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J Am Coll Cardiol, 2000; 35:382-388
© 2000 by the American College of Cardiology Foundation
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CLINICAL STUDIES

Greater late lumen loss after successful coronary balloon angioplasty in the proximal left anterior descending coronary artery is not explained by extent of vessel wall damage or plaque burden

Wouter E. M. Kok, MD*, Ron J. G. Peters, MD{dagger}, Gerard Pasterkamp, MD{ddagger}, Carlo Di Mario, MD§, Patrick W. Serruys, MD, FACC, Martin Prins, MD#, Cees A. Visser, MD, FACC* for the PICTURE study groupg

* Department of Cardiology, Free University Hospital Amsterdam, Amsterdam, the Netherlands
{dagger} Department of Cardiology, Academic Medical Center, Amsterdam, the Netherlands
{ddagger} the Heart Lung Institute, Utrecht University Hospital, Utrecht, the Netherlands
§ Department of Cardiology, Centro Cuore Columbus, Milan, Italy
Department of Cardiology, University Hospital Rotterdam, Rotterdam, the Netherlands
# Department of Clinical Epidemiology, Academic Medical Center, Amsterdam, the Netherlands
g for the PICTURE study group, Interuniversity Cardiology Institute, Utrecht, the Netherlands

Manuscript received August 24, 1998; revised manuscript received September 20, 1999, accepted October 25, 1999.

Reprint requests and correspondence: Dr. Ron J.G. Peters, Department of Cardiology, F3-236, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam Z-O
rjpeters{at}amc.uva.nl


   Abstract
Top
 Abstract
Methods
 Results
 Discussion
 References
 
OBJECTIVES

We investigated whether the greater late lumen loss after coronary balloon angioplasty in the proximal left anterior descending artery (P-LAD) compared with that in other segments might be related to differences in vascular dimensions or morphology as determined by angiography and intravascular ultrasound imaging.

BACKGROUND

The greater late lumen loss after angioplasty in the P-LAD that has been observed in several studies has not been explained.

METHODS

We studied 178 patients and 194 coronary artery lesions by quantitative angiography and 30 MHz intravascular ultrasound imaging after successful balloon angioplasty. Vessel wall morphology was compared among three proximal and three nonproximal segments. Follow-up quantitative angiography for late lumen loss calculation was performed in 168 lesions. Multivariate analysis was used to determine predictors of late lumen loss.

RESULTS

Absolute and relative late loss were significantly greater at the P-LAD compared with the pooled group of other segments (0.42 ± 0.60 mm vs. 0.10 ± 0.48 mm, p = 0.0008 and 0.14 ± 0.24 vs. 0.03 ± 0.17, p < 0.001). Also, a greater percentage of calcific lesions (65% vs. 44%, p = 0.034), a lower incidence of rupture (51% vs. 74%, p = 0.009) and a larger reference segment plaque area (5.4 ± 2.2 mm2 vs. 4.7 ± 1.9 mm2, p = 0.05) were found in the P-LAD. In multivariate analysis however, these variables were not predictive of late loss.

CONCLUSIONS

Greater late lumen loss after coronary balloon angioplasty of the P-LAD is not explained by differences in atherosclerotic plaque burden or in vessel wall damage.

Abbreviations and Acronyms
  ANOVA = analysis of variance
  CV = coefficient of variation
  IVUS = intravascular ultrasound imaging
  MLD = minimal lumen diameter
  P-LAD = proximal left anterior descending artery
  PTCA = percutaneous transluminal coronary angioplasty
  SD = standard deviation

A stenosis in the proximal left anterior descending coronary artery (P-LAD) has been associated with long-term morbidity and mortality (1). Percutaneous transluminal coronary angioplasty (PTCA) is an effective treatment, but several studies have demonstrated a higher restenosis rate at this lesion location compared with that in other segments (2–9) although this finding was not confirmed in other studies (10–14). In a previous report from our group in which intravascular ultrasound imaging (IVUS) was used after successful PTCA, lesion location in the proximal two segments of the left anterior descending coronary artery was independently related to late lumen loss (15). In this study, P-LAD location was restricted to the segment proximal to the first diagonal branch, to confirm the role of this lesion location as a clinical entity (1) as well as to ensure comparability with other studies (2–14). The purpose of our study was to identify morphologic and morphometric parameters possibly explaining the increased late lumen loss after balloon angioplasty in the P-LAD.


   Methods
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 Abstract
 Methods
Results
 Discussion
 References
 
Patients.   The study was part of the Dutch multicenter PICTURE (Post IntraCoronary Treatment Ultrasound Result Evaluation) study (15). Inclusion criteria for patients enrolled in the study were successful coronary balloon angioplasty of a single coronary artery with a proximal reference diameter of at least 2.5 mm. Patients with prior angioplasty at the same site and recent myocardial infarction less than 2 weeks before coronary balloon angioplasty were excluded. All patients gave written, informed consent before the intervention. Follow-up angiography at six months was part of the study protocol. The study was approved by ethics committees of all participating centers. Two hundred patients were enrolled in the study. Fifteen patients had repeat coronary angioplasty or stenting after IVUS without repeat intravascular imaging and were excluded from further analysis. Of the remaining 185 patients, 178 patients and 194 lesions had adequate intravascular ultrasound images. Twenty-five patients were lost to follow-up, leaving a total of 153 patients and 168 lesions to be studied at follow-up. Patient characteristics are presented in Table 1.


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  		Table 1 Patient Characteristics at Baseline

 
Definition of coronary artery segments.   Coronary artery segments were divided into three proximal and three nonproximal segments. The P-LAD was defined as the segment between the branching point off the left main stem and the first diagonal branch. This definition differs from the main study (15) where the P-LAD segment included the segment distal to the first diagonal branch. The proximal right coronary artery segment extended from the right coronary ostium to the first major right ventricular branch. The proximal left circumflex coronary artery segment was demarcated by the branching point with the left main stem and the first marginal branch. Midportions and distal segments of each coronary artery were taken together as distal lesion location.

Quantitative coronary angiography.   Angiography was performed in multiple projections after intracoronary administration of nitroglycerin or isosorbide dinitrate and identical projections were used for follow-up angiography. Quantitative coronary angiographic analysis was performed by the angiography core-lab (Cardialysis, Rotterdam, the Netherlands) using the validated digital CAAS-II system (17). Calibration was performed on saline-filled guiding catheters, and for every participating center, a correction was made for pincushion distortion. Output consisted of the means of the absolute minimal lumen diameters (MLDs) measured in two or more angiographic projections of the vessel segment after coronary balloon angioplasty and at follow-up. The reference lumen diameters were measured using an interpolating algorithm between normal appearing proximal and distal segments on the angiogram. Percent diameter stenosis was calculated as the difference between reference and lumen diameter as percentage of the reference lumen diameter. Balloon-artery-ratio was calculated as the ratio between the nominal balloon size used for PTCA and the reference lumen diameter. Late loss was defined as MLD after balloon angioplasty minus MLD at follow-up and relative late loss was defined as late loss divided by the angiographic reference lumen diameter. Late loss and relative late loss were used as continuous end points in the evaluation of the process of restenosis.

Percutaneous coronary balloon angioplasty.   Using the standard femoral approach, coronary balloon angioplasty was performed with balloon sizes matched to the reference diameters. Success of coronary balloon angioplasty was defined as a residual diameter stenosis smaller than 50% and a diameter stenosis decrease by at least 30% by visual inspection.

Intravascular ultrasound procedure.   We used 30 MHz mechanical monorail IVUS catheters, 4.3F (Cardiovascular Imaging Systems, Sunnyvale, California), 4.1F (DuMED, Rotterdam, the Netherlands) and 3.5F (Hewlett Packard, Andover, Massachusetts) in outer diameter.

The IVUS procedure after successful coronary balloon angioplasty was reported previously (15). In short, after intracoronary administration of nitroglycerin or isosorbide dinitrate, the ultrasound catheter was advanced distally to the previously dilated coronary artery segment and a slow manual pullback maneuver was made until the ultrasound catheter had entered the guiding catheter. The complete ultrasound imaging procedure was recorded on videotape for later review.

Analysis of IVUS.   Intravascular ultrasound recordings were reviewed by a committee of five observers with an independent analysis of each case by at least three observers and a final report made by consensus agreement. The cross-section with the narrowest lumen area during the pullback maneuver in the dilated coronary segment was indicated by a frame number on the videorecording and was used for quantitative IVUS. The echogenicity of the intima at the cross-section with the narrowest lumen area was classified as soft, hard or calcified. Soft was defined as echogenicity less than that of the surrounding adventitia, hard was defined as echogenicity equal or more bright than that of the surrounding adventitia. In the presence of a circumferential calcium arc of equal or greater than 90 degrees, the lesion was classified as calcified. The entire dilated segment was analyzed for the presence of plaque tears. A rupture was defined as a plaque tear perpendicular to the vessel wall layers; a dissection was defined as a plaque tear parallel to the vessel wall layers. Location of the tear was related to the narrowest site as distal, at or proximal. For this study, only tears present at the narrowest site were used for analysis.

Two observers independently analyzed the narrowest cross-section in the dilated segment as indicated by a video-frame number on the report form. Measurements were made on digitized video-frames using a previously validated software program that permits distance measurements and manual contour tracings for area measurements (18). Lumen area included the dissected or ruptured spaces. Vessel area was defined as the area confined by the adventitia, including the media. Plaque area was calculated from the difference between vessel area and lumen area. Obstruction was calculated as the percent vessel area occupied by plaque area. In addition to the analysis of the narrowest cross-section, the same observers also analyzed the proximal and distal reference segments. A reference segment was defined as the segment with the least amount of plaque area outside the balloon area, without crossing any large side-branch. Lumen area and vessel area were measured at proximal and distal reference segments, and the means of the two reference segments were used. All measurements of the two observers were averaged. Interobserver variability of these measurements was as follows. For lumen area, the standard deviation of mean difference (SD) was 0.66 mm2 and the coefficient of variation (CV) was 12.6%, for plaque area SD was 1.34 mm2 and CV 15.7%, for vessel area SD was 1.43 mm2 and CV 10.4% and for percent obstruction SD was 5.22% and CV 8.6%.

Statistical analysis.   Statistical analysis was performed using SPSS 8.0. Continuous variables were compared by a two-factor model analysis of variance (ANOVA) with post-hoc Bonferroni correction to discriminate between effects of proximal and distal lesion location and coronary artery, also testing their interaction. To find dimensional characteristics prevalent in the P-LAD that may have been missed by comparison between small numbers of segments, we compared dimensions between the P-LAD and the pooled group of other segments using the two-sided t test and for categorical variables the nonparametric Mann-Whitney U test. Univariate variables that were shown to be different (p < 0.1) between P-LAD location and other locations were entered in a stepwise linear regression analysis of late lumen loss and relative late lumen loss, with inclusion of variables when probability of F ≤ 0.05 and exclusion when probability of F ≥ 1.0. Additional variables were entered that were found to be predictive of lumen loss in the previous study (P-LAD lesion location, angiographic MLD after PTCA, percent diameter stenosis after PTCA and dissection on IVUS after PTCA). Statistical significance was accepted at p < 0.05.


   Results
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 Abstract
 Methods
 Results
Discussion
 References
 
Patient baseline characteristics are shown in Table 1. No differences between the 43 patients with stenosis in the P-LAD and other patients were found for age, sex, risk factors for coronary artery disease, unstable or stable angina pectoris. Angiographic follow-up was available in 38 P-LAD lesions (88%) and in 130 lesions (86.1%) of other segments.

Late loss and relative late loss.   Late loss was significantly different between proximally and distally located segments but not between coronary arteries (Table 2). Post-hoc analysis showed that the largest and only significant differences occurred between the P-LAD and lesion location in distal left anterior descending coronary artery and distal right coronary artery. Late loss at the P-LAD was significantly larger than at other lesion locations (0.42 ± 0.6 mm vs. 0.10 ± 0.48 mm, p = 0.0008). Distribution of late loss in a cumulative frequency diagram in the P-LAD versus other segments is shown in Figure 1A.


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  		Table 2 Late Lumen Loss and Relative Late Lumen Loss in Different Segments

 


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  		Figure 1 Cumulative frequency distribution of (A) late lumen loss (mm) and (B) relative late lumen loss after PTCA in the proximal left anterior descending coronary artery (LAD prox) lesions compared with other lesions.

 
Relative late loss was also different between proximal and distal lesion locations, albeit of lesser magnitude, while no difference was detected between coronary arteries (Table 2). Post-hoc analysis demonstrated a significantly increased relative late loss in the P-LAD versus the distal left anterior descending and distal right coronary artery. Again, in the P-LAD, relative late loss was significantly larger than at other lesion locations (0.14 ± 0.21 vs. 0.03 ± 0.17, p = 0.001, distribution curves are shown in Fig. 1B).

Angiographic and intravascular ultrasound dimensions after balloon angioplasty.   Although significant differences (by two-factorial ANOVA) between the segments were found in MLD, reference lumen diameter, lumen area, vessel area and plaque area, they occurred primarily between coronary arteries, proximal or distal lesion location being less important (Table 3). Post-hoc tests, however, showed only few significant differences between P-LAD and the distal left anterior descending segment, i.e., in MLD, reference diameter, vessel area and plaque area. The P-LAD segments and the pooled group of other segments had a similar MLD after coronary angioplasty (1.89 ± 0.36 mm vs. 1.82 ± 0.39 mm, p = 0.30), similar reference lumen diameter after angioplasty (2.95 ± 0.48 mm vs. 2.92 ± 0.48 mm, p = 0.72), similar percent diameter stenosis (35.9 ± 8.4% vs. 37.8 ± 8.6%, p = 0.20) and similar balloon-artery-ratio (1.08 ± 0.18 vs. 1.09 ± 0.23, p = 0.83). Comparison of ultrasound dimensions between P-LAD segments and other segments revealed no significant differences in lumen area (5.4 ± 1.7 mm2 vs. 5.2 ± 1.7 mm2, p = 0.49), vessel area (14.8 ± 3.5 mm2 vs. 13.7 ± 4.3 mm2, p = 0.13), plaque area (9.4 ± 2.5 mm2 vs. 8.5 ± 3.4 mm2, p = 0.10) or in percent obstruction (63.1 ± 7.5% vs. 60.7 ± 9.0%, p = 0.11). Ultrasound dimensions at the reference segments showed slight differences between P-LAD segments and other segments in percent obstruction (36.9 ± 11.5% vs. 34.2 ± 8.5%, p = 0.09) and plaque area (5.4 ± 2.2 mm2 vs. 4.7 ± 1.9 mm2, p = 0.05), while no significant differences were found in lumen area (8.9 ± 2.4 mm2 vs. 8.7 ± 3.0 mm2, p = 0.73) or in vessel area (14.3 ± 3.1 mm2 vs. 13.5 ± 4.3 mm2, p = 0.26). The only consistent differences between segments that were accounted for by the P-LAD lesion location were, therefore, the reference plaque area and reference percent obstruction.


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  		Table 3 Distribution of Angiographic and IVUS Dimensions After PTCA Among Different Segments

 
Vessel wall damage and lesion type at coronary segments.   Comparison between segments in the P-LAD and the pooled group of other lesion locations revealed significant differences in lesion type (soft: 33% vs. 45%, hard: 2% vs. 11%, calcified: 65% vs. 44%, Mann-Whitney U test, p = 0.01) and presence of rupture (51% vs. 74%, Mann-Whitney U test, p = 0.06), while similar distributions were found for presence of dissection (40% and 46%, Mann-Whitney U test, p = 0.53).

Multivariate analysis of determinants of increased late loss at the proximal left anterior descending coronary artery.   Variables that were different between the P-LAD and other segments were entered in multivariate analysis of late lumen loss, i.e., presence of rupture, calcified segments, reference plaque area and reference obstruction. No predictor of late lumen loss was found among these variables that could substitute and explain the effect of the P-LAD lesion location on late lumen loss. However, as in our previous study, lesion location at the P-LAD, postintervention MLD and absence of dissection as demonstrated with IVUS were independent predictors of late loss (Table 4). Analysis of relative late lumen loss, using the same variables, demonstrated the following independent predictors: lesion location at the P-LAD, absence of dissection on IVUS and percent diameter stenosis after balloon angioplasty (Table 4).


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  		Table 4 Multivariate Predictors of Late Lumen Loss and Relative Late Lumen Loss

 

   Discussion
Top
 Abstract
 Methods
 Results
 Discussion
References
 
This study sought to find angiographic and IVUS morphologic differences after PTCA between the P-LAD and other coronary artery segments in order to explain the increased late lumen loss at the P-LAD, observed in our previous study (15). This study redefined the P-LAD according to other studies (2–14) and confirms other studies (3,7,9) in a significantly increased late lumen loss after PTCA in the P-LAD segment. This finding can also be translated in increased restenosis percentage, which, in our study, was found in 39.5% of the P-LAD lesions versus 28.5% in other segments, with a relative risk of 1.39 (p = 0.23). This observation is in agreement with studies, demonstrating a higher restenosis percentage at this lesion location with relative risk varying from 1.2 to 2.2 (2–9).

From large scale studies (9,14) it is clear that vessel size is a major determinant of late lumen loss. To account for differences in vessel size, relative late lumen loss (14) was calculated. Relative late lumen loss in the P-LAD in our study was significantly higher than in other lesion locations (14% vs. 3%); therefore, vessel size in our study was not a confounding factor.

Our data were analyzed per lesion. To exclude the possibility of a bias toward patient-related restenosis risk, analysis was also performed using one lesion per patient. Late lumen loss was 0.42 ± 0.61 mm in the P-LAD (n = 38) versus 0.11 ± 0.45 mm in 114 other lesions (p = 0.01). Patient-based stepwise linear regression analysis revealed the same predictors of late lumen loss as were found in the lesion-based analysis, i.e., P-LAD location, postintervention MLD and dissection in IVUS, with the same explanatory power (R2 = 0.13).

The hypothesis of advanced atherosclerosis in the P-LAD as a possible explanation of increased lumen loss fails.   The hypothesis of the influence on outcome after PTCA by a different morphologic appearance of P-LAD segments compared with other segments was based on several observations. Advanced atherosclerosis has been demonstrated in pathology studies in proximal segments of the coronary artery tree (19,20) and in segments near bifurcations or side-branches such as the P-LAD (21,22). Parameters of atherosclerosis such as type of lesion and plaque area, obtained after PTCA as in our study, were expected to differ with only minor changes from morphology before PTCA since the impact of PTCA on reduction of the atherosclerotic plaque burden is only 4% to 12% of the plaque area present before angioplasty (23,24). In this study, plaque area, percent obstruction and reference plaque area were, however, only slightly greater in the P-LAD compared with the pooled group of other segments and did not contribute to increased late lumen loss in the P-LAD. Similarly, although a higher calcific content was found in the P-LAD segments—as would be expected in advanced atherosclerotic lesions (21)—we did not find an influence of calcification on late lumen loss. The hypothesis of advanced atherosclerosis as predictor of later restenosis may be endorsed by the finding of Mintz et al. (25) of the predictive value of residual plaque burden to restenosis after transcatheter nonstenting coronary procedures. However, it has also been previously demonstrated that angiographic restenosis is not explained by greater plaque burden at follow-up (26). Instead, vessel wall remodelling may determine lumen preservation or degradation at follow-up (26). In this respect, it has been reported that de novo atherosclerotic lesions in the P-LAD lack the possibility of compensatory enlargement (27). An alternative explanation of increased restenosis in the P-LAD could therefore be the failure of compensatory enlargement in this particular lesion type after PTCA and higher chance of constrictive remodelling in the P-LAD than in other segments.

Clinical implications.   Interventions other than PTCA have been used for the treatment of stenosis in the P-LAD. In the Coronary Angioplasty Versus Excisional Atherectomy Trial (CAVEAT) and Canadian Coronary Atherectomy Trial (CCAT) studies (28), directional atherectomy was compared with conventional coronary balloon angioplasty. Atherectomy in the P-LAD resulted in a greater initial lumen gain than in balloon angioplasty but was followed by increased late lumen loss, resulting in no net benefit over the result obtained by PTCA (28). A recent trial comparing stent placement to PTCA in the P-LAD demonstrated a significant reduction in restenosis despite a significantly increased late lumen loss after stent placement (29). Apart from suggesting improved treatment of P-LAD lesions by stent placement, these trials support the role of vascular remodelling independent of residual plaque burden as the cause of late lumen loss.

Study limitations.   We did not perform IVUS or quantitative angiography before coronary balloon angioplasty. Lumen gain and stretching of the vessel wall could therefore not be measured. Late lumen loss has been related to acute gain after any coronary intervention (30). Choice of balloon size in our study was well matched with the angiographic reference diameter in all vessels studied (Table 2), and the results cannot be explained by a more or less aggressive angioplasty approach in P-LAD segments. On the contrary, advanced atherosclerosis as we have found with more calcified plaques and with greater plaque burden in reference segments of the P-LAD may have decreased the amount of stretch by balloon dilatation by using undersized balloons for this lesion location as compared with balloon sizes for other segments with less plaque at the reference segments. So if any influence of lumen gain would have occurred on the late lumen loss, it would have resulted in decreased gain and therefore decreased loss in the P-LAD segment, which was not the case. A second limitation of our study is that the differences found in late lumen loss between segments of the coronary tree may have been increased by a relatively decreased lumen loss at distal segments, compared with findings in other studies (14). Notwithstanding this limitation, late lumen loss in the P-LAD was comparable with late lumen loss in other studies, demonstrating an increased late lumen loss in similar sized P-LAD’s (28–30). Finally, the explanatory power of the model for late lumen loss was low (12% of variance), and the P-LAD location alone explained 7% of variance of late lumen loss. This underscores the importance of other, unknown factors related to the mechanism(s) of vascular remodelling.

Conclusion.   The P-LAD is subjected to greater late lumen loss at follow-up after PTCA than other coronary segments. Plaque characteristics determined by IVUS and dimensional variables determined by IVUS or coronary angiography did not explain this observation.


   Footnotes
 
This study was supported by a grant from the Netherlands Heart Foundation.


   References
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 Abstract
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 Discussion
 References
 

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