Evolution and stabilization of vulnerable atherosclerotic plaques

Imaging of the high-risk carotid plaque: magnetic resonance imaging

The emergence of the concept of high-risk atherosclerotic plaque has led to considerable interest in noninvasive imaging techniques to identify high-risk features before clinical sequelae. For plaques in the carotid arteries, magnetic resonance imaging has undergone considerable histologic validation to link imaging features to indicators of plaque instability, including plaque burden, intraplaque hemorrhage, fibrous cap disruption, lipid rich necrotic core, and calcification. Recently introduced imaging technologies, especially those focused on three-dimensional imaging sequences, are now poised for integration into the clinical workup of patients with suspected carotid atherosclerosis. The purpose of this article is to review the carotid plaque magnetic resonance imaging techniques that are most ready for integration into the clinic.

Neutrophil-to-lymphocyte ratio is associated with severity of coronary artery ectasia

We investigated the association between coronary artery ectasia (CAE) and Neutrophil-to-lymphocyte ratio (NLR), an indicator of the inflammatory state. The study population included 434 patients (247 males, mean age 62 ± 10 years) including 230 patients with isolated CAE and 104 patients with coronary artery disease and 100 patientss with normal coronary arteries. The NLR was measured at admission and 30 days after coronary angiography in all the patients. The NLR was significantly higher in patients with CAE than those with normal coronary arteries (2.2 ± 0.6-1.3 ± 0.6, P < .001). Linear regression analyses revealed that NLR (coefficient β = -.61, P < .001) was significantly associated with severity of CAE. The NLR is significantly higher in patients with CAE compared to controls with normal coronary arteries, and NLR is associated with severity of CAE.

Inflammation and the development of atherosclerosis

Atherosclerosis is a progressive disease causally associated with multiple cardiovascular risk factors, including dyslipidemia. Without effective intervention, atherosclerosis becomes evidenced clinically as coronary artery and cerebrovascular disease, both of which remain the leading causes of death worldwide. Multiple lines of investigation indicate a central role for inflammation in atherosclerotic plaque progression, vulnerability and thrombogenicity. Randomized clinical trials have documented the benefit of lipid-lowering therapy for both primary and secondary prevention of cardiovascular events. Statins, a class of drugs that lower cholesterol levels by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, have been shown to slow the progression of the atheroma and the frequency of associated clinical events to an extent that cannot be attributed solely to LDL reduction. The non-LDL or pleiotropic effects of statins are attributed to anti-inflammatory activity, enhanced endothelial function, and inhibition of oxidative stress. In this review, we discuss the role of inflammation in atherogenesis along with the effects of statins in slowing this process through LDL-dependent and -independent mechanisms.

Activation of intracellular signaling systems by high-density lipoproteins

The proteosome of high-density lipoprotein particles is quite complex and consists of up to 75 different proteins and enzymes. The specific protein cargo of HDL particles regulates their functionality. In addition to their documented capacity to engage in reverse cholesterol transport, reduce oxidized lipid, and function as apoprotein donors, HDL particles can activate a variety of signaling systems in endothelial cells, smooth muscle cells, and platelets. The HDLs can deliver sphingolipids to the surface of these cell types and activate sphingosine phosphate receptors. Sphingosine phosphate receptors are coupled to numerous different intracellular signaling cascades exerting roles in vasodilatation, inflammation, cell migration and apoptosis, inhibition of platelet activation, and endothelial adhesion molecule expression, among other functions. The ability of HDL to influence such a diverse array of cellular functions lends biological plausibility to the substantial epidemiological and clinical evidence suggesting that the HDLs are unique among lipoproteins in that they are vasculoprotective and antiatherogenic.

Dietary mucilage promotes regression of atheromatous lesions in hypercholesterolemic rabbits

The antihypercholesterolemic and antiatherogenic effect of the mucilage galactomannan isolated from fenugreek seeds was studied in experimental rabbits maintained on a high cholesterol diet for 3 months. Changes in the levels of cholesterol and triglycerides in serum and tissues and aortic fatty lesions were analysed in animals receiving mucilage (40 mg/kg body weight) daily and compared with the control. A significant decrease in serum total cholesterol, LDL cholesterol and triglycerides and cholesterol and triglycerides in liver and aorta and a decrease in Sudan IV staining of aorta indicated antihypercholesterolemic and antiatherogenic effects of the mucilage. Regression studies showed that administration of mucilage for 3 months caused a significant decrease in serum total and LDL cholesterol and aortic cholesterol. Mucilage accelerated the regression of atheromatous lesions in the aorta as evidenced by significantly low sudanophilic staining. Recovery from inflammation in hypercholesterolemic animals receiving mucilage was evidenced by a faster decrease in C-reactive protein (CRP) in serum to basal levels. The lipid lowering and antiatherogenic effects of mucilage from fenugreek which is used as a food flavoring spice highlights the importance of dietary intervention in the regression of atherosclerosis.

Atherothrombosis: Epidemiology, Pathophysiology, and Prevention

OBJECTIVES

To review the pathophysiology of atherothrombosis (atherosclerosis with superimposed platelet-rich thrombus formation) and the measures that can be taken to prevent its clinical sequelae through lifestyle modifications and pharmacotherapy, with emphasis on the role of antiplatelet agents.

DATA SOURCES

Recent (1995-2003) published scientific literature, as identified by the authors through Medline searches using the terms atherothrombosis, pathophysiology, risk factors, prevention, and reviews on treatment.

STUDY SELECTION

Recent systematic English-language review articles were screened for relevant material.

DATA SYNTHESIS

Atherothrombosis is a generalized and diffuse progressive process affecting multiple vascular beds; its clinical consequences, including acute coronary syndromes (unstable angina, acute myocardial infarction, and sudden cardiac death), ischemic stroke, and peripheral arterial disease, are unpredictable in their time course and potentially life-threatening. Atherothrombosis rather than arterial stenosis appears to account for most of the acute ischemic manifestations of the atherosclerotic process. Interventions that can favorably influence atherosclerotic progression include lifestyle modifications (dietary control, exercise, and smoking cessation) and pharmacotherapy (lipid-lowering, antihypertensive, antiglycemic, and antiplatelet drugs). The pivotal role played by the platelet in thrombus formation provides the rationale for employing antiplatelet drugs with complementary modes of action (e.g., aspirin, clopidogrel) to prevent atherothrombosis.

CONCLUSION

Ischemic cerebrovascular, coronary, and peripheral arterial disease can be regarded as diverse manifestations of a common underlying systemic pathology, namely atherothrombosis. Secondary prevention of an ischemic event in an affected arterial bed confers the added benefit of primary prevention against potential ischemic events in other arterial beds.

Response of the left anterior descending coronary artery to acetylcholine in patients with chest pain and angiographically normal coronary arteries

Because atherosclerotic plaque burden affects the likelihood of plaque rupture, it is important to determine the presence and extent of atherosclerotic plaque. We hypothesized that endothelial dysfunction becomes more prominent with development of atherosclerotic plaque; therefore, we examined the relation between coronary endothelial dysfunction and the presence of atherosclerotic plaque. In 36 patients with normal coronary arteries, acetylcholine (ACh; 3 and 30 microg/min) and nitroglycerin were infused into the left coronary ostium, and the diameter of the left anterior descending (LAD) coronary artery was quantitatively measured in response to each drug. The plaque burden was measured in the same segment using intravascular ultrasonography. The plaque burden was 31.2 +/- 2.1% and correlated inversely with changes in coronary diameter induced by 3 microg/min of ACh (r = -0.754, p <0.0001), 30 microg/min of ACh (r = -0.552, p = 0.0005), and nitroglycerin (r = -0.531, p = 0.0009). Multivariate regression analysis showed that the change in coronary diameter induced by 3 microg/min of ACh was associated with plaque burden, independent of the effects of nitroglycerin-induced dilation. Receiver-operating characteristics analysis demonstrated that a cut-off value for the change in coronary diameter induced by 3 microg/min of ACh for predicting a plaque burden of >30% was 0%, with a sensitivity of 0.82 and a specificity of 0.95. These findings suggest that coronary endothelial dysfunction is correlated with atherosclerotic plaque burden, indicating that atherosclerotic plaque may be detected based on coronary endothelial function as assessed by low-dose ACh infusion.

Integration of vascular biology and magnetic resonance imaging in the understanding of atherothrombosis and acute coronary syndromes

The interaction between the vulnerable atherosclerotic plaque prone to disruption and thrombus formation is the cornerstone of acute coronary syndrome (ACS). Although distinct from one another, the atherosclerotic and thrombotic processes appear to be interdependent, hence the term atherothrombosis. Inflammation is a crucial common pathophysiological mechanism. Overall, the association of plaque vulnerability and ACS has been well documented. Given the multifactorial origin of atherothrombosis the best preventive approach should be aggressive management of all the risk factors. New interventions should be directed toward decreasing vulnerability of the lesions thereby decreasing the risk of ACS.

Pathogenetic concepts of acute coronary syndromes

The propensity of plaque to disrupt is a major determinant of future ischemic events. Although they are distinct from one another, the atherosclerotic and thrombotic processes appear to be interdependent and may be integrated under the term "atherothrombosis." It is now clear that plaque composition, rather than the percent stenosis, is a major determinant of plaque vulnerability. Plaque disruption seems to depend on both passive and active phenomena and is not purely mechanical. Inflammation (activation of monocytes/macrophages) is a major determinant of both plaque vulnerability and thrombogenicity as they relate to plaque disruption. In one-third of acute coronary syndromes, there is, however, no plaque disruption but only superficial erosion of a markedly stenotic, fibrotic plaque. In these cases, thrombus formation may be exacerbated by a hyperthrombogenic state present in patients with certain systemic risk factors. The endothelium plays a pivotal role in vascular homeostasis and hemostasis. This dynamic organ regulates blood thrombogenicity as well as contractile, secretory, and mitogenic activities in the vessel wall. Some classic risk factors induce endothelial dysfunction by reducing the bioavailability of nitric oxide, increasing tissue endothelin-1, and activating pro-inflammatory signaling pathways. Vascular hemostasis, which is the maintenance of blood fluidity and vascular integrity, is achieved by counter-balancing the intrinsic clotting tendency of blood. As a consequence of the central role of endothelial cells in hemostatic control, a dysfunctional endothelium will generate a pro-thrombotic environment favoring development of atherosclerotic lesions and thrombotic complications.

New understanding, diagnosis, and prognosis of atherothrombosis and the role of imaging

Despite crucial advances in our knowledge of the pathologic mechanisms and the availability of effective diagnostic and treatment modalities, coronary atherothrombosis remains the most frequent cause of ischemic heart disease. Plaque disruption with superimposed thrombosis is the main cause of unstable angina, myocardial infarction, and sudden death. New findings have recently introduced exciting concepts that could have major impact on the treatment of the atherothrombotic disease. We will discuss the mechanisms that lead to the development of atherothrombosis and those responsible for the acute coronary syndromes, as well as some of the concepts derived from in vivo observations using new imaging technologies (eg, high-resolution magnetic resonance imaging).

The vulnerable plaque and acute coronary syndromes

The interaction between the vulnerable atherosclerotic plaque and thrombus formation, a process referred to as atherothrombosis, is the cornerstone of acute coronary syndromes. Advances in noninvasive imaging have helped to identify novel approaches to plaque stabilization, with the potential to prevent plaque rupture, including lifestyle modification and dietary adjustments, as well as pharmacologic interventions such as statins. Following an acute coronary event, strategies combining mechanical and pharmacologic therapies provide considerable advances in prevention of subsequent cardiac events. Pharmacologic strategies to prevent and treat thrombotic complications related to acute coronary syndromes have been developed to dissolve preformed thrombi and to inhibit thrombogenesis. These regimens focus on inhibiting thrombin, preventing thrombi generation, blocking the initiation of coagulation, inhibiting platelet activation, and increasing fibrinolysis.

Clinical significance of coronary calcification

Coronary artery calcification (CAC) was assessed by cinefluoroscopy and its extent was scored (CAC score) in 2,163 consecutive patients undergoing coronary angiography, based on the angiographic and clinical data, the patients were categorized into 8 types of coronary artery disease (CAD). The CAC score was lowest in angiographically normal subjects (0.12+/-0.60) and highest in patients with silent myocardial ischemia (14.31+/-8.61). Risk factors for CAC were advanced age, male sex (at age <80 years), hypertension, diabetes mellitus, and a high grade of organic coronary stenosis. The CAC score in patients with acute coronary syndrome (unstable angina+acute myocardial infarction; 5.48+/-7.42) was significantly lower than that in those with chronic CAD (silent ischemia+stable angina; 9.72+/-8.73; p<0.0001), but was still higher than that in normal subjects or those with vasospastic angina (0.92+/-2.88; p<0.0001). The results indicate that CAC is a manifestation of coronary atherosclerosis and its appearance depends on the pathological type of ischemic heart disease. Fixed stenosis with a slow and chronic process tends to be associated with CAC. The clinical implication of extensive CAC in acute coronary syndrome compared with normal subjects should be further investigated.

Atherosclerotic plaque characterization by quantitative analysis using intravascular ultrasound: correlation with histological and immunohistochemical findings

The aim of this study was to clarify whether atherosclerotic plaque morphology, as defined by quantitative analysis with intravascular ultrasound (IVUS) images, was related to the immunohistochemical findings. Twenty-five coronary lesions in 25 patients who had ultrasound guidance during directional coronary atherectomy (DCA) were enrolled. The lesions retrieved by DCA were analyzed and divided into 3 groups (lesions infiltrated with both macrophages and lymphocytes: group IML; lesions infiltrated with macrophages but not lymphocytes: group IM; and non-infiltrated lesions: group NI). The mean plaque echo level divided by the mean adventitia echo level (MPEL/MAEL) and the heterogeneity of the distribution of plaque echo levels (HDPEL) were calculated. The proportion of patients with acute coronary syndromes was significantly different among the groups: IML (n=14), IM (n=5), and NI (71%, 0% and 17%, respectively; p<0.01). The pre-DCA HDPEL value was highest in group IML and lowest in group NI; however, no significant differences in MPEL/MAEL values were found. The results suggest that plaque morphology, as defined by IVUS images, was related to the immunohistochemical findings. The increase in HDPEL correlated with the presence of immune inflammation.