Conversion from chronic to acute coronary artery disease: speculation regarding mechanisms

Mechanical and structural properties of different types of human aortic atherosclerotic plaques

Atherosclerotic plaques are characterized by structural heterogeneity affecting aortic behaviour under mechanical loading. There is evidence of direct connections between the structural plaque arrangement and the risk of plaque rupture. As a consequence of aortic plaque rupture, plaque components are transferred by the bloodstream to smaller vessels, resulting in acute cardiovascular events with a poor prognosis, such as heart attacks or strokes. Hence, evaluation of the composition, structure, and biochemical profile of atherosclerotic plaques seems to be of great importance to assess the properties of a mechanically induced failure, indicating the strength and rupture vulnerability of plaque. The main goal of the research was to determine experimentally under uniaxial loading the mechanical properties of different types of the human abdominal aorta and human aortic atherosclerotic plaques identified based on vibrational spectra (ATR-FTIR and FT-Raman spectroscopy) analysis and validated by histological staining. The potential of spectroscopic techniques as a useful histopathological tool was demonstrated. Three types of atherosclerotic plaques - predominantly calcified (APC), lipid (APL), and fibrotic (APF) - were distinguished and confirmed by histopathological examinations. Compared to the normal aorta, fibrotic plaques were stiffer (median of E_H for circumferential and axial directions, respectively: 8.15 MPa and 6.56 MPa) and stronger (median of σ_M for APLc = 1.57 MPa and APLa = 1.64 MPa), lipidic plaques were the weakest (median of σ_M for APLc = 0.76 MPa and APLa = 0.51 MPa), and calcified plaques were the stiffest (median of E_H for circumferential and axial directions, respectively: 13.23 MPa and 6.67 MPa). Therefore, plaques detected as predominantly lipid and calcified are most prone to rupture; however, the failure process reflected by the simplification of the stress-stretch characteristics seems to vary depending on the plaque composition.

Advances in Intravascular Imaging: New Insights into the Vulnerable Plaque from Imaging Studies

The term “vulnerable plaque” denotes the plaque characteristics that are susceptible to coronary thrombosis. Previous post-mortem studies proposed 3 major mechanisms of coronary thrombosis: plaque rupture, plaque erosion, and calcified nodules. Of those, characteristics of rupture-prone plaque have been extensively studied. Pathology studies have identified the features of rupture-prone plaque including thin fibrous cap, large necrotic core, expansive vessel remodeling, inflammation, and neovascularization. Intravascular imaging modalities have emerged as adjunctive tools of angiography to identify vulnerable plaques. Multiple devices have been introduced to catheterization laboratories to date, including intravascular ultrasound (IVUS), virtual-histology IVUS, optical coherence tomography (OCT), coronary angioscopy, and near-infrared spectroscopy. With the use of these modalities, our understanding of vulnerable plaque has rapidly grown over the past several decades. One of the goals of intravascular imaging is to better predict and prevent future coronary events, for which prospective observational data is still lacking. OCT delineates microstructures of plaques, whereas IVUS visualizes macroscopic vascular structures. Specifically, plaque erosion, which has been underestimated in clinical practice, is gaining an interest due to the potential of OCT to make an in vivo diagnosis. Another potential future avenue for intravascular imaging is its use to guide treatment. Feasibility of tailored therapy for acute coronary syndromes (ACS) guided by OCT is under investigation. If it is proven to be effective, it may potentially lead to major shift in the management of millions of patients with ACS every year.

Future directions in thrombolysis

An extensive body of research conducted in the past 25 years has helped foster understanding of the mechanisms and pathogenesis of the acute coronary syndromes and occlusive disease. Thus, it is well established that thrombosis is caused by vascular injury and that immediate lysis of the arterial thrombus and subsequent prevention of thrombotic reocclusion are critical to the treatment of these disorders. Remarkable progress in the understanding of the biological and molecular mechanisms involved in vascular-wall-platelet interactions, platelet-platelet interactions, and coagulation has led to the identification of multiple targets for drug discovery and the development of numerous antithrombotic drugs. The purpose of this article is to review emerging antithrombotic therapies, introduce potential future molecular targets for drug discovery efforts, and discuss novel strategies for managing patients with coronary disease.

Use of near-infrared Raman spectroscopy for identification of atherosclerotic plaques in the carotid artery

OBJECTIVES

The aim of this work was to identify the presence of atherosclerotic plaque in the human carotid artery using near infrared Raman spectroscopy.

BACKGROUND DATA

Atherosclerosis is the most common and serious pathology of the cardiovascular system. Raman spectroscopy is an analytical tool that can be used to gather information about both the morphology and chemical composition of tissues.

METHODS

A Ti:sapphire laser operating at the near-infrared wavelength of 830 nm pumped by an argon laser was used for excitation of the samples, and the Raman scattering was detected by an optical spectrometer with a liquid-nitrogen-cooled CCD detector. Carotid artery samples were classified into five groups: normal, intimal thickening, fatty plaque, fibrous-fatty plaque, and fibrous-calcified plaque.

RESULTS

It was observed that the Raman spectrum of atheromatous plaque was different that that of normal tissue. The spectra of atheromatous plaques had bands due to the presence of cholesterol and its esters, with major bands at 1439 and 1663 cm(1), respectively. In normal tissues a peak related to C-H bending appears at 1451 cm(1). Calcified atheromatous plaques had primary bands at 961 and 1071 cm(1), which were due to the presence of phosphate and carbonate in the accumulated calcium. Peaks were seen at 1451 and 1655 cm(1) in the non-atherosclerotic tissue, which were shifted to 1439 and 1663 cm(1) in the atherosclerotic plaque.

CONCLUSIONS

Our results indicate that this technique could be used to detect the presence of atherosclerotic plaques in carotid arterial tissue.

Therapeutic Potentials of Sarpogrelate in Cardiovascular Disease*

In view of the pivotal role of serotonin (5-HT) in a wide variety of cardiovascular disorders, extensive effort has been made to develop different types of 5-HT receptor antagonists for therapeutic use. On the basis of experimental studies, this article is focused on the potentials of sarpogrelate, a specific 5-HT2A receptor antagonist as an antiplatelet, antithrombotic, antiatherosclerotic and antianginal agent. The major effects of sarpogrelate are due to the inhibition of 5-HT-induced platelet aggregation and smooth muscle cell proliferation. This agent was found to attenuate the 5-HT-mediated increase in intracellular Ca2+ and ischemia-reperfusion injury in the heart. Sarpogrelate has been found to have beneficial effects in peripheral vascular disease, restenosis after coronary stenting, pulmonary hypertension, acute and chronic myocardial infarction.

Different effects of optical isomers of the 5-HT1A receptor antagonist pyrapyridolol against postischemic guinea-pig myocardial dysfunction and apoptosis through the mitochondrial permeability transition pore

The recovery (%) of the left ventricular developed pressure by (S)-(-)-pyrapyridolol (5 x 10(-8) M) (90.7%), an optical isomer of a new 5-HT1A receptor antagonist, was greater than that by (R)-(+)-pyrapyridolol (66.2%, control: 34.4%) against ischemia-reperfusion injury in perfused Langendorff guinea-pig hearts. In the perfused mitochondrial preparation, (S)-(-)-pyrapyridolol inhibited the mitochondrial Ca2+ (Cam) elevation that was brought about by the change of Ca2+ content or pH of perfusate, similar to findings with cyclosporin A, well known to be an inhibitor of the mitochondrial permeability transition pore (MPTP). The mitochondrial K(ATP) channel opener, diazoxide, also inhibited the Cam elevation, but the mitochondrial K(ATP) channel antagonist, 5-hydroxydecanoic acid, attenuated it. There were significantly fewer numbers of TUNEL-positive cells in these (S)-(-)-pyrapyridolol-treated hearts than the control or (R)-(+)-pyrapyridolol, with decreases of the caspase-3 activity. Therefore, these results suggest that (S)-(-)-pyrapyridolol likely inhibits the opening of the MPTP by preventing the Cam overload induced apoptosis related to endogenous 5-HT accumulation in ischemia-reperfusion hearts.

Clinical implications and mechanisms of plaque rupture in the acute coronary syndromes

Coronary atherosclerosis complicated by plaque rupture or disruption and thrombosis is primarily responsible for the development of acute coronary syndromes. Plaques with a large extracellular lipid-rich core, a thin fibrous cap due to reduced collagen content and smooth muscle density, and increased numbers of activated macrophages and mast cells appear to be vulnerable to rupture. Plaque disruption tends to occur at points at which the plaque surface is weakest and most vulnerable, which coincide with points at which stresses resulting from biomechanical and hemodynamic forces acting on plaques are concentrated. Reduced matrix synthesis as well as increased matrix degradation predisposes vulnerable plaques to rupture in response to extrinsic mechanical or hemodynamic stresses. Modification of endothelial dysfunction and reduction of vulnerability to plaque rupture and thrombosis may lead to plaque stabilization. These concepts have significant clinical implications that are just beginning to be explored and incorporated into clinical practice. This article reviews the mechanism of coronary atherosclerosis development and the pathophysiology of acute coronary syndromes to provide a framework for understanding how plaque passivation might be accomplished in clinical medicine.

The use of myeloperoxidase as a risk marker for atherosclerosis

The mechanisms of atheroma formation and their ensuing complications and methods by which these can be detected have been the focus of several in vitro, in vivo, and clinical studies. Myeloperoxidase (MPO) is a microbicidal hemoprotein that serves as a part of the neutrophils' armory in host defense. However, the oxidation products generated by MPO have now been shown to be related to various stages of atheroma development. MPO and its oxidant products have been shown to be capable of modifying low-density lipoprotein cholesterol and to be enriched in human atheromas and rupture-prone plaques. Clinical studies have suggested an association between levels of MPO and the presence of coronary artery disease and endothelial dysfunction, and have shown a possible additional role to troponin in patients with chest pain.

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I

Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document focuses on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Nitric oxide, platelet function, myocardial infarction and reperfusion therapies

Platelets play an important role in physiologic hemostasis and pathologic thrombosis that complicate the course of vascular disorders. A number of platelet functions including adhesion, aggregation and recruitment are controlled by nitric oxide (NO) generated by platelets and the endothelial cells. Derangements in this generation may contribute to the pathogenesis of thrombotic complications of vascular disorders. The pharmacologic supplementation of the diseased vasculature with drugs releasing NO may help to restore the hemostatic balance.

Near-infrared spectroscopic characterization of human advanced atherosclerotic plaques

OBJECTIVES; Living human carotid atherosclerotic plaques were examined in vitro by near-infrared (NIR) spectroscopy to determine the spectral features of plaque vulnerability.

BACKGROUND

Plaque disruption, a major cause of heart attacks and strokes, cannot generally be predicted, but is thought to depend mainly on plaque composition. Near-infrared spectroscopy has been used to detect components in tissues noninvasively.

METHODS

Using an NIR spectrometer fitted with a fiberoptic probe, living human carotid atherosclerotic plaques (from 25 patients) were examined ex vivo for plaque vulnerability. The plaques were cut into smaller sections according to their gross pathologic features, and NIR measurements were done at 20 degrees C, usually within 10 min.

RESULTS

According to the American Heart Association's recommended classification scheme, the lesions were classified into three groups: the first group comprised of vulnerable type V/VI lesions; the second group, stable type I/II lesions; and the third (intermediate) group, mainly type III/IV lesions. Cluster analysis of the specimens' NIR spectra identified three major composition groups in each of the three NIR spectral regions: 2,200 to 2,330 nm, 1,620 to 1,820 nm and 1,130 to 1,260 nm. Calculation of the lipid/protein ratios in each group at two NIR regions (2,200 to 2,330 nm) revealed ratios of 1.49 +/- 1.20, 2.12 +/- 1.00 and 3.37 +/- 0.88 for type I/II, type III/IV and advanced type V/VI lesions, respectively (p < 0.03). At 1,620 to 1,820 nm, the respective ratios for these histologic groups were 0.57 +/- 0.21, 1.54 +/- 0.46 and 2.40 +/- 0.44 (p < 0.00003).

CONCLUSIONS

The good ex vivo discrimination of histologically vulnerable and stable plaques in this study suggests that NIR spectroscopy has the potential to identify vulnerable atherosclerotic plaques in vivo.

Serotonin induces the expression of tissue factor and plasminogen activator inhibitor-1 in cultured rat aortic endothelial cells

Serotonin (5-hydroxytryptamine, or 5-HT), released from activated platelets, not only accelerates aggregation of platelets but also is known to promote mitosis, migration, and contraction of vascular smooth muscle cells (VSMCs). These effects are considered to contribute to thrombus formation and atherosclerosis. The aim of this study was to investigate the effects of 5-HT on the expressions of coagulative and fibrinolytic factors in rat aortic endothelial cells. Endothelial cells were stimulated with various concentrations of 5-HT (0.1 approximately 10 microM), and the expressions of tissue factor (TF), tissue factor pathway inhibitor (TFPI), plasminogen activator inhibitor-1 (PAI-1), and tissue-type plasminogen activator (TPA) messenger RNAs (mRNAs) were evaluated by Northern blot analysis. The activities of TF and PAI-1 were also measured. TF and PAI-1 mRNA were increased significantly in a concentration- and time-dependent manner. However, TFPI and TPA mRNA expression did not change. The inductions of TF and PAI-1 mRNAs were inhibited by a 5-HT1/5-HT2 receptor antagonist (methiothepin) and a selective 5-HT2A receptor antagonist (MCI-9042). These results indicate that 5-HT increases procoagulant activity and reduces fibrinolytic activities of endothelial cells through the 5-HT2A receptor. It was concluded that the modulation of procoagulant and hypofibrinolytic activities of endothelial cells by 5-HT synergistically promotes thrombus formation at the site of vessel injury with the platelet aggregation, VSMC contraction, and VSMC proliferation.

Transforming growth factor-beta(1) restores antiplatelet function of endothelial cells exposed to anoxia-reoxygenation injury

Transforming growth factor-beta(1) released from platelet alpha-granules may preserve endothelial functions in injured vessels. However, direct evidence is lacking regarding how this cytokine modifies the antithrombotic function of injured endothelial cells. We performed an in vitro study to investigate the effects of transforming growth factor-beta(1) on platelet functions in the presence of cultured endothelial cells exposed to anoxia-reoxygenation injury. Cultured bovine aorta endothelial cells were placed in an anoxic chamber (0.5% O(2), 5% CO(2)) for 60 minutes followed by a 90-minute reoxygenation. Collagen (2 microg/mL)-induced platelet aggregation (10(8) platelets/mL), as determined by impedance aggregometry, was potently inhibited in the presence of control endothelial cells (17.4+/-3.3 Omega) at a concentration of 5x10(4) cells/mL, as compared to their absence (68. 2+/-2.2 Omega). Inhibition of platelet aggregation was attenuated in endothelial cells exposed to anoxia-reoxygenation (54.6+/-2.5 Omega). However, preincubation of endothelial cells with transforming growth factor-beta(1) (1.0 ng/mL) for 16 hours partially recovered the inhibitory capability of platelet aggregation by injured endothelial cells (40.6+/-3.8 Omega). Cell viability, confirmed by a trypan blue dye exclusion test, was similar (93-96%), including control, 1.0 ng/mL transforming growth factor-beta(1)- and/or anoxia-reoxygenation-pretreated cells. The capability of platelet inhibition was restored when the endothelial cells were preincubated for 4 hours or more. Restoration of antiplatelet capacity in endothelial cells by transforming growth factor-beta(1) was suggested to be due to several mechanisms, including an increase in nitric oxide synthase activity, up-regulation of prostacyclin release, and restoration of adenosine triphosphate diphosphohydrolase activity, which was attenuated by anoxia-reoxygenation pretreatment. In summary, transforming growth factor-beta(1) released from activated platelets may play a compensatory role in the preservation of endothelial functions to inhibit platelet activation.

Dynamic Nature of Thrombin Generation, Fibrin Formation, and Platelet Activation in Unstable Angina and Non-Q-Wave Myocardial Infarction

Thrombin and platelets are directly involved in arterial thrombosis, typically occurring at sites of atherosclerotic plaque rupture among patients with acute coronary syndromes. Understanding the dynamic nature of pathologic thrombosis has important clinical implications. Methods: Fibrinopeptide A (FPA), thrombin-antithrombin complexes (TAT), and prothrombin activation fragment 1.2 (F1.2), plasma markers of fibrin formation (thrombin activity) and thrombin generation, and platelet activation, determined by the recognition of a surface-expressed platelet alpha-granule protein, P-selectin, using flow cytometry, were measured in 36 consecutive patients with unstable angina and non-Q-wave myocardial infarction participating in the Thrombolysis In Myocardial Ischemia (TIMI) III B trial. Results: Thrombin generation (TAT 12.1 +/- 17.8 ng/ml vs. 3.4 +/- 1.0 ng/ml; F1.2 0.19 +/- 0.14 nmol/l vs. 0.12 +/- 0.8 nmol/l), fibrin formation (FPA 15.8 +/- 23.5 ng/ml vs. 7.5 +/- 2.3 ng/ml), and platelet activation) 10.6 +/- 2.4% vs. 2.5 +/- 2.0%) were increased significantly in patients compared with healthy, age-matched controls (p < 0.01). Fibrin formation, represented by plasma FPA levels, did not correlate with the percentage of activated platelets (r = -.10, p = 0.69). Thrombin generation and platelet activation also did not correlate. A statistically insignificant trend between TAT and platelet activation was observed (r =.42, p = 0.07); however, even with TAT levels in excess of 20 ng/ml (nearly sixfold greater than normal healthy controls) platelet activation was increased by only 1.7-fold. Conclusions: Thrombin generation, fibrin formation, and platelet activation are increased modestly among patients with unstable angina and non-Q-wave myocardial infarction. Despite the involvement of platelets and coagulation proteins in arterial thrombotic processes, their relative contributions may vary, providing a pathophysiologic basis for the dynamic expression of di sease and response to treatment observed commonly in clinical practice.

Soluble E-selectin is not a marker of unstable coronary plaque in serum of patients with ischemic heart disease

Increased level of soluble cell adhesion molecules may be a marker for atherosclerosis and/or reflect complication of the atherosclerotic plaque. To test whether expression of cell adhesion molecules is more pronounced in unstable versus stable coronary plaques, we measured the serum level of soluble E-selectin (sE-selectin) in 99 consecutive patients admitted to the hospital for acute coronary syndromes (ACS) and in 61 patients with chronic coronary artery disease (CAD) using a commercially available ELISA kit. We also measured the sE-selectin concentration in 20 sex- and age-matched subjects without clinical evidence of atherosclerosis, who served as controls. The mean sE-selectin level was higher in both groups of patients compared with controls (ACS, 35.0 +/- 23.4 ng/mL; chronic CAD, 32.9 +/- 21.0 ng/mL; controls, 14.5 +/- 6.6 ng/mL; one-way ANOVA, P = 0.001), but there was no difference between patients with ACS and chronic CAD. Furthermore, there was a trend (P = 0.08) toward a decrease in sE-selectin with an increase in the extent and severity of CAD. In patients with ACS, the in-hospital cardiac event rate was 8%. Although mean sE-selectin concentration tended to be higher in patients with (49.2 +/- 42.1 ng/mL) than in those without (33.8 +/- 21.3 ng/mL) in-hospital cardiac events, the difference was not significant. In 53 patients with ACS, C-reactive protein was measured and showed no correlation with the sE-selectin concentration. These findings show that although sE-selectin concentration is elevated in the presence of clinically relevant atherosclerosis, it does not further increase during the unstable phase of the disease, indicating that sE-selectin is not a reliable indicator of a complicated atherosclerotic plaque.

Occlusions of epicardial arteries might not directly induce symptoms in ischemic heart disease

It is accepted that primary occlusions of epicardial arteries by thromboses, stenotic coronary artery disease (CAD), and spasm directly induce symptoms in ischemic heart disease (IHD). Because of this acceptance, there has been little interest in alternate mechanisms for IHD--as the spasm of resistance vessel (S-RV) concept of IHD, which asserts that S-RV directly induces symptoms in IHD. To stimulate interest in the S-RV concept, evidence against the primacy of occlusions of epicardial arteries was presented, as well as evidence for this position to provide a balanced discussion; while the evidence was mixed, overall findings appeared to weigh significantly against the primacy of occlusions of epicardial arteries. Also, the S-RV concept was discussed; the discussion included presenting the theory's explanations for events in epicardial arteries, with the aim of demonstrating that the concept provides more consistent explanations than the standard position. It is suggested that there is sufficient information to warrant renewed consideration of the S-RV concept.

A perspective on the potential problems with aspirin as an antithrombotic agent: a comparison of studies in an animal model with clinical trials

Aspirin is the most widely prescribed agent to reduce the platelet-mediated contributions to atherosclerosis, coronary thrombosis and restenosis after angioplasty. While aspirin treatment has led to significant reductions in morbidity and mortality in many clinical trials, there are several scenarios in which aspirin may fail to provide a full antithrombotic benefit. The cyclic flow model of experimental coronary thrombosis suggests that elevations of plasma catecholamines, high shear forces acting on the platelets in the stenosed lumen and the presence of multiple, input stimuli can activate platelets through different mechanisms that may lead to thrombosis despite aspirin therapy. Aspirin therapy is limited because it only blocks some of the input stimuli, leaving aspirin-independent pathways through which coronary thrombosis can be precipitated. These include thrombin and thrombogenic arterial wall substrates such as tissue factor. New agents that block the adenosine diphosphate (ADP) receptor, or regulate platelet free cytosolic calcium, such as direct nitric oxide donors, may be more potent overall than aspirin. Agents that block the platelet integrin GPIIb-IIIa receptor inhibit the binding of fibrinogen to platelets regardless of which input stimuli activate the platelet and, thus, as demonstrated in the cyclic flow model, would be much more potent than aspirin as an antithrombotic agent. The cyclic flow model has been useful in predicting which agents are likely to be of benefit in clinical trials.

Diagnosis of coronary vasospasm in patients with clinical presentation of unstable angina pectoris using ergonovine echocardiography

Although coronary vasospasm can contribute to the development of unstable angina, the definite diagnostic method has not been established. The purpose of this study was to determine if ergonovine echocardiography (detection of regional wall motion abnormality during bedside ergonovine challenge) after angiographic confirmation of insignificant fixed disease would be useful and safe in detecting coronary vasospasm in patients with unstable angina. After control of chest pain with medications in patients admitted to the coronary care unit under the tentative diagnosis of unstable angina, diagnostic coronary angiography was performed. All patients with normal or insignificant fixed disease underwent ergonovine echocardiography after discontinuation of medications for 4+/-1 days. Among 208 consecutive patients enrolled for this study, 75% (156 of 208) showed significant fixed disease in the angiography. Ergonovine echocardiography was performed in 52 patients with insignificant disease, and coronary vasospasm was documented in 33 (63%, 33 of 52). No serious procedure-related arrhythmia or myocardial infarction occurred. Esophageal motility disorder and hypertrophic cardiomyopathy were diagnosed in 6 and 3 patients, respectively. Chest pain of undetermined etiology was the final diagnosis at discharge in 10 patients (5%, 10 of 208); among them chest pain redeveloped in 2 patients, and repeated ergonovine echocardiography revealed positive results. Our data suggest that among patients with the clinical presentation of unstable angina, coronary vasospasm is the main cause of myocardial ischemia in a considerable number of patients with a normal or near-normal angiogram, and ergonovine echocardiography after confirmation of absence of significant fixed disease is useful and safe for noninvasive diagnosis of coronary vasospasm in this setting.

Transcardiac 5-hydroxytryptamine release and impaired coronary endothelial function in patients with vasospastic angina

1. The present study was designed to test the hypotheses whether platelet degranulation across the coronary bed is detectable during non-ischaemic periods in patients with vasospastic angina (VSA) and whether the exogenous nitric oxide (NO) donor nitroglycerin (GTN) is able to modify platelet degranulation, reflecting an impaired endothelial production of NO. 2. We studied 13 patients with VSA and 10 controls. The time course of coronary sinus (CS) plasma 5-hydroxytryptamine (5-HT) levels was evaluated every 4 h before and after intravenous infusion of GTN over a period of 40 h. Coronary sinus plasma 5-HT levels were significantly higher at any measured time point in patients with VSA compared with control and were significantly decreased in patients with VSA following treatment with GTN, but not in controls. Femoral artery plasma 5-HT levels remained almost constant throughout the study. The ratio of CS:aorta 6-keto-prostaglandin F1 alpha was significantly and inversely correlated with the transcardiac plasma 5-HT difference only in patients with VSA (r = -0.68; P < 0.02; n = 13). 3. The time course of CS 5-HT levels confirmed significant platelet degranulation across the coronary bed supplied by the spasming artery in patients with VSA and this was modified by GTN. The present data suggest that platelet degranulation occurs during non-ischaemic periods in patients with VSA and that prostacyclin biosynthesis may be a compensatory response to an impaired endothelial release of NO, limiting the degree of the effects of platelet degranulation.

Platelet aggregation in acute coronary syndromes: use of a new aggregometer with laser light scattering to assess platelet aggregability

OBJECTIVE

Platelet aggregation has been implicated in the pathogenesis of acute coronary syndromes. Small aggregates consisting of < or = 100 platelets cannot be quantified with a conventional aggregometer employing optical density. Using a recently developed aggregometer based on laser light scattering, we studied platelet aggregability in patients with acute coronary syndromes.

METHODS

Peripheral blood samples were obtained from 39 patients with acute myocardial infarction or unstable angina who had received no prior antiplatelet or anticoagulant therapy, to be assayed immediately using a PA-100 platelet aggregometer. Blood samples from 14 healthy volunteers were used as controls.

RESULTS

Spontaneous formation of platelet aggregates was observed only in patients with acute coronary syndromes. The size of these aggregates was small, consisting of < or = 100 platelets (primary aggregation). Agonist-induced aggregation consisted of two phases. In the first few minutes, the number of small aggregates increased markedly (primary aggregation), followed by an increase in larger aggregates (secondary aggregation). The EC50 of epinephrine for primary aggregation was nearly 50 times lower in acute coronary patients than in controls (P < 0.001), while the EC50 for secondary aggregation was only 2 times lower (P < 0.001).

CONCLUSIONS

Aggregometry using light scattering suggests that platelet hyperaggregability and hypersensitivity in acute coronary syndromes may occur in primary but not secondary aggregation.

The role of myocardial revascularization preceding noncardiac surgery

Of about 6.7 million Americans who have coronary artery disease, approximately 700,000 undergo various noncardiac operations annually in the United States. Perioperative cardiac complications remain the leading cause of morbidity and mortality not related to the primary operative procedure; the mechanisms of perioperative ischemia and infarction are unclear. Currently, clinicians, using a combination of clinical and laboratory findings, can estimate the risk of noncardiac surgical procedures with a high degree of precision, but much less is known about the preferred approach to patient management after noninvasive risk stratification. Coronary angiography and revascularization are frequently recommended for those determined by functional tests to be at moderate and high risk, but the risks of revascularization are often substantially higher among these patients. No randomized, controlled trials exist to guide patient management. Quantitative decision analysis based on published nonrandomized data suggests that coronary angiography with selective myocardial revascularization should be performed to reduce the risk of noncardiac surgery only if the risk of noncardiac surgery is greater than 5% and the risk of coronary angiography with selective revascularization is less than 3%. On the other hand, if independent indications exist for myocardial revascularization, it should generally be performed before the noncardiac operation.

Surgery-specific considerations in the cardiac patient undergoing noncardiac surgery

Myocardial infarction after noncardiac surgery in patients with coronary artery disease results from the interplay of patient-specific, anesthetic-specific, and surgery-specific factors. Surgery-specific factors include the stress response to injury, both neurohormonal and hemostatic alterations, and clinically-significant operative parameters such as urgency, duration, blood loss, body core temperature, fluid shifts, and location of surgery. The impact of these factors bears out during the entire perioperative period and influences preoperative risk assessment, cardiac evaluation and intervention, intraoperative strategy, and postoperative management. Overall, the morbidity and mortality of surgery is minimal even in high-risk patients, and the contribution of surgery-specific factors to operative risk is subtle compared with that of patient specific-factors such as severity of coronary disease and other comorbid conditions. Nonetheless, the optimal surgical management of patients with coronary disease requires the collaborative effort of the anesthesiologist, cardiologist, and surgeon.

ADP-induced platelet activation

Platelet activation is central to the pathogenesis of hemostasis and arterial thrombosis. Platelet aggregation plays a major role in acute coronary artery diseases, myocardial infarction, unstable angina, and stroke. ADP is the first known and an important agonist for platelet aggregation. ADP not only causes primary aggregation of platelets but is also responsible for the secondary aggregation induced by ADP and other agonists. ADP also induces platelet shape change, secretion from storage granules, influx and intracellular mobilization of Ca2+, and inhibition of stimulated adenylyl cyclase activity. The ADP-receptor protein mediating ADP-induced platelet responses has neither been purified nor cloned. Therefore, signal transduction mechanisms underlying ADP-induced platelet responses either remain uncertain or less well understood. Recent contributions from chemists, biochemists, cell biologists, pharmacologists, molecular biologists, and clinical investigators have added considerably to and enhanced our knowledge of ADP-induced platelet responses. Although considerable efforts have been directed toward identifying and cloning the ADP-receptor, these have not been completely successful or without controversy. Considerable progress has been made toward understanding the mechanisms of ADP-induced platelet responses but disagreements persist. New drugs that do not mimic ADP have been found to inhibit fairly selectively ADP-induced platelet activation ex vivo. Drugs that mimic ADP and selectively act at the platelet ADP-receptor have been designed, synthesized, and evaluated for their therapeutic efficacy to block selectively ADP-induced platelet responses. This review examines in detail the developments that have taken place to identify the ADP-receptor protein and to better understand mechanisms underlying ADP-induced platelet responses to develop strategies for designing innovative drugs that block ADP-induced platelet responses by acting selectively at the ADP-receptor and/or by selectively interfering with components of ADP-induced platelet activation mechanisms.

Acute vigorous exercise attenuates sensitivity of platelets to nitric oxide

We tested whether inhibition of platelet activation by nitric oxide (NO) might be altered by strenuous exercise. Sixteen healthy male non-smokers, aged 20-26 years, underwent treadmill testing. All subjects reached Bruce stage IV without chest pain or abnormal ST-T wave changes. Platelet aggregation by Born's method and cyclic GMP accumulation in the washed platelets were determined before and immediately after exercise. Dose-response curves for platelet aggregation by collagen were constructed both in the absence and presence of 2 microM SIN-1, an NO donor, to quantify the antiaggregation effects of NO. After exercise, platelet aggregation by collagen was modestly enhanced and inhibition of platelet aggregation by SIN-1 was significantly attenuated by exercise. This attention was accompanied by a blunted cyclic GMP response of the platelets to the NO donor. We conclude that impaired sensitivity of the platelets to NO, in addition to the enhancement of platelet aggregation, may partially explain the epidemiological evidence that acute strenuous exercise precipitates coronary events.

Levels of expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 in coronary atherectomy specimens from patients with stable and unstable angina pectoris

Unstable angina occurs when atherosclerotic plaque ruptures. Recent evidence suggests a role for inflammation in this process. Leukocyte-endothelial cell interactions are important in inflammation and are regulated by cell adhesion molecules. This study was designed to examine the vascular expression of cell adhesion molecules and cytokines in patients with unstable angina. Directional coronary atherectomy was performed in patients with unstable and stable angina. Expression of the cell adhesion molecules P-selectin, E-selectin, and intercellular adhesion molecule-1 in the tissue obtained was examined using immunohistochemistry. In addition, expression of the cytokines tumor necrosis factor-alpha and interleukin-1beta, which participate in the regulation of cell adhesion molecule expression, was also examined. Atherectomy specimens had significantly greater P-selectin expression from patients with unstable angina than from patients with stable angina. P-selectin expression was observed primarily on endothelial cells. There were no differences in any of the other factors between patients with unstable and stable angina. In addition, other clinical and angiographic variables were not associated with differential expression of any of the cell adhesion molecules or cytokines. These results indicate a possible role for P-selectin in the process of unstable angina.

Increased serotonin release across the coronary bed during a nonischemic interval in patients with vasospastic angina

BACKGROUND

Platelet activation and coagulation abnormality have been observed during coronary spasm. It is crucial whether platelet activation occurs even during a nonischemic period.

HYPOTHESIS

This study was designed to determine whether platelets might be activated across the coronary bed during a nonischemic interval in patients with vasospastic angina.

METHODS

Plasma levels of serotonin, 6-keto-prostaglandin F1 alpha, and catecholamines in the aorta and the coronary sinus were simultaneously measured in 16 patients with vasospastic angina and 13 control patients with nonischemic heart disease.

RESULTS

None of these patients showed myocardial ischemia during sampling. The difference in transcardiac plasma levels of serotonin in patients with vasospastic angina was significantly higher than that in controls (1.48 +/- 1.08 ng/ml vs. 0.07 +/- 0.12 ng/ml, respectively, p < 0.001). Coronary sinus plasma norepinephrine levels in these two groups were almost the same (204.8 +/- 110.8 pg/ml vs. 190.4 +/- 131.6 pg/ml, respectively). The ratio of 6-keto-prostaglandin F1 alpha in the coronary sinus and the aorta was not different between the two groups (1.17 +/- 0.96 in patients with vasospastic angina vs. 1.15 +/- 0.68 in controls).

CONCLUSIONS

These data suggest that platelet activation across the coronary bed should be ascribed to endothelial dysfunction. Lack of compensatory enhancement of prostacyclin production might be concerned with dysfunction of coronary endothelial cells in these patients.

Thrombogenesis in acute coronary syndromes

It is well-established that intracoronary thrombosis, which may be associated with plaque fissure and enhanced coronary vasoconstriction, is the immediate cause of a sudden impairment of regional myocardial perfusion, which is transient in unstable angina and is, eventually, irreversible in acute myocardial infarction. It is also well-known that increased platelet reactivity, increased procoagulant activity, and reduced endogenous fibrinolysis are risk factors for acute coronary events. Nevertheless, the primary causes responsible for sudden intracoronary thrombosis and for coronary vasoconstriction causing acute coronary syndromes are still largely speculative. Recent studies have shown activated inflammatory cells both in the coronary arterial wall and in the systemic circulation of patients with unstable angina. Furthermore, the intensity of the inflammatory response is correlated with an adverse prognosis. This inflammatory component may have important pathogenetic and prognostic roles because an outburst of inflammatory cytokines has the potential to increase the sensitivity of platelets to agonists, to turn the anticoagulant and vasodilator physiological properties of the endothelium into procoagulant and vasoconstrictor properties, and to cause plaque fissure by the release of proteolytic enzymes.

One-year results of the Thrombolysis in Myocardial Infarction (TIMI) IIIB clinical trial. A randomized comparison of tissue-type plasminogen activator versus placebo and early invasive versus early conservative strategies in unstable angina and non-Q wave myocardial infarction

OBJECTIVES

We report mortality, infarction, revascularization and repeat hospital admission events for 1 year after enrollment and randomization in the Thrombolysis in Myocardial Ischemia (TIMI) IIIB clinical trial.

BACKGROUND

The purpose of this trial was to investigate the role of a thrombolytic agent added to conventional medical therapies and to compare an early invasive management strategy to a more conservative early strategy in patients with unstable angina and non-Q wave myocardial infarction.

METHODS

There were 1,473 patients enrolled, and they received conventional anti-ischemic medical therapies. They were randomized to therapy with either tissue-type plasminogen activator (t-PA) or placebo and also to an early invasive management strategy with coronary arteriography at 18 to 48 h, followed by revascularization as soon as possible if appropriate, or, alternatively, to an early conservative strategy with arteriography and revascularization reserved for failure of initial therapy to prevent recurrent ischemia. The primary end point was a composite outcome variable and was assessed at 42 days. Patients were then managed entirely at the discretion of their treating physician. Follow-up contacts were made at 1 year.

RESULTS

The incidence of death or nonfatal infarction for the t-PA- and placebo-treated groups was similar after 1 year (12.4% vs. 10.6%, p = 0.24). The incidence of death or nonfatal infarction was also similar after 1 year for the early invasive and early conservative strategies (10.8% vs. 12.2%, p = 0.42). A trial of this size should be able to detect differences in relative risk for death or infarction > or = 1.81 with a power of 80% at a significance level (alpha) of 0.01. Revascularization by 1 year was common, but was slightly more common with the early invasive than the early conservative strategy (64% vs. 58%, p < 0.001). This result was related entirely to a small difference in angioplasty rates (39% vs. 32%, p < 0.001) inasmuch as rates of bypass grafting by 1 year were equivalent (30% in each group, p = 0.50). The high rate of revascularization in both strategies was accompanied by comparable clinical status at the 1-year follow-up contact.

CONCLUSIONS

In this large study of unstable angina and non-Q wave myocardial infarction, the incidence of death and nonfatal infarction or reinfarction was low but not trivial after 1 year (4.3% mortality, 8.8% nonfatal infarction). An early invasive management strategy was associated with slightly more coronary angioplasty procedures but equivalent numbers of bypass surgery procedures than a more conservative early strategy of catheterization and revascularization only for signs of recurrent ischemia. The incidence of death or nonfatal infarction, or both, did not differ after 1 year by strategy assignment, but fewer patients in the early invasive strategy group underwent later repeat hospital admission (26% vs. 33%, p < 0.001). Either strategy is appropriate for patient management; differences in hospital admissions and revascularization procedures, with their attendant costs, are likely to be minimal.

Mechanical and metabolic functions in pig hearts after 4 days of chronic coronary stenosis

OBJECTIVES

This study sought to evaluate the functional and metabolic consequences of imposing a chronic external coronary stenosis around the left anterior descending coronary artery for 4 days in an intact pig model.

BACKGROUND

A clinical condition termed hibernating myocardium has been described wherein as a result of chronic sustained or intermittent coronary hypoperfusion, heart muscle minimizes energy demands by decreasing mechanical function and thus avoids cell death. The use of chronic animal models to stimulate this disorder may assist in establishing causative associations among determinants to explain this phenomenon.

METHODS

A hydraulic cuff occluder was placed around the left anterior descending coronary artery in eight pigs. Coronary flow velocity was reduced by a mean (+/- SE) of 49 +/- 5% of prestenotic values, as estimated by a Doppler velocity probe. After 4 days the pigs were prepared with extracorporeal coronary circulation and evaluated at flow conditions dictated by the cuff occluder. Substrate utilizations were described using equilibrium labeling with [U-14C]palmitate and [5-3H]glucose. Results were compared with a combined group of 21 acute and chronic (4 day) sham animals.

RESULTS

Four days of partial coronary stenosis significantly decreased regional systolic shortening by 54%. Myocardial oxygen consumption was maintained at aerobic levels, and rest coronary flows were normal. Fatty acid oxidation was decreased by 43% below composite sham values, and exogenous glucose utilization was increased severalfold. Alterations in myocardial metabolism were accompanied by a decline in tissue content of adenosine triphosphate.

CONCLUSIONS

These data suggest that chronic coronary stenosis in the absence of macroscarring imparts an impairment in mechanical function, whereas coronary flow and myocardial oxygen consumption are preserved at rest. The increases in glycolytic flux of exogenous glucose are similar to observations on glucose uptake assessed by fluorine-18 2-deoxy-2-fluoro-D-glucose in patients with advanced coronary artery disease. We speculate that intermittent episodes of ischemia and reperfusion are the cause of this phenomenon.

Comparison of early invasive and conservative treatments in patients with anterior wall non-Q-wave acute myocardial infarction

To compare the long-term prognosis of a group of patients treated by an early invasive approach after a non-Q-wave anterior wall acute myocardial infarction (AMI) with a similar group treated conservatively, data from 110 consecutive patients with non-Q-wave AMI were retrospectively obtained from 3 different hospitals: (1) a hospital with coronary angioplasty and coronary bypass facilities favoring on early invasive approach, (2) a hospital with a catheterization laboratory and no coronary angioplasty or coronary bypass facilities, and (3) a community hospital without a catheterization laboratory. Patients were divided according to the presence or absence of an early invasive approach: those who had undergone in-hospital catheterization and revascularization (n = 55) and those with a conservative approach (n = 55). The early invasive approach resulted in a significant decrease in major events. The rate of recurrent myocardial infarction was 29% in the conservative group versus 7.2% in the invasive group (p = 0.025). Survival rate curves at 3-year follow-up showed significant differences in mortality (p = 0.001), recurrent myocardial infarction (p = 0.002), recurrent angina pectoris (p = 0.001), and development of congestive heart failure (p = 0.05). Multivariate analysis disclosed the early invasive approach to be an independent predictor for decreasing the likelihood of recurrent infarction by 86% (odds ratio 0.14, confidence intervals 0.04 to 0.48, p = 0.0006), and for decreasing the likelihood of recurrent angina by 66% (odds ratio 0.34, confidence intervals 0.18 to 0.63, p < 0.005). The early invasive strategy may result in an improved outcome in the treatment of patients with non-Q-wave anterior wall AMI compared with patients treated conservatively.

How safe is the readministration of streptokinase?

Streptokinase is an antigenic thrombolytic agent used for the treatment of acute myocardial infarction. It reduces mortality as effectively as the nonantigenic alteplase in most infarct patients while having the advantage of being much less expensive. This cost implication is important since myocardial reinfarction is common, with fibrinolytic therapy indicated in many patients with reinfarction. Following streptokinase, antistreptokinase antibodies and neutralisation titres can rise to significant levels from 4 days after the initial dose. These antibodies can presist for at least 4 years in up to 50% of patients. It is possible that these antibodies may cause allergic reactions or neutralisation of a further dose of streptokinase, rendering it ineffective for the treatment of myocardial reinfarction. To date, 2 small studies of patients without previous streptokinase exposure suggest that higher antibody titres are associated with a lower rate of coronary reperfusion, while a further study suggests that high titres are associated with hypersensitivity reactions. At present the readministration of streptokinase cannot be recommended from 4 days after a first dose. Further larger studies are needed to assess the effect of high neutralisation titres on coronary reperfusion.

Effects of gallopamil on epinephrine and norepinephrine plasmatic levels and on TxB2 and beta-tg release in patients with coronary artery disease during adrenergic stimulus with cold pressor test

We investigated the effect of gallopamil administration during a cold pressor test (CPT) in 18 patients suffering from chronic angina (CA) and in 21 healthy subjects. CA patients showed increased basal levels of beta-thromboglobulin and thromboxane B2 compared to control patients and normal plasma levels of catecholamines. CPT caused plasma catecholamines, beta-thromboglobulin and TxB2 levels to rise. This rise was greater in CA patients than in control patients. Administration of gallopamil (50 mg kg-1 three times a day for 30 days) reduced plasma levels of catecholamines, beta-thromboglobulin and TxB2 blood concentrations either under basal conditions or after CPT. Our data suggest that gallopamil is able to modulate the response induced by adrenergic stress.

Inhibitory effect of nitroglycerin and sodium nitroprusside on platelet activation across the coronary circulation in stable angina pectoris

This study assessed the inhibitory effect of nitroglycerin and sodium nitroprusside on platelet aggregation in a model of platelet activation across coronary circulation. Platelet aggregation is believed to contribute to the precipitation of acute ischemic syndromes. We previously showed that rapid atrial pacing in patients with stable coronary artery disease (CAD) causes platelet hyperaggregability during blood passage in coronary circulation. Because nitroglycerin and sodium nitroprusside have been shown to inhibit platelet aggregation, we examined the effect of these drugs on this model of platelet activation. During catheterization of 19 patients with CAD (> 50% diameter narrowing of epicardial coronary arteries), we measured platelet aggregation (using whole blood platelet aggregometry) on blood samples obtained simultaneously from the coronary sinus and aorta at rest, and 2 minutes after onset of rapid atrial pacing. This procedure was repeated during an intravenous infusion of either nitroglycerin (n = 9) or sodium nitroprusside (n = 10). There was no arteriovenous difference in platelet aggregation under resting conditions. Atrial pacing caused an increase in platelet aggregation in coronary sinus blood (+64 +/- 9%; p < 0.01), but not in arterial blood (15 +/- 12% decrease; p = NS). This increase was transient and returned toward baseline 10 minutes after termination of pacing. Although resting platelet aggregation was not affected by nitroglycerin or sodium nitroprusside, activation of platelets with atrial pacing across the coronary bed was stopped by pretreatment with therapeutic doses of nitroglycerin or sodium nitroprusside. When coronary blood flow increases in patients with CAD, platelets are activated and aggregate more easily. This activation can be blunted by pretreatment with nitroglycerin or sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Myocardial Infarction: Diagnosis and Management

Acute myocardial infarction is caused by abrupt thrombotic coronary occlusion. About 1.5 million patients will suffer a heart attack and 10 to 20% of them will die in the U.S.A. annually. Accurate diagnosis and early reopening (reperfusion) of infarct-related coronary artery will lower mortality (2 to 7%) and morbidity of patients and improve their post-MI recovery. There are several effective therapies available to reopen closed infarct-related coronary arteries. Thrombolytic or clot dissolving therapy can be safely used in about one-third of heart attack stricken patients. The expected effectiveness of thrombolytic therapy in treated patients is 70 to 80% of reperfusion rates and 7 to 8% mortality rates. Direct coronary angioplasty of the infarct-related coronary artery represents the most aggressive, yet the most effective reperfusion modality available to all patients suffering from acute MI. Direct angioplasty, when used appropriately, will result in 97 to 99% reperfusion rates and 2 to 3% mortality rates. Aggressive approach to the diagnosis and the treatment of acute MI using either thrombolytic therapy or direct coronary angioplasty holds the greatest promise for clinical success.

Abolition of cyclic flow variations in stenosed, endothelium-injured coronary arteries in nonhuman primates with a peptide fragment (VCL) derived from human plasma von Willebrand factor-glycoprotein Ib binding domain

BACKGROUND

Platelets play an important role in the pathophysiology of acute coronary syndromes. The interaction between the platelet glycoprotein Ib receptor and von Willebrand factor is a critical event allowing platelet adhesion and aggregation and subsequent thrombus formation in vessels with high shear rates and damaged endothelium. Therefore, we tested the hypotheses that VCL, an antagonist of von Willebrand-glycoprotein Ib binding domain, (1) attenuates/abolishes cyclic flow variations in stenosed, endothelium-injured coronary arteries in nonhuman primates and (2) reduces botrocetin-induced platelet aggregation in vitro after intravenous in vivo administration.

METHODS AND RESULTS

Cyclic flow variations were established in anesthetized, open-chest baboons (n = 18). The baboons were divided into three groups. One group (n = 8) received a bolus of VCL (4 mg/kg IV) followed by an infusion (6 mg.kg-1.h-1) for 90 minutes (schedule A). Another group (n = 6) received a 2-mg/kg bolus followed by an infusion of 3 mg.kg-1.h-1 for 90 minutes (schedule B). The third group received a placebo infusion of normal saline. Under dosing schedule A, cyclic flow variations were abolished in 7 of 8 baboons after 33 +/- 18 minutes and markedly attenuated in 1. The frequency of cyclic flow variations fell from 18 +/- 9.4 per hour during the control period to 1 +/- 2.5 per hour after VCL infusion, P < .002. After cessation of infusion, cyclic flow variations remained abolished in 5 of 7 animals for > 3 hours and returned in 2 of 7 after 2 to 2.5 hours. Under schedule B, cyclic flow variations were abolished in 3 of 6 baboons and markedly reduced in the remainder. The number of cyclic flow variations fell from 17 +/- 4.8 per hour during the control period to 5 +/- 4.9 per hour after the VCL infusion, P < .001. The cyclic flow variations returned spontaneously at 38 +/- 40 minutes under this dosing schedule. Placebo infusion of saline had no effect on cyclic flow frequency or severity. VCL administration was associated with slight prolongation in bleeding time and a reduction in botrocetin-induced platelet aggregation. The bleeding time increased from a control time of 88 +/- 32 to 276 +/- 204 seconds, P < .03, and from 142 +/- 28 to 176 +/- 36 seconds, P = .056, for schedules A and B, respectively. VCL decreased platelet aggregation in response to botrocetin (20 micrograms/mL), from a control value of 66 +/- 30.3 to 33 +/- 31.3 omega, P < .05, and from 64 +/- 23.5 to 46 +/- 15.8 omega, P = .006, for dosing schedules A and B, respectively.

CONCLUSIONS

Therefore, administration of a peptide fragment corresponding to von Willebrand-glycoprotein Ib binding domain (1) is effective in abolishing cyclic flow variations in stenosed, endothelium-injured coronary arteries and (2) reduces platelet aggregation in vivo in response to botrocetin in nonhuman primates.

Lack of correlation between coronary risk factors and CAD severity

The coronary arterial lesions seen by angiography in 1666 consecutive male patients were converted to a score by the standardized scoring system advocated by Gensini. The resulting score, which allowed the disease to be expressed as a continuous variable, was effectively utilized to see the correlations between the severity of coronary arterial disease (CAD) and individual risk factors/risk markers. Significant correlations were seen between severity and age (P < 0.001), with a very low coefficient of correlation of 0.0873. On univariate analysis, no correlation was found between CAD severity and diabetes, smoking, positive family history of CAD, hypertension and other lipid fractions. On multiple regression analysis, significant correlations were found between severity and LDL Cholesterol, family history and total cholesterol after adjusting for other factors. The R2 for all these risk factors was only 14.1%. It is concluded that, although strong associations exist between risk factors and the occurrence of CAD, the small quantitative association detected between the presence of risk factors and the severity of disease is weak.

Lewis A. Conner Memorial Lecture. Mechanisms leading to myocardial infarction: insights from studies of vascular biology

Myocardial infarction is the most frequent cause of mortality in the United States as well as in most western countries. In this review, the processes leading to myocardial infarction are described based on the most recent studies of vascular biology; in addition, evolving strategies for prevention are outlined. The following was specifically discussed. (1) Five phases of the progression of coronary atherosclerosis (phases 1 to 5) and eight morphologically different lesions (types I, II, III, IV, Va, Vb, Vc, and VI) in the various phases are defined. (2) The present understanding of the pathogenesis of each of the phases of progression and of the various lesion types preceding myocardial infarction is described; particular emphasis is placed on the physical, structural, cellular, and chemical characteristics of the "vulnerable or unstable plaques" prone to disruption (types IV and Va lesions). (3) The fate of plaque disruption (type VI lesion) in the genesis of the various coronary syndromes and especially acute myocardial infarction is defined; particular emphasis is placed on the combination of plaque disruption and a high thrombogenic risk profile--local factors (ie, degree of plaque disruption, exposure of lipid-macrophage-rich plaque, etc) and systemic factors (ie, catecholamines, RAS, fibrinogen, etc)--in the genesis of myocardial infarction. (4) Strategies of regression or stabilization of "vulnerable or unstable plaques" for prevention of myocardial infarction are presented within the context of recent favorable experience with risk factor modification and lipid-modifying angiographic trials, beta-blockade and angiotensin-converting enzyme inhibition, antithrombotic strategies, and the possible role of estrogens. The recent past has been very fruitful in yielding a better understanding of the processes leading to myocardial infarction, and the near future appears very promising in terms of preventing the number 1 killer in the western world.

Effects of tissue plasminogen activator and a comparison of early invasive and conservative strategies in unstable angina and non-Q-wave myocardial infarction. Results of the TIMI IIIB Trial. Thrombolysis in Myocardial Ischemia

BACKGROUND

Although coronary thrombosis plays a critical role in the pathogenesis of unstable angina and non-Q-wave myocardial infarction (NQMI), the effects of thrombolytic therapy in these disorders is not clear. Also, the role of routine early coronary arteriography followed by revascularization has not been established.

METHODS AND RESULTS

Patients (n = 1473) seen within 24 hours of ischemic chest discomfort at rest, considered to represent unstable angina or NQMI, were randomized using a 2 x 2 factorial design to compare (1) TPA versus placebo as initial therapy and (2) an early invasive strategy (early coronary arteriography followed by revascularization when the anatomy was suitable) versus an early conservative strategy (coronary arteriography followed by revascularization if initial medical therapy failed). All patients were treated with bed rest, anti-ischemic medications, aspirin, and heparin. The primary end point for the TPA-placebo comparison (death, myocardial infarction, or failure of initial therapy at 6 weeks) occurred in 54.2% of the TPA-treated patients and 55.5% of the placebo-treated patients (P = NS). Fatal and nonfatal myocardial infarction after randomization (reinfarction in NQMI patients) occurred more frequently in TPA-treated patients (7.4%) than in placebo-treated patients (4.9%, P = .04, Kaplan-Meier estimate). Four intracranial hemorrhages occurred in the TPA-treated group versus none in the placebo-treated group (P = .06). The end point for the comparison of the two strategies (death, myocardial infarction, or an unsatisfactory symptom-limited exercise stress test at 6 weeks) occurred in 18.1% of patients assigned to the early conservative strategy and 16.2% of patients assigned to the early invasive strategy (P = NS). In the latter, the average length of initial hospitalization, incidence of rehospitalization within 6 weeks, and days of rehospitalization all were significantly lower.

CONCLUSIONS

In the overall trial, patients with unstable angina and NQMI were managed with low rates of mortality (2.4%) and myocardial infarction or reinfarction (6.3%) at the time of the 6-week visit. These results can be achieved using either an early conservative or early invasive strategy, the latter resulting in a reduced incidence of days of hospitalization and of rehospitalization and in the use of antianginal drugs. The addition of a thrombolytic agent is not beneficial and may be harmful.