Plaque Vulnerability Phenotype in Patients with Coronary Artery

Disease

An Intravascular Ultrasound Radiofrequency Analysis

T. Pinheiro

, C. Ramos

, P. Napoleão

, C. Mendonça

, C. Fondinho

, M. Selas

, M. Mota Carmo

3,4

and R. Cruz Ferreira

3,4

IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa, E.N. 10, Sacavém, Portugal

Instituto de Medicina Molecular, Av. Prof. Gama Pinto, Lisboa, Portugal

Serviço de Cardiologia. Hospital de Santa Marta CHLC, Lisboa, Portugal

CEDOC, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Campo Santana, Lisboa, Portugal

Keywords: Coronary Artery Disease, Atherosclerosis, Vulnerable Plaque Phenotype.

Abstract: The relationship between plaque morphology and clinical presentation was examined. Lumen dimensions,

atheroma morphology and composition were assessed by virtual histology intravascular ultrasound (VH-

IVUS) in 1757 frames of coronary segments of interest of 17 patients with acute and chronic coronary artery

disease, i.e., ST-elevation (STEMI) and non-ST-elevation (NSTEMI) myocardial infarction, unstable angina

(UA) and stable angina (SA). Large plaque areas with distended elastic lamina (EEL), rich in fibrotic (FB)

and fibro-fatty (FF) tissues associated with STEMI and UA. Variants of this phenotype consisting of large

calcium deposits and reduced lumen area were prevalent in NSTEMI patients. SA patients consistently

showed plaques with small areas, marked constrictive growth and low FF content. IVUS-derived plaque

measures provided phenotypes of vulnerability and rupture that may help improving risk stratification of

both symptomatic and asymptomatic patients.

1 INTRODUCTION

Coronary artery disease is still the main cause of

death worldwide. This disease is characterized by

impaired function of endothelial cells, which line the

vessel luminal surface. The endothelial dysfunction

promotes the adhesion of leukocytes and their

migration into the vessel wall. Atherosclerosis is a

pathological process of the vasculature causing a

progressive thickening of artery intima. As

atherosclerosis progresses the atheroma builds up in

the vessel wall in consequence of abnormal transport

of low density lipoproteins (LDL) in endothelial

cells, inflammatory cell recruitment to the vessel

wall and inefficient turnover of debris of modified

and/or oxidized products of metabolism. Several

events such as, cell apoptosis of macrophage-derived

lipid-load cells, increased secretion of inflammatory

molecules and proteases by activated cells in the

intima, which damage the extracellular matrix,

promote cell activation and smooth cell migration

from arterial media, contribute to plaque fibrosis and

development of the necrotic core and calcified areas.

The perpetuation of oxidative, inflammatory and

proteolytic activity originates an inflamed plaque

with a metabolically active fibrous cap. Eventually

the plaque ruptures, which results in a clinical

spectrum of presentations ranging from sudden

cardiac death, myocardial infarction and unstable

angina, to an asymptomatic event with plaque

progression (Stone, 2011).

Intravascular ultrasound (IVUS) is a catheter

based imaging modality providing two-dimensional

visualization of the arterial wall. The analysis of the

radiofrequency spectrum, usually called Virtual

Histology IVUS (VH-IVUS), allows determining the

fibrotic, fibro-fatty, necrotic and calcium contents in

plaques (Vancraeynest, 2011); (Nair, 2007); (Fayad

and Fuster, 2001).

In coronary segments of interest the VH-IVUS–

derived plaque dimensions and composition data

may help characterizing the high-risk and vulnerable

atherosclerotic plaques. The relationship between

Pinheiro T., Ramos C., Napoleão P., Mendonça C., Fondinho C., Selas M., Mota Carmo M. and Cruz Ferreira R..

Plaque Vulnerability Phenotype in Patients with Coronary Artery Disease - An Intravascular Ultrasound Radiofrequency Analysis.

DOI: 10.5220/0004664400840089

In Proceedings of the International Congress on Cardiovascular Technologies (VisualCardio-2013), pages 84-89

ISBN: 978-989-8565-78-5

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

atheroma composition and arterial remodelling

characteristics in patients with acute and non-acute

coronary artery syndromes would dramatically

improve risk stratification of both symptomatic and

asymptomatic patients (Ramos et al, 2013); (Garcia-

Garcia, 2012); (Calvert, 2011).

2 OBJECTIVES

The aim of this study was to examine the plaque

morphological and histological characteristics

obtained with VH-IVUS, and associate these

features with clinical symptoms.

In particular, we investigated how vessel

measures, indicative of plaque expansive and

constrictive growth, were predicted by plaque

composition changes.

It can be anticipated that plaque phenotype may

be related to vulnerability and plaque rupture.

3 METHODS

3.1 Patients

Seventeen patients of both sexes with coronary

artery disease (CAD) presenting to the Cardiology

Service of Santa Marta Hospital (CHLC, Lisbon,

Portugal) undergoing percutaneous coronary

intervention (PCI) for troponine-positive acute

coronary syndrome (ACS), such as, ST elevation

myocardial infarction (STEMI), non-ST-elevation

myocardial infarction (NSTEMI), and absence of

biochemical evidence of myocardial damage such

as, unstable angina (UA) were prospectively eligible

non-ACS such as, chronic stable angina were also

included in the study.

ACS patients were assessed within 6 hours after

onset of symptoms and before medication

administration. Non-ACS patients were assessed

before PCI. Demographics, risk factors, clinical

history, and angiographic data were recorded for

each patient. Biochemical tests were also carried out,

which included creatinine kinase (CK), troponin T,

N-terminal pro-brain natriuretic peptide (NT-

proBNP) and C-reactive protein (CRP)

determination (Table 1).

The Ethical Committee of the CHLC approved

the study protocol. All participants gave written

consent before enrolment.

3.2 VH-IVUS

The VH-IVUS acquisition was performed using an

EagleEye catheter (20 MHz) at pullback speed of 0.5

mm/sec. For each coronary segment, vessel, lumen

and atheroma measurements were obtained for every

VH-IVUS frame (0.5 mm thickness) throughout the

region of interest and lesion borders established

using the leading edges of external elastic lamina

(EEL) and the luminal contour.

Atheroma area (AAT) was determined as the

difference between EEL and lumen areas. Atheroma

volume was calculated as the differences between

EEL and lumen areas across all evaluable slices.

Plaque burden was calculated as plaque area divided

by EEL area.

Table 1: Patients characterization. Results are medians and

interquartile range (Q25 – Q75), unless otherwise

specified. Abbreviations: ACS - Acute Coronary

Syndrome; TIMI (Thrombolysis In Myocardial Infarction)

grade flow 0 – no perfusion to 3 – complete perfusion;

Multivessel ≥ 1 vessel affected.

Patient’s Characterization

Male sex (%) 66

Age (y) 66 (57 – 76)

Risk factors >2 (%) 67

Previous medication (%) 89

ACS (%) 41

Multivessel (%) 47

TIMI ≤2 94

CK (U/l) 125 (87 – 424)

Troponin T (U/l) 0.05 (0.01 – 1.87)

CRP (mg/l) 5.6 (1.0 – 8.2)

NT-proBNP (pg/ml) 162 (0.01 – 219)

IVUS data was recorded for the reconstruction of

the radiofrequency backscatter information using In-

Vision gold commercial software (Volcano

Corporation, USA). Following spectral analysis, the

areas and percentages of fibrotic (FB), fibro-fatty

(FF), calcified (Ca) and necrotic core (NC) were

calculated for each frame. A colour image of the

plaque is formed using a colour code: green (FB);

light green (FF); red (necrotic core); white (Ca).

3.3 Statistical Analysis

Statistical analysis was performed with SPSS V.21.

IVUS data was evaluated taking into account all

frames in every segment of interest and single cross-

sections selected at larger stenosis, distal and

proximal regions of the coronary segment.

The correlation between VH-IVUS derived

measurements was calculated using Kendall's Tau

PlaqueVulnerabilityPhenotypeinPatientswithCoronaryArteryDisease-AnIntravascularUltrasoundRadiofrequency

Analysis

algorithm. Linear regression (stepwise selection of

variables) was applied to estimate plaque

composition in positive or negative growth.

Discriminant analysis was used to correlate plaque

morphology and composition in combination to

clinical symptoms. Variables were transformed

whenever appropriate. Continuous variables were

compared by Mann-Whitney U statistic test.

A p-level <0.05 was considered statistically

significant for all analysis.

4 RESULTS

4.1 Plaque Characterization

The coronary segments of each patient were

evaluated by extracting selected frames in three

distinct regions, i.e, distal, proximal and major

stenosis region and by using the total number of

frames recorded in each visualized segment (multi-

frame analysis).

In the multi-frame approach a total of 1757 VH-

IVUS frames were analysed (median = 56; IQ25-

IQ75: 26-93 frames per coronary segment).

The results obtained using both approaches are

summarized in Table 2. When plaque data was

assessed using a reduced number of frames luminal

dimensions were underestimated relative to multi-

frame approach.

Table 2: Patients characteristics using selected frames and

total number of frames. Significant differences (pair-test)

for p<0.05. Abbreviations: EEL - external elastic lamina;

AAT - atheroma area; PB -plaque burden; FB - fibrotic

tissue; FF - fibro-fatty tissue; Ca - calcified tissue; NC -

necrotic core.

Plaque characteristics

Analysis of 3

frames

Multi-frame

analysis

FB (%) 57 (50 – 69) 51 (45 – 61) 0.877

FF (%) 12 (8– 17) 11 (6 – 17) 0.234

Ca (%) 11 (5 – 19) 10 (3 – 16) 0.017

NC (%) 16 (10 – 21) 21 (14 – 25) 0.056

Lumen

diameter

(mm)

2.2 (1.9 – 2.7) 2.6 (2.4 – 2.9) 0.005

area (mm

) 3.6 (2.9 – 5.1) 5.1 (4.6 – 6.7) 0.001

EEL

diameter

(mm)

4.5 (4.2 – 4.9) 4.5 (4.0 – 4.8) 0.326

area (mm

) 17 (14 – 19) 16 (12 – 18) 0.215

AAT (mm

) 13 (10 – 15) 10 (7 – 12) 0.001

PB (%) 77 (66 – 84) 60 (50 – 68) <0.001

Consequently plaque area and plaque burden

become overestimated as can be inferred from data

listed in Table 2. Data for plaque composition using

selected frames from each coronary segment

depicted higher values of Ca tissue content

(p=0.017), whereas NC content was marginally

reduced (p=0.056).

4.2 Relationship between Plaque

Morphology and Composition

Lumen and EEL dimensions, whether minimum or

maximum diameters, area or volumes, were

positively correlated (p<0.05). The NC content of

the plaque failed to correlate with lumen, EEL or

plaque dimensions.

Considering EEL area (or volume) as dependent

variable in the regression model and plaque

composition (FB, FF, Ca, and NC) as predictor

variables, EEL was positively associated to plaques

rich in FB, FF. The regression model became more

significant when plaque area was considered as

dependent variable. The model accuracy was above

68% and both the model fitted and variables retained

were highly significant (p<0.001). The FB and FF

contents were moderately useful to estimate plaque

size (r=0.355, p<0.0001). The plaque outwards

enlargement was related to FF increases in detriment

of plaque FB content.

However, the plaque composition failed to

associate with lumen dimensions (diameter, area or

volume).

To further estimate the importance of plaque

composition and morphology to the plaque

phenotype having into account patient clinical

presentation, i.e., STEMI, NSTEMI, UA and SA, the

concordance correlation, not dependent on linear

combinations, between area of EEL or plaque area

and plaque components was studied.

More expansive plaques (large EEL area or

plaque area) are rich in FF and FB and this pattern

was associated to STEMI and UA patients.

Results

showed that the shared correlation between the

atheroma area, FB and FF content accounted for

48% of the total variability, and enabled to

discriminate STEMI and UA patients (Function 1,

negative scores) from SA patients (Function 1,

positive scores) (Figure 1). The plaque Ca content

expressed 44% of the total variability identifying

NSTEMI patients whereas the remaining 8%

discriminated plaques with low NC content.

Both STEMI and UA patients showed plaques

with significantly higher FF content (median and IQ

of normalized area: STEMI - 14%, 8-20%; UA -

CARDIOTECHNIX2013-InternationalCongressonCardiovascularTechnologies

16%, 8-27%) when compared to NSTEMI and SA

patients (median and IQ of normalized area:

NSTEMI - 9%, 6-14%; SA - 6%, 3-12%) (p<0.001).

Plaques from STEMI and UA patients were also rich

in FB content (normalized areas of approximately

57% in both groups, contrasting with NSTEMI and

SA patients showing atheromas with lower content

of FB (normalized areas of 37% and 47%,

respectively) (p<0.001).

These two plaque components were positively

correlated with atheroma area, indicating that

increased contents of FB and/or FF were consistent

with large plaque areas. The atheroma area did not

differ between ACS groups. However all ACS

groups differ from SA, which showed the lowest

plaque areas (median, IQ25-IQ75: SA -7mm

, 5-

10mm

; STEMI - 12mm

, 7-13mm

; NSTEMI -

11mm

, 9-13mm

;

UA - 11mm

, 8-15mm

)

(p<0.001).

Figure 1: Scatterplot of the two first discriminant

functions. The atheroma area, FB and FF correlated with

function 1, whereas Ca was correlated with the

discriminant function 2.

The Ca content of plaques clearly identified

NSTEMI patients, as can be observed in Figure 1. In

fact, plaques of NSTEMI patients showed the

highest levels of calcified tissue (median, IQ25-

IQ75: 28%, 12%-35%) which were highly

significant when compared to the other groups of

patients (median, IQ25-IQ75: STEMI - 6%, 2%-

13%; UA - 6%, 2%-15%; SA - 14%, 3%-23%)

(p<0.001).

The highest correlation with the third

discriminant function (which had a limited

discriminating power) was observed for NC. The

limited importance of NC in group stratification, and

therefore in phenotype identification is consistent

with the similar variance of NC, although the plaque

NC contents significantly differed between groups,

as will be referred below.

The influence of plaque constriction was also

evaluated in addition to plaque outward expansion.

Both the discriminating models showed similar

solutions. When the lumen area was added, three

significant functions were obtained, of which the

two first discriminating functions explained most of

the variability (92%). The first discriminating

function clearly correlated plaque FB and FF

contents (51% of total variance explained)

differentiating STEMI from UA patients whereas the

second discriminating function correlated the

atheroma size with Ca distinguishing NSTEMI from

SA.

Thus, the results obtained were similar to the

previous model, which only considered atheroma

area and plaque structure.

The third function, although significant only

explained a moderate 8% of the total variance and

correlated the decrease of luminal area with the rise

of NC content and helped distinguishing STEMI and

UA patients. In fact UA showed larger luminal areas

(median, IQ25-75: 9mm

, 5-16 mm

) and diminished

NC area (median, IQ25-75: 1.1mm

, 0.4-2.2mm

)

when compared to STEMI (median, IQ25-75: lumen

area - 6mm

, 3-10mm

; NC – 1.5mm

, 0.8-2.3mm

However the differences between these two groups

for NC plaque content were as relevant as those

observed for NSTEMI and SA patients (p≤0.001).

The latest showed large necrotic areas when

compared to UA and STEMI patients (median of

normalized area NC>23% vs NC<17% for STEMI

and UA).

Moreover, if plaque burden is included in the

model, the plaque content relationship was

maintained and equally explained by the two first

functions as previously described. The third

component of the model expresses minor variance

associated with lumen area, which changes are

opposite to plaque burden and NC content.

This reinforces the view that large luminal areas

associate to expansive plaques and that NC may play

a role in constrictive plaque phenotype, as observed

in SA patients.

5 DISCUSSION

The structure of atheroma was assessed in depth and

along the length of coronary segments of interest

PlaqueVulnerabilityPhenotypeinPatientswithCoronaryArteryDisease-AnIntravascularUltrasoundRadiofrequency

Analysis

using VH-IVUS modality. The plaque

characteristics were studied by extracting data of

selected cross-sections and of the total number of

frames of the scanned region of the vessel.

The study showed that both vessel characteristics

and morphology were underestimated when

selecting few points along the vessel by report to a

multiframe approach covering the whole length of

the injured region of the coronary. The detailed

evaluation of the atheroma structure paved the way

to define plaque phenotypes describing different

clinical presentations of CAD.

Large plaque areas with distended elastic lamina,

rich in fibrotic and fibro-fatty tissues were

associated with STEMI and UA. Variants of this

phenotype consisting of large calcium deposits and

reduced lumen area were prevalent in NSTEMI

patients. SA patients consistently showed plaques

with small areas, marked constrictive growth and

low FF content.

These findings suggest that SA and NSTEMI

were associated with more constrictive remodelling

whereas STEMI and UA were associated to

expansive remodelling. In addition, the phenotype

associated to STEMI and UA patients, can be

connected to plaque rupture and/or plaque

instability.

In previous studies using VH IVUS the plaque

instability had been associated to nonrestenotic thin-

capped fibroatheroma and adverse outcomes

(Calvert et al., 2011). Samady et al (2011) reported

on the influence of shear stress in plaque constrictive

and expansive remodelling was associated with the

development of necrotic core and FB and FF content

suggesting that the excessive expansive remodelling

is indicative of plaque vulnerability.

The limited importance of necrotic core for

plaque phenotypes and the association with luminal

areas and plaque burden suggests that this plaque

component may be involved in constrictive plaque

growth, possibly having a limited value to plaque

vulnerability occurring in ACS.

However, a thoroughly evaluation of the

atheroma in terms of necrotic core depth and thin

cap extension should be further addressed (Fayad

and Fuster, 2001); (Goldstein, 2000). These features

may help improving vulnerability phenotype

definition.

6 CONCLUSIONS

Specific plaque phenotypes were associated to ACS

and non-ACS.

Vessels with enlarged lumens and with plaques

characterized by marked outward growth and high

fibrotic and fibro-fatty contents were found in

STEMI and SA patients. NSTEMI patients allied to

the above plaque structure an important increase of

calcified tissue and a plaque bi-directional growth,

both outwards and inwards the vessel lumen.

A second plaque phenotype characterized by

small constrictive and fibrotic plaques, with low

fibro-fatty content was associated with SA patients

Therefore, IVUS-derived plaque measures

provided phenotypes of plaque vulnerability and

rupture that may help improving risk stratification of

symptomatic patients.

ACKNOWLEDGEMENTS

The study was carried out under Fundação para a

Ciência e Tecnologia PIC/IC/82734/2007 research

contract.

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PlaqueVulnerabilityPhenotypeinPatientswithCoronaryArteryDisease-AnIntravascularUltrasoundRadiofrequency

Analysis