apposition. The natural combination of the two technologies shows promise for improvement of patient outcomes by informing decisions such as determination of length of artery to stent, choice of stent, intensity of medical therapy, and use of measures to prevent peri-procedural infarction. Randomized trials of PCI strategy modifications are needed to prove these hypotheses. A trial is underway to investigate the utility of a distal embolic protection device (Boston Scientific FilterWire EZ) to prevent peri-procedural MI when large LCPs are found and treated (CANARY Trial). An ongoing registry (COLOR) will determine the relationship between NIRS findings and new coronary events.
Left
High plaque burden, calcium shadowing and signal dropout by IVUS, but no lipid core plaque by NIRS
Histology confirms calcified fibrous plaque
Center
High plaque burden, calcium shadowing and signal dropout by IVUS, and substantial lipid core plaque by NIRS
Histology confirms large lipid core plaque
Right
No plaque burden by IVUS and no lipid core plaque by NIRS
Histology confirms normal vessel section
Calculation of the maximum LCBI in 4mm segments (maxLCBI4mm) provides an objective and automatable means of identifying a large lipid core plaque in an artery, which portends higher risk of peri-procedural MI. A boxplot of maxLCBI4mm grouped by occurrence of peri-procedural MI (left), and a mosaic of the 62 study chemogram intervention zones (right) are shown above. All patients had a coronary stenosis that required stenting. Chemograms from patients experiencing a peri-procedural myocardial infarction (MI) are shown to the left of the black line, and those without on the right. Chemograms with maxLCBI4mm≥500 are indicated with an asterisk.
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