Extent and distribution of atherosclerotic plaque in relation to major coronary side-branches: an intravascular ultrasound study in vivo

BACKGROUND

The non-uniform extent and distribution of atherosclerotic plaque at bifurcations have been described by necropsy studies and they are related to local blood-flow disturbances. Systematic evaluation of plaque extent and distribution upstream and downstream of major coronary side-branches has not yet been evaluated in vivo.

METHODS

We used intravascular ultrasound imaging in 41 patients with atherosclerotic disease to study the region of 73 major coronary side-branches at 2 mm increments proximal and distal to the side-branch (657 images: 73 at origin of side-branch; 292 proximal; 292 distal). The maximum (MXT) and minimum (MINT) plaque thickness and the plaque burden percentage (% PB) were measured in all the segments. The angle of distribution of maximum plaque thickness with respect to the origin of the side-branch was determined in each cross-section and assigned to S1 when located on the semicircle in the direction of the origin of the side-branch and to S2 when located on the opposite wall.

RESULTS

The mean value of maximum plaque thickness and the plaque burden percentage were similar at the origin and in the two adjacent segments proximal and distal to the side-branch (1.0 +/- 0.48 mm, 1.06 +/- 0.48 mm and 0.98 +/- 0.48 mm; 45 +/- 19%, 46 +/- 19% and 44 +/- 18%). In distal sites of analysis, the plaque was more frequently eccentric in comparison to proximal sites (presence of an arc of plaque-free wall: 79% versus 62% in very distal and in very proximal sites respectively; p < 0.05). The prevalence of maximum plaque in S2 was higher at the origin (84%) and in adjacent distal segments (86%) as compared with the adjacent proximal segments (60%; p < 0.0001).

CONCLUSIONS

The distribution of plaque is influenced by the origin of a major coronary side-branch in patients with coronary atherosclerosis: in distal sites the location of maximum plaque is almost always eccentrically distributed on the wall opposite the take-off.

[Intravascular ultrasound--the new gold standard?]

Intravascular ultrasound (IVUS) has evolved to a research tool to an intrinsic part of modern invasive cardiology. The main reason is the capability to obtain "in-vivo" micro anatomy by means of miniaturized echo-transducers with an outer diameter of 2.9-3.5 French. For the first time it is possible to base decisions not only on lumenograms but also on vessel wall assessment. The capabilities of IVUS can be divided in its diagnostic and intervention associated potentials. The diagnostic strength of IVUS is the ability to monitor compensatory coronary artery enlargement as a response to arteriosclerosis, to assess intermediate lesions, to reveal occult left main stem disease, and angiographically "silent" arteriosclerosis. In conjunction with the estimation of intracoronary flow reserve, patients with the diagnosis of coronary "syndrome X" can be better classified into those with or without early signs of arteriosclerosis. Additionally, IVUS is at present the only method allowing the classification of coronary artery lesions according to the AHA/ACC Stary classification. The intervention associated potentials of IVUS are the ability to allow optimal device selection, i.e. rotablators in calcified lesions or atherectomy devices in large plaque burden. The effects of PTCA on vessel wall morphology can be studied in great detail and the effect on luminal gain can be assessed almost on-line. The correlation between IVUS and angiography for estimation of luminal dimensions is inferior, because angiography is not able to describe complex luminal geometries. Several groups showed that the residual plaque area even after angiographically successful PTCA lies still in the range of 60%. A significant reduction of this number may influence long-term outcome after PTCA. Minimal luminal areas and residual plaque area after PTCA seem to be an indicator of restenosis, while the presence or absence of dissections seem to be less predictive. Additionally, the main mechanism of restenosis after PTCA is vessel shrinkage, not intimal hyperplasia. Intravascular monitoring of stent expansion led to high-pressure stent deployment with significant increase in post-procedural luminal diameters and finally the ability to withhold anticoagulation in patients with optimal stent deployment and to lower subacute stent thrombosis rates. First results for IVUS guided PTCA show a superior gain in post procedural free lumen without an increased complication rate. In the future, integrated devices, like balloons on IVUS catheters, steerable catheters, integrated flow and pressure transducers, tissue characterisation, and 0.018 inch IVUS guidewires will further enhance the usefulness of IVUS.

In vivo tomographic assessment of the heart and blood vessels with intravascular ultrasound

Intravascular ultrasound (IVUS) has emerged from being a research tool to becoming an intrinsic part of modern invasive cardiology mainly due to imaging micro anatomy in vivo. For the first time, it is possible to base therapeutic decisions not only on lumenograms but also on vessel wall assessment. IVUS has both diagnostic and intervention associated potential. The diagnostic strength of IVUS is its ability to describe compensatory coronary artery enlargement as a response to arteriosclerosis, to assess intermediate lesions, and to reveal occult left main stem disease and angiographically "silent" arteriosclerosis. The intervention associated potential of IVUS is the optimal device selection, i.e., rotablators in calcified lesions or atherectomy devices in large plaque burden. The effects of PTCA on vessel wall morphology can be studied in great detail and the effect on luminal gain can be assessed. Several groups have shown that the residual plaque area ("plaque burden") even after angiographically successful PTCA still lies in the range of 60%. A significant reduction in this number may influence long-term outcome after PTCA. Minimal luminal area and residual plaque area after PTCA seem to be indicators of restenosis, while the presence or absence of dissections seems to be less predictive. The main mechanism of restenosis after PTCA is vessel shrinkage, not intimal hyperplasia. Intravascular monitoring of stent expansion led to high-pressure stent deployment with a significant increase in post-procedural luminal diameters and the ability to withhold anticoagulation in patients with optimal stent deployment. In pulmonary and aortic diseases, IVUS contributed significantly to the understanding of aortic dissection and pulmonary hypertension. Additionally, with intracardiac ultrasound left and right ventricular function can be assessed. Intracardiac ultrasound has gained clinical usefulness for guiding transcatheter ablation in patients with conduction system abnormalities. In the future, integrated devices, such as balloons on IVUS catheters, steerable catheters, integrated flow and pressure transducers, tissue characterization, and 0.018" IVUS guide wire will further enhance the usefulness of IVUS.

Coronary wallstents show significant late, postprocedural expansion despite implantation with adjunct high-pressure balloon inflations

Adjunct high-pressure balloon inflations following the delivery of oversized self-expandable Wallstents may affect their implied late, postprocedural self-expansion. Consequently, we examined 15 "Magic" Wallstents, which were implanted following a strategy of stent oversizing and subsequent adjunct high-pressure balloon inflations (16 +/- 2 atm; all > or = 12 atm). The excellent radiographic visibility of this stent permitted reliable quantitative coronary angiographic measurement of both lumen and stent dimensions (before and after stenting, and at follow-up). At follow-up, extent and distribution of in-stent neointimal proliferation were evaluated with volumetric intravascular ultrasound. Between postintervention and follow-up examination, mean stent diameter increased from 3.7 +/- 0.4 to 4.2 +/- 0.4 mm (p <0.0001); there was no significant difference in late stent expansion between proximal, mid-, and distal stent subsegments. Late stent expansion showed a significant (reverse) relation to maximum balloon size (r = -0.56, p <0.04), but not with follow-up lumen size or late lumen loss. On average, 52 +/- 18% of the stent was filled with neointimal ingrowth; neointimal volume/cm stent length was 64 +/- 22 mm3. Both late stent expansion (r = 0.36, p <0.02) and maximum balloon pressure (r = 0.41, p <0.001) were related to neointimal volume/cm stent but not to follow-up lumen size. Thus, despite high-pressure implantation, Wallstents showed significant late self-expansion, which resulted in larger stent dimensions at follow-up that assisted in accommodating in-stent neointimal proliferation. Conversely, late stent expansion had a significant relation to the extent of in-stent neointimal ingrowth. Beneficial and disadvantageous effects of the late stent expansion appear to be balanced, because a relation to late lumen loss or follow-up lumen dimensions was not found to be present.

Dynamic imaging of coronary stent structures: an ECG-gated three-dimensional intracoronary ultrasound study in humans

Three-dimensional (3D) intracoronary ultrasound (ICUS) systems allow dynamic 3D reconstruction of coronary segments after stent deployment, but motion artifacts are frequently present. The use of an electrocardiographic-gated ICUS image acquisition workstation and a dedicated pullback device may overcome this problem. In the present study, we evaluated the potential of dynamic 3D reconstruction of intracoronary stents in 51 patients. Two different types of stent designs were investigated: (1) the Wallstent (mesh type; n = 36) and (2) the Cordis Coronary stent (coil type; n = 15). There was a tendency for imaging of the mesh stent type to be better than imaging of coil type stents (p = 0.06). Differences in the orientation of the stent struts (mesh:longitudinal; coil:transversal) most likely explain this difference. These in vivo observations were tested and confirmed in in vitro experiments. In conclusion, dynamic 3D ICUS reconstruction of the entire stent architecture in vivo was feasible for stents of mesh type, while stents of coil type were incompletely visualized.

[Treatment of coronary pseudoaneurysm by stent-graft implantation]

HISTORY AND CLINICAL FINDINGS

A 54-year-old man was urgently admitted because of sudden onset of progressively worsening angina pectoris, his first attack. Physical examination was unremarkable.

INVESTIGATIONS

Electrocardiography and laboratory tests excluded acute myocardial infarction. With the exception of hypercholesterolemia (total cholesterol 247 mg/dl) laboratory tests were normal. Coronary angiography revealed a 60% eccentric narrowing in the proximal part of the interventricular branch with adjacent aneurysmatic dilatation. Intravascular ultrasound (IVUS) showed a coronary pseudoaneurysm, its cavity communicating with the empty atheroma hole of an adjacent ruptured coronary plaque.

TREATMENT AND COURSE

A 19 mm stent graft was implanted, via a percutaneously inserted balloon-catheter system, in the region of the stenosis and the pseudoaneurysm. Subsequent angiography demonstrated a smooth nonstenotic lumen. The membrane of the graft (made of polytetrafluoroethylene [PTFE]), fixed between two thin metal stents, had occluded the pseudoaneurysm. Occlusion of an immediately distal septal branch briefly produced an asymptomatic rise of creatine kinase to maximally 173 U/l. Oral medication included ticlopidine hydrochloride (2 x 250 mg daily for 4 weeks). The patient was symptom-free after the procedure and was discharged 5 days later.

CONCLUSION

Implantation of a new type of stent-graft provides quick and uncomplicated treatment of a coronary aneurysm. The membrane fixed between two stents prevents wash out of any thrombi. The method may also be applicable to other potentially thrombus-containing lesions.

ECG-gated versus nongated three-dimensional intracoronary ultrasound analysis: implications for volumetric measurements

The quantitative analysis of a three-dimensional (3-D) intracoronary ultrasound (ICUS) image data set permits a more comprehensive assessment of coronary arterial segments. The 3-D image sets are generally acquired during continuous motorized pullbacks. However, the cyclic changes of vascular dimensions and the cyclic spatial displacement of the ICUS transducer relative to the vessel wall can result in characteristic image artifacts, which may limit the applicability of quantitative automated analysis systems. This limitation may be overcome by an ECG-gated image acquisition. In the present study we acquired in vivo (1) nongated and (2) ECG-gated 3-D ICUS image sets of 15 human atherosclerotic coronary arteries and performed a computer-assisted contour detection of the lumen and total vessel boundaries. Total vessel and lumen volumes measured significantly larger in the nongated versus ECG-gated end-diastolic image sets (753+/-307 mm3 vs. 705+/-305 mm3; 411+/-154 mm3 vs. 388+/-165 mm3, both: P < 0.05). Both end-diastolic and systolic measurements were available in nine arteries, showing a larger total vessel and lumen volume at systole (664+/-221 mm3 vs. 686+/-227 mm3, P=0.03; 384+/-164 mm3 vs. 393+/-170 mm3, P=0.08). The differences observed may be of particular interest for volumetric ICUS studies, addressing presumably small differences in vessel or lumen dimensions.

Atherosclerotic coronary lesions with inadequate compensatory enlargement have smaller plaque and vessel volumes: observations with three dimensional intravascular ultrasound in vivo

OBJECTIVE

To compare vessel, lumen, and plaque volumes in atherosclerotic coronary lesions with inadequate compensatory enlargement versus lesions with adequate compensatory enlargement.

DESIGN

35 angiographically significant coronary lesions were examined by intravascular ultrasound (IVUS) during motorised transducer pullback. Segments 20 mm in length were analysed using a validated automated three dimensional analysis system. IVUS was used to classify lesions as having inadequate (group I) or adequate (group II) compensatory enlargement.

RESULTS

There was no significant difference in quantitative angiographic measurements and the IVUS minimum lumen cross sectional area between groups I (n = 15) and II (n = 20). In group I, the vessel cross sectional area was 13.3 (3.0) mm2 at the lesion site and 14.4 (3.6) mm2 at the distal reference (p < 0.01), whereas in group II it was 17.5 (5.6) mm2 at the lesion site and 14.0 (6.0) mm2 at the distal reference (p < 0.001). Vessel and plaque cross sectional areas were significantly smaller in group I than in group II (13.3 (3.0) v 17.5 (5.6) mm2, p < 0.01; and 10.9 (2.8) v 15.2 (4.9) mm2; p < 0.005). Similarly, vessel and plaque volume were smaller in group I (291.0 (61.0) v 353.7 (110.0) mm3, and 177.5 (48.4) v 228.0 (92.8) mm3, p < 0.05 for both). Lumen areas and volumes were similar.

CONCLUSIONS

In lesions with inadequate compensatory enlargement, both vessel and plaque volume appear to be smaller than in lesions with adequate compensatory enlargement.

Reliability and reproducibility of automated contour analysis in intravascular ultrasound images of femoropopliteal arteries

An automated contour analysis system was previously developed to increase reproducibility and facilitate quantitative analyses of intravascular ultrasound (IVUS) images. The aim of this study was to compare measurements by this automated system with those obtained by conventional manual tracing, and to determine the intra- and interobserver variability of the automated system. IVUS images obtained in the femoropopliteal artery (n = 12) were analyzed with both systems. Area measurements by the automated system agreed well with the results obtained by manual tracing, displaying low coefficients of variation (8.5 to 15.7%) and high correlation coefficients (r = 0.92 to 0.98). Intra- and interobserver comparison of lumen area, vessel area, plaque area and percentage area stenosis showed low coefficients of variation (6.0 to 15.3% and 5.7 to 14.0%, respectively) and high correlation coefficients (both: r = 0.93 to 0.99). These data indicate that the automated analysis system is a reliable tool for the quantitative assessment of vessel dimensions in IVUS images obtained during clinical examination of peripheral arteries.

Successful directional atherectomy of de novo coronary lesions assessed with three-dimensional intravascular ultrasound and angiographic follow-up

Recent histopathologic and intravascular ultrasound (IVUS) data indicate that inadequate compensatory enlargement of atherosclerotic lesions contributes to the development of significant arterial stenoses. Such lesions may contain less plaque, which may have implications for atheroablative interventions. In this study, we compared lesions with (group A, n = 16) and without inadequate compensatory enlargement (group B, n = 30) as determined by IVUS. The acute results and the follow-up lumen dimensions of angiographically successful directional coronary atherectomy procedures were compared. Inadequate compensatory enlargement was considered present when the preintervention arterial cross-sectional area at the target lesion site was smaller than that at the (distal) reference site. Three-dimensional IVUS analysis and quantitative angiography were performed in 46 patients before and after intervention. IVUS measurements included the arterial, lumen, and plaque (arterial minus lumen) cross-sectional areas at the target lesion site (i.e., smallest lumen site) and the (distal) reference site. Angiographic follow-up was performed in 42 patients. Preintervention and postintervention angiographic measurements and IVUS lumen cross-sectional area measurements were similar in both groups. However, at follow-up, the angiographic minimum lumen and reference diameters were significantly smaller in group A compared with group B (1.71 +/- 0.47 mm vs 2.14 +/- 0.73 mm, p <0.03, and 2.97 +/- 0.29 mm vs 3.39 +/- 0.76 mm, p <0.02; group A vs B). The data of this observational study suggest that lesions with inadequate compensatory enlargement, as determined by IVUS before intervention, may have less favorable long-term lumen dimensions after directional coronary atherectomy procedures.

Variations of remodeling in response to left main atherosclerosis assessed with intravascular ultrasound in vivo

Histopathologic studies have demonstrated that vessels enlarge to compensate for an increase in plaque burden; this has been confirmed in vivo using intravascular ultrasound (IVUS). The initial studies suggested a biphasic course of lesion formation with (1) preservation of lumen dimensions up to a plaque burden of approximately 40%, and (2) luminal narrowing as plaque burden further increases. In this study, we used IVUS and angiography to assess the extent of left main (LM) atherosclerosis in 107 patients undergoing catheter-based procedures of the left anterior descending or left circumflex coronary arteries. Using IVUS, atherosclerotic plaques were found in all LM arteries, but only 26 (24%) had varying degrees of luminal narrowing on the angiogram. Nevertheless, there was an inverse relation (r = -0.62, p <0.0001) between the minimal lumen area and the plaque burden (i.e., plaque + media divided by total vessel area) that was not restricted to plaque burden values >40% (or >30%), but persisted at plaque burden values of 20% to 40%. In addition, LM arteries with a plaque burden <40% had a similar total vessel area as did LM arteries with a plaque burden > or =40% (22.9 +/- 6.1 vs 21.8 +/- 4.8 mm2, p = 0.30). These data suggest that lumen dimensions may not be preserved even if plaque occupies no more than 20% to 40% of the total vessel area. Thus, there is more variation in remodeling response during earlier stages of plaque accumulation within the LM artery than is commonly suggested.

Failure of intravascular ultrasound to predict dissection after balloon angioplasty by using plaque characteristics

Intravascular ultrasound (IVUS) is more sensitive than angiography in the assessment of plaque characteristics before intervention and vascular damage after balloon angioplasty. On the basis of IVUS data, this finding may improve clinical treatment by reducing the incidence of severe dissections after balloon angioplasty. We therefore studied the relation between plaque characteristics and dissections after balloon angioplasty. First, an in vitro study on atherosclerotic arteries (n = 42) was performed in which IVUS images were compared with histologic sections to validate the IVUS technique; second, the in vitro findings were compared with IVUS findings obtained in vivo (n = 73). Dissections were observed in 37 histologic sections and visualized on IVUS in 22 (59%) of the corresponding ultrasonic cross-sections; in vivo dissections were demonstrated by IVUS in 46 (63%) cases. Dissections were generally seen at the thinnest region of the plaque on both histologic sections (92%) and IVUS cross-sections (in vitro 83%; in vivo 93%). No significant relation was found between pre-interventional plaque characteristics such as composition features and eccentricity and the incidence, location, and extent of postinterventional dissections. Thus IVUS is able to identify dissections after balloon angioplasty, generally occurring at the site of the thinnest plaque diameter. However, neither the incidence nor the severity of these dissections was related to any of the preinterventional plaque characteristics.

ECG-gated three-dimensional intravascular ultrasound: feasibility and reproducibility of the automated analysis of coronary lumen and atherosclerotic plaque dimensions in humans

BACKGROUND

Automated systems for the quantitative analysis of three-dimensional (3D) sets of intravascular ultrasound (IVUS) images have been developed to reduce the time required to perform volumetric analyses; however, 3D image reconstruction by these nongated systems is frequently hampered by cyclic artifacts.

METHODS AND RESULTS

We used an ECG-gated 3D IVUS image acquisition workstation and a dedicated pullback device in atherosclerotic coronary segments of 30 patients to evaluate (1) the feasibility of this approach of image acquisition, (2) the reproducibility of an automated contour detection algorithm in measuring lumen, external elastic membrane, and plaque+media cross-sectional areas (CSAs) and volumes and the cross-sectional and volumetric plaque+media burden, and (3) the agreement between the automated area measurements and the results of manual tracing. The gated image acquisition took 3.9+/-1.5 minutes. The length of the segments analyzed was 9.6 to 40.0 mm, with 2.3+/-1.5 side branches per segment. The minimum lumen CSA measured 6.4+/-1.7 mm2, and the maximum and average CSA plaque+media burden measured 60.5+/-10.2% and 46.5+/-9.9%, respectively. The automated contour-detection required 34.3+/-7.3 minutes per segment. The differences between these measurements and manual tracing did not exceed 1.6% (SD<6.8%). Intraobserver and interobserver differences in area measurements (n=3421; r=.97 to.99) were <1.6% (SD<7.2%); intraobserver and interobserver differences in volumetric measurements (n=30; r=.99) were <0.4% (SD<3.2%).

CONCLUSIONS

ECG-gated acquisition of 3D IVUS image sets is feasible and permits the application of automated contour detection to provide reproducible measurements of the lumen and atherosclerotic plaque CSA and volume in a relatively short analysis time.

[Three dimensional reconstruction in intracoronary echography: a new system with automatic contour definition of ecg-gated image acquisition]

The use of a new automated contour-detection system (CD) allows rapid quantification of the dimensions of coronary lumen and plaque in an entire three-dimensional set of intracoronary images (ICUS), obtained during an ECG-gated pull-back image acquisition. The aim of the study was to evaluate the reproducibility, feasibility and accuracy of this approach in the clinical setting. We examined 32 coronary stents implanted in 28 patients, mean age 59 +/- 16 years. The ICUS images were acquired during a motorized uniform-speed pull-back (0.5 mm/s) of the ultrasound catheter after angiographically guided stent optimization, recorded on videotape, and analyzed during a conventional two-dimensional ICUS examination. An ECG-gated pull-back was then performed and analyzed by a second operator using CD. The minimal lumen area and diameter of the stent and the lumen area of the reference segments were measured. Comparing the analysis on- and off-line, correlation coefficients (r) not less than 0.96, with a mean difference not higher than 0.3 +/- 1.5 were found. On the other side, the comparison between the two-dimensional analysis and the analysis performed on-line showed a good correlation between the two methods. The two-dimensional method revealed a systematic overestimation (delta = -1.3 +/- 2.3) of the area and diameter. The time required for the on-line three-dimensional analysis was 9 +/- 3 min, whereas the off-line analysis was performed within 35 +/- 10 min. Focal segments of stent underexpansion were seen in 4 cases by two-dimensional ICUS and in 3 more cases by three-dimensional ICUS, analyzed on- and off-line. In order to evaluate the reproducibility of the system, we examined ICUS images after an ECG-gated pull-back of 23 segments of coronary arteries in 20 patients. The intra and interobserver variability was evaluated. The mean relative difference between the area and volume measurements of intra and interobserver variability ranged from 0.14 to 1.51%, with a standard deviation not higher than +/- 7.17, a standard error of estimate not higher than +/- 4.85 and a correlation coefficient (r) not less than 0.98. Thus, the "contour detection" in ECG-gated three-dimensional ICUS is highly reproducible, suggesting the use of the system in studies of progression-regression of atherosclerosis. It is feasible for the on-line application as it can be performed rapidly and shows good agreement with measurements obtained by off-line CD.

Electrocardiogram-gated intravascular ultrasound image acquisition after coronary stent deployment facilitates on-line three-dimensional reconstruction and automated lumen quantification

OBJECTIVE

This study evaluates the feasibility, reliability and reproducibility of electrocardiogram (ECG)-gated intravascular ultrasound (IVUS) image acquisition during automated transducer withdrawal and automated three-dimensional (3D) boundary detection for assessing on-line the result of coronary stenting.

BACKGROUND

Systolic-diastolic image artifacts frequently limit the clinical applicability of such automated analysis systems.

METHODS

In 30 patients, after successful angiography-guided implantation of 34 stents in 30 target lesions, we carried out IVUS examinations on-line with the use of ECG-gated automated 3D analyses and conventional manual analyses of two-dimensional images from continuous pullbacks. These on-line measurements were compared with off-line 3D reanalyses. The adequacy of stent deployment was determined by using ultrasound criteria for stent apposition, symmetry and expansion.

RESULTS

Gated image acquisition was successfully performed in all patients to allow on-line 3D analysis within 8.7 +/- 0.6 min (mean +/- SD). Measurements by on-line and off-line 3D analyses correlated closely (r > or = 0.95), and the minimal stent lumen differed only minimally (8.6 +/- 2.8 mm2 vs. 8.5 +/- 2.8 mm2, p = NS). The conventional analysis significantly overestimated the minimal stent lumen (9.0 +/- 2.7 mm2, p < 0.005) in comparison with results of both 3D analyses. Fourteen stents (41%) failed to meet the criteria by both 3D analyses, all of these not reaching optimal expansion, but only 7 (21%) were detected by conventional analysis (p < 0.02). Intraobserver and interobserver comparison of stent lumen measurements by the automated approach revealed minimal differences (0.0 +/- 0.2 mm2 and 0.0 +/- 0.3 mm2) and excellent correlations (r = 0.99 and 0.98, respectively).

CONCLUSIONS

ECG-gated image acquisition after coronary stent deployment is feasible, permits on-line automated 3D reconstruction and analysis and provides reliable and reproducible measurements; these factors facilitate detection of the minimal lumen site.

Simpson's rule for the volumetric ultrasound assessment of atherosclerotic coronary arteries: a study with ECG-gated three-dimensional intravascular ultrasound

BACKGROUND

Volumetric intravascular ultrasound (IVUS) assessment provides complementary information on atherosclerotic plaques. The volumes can be calculated by applying Simpson's rule to cross-sectional area data of multiple IVUS images, acquired with a fixed sample spacing, which is the distance (along the vessel's axis) between two images.

OBJECTIVE

To evaluate the effect of different sample spacings on the results of volumetric IVUS measurements.

METHODS

A stepwise electrocardiographically gated IVUS image-acquisition and automated three-dimensional analysis approach was applied to 26 patients. Twenty-eight coronary segments with mild-to-moderate coronary atherosclerosis were examined. Volumetric measurements of five images per mm (i.e. sample spacing 0.2 mm), representing a complete scanning of the coronary segment, were considered the optimal standard, against which volumetric measurements of three, one, and one-half images per mm (i.e. larger sample spacings) were compared.

RESULTS

The lumen, total vessel, and plaque volumes obtained with five images per mm were 183.3 +/- 2.8, 350.6 +/- 141.6, and 167.3 +/- 89.2 mm3. There was an excellent correlation (r = 0.99, P < 0.001) between these data and volumetric measurements with larger sample spacings. The volumetric measurements with larger sample spacings differed on average only by a little (< 0.7%) from the optimal standard measurements. However, a relatively small, but significant, increase in SD of these differences was associated with the wider sample spacings (< 3.6%, P < 0.05).

CONCLUSIONS

The width of the sample spacing has a relatively small but significant impact on the variability of volumetric intravascular ultrasound measurements. This should be considered when designing future volumetric studies. The electrocardiographically gated acquisition of five IVUS images per mm axial length during a stepwise transducer pull-back is an ideal approach, particularly when addressing with IVUS volumetric changes that are assumed small, such as those expected in studies of the progression and regression of atherosclerosis.

Intravascular elastography: principles and potentials

Many intravascular therapeutic techniques for the treatment of significant atherosclerotic lesions are mechanical in nature: angioplasty, stenting and atherectomy. The selection of the most adequate treatment would be advantageously aided by knowledge of the mechanical properties of the lesion. Based on the success of conventional intravascular ultrasound (IVUS) imaging in accurately depicting the morphology of atheromatous lesions, ultrasonic tissue characterization has been proposed to determine the composition of atherosclerotic plaques. Elastography is an ultrasound-based imaging technique capable of producing cross-sectional elasticity images called elastograms. The technique involves analysis of echo signals obtained at two states of incremental intravascular pressure. High resolution, local tissue displacement estimation by cross-correlation is followed by computation of local strain. Strain is utilized as an indicator of the local compliance of tissue under the assumption of constant stress within the scan plane. Using vessel-mimicking phantoms, we demonstrate the feasibility of intravascular elastography experimentally. The elastograms are able to depict lesions of different elasticity independently of the echogenicity contrast, since the information provided by the elastograms is generally independent of that obtained from the conventional IVUS image. Thus, the elastogram can complement the characterization of lesions from the conventional IVUS image. Progress to in vitro and in vivo testing is expected in conjunction with ongoing improvements in the current instrumentation and processing.

Is intravascular ultrasound after coronary stenting a safe procedure? Three cases of stent damage attributable to ICUS in a tantalum coil stent

The use of coronary stents decreases the morbidity associated with acute closure and restenosis after balloon angioplasty. Intracoronary ultrasound (ICUS) guidance of stent implantation has been advocated to improve stent deployment and thereby to further improve the clinical outcome after stenting, over and above balloon angioplasty. Whereas the merits of intracoronary ultrasound in this respect still remain to be proven, the present paper illustrates that ICUS itself may also entail complications. This paper reports on three cases of stent damage induced or aggravated by the ICUS procedure.

True reconstruction of vessel geometry from combined X-ray angiographic and intracoronary ultrasound data

At present a rapidly expanding variety of methods appear to provide three-dimensional (3-D) reconstructions of blood vessels in a patient. Generally the results of such methods look very realistic. However, only a few produce a true 3-D reconstruction. We strongly suggest that for a true 3-D reconstruction of a blood vessel the following criteria should at least be fulfilled: (1) the arterial wall rather than the lumen must be reconstructed; (2) the spatially curved course of the vessel must be included; and (3) the orientation of local vessel wall characteristics, for example, plaque eccentricity, with respect to the luminal course must be correctly maintained. Currently, only methods combining biplane X-ray angiography and intravascular ultrasound imaging (IVUS) have succeeded in providing true 3-D reconstruction of a segment of a vessel. Accuracy of those reconstructions is derived from studies using phantoms having precisely known geometry. In patients, data on accuracy are more difficult to obtain. Nevertheless, a comparison can be made between the actual length of an IVUS pull-back trajectory and its reconstructed length showing relative differences of less than 3%. Further knowledge can be obtained by comparing simulated angiograms derived from the 3-D reconstruction with the real contrast angiograms. True 3-D reconstruction methods of the vessel wall and lumen, applicable in the individual patient, have become feasible and produce accurate results. Application of such a method will be helpful to understand immediate and long-term vessel remodelling induced by all types of catheter interventions and in the study of progression or regression of atherosclerotic wall disease.

Quantitative three-dimensional intravascular ultrasound

Three-dimensional (3-D) intravascular ultrasound (IVUS) allows for the visualization of entire coronary segments, provides more detailed insights into the geometry of atherosclerotic plaques and facilitates serial studies. Automated quantitative 3-D IVUS methods reduce the analysis time and the subjectivity of boundary tracing, and permit complex IVUS studies. The 3-D IVUS approach is not restricted to research applications, but may be used as a valuable clinical tool. Evaluation of the coronary segment of interest before catheter-based coronary interventions provides information which may facilitate the selection of interventional devices. Moreover, 3-D IVUS allows for a careful assessment of the procedural results and potential post-procedural complications. ECG-gated image acquisition, automated contour detection, and approaches using data of both 3-D IVUS and biplane angiography represent the recent progress in this field. Three-dimensional IVUS will surely gain further importance and become a routine technique, if the interest and research effort is sustained.

On-line three-dimensional intracoronary ultrasound for guidance of catheter based interventions

Intracoronary ultrasound (ICUS) provides valuable information on the distribution and composition of atherosclerotic plaque. For this reason its use for guidance of interventional procedures has been advocated. Recently, on-line systems of three-dimensional reconstruction have been introduced and offer great potential for guidance of interventional procedures since valuable details on longitudinal architecture of the plaque under treatment are obtained. In this article we review the current clinical application of three-dimensional (3-D) ICUS and report our experience with the use of an on-line 3-D ICUS system for guidance of interventional procedures. In our experience 3-D reconstruction of ICUS proved to be a feasible method facilitating device selection and guidance of catheter based interventions.

Computerized assessment of coronary lumen and atherosclerotic plaque dimensions in three-dimensional intravascular ultrasound correlated with histomorphometry

Intravascular ultrasound (IVUS), which depicts both lumen and plaque, offers the potential to improve on the limitations of angiography for the assessment of the natural history of atherosclerosis and progression or regression of the disease. To facilitate measurements and increase the reproducibility of quantitative IVUS analyses, a computerized contour detection system was developed that detects both the luminal and external vessel boundaries in 3-dimensional sets of IVUS images. To validate this system, atherosclerotic human coronary segments (n = 13) with an area obstruction > or = 40% (40% to 61%) were studied in vitro by IVUS. The computerized IVUS measurements (areas and volumes) of the lumen, total vessel, plaque-media complex, and percent obstruction were compared with findings by manual tracing of the IVUS images and of the corresponding histologic cross sections obtained at 2-mm increments (n = 100). Both area and volume measurements by the contour detection system agreed well with the results obtained by manual tracing, showing low mean between-method differences (-3.7% to 0.3%) with SDs not exceeding 6% and high correlation coefficients (r = 0.97 to 0.99). Measurements of the lumen, total vessel, plaque-media complex, and percent obstruction by the contour detection system correlated well with histomorphometry of areas (r = 0.94, 0.88, 0.80, and 0.88) and volumes (r = 0.98, 0.91, 0.83, and 0.91). Systematic differences between the results by the contour detection system and histomorphometry (29%, 13%, -9%, and -22%, respectively) were found, most likely resulting from shrinkage during tissue fixation. The results of this study indicate that this computerized IVUS analysis system is reliable for the assessment of coronary atherosclerosis in vivo.

Quantification of the minimal luminal cross-sectional area after coronary stenting by two- and three-dimensional intravascular ultrasound versus edge detection and videodensitometry

The use of 2-dimensional intravascular ultrasound (2-D IVUS) to improve the outcome of coronary stenting has gained clinical acceptance, and recently 3-D IVUS has been introduced to clinical practice. However, there have been no comprehensive studies comparing the measurements of the coronary dimensions after stenting obtained by the different approaches of IVUS and quantitative coronary angiography. We examined the minimal luminal cross-sectional area of 38 stents using 2-D IVUS, 3-D IVUS, and 2 standard methods of quantitative coronary angiography, edge detection (ED) and videodensitometry (VD). Correlations between 2-D IVUS and ED (r = 0.72; p < 0.0001), VD (r = 0.87; p < 0.0001), and 3-D IVUS (r = 0.81; p < 0.0001) were higher than the correlations seen between 3-D IVUS and ED (r = 0.58; p < 0.0005) and VD (r = 0.70; p < 0.0001). The measurements by 2-D and 3-D IVUS (8.32 +/- 2.50 mm2 and 8.05 +/- 2.66 mm2) were larger than the values obtained by the quantitative angiographic techniques ED and VD (7.55 +/- 2.22 mm2 and 7.27 +/- 2.21 mm2). Thus, concordance was seen among all of the 4 techniques, confirming the validity of using IVUS for determination of the minimal luminal cross-sectional area after coronary stenting. A particularly good correlation was found between VD and IVUS, perhaps because measurement of the luminal area is the basic quantification approach of both techniques, whereas the lower correlations of ED with IVUS and VD may be explained by the dependence of ED on the angiographic projections used, which is especially important in eccentric stent configurations.

Morphometric analysis in three-dimensional intracoronary ultrasound: an in vitro and in vivo study performed with a novel system for the contour detection of lumen and plaque

Currently, automated systems for quantitative analysis by intracoronary ultrasound (ICUS) are restricted to the detection of the lumen. The aim of this study was to determine the accuracy and reproducibility of a new semiautomated contour detection method, providing off-line identification of the intimal leading edge and external contour of the vessel in three-dimensional ICUS. The system allows cross-sectional and volumetric quantification of lumen and of plaque. It applies a minimum-cost algorithm and the concept that edge points derived from previously detected longitudinal contours guide and facilitate the contour detection in the cross-sectional images. A tubular phantom with segments of various luminal dimensions was examined in vitro during five catheter pull-backs (1 mm/sec), and subsequently 20 diseased human coronary arteries were studied in vivo with 2.9F 30 MHz mechanical ultrasound catheters (200 images per 20 mm segment). The ICUS measurements of phantom lumen area and volume revealed a high correlation with the true phantom areas and volumes (r = 0.99); relative mean differences were -0.65% to 3.86% for the areas and 0.25% to 1.72% for the volumes of the various segments. Intraob-server and interobserver comparisons showed high correlations (r = 0.95 to 0.98 for area and r = 0.99 for volume) and small mean relative differences (-0.87% to 1.08%), with SD of lumen, plaque, and total vessel measurements not exceeding 7.28%, 10.81%, and 4.44% (area) and 2.66%, 2.81%, and 0.67% (volume), respectively. Thus the proposed analysis system provided accurate measurements of phantom dimensions and can be used to perform highly reproducible area and volume measurements in three-dimensional ICUS in vivo.

Optimized expansion of the Wallstent compared with the Palmaz-Schatz stent: on-line observations with two- and three-dimensional intracoronary ultrasound after angiographic guidance

Optimized stent expansion by high-pressure inflations of oversized balloons has initially been derived from experience obtained with the Palmaz-Schatz stent, whereas there is little experience with this strategy in the Wallstent. By using this approach with quantitative coronary angiographic guidance, 20 Wallstents and 20 Palmaz-Schatz stents were implanted in 34 patients and consecutively examined by conventional two-dimensional (2D) intracoronary ultrasound (ICUS) and three-dimensional (3D) ICUS on the basis of the application of a pattern recognition algorithm. Ultrasound criteria of adequate stent expansion were defined as a complete apposition of the stent to the vessel wall, a stent symmetry index (SSI = minimum/maximum lumen diameter) > or = O.7, and a stent-reference lumen area ratio (SRR = Minimum intrastent lumen area/Average of proximal and distal reference lumen area) > or = O.8. In all cases a smooth angiographic lumen and a negative diameter stenosis, on the basis of a distal reference, was achieved. For the Wallstents ICUS showed a higher SSI (2D, 0.95 +/- 0.04 vs 0.85 +/- 0.09; p < 0.001; 3D, 0.90 +/- 0.09 vs 0.82 +/- 0.11, p < 0.05) and a lower SRR (2D, 0.66 +/- 0.12 vs 0.81 +/- 0.13, p < 0.005; 3D, 0.63 +/- 0.14 vs 0.74 +/- 0.15, p < 0.05) than for the Palmaz-Schatz stents. Ninety percent of failure in meeting these criteria resulted from a low SRR. The incidence of incomplete stent apposition (one in both stents) or SSI <0.7 was low and generally associated with an SRR <0.8. The Wallstents met the ICUS criteria less often (2D, 2(1O%) vs 10(50%), p < 0.01; 3D, 3(15%) vs 9(45%), p < 0.05), were significantly longer (35.1 +/- 7.7 mm and 14.3 +/- 3.3 mm, p < 0.0001), and generally demonstrated a larger vessel tapering, measured as proximal minus distal ICUS reference lumen area (1.33 +/- 2.91 mm2 vs 0.44 +/- 1.97 mm(2), not significant). Wallstents meeting the ICUS criteria, however, showed less vessel tapering (0.18 +/- 1.64 mm(2)). Thus optimized stent expansion was followed by excellent angiographic results for both Palmaz-Schatz and Wallstent. Although angiographic results and visual assessment of the ICUS examination suggested a good outcome, few Wallstents met the ICUS criteria in contrast to the Palmaz-Schatz stents. The low value of the SRR in the Wallstents is likely to be caused by vessel tapering, suggesting that this criterion may be unsuitable in assessing the adequacy of the expansion of relatively long stents such as the Wallstent.

Usefulness of three-dimensional reconstruction for interpretation and quantitative analysis of intracoronary ultrasound during stent deployment

We examined 49 coronary stents in 33 patients after angiographically guided optimization of the deployment by intracoronary ultrasound, and compared the findings of a conventional 2-dimensional analysis approach with the results obtained from an automatic lumen recognition provided by a 3-dimensional reconstruction system. The automatic lumen analysis demonstrated that only 15 stents (31%) fulfilled defined ultrasound criteria of adequate stent deployment, and that 5 of these cases were missed by the conventional approach, which systematically overestimated the dimensions of the minimal stent lumen.

Usefulness of on-line three-dimensional reconstruction of intracoronary ultrasound for guidance of stent deployment

The additional information provided by automated on-line 3-dimensional (3-D) reconstruction of intracoronary ultrasound (ICUS) was assessed in 42 patients (62 stents) who underwent stent deployment after achieving an optimal quantitative angiographic result. In 10 of 42 patients, 3-D ICUS was also performed before stenting. ICUS images of stents and adjacent reference segments were acquired by using a motorized pullback at a constant speed (1 mm/s) and immediately processed in the catheterization laboratory. Optimal stent expansion was detected by 3-D ICUS in case of complete apposition of stent struts to the vessel wall. Furthermore, an attempt was made to maximize the intrastent lumen area to match lumen area of the reference segment and to cover with stents all the segments with residual significant lesions (plaque burden >50%). Three-dimensional automated reconstruction of ICUS was successful in 8 of 10 patients (80%) before, and in 36 of 42 patients (86%) after stent deployment. In all 8 patients who underwent successful 3-D ICUS assessment before stent implantation, the selection of stent length was facilitated by accurately measuring the lesion length. After stenting, 3-D ICUS modified the management strategy in 21 of 36 patients (58%), triggering additional high-pressure dilatations in 13 patients (36%) and additional stent deployment in 8 (22%). In conclusion, on-line 3-D ICUS facilitates stent selection and strongly modifies the revascularization strategy by accurately detecting stent underexpansion and presence of uncovered lesions.

Volumetric intracoronary ultrasound: a new maximum confidence approach for the quantitative assessment of progression-regression of atherosclerosis?

Quantitative assessment of atherosclerosis during its natural history and following therapeutic interventions is important, as cardiovascular disease remains the most significant cause of morbidity and mortality in industrial societies. While coronary angiography delineates the vessel lumen, permitting only the indirect determination of atherosclerotic wall changes encroaching upon the lumen, intracoronary ultrasound permits direct plaque assessment and quantification. The angiographic percent diameter stenosis, previously suggested as measure of a maximum confidence approach, is still commonly used to quantify stenosis severity, but the reference segments which are required for angiographic interpolation of the normal vessel dimensions are frequently involved in the general process of atherosclerosis, including progression or regression. Considering also the variability of vascular remodeling during the evolution of atherosclerosis, including compensatory enlargement and paradoxical arterial shrinkage, intracoronary ultrasound appears currently to be the only reliable technique to measure plaque burden and progression or regression of atherosclerosis. However, correct matching of the site of measurement at follow-up with the site of the initial ultrasound study is often difficult to achieve, but is significantly facilitated by the use of volumetric intracoronary ultrasound. This approach permits not only area measurement, but also measurement of plaque volume, which appears to be the ideal measure for quantifying the atherosclerotic plaque, as it is highly reproducible and directly reflects the changes of an entire arterial segment.

Mechanism of high-speed rotational atherectomy and adjunctive balloon angioplasty revisited by quantitative coronary angiography: edge detection versus videodensitometry

High-speed rotational coronary atherectomy (RA) is primarily used to treat complex lesions. Quantitative angiographic analysis of such complex lesions by edge detection is often unsuitable, whereas videodensitometry, measuring vessel dimensions independently of the target stenosis contours, may offer potential advantages. To gain insight into the operative mechanism of RA and to study the agreement between the two quantitative angiographic methods in measuring the minimal luminal cross-sectional area, the edge detection and videodensitometry techniques were applied to coronary angiograms of 21 lesions in 19 patients with symptoms who underwent successful RA and balloon angioplasty (BA). Obstruction diameter as determined by edge detection increased from 1.00 +/- 0.31 mm before intervention to 1.35 +/- 0.29 mm after RA (p < 0.001) and further increased to 1.74 +/- 0.33 mm after adjunctive BA (p > 0.001). The mean between-method difference (edge detection minus videodensitometry) was 0.34 mm2 before intervention, 0.13 mm2 after RA, and 0.09 mm2 after adjunctive BA (not significant). The standard deviation of the differences decreased from +/- 0.87 mm2 before intervention to +/- 0.80 mm2 after RA (not significant) and increased after BA significantly to +/- 1.21 mm2 (p < 0.05). Thus edge detection and videodensitometry provided equivalent immediate angiographic results after RA and adjunctive BA. The good agreement after RA may reflect the operative mechanism of RA, which by ablation of noncompliant plaque material yields a circular symmetric lumen with smooth surface. The increased dispersion of the between-method differences observed after adjunctive BA presumably results from dissections, plaque ruptures, and loss of luminal smoothness after balloon dilatation.

[Reconstruction methods for 3D imaging and quantification of intracoronary ultrasound cross-sectional images using biplanar fluoroscopy. Initial experiences in vitro and in vivo]

In this investigation, we studied the feasibility of 3D-reconstruction from 2D cross-sectional intracoronary ultrasound images. A computer-aided, automated 3D-reconstruction was used to generate cylindrical and sagittal format of vessels in vitro (n = 9) and in vivo (n = 48). Ultrasound 2D-images were acquired with a 20 MHz mechanical intracoronary ultrasound catheter (Boston Scientific). A slow pullback (about 1 mm/s) of the catheter was performed during continuous recording of the ultrasound images. The recorded 2D-images were then fed to an image processing computer. Correction and scaling of the axial vessel dimensions was performed by the assessment of the catheter position in the simultaneously recorded biplane fluoroscopy. Digitized data were then processed to 3D-images with use of voxel space modeling. The 3D-views from any plane can be reconstructed. The in-vitro study demonstrated that the reconstructed images were able to correctly portray the pathological changes of the vessel wall in all specimen as proved by pathologic examination. In the in-vivo study, 3D-reconstruction provided not only a spatial visualization of the coronary arterial disorders (such as coronary aneurysm, coronary dissection, spontaneous plaque rupture etc.) but also provides the potential to quantify the mass of lesions. By combining sagittal and cylindrical views, 3D-reconstruction enables longitudinal and orthogonal imaging of the both the vessel lumen and vessel wall, therefore, it has the advantage of cross-sectional viewing as obtained from intracoronary ultrasound and the longitudinal viewing as derived from coronary angiography. These preliminary results of the study indicate that 3D-reconstruction of coronary segments is a promising technique for studying coronary artery disease. Analysis can be based not only on single or multiple cross-sectional images but also on vessel segments facilitating serial studies as for instance studies assessing the progression and regression of atherosclerosis.

Angiographic, ultrasonic, and angioscopic assessment of the coronary artery wall and lumen area configuration after directional atherectomy: the mechanism revisited

The purpose of the present study was to use the complementary information of angiography, intravascular ultrasound, and intracoronary angioscopy before and after directional atherectomy to characterize the postatherectomy appearance of vessel wall contours and the mechanism of lumen enlargement. Directional coronary atherectomy aims at debulking rather than dilating a coronary artery lesion. The selective removal of the plaque may potentially minimize the vessel wall damage and lead to subsequent better late outcome. Whether plaque removal is the main mechanism of action has only to be assessed indirectly by angiography and warrants further investigation with detailed analysis of luminal changes and vessel wall damage by ultrasound and direct visualization with angioscopy. Twenty-six patients have been investigated by quantitative angiography, intravascular ultrasound, and intracoronary angioscopy (n = 19) before and after atherectomy. In addition, all retrieved specimens were microscopically examined. Ultrasound imaging showed an increase in lumen area from 1.95 +/- 0.70 mm2 to 7.86 +/- 2.16 mm2 at atherectomy. The achieved gain mainly resulted from plaque removal because plaque plus media area decreased from 18.16 +/- 4.47 mm2 to 13.13 +/- 3.10 mm2. Vessel wall stretching (i.e., change in external elastic lamina area) accounted for only 15% of lumen area gain. Luminal gain was higher in noncalcified (6.52 +/- 2.12 mm2) lesions than in lesions containing deeply located calcium (5.19 +/- 0.99 mm2) and lowest in superficially calcified lesions (5.41 +/- 2.41 mm2). Ultrasound imaging identified an atherectomy byte in 85% of the cases, whereas angioscopy revealed such a crevice in 74%. The complementary use of the three techniques revealed an underestimation of the presence of dissection/tear and new thrombus by angiography (10% and 4%) and ultrasound imaging (12% and 0%) compared with angioscopy (26% and 21%). The combined use of angiography, ultrasound, and angioscopy reveals that the postatherectomy luminal lining is not as regular and smooth as that seen by angiography. Luminal enlargement with atherectomy is achieved by plaque excision rather than arterial expansion.

Three-dimensional reconstruction of coronary arteries with intravascular ultrasound

Three-dimensional (3D-) reconstruction of intravascular ultrasound (IVUS) images is a recently introduced technical method which has rapidly grown in science and clinical practice. In the catheterization laboratory it is particularly important to obtain the 3D-reconstruction on-line, since the dimensions measured and the plaque attributes displayed may guide the therapeutic decision. Off-line reconstruction, however, provides very accurate and reproducible area and volume measurements of lumen and plaque and is thus exceptionally qualified for studying progression/regression of atherosclerosis or restenosis after catheter-based interventions. Complementary 3D-reconstruction methods, revealing specific advantages and limitations, meet the requirements by slightly different technical approaches, but each 3D-reconstruction of two-dimensional IVUS images requires some basic procedural steps. The IVUS images can be acquired during continuous or ECG-gated withdrawals of the IVUS imaging catheter. The latter permits even to visualize the cyclic pulsation of the reconstructed arteries. As an alternative approach a sensing device recognizes the insertion depth of the IVUS catheter and permits reliable measurements even during manual handling of the IVUS catheter. A discrimination between the blood-pool and structures of the vascular wall, performed in the digitized images, can be achieved by the application of different techniques. This processing step which is called segmentation and the image acquisition are particularly crucial with regards to the final quality of the 3D-reconstruction. Currently there are still limitations of 3D-IVUS, but a new approach combining data obtained from 3D-IVUS and biplane angiography offers a promising potential to solve most of the remaining problems in the future. Thus, three-dimensional IVUS offers a great clinical and scientific potential since it provides spatial visualization of vascular pathology, longitudinal and volumetric measurement of luminal and plaque dimensions, and facilitated guidance of catheter-based interventions. Assuming a technical development similar to the progress of the previous years. 3D-IVUS has a realistic chance to gain significant importance and to become a routine technique in the future.

Three dimensional reconstruction of cross sectional intracoronary ultrasound: clinical or research tool?

Images

Quantitative assessment with intracoronary ultrasound of the mechanisms of restenosis after percutaneous transluminal coronary angioplasty and directional coronary atherectomy

The mechanisms of immediate and late changes after percutaneous transluminal coronary angioplasty (PTCA) and directional coronary atherectomy (DCA) were assessed by serial ultrasound imaging in 18 patients treated with PTCA and 16 treated with DCA before, immediately after, and 6 months after coronary interventions. A reduction in plaque area was the main operative mechanism of DCA, explaining 66% of lumen enlargement. In the PTCA group, the increase in lumen area was the result of a more balanced combination of plaque reduction (52% of lumen increase) and increase in total lumen area (48%); p < 0.05 versus DCA. In the PTCA group, this last mechanism was prevalent (p < 0.05) in the lesions showing wall fracture or dissection after treatment and in the lesions with a mixed or calcific composition. In the PTCA group, concentric lesions showed a greater plaque compression than eccentric lesions (p < 0.02). Plaque increase was responsible for 92% and 32% of the late lumen loss after DCA and after PTCA, respectively (p < 0.05). In PTCA patients, a chronic reduction in total vessel area was the main operative mechanism of lumen reduction (67%) and was prevalent in lesions with a mixed or calcific composition. (p < 0.05).

The beta-adrenoceptor subtype(s) mediating adrenaline- and dobutamine-induced blood pressure and heart rate changes in healthy volunteers

In order to characterize the beta-adrenoceptor subtype(s) mediating blood pressure and heart rate changes induced by adrenaline and dobutamine, we compared the effects in healthy male volunteers of propranolol (5 mg i.v.) and of the beta 1-adrenoceptor selective antagonist bisoprolol (15 mg p.o.) on adrenaline- and dobutamine-infusion induced changes in systolic (P(syst)) and diastolic blood pressure (P(diast)) and heart rate with those on blood pressure and heart rate (HR) changes induced by "pure" alpha- or beta-adrenoceptor agonists (phenylephrine, selective alpha, terbutaline, selective beta 2, isoprenaline, non-selective beta 1 and beta 2). Both beta-adrenoceptor antagonists did not affect phenylephrine (0.25 -1.0 microgram/kg/min for 10 min) infusion induced P(syst)- and P(diast)-increases and HR-decreases. On the other hand, propranolol completely suppressed terbutaline (25-150 ng/kg/min for 15 min) and isoprenaline (3.5-35 ng/kg/min for 8 min) infusion induced P(syst)- and HR-increases and P(diast)-decreases while bisoprolol significantly attenuated only isoprenaline-effects but had nearly no effect on terbutaline effects. Thus, in these doses bisoprolol antagonized only beta 1-adrenoceptor mediated effects, propranolol both beta 1- and beta 2-adrenoceptor mediated effects, but both antagonists had no alpha-adrenoceptor antagonistic effects. Dobutamine (1.0-6.0 micrograms/kg/min for 15 min) infusion significantly increased P(syst), but did not significantly affect P(diast) and HR; bisoprolol markedly reduced dobutamine-induced P(syst)-increase. In the presence of propranolol, however, dobutamine caused P(syst)- and P(diast)-increases and HR-decreases. Adrenaline (20-120 ng/kg/min for 15 min) infusion increased P(syst) and HR and decreased P(diast). Bisoprolol did not affect P(syst)- and HR-increases, but significantly attenuated P(diast)-decreases.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis and therapeutic consequences of intramural aortic hematoma

The classical triad of sudden devastating chest pain, electrocardiographic absence of acute myocardial infarction, and identification of an upstream flap in the ascending aorta by transesophageal echocardiography (TEE) indicates aortic type A dissection requiring emergent surgery. Among 34 patients presenting with clinical signs and symptoms of an aortic dissection, three did not show the mandatory flap in the upstream aorta. The only echocardiographic finding was aortic wall thickening indicating an intramural hematoma. Two of these patients showed early aortic ectasia and one showed a pericardial effusion. Despite the missing flap echocardiographically, surgery was performed in all three patients. The surgical approach was the same as that for patients with a type A dissection. Two patients are doing well after the procedure, and one patient died after reoperation. The postoperative histologic work-up confirmed that there was no intimal tear or dissection of the intimal layer. We conclude that the echocardiographic finding of an intramural hematoma combined with typical clinical signs of chest pain, with myocardial infarction ruled out, requires emergent surgical intervention.

[Amebic liver abscess with hepatobronchial fistula]

Four weeks after a holiday in Kenya a 57-year-old woman developed a fever up to 40 degrees C, right upper abdominal pain, icteric sclerae, nausea and vomiting. Laboratory tests revealed leukocytosis (24,400/microliters), markedly accelerated erythrocyte sedimentation rate (123 mm/h) and moderately increased activity of liver enzymes in serum. The liver was unremarkable on ultrasound. Four days after hospitalization the patient complained of dyspnoea and pleuritic pain. Ultrasound examination and computed tomography showed an abscess in the right lobe of the liver. Amoebic abscess of the liver being the most likely diagnosis, although the relevant serological tests were unremarkable and a titre increase occurred only later, treatment was started with metronidazole (four times 500 mg daily intravenously) and paromomycin (three times 10 mg/kg daily). Her condition significantly improved within a day. Two weeks later, however, she developed chest pain, dyspnoea and cough productive of large amounts of white-yellow sputum, even though antibiotic treatment was continuing. A transdiaphragmatic rupture of the abscess with formation of a hepatobronchial fistula proved to be the cause of these symptoms. The patient was treated surgically by drainage and suturing-over of the extensive diaphragmatic defect and after 2 weeks she was discharged symptom-free on a maintenance dose of diloxanide furoate (three times 500 mg/d orally).