Acute plaque rupture and myocardial stunning in patient with normal coronary arteriography

Acute coronary syndromes without coronary plaque rupture

The latest advances in plaque imaging have provided clinicians with opportunities to treat acute coronary syndrome (ACS) and provide individualized treatment recommendations based not only on clinical manifestations, angiographic characteristics, and biomarker data, but also on the findings of plaque morphology. Although a substantial proportion of ACS events originate from plaques with an intact fibrous cap (IFC), clinicians predominantly equate ACS with plaque rupture arising from thin-cap fibroatheromas. In this Review, we discuss the recent advances in our understanding of plaque morphology in ACS with IFC, reviewing contemporary data from intravascular imaging. We also explore whether use of such imaging might provide a roadmap for more effective management of patients with ACS.

Coronary Microembolization with Normal Epicardial Coronary Arteries and No Visible Infarcts on Nitrobluetetrazolium Chloride-Stained Specimens: Evaluation with Cardiac Magnetic Resonance Imaging in a Swine Model

Objective

To assess magnetic resonance imaging (MRI) features of coronary microembolization in a swine model induced by small-sized microemboli, which may cause microinfarcts invisible to the naked eye.

Materials and Methods

Eleven pigs underwent intracoronary injection of small-sized microspheres (42 µm) and catheter coronary angiography was obtained before and after microembolization. Cardiac MRI and measurement of cardiac troponin T (cTnT) were performed at baseline, 6 hours, and 1 week after microembolization. Postmortem evaluation was performed after completion of the imaging studies.

Results

Coronary angiography pre- and post-microembolization revealed normal epicardial coronary arteries. Systolic wall thickening of the microembolized regions decreased significantly from 42.6 ± 2.0% at baseline to 20.3 ± 2.3% at 6 hours and 31.5 ± 2.1% at 1 week after coronary microembolization (p < 0.001 for both). First-pass perfusion defect was visualized at 6 hours but the extent was largely decreased at 1 week. Delayed contrast enhancement MRI (DE-MRI) demonstrated hyperenhancement within the target area at 6 hours but not at 1 week. The microinfarcts on gross specimen stained with nitrobluetetrazolium chloride were invisible to the naked eye and only detectable microscopically. Increased cTnT was observed at 6 hours and 1 week after microembolization.

Conclusion

Coronary microembolization induced by a certain load of small-sized microemboli may result in microinfarcts invisible to the naked eye with normal epicardial coronary arteries. MRI features of myocardial impairment secondary to such microembolization include the decline in left ventricular function and myocardial perfusion at cine and first-pass perfusion imaging, and transient hyperenhancement at DE-MRI.

Magnetic resonance imaging and multi-detector computed tomography assessment of extracellular compartment in ischemic and non-ischemic myocardial pathologies

Myocardial pathologies are major causes of morbidity and mortality worldwide. Early detection of loss of cellular integrity and expansion in extracellular volume (ECV) in myocardium is critical to initiate effective treatment. The three compartments in healthy myocardium are: intravascular (approximately 10% of tissue volume), interstitium (approximately 15%) and intracellular (approximately 75%). Myocardial cells, fibroblasts and vascular endothelial/smooth muscle cells represent intracellular compartment and the main proteins in the interstitium are types I/III collagens. Microscopic studies have shown that expansion of ECV is an important feature of diffuse physiologic fibrosis (e.g., aging and obesity) and pathologic fibrosis [heart failure, aortic valve disease, hypertrophic cardiomyopathy, myocarditis, dilated cardiomyopathy, amyloidosis, congenital heart disease, aortic stenosis, restrictive cardiomyopathy (hypereosinophilic and idiopathic types), arrythmogenic right ventricular dysplasia and hypertension]. This review addresses recent advances in measuring of ECV in ischemic and non-ischemic myocardial pathologies. Magnetic resonance imaging (MRI) has the ability to characterize tissue proton relaxation times (T1, T2, and T2*). Proton relaxation times reflect the physical and chemical environments of water protons in myocardium. Delayed contrast enhanced-MRI (DE-MRI) and multi-detector computed tomography (DE-MDCT) demonstrated hyper-enhanced infarct, hypo-enhanced microvascular obstruction zone and moderately enhanced peri-infarct zone, but are limited for visualizing diffuse fibrosis and patchy microinfarct despite the increase in ECV. ECV can be measured on equilibrium contrast enhanced MRI/MDCT and MRI longitudinal relaxation time mapping. Equilibrium contrast enhanced MRI/MDCT and MRI T1 mapping is currently used, but at a lower scale, as an alternative to invasive sub-endomyocardial biopsies to eliminate the need for anesthesia, coronary catheterization and possibility of tissue sampling error. Similar to delayed contrast enhancement, equilibrium contrast enhanced MRI/MDCT and T1 mapping is completely noninvasive and may play a specialized role in diagnosis of subclinical and other myocardial pathologies. DE-MRI and when T1-mapping demonstrated sub-epicardium, sub-endocardial and patchy mid-myocardial enhancement in myocarditis, Behcet’s disease and sarcoidosis, respectively. Furthermore, recent studies showed that the combined technique of cine, T2-weighted and DE-MRI technique has high diagnostic accuracy for detecting myocarditis. When the tomographic techniques are coupled with myocardial perfusion and left ventricular function they can provide valuable information on the progression of myocardial pathologies and effectiveness of new therapies.

TNF-α-induced cardiomyocyte apoptosis contributes to cardiac dysfunction after coronary microembolization in mini-pigs

This experimental study was designed to clarify the relationship between cardiomyocyte apoptosis and tumour necrosis factor-alpha (TNF-α) expression, and confirm the effect of TNF-α on cardiac dysfunction after coronary microembolization (CME) in mini-pigs. Nineteen mini-pigs were divided into three groups: sham-operation group (n = 5), CME group (n = 7) and adalimumab pre-treatment group (n = 7; TNF-α antibody, 2 mg/kg intracoronary injection before CME). Magnetic resonance imaging (3.0-T) was performed at baseline, 6th hour and 1 week after procedure. Cardiomyocyte apoptosis was detected by cardiac-TUNEL staining, and caspase-3 and caspase-8 were detected by RT-PCR and immunohistochemistry. Furthermore, serum TNF-α, IL-6 and troponin T were analysed, while myocardial expressions of TNF-α and IL-6 were detected. Both TNF-α expression (serum level and myocardial expression) and average number of apoptotic cardiomyocyte nuclei were significantly increased in CME group compared with the sham-operation group. Six hours after CME, left ventricular end-systolic volume (LVESV) was increased and the left ventricular ejection fraction (LVEF) was decreased in CME group. Pre-treatment with adalimumab not only significantly improved LVEF after CME (6th hour: 54.9 ± 2.3% versus 50.4 ± 3.9%, P = 0.036; 1 week: 56.7 ± 4.2% versus 52.7 ± 2.9%, P = 0.041), but also suppressed cardiomyocyte apoptosis and the expression of caspase-3 and caspase-8. Meanwhile, the average number of apoptotic cardiomyocytes nuclei was inversely correlated with LVEF (r = −0.535, P = 0.022). TNF-α-induced cardiomyocyte apoptosis is likely involved in cardiac dysfunction after CME. TNF-α antibody therapy suppresses cardiomyocyte apoptosis and improves early cardiac function after CME.

Persistent decline in longitudinal and radial strain after coronary microembolization detected on velocity encoded phase contrast magnetic resonance imaging

PURPOSE

To use velocity-encoded phase contrast (PC) MRI in assessing the effect of coronary microembolization on longitudinal and radial myocardial strain.

MATERIALS AND METHODS

A combined X-ray and MR system (XMR) was used for selective left anterior descending artery catheterization and microinfarct assessment in swine (n = 6). The embolized area at risk was defined on perfusion MRI followed by administration of a 7500 count (size = 100-300 microm) of the embolic agent. Quantification of strain and microinfarction was performed at 1 h and 1 week using PC-MRI and delayed enhancement (DE) MRI, respectively. At postmortem, sliced hearts were stained to define microinfarction.

RESULTS

Baseline longitudinal and radial strain did not differ between area-at-risk and remote myocardium. The embolized territory (area at risk) showed significant decline in longitudinal strain from -11.5 +/- 3.2% to 1.8 +/- 2.5% at 1 h (P < 0.05) and -3.9 +/- 1.1% at 1 week (P < 0.05). Similarly, regional radial strain progressively declined from 23.6 +/- 2.5% at baseline to 12.5 +/- 3.7% at 1 h (P < 0.05) and 4.8 +/- 5.0% at 1 week (P < 0.01). The size of microinfarction was not significantly different between DE-MRI and histochemical staining.

CONCLUSION

PC-MRI is sensitive in assessing changes in regional longitudinal and radial strain after coronary embolization. Longitudinal and radial strain of the hyperenhanced patchy microinfarction demonstrates persistent decline over the course of 1 week.

Myocardial microinfarction after coronary microembolization in swine: MR imaging characterization

PURPOSE

To use first-pass perfusion and delayed-enhanced (DE) magnetic resonance (MR) imaging for the detection of the early effects of coronary microembolization on myocardial perfusion and viability.

MATERIALS AND METHODS

Approval was obtained from the institutional committee on animal research. A hybrid x-ray and MR imaging system was used to guide the endovascular catheter and quantify the left anterior descending coronary artery (LAD) perfusion territory before microembolization and ischemic myocardium and microinfarction after microembolization. The embolic agent was selectively delivered in the LAD in six pigs. First-pass perfusion MR imaging was performed 1 hour and 1 week after microembolization. Microinfarction was measured on DE MR images in beating and nonbeating hearts (high-spatial-resolution sequence) by using extracellular and blood pool MR contrast media and after death. The Wilcoxon signed rank test and correlation analysis were used.

RESULTS

The LAD perfusion territory was 35% of left ventricular (LV) mass +/- 2 (standard error of the mean). Microembolization caused perfusion deficit in 15.7% of LV mass +/- 2.6 compared with that of LAD territory (P = .03). At 1 week, perfusion parameters improved and the extent of hypoperfused territory declined (4.6% of LV mass +/- 1.4, P = .03). Microinfarction size expanded from 1.4% of LV mass +/- 0.2 at 1 hour to 7.5% of LV mass +/- 1.2 at 1 week. In nonbeating hearts and at triphenyltetrazolium chloride staining at 1 week, microinfarction size was 7.6% of LV mass +/- 1.4 and 7.2% of LV mass +/- 1.5, respectively. There was no correlation between the ejection fraction and the extents of microinfarction or hypoperfused territory. Histopathologic findings confirmed the presence of patchy microinfarction.

CONCLUSION

Coronary microembolization caused persistent decline in myocardial perfusion at first-pass perfusion imaging. DE MR imaging has the potential to help reliably quantify subacute microinfarction. The magnitude of LV dysfunction is not related to the extents of microinfarction or hypoperfused territory.

Coronary microembolization

Atherosclerotic plaque rupture is the key event in the pathogenesis of acute coronary syndromes and it also occurs during coronary interventions. Atherosclerotic plaque rupture does not always result in complete thrombotic occlusion of the epicardial coronary artery with subsequent impending myocardial infarction, but may in milder forms result in the embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. This review summarizes the present experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and highlights the main consequences of coronary microembolization--reduced coronary reserve, microinfarction, inflammation and oxidative modification of contractile proteins, contractile dysfunction and perfusion-contraction mismatch.Furthermore, the review presents the available clinical evidence for coronary microembolization in patients and compares the clinical observations with observations in the experimental model.

Prevalence of normal coronary angiography in the acute phase of suspected ST-elevation myocardial infarction: experience from the PRAGUE studies

BACKGROUND

Acute ST-elevation myocardial infarction in patients with normal coronary arteries has previously been described, but coronary angiography in these patients was performed after the acute phase of the infarction. It is possible that these patients did not have normal angiograms during the acute phase (transient coronary thrombosis or spasm were usually suspected to be the cause). Information on the prevalence of truly normal coronary angiograms during the acute phase of a suspected ST-elevation myocardial infarction is lacking.

PATIENTS AND METHODS

The Primary Angioplasty in patients transferred from General community hospitals to specialized PTCA Units with or without Emergency thrombolysis-1 (PRAGUE-1) and PRAGUE-2 studies enrolled 1150 patients with ST-elevation acute myocardial infarction, in whom 625 coronary angiograms were performed within 2 h of the initial electrocardiogram. A simultaneous registry included an additional 379 coronary angiograms performed during the ST-elevation phase of a suspected myocardial infarction. Thus, a total of 1004 angiograms were retrospectively analyzed. A normal coronary angiogram was defined as one with the absence of any visible angiographic signs of atherosclerosis, thrombosis or spontaneous spasm.

RESULTS

Normal coronary angiograms were obtained for 26 patients (2.6%). Among these, the diagnosis at discharge was a small myocardial infarction in seven patients (0.7%), acute (peri)myocarditis in five patients, dilated cardiomyopathy in four patients, hypertension with left ventricular hypertrophy in three patients, pulmonary embolism in two patients and misinterpretation of the electrocardiogram (ie, no cardiac disease) in five patients. Seven patients with small infarctions underwent angiography within 30 min to 90 min of complete relief of the signs of acute ischemia, and thus, angiograms during pain were not taken. None of the 898 patients catheterized during ongoing symptoms of ischemia had a normal coronary angiogram. Spontaneous coronary spasm as the only cause (without underlying coronary atherosclerosis) for the evolving infarction was not seen among these 898 patients. Thus, the causes of the seven small infarcts in patients with normal angiograms remain uncertain.

CONCLUSIONS

The observed prevalence of normal coronary angiography in patients presenting with acute chest pain and ST elevations was 2.6%. Most of these cases were misdiagnoses, not infarctions. A normal angiogram during a biochemically confirmed infarction is extremely rare (0.7%) and was not seen during the ongoing symptoms of ischemia.

Intravascular ultrasound evaluation of ruptured plaque in the left main coronary artery misinterpreted as an aneurysm by angiography

We report a patient who demonstrated a left main coronary aneurysm by angiography. Intravascular ultrasound (IVUS) revealed that it was in fact an ulceration, which indicated ruptured plaque. This case provides evidence that IVUS can permit a more powerful definition of ruptured plaque than angiography. On IVUS, ulceration exhibits significantly different characteristics from aneurysm.

Coronary microembolization

Atherosclerotic plaque rupture is a key event in the pathogenesis of acute coronary syndromes and during coronary interventions. However, it does not always result in complete thrombotic occlusion of the entire epicardial coronary artery with subsequent acute myocardial infarction; in milder forms the result can be embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. This review summarizes the available morphological evidence for coronary microembolization in patients who died from coronary artery disease, most notably from sudden death, and then goes on to address the experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and heart failure. Finally, the review presents the available clinical evidence for coronary microembolization in patients, highlights its key features (ie, arrhythmias, contractile dysfunction, infarctlets and reduced coronary reserve) and addresses its prevention by mechanical protection devices and glycoprotein IIb/IIIa antagonism.

Assessment of ambiguous coronary lesions by intravascular ultrasound

Until recently, coronary angiography has been regarded as the 'gold standard' for visualizing and quantifying coronary artery disease. Coronary angiography, however, is a luminographic technique revealing only the inner lumen of the coronary artery. In contrast, intravascular ultrasound investigations yield a detailed morphological description of the vessel wall and plaque characteristics. Based on these analyses, new insights into the pathogenesis of atherosclerotic coronary disease have evolved, including the remodeling phenomena. Thus, nowadays intravascular ultrasound can be regarded as the new 'gold standard' for the morphological assessment of lesion severity during cardiac catheterizations. Likewise, intracoronary Doppler and intracoronary pressure measurements have demonstrated their superiority in the functional assessment of coronary stenoses. Intravascular ultrasound investigations can be performed with high success and low complication rates. The present manuscript concentrates on the value of IVUS for the assessment of ambiguous lesions. Several forms of ambiguous lesions based on the angiographic appearance, i.e. intermediate lesion with undetermined stenosis severity, aneurysmatic widening of the coronary segment, ostial lesions, branching vessels, vessel tortuosity, main stem lesions, focal spasm, sites of plaque rupture, dissections, unclear haziness and contrast density changes are discussed and illustrated by respective angiographic and IVUS examples. Both the advantages and the limitations of angiographic and intravascular ultrasound examination are discussed in detail. In conclusion, additional intravascular ultrasound examination helps to diagnose accurately the underlying atherosclerotic disease, to define lesion characteristics and to optimize individual patient care and cost with respect to diagnostic catheterizations and coronary interventions.

Coronary microembolization

Atherosclerotic plaque rupture is a key event in the pathogenesis of acute coronary syndromes and during coronary interventions. Atherosclerotic plaque rupture does not always result in complete thrombotic occlusion of the entire epicardial coronary artery with subsequent acute myocardial infarction; however, in milder forms it may result in the embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. The present report summarizes the available morphologic evidence for coronary microembolization in patients who died of coronary artery disease, especially sudden death. The report then goes on to address the experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and heart failure. Finally, the report presents the available clinical evidence for coronary microembolization, highlights its key features--arrhythmias, contractile dysfunction, infarctlets and reduced coronary reserve--and addresses prevention by mechanical protection devices and glycoprotein IIb/IIIa antagonism.

Unstable coronary plaque and its relation to coronary calcium

Coronary calcium is intimately associated with coronary atherosclerotic plaque development. The use of electron-beam computed tomography (EBCT) for accurate quantitative measurements has led to an increased interest in understanding the clinical importance of coronary calcium, particularly in terms of the ability to identify unstable coronary plaques that underlie the clinical acute coronary syndromes. Histopathologic studies have demonstrated that calcium is a frequent feature of ruptured plaques, but the presence or absence of calcium does not allow for reliable distinction between unstable versus stable plaques. This issue is complicated by the lack of a prospective definition for "unstable." Plaque rupture is sometimes found in apparently healthy subjects and in patients with clinically stable disease. Coronary atherosclerosis is a coronary systemic disease process. Imaging of coronary calcium, although unable to identify a localized unstable plaque, potentially can identify the more clinically pertinent "unstable patient." Almost all patients with a recent acute coronary syndrome have measurable coronary calcium because moderate-to-advanced coronary plaque disease is already present, although obstructive disease frequently is not. Prospective studies have demonstrated that extensive coronary calcium detected by EBCT is associated with a significantly increased incidence of subsequent myocardial infarction, need for revascularization, and coronary death. The incremental prognostic value of coronary calcium compared with that of risk factor assessment remains to be fully defined. The occurrence of an acute coronary syndrome is determined by many factors apart from the extent of atherosclerotic plaque disease. Large prospective trials in the general population are needed to define the subgroups that will benefit most from quantitative assessment of coronary calcium.

Plaque distribution and vascular remodeling of ruptured and nonruptured coronary plaques in the same vessel: an intravascular ultrasound study in vivo

OBJECTIVES

This study was designed to identify potential differences between the intravascular ultrasound (IVUS) characteristics of spontaneously ruptured and nonruptured coronary plaques.

BACKGROUND

The identification of vulnerable plaques in vivo may allow targeted prevention of acute coronary events and more effective evaluation of novel therapeutic approaches.

METHODS

Intravascular ultrasound was used to identify 29 ruptured plaques in arteries containing another nonruptured plaque in an adjacent segment. Intravascular ultrasound characteristics of these plaques were compared with plaques of computer-matched controls without evidence of plaque rupture. Plaque distribution was assessed by measuring the eccentricity of lumen location (inside the total vessel). Lumen cross-sectional area narrowing was calculated as [1 - (target/reference lumen area)] x 100%. A remodeling index was calculated as lesion/reference arterial area (>1.05 = compensatory enlargement, <0.95 = shrinkage).

RESULTS

Among the three groups of plaques, there was no significant difference in quantitative angiographic parameters, IVUS reference dimensions and IVUS lumen cross-sectional area narrowing. There was a difference in plaque distribution; lumen location by IVUS was significantly more eccentric in ruptured than in nonruptured (p = 0.002) and control plaques (p < 0.0001). The arc of disease-free vessel wall was larger in ruptured than in control plaques (p < 0.0001). The remodeling pattern of ruptured and nonruptured plaques differed significantly from that of the control plaques (p = 0.0001 and 0.003); compensatory enlargement was found in 66%, 48%, and 17%, whereas shrinkage was found in 7%, 10% and 48%, respectively.

CONCLUSIONS

Intravascular ultrasound assessment of plaque distribution and vascular remodeling may help to classify plaques with the highest probability of spontaneous rupture.

Perfusion-contraction mismatch with coronary microvascular obstruction: role of inflammation

A close relationship exists between regional myocardial blood flow (RMBF) and function during acute coronary inflow restriction (perfusion-contraction matching). However, the relationship of flow and function during coronary microvascular obstruction is unknown. In 12 anesthetized dogs, the left circumflex coronary artery was perfused from an extracorporeal circuit. After control measurements, 3,000 microspheres (42 micrometer diameter) per milliliter per minute inflow were injected to cause a microembolism (ME, n = 6). With unchanged systemic hemodynamics and RMBF, posterior systolic wall thickening (PWT) decreased from 19.8 +/- 1.9% SD at control to 13.3 +/- 4.0, 10.3 +/- 3.8, and 6.9 +/- 4.7% (P < 0.05 vs. control) at 1, 4, and 8 h, respectively. For comparison, inflow was progressively reduced to match PWT to that of the ME group at 1, 4, and 8 h (stenosis, STE, n = 6). RMBF in the STE group was reduced in proportion to PWT. Infarct size was not different among groups (6.5 +/- 4.5 vs. 3.4 +/- 3.2%). However, the number of leukocytes infiltrating the area at risk was significantly greater in the ME group than in the STE group. Coronary microembolization results in perfusion-contraction mismatch and is associated with an inflammatory response.

Coronary microembolization--its role in acute coronary syndromes and interventions

The diagnosis coronary artery disease is classically based on patient's symptoms and morphology, as analyzed by angiography. The importance of risk factors for the development of coronary atherosclerosis and disturbance of coronary vasomotion is clearly established. However, microembolization of the coronary circulation has also to be taken into account. Microembolization may occur as a single or as multiple, repetitive events, and it may induce inflammatory responses. Spontaneous microembolization may occur, when the fibrous cap of an atheroma or fibroatheroma (Stary i.v. and Va) ruptures and the lipid pool with or without additional thrombus formation is washed out of the atheroma into the microcirculation. Such events with progressive thrombus formation are known as cyclic flow variations. Plaque rupture occurs more frequently than previously assumed, i.e. in 9% of patients without known heart disease suffering a traffic accident and in 22% of patients with hypertension and diabetes. Also, in patients dying from sudden death microembolization is frequently found. Patients with stable and unstable angina show not only signs of coronary plaque rupture and thrombus formation, but also microemboli and microinfarcts, the only difference between those with stable and unstable angina being the number of events. Appreciation of microembolization may help to better understand the pathogenesis of ischemic cardiomyopathy, diabetic cardiomyopathy and acute coronary syndromes, in particular in patients with normal coronary angiograms, but plaque rupture detected by intravascular ultrasound. Also, the benefit from glycoprotein IIb/IIIa receptor antagonist is better understood, when not only the prevention of thrombus formation in the epicardial atherosclerotic plaque, but also that of microemboli is taken into account. Microembolization also occurs during PTCA, inducing elevations of troponin T and I and elevations of the ST segment in the EKG. Elevated baseline coronary blood flow velocity, as a potential consequence of reactive hyperemia in myocardium surrounding areas of microembolization, is more frequent in patients with high frequency rotablation than in patients with stenting and in patients with PTCA. The hypothesis of iafrogenic microembolization during coronary interventions is now supported by the use of aspiration and filtration devices, where particles with a size of up to 700 microns have been retrieved. In the experiment, microembolization is characterized by perfusion-contraction mismatch, as the proportionate reduction of flow and function seen with an epicardial stenosis is lost and replaced by contractile dysfunction in the absence of reduced flow. The analysis of the coronary microcirculation, in addition to that of the morphology and function of epicardial coronary arteries, and in particular appreciation of the concept of microembolization will further improve the understanding of the pathophysiology and clinical symptoms of coronary artery disease.

Role of intravascular ultrasound imaging in identifying vulnerable plaques

A plaque that has a large lipid core and a thin fibrous cap may undergo rupture. Once it ruptures, it may lead to thrombus formation and subsequent vessel occlusion. To identify unstable plaques before they rupture is essential for clinical management and patient's prognosis. Intravascular ultrasound (IVUS) opens a new window for the assessment of plaque morphology to identify vulnerable plaques and plaque rupture. We examined 144 patients with angina and ischemic ECG changes using IVUS. Ruptured plaques, characterized by a plaque cavity and a tear on the thin fibrous cap, were identified in 31 patients (group A) of which 23/31 (74%) clinically presented as unstable angina. Plaque rupture was confirmed by injecting contrast medium filling the plaque cavity during IVUS examination. Of the patients without plaque rupture (group B, n = 108), only 19 (18%) had unstable angina. No significant differences between the 2 groups were found concerning the vessel and plaque areas (p > 0.05). The percent stenosis in group A (56.2 +/- 16.5%) was significantly lower than in group B (67.9 +/- 13.4%) (p < 0.001). Area of the plaque cavity in group A (4.1 +/- 3.2 mm2) was significantly larger than the echolucent zone in group B (1.32 +/- 0.79 mm2) (p < 0.001). The plaque cavity/plaque ratio in group A (38.5 +/- 17.1%) was larger than the echolucent area/plaque ratio in group B (11.2 +/- 8.9%) (p < 0.001). The thickness of the fibrous cap in group A (0.47 +/- 0.20 mm) was significantly thinner than that (0.96 +/- 0.94 mm) in group B (p < 0.001).

CONCLUSIONS

Plaques seem to be prone to rupture when the echolucent area is larger than 1 mm2, the echolucent area/plaque ratio greater than 20% and the fibrous cap thinner than 0.7 mm. IVUS has the capacity of identifying plaque rupture and vulnerable plaques. This may have potential influence on patients management and therapy.

Coronary artery calcium in acute coronary syndromes: a comparative study of electron-beam computed tomography, coronary angiography, and intracoronary ultrasound in survivors of acute myocardial infarction and unstable angina

BACKGROUND

Quantification of coronary artery calcified plaques by electron-beam CT (EBCT) may predict cardiovascular events. However, whereas advanced coronary atherosclerotic plaques can be identified, mildly stenotic lipid-rich (soft) plaques may be difficult to detect. The value of EBCT in a subgroup of patients has therefore been questioned. To investigate this, we evaluated patients with acute coronary syndromes by EBCT and compared the results with coronary angiography and, in patients with an indeterminate angiogram, intracoronary ultrasound (ICUS).

METHODS AND RESULTS

EBCT was performed in 118 consecutive patients (57+/-11 years of age) with previous myocardial infarction (n=101) or unstable angina (n=17). A standard protocol requiring a CT density >130 Hounsfield units in an area > or =1.03 mm2 was used for the definition of coronary artery calcium. We found that 110 patients had moderate to severe coronary artery disease by coronary angiography, and 8 had either mildly stenotic plaques at a single site (4 patients, confirmed by ICUS) or nonatherosclerotic causes of the unstable coronary syndrome (4 patients). One hundred and five of the 110 patients (96%) with moderate to severe angiographic disease but only 1 of the 8 other patients (13%) had a positive EBCT. Patients with acute coronary syndromes and negative EBCTs were significantly younger than patients with positive EBCTs (46+/-12 versus 58+/-10 years, P<.001), and a higher percentage was actively smoking (100% of the smokers versus 46%, P<.05).

CONCLUSIONS

The vast majority of patients with acute coronary syndromes and at least moderate angiographic disease have identifiable coronary calcium by EBCT. Those patients with negative EBCTs have minimal or no atherosclerotic plaque formation. They are younger and tend to be active cigarette smokers.