Intravascular ultrasound predictors of major adverse cardiac events in patients with unstable angina

Noninvasive Tissue Characterization of Coronary Arterial Plaque by 16-Slice Computed Tomography in Acute Coronary Syndrome

Noninvasive characterization of coronary plaques is challenging for cardiologists. The authors’ goal was to explore the clinical feasibility of newly developed 16-slice computed tomography (CT) in tissue characterization of coronary arterial plaques in patients with acute coronary syndrome. Sixteen patients with acute coronary syndrome underwent 16-slice CT (Aquillion, Toshiba) and coronary arteriography with intravascular ultrasound (IVUS) within 7 days. Twenty-three plaques were classified by IVUS according to plaque echogenicity: 6 soft plaques, 11 intermediate plaques, and 6 calcified plaques. Mean (±SD) CT numbers (Hounsfield units [HU]) of these 3 types of plaques were 50.6 ±14.8 HU, 131 ±21.0 HU, and 721 ±231 HU, respectively. Sixteen-slice CT facilitates noninvasive tissue characterization of coronary arterial plaques.

Imaging plaques to predict and better manage patients with acute coronary events

Culprit lesions of patients, who have had an acute coronary syndrome commonly, are ruptured coronary plaques with superimposed thrombus. The precursor of such lesions is an inflamed thin-capped fibroatheroma. These plaques can be imaged by means of invasive techniques, such as intravascular ultrasound (and derived techniques), optical coherence tomography, and near-infrared spectroscopy. Often these patients exhibit similar (multiple) plaques beyond the culprit lesion. These remote plaques can be assessed noninvasively by computed tomographic angiography and MRI and also using invasive imaging. The detection of these remote plaques is not only feasible but also in natural history studies have been associated with clinical coronary events. Different systemic pharmacological treatments have been studied (mostly statins) with modest success and, therefore, newer approaches are being tested. Local treatment for such lesions is in its infancy and larger, prospective, and randomized trials are needed. This review will describe the pathological and imaging findings in culprit lesions of patients with acute coronary syndrome and the assessment of remote plaques. In addition, the pharmacological and local treatment options will be reviewed.

Coronary CT angiography in the quantitative assessment of coronary plaques

Coronary computed tomography angiography (CCTA) has been recently evaluated for its ability to assess coronary plaque characteristics, including plaque composition. Identification of the relationship between plaque composition by CCTA and patient clinical presentations may provide insight into the pathophysiology of coronary artery plaque, thus assisting identification of vulnerable plaques which are associated with the development of acute coronary syndrome. CCTA-generated 3D visualizations allow evaluation of both coronary lesions and lumen changes, which are considered to enhance the diagnostic performance of CCTA. The purpose of this review is to discuss the recent developments that have occurred in the field of CCTA with regard to its diagnostic accuracy in the quantitative assessment of coronary plaques, with a focus on the characterization of plaque components and identification of vulnerable plaques.

A gene-centric study of common carotid artery remodelling

Background

Expansive remodelling is the process of compensatory arterial enlargement in response to atherosclerotic stimuli. The genetic determinants of this process are poorly characterized.

Methods

Genetic association analyses of inter-adventitial common carotid artery diameter (ICCAD) in the IMPROVE study (n = 3427) using the Illumina 200k Metabochip was performed. Single nucleotide polymorphisms (SNPs) that met array-wide significance were taken forward for analysis in three further studies (n = 5704), and tested for association with Abdominal Aortic Aneurysm (AAA).

Results

rs3768445 on Chromosome 1q24.3, in a cluster of protein coding genes (DNM3, PIGC, C1orf105) was associated with larger ICCAD in the IMPROVE study. For each copy of the rare allele carried, ICCAD was on average 0.13 mm greater (95% CI 0.08–0.18 mm, P = 8.2 × 10⁻⁸). A proxy SNP (rs4916251, R² = 0.99) did not, however, show association with ICCAD in three follow-up studies (P for replication = 0.29). There was evidence of interaction between carotid intima-media thickness (CIMT) and rs4916251 on ICCAD in two of the cohorts studies suggesting that it plays a role in the remodelling response to atherosclerosis. In meta-analysis of 5 case–control studies pooling data from 5007 cases and 43,630 controls, rs4916251 was associated with presence of AAA 1.10, 95% CI 1.03–1.17, p = 2.8 × 10⁻³, I² = 18.8, Q = 0.30). A proxy SNP, rs4916251 was also associated with increased expression of PIGC in aortic tissue, suggesting that this may the mechanism by which this locus affects vascular remodelling.

Conclusions

Common variation at 1q24.3 is associated with expansive vascular remodelling and risk of AAA. These findings support a hypothesis that pathways involved in systemic vascular remodelling play a role in AAA development.

Culprit lesion remodelling and long-term prognosis in patients with acute coronary syndrome: an intravascular ultrasound study

AIMS

Positive arterial remodelling is recognized as one of the morphological characteristics of the vulnerable plaque. Limited data are available on a long-term outcome of acute coronary syndrome (ACS) patients with culprit lesion positive arterial remodelling (PR). The aim of this study was to investigate the long-term impact of culprit lesion PR in patients with ACS.

METHODS AND RESULTS

In 134 patients with ACS, intravascular ultrasound (IVUS) was performed to assess target lesion remodelling before percutaneous coronary intervention. PR was defined as the ratio of the external elastic membrane cross-sectional area at the target lesion to that of at the proximal reference of >1.05, and intermediate or negative remodelling (IR/NR) was defined as that of ≤1.05. Major adverse cardiac event (MACE) was defined as a composite of death, ACS, and target lesion revascularization. During the follow-up (median 5.8 years), MACE-free survival was significantly lower in the PR group than that in the IR/NR group (log-rank, P = 0.005). Survival and ACS-free survival were also significantly lower in the PR group than that in the IR/NR group (log-rank, both P = 0.04). By multivariable Cox regression analysis, PR (hazard ratio = 2.4, P = 0.02) and diabetes (hazard ratio = 1.9, P = 0.03) were independent predictors of MACE.

CONCLUSION

Culprit lesion PR was associated with a poor long-term prognosis in patients with ACS. PR may be a marker of vulnerable patients.

Assessment of coronary atherosclerosis by IVUS and IVUS-based imaging modalities: progression and regression studies, tissue composition and beyond

Cardiovascular disease remains the leading cause of mortality, morbidity and disability in the developed world, predominantly affecting the adult population. In the early 1990s coronary heart disease (CHD) was established as affecting one in two men and one in three women by the age of forty. Despite the dramatic progress in the field of cardiovascular medicine in terms of diagnosis and treatment of heart disease, modest improvements have only been achieved when the reduction of cardiovascular mortality and morbidity indices are assessed. To better understand coronary atherosclerosis, new imaging modalities have been introduced. These novel imaging modalities have been used in two ways: (1) for the characterization of plaque types; (2) for the assessment of the progression and regression of tissue types. These two aspects will be discussed in this review.

Phase-sensitive black-blood coronary vessel wall imaging

Black-blood MR coronary vessel wall imaging may become a powerful tool for the quantitative and noninvasive assessment of atherosclerosis and positive arterial remodeling. Although dual-inversion recovery is currently the gold standard, optimal lumen-to-vessel wall contrast is sometimes difficult to obtain, and the time window available for imaging is limited due to competing requirements between blood signal nulling time and period of minimal myocardial motion. Further, atherosclerosis is a spatially heterogeneous disease, and imaging at multiple anatomic levels of the coronary circulation is mandatory. However, this requirement of enhanced volumetric coverage comes at the expense of scanning time. Phase-sensitive inversion recovery has shown to be very valuable for enhancing tissue-tissue contrast and for making inversion recovery imaging less sensitive to tissue signal nulling time. This work enables multislice black-blood coronary vessel wall imaging in a single breath hold by extending phase-sensitive inversion recovery to phase-sensitive dual-inversion recovery, by combining it with spiral imaging and yet relaxing constraints related to blood signal nulling time and period of minimal myocardial motion.

Relationship between degree of remodeling and CT attenuation of plaque in coronary atherosclerotic lesions: An in-vivo analysis by multi-detector computed tomography

Multi-detector CT (MDCT) permits non-invasive visualization of the coronary arteries. Coronary plaque can be visualized, and earlier studies have indicated that the CT attenuation measured in atherosclerotic plaques is influenced by plaque composition. Also, MDCT has been shown to permit assessment of remodeling of coronary atherosclerotic lesions. It is assumed that both lipid-rich plaques and those that display positive remodeling are more prone to rupture and erosion. We thus evaluated the relationship between remodeling and CT attenuation of coronary atherosclerotic plaque by MDCT.

METHODS

Seventy-six patients were investigated by contrast-enhanced 64-slice CT. One-hundred twelve atherosclerotic lesions without substantial calcification and visualized with high image quality were selected. Multiplanar reconstructions orthogonal to the coronary artery were rendered at the lesion and the proximal reference site. Cross-sectional vessel areas were measured to determine the remodeling index (RI: lesion vessel area/reference vessel area) and the CT attenuation of plaque was measured by fitting a region of interest to the plaque area. CT attenuation of plaque was correlated to the presence of positive remodeling index (RI>1.05).

RESULTS

The mean cross-sectional vessel area in the lesion was 0.25+/-0.08 cm(2), the mean reference vessel area was 0.22+/-0.09 cm(2). The mean CT attenuation of the atherosclerotic plaque in the lesions was 71+/-26 HU. CT attenuation of plaque was significantly lower in 72 lesions that displayed positive remodeling (59+/-22 HU) than in 40 lesions with no or with negative remodeling (91+/-20 HU, p<0.001).

CONCLUSIONS

Positive remodeling of coronary atherosclerotic lesions correlates to lower CT attenuation of plaque, which has been demonstrated to be associated with lipid-rich plaque. Both characteristics indicate increased risk for plaque rupture and subsequent events and could thus prove useful when the use of CT imaging for the detection of "vulnerable plaque" is considered.

Intravascular ultrasound assessment of atherosclerotic plaque in the aorta

BACKGROUND

Intravascular ultrasound (IVUS) has been used for assessment of the coronary arteries. However, few IVUS studies have been reported on the aorta.

MATERIALS AND METHODS

To assess the presence of atherosclerotic disease in the aorta by the use of IVUS, 29 patients with heart disease (24 men and 5 women; mean age, 61+/-11 years) including ischemic heart disease (n=21) and valvular disease or dilated cardiomyopathy (n=8) were enrolled in the study. An IVUS catheter was inserted through the femoral artery, and IVUS images were obtained in the descending aorta (DA) at the level of the pulmonary artery bifurcation, and in the proximal and distal regions of the abdominal aorta (AA) at the level of the renal artery bifurcation. Percent plaque area (%PA) was calculated as vessel cross-sectional area surrounded by media minus lumen cross-sectional area divided by vessel cross-sectional area.

RESULTS

%PAs differed significantly between the three aortic levels: DA, 14.9+/-5.5%; proximal AA, 19.0+/-6.9%; and distal AA, 28.3+/-9.7% (p<0.05). However, PA did not differ significantly between the three levels (DA, 94.7+/-38.0 mm2; proximal AA, 90.9+/-35.0 mm2; distal AA, 79.7+/-32.3 mm2). %PA and PA in the DA and proximal AA correlated with age (r=0.39-0.46, p<0.05), but not with coronary angiography findings or multiple risk factors.

CONCLUSIONS

The aortic plaque is clearly observed by IVUS. The plaque is diffuse at the 3 levels, had little relationship with risk factor of arteriosclerosis or coronary artery disease, and aging affected the increase of plaque.

Impact of arterial remodelling and plaque rupture on target and non-target lesion revascularisation after stent implantation in patients with acute coronary syndrome: an intravascular ultrasound study

OBJECTIVES

To investigate the impact of arterial remodelling on long-term clinical outcome after stent implantation in patients with acute coronary syndrome (ACS).

METHODS

134 patients with ACS were enrolled. External elastic membrane (EEM) cross-sectional area (CSA) and lumen CSA were measured. Plaque and media CSA was calculated as EEM minus lumen CSA. Final minimal stent area (MSA) was also measured after stenting. Positive remodelling (PR) was defined as the ratio of the EEM CSA at the target lesion to that at the proximal reference of >1.05, and intermediate or negative remodelling (IR/NR) was defined as that of < or =1.05.

RESULTS

Although final MSA was similar, target lesion revascularisation (TLR) rates at 2 years were significantly higher in patients with PR (33.7%) than in those with IR/NR (13.7%; p = 0.01). In addition, non-TLR rates were also significantly higher in patients with PR (42.2%) than in those with IR/NR (23.5%; p = 0.03). Cardiac event-free survival (for events such as death, myocardial infarction, TLR and non-TLR) was significantly lower in patients with PR than in those with IR/NR (log rank, p = 0.001). By multivariate logistic regression analysis, PR (chi2 6.57, OR 2.70; 95% CI, 1.27 to 5.78; p = 0.01) and plaque rupture (chi2 4.17, OR 2.38; 95% CI, 1.04 to 5.45; p = 0.04) were independent predictors of cardiac events.

CONCLUSION

In patients with ACS, PR and intravascular ultrasound findings that may correspond with plaque rupture predict cardiac events including both TLR and non-TLR at 2 years.

Remodeling Index Compared to Actual Vascular Remodeling in Atherosclerotic Left Main Coronary Arteries as Assessed With Long-Term (≥12 Months) Serial Intravascular Ultrasound

OBJECTIVES

We present the remodeling index (RI) versus serial intravascular ultrasound (IVUS) data.

BACKGROUND

The RI, derived by comparing lesion external elastic membrane (EEM) cross-sectional area versus the reference at one time point, is used in various IVUS studies as a substitute of true remodeling (change in EEM over time), assuming that it represents true remodeling.

METHODS

We studied 46 non-stenotic left main arteries using serial IVUS (follow-up 18 +/- 8 months). Plaques were divided into subgroups according to the follow-up RI: follow-up RI >1 (n = 27) versus follow-up RI < or =1 (n = 19).

RESULTS

Lesions with a follow-up RI >1 had an increase in lumen despite an increase in plaque because of an increase in EEM. Conversely, lesions with a follow-up RI < or =1 had a reduction in lumen as a result of both a plaque increase and EEM decrease. Overall, the follow-up RI correlated directly with changes in lesion site EEM (baseline-to-follow-up). Although there was no correlation between the follow-up RI and changes in reference EEM area, changes in reference EEM area did correlate directly with changes in lesion EEM area. In nearly 90% of lesions with a follow-up RI >1, there was a previously documented increase in EEM area. Using multivariate linear regression analysis, the follow-up RI was dependent on the baseline RI, the increase in lesion EEM area, and the decrease in reference EEM area. The follow-up RI was not dependent on changes in lesion plaque area.

CONCLUSIONS

The vast majority of left main lesions with a remodeling index >1 had evidence of a previous increase in lesion-site EEM area.

assessment of coronary remodeling in stenotic and nonstenotic coronary atherosclerotic lesions by multidetector spiral computed tomography

OBJECTIVES

This study was designed to investigate whether contrast-enhanced multidetector spiral CT (MDCT) permits assessment of remodeling in coronary atherosclerotic lesions.

BACKGROUND

With sufficient image quality, MDCT permits noninvasive visualization of the coronary arteries, but its ability to assess remodeling has not been evaluated.

METHODS

Out of 102 patients in whom MDCT (16-slice scanner, intravenous contrast, 0.75-mm collimation, 420 ms rotation) was performed before invasive coronary angiography, 44 patients with high-quality MDCT data sets showing atherosclerotic plaque in a proximal coronary artery segment were chosen for evaluation. In multiplanar reconstructions orthogonal to the coronary artery, the cross-sectional vessel area was measured for the respective lesion and for a reference segment proximal to the lesion. The "Remodeling Index" was calculated by dividing the vessel area in the lesion by the reference segment. Results were correlated to the presence of stenosis (>50% diameter reduction) in invasive angiography. In a subset of 13 patients, MDCT measurements were verified by IVUS.

RESULTS

Reference vessel area was not significantly different between nonstenotic versus stenotic lesions (20 +/- 8 mm(2), n = 23 vs. 22 +/- 8 mm(2), n = 21). The mean Remodeling Index was significantly higher in nonstenotic than in stenotic lesions (1.3 +/- 0.2 vs. 1.0 +/- 0.2, p < 0.001). In five stenotic lesions, "negative remodeling" (Remodeling Index < or = 0.95) was observed. Cross-sectional vessel areas and Remodeling Indices measured by MDCT correlated closely to IVUS (r(2) = 0.77 and r(2) = 0.82, respectively).

CONCLUSIONS

Multidetector spiral CT may permit assessment of remodeling of coronary atherosclerotic lesions in selected data sets of sufficient quality.

Association between plasmin activation system and intravascular ultrasound signs of plaque instability in patients with unstable angina and non-st-segment elevation myocardial infarction

BACKGROUND

The association between intravascular ultrasound (IVUS) signs of plaque instability and plasma levels of biomarkers was determined in patients with unstable angina and non-ST-segment elevation myocardial infarction (UA/NSTEMI).

METHODS

Fifty-two patients underwent coronary angiography and IVUS 8 +/- 5 hours after the onset of chest pain. IVUS analysis included plaque morphology, disruption, thrombi and eccentricity, lumen, external elastic membrane, and plaque plus media areas of culprit lesion and reference segments and arterial remodeling. Plasma levels of the thrombin activation system (thrombin-antithrombin complex [TAT], tissue factor pathway inhibitor [TFPI], and prothrombin fragments 1+2 [F1+2]) and plasmin activation system (tissue and urokinase-type plasminogen activator [t-PA and u-PA], plasminogen activator inhibitor-1 [PAI-1], and D-dimer) were measured with enzyme-linked immunosorbent assay kits before angiography.

RESULTS

Elevated levels of TAT (7.2 +/- 6.0 microg/L), F1+2 (1.8 +/- 1.0 nmol/L), TFPI (179.1 +/- 131.0 ng/mL), PAI-1 (95.4 +/- 54.6 ng/mL), t-PA (10.6 +/- 8.8 ng/mL), and u-PA (2.6 +/- 0.9 ng/mL) were found in patients with UA/NSTEMI. The serum levels of D-dimer (40.0 +/- 39.5 ng/mL) remained in reference range. Expansive and constrictive remodeling were found in 18 (35%) and 12 (23%) patients, respectively. Expansive remodeling of the culprit lesion was associated with significantly higher plasma levels of PAI-1 (121.6 +/- 55.0 vs 87.7 +/- 61.5 and 77.4 +/- 42.8 ng/ml, P =.039), and u-PA (3.0 +/- 1.2 vs 2.2 +/- 0.5 and 2.5 +/- 0.7 ng/mL, P =.026) as compared with constrictive and neutral remodeling. Increased plasma levels of u-PA were associated with plaque rupture (3.0 +/- 0.7 vs 2.5 +/- 0.9 ng/mL, P =.062). Plasma levels of PAI-1 and u-PA correlated positively with plaque plus media (P =.0297 and P =.0093) and external elastic membrane areas (P =.010 and P =.0002).

CONCLUSIONS

Elevated levels of biomarkers of plasmin activation system are associated with signs of plaque instability of culprit lesion in UA/NSTEMI and might therefore serve as non-invasive determinants of the population that is at high risk for subsequent adverse events.

Adaptive remodeling of the infarct-related artery is associated with recurrent ischemic events after thrombolysis in acute myocardial infarction

BACKGROUND

Recurrent ischemic events occur during the hospital stay of 7-32% of patients after successful thrombolytic treatment of acute myocardial infarction (AMI).

OBJECTIVE

To define the association between postinfarction angina pectoris and the clinical, angiographic, and intravascular ultrasound (IVUS) parameters of the infarct-related artery for consecutive prospectively included patients.

METHODS

Clinical, qualitative, and quantitative angiographic and IVUS data for 64 patients (56 men, aged 53+/-12 years) with thrombolysis of AMI were analyzed. All patients underwent coronary angiography and pre-interventional IVUS measurement electively within 1 month of AMI or at the time of the occurrence of postinfarction angina pectoris. Classification as adaptive or constrictive remodeling was according to whether the cross-sectional area of a vessel was larger or smaller than that of the proximal or distal reference segment.

RESULTS

Nineteen of the 64 patients (29.7%) suffered from recurrence of ischemic events (group 1), whereas 45 patients (60.3%, group 2) remained free from symptoms. In univariate analyses, multivessel disease (42 versus 24%, P= 0.0236) and adaptive remodeling (63 versus 24%, P= 0.0032) were found to occur more commonly among patients in group 1. The patients in group 1 exhibited larger total vessel cross-sectional areas than did the patients in group 2 (17.5+/-4.2 versus 14.9+/-6.1 mm2, P = 0.0556). In multivariate regression analysis, adaptive remodeling proved to be a significant predictor (P = 0.0145) of the recurrence of ischemic events after thrombolysis of AMI.

CONCLUSIONS

Adaptive remodeling of the infarct-related artery is associated with early postinfarction angina pectoris after thrombolysis of AMI.

What has intravascular ultrasound taught us about plaque biology?

Intravascular ultrasound (IVUS) has a defined role in the cardiac catheterization laboratory to assess lesion severity and the procedural success of vascular interventions. However, IVUS has also contributed to our understanding of the biology of atherosclerosis and restenosis. In acute coronary syndromes, IVUS has revealed varying degrees of stenosis, thrombosis, and plaque derangement typical of the plaque disruption seen in many pathologic studies of patients who have died of this condition. IVUS has demonstrated that the culprit lesions of patients surviving acute coronary syndromes also tend to be softer, with less calcium, and tend to have more plaque with positive arterial remodeling (compensatory enlargement) than lesions causing stable coronary syndromes. Arterial remodeling is also an important component of restenosis after coronary interventions. IVUS has suggested that interventions that reduce restenosis tend to have a greater impact on preventing negative remodeling (constriction) rather than reducing neointimal proliferation. Oxidant stress may be an important contributor to negative remodeling, as IVUS has demonstrated this anatomy at sites of coronary artery spasm. Positive remodeling seen by IVUS is also associated with impaired endothelial vasomotor dysfunction, and IVUS studies have demonstrated the contribution of vasomotor tone to arterial elasticity. Future directions include integrating IVUS with other imaging modalities, such as angiography, to study the interaction of anatomic and physiologic factors in atherosclerosis progression, and using the raw ultrasound signal to distinguish plaque components and differences in wall strain that may identify vulnerable plaques.

Pre-existing arterial remodeling is associated with in-hospital and late adverse cardiac events after coronary interventions in patients with stable angina pectoris

OBJECTIVES

The goal of this study was to investigate the association between the atherosclerotic arterial remodeling and the incidence of cardiac events after coronary interventions in patients with stable angina.

BACKGROUND

The local mode of de novo atherosclerotic remodeling is associated with plaque vulnerability and clinical symptoms. It may, therefore, reflect plaque morphology influencing the long-term outcome after coronary interventions.

METHODS

Quantitative angiography and intravascular ultrasound were obtained in 244 patients with stable angina before and after single-vessel revascularization. On the basis of the lesion and the reference segment vessel size, patients were categorized into three groups (adaptive [AR], constrictive [CR] and intermediate [IR] remodeling). The lesion was analyzed for lumen, total vessel and plaque areas. Clinical follow-up was obtained at a mean period of 7.7+/-3.7 months.

RESULTS

Patients with CR had a higher rate of in-hospital complications (10.9% vs. 2.9% and 2.7% in group CR vs. AR and IR, p = 0.035). In contrast, patients with AR had the highest rate of major adverse cardiac events (MACE) (44.3% vs. 25.5% in IR and 28.1% in CR, p = 0.024) with a predominance of revascularization at follow-up. Both target lesion restenosis (p = 0.036) and nontarget lesion de novo stenosis (p = 0.007) occurred more frequently in this group. Adaptive remodeling was a significant predictor of MACE in multivariate analysis.

CONCLUSIONS

Adaptive remodeling is associated with a higher rate of MACE, target lesion restenosis and nontarget de novo stenosis. This finding may be due to differential responses of the adaptively remodeled vessel to revascularization and a generally accelerated course of systemic atherosclerosis.