Effect of lipid-lowering therapy with atorvastatin on atherosclerotic aortic plaques detected by noninvasive magnetic resonance imaging

Strategies to reverse atherosclerosis: an imaging perspective

Several treatment strategies, including lowering low-density lipoprotein cholesterol with intensive statin therapy, reducing triglycerides with fibrates, and raising high-density lipoprotein cholesterol with nicotinic acid, have the potential to induce atherosclerosis regression. Atherosclerosis imaging techniques including intravascular ultrasound, carotid ultrasound to measure carotid intima-media thickness, and cardiovascular MRI are established modalities for describing longitudinal changes in the quantity and quality of atherosclerotic plaque. An increasing number of clinical trials are using radiologic measures of subclinical atherosclerosis as surrogate end points in lieu of the traditional "hard" end points of myocardial infarction and death. This approach has great appeal, as improvements in atherosclerosis imaging now enable the characterization of early atheromas and positive remodeling within the vessel wall before the plaque becomes obstructive. Additional prospective data correlating these surrogate end points with hard outcomes are needed to determine whether atherosclerosis regression will be the major determinant of future treatment strategies.

The aorta wall of patients presenting to the emergency department with acute myocardial infarction by cardiac magnetic resonance

BACKGROUND

Inflammation has been shown to be a major component in the pathophysiology of acute coronary syndrome (ACS). In patients presenting with acute myocardial infarction (AMI), a critical component of the ACS spectrum, multiple coronary arteries are involved during this inflammatory process. In addition to the coronary vasculature, the inflammatory cascade has also been shown to affect the carotid arteries and possibly the aorta.

PURPOSE

To assess the involvement of the aorta during AMI by cardiac magnetic resonance (CMR).

METHODS

We prospectively evaluated the aortic wall by CMR in 123 patients. 78 patients were enrolled from the emergency department (ED), who presented with chest pain and were classified as either: (1) AMI: elevated troponin levels and typical chest pain or (2) non-cardiac chest pain (CP): negative troponins and a normal stress test or normal cardiac catheterization. We compared these 2 groups to a group of 45 asymptomatic diabetic patients. The descending thoracic aortic wall area (AWA) and maximal aortic wall thickness (AWT) were measured using a double inversion recovery T-2 weighted, ECG-gated, spin echo sequence by CMR.

RESULTS

Patients with AMI were older, more likely to smoke, had a higher incidence of claudication, and had higher CRP levels. The AWA and maximal AWT were greater in patients who presented to the ED with ACS (2.11+/-0.17 mm(2), and 3.17+/-0.19 mm, respectively) than both patients presenting with non-cardiac CP (1.52+/-0.58 mm(2), p<0.001; and 2.57+/-0.10 mm, p<0.001) and the diabetic patients (1.38+/-0.58 mm(2), p<0.001; and 2.30+/-0.131 mm, p<0.001). The difference in the aortic wall characteristics remained significant after correcting for body mass index, hyperlipidemia, statins and C-reactive protein. There was no difference in maximal AWT or AWA between patients with non-cardiac CP and patients with diabetes.

CONCLUSION

Patients with AMI have a significantly greater maximal aortic wall thickness and area compared to patients with non-cardiac CP. Longitudinal studies are needed to assess whether this increase is due to inflammation or a higher atherosclerotic burden.

Variations in atherosclerosis and remodeling patterns in aorta and carotids

BACKGROUND

Atherosclerosis is a progressive disease that causes vascular remodeling that can be positive or negative. The evolution of arterial wall thickening and changes in lumen size under current "standard of care" in different arterial beds is unclear. The purpose of this study was to examine arterial remodeling and progression/regression of atherosclerosis in aorta and carotid arteries of individuals at risk for atherosclerosis normalized over a 1-year period.

METHODS

In this study, 28 patients underwent at least 2 black-blood in vivo cardiovascular magnetic resonance (CMR) scans of aorta and carotids over a one-year period (Mean 17.8 +/- 7.5 months). Clinical risk profiles for atherosclerosis and medications were documented and patients were followed by their referring physicians under current "standard of care" guidelines. Carotid and aortic wall lumen areas were matched across the time-points from cross-sectional images.

RESULTS

The wall area increased by 8.67%, 10.64%, and 13.24% per year (carotid artery, thoracic aorta and abdominal aorta respectively, p < 0.001). The lumen area of the abdominal aorta increased by 4.97% per year (p = 0.002), but the carotid artery and thoracic aorta lumen areas did not change significantly. The use of statin therapy did not change the rate of increase of wall area of carotid artery, thoracic and abdominal aorta, but decreased the rate of change of lumen area of carotid artery (-3.08 +/- 11.34 vs. 0.19 +/- 12.91 p < 0.05).

CONCLUSIONS

Results of this study of multiple vascular beds indicated that different vascular locations exhibited varying progression of atherosclerosis and remodeling as monitored by CMR.

Findings of clinical trials that evaluate the impact of medical therapies on progression of atherosclerosis

BACKGROUND

Arterial wall imaging has been increasingly employed in clinical trials to evaluate the impact of medical therapies on progression of atherosclerosis.

SCOPE

A selective overview of major findings from clinical trials that assessed the impact of medical therapies on atherosclerosis progression.

FINDINGS

Targeting established risk factors including LDL cholesterol, HDL cholesterol and blood pressure has a beneficial impact on disease progression.

CONCLUSION

As a result, vascular imaging has been employed in the early evaluation of experimental therapies.

Inflammation imaging in atherosclerosis

Inflammation is important at many stages of atherosclerotic plaque development. We highlight several imaging modalities that can quantify the degree of plaque inflammation noninvasively. Imaging of this type might allow testing of novel antiatherosclerosis drugs, identification of patients at risk of plaque rupture, and deeper insight into the biology of the disease. The imaging modalities are discussed in relation to their potential use in these areas.

Effect of lipid-lowering therapy with atorvastatin on atherosclerotic aortic plaques: a 2-year follow-up by noninvasive MRI

BACKGROUND

Using MRI, we reported plaque regression in thoracic aorta and retardation of plaque progression in abdominal aorta by 1-year atorvastatin. However, association between serial plaque changes and LDL-cholesterol levels was not fully elucidated.

DESIGN

A prospective, randomized, open-label trial.

METHODS

We investigated the long-term effect of 20 versus 5-mg atorvastatin on thoracic and abdominal plaques and the association between plaque progression and on-treatment LDL-cholesterol levels in 36 hypercholesterolemic patients. MRI was performed at baseline and 1 and 2 years of treatment. Vessel wall area change was evaluated.

RESULTS

The 20-mg dose markedly reduced LDL-cholesterol levels (-47%) versus 5-mg (-35%) dose. After 2 years of treatment, regression of thoracic plaques was found in the 20-mg group (-15% vessel wall area reduction), but not in the 5-mg group (+7%). Although the 20-mg dose induced plaque regression (-14%) from baseline to 1 year, no further regression was seen from 1 to 2 years of treatment (-1%). Regarding abdominal plaques, progression was found in the 5-mg group (+10%), but not in the 20-mg group (+2%). Plaque progression in the 5-mg group was found from baseline to 1 year (+8%), but not from 1 to 2 years (+2%). The degree of thoracic plaque regression correlated with LDL-cholesterol reduction (r = 0.61), whereas thoracic plaque change from 1 to 2 years correlated with on-treatment LDL-cholesterol levels (r = 0.64).

CONCLUSION

Twenty milligrams of atorvastatin regressed thoracic plaques. However, maintaining low LDL-cholesterol levels was needed to prevent plaque progression. In abdominal aorta, only retardation of plaque progression was found after 2 years of 20-mg treatment.

Fine particulate matter air pollution, proximity to traffic, and aortic atherosclerosis

BACKGROUND

The initiation and acceleration of atherosclerosis is hypothesized as a physiologic mechanism underlying associations between air pollution and cardiovascular effects. Despite toxicologic evidence, epidemiologic data are limited.

METHODS

In this cross-sectional analysis we investigated exposure to fine particulate matter (PM2.5) and residential proximity to major roads in relation to abdominal aortic calcification, a sensitive indicator of systemic atherosclerosis. Aortic calcification was measured by computed tomography among 1147 persons, in 5 US metropolitan areas, enrolled in the Multi-Ethnic Study of Atherosclerosis. The presence and quantity of aortic calcification were modeled using relative risk regression and linear regression, respectively, with adjustment for potential confounders.

RESULTS

We observed a slightly elevated risk of aortic calcification (RR = 1.06; 95% confidence interval = 0.96-1.16) with a 10 microg/m contrast in PM2.5. The PM2.5-associated risk of aortic calcification was stronger among participants with long-term residence near a PM2.5 monitor (RR = 1.11; 1.00-1.24) and among participants not recently employed outside the home (RR = 1.10; 1.00-1.22). PM2.5 was not associated with an increase in the quantity of aortic calcification (Agatston score) and no roadway proximity effects were noted. There was indication of PM2.5 effect modification by lipid-lowering medication use, with greater effects among users, and PM2.5 associations were observed most consistently among Hispanics.

CONCLUSIONS

Although we did not find persuasive associations across our full study population, associations were stronger among participants with less exposure misclassification. These findings support the hypothesis of a relationship between particulate air pollution and systemic atherosclerosis.

Medicare-eligible patients diagnosed with atherosclerosis: patterns in statin therapy and lipid monitoring

BACKGROUND

This study assessed lipid-monitoring and statin therapy patterns in routine clinical practice for Medicare-eligible patients diagnosed with atherosclerosis.

METHODS

A retrospective study using a random sample of 1 million patients (>17 years of age) from a US outpatient electronic medical record database was conducted with patients > or =65 years of age having a diagnostic code for atherosclerosis between January 2004 and March 2006. Use of statin therapy at the time of and for 12 months after atherosclerosis diagnosis, in addition to patient demographics, comorbid conditions, baseline and post-diagnosis LDL-C, were recorded.

RESULTS

In the million-patient sample, 3303 patients were > or =65 years of age and had a diagnostic code of atherosclerosis. Overall, 63% of these patients were not prescribed statin therapy at the time of or within 12 months after diagnosis. Lipid monitoring within 6 months before diagnosis occurred in 37% of patients. Of those with a recorded baseline LDL-C (n = 1213), 50% had LDL-C > or =100 mg/dL and 87% had LDL-C > or =70 mg/dL. Among patients with baseline LDL-C > or =100 mg/dL, 55% were not prescribed statin therapy at or after their diagnosis compared with 49% of patients with baseline LDL-C <100 mg/dL (p = 0.0001). There were significantly more patients who were prescribed statin therapy with LDL-C <100 mg/dL after diagnosis (67%) than at diagnosis (55%) (p = 0.0008).

LIMITATIONS

Patients were required to have an ICD-9 diagnosis of atherosclerosis, which may have underestimated those with atherosclerosis that was not coded specifically as atherosclerosis. Because the study included patients treated in physician practice with an electronic medical record system (EMR), they may be different from patients who are treated by physicians not equipped with an EMR. Pharmacy data were the prescription ordered and not the drug claim indicating that the prescription was dispensed. This may overestimate the statin therapy utilization estimates.

CONCLUSIONS

A substantial gap in the management of diagnosed atherosclerosis was found among Medicare-eligible patients treated in the usual-care setting. There is a need to raise awareness of the importance of lipid monitoring and treatment of hypercholesterolemia in this at-risk population.

Clinical and research applications of carotid intima-media thickness

Cardiovascular imaging modalities such as coronary computed tomography, carotid ultrasonography, and cardiovascular magnetic resonance imaging are increasingly being used to measure cardiovascular disease progression. Imaging measures, most notably carotid intima-media thickness (CIMT), are being applied as surrogate markers for clinical end points such as myocardial infarction and death in clinical trials. Clinicians and their patients are faced with the challenge of evaluating these imaging measures for their efficacy and practicality in clinical practice, as well as in clinical trials. The investigators determined from a review of clinical trials and guidelines that CIMT measurement may be useful in evaluating cardiovascular disease risk in select patient populations but may not always be an appropriate surrogate for clinical end points. In conclusion, although CIMT has clear advantages over alternative cardiovascular imaging modalities, ultimately, prospective trials comparing the effectiveness of CIMT as a predictive tool of cardiovascular risk with that of other novel markers would best direct clinical recommendations for this imaging measure.

Cardiovascular magnetic resonance parameters of atherosclerotic plaque burden improve discrimination of prior major adverse cardiovascular events

AIMS

Patients with prior major cardiovascular or cerebrovascular events (MACE) are more likely to have future recurrent events independent of traditional cardiovascular disease risk factors. The purpose of this study was to determine if patients with traditional risk factors and prior MACE had increased cardiovascular magnetic resonance (CMR) plaque burden measures compared to patients with risk factors but no prior events.

METHODS AND RESULTS

Black blood carotid and thoracic aorta images were obtained from 195 patients using a rapid extended coverage turbo spin echo sequence. CMR measures of plaque burden were obtained by tracing lumen and outer vessel wall contours. Patients with prior MACE had significantly higher MR plaque burden (wall thickness, wall area and normalized wall index) in carotids and thoracic aorta compared to those without prior MACE (Wall thickness carotids: 1.03 +/- 0.03 vs. 0.93+/- 0.03, p = 0.001; SD wall thickness carotids: 0.137 +/- 0.0008 vs. 0.102 +/- 0.0004, p < 0.001; wall thickness aorta: 1.63 +/- 0.10 vs. 1.50 +/- 0.04, p = 0.009; SD wall thickness aorta: 0.186 +/- 0.035 vs. 0.139 +/- 0.012, p = 0.009 respectively). Plaque burden (wall thickness) and plaque eccentricity (standard deviation of wall thickness) of carotid arteries were associated with prior MACE after adjustment for age, sex, and traditional risk factors. Area under ROC curve (AUC) for discriminating prior MACE improved by adding plaque eccentricity to models incorporating age, sex, and traditional CVD risk factors as model inputs (AUC = 0.79, p = 0.05).

CONCLUSION

A greater plaque burden and plaque eccentricity is prevalent among patients with prior MACE.

In vivo quantification of carotid artery wall dimensions: 3.0-Tesla MRI versus B-mode ultrasound imaging

BACKGROUND

Our aim was to compare common carotid mean wall thickness (MWT) measurements by 3.0-T MRI with B-mode ultrasound common carotid intima-media thickness (CCIMT) measurements, a validated surrogate marker for cardiovascular disease.

METHODS AND RESULTS

B-mode ultrasound and 3.0-T MRI scans of the left and right common carotid arteries were repeated 3 times in 15 healthy younger volunteers (age, 26+/-2.6 years), 15 healthy older volunteers (age, 57+/-3.2 years), and 15 subjects with cardiovascular disease and carotid atherosclerosis (age, 63+/-9.8 years). MWT was 0.711 (SD, 0.229) mm and mean CCIMT was 0.800 (SD, 0.206) mm. MWT and CCIMT were highly correlated (r=0.89, P<0.001). The intraclass correlation coefficients for interscan and interobserver and intraobserver agreements of MRI MWT measurements were larger than 0.95 with small confidence intervals, indicating excellent reproducibility. Power calculations indicate that 89 subjects are required to detect a 4% difference in MRI MWT compared with 469 subjects to detect similar differences with ultrasound IMT in follow-up studies.

CONCLUSIONS

The study data for carotid MRI and ultrasound IMT showed strong agreement, indicating that both modalities measure the thickness of the intima and media. The advantage of MRI over ultrasound is that the measurement variability is smaller, enabling smaller sample sizes and potentially shorter study duration in cardiovascular prevention trials.

Aortic vessel wall magnetic resonance imaging at 3.0 Tesla: a reproducibility study of respiratory navigator gated free-breathing 3D black blood magnetic resonance imaging

The purpose of this study was to evaluate a free-breathing three-dimensional (3D) dual inversion-recovery (DIR) segmented k-space gradient-echo (turbo field echo [TFE]) imaging sequence at 3T for the quantification of aortic vessel wall dimensions. The effect of respiratory motion suppression on image quality was tested. Furthermore, the reproducibility of the aortic vessel wall measurements was investigated. Seven healthy subjects underwent 3D DIR TFE imaging of the aortic vessel wall with and without respiratory navigator. Subsequently, this sequence with respiratory navigator was performed twice in 10 healthy subjects to test its reproducibility. The signal-to-noise (SNR), contrast-to-noise ratio (CNR), vessel wall sharpness, and vessel wall volume (VWV) were assessed. Data were compared using the paired t-test, and the reproducibility of VWV measurements was evaluated using intraclass correlation coefficients (ICCs). SNR, CNR, and vessel wall sharpness were superior in scans performed with respiratory navigator compared to scans performed without. The ICCs concerning intraobserver, interobserver, and interscan reproducibility were excellent (0.99, 0.94, and 0.95, respectively). In conclusion, respiratory motion suppression substantially improves image quality of 3D DIR TFE imaging of the aortic vessel wall at 3T. Furthermore, this optimized technique with respiratory motion suppression enables assessment of aortic vessel wall dimensions with high reproducibility.

Integrated backscatter and intima-media thickness of the thoracic aorta evaluated by transesophageal echocardiography in hypercholesterolemic patients: effect of pitavastatin therapy

The effect of a strong, lipophilic statin (pitavastatin) on the thoracic aorta has not yet been elucidated. The purpose of the present study was to evaluate the effects of pitavastatin (P) therapy on plaque components and morphology in the thoracic aorta by transesophageal echocardiography (TEE) and clarify the impact of the therapy on media and intima in patients with hypercholesterolemia. Sixty-four media and 64 intima of the thoracic aorta were investigated in 32 patients with hypercholesterolemia. The corrected integrated backscatter (c-IBS) values in the thoracic aortic wall and intima-media thickness (IMT) at the same site were measured before and after P therapy or diet (D) for 7 mo. Moreover, c-IBS values in media were measured in 168 patients without hypercholesterolemia to estimate age-dependent changes. C-IBS values in media were correlated with age (r = 0.84, p < 0.001). C-IBS and IMT of media in the P group significantly decreased from -17.8 +/- 2.4 to -20.1 +/- 3.7 dB and from 1.7 +/- 0.3 to 1.5 +/- 0.3 mm, respectively (p < 0.001), whereas those in the D group significantly increased from -18.3 +/- 2.0 to -16.7 +/- 2.1 dB and from 1.6 +/- 0.3 to 1.7 +/- 0.2 mm, respectively (p < 0.001). IMT in intima in the P group significantly decreased from 3.7 +/- 0.4 to 3.3 +/- 0.4 mm (p < 0.001). C-IBS in intima in the P group significantly increased from -10.2 +/- 2.2 to -6.9 +/- 1.7 dB, which indicated plaque stabilization. Pitavastatin improved the atherosis measured by IMT and sclerosis measured by c-IBS values in the media and induced stabilization and regression of plaques in the intima of the thoracic aorta.

Aorta of young and middle-aged heterozygous familial hypercholesterolemia patients shows no functional or morphological impairment assessed by MRI

In familial hypercholesterolemia (FH) the level of LDL cholesterol is 2–3 times that of the normal population and leads to accelerated atherosclerosis. Improved care for risk factors has decreased cardiovascular mortality of these patients. We studied subclinical atherosclerotic changes with morphologic and functional aortic magnetic resonance imaging (MRI) in FH patients under the age of 50. 39 DNA test-verified heterozygous FH-North Karelia patients, aged 6–48, 28 of them treated with statins, and 25 healthy controls, aged 12 to 50, underwent aortic MRI, carotid ultrasound (US), and risk-factor assessment. No differences in any of the morphologic or functional aortic parameters appeared between patients and controls. Age and gender were independent predictors of the majority of the morphologic and functional measures. Carotid intima-media thickness assessed by US was greater in patients (0.57 mm ± 0.13 vs 0.48 ± 0.13 mm, p = 0.005) as was cholesterol-years score (243 ± 122 vs 137 ± 74, p < 0.001). Patients had thicker intima-media of the common carotid artery and higher cholesterol burden as indicated by their cholesterol-years score. Despite this, no differences existed in morphologic or functional aortic parameters assessed with MRI. The improved care of cardiovascular risk factors, especially statin treatment, may protect the aorta of FH patients. However, larger confirmatory studies are needed.

Quantitative 3T MR imaging of the descending thoracic aorta: patients with familial hypercholesterolemia have an increased aortic plaque burden despite long-term lipid-lowering therapy

PURPOSE

To compare the aortic plaque burden in patients with heterozygous familial hypercholesterolemia on long-term statin treatment with that of matched control subjects.

MATERIALS AND METHODS

The authors studied 11 heterozygous, nonsmoking, nondiabetic, and nonhypertensive patients with familial hypercholesterolemia (mean age, 44 years +/- 10) who had been receiving cholesterol-lowering management for a mean of 12 years +/- 5, including 8.25 years +/- 4.24 with the highest tolerable doses of a statin (or a statin plus ezetimibe), and 26 age- and sex-matched control subjects with 3T magnetic resonance (MR) imaging of the descending thoracic aorta by using an axial T2-weighted turbo spin-echo sequence.

RESULTS

Quantitative analysis demonstrated that the aortic vessel wall area was significantly larger in patients with familial hypercholesterolemia than in control subjects (123 mm(2) +/- 23 vs 102 mm(2) +/- 18, respectively; P < .007), as was vessel wall thickness (1.63 mm +/- 0.28 vs 1.37 mm +/- 0.16, respectively; P < .001). No significant difference was found between mean values of routine serum lipid and lipoprotein parameters.

CONCLUSIONS

The results of this preliminary study show that patients with heterozygous familial hypercholesterolemia have a higher aortic atherosclerotic plaque burden than control subjects at quantitative MR imaging despite long-term lipid-lowering therapy. This information may help design future studies evaluating plaque burden and cardiovascular risk.

Impact of plasma oxidized low-density lipoprotein removal on atherosclerosis

BACKGROUND

Several clinical studies of statin therapy have demonstrated that lowering low-density lipoprotein (LDL) cholesterol prevents atherosclerotic progression and decreases cardiovascular mortality. In addition, oxidized LDL (oxLDL) is suggested to play roles in the formation and progression of atherosclerosis. However, whether lowering oxLDL alone, rather than total LDL, affects atherogenesis remains unclear.

METHODS AND RESULTS

To clarify the atherogenic impact of oxLDL, lectin-like oxLDL receptor 1 (LOX-1), an oxLDL receptor, was expressed ectopically in the liver with adenovirus administration in apolipoprotein E-deficient mice at 46 weeks of age. Hepatic LOX-1 expression enhanced hepatic oxLDL uptake, indicating functional expression of LOX-1 in the liver. Although plasma total cholesterol, triglyceride, and LDL cholesterol levels were unaffected, plasma oxLDL was markedly and transiently decreased in LOX-1 mice. In controls, atherosclerotic lesions, detected by Oil Red O staining, were markedly increased (by 38%) during the 4-week period after adenoviral administration. In contrast, atherosclerotic progression was almost completely inhibited by hepatic LOX-1 expression. In addition, plasma monocyte chemotactic protein-1 and lipid peroxide levels were decreased, whereas adiponectin was increased, suggesting decreased systemic oxidative stress. Thus, LOX1 expressed in the livers of apolipoprotein E-deficient mice transiently removes oxLDL from circulating blood and possibly decreases systemic oxidative stress, resulting in complete prevention of atherosclerotic progression despite the persistence of severe LDL hypercholesterolemia and hypertriglyceridemia.

CONCLUSIONS

OxLDL has a major atherogenic impact, and oxLDL removal is a promising therapeutic strategy against atherosclerosis.

Early changes in arterial structure and function following statin initiation: quantification by magnetic resonance imaging

Effective LDL-cholesterol (LDL-C) reduction improves vascular function and can bring about regression of atherosclerosis. Alterations in endothelial function can occur rapidly, but changes in atherosclerosis are generally considered to occur more slowly. Vascular magnetic resonance imaging (MRI) is a powerful technique for accurate non-invasive assessment of central and peripheral arteries at multiple anatomical sites. We report the changes in atherosclerosis burden and arterial function in response to open label statin treatment, in 24 statin-naïve newly diagnosed stable coronary artery disease patients. Patients underwent MRI before, and 3 and 12 months after commencing treatment. Mean LDL-C fell by 37% to 70.8 mg/dL (P<0.01). The plaque index (normalised vessel wall area) showed reductions in the aorta (2.3%, P<0.05) and carotid (3.1%, P<0.05) arteries at 3 months. Early reductions in atherosclerosis of aorta and carotid observed at 3 months were significantly correlated with later change at 12 months (R(2)=0.50, P<0.001; R(2)=0.22, P<0.05, respectively). Improvements in aortic distensibility and brachial endothelial function that were apparent after 3 months treatment were sustained at the 12-month time point.

Multimodality imaging of atherosclerosis (magnetic resonance imaging/computed tomography/positron emission tomography-computed tomography)

This review discusses the field of atherosclerosis imaging with magnetic resonance imaging, computed tomography and positron emission tomography techniques, and highlights important publications in this area. Future directions and challenges ahead for plaque imaging are also highlighted.

Aortic plaque imaging and monitoring atherosclerotic plaque interventions

The atherosclerotic process that results in coronary artery disease (CAD) is recognized to be a generalized process that may involve the entire vasculature. The association between CAD and atherosclerotic plaques in the thoracic aorta has often been reported using transesophageal echocardiography. An autopsy study showed plaques in the abdominal aorta, but not in the thoracic aorta, to be severe in patients with cardiac events. However, studies evaluating an association between abdominal aortic plaques and CAD are scarce. Recently, magnetic resonance imaging (MRI) has become a useful tool for the noninvasive evaluation of atherosclerotic plaques in both the thoracic and abdominal aortas. Plaques in the thoracic and abdominal aortas were found to be characteristically associated with hypercholesterolemia and smoking, respectively, suggesting different susceptibilities to risk factors. Because patients have various risk factors, it seems to be preferable to evaluate atherosclerosis in multiple vascular beds than in just 1 bed. Magnetic resonance imaging can evaluate atherosclerosis in multiple vascular beds in the same examination session. Complex aortic plaques, especially in the abdominal aorta, were found to be associated with myocardial infarction and complex coronary lesions, suggesting a link between aortic and coronary plaque instability. Aortic MRI may thus be useful for identifying vulnerable patients. Moreover, MRI is a powerful tool to serially evaluate plaque progression and regression. Intensive lipid-lowering therapy can regress aortic plaques, but the susceptibility to lipid lowering and the process of plaque regression may differ between the thoracic and abdominal aortic plaques.

MRI of early- and late-stage arterial remodeling in a low-level cholesterol-fed rabbit model of atherosclerosis

PURPOSE

To monitor early- and late-stage arterial remodeling following low-level cholesterol (CH) feeding in rabbits using a standardized MRI protocol.

MATERIALS AND METHODS

New Zealand White rabbits were fed a CH diet (0.25% w/w) (n = 15) or normal chow (n = 6) and imaged either at 0, 2, 6, 8, and 11 months ("early-stage") or 12, 14, 16, 18, and 20 months ("late-stage"). T2-weighted fast-spin-echo images ( approximately 200 microm in-plane resolution) of aortic lesions were collected using either a 1.5 or 3.0T MR scanner interfaced with a customized surface RF coil. Luminal (LA), outer vessel wall boundary (OVBA), and vessel wall areas (VWA) were assessed.

RESULTS

Among CH-fed animals in the early-stage group, increased VWA associated with decreased OVBA and a more pronounced decrease in LA was first detectable at 8 months. These changes became more evident between 8 and 11 months. In the late-stage group, lesions continued to grow in response to CH-feeding, as VWA significantly increased at regular 2-month intervals. Beyond 16 months, signal intensity differences (reflecting increased lesion complexity) within the vessel wall were noted.

CONCLUSION

This often-overlooked rabbit model combined with customized MR technology holds tremendous promise for studying the natural progression, regression, and remodeling of atherosclerotic lesions.

Atherosclerosis imaging as a benchmark in the development of novel cardiovasular drugs

PURPOSE OF REVIEW

Imaging of the arterial wall yields validated surrogate markers that can provide an early indication with regards to efficacy of novel cardiovascular drugs. This paper attempts to address the use of atherosclerosis imaging as a benchmarking tool for a well informed decision whether to proceed to large morbidity and mortality studies in the assessment of a novel therapeutic strategy.

RECENT FINDINGS

Imaging of the artery wall can be used to evaluate individual cardiovascular risk and has additive value over conventional risk scores as it directly addresses the disease process. In controlled clinical trials, vascular imaging has shown that the efficacy of lipid-modifying pharmacotherapy can be evaluated in both high and low-risk populations and that the findings parallel outcomes of clinical studies with similar interventions.

SUMMARY

Arterial imaging may provide the first glimpse of the efficacy or failure of a novel strategy to combat atherosclerosis. These findings suggest that vascular imaging could be employed to probe whether or not a large morbidity and mortality endpoint study should be the next step in a clinical development program.

Reader and platform reproducibility for quantitative assessment of carotid atherosclerotic plaque using 1.5T Siemens, Philips, and General Electric scanners

PURPOSE

To evaluate the platform and reader reproducibility of quantitative carotid plaque measurements.

MATERIALS AND METHODS

A total of 32 individuals with >or=15% carotid stenosis by duplex ultrasound were each imaged once by a 1.5T General Electric (GE) whole body scanner and twice by either a 1.5T Philips scanner or a 1.5T Siemens scanner. A standardized multisequence protocol and identical phased-array carotid coils were used. Expert readers, blinded to subject information, scanner type, and time point, measured the lumen, wall, and total vessel areas and determined the modified American Heart Association lesion type (AHA-LT) on the cross-sectional images.

RESULTS

AHA-LT was consistently identified across the same (kappa = 0.75) and different scan platforms (kappa = 0.75). Furthermore, scan-rescan coefficients of variation (CV) of wall area measurements on Siemens and Philips scanners ranged from 6.3% to 7.5%. However, wall area measurements differed between Philips and GE (P = 0.003) and between Siemens and GE (P = 0.05). In general, intrareader reproducibility was higher than interreader reproducibility for AHA-LT identification as well as for quantitative measurements.

CONCLUSION

All three scanners produced images that allowed AHA-LT to be consistently identified. Reproducibility of quantitative measurements by Siemens and Philips scanners were comparable to previous studies using 1.5T GE scanners. However, bias was introduced with each scanner and the use of different readers substantially increased variability. We therefore recommend using the same platform and the same reader for scans of individual subjects undergoing serial assessment of carotid atherosclerosis.

3.0 T plaque imaging

OBJECTIVES

The aim of this article is to evaluate 3.0 T magnetic resonance imaging for characterization of vessel morphology and plaque composition. Emphasis is placed on early and moderate stages of carotid atherosclerosis, where increases in signal-to-noise (SNR) and contrast-to-noise (CNR) ratios compared with 1.5 T are sought. Comparison of in vivo 3.0 T imaging to histopathology is performed for validation. Parallel acceleration methods applied with an 8-channel carotid array are investigated as well as higher field ex vivo imaging to explore even further gains. The overall endeavor is to improve prospective assessment of atherosclerosis stage and stability for reduction of atherothrombotic event risk.

METHODS

A total of 10 male and female subjects ranging in age from 22 to 72 years (5 healthy and 5 with cardiovascular disease) participated. Custom-built array coils were used with endogenous and exogenous multicontrast bright and black-blood protocols for 3.0 T carotid imaging. Comparisons were performed to 1.5 T, and ex vivo plaque was stained with hematoxylin and eosin for histology. Imaging (9.4 T) was also performed on intact specimens.

RESULTS

The factor of 2 gain in signal-to-noise SNR is realized compared with 1.5 T along with improved wall-lumen and plaque component CNR. Post-contrast black-blood imaging within 5-10 minutes of gadolinium injection is optimal for detection of the necrotic lipid component. In a preliminary 18-month follow-up study, this method provided measurement of a 50% reduction in lipid content with minimal change in plaque size in a subject receiving aggressive statin therapy. Parallel imaging applied with signal averaging further improves 3.0 T black-blood vessel wall imaging.

CONCLUSIONS

The use of 3.0 T for carotid plaque imaging has demonstrated increases in SNR and CNR compared with 1.5 T. Quantitative prospective studies of moderate and early plaques are feasible at 3.0 T. Continued improvements in coil arrays, 3-dimensional pulse sequences, and the use of novel molecular imaging agents implemented at high field will further improve magnetic resonance plaque characterization.

The vulnerable, or high-risk, atherosclerotic plaque: noninvasive MR imaging for characterization and assessment

"Vulnerable" plaques are atherosclerotic plaques that have a high likelihood to cause thrombotic complications, such as myocardial infarction or stroke. Plaques that tend to progress rapidly are also considered to be vulnerable. Besides luminal stenosis, plaque composition and morphology are key determinants of the likelihood that a plaque will cause cardiovascular events. Noninvasive magnetic resonance (MR) imaging has great potential to enable characterization of atherosclerotic plaque composition and morphology and thus to help assess plaque vulnerability. A classification for clinical, as well as pathologic, evaluation of vulnerable plaques was recently put forward in which five major and five minor criteria to define vulnerable plaques were proposed. The purpose of this review is to summarize the status of MR imaging with regard to depiction of the criteria that define vulnerable plaques by using existing MR techniques. The use of MR imaging in animal models and in human disease in various vascular beds, particularly the carotid arteries, is presented.

Complications of aortic atherosclerosis: Atheroemboli and thromboemboli

Patients with severe aortic atherosclerosis are at high risk for stroke and other embolic complications. Therapy to prevent emboli from aortic plaque is not yet established. Therefore, patients with atherosclerosis or risk factors for embolic disease should be identified and treated aggressively. Aspirin, smoking cessation, and control of blood pressure and glucose are important. Retrospective data in patients with severe aortic plaque support the use of statins to prevent stroke. Iatrogenic embolization can occur as a result of aortic manipulation during invasive vascular procedures or cardiovascular surgery. The risks and benefits of these procedures must be carefully weighed, and alternate approaches should be considered for patients with severe aortic atherosclerosis. For those who require coronary artery bypass graft (CABG) surgery, off-pump CABG is an option. Prophylactic aortic arch atherectomy should not be routinely performed. Aortic filters or stenting have been introduced but have not yet been fully evaluated. For patients who require angiography and have severe descending aortic, aortic arch, or abdominal aortic plaque, it is possible that a brachial (rather than a femoral) approach may avoid embolic complications.

Low-density lipoprotein-dependent and -independent effects of cholesterol-lowering therapies on C-reactive protein: a meta-analysis

OBJECTIVES

This study sought to assess the contribution of low-density lipoprotein (LDL)-dependent and LDL-independent effects of LDL-lowering therapies to changes in C-reactive protein (CRP) in healthy or stable subjects.

BACKGROUND

Correlations of change in LDL and CRP in individuals are lowered by their measurement variability. By using average changes in LDL and CRP in study groups, meta-analysis reduces this variability to better assess their correlation.

METHODS

A systematic search for randomized placebo-controlled trials reporting change in LDL and CRP with LDL-lowering interventions retrieved 23 studies with 57 groups treated with a variety of statins, nonstatin drugs, or other regimens. Meta-analysis techniques assessed the relationships between average mean differences (placebo - treatment) in change in CRP and LDL.

RESULTS

The overall reduction in CRP was 28% (95% confidence interval 26% to 30%). Significantly greater CRP reduction occurred in statin and statin-ezetimibe interventions, interventions using 80 mg/day of statins, and with greater LDL lowering. Meta-regression analysis showed a strong correlation between the change in LDL and CRP (r = 0.80, p < 0.001). Statin therapies had no significant effect on CRP after adjusting for the change in LDL. In a multivariate model applied to a range of LDL reduction typically seen with statins (20% to 60%), 89% to 98% of CRP change was related to LDL lowering and 2% to 11% was related to non-LDL effects of statins.

CONCLUSIONS

In clinical practice, most of the anti-inflammatory effect of LDL-lowering therapies is related to the magnitude of change in LDL. The potential non-LDL effects of statins on inflammation are much smaller in magnitude.

Gene therapy and stem cell therapy for cardiovascular diseases today: a model for translational research

Clinical trials looking at ways to promote myocardial regeneration have reported that the administered therapies have either neutral effects or modest benefits of questionable impact. These somewhat disappointing results should emphasize the need for translational research, with bidirectional feedback between the basic research laboratory and the clinical arena. Such a translational pathway is illustrated by the quest to find an effective therapy for restenosis, which culminated in the development of sirolimus. At this point a move away from the bedside and a return to the bench seems necessary to better understand the mechanisms of action of progenitor cells and stimulating factors. Without such basic knowledge research might be prematurely discouraged and the opportunity to fully understand the true potential of cardiovascular regenerative therapy might be missed.

MRI of atherosclerosis: diagnosis and monitoring therapy

Atherosclerosis is a prevalent disease affecting millions of Americans. Despite our advances in diagnosis and treatment, atherosclerosis is the leading cause of death in America. High-resolution magnetic resonance imaging has overcome the limitations of current angiographic techniques and has emerged as a leading noninvasive imaging modality for atherosclerotic disease. Atherosclerosis of the arterial wall of the human carotid, aortic, peripheral and coronary arteries have all been successfully evaluated. In addition, the power of magnetic resonance imaging to differentiate the major components of atherosclerotic plaque has been validated. The ability to image the vessel wall and risk stratify atherosclerotic plaque will create management decisions not previously faced, and has the potential to change the way atherosclerosis is treated.

Effect of bezafibrate therapy on atherosclerotic aortic plaques detected by MRI in dyslipidemic patients with hypertriglyceridemia

Fibrates reduce triglycerides (TG) and increase HDL-cholesterol levels, but there was no report showing plaque regression by fibrates. Using MRI, we investigated the effects of bezafibrate on aortic plaques in 22 dyslipidemic patients. All patients were asked to receive 400mg bezafibrate, but 8 who declined to have bezafibrate became the control group. Changes in vessel wall area (VWA) and lumen area (LA) from baseline to 1-year were evaluated. Bezafibrate reduced TG (-55%) and increased HDL-cholesterol levels (+29%). Bezafibrate reduced HDL size and increased LDL size. In thoracic plaques, bezafibrate reduced VWA (-6%, P<0.001) with no LA change, but VWA slightly progressed without bezafibrate (+5%). In abdominal plaques, bezafibrate reduced VWA (-8%, P<0.001) with LA increase (+3%, P<0.02), but VWA progressed without bezafibrate (+6%). VWA changes in thoracic and abdominal plaques correlated with TG reduction and HDL-cholesterol increase. Notably, VWA change in only abdominal plaques correlated with HDL size reduction and LDL size increase. Thus, bezafibrate induced plaque regression in thoracic and abdominal aortas with marked TG reduction and HDL-cholesterol increase, but the processes of plaque regression and vascular remodeling may differ between thoracic and abdominal aortas. However, because our study was not a controlled, randomized trial, further study is needed.

Actualización en técnicas de imagen cardiaca. Ecocardiografía, resonancia magnética en cardiología y tomografía computarizada con multidetectores

This article contains a review of the most significant publications on non-invasive recent cardiac imaging techniques in 2005. The increasing importance of technological innovation in echocardiography is reflected in the sections on three dimensional echocardiography, contrast echocardiography, and myocardial deformation measurement techniques (i.e., strain echocardiography). The most important developments affecting cardiology in the techniques of magnetic resonance imaging and multidetector computed tomography are also summarized. This review ends with a detailed description of the contributions made by imaging techniques to the diagnosis of aortic disease.

Meta-analysis of the studies assessing temporal changes in coronary plaque volume using intravascular ultrasound

To assess the temporal effect of statin therapy on coronary atherosclerotic plaque volume measured by intravascular ultrasound (IVUS), we searched PubMed for eligible studies published between 1990 and January 2006. Inclusion criteria for retrieved studies were (1) IVUS volume analysis at baseline and follow-up and (2) statin therapy in > or =1 group of patients. All data of interest were abstracted in prespecified structured collection forms. Statistical analysis was performed with Review Manager 4.2. Random-effect weighted mean difference (WMD) was used as summary statistics for comparison of continuous variables. Nine studies of 985 patients (with 11 statin treatment arms) were selected. After a mean follow-up of 9.8 +/- 4.9 months, we found a significant decrease in coronary plaque volume (WMD -5.77 mm(3), 95% confidence interval -10.36 to -1.17, p = 0.01), with no significant heterogeneity across studies (p = 0.47). Prespecified subgroup analyses showed similar trends. Studies in which the achieved low-density lipoprotein (LDL) cholesterol level was <100 mg/dl showed a trend for plaque regression (WMD -7.88 mm(3), 95% confidence interval -16.31 to 0.55, p = 0.07), whereas studies in which the achieved level of LDL cholesterol was > or =100 mg/dl, the trend was less evident (WMD -4.22 mm(3), 95% confidence interval -10.27 to 1.82, p = 0.17). Plaque volume remained essentially unchanged in patients not treated with statins (WMD 0.13 mm(3), 95% confidence interval -4.42 to 4.68, p = 0.96). In conclusion, statin therapy, particularly when achieving the target LDL level, appears to promote a significant regression of coronary plaque volume as measured by IVUS.

In-stent restenosis in idiopathic isolated ostial left main coronary artery stenosis

Idiopathic isolated ostial left main artery stenosis is a rare disease with uncertain etiology, clinical course and prognosis. We described a young woman with no cardiovascular risk factors, who developed the disease 3 years ago with a bare-metal stent implanted in the left main artery ostium. She presented again with severe angina of rapid onset. Coronary angiography revealed ostial left main artery in-stent restenosis. A drug-eluting stent was successfully deployed over the previous stent with good angiographic result. The etiology and management of this disorder were briefly discussed.

Plant sterol or stanol esters retard lesion formation in LDL receptor-deficient mice independent of changes in serum plant sterols

Statins do not always decrease coronary heart disease mortality, which was speculated based on increased serum plant sterols observed during statin treatment. To evaluate plant sterol atherogenicity, we fed low density lipoprotein-receptor deficient (LDLr(+/-)) mice for 35 weeks with Western diets (control) alone or enriched with atorvastatin or atorvastatin plus plant sterols or stanols. Atorvastatin decreased serum cholesterol by 22% and lesion area by 57%. Adding plant sterols or stanols to atorvastatin decreased serum cholesterol by 39% and 41%. Cholesterol-standardized serum plant sterol concentrations increased by 4- to 11-fold during sterol plus atorvastatin treatment versus stanol plus atorvastatin treatment. However, lesion size decreased similarly in the sterol plus atorvastatin (-99% vs. control) and the stanol plus atorvastatin (-98%) groups, with comparable serum cholesterol levels, suggesting that increased plant sterol concentrations are not atherogenic. Our second study confirms this conclusion. Compared with lesions after a 33 week atherogenic period, lesion size further increased in controls (+97%) during 12 more weeks on the diet, whereas 12 weeks with the addition of plant sterols or stanols decreased lesion size (66% and 64%). These findings indicate that in LDLr(+/-) mice 1) increased cholesterol-standardized serum plant sterol concentrations are not atherogenic, 2) adding plant sterols/stanols to atorvastatin further inhibits lesion formation, and 3) plant sterols/stanols inhibit the progression or even induce the regression of existing lesions.

MRI of atherosclerosis in clinical trials

Magnetic resonance imaging (MRI) of the arterial wall has emerged as a viable technology for characterizing atherosclerotic lesions in vivo, especially within carotid arteries and other large vessels. This capability has facilitated the use of carotid MRI in clinical trials to evaluate therapeutic effects on atherosclerotic lesions themselves. MRI is specifically able to characterize three important aspects of the lesion: size, composition and biological activity. Lesion size, expressed as a total wall volume, may be more sensitive than maximal vessel narrowing (stenosis) as a measure of therapeutic effects, as it reflects changes along the entire length of the lesion and accounts for vessel remodeling. Lesion composition (e.g. lipid, fibrous and calcified content) may reflect therapeutic effects that do not alter lesion size or stenosis, but cause a transition from a vulnerable plaque composition to a more stable one. Biological activity, most notably inflammation, is an emerging target for imaging that is thought to destabilize plaque and which may be a systemic marker of vulnerability. The ability of MRI to characterize each of these features in carotid atherosclerotic lesions gives it the potential, under certain circumstances, to replace traditional trials involving large numbers of subjects and hard end-points--heart attacks and strokes--with smaller, shorter trials involving imaging end-points. In this review, the state of the art in MRI of atherosclerosis is presented in terms of hardware, image acquisition protocols and post-processing. Also, the results of validation studies for measuring lesion size, composition and inflammation will be summarized. Finally, the status of several clinical trials involving MRI of atherosclerosis will be reviewed.

Predictors of carotid atherosclerotic plaque progression as measured by noninvasive magnetic resonance imaging

The purpose of this in vivo MRI study was to quantify changes in atherosclerotic plaque morphology prospectively and to identify factors that may alter the rate of progression in plaque burden. Sixty-eight asymptomatic subjects with >or=50% stenosis, underwent serial carotid MRI examinations over an 18-month period. Clinical risk factors for atherosclerosis, and medications were documented prospectively. The wall and total vessel areas, matched across time-points, were measured from cross-sectional images. The normalized wall index (NWI=wall area/total vessel area), as a marker of disease severity, was documented at baseline and at 18 months. Multiple regression analysis was used to correlate risk factors and morphological features of the plaque with the rate of progression/regression. On average, the wall area increased by 2.2% per year (P=0.001). Multiple regression analysis demonstrated that statin therapy (P=0.01) and a normalized wall index >0.64 (P=0.001) were associated with a significantly reduced rate of progression in mean wall area. All other documented risk factors were not significantly associated with changes in wall area. Findings from this study suggest that increased normalized wall index and the use of statin therapy are associated with reduced rates of plaque progression amongst individuals with advanced, asymptomatic carotid atherosclerosis.

Recent Advances of Intervention to Inhibit Progression of Carotid Intima-Media Thickness in Patients With Type 2 Diabetes Mellitus

BACKGROUND AND PURPOSE

Type 2 diabetes is associated with a high cardiovascular morbidity and mortality. Recent advances of intervention studies in type 2 diabetes with use of carotid intima-media thickness (CIMT) measurement as a surrogate end point may allow for better understanding of the undetermined process of atherosclerosis, the effect of interventions, and the usefulness of CIMT to inhibit events of cardiovascular disease.

SUMMARY OF REVIEW

Data were available from 11 studies (n=1578) in subjects with type 2 diabetes (including impaired glucose tolerance, n=132) that evaluated the effect of interventions on change in CIMT. The overall weighed rate of change in mean CIMT based on data among control groups (ie, type 2 diabetes without interventions) was 0.034 mm/y (95% CI, 0.029 to 0.039; median SD, 0.054), in which mean HbA(1c) was 7.86% (95% CI, 7.72 to 8.00; median SD, 1.5). A significant close correlation of HbA(1c) with rate of CIMT change was found (R(2)=0.35, P=0.01). Agents for lowering of blood glucose, platelet activation, or blood pressure significantly reduced the CIMT increase, independent of blood glucose control. This implies that other mechanisms of such agents to diminish CIMT increase should be explored.

CONCLUSIONS

CIMT measurement may contribute to elucidating the short- and/or long-term effect of interventions on the rate of change in CIMT in relation to the levels of various risk factors. Although the method needs further standardization, pharmacological interventions are likely to inhibit progression of CIMT, leading to a reduction of cardiovascular events.