Prediction of Restenosis After Coronary Balloon Angioplasty
Results of PICTURE (Post–IntraCoronary Treatment Ultrasound Result Evaluation), a Prospective Multicenter Intracoronary Ultrasound Imaging Study
Background Intracoronary ultrasound (ICUS) imaging is potentially suitable to identify lesions at high risk of restenosis after percutaneous transluminal coronary angioplasty (PTCA), but it has not been studied systematically.
Methods and Results We recruited 200 patients in whom ICUS studies were performed after successful PTCA and related their ICUS parameters to 6-month follow-up quantitative coronary angiography. This was performed in 164 patients (82%), yielding 170 lesions for analysis. The overall incidence of a ≥50% diameter stenosis at follow-up (categorical restenosis) was 29.4%. Quantitative ICUS parameters were weakly but significantly related to follow-up minimal luminal diameter on quantitative coronary angiography (lumen area: R2=.36, P=.0001; vessel area: R2=.29, P=.0002; plaque area: R2=−.18, P=.021; percent obstruction: R2=−.15, P=.05), but categorical restenosis was not significantly related to these parameters (P=.63, .77, .38, and .08, respectively). There were no significant predictors of restenosis in ICUS parameters of plaque morphology: eccentric versus concentric (P=1.0), plaque type (hard, soft, or calcific, P=.98), or the number of calcified quadrants (P=.41). There were no significant predictors of restenosis in two predefined types of vessel-wall disruptions: (1) rupture: presence (P=.79), depth (partial versus complete, P=.85), or extent in quadrants (P=.6), and (2) dissection: presence (P=.31), depth (P=.82), or extent (P=.38).
Conclusions Qualitative ICUS parameters after PTCA did not predict restenosis. A larger lumen and vessel area and a smaller plaque area by ICUS were associated with a larger angiographic minimal lumen diameter at follow-up, but these parameters were not significantly related to categorical restenosis.
Coronary artery restenosis remains a major limitation of PTCA, and a method to identify lesions at high risk for this complication immediately after the procedure is urgently needed. Patient-related predictors of restenosis have been described, such as age, diabetes mellitus, duration of anginal complaints, and unstable angina pectoris.1 2 3 4 5 A number of angiographic lesion-related predictors have also been reported. However, these findings have not been consistent in various reports,4 5 6 7 and their predictive power is very limited.
Because angiography provides information on the lumen only, information on vessel-wall morphology is very limited,8 and this technique therefore may not be sufficiently sensitive to detect morphological predictors of restenosis after PTCA. ICUS provides direct in vivo morphological and quantitative information on the vessel wall and atherosclerotic plaque9 10 11 12 and on the presence and extent of the disruptions resulting from the intervention.13 14 15 It was therefore thought to be very suitable for the study of lesion-related predictors of restenosis. However, the study of restenosis after PTCA by ICUS has been limited to a number of relatively small series with inconclusive results.14 16 We conducted a prospective multicenter study in 200 patients to establish whether morphological features of the dilated segment, as assessed by ICUS after the procedure, are predictive of subsequent restenosis.
Patients were included in the study if they met the following criteria: (1) successful PTCA of a single coronary artery, defined as a decrease of ≥30% in angiographic diameter stenosis after PTCA, a residual diameter stenosis <50% (by visual assessment), and normal blood flow in the dilated artery (TIMI grade 3); and (2) reference diameter of the target vessel ≥2.5 mm.
Exclusion criteria included the following: (1) prior PTCA at the same site; (2) acute myocardial infarction <2 weeks before PTCA; (3) prominent coronary spasm; and (4) sharp bends and curves proximal to the segment of interest, precluding the passage of the ICUS catheter. Informed consent was obtained from all patients, and the protocol was approved by the local ethics committees of all participating centers. The centers and investigators participating in the study are listed in the “Appendix.”
Standard PTCA was performed from the femoral artery approach. Balloon size was chosen with a nominal diameter to match the angiographic lumen diameter of an adjacent segment that appeared normal on the angiogram. The number of balloons and the number and pressure of the inflations were left to the discretion of the operator and were based on angiography only. After completion of the procedure, when the angiographic result met the inclusion criteria, the dilated artery was studied by ICUS (see below). If, in spite of a satisfactory initial result, the operator could not accept the angiographic appearance of the lesion after completion of the ICUS study (because of deterioration that had occurred during the time required for the ICUS study), by protocol a second ICUS study was performed after additional balloon inflations, and only this second study was used for analysis. After the ICUS study, QCA was performed. Follow-up coronary angiography was performed after 6 months. If symptoms recurred within 6 months, coronary angiography was performed earlier. If angiography was performed within 4 months but the index lesion was not redilated, the protocol required that angiography be repeated at 6 months.
The angiograms after the ICUS study and at 6-month follow-up were recorded after intracoronary injection of isosorbide dinitrate or nitroglycerin. At least two orthogonal projections were selected for analysis, and these projections were repeated at follow-up. To standardize the method of data acquisition and to ensure exact reproducibility of the angiographic studies, measurements were taken as described previously.17 18 For calibration purposes, the catheter tip was cut off for later measurement with a microcaliper. All angiograms were analyzed by a central core laboratory (Cardialysis, Rotterdam, Netherlands) using the computer-assisted CAAS-II technique, which has been described and validated previously.19 20 Restenosis, the primary end point of the study, was analyzed in two ways: as a binary definition of ≥50% diameter stenosis in the dilated lesion at follow-up and as a continuous variable, both as absolute MLD and as reduction in absolute luminal diameter in the dilated lesion at follow-up (“late loss”).
ICUS Imaging Protocol
All ICUS studies were performed with three mechanical, single-element, 30-MHz systems: (1) the Insight system (Cardiovascular Imaging Systems Inc) using 4.3F catheters, (2) the Intrasound system (Du-MED) using 4.1F catheters; and (3) the Boston Scientific system using 3.5F catheters with a Hewlett-Packard ICUS console.
After completion of the PTCA procedure, if the patient fulfilled the criteria mentioned above, intracoronary nitroglycerin or isosorbide dinitrate was administered and an ICUS catheter was introduced over the guidewire left in place after PTCA. Settings for gain and filters were adjusted to result in an optimal visual image. The entire procedure was stored on VHS or super VHS videotape, including annotations and audio recordings. The ICUS catheter was advanced to the dilated segment for close examination of vessel morphology and disruptions. At the narrowest site, 10 mL of saline and x-ray contrast flushes through the guiding catheter were performed to facilitate the recognition of disruptions and to confirm that the narrowest point on angiography was being examined. Additional flushing at other sites was left to the discretion of the operator. The timing of this flushing and of all other relevant events during the ICUS study was marked by voice recordings on the videotape. After the morphology was carefully explored, the transducer was advanced to a site distal to the lesion, and a slow, manual pullback maneuver was performed until the transducer reached the guiding catheter.
After the ICUS study, both the catheter and the guidewire were removed and a final angiogram (for quantitative analysis) was made.
Ultrasound Image Analysis
All images were analyzed by a committee of five observers (see “Appendix”) unaware of the results of angiography and follow-up examinations. Qualitative analysis of the images was performed independently by each member of the committee on a dedicated form, and all cases were reviewed in a panel discussion to reach consensus on all diagnostic parameters. The analysis consisted of two parts. First, the entire dilated segment was analyzed qualitatively (see below). Second, a single video frame in the cross section with the smallest lumen area (visually) was indicated as the narrowest site of the dilated lesion. This cross section was used for quantitative analysis (see below).
The following parameters (with definitions where appropriate) were assessed: image quality, classified as either acceptable or not acceptable; lesion morphology, classified as either eccentric or concentric (maximal plaque thickness/minimal plaque thickness ≥2 or <2, respectively) (this was performed subjectively because in the complex post-PTCA ultrasound images of dilated lesions, the accepted criteria for eccentricity cannot be applied); lesion type, classified as soft (less echogenic than adventitia), hard (as echogenic as adventitia), or calcific (at least one quadrant of calcium present)12 21 ; calcium (defined as dense reflections with acoustic shadowing9 11 ), with the number of deposits, their location relative to the narrowest point, their cumulative arc (in hours) in the dilated segment, and their depth (superficial, defined as no tissue between the deposit and the lumen; deep, all other depths; or both); rupture of the vessel wall, defined as a radial tear, ie, perpendicular to the vessel-wall layers; and dissection of the vessel wall, defined as a tear parallel to the vessel-wall layers. Regarding these disruptions, the following characteristics were noted: (1) location relative to the narrowest point; (2) the total circumferential arc in hours (with a minimum of 1); (3) maximal depth, classified as either partial (some plaque remaining intact between the rupture and the underlying media) or complete (extending through the plaque completely); and (4) the presence of calcium adjacent to the tear. Thrombus was not diagnosed by ICUS because the investigators did not feel confident making this diagnosis with existing criteria.22 23
Measurements on the cross section designated as the narrowest point in the panel discussion were performed independently by two observers (W.E.M.K. and G.P.). After calibration by use of the markers in the ICUS image, the circumference of the lumen (including extensions created by ruptures or dissections) and of the media/adventitia border were traced manually by use of computer-assisted planimetry24 (Fig 1⇓). If part of the media-adventitia interface was invisible owing to shadowing behind calcium deposits, the tracing was extrapolated from the adjacent sectors of the circumference. In cross sections with more than one quadrant of acoustic shadowing, the tracing was extrapolated from neighboring cross sections, as described by others.25 All tracings were performed according to the consensus interpretation of the image. From this, the following parameters were derived: lumen area, vessel area (area encompassed by the media-adventitia border), plaque area (defined as Vessel Area−Lumen Area), and percent obstruction (defined as [Plaque Area/Vessel Area]×100). The mean value of the two independent measurements for each parameter was entered in the database.
Interobserver variation of the measurements (199 baseline ICUS studies) was as follows: minimal lumen area, SD=0.66 mm2, CV=12.6%; plaque area, SD=1.34 mm2, CV=15.7%; vessel area, SD=1.43 mm2, CV=10.4%; and percent obstruction, SD=5.22%, CV=8.6%. Consistent errors were 0.02 mm2 for lumen area, −0.20 mm2 for vessel area, −0.22 mm2 for plaque area, and −0.89% for percent obstruction. Exclusion of lesions with more than one quadrant of calcium did not significantly alter the reproducibility.
All variables were related to measures of restenosis in univariate analysis by use of the unpaired Student's t test, ANOVA, and χ2 tests where appropriate. Variables significantly related to restenosis in univariate analysis were analyzed in multivariate analysis. For late loss, stepwise linear regression analysis was performed. For categorical restenosis, stepwise logistic regression analysis was performed.
ICUS imaging was performed after PTCA in 200 patients. The PTCA operator did not accept the angiographic appearance of the lesion after completion of the ICUS study in 46 patients because early loss of initial result (<30 minutes) occurred during the ICUS study. In 35 of these cases, a second ICUS study was performed after additional balloon inflations. The remaining 11 were excluded from the analysis because of stenting, refusal of a repeat ICUS study by the patient or physician, or incomplete data. Of the 200 patients included, 164 returned for repeat angiography (82%) within 6 months, with a total of 178 lesions. In 170 lesions (96%) in 154 patients, an acceptable ICUS examination was available, and these lesions were used in the analysis.
Baseline characteristics and procedural results of the patients included in the analysis are summarized in Table 1⇓. These characteristics did not differ from those of the entire study group (n=200). Tables 2⇓ and 3⇓ summarize the angiographic findings after PTCA and at follow-up. There was little late loss at follow-up (average of 0.17±0.51 mm), but otherwise the results were as expected for balloon angioplasty. Clinical parameters, such as age, sex, diabetes, or the duration of anginal complaints, had no predictive value for angiographic restenosis in univariate analysis. The MLD after intervention was significantly greater in lesions that did not develop a ≥50% diameter stenosis than in those that did, and similarly, percent diameter stenosis was greatest in the group with restenosis (Table 3⇓). Qualitative ICUS parameters and their relation with angiography are summarized in Table 4⇓. No significant relations with restenosis were found. The relation between ruptures and dissections on ICUS imaging and the MLD as a continuous variable at follow-up angiography is presented in Figs 2⇓ and 3⇓. The presence of these disruptions in the dilated segment did not significantly influence the MLD at follow-up. Fig 4⇓ presents the relation between quantitative ICUS parameters and categorical angiographic restenosis. No significant differences were found between the groups with and without categorical restenosis. In univariate analysis, quantitative ICUS parameters showed significant relations with the angiographic MLD and late luminal loss at follow-up (Table 5⇓). In logistic regression analysis, no parameter was significantly related to categorical restenosis. Five parameters (Table 6⇓) showed a statistically significant relation in multivariate analysis with late luminal loss on angiography. Of these, dissection at the narrowest point of the dilated segment was the only ICUS parameter with a significant relation. It was the strongest predictor of late loss (P=.009), but the predictive value was low (partial R2=.041). On the basis of observations by Honye et al,14 we compared concentric lesions without disruptions to all others. Restenosis rates were similar (2 [20%] of 10 versus 48 [30%] of 160, respectively; P=.72). Exclusion of the 35 patients in whom a second ICUS study was performed after additional balloon inflations did not alter the results of any of the comparisons. Similarly, exclusion of lesions with more than one quadrant of calcium (n=97) did not alter any of the results.
This study was designed to identify ICUS characteristics of dilated coronary arterial wall segments that would predict the development of restenosis after successful PTCA. This study represents the largest series of patients specifically studied for this purpose. The type and extent of vessel-wall disruption were not related to angiographic dimensions, either directly after the procedure or at follow-up, with the exception of dissection diagnosed at the narrowest cross section, which was associated with a larger MLD at follow-up. However, this was not associated with a statistically significant difference in the incidence of a ≥50% diameter stenosis at follow-up.
Quantitative ICUS parameters were not significantly associated with ≥50% diameter stenosis at follow-up, although there was a trend toward a greater extent of percent obstruction in the restenosis group, consistent with other reports.28 29 30 However, there were significant relations in univariate analysis between quantitative ICUS parameters and MLD at follow-up and late luminal loss. These relations were weak, but they are consistent with the angiographic findings of the present study and other angiographic restenosis studies6 31 and with the previously mentioned ICUS studies.28 29 30 They support the concept that residual stenosis is a significant component of the restenosis problem and that strategies aimed at reducing restenosis should include the achievement of a maximal initial result.
Until recently, the prevailing hypothesis on the mechanism of restenosis was that neointima formation is the predominant factor leading to a decrease of luminal dimensions. It has been suggested that the response of neointimal formation is related to the severity of the damage inflicted on the vessel wall during PTCA,32 33 34 and therefore the demonstration of such disruptions by ICUS could provide prognostic information. As outlined above, we did not find such a relationship.
The lack of success of trials aimed at limiting neointimal growth35 suggests that neointima formation may not be the most important factor. There is now evidence that other mechanisms dominate the development of restenosis. In particular, ICUS studies have shown that geometric remodeling is responsible for ≈60% to 80% of late luminal loss after transcatheter intracoronary interventions.36 37 38 Our study could not confirm these findings because no follow-up ultrasound studies were performed. It is presently unknown which factors determine the magnitude and direction of geometric remodeling.
Considering the proposed mechanisms of restenosis outlined above, the absence of a relationship between ICUS-determined disruptions and restenosis is unexpected. However, our results confirm previous preliminary studies.13 16 As described above, we could not confirm the conclusion of Honye et al14 that concentric lesions without disruptions are predisposed to restenosis.
ICUS parameters appear to be more predictive of restenosis in studies of mixed interventional devices (balloon angioplasty, rotational and directional atherectomy, laser angioplasty).31 39 40 41 In these series, a larger lumen and smaller plaque burden at the end of the intervention were consistently associated with lower restenosis rates. However, it is difficult to compare studies with mixed interventional devices with those concerning PTCA only, such as the present study. First, it is conceivable that plaque removal (and mechanical scaffolding of the vessel wall) results in different mechanisms of vessel-wall remodeling and different degrees of intimal hyperplasia compared with PTCA. Second, the coronary arteries studied in these series were generally larger than those in PICTURE, presumably because of the inclusion of cases selected for directional atherectomy. This may affect the restenosis rates, because vessel size is one of the determinants of restenosis in multivariate analysis.7 42 Third, in most of the series with mixed devices described above, the selection of the therapeutic modality was based on preintervention ICUS studies, which results in selection of lesion types for the different devices. This selection makes a comparison with our results difficult. Consequently, ICUS may yield useful predictors in patients treated with other transcatheter devices, and this should be explored further.
There are several limitations to this study. We included nontortuous coronary arteries, and a satisfactory angiographic result was required. These criteria may have resulted in the selection of favorable cases.
The late loss in MLD observed by QCA (0.17 mm) is low compared with other reports. With an average reference-segment diameter of 2.95 mm, a mean late loss of ≈0.26 mm is expected.42 Several factors may contribute to this discrepancy. First, although percent diameter stenosis was <50% visually in all lesions (inclusion criterion), there was in fact a >50% diameter stenosis on off-line QCA in 17 lesions (10%). In these cases, late loss is expected to be lower, and categorical 6-month restenosis (>50%) is actually pseudorestenosis. This may explain why a normal incidence (29.4%) of categorical restenosis was found in spite of the limited late loss. Second, it is possible that in the lesions with additional balloon dilations after the initial ICUS study, the early component of MLD loss was abolished, thereby lowering total 6-month loss.
We found a trend toward a greater percent area obstruction on ICUS in the restenosis group. With a greater number of observations, this relation would possibly reach statistical significance, consistent with the findings of others.28 29 30 It is doubtful, however, if the difference could reach clinical significance.
The use of an early generation of ICUS catheters may have influenced the results in two ways. First, image quality was not yet optimal. Second, the relatively large diameter of the catheters may have resulted in false-negative observations on vessel-wall dissections because the catheters may have “tacked” intimal flaps during the ICUS study. However, with a rupture incidence of 89% on ICUS, it is not likely that we have underestimated the degree of vessel-wall damage.Potentially, the patients who had additional dilations after the ICUS examination were a specific subgroup at high risk. By using the second, final ICUS examination for analysis, predictors present in the first ICUS examination may have remained undetected. However, it is unlikely that plaque composition is altered by additional dilations, and the incidence of disruptions remained high. In addition, we repeated the analysis of the relation of vessel-wall disruptions and restenosis after exclusion of this subgroup of patients, and this did not alter the findings.
We conclude that after angiographically and clinically successful balloon angioplasty, a larger lumen and vessel area and a smaller plaque area as determined by ICUS were associated with a larger angiographic MLD at follow-up. However, these relations were weak, and the study did not identify ICUS parameters predictive of restenosis after PTCA.
Interuniversity Cardiology Institute of the Netherlands: Klaas Bom, PhD; Elma J. Gussenhoven, MD; Hans Rijsterborgh, PhD (†deceased).
Academic Hospital Free University, Amsterdam, Netherlands: Otto Kamp, MD (center coordinator); Jean G.F. Bronswaer, MD; Carel C. de Cock, MD; Cees A. Visser, MD.
Academic Hospital, University of Leiden, Netherlands: Lucas Savalle, MD (center coordinator); Bert Buys, MD (†deceased).
Academic Hospital, University of Maastricht, Netherlands: Frits W.H.M. Bär, MD (center coordinator); H. Quint.
Academic Hospital, University of Amsterdam, Netherlands: George K. David, MD; Karel T. Koch, MD; Wouter E.M. Kok, MD (center coordinator); Ron J.G. Peters, MD (principal investigator); Jan J. Piek, MD.
Academic Hospital, University of Utrecht, Netherlands: Piet W. Westerhof, MD; Cornelius Borst, MD; Gerard Pasterkamp, MD (center coordinator).
Sint Antonius Hospital, Nieuwegein, Netherlands: W. Jaarsma, MD (center coordinator); H.W. Thijs Plokker, MD; V. Radjan N. Panday, MD.
Thoraxcenter, Academic Hospital Dijkzigt, Erasmus University, Rotterdam, Netherlands: Pim J. de Feyter, MD; David T. Linker, MD; Carlo di Mario, MD (center coordinator); Patrick W. Serruys, MD.
Department of Clinical Epidemiology and Biostatistics, Academic Medical Center, Amsterdam, Netherlands: Martin H. Prins, MD.
Angiographic Core Laboratory
Cardialysis, Rotterdam, Netherlands: Eline Montauban van Swijndrecht, Edwin Mibbering, Patrick W. Serruys.
ICUS Analysis Committee
Otto Kamp, MD; Wouter E.M. Kok, MD; Carlo di Mario, MD; Gerard Pasterkamp, MD; Ron J.G. Peters, MD.
Selected Abbreviations and Acronyms
|CV||=||coefficient of variation|
|MLD||=||minimal lumen diameter|
|PICTURE||=||Post–IntraCoronary Treatment Ultrasound Result Evaluation|
|TCA||=||percutaneous transluminal coronary angioplasty|
|QCA||=||quantitative coronary angiography|
This study was supported by a grant from the Netherlands Heart Foundation, and the protocol was approved by The Netherlands Organisation for Scientific Research (0706/900-574-003).
- Received September 5, 1996.
- Revision received November 25, 1996.
- Accepted December 16, 1996.
- Copyright © 1997 by American Heart Association
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