Differences in the morphology of unstable and stable coronary lesions and their impact on the mechanisms of angioplasty. An in vivo study with intravascular ultrasound

CVIT 2023 clinical expert consensus document on intravascular ultrasound

Intravascular ultrasound (IVUS) provides precise anatomic information in coronary arteries including quantitative measurements and morphological assessment. To standardize the IVUS analysis in the current era, this updated expert consensus document summarizes the methods of measurements and assessment of IVUS images and the clinical evidence of IVUS use in percutaneous coronary intervention.

Clinical expert consensus document on intravascular ultrasound from the Japanese Association of Cardiovascular Intervention and Therapeutics (2021)

Intravascular ultrasound (IVUS) provides precise anatomic information in coronary arteries including quantitative measurements and morphological assessment. To standardize the IVUS analysis in the current era, this updated expert consensus document summarizes the methods of measurements and assessment of IVUS images and the clinical evidence of IVUS use in percutaneous coronary intervention.

Clinical expert consensus document on standards for measurements and assessment of intravascular ultrasound from the Japanese Association of Cardiovascular Intervention and Therapeutics

Intravascular ultrasound (IVUS) provides precise anatomic information in coronary arteries including quantitative measurements and morphological assessment. To standardize the IVUS analysis in the current era, this expert consensus document summarizes the methods of measurements and assessment of IVUS images.

Expectations and limitations of contemporary intravascular imaging: lessons learned from pathology

Acute coronary syndrome is the leading cause of death worldwide and plaque rupture is the most common underlying mechanism of coronary thrombosis. During the last 2 decades the understanding of atherosclerotic plaque progression advanced dramatically and pathology studies provided fundamental insights of underlying plaque morphology, which paved the way for invasive imaging modalities, which bring a new area of atherosclerotic plaque characterization in vivo. The development of intravascular ultrasound (IVUS) allowed the field to evaluate the principles of vascular anatomy, which is often underestimated by coronary angiography. Furthermore, IVUS image technologies were developed to obtain improved characterization of plaque composition. However, since spatial resolution of IVUS is insufficient to distinguish details of plaque morphology, a broad adoption of this technology in clinical practice was missing. Optical coherence tomography is a light-based imaging modality with higher spatial resolution compared to IVUS, which enables the assessment of vascular anatomy with great detail.

Repeated episodes of thrombosis as a potential mechanism of plaque progression in cardiac allograft vasculopathy

AIMS

The pathogenesis of cardiac allograft vasculopathy (CAV) remains complex and may involve multiple mechanisms. We tested the hypothesis that the multilayer (ML) appearance, an intravascular ultrasound (IVUS) finding suggestive of repetitive thrombosis, is associated with plaque progression in heart transplant (HTx) recipients.

METHODS AND RESULTS

Our study population consisted of 132 HTx recipients undergoing at least two grayscale and virtual histology (VH)-IVUS examinations. A retrospective serial analysis was performed between the first (baseline) and the last (follow-up) IVUS data during a median follow-up of 3.0 years. The subjects were divided into two groups based on the presence of the ML appearance on the baseline IVUS. At baseline, subjects with ML appearance (n = 38) had a longer time elapsed since transplant, larger vessel volume, and larger plaque volume than those without (n = 94) (all P < 0.01). Intraluminal thrombi and plaque ruptures were identified only in subjects with ML appearance (P < 0.01 vs. those without). More subjects with ML appearance at baseline developed subsequent ML formation compared with those without [21 (55%) vs. 22 (23%), P < 0.01] during follow-up. There was an increase in plaque volume, necrotic core volume, and dense calcium volume in subjects with ML appearance (all P < 0.01 vs. those without). Multivariable linear regression analysis showed that ML appearance was a potential predictor of plaque progression (regression coefficient 0.28, 95% CI 0.10-0.45, P < 0.01).

CONCLUSIONS

The current study demonstrates that a finding of ML appearance, indicative of repeated episodes of mural thrombosis, is not infrequent in asymptomatic HTx recipients and possibly contributes to progression of CAV.

Endothelial shear stress: a critical determinant of arterial remodeling and arterial stiffness in humans--a carotid 3.0-T MRI study

BACKGROUND

Low endothelial shear stress (ESS) elicits endothelial dysfunction. However, the relationship between ESS and arterial remodeling and arterial stiffness is unknown in humans. We developed a 3.0-T MRI protocol to evaluate the contribution of ESS to arterial remodeling and stiffness.

METHODS AND RESULTS

Fifteen young (aged 26 ± 3 years) and 15 older (aged 57 ± 3 years) healthy volunteers as well as 15 patients with cardiovascular disease (aged 63 ± 10 years) were enrolled. Phase-contrast MRI of the common carotid arteries was used to derive ESS data from the spatial velocity gradients close to the arterial wall. ESS measurements were performed on 3 occasions and showed excellent reproducibility (intraclass correlation coefficient, 0.79). Multiple linear regression analysis accounting for age and blood pressure revealed that ESS was an independent predictor of the following response variables: carotid wall thickness (regression coefficient [b], -0.19 mm(2) per N/m(2); P=0.02), lumen area (b, -15.5 mm(2) per N/m(2); P<0.001), and vessel size (b, -24.0 mm(2) per N/m(2); P<0.001). Segments of the artery wall exposed to lower ESS were significantly thicker than segments exposed to higher ESS within the same artery (P=0.009). Furthermore, ESS was associated with arterial compliance, accounting for age, blood pressure, and wall thickness (b, -0.003 mm(2)/mm Hg per N/m(2); P=0.04).

CONCLUSIONS

Our carotid MRI data show that ESS is an important determinant of arterial remodeling and arterial stiffness in humans. The data warrant further studies to evaluate use of carotid ESS as a noninvasive tool to improve the understanding of individual cardiovascular disease risk and to assess novel drug therapies in cardiovascular disease prevention.

Changes in unstable coronary atherosclerotic plaque composition after balloon angioplasty as determined by analysis of intravascular ultrasound radiofrequency

The effects of balloon angioplasty (BA) on plaque distribution remain incompletely documented. In 20 patients with unstable angina pectoris, intravascular ultrasound gray scale and radiofrequency analyses were performed before and after BA. Composition of the plaque was 61% fibrotic tissue, 15% fibrofatty tissue, 15% necrotic tissue, and 7% dense calcium tissue. After BA, 35% of lumen enlargement was due to an increase in total vessel area and 65% to a significant decrease in plaque area. This resulted from a longitudinal redistribution of the tissue toward the reference segments. Radiofrequency analysis showed that the fibrous and fibrofatty tissues were able to redistribute longitudinally, whereas calcium remained at the same level. A third of necrotic tissue was lost after BA. In conclusion, in unstable plaques, BA resulted in a longitudinal redistribution of fibrotic and fibrofatty tissues and disappearance of 1/3 of necrotic tissue.

Large brachial and common carotid artery diameter in postmenopausal women with carotid atherosclerosis

BACKGROUND AND PURPOSE

It is recognized that arteries can enlarge to compensate atherosclerosis. The role of diameter enlargement of unaffected arteries is not well known. We hypothesized that brachial and common carotid arteries diameters were larger in subjects with carotid atherosclerosis compared to subjects without these lesions.

METHODS

We measured diameters in the common carotid and brachial arteries. Intimal medial thickness (IMT) of carotid arteries and carotid atherosclerosis were also evaluated using ultrasound in 83 cases and 83 disease-free control subjects.

RESULTS

Common carotid and brachial diameter was greater in cases (subjects with carotid atherosclerosis) than controls (subjects without carotid atherosclerosis) after adjustment for confounding variables (P<0.02). Common carotid diameter was also larger in individuals with greater IMT (P<0.0001), whereas brachial artery diameter was not. Subjects with more than one carotid plaque had larger arterial diameters than those with one or without plaques.

CONCLUSIONS

Common carotid and brachial artery diameters are both larger in cases than controls. This result suggests that vascular remodeling is a systemic process and not only a local response to atherosclerosis. The relationship between diameters and burden of disease could also suggest a link between vascular remodeling and severity of disease. Finally, if confirmed in prospective studies, brachial artery diameter could help to identify subjects at high cardiovascular risk, at least in postmenopausal women.

Intravascular Ultrasound Assessment of Ulcerated Ruptured Plaques

Background— It is not clear why some plaque ruptures lead to acute coronary syndromes (ACS) but others do not.

Methods and Results— We analyzed 80 plaque ruptures in 74 patients and compared culprit lesions of ACS patients with nonculprit lesions of ACS patients and lesions of non-ACS patients; both culprit and nonculprit plaque ruptures were studied in 6 of 54 ACS patients. Intravascular ultrasound findings suggesting thrombus were observed more frequently in culprit lesions of ACS patients (n=35) compared with nonculprit lesions of ACS patients (n=19) and lesions of non-ACS patients (n=26): 60% versus 32% versus 8% ( P <0.001). At the minimal lumen site, smaller lumen areas (3.3±1.5 versus 5.4±2.6 versus 6.1±2.0 mm 2 , P <0.001) and greater area stenosis (61±15% versus 50±14% versus 46±18%, P =0.002) and plaque burden (80±8% versus 71±8% versus 69±10%, P <0.001) were observed in culprit lesions of ACS patients compared with nonculprit lesions of ACS patients and lesions of non-ACS patients. Lesions were longer (18.7±6.4 versus 154.9±6.1 versus 12.0±4.9 mm, P <0.001) and rupture site remodeling indices were greater (1.26±0.21 versus 1.24±0.21 versus 1.09±0.05, P =0.002). Independent predictors of culprit plaque ruptures in ACS patients were smaller minimum lumen areas ( P =0.02) and presence of thrombus ( P =0.01).

Conclusions— Ruptured plaques in culprit lesions of ACS patients have smaller lumens; greater plaque burdens, area stenosis, and remodeling indices; and more thrombus. Plaque rupture itself does not lead to symptoms. The association of plaque rupture with a smaller lumen area and/or thrombus formation causes lumen compromise and leads to symptoms.

Morphologic and angiographic features of coronary plaque rupture detected by intravascular ultrasound

OBJECTIVES

This study was designed to report the clinical and angiographic correlates of plaque rupture detected by intravascular ultrasound (IVUS).

BACKGROUND

Acute coronary syndromes result from spontaneous plaque rupture and thrombosis.

METHODS

We report 300 plaque ruptures in 257 arteries in 254 patients. Plaque ruptures were detected during pre-intervention IVUS. Standard clinical, angiographic, and IVUS parameters were collected and/or measured. One lesion per patient was analyzed.

RESULTS

Multiple ruptures were observed in 39 of 254 patients (15%), 36 in the same artery. Plaque rupture occurred not only in patients with unstable angina (46%) or myocardial infarction (MI, 33%), but also stable angina (11%) or no symptoms (11%). The tear in the fibrous cap could be identified in 157 of 254 patients; 63% occurred at the shoulder of the plaque and 37% in the center of the plaque. Thrombi were more common in patients with unstable angina or MI (p = 0.02) and in multiple ruptures (p = 0.04). The plaque rupture site contained the minimum lumen area (MLA) site in only 28% of patients; rupture sites had larger arterial and lumen areas and more positive remodeling than MLA sites. Intravascular ultrasound plaque rupture strongly correlated with complex angiographic lesion morphology: ulceration in 81%, intimal flap in 40%, thrombus in 7%, and aneurysm in 7%.

CONCLUSIONS

Plaque ruptures occur with varying clinical presentations, strongly correlate with angiographic complex lesion morphology, may be multiple, and usually do not cause lumen compromise.

Plaque distribution and vascular remodeling of ruptured and nonruptured coronary plaques in the same vessel: an intravascular ultrasound study in vivo

OBJECTIVES

This study was designed to identify potential differences between the intravascular ultrasound (IVUS) characteristics of spontaneously ruptured and nonruptured coronary plaques.

BACKGROUND

The identification of vulnerable plaques in vivo may allow targeted prevention of acute coronary events and more effective evaluation of novel therapeutic approaches.

METHODS

Intravascular ultrasound was used to identify 29 ruptured plaques in arteries containing another nonruptured plaque in an adjacent segment. Intravascular ultrasound characteristics of these plaques were compared with plaques of computer-matched controls without evidence of plaque rupture. Plaque distribution was assessed by measuring the eccentricity of lumen location (inside the total vessel). Lumen cross-sectional area narrowing was calculated as [1 - (target/reference lumen area)] x 100%. A remodeling index was calculated as lesion/reference arterial area (>1.05 = compensatory enlargement, <0.95 = shrinkage).

RESULTS

Among the three groups of plaques, there was no significant difference in quantitative angiographic parameters, IVUS reference dimensions and IVUS lumen cross-sectional area narrowing. There was a difference in plaque distribution; lumen location by IVUS was significantly more eccentric in ruptured than in nonruptured (p = 0.002) and control plaques (p < 0.0001). The arc of disease-free vessel wall was larger in ruptured than in control plaques (p < 0.0001). The remodeling pattern of ruptured and nonruptured plaques differed significantly from that of the control plaques (p = 0.0001 and 0.003); compensatory enlargement was found in 66%, 48%, and 17%, whereas shrinkage was found in 7%, 10% and 48%, respectively.

CONCLUSIONS

Intravascular ultrasound assessment of plaque distribution and vascular remodeling may help to classify plaques with the highest probability of spontaneous rupture.

Intravascular ultrasound: novel pathophysiological insights and current clinical applications

Intravascular ultrasound (IVUS) is a valuable adjunct to angiography, providing new insights in the diagnosis of and therapy for coronary disease. Angiography depicts only a 2D silhouette of the lumen, whereas IVUS allows tomographic assessment of lumen area, plaque size, distribution, and composition. The safety of IVUS is well documented, and the assessment of luminal dimensions represents an important application of this modality. Comparative studies show the greatest disparities between angiography and ultrasound after mechanical interventions. In young subjects, normal intimal thickness is typically approximately 0.15 mm. With IVUS, lipid-laden lesions appear hypoechoic, fibromuscular lesions generate low-intensity echoes, and fibrous or calcified tissues are echogenic. Calcium obscures the underlying wall (acoustic shadowing). The extent and severity of disease by angiography and ultrasound are frequently discrepant. Arterial remodeling refers to changes in vascular dimensions during the development of atherosclerosis. At diseased sites, the external elastic membrane may actually shrink in size, contributing to luminal stenosis. The interpretation of IVUS relies on simple visual inspection of acoustic reflections to determine plaque composition. However, different tissue components may look quite similar, and artifacts may adversely affect ultrasound images. IVUS commonly detects occult disease in angiographically "normal" sites. In ambiguous lesions, ultrasound permits lesion quantification, particularly for left main coronary disease. IVUS has emerged as the optimal method for the detection of transplant vasculopathy. An important potential application of ultrasound is the identification of atheromas at risk of rupture. The mechanisms of action of interventional devices have been elucidated using IVUS, and ultrasound is used by some operators to select the most suitable interventional device. IVUS-derived residual plaque burden is the most useful predictor of clinical outcome. In restenosis after balloon angioplasty, negative remodeling is a major mechanism of late lumen loss. IVUS is not routinely used for stent optimization, and there is no consensus regarding optimal procedural end points. Ultrasound has proven useful in evaluating brachytherapy. New and emerging applications for IVUS are continuing to evolve, particularly in atherosclerosis regression-progression trials.

Size of emptied plaque cavity following spontaneous rupture is related to coronary dimensions, not to the degree of lumen narrowing. A study with intravascular ultrasound in vivo

OBJECTIVE

To identify any potential relations between the size of an emptied plaque cavity and the remodelling pattern, plaque or vessel dimensions, lumen narrowing, and other ultrasonic lesion characteristics.

DESIGN

Intravascular ultrasound was used to examine prospectively 51 ruptured ulcerated coronary plaques. Cross sectional area measurements comprised lumen, vessel, plaque, and emptied plaque cavity. Lumen narrowing was calculated as 1 - (lesion lumen area/reference lumen area) x 100%. A remodelling index was calculated as lesion vessel area/reference vessel area, and plaques were divided into those with values > 1.05 (group A) and </= 1.05 (group B).

RESULTS

Of the total of 51 plaques, 36 (71%) were assigned to group A and 15 (29%) to group B. In neither group was there a significant difference in reference dimensions and lumen narrowing. However, lesion vessel (mean (SD): 22.6 (8.1) mm(2) v 17. 5 (4.3) mm(2); p = 0.006) and plaque areas (15.8 (6.2) mm(2) v 12.8 (3.2) mm(2); p = 0.03) were greater in group A than in group B. The cavity inside the plaque was larger in group A than in group B (2.8 (1.6) mm(2) v 1.8 (0.9) mm(2); p = 0.007) and showed a positive linear relation with lesion and reference vessel size (r = 0.58 and 0.56, respectively; p < 0.001), but not with lumen narrowing.

CONCLUSIONS

The size of the emptied cavity inside ruptured plaques is on average larger in lesions with adaptive vascular remodelling, and shows a linear relation with lesion plaque and vessel size and with the reference dimensions, but not with the degree of lumen narrowing.

Assessment of coronary compensatory enlargement by three-dimensional intravascular ultrasound

Several techniques have been used to demonstrate that human arteries respond to atherosclerosis by increasing their total arterial area to prevent a decrease in blood flow. Three-dimensional reconstructions of coronary arteries can document this compensatory response accurately and specifically. Seven human coronary arteries were reconstructed using intravascular ultrasound and biplane angiography, and vessel geometries were quantified. In all seven vessels, as plaque area increased, overall vessel area increased (R = 0.986, 0.933, 0.984, 0.678, 0.763, 0.963, and 0.830), but luminal cross-sectional area did not significantly decrease. Focal compensatory enlargement was identified in each vessel, and in some cases this response appeared to occur until the vessel was 65% occluded. Luminal enlargement near the proximal ends was attributed to the natural taper of the vessel. The semi-automated, three-dimensional segmentation technique used in this study allows reproducible quantification, as there is no subjective manual tracing involved. Following the intravascular ultrasound transducer in time and space with biplane angiography allows for accurate reconstruction with or without automated pullback devices. Information on the rate of change of vessel measurements is also presented, which, when combined with visualization of accurate 3D geometry, provides a unique assessment of coronary compensatory enlargement. This reconstruction technique can be applied in a clinical environment with no major modification.

Coronary microembolization--its role in acute coronary syndromes and interventions

The diagnosis coronary artery disease is classically based on patient's symptoms and morphology, as analyzed by angiography. The importance of risk factors for the development of coronary atherosclerosis and disturbance of coronary vasomotion is clearly established. However, microembolization of the coronary circulation has also to be taken into account. Microembolization may occur as a single or as multiple, repetitive events, and it may induce inflammatory responses. Spontaneous microembolization may occur, when the fibrous cap of an atheroma or fibroatheroma (Stary i.v. and Va) ruptures and the lipid pool with or without additional thrombus formation is washed out of the atheroma into the microcirculation. Such events with progressive thrombus formation are known as cyclic flow variations. Plaque rupture occurs more frequently than previously assumed, i.e. in 9% of patients without known heart disease suffering a traffic accident and in 22% of patients with hypertension and diabetes. Also, in patients dying from sudden death microembolization is frequently found. Patients with stable and unstable angina show not only signs of coronary plaque rupture and thrombus formation, but also microemboli and microinfarcts, the only difference between those with stable and unstable angina being the number of events. Appreciation of microembolization may help to better understand the pathogenesis of ischemic cardiomyopathy, diabetic cardiomyopathy and acute coronary syndromes, in particular in patients with normal coronary angiograms, but plaque rupture detected by intravascular ultrasound. Also, the benefit from glycoprotein IIb/IIIa receptor antagonist is better understood, when not only the prevention of thrombus formation in the epicardial atherosclerotic plaque, but also that of microemboli is taken into account. Microembolization also occurs during PTCA, inducing elevations of troponin T and I and elevations of the ST segment in the EKG. Elevated baseline coronary blood flow velocity, as a potential consequence of reactive hyperemia in myocardium surrounding areas of microembolization, is more frequent in patients with high frequency rotablation than in patients with stenting and in patients with PTCA. The hypothesis of iafrogenic microembolization during coronary interventions is now supported by the use of aspiration and filtration devices, where particles with a size of up to 700 microns have been retrieved. In the experiment, microembolization is characterized by perfusion-contraction mismatch, as the proportionate reduction of flow and function seen with an epicardial stenosis is lost and replaced by contractile dysfunction in the absence of reduced flow. The analysis of the coronary microcirculation, in addition to that of the morphology and function of epicardial coronary arteries, and in particular appreciation of the concept of microembolization will further improve the understanding of the pathophysiology and clinical symptoms of coronary artery disease.

Coronary artery disease: arterial remodelling and clinical presentation

OBJECTIVE

To investigate the hypothesis that in coronary artery disease large plaques in compensatorily enlarged segments are associated with acute coronary syndromes, whereas smaller plaques in shrunken segments are associated with stable angina pectoris.

METHODS

Patients selected for percutaneous transluminal coronary angioplasty (PTCA) were divided into two groups, one with stable angina pectoris (stable group, n = 37) and one with unstable angina or postmyocardial infarction angina of the infarct related artery (unstable group, n = 32). In both groups, remodelling at the culprit lesion site was determined by intravascular ultrasound before the intervention. Remodelling was calculated as relative vessel area: [vessel area culprit lesion site / mean vessel area of both proximal and distal reference sites] x 100%. Compensatory enlargement was defined as remodelling of >/= 105%, whereas shrinkage was defined as remodelling of </= 95%.

RESULTS

In the unstable group, the vessel area at the culprit lesion site was larger than in the stable group, at mean (SD) 18.1 (5.3) v 14.6 (5.4) mm(2) (p = 0.008). Lumen areas were similar. Consequently, plaque area and percentage remodelling were larger in the unstable group than in the stable group: mean (SD) 14.8 (4.8) v 11.6 (4.9) mm(2) (p = 0.009) and 112 (31)% v 95 (17)% (p = 0.005), respectively. Significantly more culprit lesion sites were classified as shrunken in the stable group (21/37) than in the unstable group (8/32; p = 0.014). On the other hand, more lesion sites were classified as enlarged in the unstable group (16/23) than in the stable group (8/37; p = 0.022).

CONCLUSIONS

In patients selected for PTCA, the mode of remodelling is related to clinical presentation.

Arterial remodelling of native human coronary arteries in patients with unstable angina pectoris: a prospective intravascular ultrasound study

OBJECTIVE

To investigate the use of intravascular ultrasound (IVUS) in detecting the presence of arterial remodelling in patients with unstable angina.

DESIGN

Prospective case study.

PATIENTS

60 of 95 consecutively admitted patients with unstable angina (41 male, 19 female), mean (SD) age 61.2 (8.1) years.

INTERVENTIONS

Qualitative and quantitative coronary angiography and IVUS.

MAIN OUTCOME MEASURES

Adaptive or constrictive remodelling (AR, CR) was considered present when the cross sectional area of the external elastic membrane at the lesion site was larger than the proximal cross sectional area or smaller than the distal cross sectional area, respectively.

RESULTS

22 of the 60 patients (37%) showed AR and 14 (23%) showed CR. No remodelling was seen in 24 patients (group NR). The plaque contained more thrombus and plaque rupture in group AR than in groups CR and NR (thrombus: 91% v 50% and 67%, respectively, p = 0.023; rupture: 73% v 29% and 42%, p = 0.020). AR was associated with a larger plaque cross sectional area (12.6 (SD 4.6) mm2 v 10.8 (6.3) and 9.2 (3.7) mm2, p = 0.001) and larger external elastic membrane cross sectional area (16.5 (5.8) mm2 v 13.2 (5.2) and 14.4 (3.6) mm2, p = 0.01 in group AR v groups CR and NR, respectively), while the plaque burden was larger in groups AR (74.9 (9.1)%) and CR (72.4 (16.6)%) than in group NR (66.2 (18.1)%, p = 0.005).

CONCLUSIONS

IVUS is capable of detecting adaptive and constrictive remodelling of target lesions and its relation to plaque morphology in unstable angina.

Review: Clinical aspects of vascular remodeling

Vascular remodeling represents a spectrum of structural changes whereby the vascular wall responds to changes in its hemodynamic environment. Such changes may be classified as vessel enlargement (outward remodeling), diminution (inward remodeling), alternatively as adaptive (compensatory, appropriate to the hemodynamic stimulus), or maladaptive (dysfunctional, inappropriate). The direction and scale of remodeling are coordinated by endothelial production of growth factors, proteases, and cellular adhesion molecules in response to sensed changes in blood flow. In early atherosclerosis, outward remodeling preserves lumen size. Although protective in the long-term, the matrix degradation involved in this process may predispose atherosclerotic plaques to rupture, hence increasing the risks of acute coronary syndromes. Inward remodeling also occurs in advanced atherosclerotic lesions, whereby the vessel shrinks rather than enlarging, exacerbating rather than ameliorating stenosis. In transplant coronary artery disease, early inward remodeling may be a more important component of vessel stenosis than intimal thickening, while inappropriate inward remodeling appears to be as least as important as excessive intimal growth in the development of restenosis after angioplasty. Increased awareness of vascular remodeling, and in particular its malaptive forms, may provide new therapeutic insights for the future.

Screening of ruptured plaques in patients with coronary artery disease by intravascular ultrasound

AIM

To visualise the characteristics of ruptured plaques by intravascular ultrasound (IVUS) and to correlate plaque characteristics with clinical symptoms to establish a quantitative index of plaque vulnerability.

METHODS

144 consecutive patients with angina were examined using IVUS. Ruptured plaques, characterised by a plaque cavity and a tear on the thin fibrous cap, were identified in 31 patients (group A), of whom 23 (74%) presented with unstable angina. Plaque rupture was confirmed by injecting contrast medium filling the plaque cavity during IVUS examination. Of the patients without plaque rupture (group B, n = 108), only 19 (18%) had unstable angina.

RESULTS

No significant differences were found between groups A and B in relation to plaque and vessel area (p > 0.05). Mean (SD) per cent stenosis in group A was less than in group B, at 56.2 (16.5)% v 67.9 (13.4)%; p < 0.001. Area of the emptied plaque cavity in group A (4.1 (3.2) mm2) was larger than the echolucent zone in group B (1.32 (0.79) mm2) (p < 0.001). The plaque cavity to plaque ratio in group A (38.5 (17.1)%) was larger than the echolucent area to plaque ratio in group B (11.2 (8.9)%) (p < 0.001). The thickness of the fibrous cap in group A was less than in group B, at 0.47 (0.20) mm v 0.96 (0.94) mm; p < 0.001.

CONCLUSIONS

Plaques seem to be prone to rupture when the echolucent area is larger than 4.1 (3.2) mm2, when the echolucent area to plaque ratio is greater than 38.5 (17.1)%, and when the fibrous cap is thinner than 0.7 mm. IVUS can identify plaque rupture and vulnerable plaques. This may influence patient management and treatment.

Role of intravascular ultrasound imaging in identifying vulnerable plaques

A plaque that has a large lipid core and a thin fibrous cap may undergo rupture. Once it ruptures, it may lead to thrombus formation and subsequent vessel occlusion. To identify unstable plaques before they rupture is essential for clinical management and patient's prognosis. Intravascular ultrasound (IVUS) opens a new window for the assessment of plaque morphology to identify vulnerable plaques and plaque rupture. We examined 144 patients with angina and ischemic ECG changes using IVUS. Ruptured plaques, characterized by a plaque cavity and a tear on the thin fibrous cap, were identified in 31 patients (group A) of which 23/31 (74%) clinically presented as unstable angina. Plaque rupture was confirmed by injecting contrast medium filling the plaque cavity during IVUS examination. Of the patients without plaque rupture (group B, n = 108), only 19 (18%) had unstable angina. No significant differences between the 2 groups were found concerning the vessel and plaque areas (p > 0.05). The percent stenosis in group A (56.2 +/- 16.5%) was significantly lower than in group B (67.9 +/- 13.4%) (p < 0.001). Area of the plaque cavity in group A (4.1 +/- 3.2 mm2) was significantly larger than the echolucent zone in group B (1.32 +/- 0.79 mm2) (p < 0.001). The plaque cavity/plaque ratio in group A (38.5 +/- 17.1%) was larger than the echolucent area/plaque ratio in group B (11.2 +/- 8.9%) (p < 0.001). The thickness of the fibrous cap in group A (0.47 +/- 0.20 mm) was significantly thinner than that (0.96 +/- 0.94 mm) in group B (p < 0.001).

CONCLUSIONS

Plaques seem to be prone to rupture when the echolucent area is larger than 1 mm2, the echolucent area/plaque ratio greater than 20% and the fibrous cap thinner than 0.7 mm. IVUS has the capacity of identifying plaque rupture and vulnerable plaques. This may have potential influence on patients management and therapy.

Intravascular ultrasound imaging of ruptured atherosclerotic plaques in coronary arteries

Intravascular ultrasound demonstrated plaque ruptures that occurred in regions involved with large complicated atherosclerotic plaques in the coronary artery. Because intravascular ultrasound evaluates both plaque and luminal dimensions, it contributes to our understanding of the pathophysiology of coronary artery disease.

Comparison of angioscopic, intravascular ultrasonic, and angiographic detection of thrombus in coronary stenosis

Coronary angioscopy, intravascular ultrasound, and angiography were compared in 20 patients regarding their sensitivity and specificity in the detection of thrombus. Although all imaging procedures demonstrate a high specificity, only coronary angioscopy has a sensitivity high enough to provide sufficient evidence of thrombus, even in patients with stable angina.

In vitro examination of the coronary artery wall after balloon angioplasty using intracoronary ultrasound

After autopsy 12 human coronary arteries were investigated by intracoronary ultrasound in order to measure the vessel wall dimensions and to detect damage on the vessel wall architecture after balloon angioplasty. Histology revealed artherosclerosis in 11/12 arteries. A total of 41 representative coronary segments were selected for further off-line ultrasound and histological analysis. Intracoronary ultrasound and histological measurements of the vessel wall thickness after balloon dilatation demonstrated a good correlation between the maximum thickness of the intima (histology 0.62 mm vs. intracoronary ultrasound 0.65 mm, r = 0.87) and the intima-media complex (0.80 mm vs. 0.83 mm, r = 0.87), in contrast to a weak one between the minimum thickness (r = 0.46 and r = 0.37). A total of 21 cases of damage occurred during angioplasty; intracoronary ultrasound detected 17. Further analysis showed that it imaged 10 of 11 cases of damage involving more than 30 degrees of the vessel circumference and 7 of 10 cases of damage involving less than 30 degrees of the vessel circumference. After balloon angioplasty of diseased coronary arteries, intracoronary ultrasound is therefore reliable in measuring the maximum wall thickness and in imaging damage involving more than 30 degrees of the vessel wall circumference.

Morphology of chronic coronary occlusions and response to interventional therapy--a study by intracoronary ultrasound

OBJECTIVES

Balloon angioplasty of chronic coronary occlusions has a low procedural success and a high recurrence rate. Better tomographic insights into the lesion morphology may improve the interventional strategy and results.

METHODS

Intracoronary ultrasound was used during the recanalizaton procedure of 45 chronic coronary occlusions (2 weeks to 14 months; average 3.4 months) to determine the lesion morphology and to assess the angioplasty result. The luminal area and the plaque burden were measured proximal and distal to the occlusion, and within the occlusion. The ultrasonographic characteristics of the occlusive lesions were compared to 45 nonocclusive lesions of age-matched patients with stable angina pectoris.

RESULTS

Occlusive lesions were more often echodense as compared to nonocclusive lesions (35% vs. 20%; p = 0.10). In chronic occlusions a multi-layered plaque morphology was observed in 22%, and this morphology was not found in nonocclusive lesions. Angiographic characteristics were not related to the ultrasonographic morphology of the lesion. Despite similar vessel areas in occlusive and nonocclusive lesions, the balloon size selected according to the angiographic image was underestimated in occlusive lesions. Based on the quantitative ultrasound measurement the balloon size was increased from 2.6 +/- 0.3 mm to 3.3 +/- 0.5 mm in 53% of the lesions. This resulted in an increase of the luminal area from 3.51 +/- 0.92 to 5.08 +/- 1.43 mm2 (p < 0.001). The acute recoil after balloon angioplasty was similar (34 +/- 18%) in hypodense and echodense plaques, but was significantly higher in lesions with a multi-layered plaque morphology (49 +/- 22%; p < 0.05). In 19 patients with severe dissections or extreme acute recoil (residual stenosis > 50%) the use of a stent increased the luminal area from 3.94 +/- 0.81 to 7.51 +/- 1.71 mm2 (p < 0.001).

CONCLUSIONS

Intracoronary ultrasound demonstrated a multi-layered plaque morphology in one fourth of the chronic occlusions. This type of plaque was associated with a significant acute recoil. The presence of diffuse atherosclerosis in neighbouring segments of chronic coronary occlusions leads to underestimation of the balloon size. Quantitative assessment by intracoronary ultrasound helped to optimize the balloon size leading to a significant luminal area gain. The detection of excessive acute recoil should be considered an indication for stent deployment.