Morphodynamic interpretation of acute coronary thrombosis, with special reference to volcano-like eruption of atheromatous plaque caused by coronary artery spasm

Cellular Mechanisms of Coronary Artery Spasm

Coronary artery spasm (CAS) is a reversible phenomenon caused by spontaneous excessive vascular smooth muscle contractility and vascular wall hypertonicity, which results in partial or complete closure of the lumen of normal or atherosclerotic coronary arteries. The clinical picture of CAS includes chest discomfort which is similar in quality to that of stable effort angina. Mechanisms underlying the development of CAS are still unclear. CAS certainly is a multifactorial disease. In this review, we paid attention to the role of the main pathophysiologic mechanisms in CAS: endothelial dysfunction, chronic inflammation, oxidative stress, smooth muscle hypercontractility, atherosclerosis and thrombosis, and mutations leading to deficient aldehyde dehydrogenase 2 (ALDH2) activity. These findings might shed novel insight on the underlying mechanisms and identify potential diagnostic and therapeutic targets for cardiovascular diseases in the future.

Out-of-hospital cardiac arrest due to acute myocardial infarction possibly caused by coronary vasospasm

A 60-year-old man with out-of-hospital cardiac arrest was transported to our hospital by an emergency medical service. Ventricular fibrillation was finally terminated after the initiation of circulation support by percutaneous cardiopulmonary support device. Although acute myocardial infarction was suspected, emergency coronary angiography could not identify the culprit lesion of myocardial infarction while there were multiple intermediate stenotic lesions. Since re-elevation of troponin I was recorded on the 4^th day after admission, coronary angiography was performed again, and diffuse severe stenosis in the right coronary artery and total occlusion in the left circumflex coronary artery that disappeared by the injection of isosorbide dinitrate was detected. Therefore, we reached the diagnosis of acute myocardial infarction due to coronary vasospasm. It is very rare that emergency coronary angiogram reveals coronary vasospasm at the culprit lesion of myocardial infarction. The guideline recommends calcium channel antagonist and long-acting nitrates for vasospastic angina; however, it would be really difficult to make correct diagnosis of coronary vasospasm among the patients with acute myocardial infarction or out-of-hospital cardiac arrest. Repeated measurements of troponin and coronary angiography identified the cause of acute myocardial infarction as coronary vasospasm in the present case. <Learning objective: Coronary vasospasm may be one of important causes of acute MI and of OHCA, although it is difficult to be diagnosed correctly. We should always take into consideration the possibility of coronary vasospasm as the cause of acute MI or OHCA. Repeated measurements of troponin and coronary angiography were useful for the diagnosis of coronary vasospasm in the present case.>.

Favorable Vasomotor Function after Drug-Coated Balloon-Only Angioplasty of De Novo Native Coronary Artery Lesions

Balloon-injured coronary segments are known to harbor abnormal vasomotion. We evaluated whether de novo coronary lesions treated using drug-coated balloon (DCB) are prone to vasospasm and how they respond to ergonovine and nitrate. Among 132 DCB angioplasty recipients followed, 89 patients underwent ergonovine provocation test at 6–9 months follow-up. Within-subject ergonovine- and nitrate-induced diameter changes were compared among three different sites: DCB-treated vs. angiographically normal vs. segment showing prominent vasoreactivity (spastic). No patient experienced clinically refractory vasospastic angina or symptom-driven revascularization during follow-up. Ergonovine induced vasospasm in seven patients; all were multifocal spasm either involving (n = 2) or rather sparing DCB-treated segments (n = 5). None showed focal spasm that exclusively involved DCB-treated lesions. Among 27 patients with vasospastic features, DCB-treated segments showed less vasoconstriction than spastic counterparts (p < 0.001). A total of 110 DCB-treated lesions were analyzed to assess vasomotor function. Vasomotor function, defined as a combined constrictor and dilator response, was comparable between DCB-treated and angiographically normal segments (p = 0.173), while significant differences were observed against spastic counterparts (p < 0.001). In our study, DCB-treated lesions were not particularly vulnerable to vasospasm and were found to have vasomotor function similar to angiographically normal segments, supporting safety of DCB-only strategy in treating de novo native coronary lesions.

Intracoronary Thrombogenicity in Patients with Vasospastic Angina: An Observation Using Coronary Angioscopy

BACKGROUND

Despite significant interest in intracoronary thrombi in patients with vasospastic angina (VSA), the phenomenon remains unclarified. Therefore, we investigated a possible relationship using coronary angioscopy (CAS) in VSA patients.

METHODS

Sixty patients with VSA, for whom we could assess the spastic segment using CAS, were retrospectively studied. An intracoronary thrombus on CAS was a white thrombus and an erosion-like red thrombus. We verified the clinical characteristics and lesional characteristics as they determined the risk of intracoronary thrombus formation.

RESULTS

There were 18 (30%) patients with intracoronary thrombi. More of the patients with intracoronary thrombi were male, current smokers and had severe concomitant symptoms; however, no statistically significant difference was observed upon logistic regression analysis. There were 18 (26%) coronary arteries with intracoronary thrombi out of 70 coronary arteries recognised in the spastic segments. Furthermore, atherosclerotic changes and segmental spasms were significant factors responsible for such lesions.

CONCLUSION

Intracoronary thrombi occurred in 30% of VSA patients and much attention should be paid to the intracoronary thrombogenicity of VSA patients.

Sudden coronary death in the young: Evidence of contractile phenotype of smooth muscle cells in the culprit atherosclerotic plaque

BACKGROUND

Culprit coronary atherosclerotic plaques (APs) from young sudden cardiac death (SCD) victims are mostly non-atheromatous, i.e., consisting of proliferative smooth muscle cells (SMCs). Coronary vasospasm has been advocated to explain plaque instability in the absence of thrombosis. Our aim was to characterize the SMC phenotype in the intima and media of coronary arteries from young SCD victims.

METHODS AND RESULTS

A total of 38 coronary artery segments were studied: (a) 18 APs from young (≤40 years old) SCD patients, (b) 9 APs from old (>40 years old) SCD patients, (c) 11 non-atherosclerotic coronary arteries from young patients (≤40 years old). Markers of differentiated SMCs such as α-smooth muscle actin (α-SMA), smooth muscle myosin heavy chains (SMMHCs), and heavy-caldesmon (h-CaD), were assessed in intima and media by immunohistochemistry and quantified morphometrically. In the intima, their expression was higher in non-atherosclerotic arteries (44.37 ± 3.03% for α-SMA, 14.21 ± 2.01% for SMMHCs, 8.90 ± 1.33% for h-CaD) and APs from young SCD victims (38.95 ± 2.29% for α-SMA, 11.92 ± 1.92% for SMMHCs, 8.93 ± 1.12% for h-CaD) compared with old patients (22.01 ± 3.56% for α-SMA, 6.39 ± 0.7% for SMMHCs, 3.00 ± 0.57% for h-CaD; all P statistically significant). The media of non-atherosclerotic arteries and APs from young SCD victims exhibited strong positivity for the differentiation markers unlike that of old patients.

CONCLUSIONS

SMCs of coronary APs as well as from the underlying media from young SCD victims exhibit strong contractile phenotype. In the setting of critical stenosis, both intima and media SMC contractility might contribute to transient coronary spasm leading to myocardial ischemia and SCD.

Efficacy of Corticosteroid Treatment for Refractory Multivessel Vasospastic Coronary Angina with Hypereosinophilia

A 43-year-old man was diagnosed with acute myocardial infarction (AMI) due to multivessel coronary vasospasm. Accordingly, two coronary vasodilators were administered, and he was discharged without an angina attack. However, from the following day, he reported frequent chest pain and was re-hospitalized. Despite adding multiple coronary vasodilators, it was difficult to completely suppress the angina attack. He also demonstrated hypereosinophilia from the onset of AMI, and his eosinophil count gradually increased up to 6,238/μL. After corticosteroid administration was started, the vasospasm was completely controlled, and his eosinophil count normalized. He remained free from angina attacks for two years with corticosteroid therapy.

In-hospital mortality analysis of Japanese patients with acute coronary syndrome using the Tokyo CCU Network database: Applicability of the GRACE risk score

BACKGROUND

The GRACE risk score was developed to predict in-hospital mortality for acute coronary syndrome (ACS) using multinational registries, but did not include Japanese data. Therefore, GRACE risk scores are not extensively used in Japan. The present study aimed to evaluate the relationship between the GRACE risk score and in-hospital mortality among Japanese patients with ACS using the Tokyo CCU (cardiovascular care unit) Network Database.

METHODS AND RESULTS

A total of 9460 patients with ACS hospitalized at 67 Tokyo CCUs between January 2011 and December 2013 were retrospectively reviewed and GRACE risk scores were calculated. Patients in the Tokyo CCU Network database had more severe conditions compared to those of the original GRACE study. There was a strong correlation between the GRACE risk score and in-hospital mortality for patients with ST-segment elevation myocardial infarction (STEMI) or non ST-segment elevation myocardial infarction (NSTEMI) (r=0.99, p<0.001); however, the correlation was not significant for patients with unstable angina (r=0.35, p=0.126). For STEMI+NSTEMI patients, the discrimination ability of the GRACE risk score was excellent, with a c statistic of 0.87 (95% confidence interval, 0.86-0.89).

CONCLUSIONS

The GRACE risk score is a good predictor of in-hospital mortality for Japanese patients with STEMI or NSTEMI, and can help clinicians stratify patients by risk for optimal patient triage and early treatment management.

Thrombus and Plaque Erosion Characterized by Optical Coherence Tomography in Patients With Vasospastic Angina

INTRODUCTION AND OBJECTIVES

Vasospastic angina (VSA) can result in endothelial damage and thrombus formation. The aim of this study was to evaluate the incidence of thrombus and plaque characteristics at coronary spasm segments compared with nonspasm segments by using optical coherence tomography (OCT) in patients with suspected VSA.

METHODS

One hundred and eighty-three patients with suspected VSA were enrolled in this study. The ergonovine provocation test was performed in all patients for the diagnosis of VSA except in patients with spontaneous spasm. All target lesions were analyzed by OCT. Plaque erosion was defined as the presence of attached thrombus overlying an intact fibrous cap and visualized plaque on multiple adjacent OCT frames.

RESULTS

One hundred and nine spasm segments (93 patients) were compared with 55 nonspasm segments (39 patients). Thrombus was more frequently seen at spasm segments than at nonspasm segments (28.4% vs 7.3%; P = .026) and thrombus size was larger at spasm segments than at nonspasm segments (0.26 ± 0.50 mm² vs 0.04 ± 0.01 mm²; P = .023). Thin-cap fibroatheroma was more frequently seen at nonspasm segments than at spasm segments (16.4% vs 1.8%; P = .006). Plaque erosion was more prevalent at spasm segments than at nonspasm segments (25.7% vs 5.4%; P = .001).

CONCLUSIONS

Thrombus and plaque erosion were more common at spasm segments than at nonspasm segments assessed by OCT in patients with suspected VSA. These findings suggest the potential benefit and treatment role of antiplatelet therapy in vasospastic angina.

OCT-Defined Morphological Characteristics of Coronary Artery Spasm Sites in Vasospastic Angina

OBJECTIVES

The aim of this study was to define the morphological features of coronary artery spasm sites using optical coherence tomography (OCT) in patients with vasospastic angina (VSA).

BACKGROUND

Plaque characteristics at coronary artery spasm sites have not been investigated systematically.

METHODS

Sixty-nine consecutive patients (80 spasm sites) presenting with VSA who underwent OCT imaging were included in this study. Fibrous cap disruption was identified by the discontinuation of fibrous cap with or without intraplaque cavity formation. OCT-defined erosion was established by the presence of thrombus with or without lumen irregularity overlying an intact fibrous cap on multiple adjacent OCT frames. Other morphological features such as the absence of thrombus with or without lumen irregularity and those not in the previously mentioned criteria were also documented.

RESULTS

Plaque was seen on OCT in 79 of the 80 spasm sites. Fibrous cap disruption was detected at 3 sites (4%). OCT-defined erosion was observed at 21 spasm sites (26%). Thrombus with lumen irregularity was observed in 20 sites, whereas 1 site had thrombus without lumen irregularity. Lumen irregularity without thrombus was observed at 49 spasm sites (61%). Spontaneous spasm was seen more frequently in patients with acute myocardial infarction and out-of-hospital cardiac arrest than in patients without these conditions (50.0% vs. 19.3%, p = 0.025).

CONCLUSIONS

Our results show that OCT-defined erosion at spasm sites occurred in more than one-fourth of patients in this study. Luminal irregularity was observed in nearly two-thirds of the patients without overlying thrombus. These findings suggest the potential role of antiplatelet therapy in VSA.

Human vascular endothelial cells reduce sphingosylphosphorylcholine-induced smooth muscle cell contraction in co-culture system through integrin β4 and Fyn

AIM

In vascular strips, the adjacent endothelial cells modulate the contraction of vascular smooth muscle cells (VSMCs) induced by sphingosylphosphorylcholine (SPC) through nitric oxide (NO). The aim of this study was to elucidate the mechanisms by which vascular endothelial cells (VECs) reduce the SPC-induced contraction of VSMCs in a co-culture system.

METHODS

Human umbilical VECs and VSMCs were co-cultured. The VECs were transfected with integrin β4- or Fyn-specific siRNA. The areas of VSMCs that are involved in cell contractility were quantified using the Leica confocal software and collagen contractility assay. The production of NO in VECs was measured in the cell supernatants using NO Detection Kit. The levels of integrin β4 and Fyn in VECs and the levels of Rho kinase (ROCK) in VSMC were detected using immunofluorescence assays or Western blots.

RESULTS

Co-culture with VECs reduced the contraction of VSMCs induced by SPC (30 μmol/L). The down-regulation of integrin β4 or Fyn in VECs by the specific siRNA (20 nmol/L) was able to counteract the effects of VECs on the SPC-induced VSMC contractions. Furthermore, the integrin β4-specific siRNA (20 and 40 nmol/L) significantly reduced the level of Fyn protein and the production of NO in VECs, while increased the level of ROCK in VSMCs that had been stimulated by SPC.

CONCLUSION

The VECs reduced the SPC-induced contraction of VSMCs in the co-culture system through integrin β4 and Fyn proteins. In this process, NO may be the factor downstream of integrin β4 in VECs, while ROCK may be the key protein regulating the contraction of VSMCs.

From embolization to remodeling: the need for early carotid endarterectomy in symptomatic carotid plaques

Atheromatous plaques are dynamic structures undergoing continuous remodeling. Duplex ultrasound is now an accepted technique to classify the severity of arterial stenoses. It gives information about the ultrasonic echogenicity of tissue, the plaque surface and the velocity of blood flowing through vessels with the latest equipment. We report the case of a 59-year-old male patient with left hemispheric stroke and a 50% left carotid artery stenosis whose remodeling and reabsorption developed throughout three months from the onset of symptoms. Plaque surface and structural echomorphology assessment and standardization, along with the degree of carotid stenosis, might be helpful in identifying patients most likely to benefit from carotid endarterectomy.

Role of acute infection in triggering acute coronary syndromes

Acute coronary syndromes are a leading cause of morbidity and mortality worldwide. The mechanisms underlying the triggering of these events are diverse and include increased coronary and systemic inflammatory activity, dominant prothrombotic conditions, increased biomechanical stress on coronary arteries, variations in the coronary arterial tone, disturbed haemodynamic homoeostasis, and altered myocardial metabolic balance. There is experimental evidence that acute infections can promote the development of acute coronary syndromes, and clinical data strongly support a role for acute infections in triggering these events. In our Review, we summarise the pathogenesis of coronary artery disease and present the evidence linking acute infections with the development of acute coronary syndromes. Greater awareness of this association is likely to encourage research into ways of protecting patients who are at high risk.

Developing a novel rabbit model of atherosclerotic plaque rupture and thrombosis by cold-induced endothelial injury

Background

It is widely believed that atherosclerotic plaque rupture and subsequent thrombosis leads to acute coronary events and stroke. However, study of the mechanism and treatment of human plaque rupture is hampered by lack of a suitable animal model. Our aim was to develop a novel animal model of atherosclerotic plaque rupture to facilitate the study of human plaque disruption and thrombosis.

Methods

28 healthy male New Zealand white rabbits were randomly divided into two groups: rabbits in group A (n = 12) were only fed a high-fat diet for eight weeks; rabbits in group B (n = 16) underwent cold-induced endothelial injury with liquid nitrogen, then were given a high-fat diet for eight weeks. After completion of the preparatory regimen, triggering of plaque rupture was attempted by local injection of liquid nitrogen in both groups.

Results

All rabbits in group B had disrupted plaques or rupture-driven occlusive thrombus formation, but none in group A showed any effects. More importantly, the cold-induced plaques in our model were reminiscent of human atherosclerotic plaques in terms of architecture, cellular composition, growth characteristics, and patterns of lipid accumulation.

Conclusion

We successfully developed a novel rabbit model of atherosclerotic plaque rupture and thrombosis, which is simple, fast, inexpensive, and reproducible, and has a low mortality and a high yield of triggering. This model will allow us to better understand the mechanism of human plaque rupture and also to develop plaque-stabilizing therapies.

Hemodynamic factors and atheromatic plaque rupture in the coronary arteries: from vulnerable plaque to vulnerable coronary segment

Coronary plaque disruption with superimposed thrombosis is the underlying pathology in the acute coronary syndromes and sudden death. Coronary plaques are constantly stressed by a variety of mechanical and hemodynamic forces that may precipitate or 'trigger' disruption of vulnerable or, at extreme conditions, even stable plaques. This paper reviews the exciting new evidence on the hemodynamic factors that may play a role in this process and provides the rationale for the introduction of the concept of the vulnerable coronary segment in the study of acute coronary syndromes.

"Vulnerable plaques" — ticking of the time bomb

Atherosclerosis and its sequelae are one of the leading causes of morbidity and mortality, especially in the developed nations. Over the years, treatment protocols have changed with the changing understanding of the disease process. Inflammatory mechanisms have emerged as key players in the formation of the atherosclerotic plaque. For the majority of its life span, the plaque develops silently and only some exhibit overt clinical manifestations. The purpose of this review is to examine the inherent properties of some of these "vulnerable" or symptomatic plaques. Rupture of the plaque is related to the thickness of the fibrous cap overlying the necrotic lipid core. A thin cap is more likely to lead to rupture. Multiple factors broadly grouped as the "determinants of vulnerability" are responsible for directly or indirectly influencing the plaque dynamics. Apoptosis is considered an important underlying mechanism that contributes to plaque instability. Inflammatory reactions within the plaque trigger apoptosis by cell–cell contact and intra cellular death signaling. Once started, the apoptotic process affects all of the components that make up the plaque, including vascular smooth muscle cells, endothelial cells, and macrophages. Extensive research has identified many of the key cellular and molecular regulators that play a part in apoptosis within the atherosclerotic lesion. This information will help us to gain a better understanding of the underlying mechanisms at the cellular and molecular level and enable us to formulate better therapeutic strategies to combat this disease.Key words: apoptosis, atherosclerosis, inflammation, plaque stability, vulnerable plaques.

Plaque instability in peripheral vessels

Vulnerable atherosclerotic plaques, those that are prone to rupture, are soft and lipid rich. Other factors that contribute to destabilizing these plaques are inflammation and vasoconstriction. Although less information is available regarding noncoronary vulnerable plaques than the more frequently studied coronary plaques, it appears that the amount of soft lipid "gruel" as well as in situ inflammation plays a crucial role in destabilizing peripheral vascular atherosclerotic plaque, eventually causing its rupture. As in the coronary circulation, it is likely that the majority of acute plaque rupture events are clinically silent. Nevertheless, preventing plaque rupture in the noncoronary circulation is of the utmost importance because this is the presumed mechanism of progression of peripheral vascular atherosclerotic lesions.

Impaired modulation of circadian rhythms in patients with diabetes mellitus: a risk factor for cardiac thrombotic events?

Serious adverse cardiovascular events, including myocardial infarction, sudden cardiac death, and stroke, frequently result from rupture of atherosclerotic plaques with superimposed thrombosis and exhibit a pronounced circadian rhythmicity, peaking in the morning hours. Two potentially synergistic mechanisms play a pathogenic role in the circadian variation of arterial thrombotic events. A morning surge in sympathetic activity alters hemodynamic forces and predisposes vulnerable coronary atherosclerotic plaques to rupture. Day-night variations of hemostatic and fibrinolytic factors result in morning hypercoagulability and hypofibrinolysis, promoting intraluminal thrombus formation at the same time when the risk for plaque rupture is highest. Diabetic patients have a very high cardiac event rate but fail to show normal circadian fluctuations in the occurrence of myocardial infarction. Alterations in the circadian variation autonomic tone, blood pressure, and the thrombotic-thrombolytic equilibrium have been documented in diabetic patients. These include reduced or absent 24-h periodicity in autonomic tone, fibrinolytic activity, and thrombotic tendency, and a blunted decline in nocturnal blood pressure. Disruption of these circadian rhythms explains the lack of significant circadian distribution of cardiac events in diabetic patients. Moreover, the loss of these normal biorhythms results in a continuous susceptibility to thrombotic events throughout the day and may contribute to the excess cardiovascular mortality and morbidity in these patients.

Advances in the pharmacology of acute coronary syndrome. Platelet inhibition

The development of potent inhibitors of platelet aggregation has led to significant decreases in morbidity and mortality rates among patients undergoing percutaneous coronary intervention. Clinical trials have demonstrated that agents that block glycoprotein IIb/IIIa receptor-mediated platelet aggregation have an outcome benefit when used acutely in patients with chest pain and ST depression or elevated cardiac enzymes, leading to the integration of these agents into emergency medicine clinical practice. This article provides an overview of the pathophysiology of acute coronary syndrome and the pharmacology of platelet inhibition and reviews the evidence from the clinical trials pertaining to the use of these agents in the emergency department.

The symptomatic carotid plaque

BACKGROUND

The natural histories of equally severe symptomatic and asymptomatic carotid stenoses are very different, which suggests dichotomy in plaque behavior. The vascular biology of the symptomatic carotid plaque is presented in this review.

SUMMARY OF REVIEW

Histology studies comparing asymptomatic and symptomatic plaques were identified from MEDLINE. Reports in which stenosis severity was not stated or not similar for symptomatic and asymptomatic patients were excluded. In vitro studies and reports from the coronary circulation were reviewed with regard to the vascular biology of the plaque. Histology studies comparing carotid plaques removed from symptomatic and asymptomatic patients reveal characteristic features of unstable plaques: surface ulceration and plaque rupture (48% of symptomatic compared with 31% of asymptomatic, P<0.001), thinning of the fibrous cap, and infiltration of the cap by greater numbers of macrophages and T cells. In vitro studies suggest that macrophages and T cells release cytokines and proteinase, which stimulate breakdown of cap collagen and smooth muscle cell apoptosis and thereby promote plaque rupture.

CONCLUSIONS

Infiltration of inflammatory cells to the surface of carotid plaques may be a critical step in promoting plaque rupture and resultant embolization or carotid occlusion. Further understanding of cell recruitment and behavior in carotid atherosclerosis may allow better detection of unstable plaques and therapeutic methods of plaque stabilization.

Histological evaluation of coronary plaque in patients with variant angina: relationship between vasospasm and neointimal hyperplasia in primary coronary lesions

OBJECTIVES

This study was designed to determine whether coronary vasospasm in patients with variant angina pectoris (VAP) may produce focal organic lesions at the site of vasospasm that would contribute to disease progression.

BACKGROUND

Recent clinical angiographic and experimental studies have demonstrated the potential role of vasospasm in the worsening of organic coronary stenosis.

METHODS

We studied histologically the coronary plaques obtained at atherectomy in 202 patients with moderate to severe coronary stenosis. This population included 22 patients with VAP, 100 patients with chronic stable angina and 80 patients with restenosis following angioplasty or atherectomy. Diagnosis of VAP was based on both the clinical feature of angina at rest associated with ST elevation and a positive response to acetylcholine provocation test.

RESULTS

The most common histological appearance in 92% of patients with stable angina was hypocellular fibroatheromatous plaques, whereas neointimal hyperplasia was the characteristic feature of the plaque observed in 90% of patients with restenosis. The coronary specimens at the site of spasm in 15 of the 22 patients (68%) with VAP demonstrated intimal injuries such as neointimal hyperplasia (15), thrombus formation (2), and intimal hemorrhage (3). Neointimal hyperplasia was significantly more common in the patients with VAP as compared with those with stable angina (68% vs. 8%; p < 0.0001). A rapid progression of organic stenosis within three years was angiographically found in 5 of the 22 patients with variant angina. In all five cases, neointimal hyperplasia was the main contributor to the worsening of the organic lesion at the site of spasm. These histological findings in patients with VAP extremely resembled those in restenosis. Except for vasospasm, no factors significantly predicted the presence of neointimal formations in primary coronary lesions.

CONCLUSIONS

Coronary vasospasm may provoke vascular injury that leads to the formation of neointima in VAP patients similar to that seen with restenosis. Coronary spasm may thus play a key role in the rapid coronary stenosis progression in certain patients with VAP.

Morphodynamics and pathology of blood vessels III--comparative morphologic study of contraction of smooth muscle cells of hollow viscera and its application to vasoconstriction and vasospasm

The morphologic changes in the walls of hollow viscera caused by contraction and relaxation of smooth muscle cells were studied from autopsy and surgical specimens. The specimens studied included: esophageal spasm (corkscrew and nutcracker esophagus), contraction of the lower esophageal sphincter with marked esophageal dilatation, gaseous distension of the stomach, contraction of the gastric pylorus, bladder and anal sphincter, physiological segmental constriction of the small and large intestines, constriction and distension of the gallbladder, urinary bladder and bronchi, and postpartum contraction of the uterus. In contrast to distension, the constriction of hollow viscera shows marked reduction of the external circumference and diameter with thickening of the wall, contraction of smooth muscle cells, thickening of muscle bundles, remodeling of wall structure, and narrowing or obliteration of the lumen. Morphologic evidence of contraction of smooth muscle cells is demonstrated by varying degrees of typical lengthwise shortening of the cells and squeezing and folding of the nuclei depending on the degree of cytoplasmic contraction of the smooth muscle cells. Using these same classic morphologic signs, we have attempted to study constriction and distension of arteries and arterioles. We can demonstrate contraction of smooth muscle cells and remodeling of arterial and arteriolar walls in patients with spastic coronary artery thrombosis, cocaine-induced coronary artery thrombosis, acute constriction of mesenteric arteries with lacerations of arterial wall, and dissecting hemorrhages induced by large doses of intravenous infusion of vasoconstrictors for hemorrhagic shock, and in patients with sustained, accelerated, or malignant hypertension.

Unmet therapeutic needs in the management of acute ischemia

Unstable angina and myocardial infarction (MI) continue to present a major challenge in clinical management. These acute ischemic coronary syndromes (AICS) are a spectrum of clinical presentations of the same pathophysiologic mechanism: thrombus formation superimposed on atherosclerotic plaque disruption or erosion. Current approaches to the management of AICS, which include both interventional and pharmacologic therapy, have been introduced to clinical practice during the past 20 years, and most of them have demonstrated efficacy in clinical studies. A common inadequacy of current therapies, however, is the lack of significant inhibition of platelet aggregation--the crucial event in the formation of coronary thrombi and the pathogenesis of AICS. The final common pathway to platelet aggregation is the activation of the platelet glycoprotein (GP) IIb-IIIa receptor, which allows the cross-linking of adjacent platelets by the adhesive plasma proteins fibrinogen and von Willebrand's factor. The emergence of the GP IIb-IIIa receptor as a potential treatment target has led to the development of several inhibitors of its function. The inhibitors most advanced in clinical development are the chimeric monoclonal antibody abciximab (ReoPro) and the cyclic peptide eptifibatide (INTEGRILIN). In phase III clinical trials, both abciximab and eptifibatide have been shown to reduce the incidence of cardiac events in patients at risk for abrupt vessel closure after coronary angioplasty. Inhibition of the GP IIb-IIIa receptor is the most promising novel approach to the treatment of unstable angina and MI, and it may soon be an indispensable component of the management of patients with AICS.

New insights into the pathogenesis and prevention of acute coronary syndromes

Several recent studies have shown that 60-70% of coronary occlusions that cause acute coronary syndromes (such as unstable angina, myocardial infarction, or sudden ischemic death) evolve from atherosclerotic plaques that are only mildly to moderately obstructive. Numerous studies have demonstrated that coronary thrombosis, the immediate cause of acute coronary syndromes, is a consequence of plaque disruption. Most thrombotic events are related to deep plaque fissure, while superficial plaque erosion is the cause in a significant minority of cases. Thus, the mechanisms by which stable coronary artery disease (CAD) evolves into an unstable and potentially lethal acute coronary syndrome are related to plaque disruption and thrombosis. The vulnerability of a plaque to disruption appears to be determined by the presence of a large lipid-rich core, a thin fibrous cap, and an inflammatory cellular infiltrate, rather than by the size of the plaque or the severity of stenosis caused by a plaque before disruption. In addition to plaque disruption and thrombosis, enhanced vasoconstriction--a characteristic feature of CAD and dyslipidemia-may contribute to the clinical manifestations of CAD. Angiographic studies have demonstrated that risk factor modification produces a disproportionately greater reduction in ischemic clinical events than in anatomic regression of plaque, suggesting "plaque stabilization" may be the major mechanism of such clinical benefit. The relatively rapid attenuation of endothelial-mediated vasomotor dysfunction with the treatment of dyslipidemia lends credence to this concept.

The biologic behavior of balloon hyperinflation-induced arterial lesions in hypercholesterolemic pigs depends on the presence of foam cells

Lack of a large-animal model of accelerated atherosclerosis has limited study of the biologic behavior of atherosclerotic lesions. We hypothesized that mechanical vascular trauma combined with diet-induced hypercholesterolemia would result in rapid development of complex atherosclerosis-like lesions. Accordingly, we induced deep injury to a carotid artery by repetitive balloon hyperinflations in minipigs that were fed either an atherogenic diet (n = 30) or a standard diet (controls, n = 4) and examined the resultant lesions 1 month later. The neointimal lesions that evolved in 23 patent vessels from cholesterol-fed animals were complex, exhibiting infiltration of smooth muscle and foam cells and evidence of organized thrombus, recent thrombus, hemorrhage, and calcification. Lesions were separable histologically into two groups: foam-cell rich (n = 12), with 33 +/- 10 foam cells per high-power field, and foam-cell poor (n = 11), with 4 +/- 1 foam cells per high-power field. Minipigs with foam cell-rich lesions had higher serum cholesterol levels than those with foam cell-poor lesions (712 +/- 178 vs 468 +/- 240 mg/dL, P < .02). The incidence of intralesional thrombus was also significantly greater in foam cell-rich than in foam cell-poor lesions (50% vs 9%, P < .04). In addition, the degree of luminal stenosis was greater in the presence of lesions containing thrombus compared with those without thrombus (60 +/- 38% vs 30 +/- 29%, P = .05). Lesions in the control animals were fibrocellular and lacked foam cells and thrombus. Thus, hypercholesterolemia appeared to affect lesion composition and behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary artery spasm. Multiple causes and multiple roles in heart disease

Myocardial infarction and sudden cardiac death may be initiated by a sudden intense localized contraction of coronary artery smooth muscle. When this event occurs around a vulnerable eccentric lipid-filled plaque, rupture and extrusion of plaque contents and exposure of collagen occur. This may sometimes be a silent and self-limiting event; other times it leads to thrombus formation. A second wave of spasm due to accumulated platelet and inflammatory mediators may compound the contractile consequences of the initiating event. Spasm involves intrinsic smooth muscle cell electrical mechanisms, hyper-responsive cells, and multiple agonists that synergize their actions, and the involvement of each mechanism varies at different times in the sequence of vascular occlusion. Study of spasm requires vascular systems that adequately model coronary artery responses of the ageing human heart. As previously emphasized, tissues obtained postmortem, and when possible from recipients during heart transplants, must be integral to theory building, alongside animal models, despite the experimental limitations such tissues impose. A multidisciplinary approach, at all levels of vascular physiology and pharmacology, will be necessary to understand coronary motor activity and human heart disease.

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.

Role of coronary artery spasm in progression of organic coronary stenosis and acute myocardial infarction in a swine model. Importance of mode of onset and duration of coronary artery spasm

BACKGROUND

Coronary spasm may play an important role in progression of organic coronary stenosis and myocardial infarction, but the mechanisms responsible for these complications are not known. This study aimed to examine whether the mode of onset and the duration of coronary spasm influenced progression of organic coronary stenosis and acute myocardial infarction in a swine model of coronary spasm.

METHODS AND RESULTS

Göttingen miniature pigs were subjected to cholesterol feeding, balloon-induced coronary arterial denudation, and x-ray irradiation. Five months later, coronary spasm was induced by intracoronary injection of serotonin. In 10 pigs, coronary spasm was provoked abruptly and maintained for 25 minutes by five repeated intracoronary injections of serotonin (10 micrograms/kg) every 5 minutes (group A, abrupt onset and short duration). In group B, coronary spasm was provoked gradually by intracoronary injections of serotonin at graded doses of 0.1, 0.3, and 0.6 microgram/kg every 5 minutes and was then maintained for 25 minutes in four pigs (group B1, gradual onset and short duration) and for 120 minutes in six pigs (group B2, gradual onset and long duration) by repeated intracoronary injections of serotonin (10 micrograms/kg) every 5 minutes. Intramural hemorrhage was noted histologically at the spastic site more frequently in group A with abrupt onset (nine of 10 pigs) than in group B with gradual onset (two of 10 pigs) (p < 0.01). Progression of organic coronary stenosis due to intramural hemorrhage was noted in seven pigs (six pigs in group A and one pig in group B), including three cases of total coronary occlusion. Evidence for the evolution of acute myocardial infarction (serial ECG findings, left ventriculograms, and histological findings) was noted in one pig (7%) of group A or B1 with short duration and in five of six pigs (83%) in group B2 with long duration (p < 0.01 versus group A and B1).

CONCLUSIONS

These results indicate that: 1) intramural hemorrhage was frequently induced by coronary spasm of abrupt but not of gradual onset, 2) intramural hemorrhage resulted in acute progression of coronary stenosis and sometimes resulted in persistent total coronary occlusion leading to acute myocardial infarction, and 3) prolonged coronary spasm resulted in acute myocardial infarction without progression of organic coronary stenosis.