Objective-To test the eYcacy of high frequency intravascular ultrasound (IVUS) transducers in identifying lipid/necrotic pools in atherosclerotic plaques. Methods-40 MHz transducers were used for in vitro IVUS assessment of 12 arterial segments (10 coronary and two carotid arteries, dissected from five diVerent necropsy cases). IVUS acquisition was performed at 0.5 mm/s after ligature of the branching points to generate a closed system. Lipid/necrotic areas were defined by IVUS as large echolucent intraplaque areas surrounded by tissue with higher echodensity. To obtain histopathological sections corresponding to IVUS cross sections, vessels were divided into consecutive 3 mm long segments using the most distal recorded IVUS image as the starting reference. Samples were then fixed with 10% buVered formalin, processed for histopathological study, serially cut, and stained using the Movat pentacrome method. Results-122 sections were analysed. Lipid pools were observed by histology in 30 sections (25%). IVUS revealed the presence of lipid pools in 19 of these sections (16%; sensitivity 65%, specificity 95%). Conclusions-In vitro assessment of lipid/necrotic pools with high frequency transducers was achieved with good accuracy. This opens new perspectives for future IVUS characterisation of atherosclerotic plaques. (Heart 2001;85:567-570) Keywords: intracoronary ultrasound; atherosclerosis; plaque morphology Coronary intravascular ultrasound (IVUS) provides quantitative information on lumen and vessel dimensions and plaque severity, as well as qualitative information on plaque composition in terms of hard and soft components and calcification. Previous IVUS studies on plaque composition, mainly performed in the early 1990s with 20-30 MHz transducers, showed that the technique defines calcification with high sensitivity and specificity, but is less accurate in assessing soft tissue components. [1][2][3][4][5][6][7][8][9] Thus, although 20 and 30 MHz transducers achieved appropriate definition of plaque morphology, the imaging of details such as the lipid pool and the fibrous cap remained poorly defined. No data are available on the characterisation of plaque morphology with high frequency transducers, which should allow more accurate definition of the soft components of the plaques.In this study we correlated corresponding IVUS and histopathological findings in human arterial specimens obtained at necropsy from patients with atherosclerosis, to determine how accurately 40 MHz IVUS can identify lipid/ necrotic pools. MethodsWe performed in vitro IVUS assessments, using continuous pull back, in arterial segments dissected from necropsy hearts. Arterial samples were serially sectioned in relation to IVUS markers. We then correlated the quantitative and qualitative evaluations of lipid/ necrotic pools obtained from histopathological slides with those obtained from IVUS cross sections. SAMPLE SERIESThe pathological series comprised 12 full length arteries, 10 coronary arteries (one left main, four left anterior...

Background-Intravascular ultrasound (IVUS) studies have shown that a mechanism of plaque compression/embolization contributes toward the poststenting increase in lumen area. The aim of this IVUS study was to compare the mechanisms of lumen enlargement after coronary stenting in 54 consecutive patients with unstable angina (UA) (group 1) and 56 with stable angina (group 2) to verify whether plaque embolization plays a major role in the former. Methods and Results-Both groups underwent the IVUS assessment (speed, 0.5 mm/sec) before the intervention and after stent implantation. The lumen area, the external elastic membrane area, and the plaqueϩmedia area (PA) were measured at 0.5-mm intervals. PA reduction in the lesion site was significantly greater in group 1 (Ϫ2.50Ϯ1.97 versus Ϫ0.53Ϯ1.43 mm 2 , PϽ0.001). After stenting, 47% of the lumen area increase in group 1 was obtained by means of PA reduction, and 53% was attributable to external elastic membrane area increase; the corresponding figures in group 2 were 13% and 87% (PϽ0.05). Decrease in PA after stenting was the only significant predictor of the MB fraction of creatinine kinase (CK-MB) release in a multiple regression model (Pϭ0.047). Conclusions-Serial volumetric IVUS assessment revealed in UA lesions a marked poststenting reduction in plaque volume, which is significantly greater than in stable angina and is associated with postprocedural CK-MB release. The decrease in PA during the procedure predicts CK-MB release in a multiple regression model. These findings suggest that stent deployment is often associated with plaque embolization in patients with UA. (Circulation. 2003;107:2320-2325.)

Quantitative coronary angiography (QCA) is routinely used for assessment of strategies aimed at reducing in-stent restenosis. Yet QCA enables only the measurement of luminal variation of stented segments and, unlike intravascular ultrasound (IVUS), provides only an indirect estimation of late in-stent neointimal formation, which has a key role in the process of in-stent restenosis. The aims of the present study were to correlate the IVUS measurement of in-stent intimal hyperplasia (IH) with QCA indexes of restenosis, to find out whether QCA is an adequate surrogate of IVUS, and, using either QCA and IVUS data, to define the sample sizes needed to demonstrate the effectiveness of strategies to reduce in-stent restenosis. The database of the European Imaging Laboratory was used to screen 154 stents implanted between 1997 and 2001 and studied by IVUS at 6 +/- 1 months of follow-up. All cases underwent serial QCA assessment (preintervention, postintervention, and follow-up). Only 131 cases with single stent implantation in native coronary arteries were included in the study. Stent restenosis, defined as percent diameter stenosis (DS) > 50%, was present at QCA in 69 out of 131 cases (53%). Linear regression analyses were performed to correlate the amount of IH, calculated by IVUS as the average of all cross-section areas (CSA; mean % IH CSA) and QCA indexes of restenosis (late loss and % DS). A positive significant correlation was found between IVUS mean % IH CSA and QCA % DS (r = 0.74; P < 0.0001) and between IVUS mean % IH CSA and QCA late loss (r = 0.72; P < 0.0001). Based on IVUS measurements of mean % IH CSA, a total sample size of 74 stents would be required in a two-arm comparison to have 0.80 power to detect at 0.05 significant level a 30% difference between two compared groups. Alternatively, adopting the QCA late loss, 230 stents would be required. QCA measurements of late in-stent restenosis are well correlated with IVUS calculation of in-stent neointimal formation. IVUS assessment of IH allows smaller sample sizes than QCA to document significant reductions of in-stent restenosis. Therefore, the use of IVUS should be encouraged in comparison studies aimed at revealing significant neointimal differences in small sample size populations.

High frequency transducers accurately identify lipid/necrotic pools and open new perspectives on future IVUS characterization of atherosclerotic plaques.

No abstract