Article Text

Non-invasive characterisation of coronary lesion morphology by multi-slice computed tomography: a promising new technology for risk stratification of patients with coronary artery disease
  1. STEPHEN SCHROEDER,
  2. ANDREAS F KOPP*,
  3. ANDREAS BAUMBACH,
  4. AXEL KUETTNER,
  5. CHRISTIAN GEORG*,
  6. BERND OHNESORGE,
  7. CHRISTIAN HERDEG,
  8. CLAUS D CLAUSSEN*,
  9. KARL R. KARSCH
  1. Department of Internal Medicine
  2. Division of Cardiology
  3. Eberhard-Karls-University Tuebingen
  4. Tuebingen, Germany
  5. *Department of Radiology
  6. Division of Diagnostic Radiology
  7. Eberhard-Karls-University Tuebingen
  8. Siemens AG, Medical Engineering, Computed Tomography
  9. Forchheim,Germany
  10. Bristol Heart Institute
  11. University of Bristol
  12. Bristol, UK
  1. Dr Schroeder, Medical Clinic III, University of Tuebingen, Otfried, Mueller Str. 10, 72076 Tuebingen, Germany;Dr.Schroeder{at}t-online.de

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The non-invasive detection of coronary artery disease is a prime goal for future developments in clinical cardiology. In addition to the documentation of significant stenoses, the detection of vulnerable plaques is of major importance for risk stratification and early treatment, in order to prevent plaque ruptures.1 Recently, a new generation of fast spiral computed tomography scanners has been introduced using a multi-slice technique (MSCT). This new technology allows for an almost motion free visualisation of the coronary arteries.2 3 We report on non-invasive differentiation of coronary plaque morphology by MSCT in patients with lesions in the proximal left anterior descending artery (LAD). The results were compared with the findings of intracoronary ultrasound (ICUS).

The study protocol was approved by the local ethical committee and the patients gave informed consent before inclusion in the study. All patients had chronic stable angina caused by a severe lesion in the LAD and were assigned for percutaneous transluminal coronary angioplasty (PTCA). A major inclusion criterion in the study was the presence of a clearly identifiable plaque in the proximal LAD. One plaque was selected for analysis in each patient. MSCT of the heart was performed within 24 hours before the intervention. Immediately before PTCA, ICUS was performed to analyse vessel morphology proximal to or at the target lesion. To ensure that the identical plaque was assessed by the different techniques, landmarks were used—that is, the origin of side branches.

Baseline angiograms of the LAD were conducted in at least two projections before the intervention. Continuous ultrasound images were received by motorised pullback of the catheter (0.5 mm/s, UltraCross 3.2 French, 30 MHz coronary imaging catheter, Scimed, Boston Scientific Corporation, San Jose, California, USA). The images were immediately digitalised by using echoPlaque Software (Indec Systems Inc, Mount View, California, USA). Plaque morphology was classified according to established ICUS criteria.4 Lesion severity was defined as: mild < 50%; moderate 50–75%; and severe > 75% area stenosis.

All scans of the entire heart were conducted during one breathhold (approximately 25 seconds, collimation 1.0 mm, pitch 1.5, 140 kV, 300 mAs, rotation time 500 ms, 150 ml of contrast agent) using a Somatom Volume Zoom scanner (Siemens, Forchheim, Germany). Image reconstruction was performed in the diastolic phase with a retrospective gating of 450 ms absolute reverse. For plaque detection, contrast media enhanced axial slices were analysed. To determine plaque morphology, a total of 16 density measurements within the plaque area at randomly selected points at four different axial slices were performed. Lesion severity was defined as: mild < 50%; moderate 50–75%; and severe > 75% area stenosis.

Six plaques, detected in the proximal LAD of six patients, were analysed by comparing the results of angiography, ICUS, and MSCT. The patient characteristics are summarised in table 1.

Table 1

Patient and plaque characteristics

In patients 1 and 2, angiography revealed mild atherosclerotic vessel alterations in the LAD proximal to the target lesions (fig 1). On ICUS, both plaques were classified as soft lesions. These plaques showed hypoechogenic areas in the centre, suggesting the presence of lipid cores. Area stenosis was 46%/48%. These plaques were clearly detectable by MSCT, and density measurements revealed 6 (28) Hounsfield units (HU) for plaque 1 and −5 (25) HU for plaque 2. Both plaques were classified as mild lesions < 50 % (table 1).

Figure 1

Soft plaque with a lipid core visualised by multi-slice computed tomography (MSCT), coronary angiography, and intracoronary ultrasound (ICUS). (1) MSCT: axial slice visualising the left anterior descending artery and a soft plaque (arrow). (2) Coronary angiography: visualising the soft plaque (arrow) as a minor vessel wall alteration. (3) ICUS: longitudinal view of the left anterior descending artery, visualising the soft plaque. a, vessel lumen; b, soft plaque with a lipid core; c, ultrasound catheter with guiding wire inside. Ao, aorta; PT, pulmonary trunk; LA, left atrium; LAD, left anterior descending artery.

With angiography, plaque 3 was found to be a moderate lesion (proximal to the target lesion), whereas plaque 4 was the target lesion with a severe luminal narrowing. On ICUS, both plaques were classified as intermediate lesions. Area stenosis was 73% in plaque 3 and 93% in plaque 4. These plaques were clearly detectable by MSCT, and density measurements revealed 83 (17) HU for plaque 3 and 51 (19) HU for plaque 4. Plaque 3 was correctly classified as a moderate to severe lesion, and plaque 4 as a severe lesion (table 1).

In patients 5 and 6, calcifications could already be detected in projection on the proximal LAD by angiography. Plaque 5 was proximal to the angiographically detectable severe target lesion, and was classified as a moderate lesion. Plaque 6 was the target lesion with severe luminal narrowing. On ICUS, both plaques were classified as calcified lesions. Lesion severity was 53% (arc of calcification of 185°) in plaque 5 and 93% (arc of calcification of 95°) in plaque 6. These plaques were clearly detectable by MSCT, and density measurements revealed 489 (372) HU for plaque 5 and 423 (111) HU for plaque 6. Plaque 5 was classified as an intermediate lesion, and plaque 6 as a severe lesion (table 1).

Non-invasive coronary angiography with good image quality can be performed by the use of the new generation of conventional spiral computed tomography scanners with multi-slice technology. Because of improved temporal and spatial resolution,2 this new modality seems to provide information on coronary atherosclerosis which could only be achieved by ICUS. MSCT seems to allow not only for the non-invasive detection of coronary lesions, but also for the accurate differentiation of plaque morphology. Since intracoronary soft plaques might also be detected, which are known to be prone to rupture inducing acute coronary syndromes,1 5 MSCT holds promise to allow for non-invasive risk assessment in patients with known or suspected coronary artery disease.

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