APPENDIX

Optical coherence tomography(OCT) images were analyzed by 2 independent investigators (H.R., M.G.) blinded to the angiographic and clinical findings, using previously validated criteria for OCT plaque characterization. Any discordance between the 2 investigators was resolved by consensus reading obtained from a third investigator (G.N.) [1]. Quality assessment was the first step before OCT analysis to exclude all cross-sections with poor image quality. OCT image quality was assessed by identifying the ‘clear image frame’ (CIF). The CIF is defined as an OCT cross-sectional image frame in which the boundary between the lumen and the vessel wall is discernable along a continuous arc of at least 270o around the centre of the lumen [2].

The culprit lesion was classified as plaque rupture(PR) or intact fibrous cap (IFC).The presence of PR was identified by the presence of fibrous cap disruption with the presence of a communication between the plaque and the lumen [3].PR included also fibrous cap disruption detected over a calcified plaque characterized by protruding calcification, superficial calcium and the presence of substantive calcium proximal or distal to the lesion according to recent proposed criteria. On the other hand, IFC included smooth plaques without evidence of PR as well as both definite (presence of an attached thrombus overlying an intact and visualized plaque) and probable OCT-defined erosions defined as luminal irregularity without thrombus or thrombus without a superficial lipid or calcified plaque in the proximity of the thrombus [4].

The culprit plaques were classified into 3 main categories: (1) fibrous plaques (homogeneous high signal region), (2) lipid plaques (low signal region with diffuse border), and (3) calcified plaques (signal poor or heterogeneous regions with a sharply delineated border). When lipid was present ≥180 in any of the cross sectional images within the culprit plaque, it was considered as lipid-rich plaque. Furthermore, minimal lumen area (MLA) defined as minimal lumen area along the length of the target lesion was included in OCT imaging of the culprit lesion [5].

The fibrous cap thickness of a lipid-rich plaque was measured 3 times at its thinnest part, and the average value was calculated. A lipid-rich plaque with a fibrous cap thickness ≤65 μm was defined as thin cap fibroatheroma (TCFA) [6]. Thrombus was defined as an irregular mass ≥ 200μm protruding into the lumen (mural thrombus) or a luminal mass that is not connected to the vessel wall. Thrombi were classified into red (red blood cell -rich) thrombi, which were highly backscattering with a high attenuation (resembles blood), and white (platelet-rich) thrombi, which were homogeneous and less backscattering with low attenuation [7].The total length of the analysed vessel was calculated by counting valid OCT frames multiplied by 0.2. The length of the culprit plaque, either lipid or calcific, was assessed as the sum of the plaque longitudinal length (mm) along the imaged vessel. Moreover, the percentage of these culprit plaque was assessed as the sum of the plaque longitudinal lengths (mm) along the imaged vessel divided by the length of the entire imaged vessel (mm) and multiplied by 100. The cross-section that had the highest quadrant number and the greatest arc of calcium or lipids was recorded together with the minimal fibrous cap thickness[8].

Again, in patients with reliable OCT imaging, because red thrombi may reduce the ability to assess underlying structures because of the limited depth penetration of OCT laser light (≈1.5 mm) or the high backscattering with signal-free shadowing appearance, respectively, all OCT cross sections acquired within the coronary segment with thrombus were reviewed, one by one, for its entire longitudinal extension, for sites where vessel wall and plaque morphology could be assessed, as proposed in the expert document on OCT [8].

Patients meeting any of the following criteria during the angiographic procedure were excluded from OCT assessment:

  1. Unprotected left main coronary artery disease with ≥ 50% stenosis.
  2. Angiographic evidence of spontaneous dissection of the culprit vessel.
  3. Infarction due to stent thrombosis or at the site of a previously implanted stent (within 10 mm of the target site).
  4. Infarction lesion in a bypass grafts.
  5. No suitable anatomy for OCT (extreme tortuosity, very distal culprit lesion, and large infarct vessel > 4 mm in diameter).
  6. Thrombolysis in Myocardial Infarction (TIMI) 0-2 flow grade after thrombus aspiration.

REFERENCES

  1. Tearney GJ, Regar E, Akasaka T, et al (2012) Consensus standards for acquistion, measurement, and reporting of intravascular optical coherence tomography studies: a report from the International Working Group for Intravascular Optical Cohenernce Tomography Standardization and Validation. J Am Coll Cardiol59:1058–72.
  2. Di Vito L, Yoon JK, Kato K, et al (2014) Comprehensive overview of definitions for optical coherence tomography-based plaque and stent analyses. Coron Artery Dis25:172–85.
  3. Prati F, Guagliumi G, Mintz GS, et al (2012) Expert review document part 2. Methodology, terminology and clinical applications of optical coherence tomography for the assessment of interventional procedures. Eur Heart J33:2513–22.
  4. Jang IK, Tearney GJ, Mac Neill B, et al (2005) In vivo characterization of coronary atherosclerotic plaque by use of optical coherence tomography. Circulation 111(12):1551-5.
  5. Jia H, Abtahian F, Aguirre AD, et al (2013) In vivo diagnosis of plaque erosion and calcified nodule in patients with acute coronary syndrome by intravascular optical coherence tomography. J Am Coll Cardiol 62:1748–58.
  6. Uemura S, Ishigami KI, Soeda T, et al (2011) Thin-cap fibroatheroma and microchannel findings in optical coherence tomography correlate with subsequent progression of coronary atheromatous plaques. Eur Heart J33:78–85.
  7. Kume T, Akasaka T, Kawamoto T, et al (2006) Assessment ofcoronaryarterialthrombusbyoptical coherence tomography. Am J Cardiol97(12):1713-7.
  8. Prati F, Regar E, Mintz GS, et al (2010)Expert's OCT Review Document. Expert review document on methodology, terminology, and clinical applications of optical coherence tomography: physical principles, methodology of image acquisition, and clinical application for assessment of coronary arteries and atherosclerosis. Eur Heart J31:401–15.

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