Coronary atherosclerotic disease burden: an emerging endpoint in progression/regression studies using intravascular ultrasound

In vivo critical fibrous cap thickness for rupture-prone coronary plaques assessed by optical coherence tomography

AIMS

The widely accepted threshold of <65 μm for coronary plaque fibrous cap thickness was derived from postmortem studies of ruptured plaques and may not be appropriate for in vivo rupture-prone plaques. We investigated the relationship between fibrous cap thickness and plaque rupture using optical coherence tomography (OCT).

METHODS AND RESULTS

We studied 266 lesions (103 from patients with acute coronary syndrome and 163 from patients with stable angina) before percutaneous coronary intervention using OCT. Ruptured and non-ruptured lipid-rich plaques were identified and the thinnest and most representative fibrous cap thickness were determined. Cap thickness was reliably measured in 71 ruptured and 111 non-ruptured plaques. From the ruptured plaques, the median thinnest cap thickness was 54 μm (50-60). The median most representative cap thickness was 116 μm (103-136). For non-ruptured plaques, the median thinnest cap thickness was 80 μm (67-104) and 182 μm (156-216) for most representative cap thickness. In 95% of ruptured plaques, the thinnest cap thickness and most representative cap thickness were <80 and <188 μm, respectively. The best cut-offs for predicting rupture were <67 μm (OR: 16.1, CI: 7.5-34.4, P < 0.001) for the thinnest cap thickness and <151 μm (OR: 35.6, CI: 15.0-84.3, P < 0.001) for most representative cap thickness. These two measures were modestly correlated (r(2) = 0.39) and both independently associated with rupture.

CONCLUSION

In vivo critical cap thicknesses were <80 μm for the thinnest and <188 μm for most representative fibrous cap thickness. Prospective imaging studies are required to establish the significance of these values.

A new method to measure necrotic core and calcium content in coronary plaques using intravascular ultrasound radiofrequency-based analysis

Although previous intravascular ultrasound (IVUS) radiofrequency-based analysis data showed acceptable reproducibility for plaque composition, measurements are not easily obtained, particularly that of lumen contour, because of the limited IVUS resolution. The purpose of this study was to compare a new measurement method (Shin’s method) and the conventional measurement method for necrotic core and calcium content in atherosclerotic lesions using Virtual Histology-intravascular ultrasound (VH-IVUS). Fifty-seven patients with unstable angina who underwent elective percutaneous coronary intervention were included. Shin’s method focuses on catheter contour, instead of lumen contour, and vessel contour. Patients ages ranged from 46 to 88 years, and 34 were men. A total of 1,401 frames from 59 culprit lesions were assessed. There were no significant differences in the mean area and volume of necrotic core and dense calcium between the two methods. Correlation coefficients (R) were ≥0.99 for all above mentioned parameters (P < 0.001). Between methods, the absolute differences in mean area and volume of necrotic core were 0.02 ± 0.02 mm² and 0.34 ± 0.29 mm³, respectively, while for mean area and volume of dense calcium, the absolute differences were 0.04 ± 0.07 mm² and 0.36 ± 0.52 mm³, respectively. The reproducibility of Shin’s method was excellent. For area of the necrotic core and dense calcium, the means of the differences between the two measurements were nearly zero, and the reproducibility coefficients were within 1% of the means of the two measurements. Mean analysis time for both measurements was 26.8 ± 6.7 min/segment in the conventional method and 3.3 ± 0.6 min/segment in Shin’s method. Shin’s method for measurement of necrotic core and dense calcium using VH-IVUS demonstrated a good correlation with the conventional method and excellent reproducibility. Also, Shin’s method required a significantly shorter analysis time than the conventional method. Therefore, Shin’s method could replace the conventional method for necrotic core and calcium measurement in atherosclerotic lesions, and it might be useful in the catheterization laboratory for online clinical decision.

[Cardiovascular disease in type 1 diabetes mellitus]

The association between type 1 diabetes and coronary heart disease has become very clear since the late 1970. It has been demonstrated that there is an important increased risk in morbidity and mortality caused by coronary artery disease in young adults with type 1 diabetes compared with the non diabetic population. The underlying pathogeneses is still poorly understood. While the role of glycemic control in the development of microvascular disease complication is well established its role in CVD in patients with DM1 remains unclear with epidemiologic studies reporting conflicting data. Recent findings from the DCCT/EDIC showed that prior intensive diabetes treatment during the DCCT was associated with less atherosclerosis, largely because of reduced level of HbA1c during the DCCT. The improvement of glycemic control itself appeared to be particularly effective in younger patients with shorter duration of the disease. Other analyses suggested the glycemia may have a stronger effect on CAD in patients without than in those with albuminúria. Other major determinants of coronary artery disease are the components of metabolic syndrome and the surrogate measure of insulin resistence: eGDR. It is proposed that patients with DM1 should have aggressive medical therapy, risk factor modification and careful monitoring not only of his blood sugar but also of the other processes involved in the atherosclerotic process, mostly the ones with family history of type 2 diabetes.

Serum tissue inhibitor of metalloproteinases-1 and higher risk features of coronary plaque

AIMS

The purpose of this study was to determine the relationship between higher-risk features of coronary plaque and serum levels of matrix metalloproteinase (MMP) family enzymes in the stable angina patients.

METHODS AND RESULTS

In 36 patients, 75 coronary lesions were assessed by intravascular ultrasound. For each of the plaques remodelling index, mean calcium arc and plaque burden were measured. Positive remodelling and the values of the calcium arc and plaque burden above the respective medians were regarded as the higher-risk features and summarised for each lesion. Serum levels of MMP-2, -3, -7, -9, and tissue inhibitor of MMP (TIMP)-1 and -2 were measured in all patients. TIMP-1 level was the independent predictor of presence of a lesion with positive remodelling (OR 1.032; 95% CI: 1.004-1.061) and of a lesion with higher plaque burden (OR 1.026; 95% CI: 1.003-1.049) in a given patient. Whereas, MMP-2 level was an independent predictor of presence of a lesion with higher calcium arc (OR 1.035; 95% CI: 1.001-1.071). TIMP-1 level (p=0.003) was also an independent predictor of a number of higher-risk features in the highest-risk plaque in a given patient.

CONCLUSIONS

TIMP-1 level correlates with clustering of plaque features associated with higher risk of complications in stable angina patients.

Frequency and Distribution of Thin-Cap Fibroatheroma and Ruptured Plaques in Human Coronary Arteries

OBJECTIVES

Our purpose was to quantify the frequency and distribution of suspected vulnerable lesions, defined as thin-capped fibroatheroma (TCFA) and ruptured plaque, in human coronary artery autopsy specimens.

BACKGROUND

Most acute coronary events and sudden death are believed to arise from rupture of a TCFA followed by thrombosis. Although there is general agreement that clinical events are usually caused by focal lesions, there is considerable debate over the relative importance of focal versus systemic factors in the pathogenesis of atherosclerosis.

METHODS

We longitudinally sectioned coronary arteries from 50 whole hearts taken from patients (mean age 73 years, 64% men) dying of cardiovascular (n = 33), noncardiovascular (n = 13), and unknown (n = 4) causes. A total of 3,639 longitudinal segments of length 3 mm were sectioned from 148 arteries, accounting for 10.9 m of total tissue length. Specimens were classified on the basis of histology and computer-aided morphometry.

RESULTS

Twenty-three TCFA and 19 ruptured plaques were found (mean +/- SD: 0.46 +/- 0.95 and 0.38 +/- 0.70 per heart, respectively), and these lesions accounted for only 1.6% and 1.2%, respectively, of the total length of the coronary tree examined in patients dying of cardiovascular causes. The majority of TCFA and ruptured plaque localized in the proximal third of the major coronary arteries, and in 92% of cases these lesions clustered within 2 or fewer nonoverlapping 20-mm segments.

CONCLUSIONS

The suspected precursors of rupture-mediated thrombosis occur in a limited, focal distribution in the coronary arteries.

Identification of the metabolic syndrome and imaging of subclinical coronary artery disease: early markers of cardiovascular risk

The metabolic syndrome and imaging of subclinical coronary artery disease are novel approaches to identify cardiovascular risk at an early disease stage before the onset of complications. The metabolic syndrome is defined as a combination of major and emerging cardiovascular risk factors that are related to underlying insulin resistance. These risk factors accelerate atherosclerotic disease progression and increase the risk for future cardiovascular events. Atherosclerosis imaging visualizes the presence of subclinical disease burden many years before the onset of symptoms. The early identification of asymptomatic persons with increased cardiovascular risk provides the opportunity to prevent of future disease complications. The relationship between the metabolic syndrome and sublinical disease burden is incompletely understood. Although further evaluation of the potential role for the emerging biomarkers and imaging techniques in the setting of the metabolic syndrome is needed, it is obvious that cardiovascular nurses need to develop a heightened awareness of patients at risk for future events.

Dedicated calibration formulas permit correction of differences between measurements by different IVUS devices as demonstrated in atherosclerotic human coronary arteries in vitro

Serial intravascular ultrasound (IVUS) measurements of coronary vessel dimensions are major endpoints of studies focusing on pharmacological interventions, efficiency of drug eluting stents, and vascular remodeling. In serial studies measurement variability among different IVUS devices may cause substantial misinterpretation and error. We analyzed 33 human coronary plaques in vitro using two different IVUS systems (mechanical IVUS system with a 40 MHz Atlantis SR catheter; solid-state electronic IVUS system with a 20 MHz Invision catheter) and repeatedly measured the total vessel, lumen, and plaque + media cross-sectional area and plaque burden (plaque + media area divided by total vessel area). Between the "raw" measurements made by the two devices, there was a significant difference for both plaque + media area (2.35+/-1.86 mm(2), P < 0.01) and plaque burden (5.39+/-3.68%, P < 0.05). Measurements were then corrected by use of recently introduced calibration formulas; as a result the differences decreased significantly for all IVUS parameters measured ( P < 0.0001). After correction, the remaining differences between the corrected mechanical and solid-state IVUS measurements similar to differences between repeated measurements with the same IVUS device (i.e., the intraobserver variability). Thus, in serial studies the use of different IVUS devices at index and follow-up procedure may introduce a substantial error as a result of system-related differences. The application of dedicated calibration formulas allows for correction for these differences by decreasing such differences to the level of intraobserver variability.

Influence of different lipid-lowering strategies on plaque volume and plaque composition in patients with coronary artery disease: role of intravascular ultrasound imaging

Lipid-lowering therapy has a significant impact on the prognosis and clinical course of coronary artery disease (CAD). Slowdown of plaque progression and plaque stabilization are the major cardiac goals of any lipid-lowering strategy. Until now, intravascular ultrasound imaging (IVUS) has been the only in vivo imaging modality which allows serial analysis of plaque burden and plaque composition on a volumetric basis. Several serial IVUS studies have shown that chronic statin therapy could decrease or even halt plaque growth. Moreover, aggressive lipid-lowering therapy using statins changes plaque composition over time. There is evidence that changes in plaque composition might explain the positive prognostic impact of statin therapy in patients with CAD. Beyond clinical endpoint studies, serial volumetric IVUS studies will become the standard to prove the efficacy of new lipid-lowering strategies in the future.

Atherosclerosis in childhood and adolescent type 1 diabetes: early disease, early treatment?

Autopsy studies have shown that atherosclerosis begins in adolescence in otherwise healthy individuals, and imaging techniques have shown that atherosclerosis develops earlier and is more prevalent in children with diabetes than in age-matched healthy controls. Cardiovascular disease has now overtaken diabetic nephropathy as the leading cause of premature mortality in young adults with diabetes, and the emphasis on disease prevention has accordingly shifted to a younger age group. The majority of children and adolescents with diabetes have suboptimal blood glucose control, and this contributes to accelerated arterial disease in this age group. Other conventional risk factors for coronary heart disease also need to be considered and treated aggressively. Effective early prevention of cardiovascular disease will involve lifestyle modification and full implementation of existing treatment guidelines, and large-scale prospective studies will be needed to establish the risks and benefits of early pharmacological intervention in children and adolescents.

Atherosclerosis imaging: intravascular ultrasound

Most acute coronary syndromes result from the rupture or erosion of high-risk plaques. Clinical imaging studies have shown that atherosclerotic plaque formation and rupture are widespread processes that are often asymptomatic. The rationale for atherosclerosis imaging is the in-vivo identification of high-risk lesions, which may subsequently lead to prevention of future cardiovascular events. Although intravascular ultrasound (IVUS) imaging studies demonstrated that echolucent appearance of the plaque and expansive (positive) remodelling are associated with unstable clinical presentation, these characteristics were not adequate for accurate plaque characterisation. Recent technical developments in ultrasound equipment and analytical methods, utilising several characteristics of the digitised ultrasound signal with radiofrequency analysis and elastography, promise accurate tissue characterisation. Other imaging modalities, including optical coherence tomography, also contribute to a more precise characterisation of the composition of atherosclerotic plaques. A non-imaging approach is the focal assessment of temperature differences using sensitive intravascular thermography catheters, presumably reflecting focal inflammatory changes of vulnerable lesions. Although the histological characteristics of the atheroma are critically important in the sequence of events leading to acute coronary syndromes, the clinical relevance of identifying these characteristics is not yet clear. There is increasing evidence that identifying and treating individual culprit lesions may not be enough to prevent the ischaemic cardiac events in most patients, because the acute coronary syndrome is not a disease of a single site or a few discrete segments, but rather a systemic disease that involves the entire coronary tree. In addition to detection and quantitation of early coronary atherosclerosis and disease activity, accurate and reproducible methods could help to identify high-risk patients and allow serial monitoring during various therapeutic interventions. Serial IVUS imaging makes it possible to visualise the vessel wall that harbours the atheroma at different time points. Typically, serial IVUS allows the assessment of the percentage change in atheroma volume, with considerable statistical power to detect small changes. Using this methodology, aggressive lipid lowering by a high-dose statin agent has been shown to stop the progression of atherosclerosis, and a new mutant high-density lipoprotein complex was found to be effective in regressing atheroma burden. Although intravascular ultrasound is very accurate for quantification of atheroma burden, widespread application and accurate and reproducible non-invasive imaging modalities are needed for large-scale risk assessment algorithms. Cardiovascular computed tomography is at the forefront of the non-invasive imaging modalities. Future prospective imaging studies will be necessary to identify focal or systemic characteristics of high-risk lesions and to demonstrate the relationship between plaque burden, biochemical markers and clinical events.

Comprehensive imaging of coronary artery disease: impact on contemporary treatment approaches

Coronary artery disease remains a major cause of mortality. Together with novel therapeutic and preventive approaches, important advances of coronary imaging are currently emerging. This article describes the status of modern coronary imaging and outlines expected future developments.

Coronary atherosclerosis in diabetic subjects: clinical significance, anatomic characteristics, and identification with in vivo imaging

Diabetes mellitus is an endocrine disorder that promotes the development and progression of atherosclerotic coronary disease. As a consequence, cardiovascular disease is the most important cause of morbidity and mortality in diabetics. Early identification and treatment of asymptomatic stages provides the opportunity to prevent cardiovascular end organ complications. Modem clinical imaging modalities allow the assessment of early atherosclerotic changes in coronary arteries; however, prospective evidence that atherosclerosis imaging impacts on clinical outcome is not yet available and future studies are necessary.

Antidote-mediated control of an anticoagulant aptamer in vivo

Patient safety and treatment outcome could be improved if physicians could rapidly control the activity of therapeutic agents in their patients. Antidote control is the safest way to regulate drug activity, because unlike rapidly clearing drugs, control of the drug activity is independent of underlying patient physiology and co-morbidities. Until recently, however, there was no general method to discover antidote-controlled drugs. Here we demonstrate that the activity and side effects of a specific class of drugs, called aptamers, can be controlled by matched antidotes in vivo. The drug, an anticoagulant aptamer, systemically induces anticoagulation in pigs and inhibits thrombosis in murine models. The antidote rapidly reverses anticoagulation engendered by the drug, and prevents drug-induced bleeding in surgically challenged animals. These results demonstrate that rationally designed drug-antidote pairs can be generated to provide control over drug activities in animals.