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Detection of Lipid Core Coronary Plaques in Autopsy Specimens With a Novel Catheter-Based Near-Infrared Spectroscopy System

Craig M. Gardner, PhD^_*,_*, Huwei Tan, PhD^_*, Edward L. Hull, PhD^_*, Jennifer B. Lisauskas, MS^_*, Stephen T. Sum, PhD^_*, Thomas M. Meese, BS^_*, Chunsheng Jiang, PhD^_*, Sean P. Madden, PhD^_*, Jay D. Caplan, BS, MBA^_*, Allen P. Burke, MD, Renu Virmani, MD, James Goldstein, MD, James E. Muller, MD^_*

^_* InfraReDx, Inc., Burlington, Massachusetts
Division of Cardiovascular Pathology, Armed Forces Institute of Pathology, Washington, DC
CVPath Institute, Gaithersburg, Maryland
Division of Cardiology, William Beaumont Hospital, Royal Oak, Michigan

^_* Reprint requests and correspondence: Dr. Craig M. Gardner, InfraReDx, Inc., 34 Third Avenue, Burlington, Massachusetts 01803 (Email: cgardner{at}infraredx.com).

Objectives: This study sought to assess agreement between an intravascular near-infrared spectroscopy (NIRS) system and histology in coronary autopsy specimens.

Background: Lipid core plaques cannot be detected by conventional tests, yet are suspected to be the cause of most acute coronary syndromes. Near-infrared spectroscopy is widely used to determine the chemical content of substances. A NIRS system has been developed and used successfully in 99 patients.

Methods: Scanning NIRS was performed through blood in 212 coronary segments from 84 autopsy hearts. One histologic section was analyzed for every 2 mm of artery. Lipid core plaque of interest (LCP) was defined as a lipid core >60° in circumferential extent, >200-µm thick, with a mean fibrous cap thickness <450 µm. The first 33 hearts were used to develop the algorithm; the subsequent 51 validation hearts were used in a prospective, double-blind manner to evaluate the accuracy of NIRS in detecting LCP. A NIRS-derived lipid core burden index for an entire artery was also validated by comparison to histologic findings.

Results: The LCPs were present in 115 of 2,649 (4.3%) sections from the 51 validation hearts. The algorithm prospectively identified LCP with a receiver-operator characteristic area of 0.80 (95% confidence interval [CI]: 0.76 to 0.85). The lipid core burden index detected the presence or absence of any fibroatheroma with an area under the curve of 0.86 (95% CI: 0.81 to 0.91). A retrospective analysis of lipid core burden index conducted in extreme artery segments with either no or extensive fibroatheroma yielded an area under the curve of 0.96 (95% CI: 0.92 to 1.00), confirming the accuracy of spectroscopy in identifying plaques with markedly different lipid content under ideal circumstances.

Conclusions: This novel catheter-based NIRS system accurately identified lipid core plaques through blood in a prospective study in coronary autopsy specimens. It is expected that this novel capability will be of assistance in the management of patients with coronary artery disease.

Key Words: coronary artery disease • intravascular imaging • near-infrared spectroscopy • histopathology • ex vivo validation

Abbreviations and Acronyms   AUC = area under the curve   IVUS = intravascular ultrasound   LCBI = lipid core burden index   LCP = lipid core plaque of interest   NIRS = near-infrared spectroscopy   ROC = receiver-operator characteristic

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