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- Brijeshwar Maini, MD, FACC⁎ ()
Recently, the U.S. Food and Drug Administration approved the use of a catheter-mounted near-infrared spectroscopy system (InfraReDx, Inc., Burlington, Massachusetts) for the identification of lipid core–containing coronary plaques. The readouts of chemical composition are called chemograms and lipid-rich areas are represented in yellow. The chemograms are presented as if the coronary vessel has been split open and is presented as a ribbon. The important landmarks such as major branches are imprinted on the chemogram (as vertical lines) for precise localization of the lipid cores. The whole exercise is based on the premise that the lipid core volume is the most important determinant of vulnerability of plaque to rupture (1). Although intravascular ultrasound has proffered reasonable assessment of lipid cores by demonstration of hypoechoic zones, near-infrared spectroscopy reveals the definitive presence of lipid cores. Unlike ultrasound, it is also not affected by calcific deposits in the vessel wall. Since the recent approval of the catheter for clinical use, we have investigated all proximal coronary vessels during percutaneous interventional procedures in 3 patients in the last 3 weeks and would like to share our initial observations.
Figure 1 shows coronary chemogram from all 3 patients. First, a 69-year-old woman presented with a non-Q myocardial infarction. The chemogram indicated (Fig. 1A) a significantly obstructive lesion in the proximal (yellow box 1) and a mild lesion in the mid (yellow box 2) left anterior descending coronary artery. It also showed minimal luminal irregularity in the proximal left circumflex coronary artery (yellow box 3). Based on the chemogram, the obstructive left anterior descending lesion was not lipid-rich (Fig. 1B, 2), whereas the mild lesion showed bulky lipid core (Fig. 1B, 1). The region of luminal irregularity in the left circumflex artery also showed a large lipid core (Fig. 1C, 3). Similar to the circumflex artery of the first patient, the mid right coronary irregularity (Fig. 1D) in the second patient (88-year-old female) also showed chemographic evidence of a large lipid core (Fig. 1E, 4). Of note, the lipid cores were discrete lipid-rich lesions and no diffuse fatty distribution was seen. On the other hand, when we interrogated a saphenous vein graft from an 85-year old female, multiple lipid-rich areas (Fig. 1G, 5 and 6) were identified in the absence of any demonstrable luminal stenosis (Fig. 1F).
These preliminary results suggest that intravascular investigation of chemical composition of a coronary plaque has become a clinical reality. It remains to be seen whether chemograms would perform better than the ultrasound or whether they will be able to predict adverse events and facilitate development of clinically effective strategies for management of vulnerable plaques before it is too late.
- American College of Cardiology Foundation