Author + information
- Received February 6, 2012
- Revision received March 26, 2012
- Accepted May 12, 2012
- Published online August 1, 2012.
- Jin Joo Park, MD⁎,
- In-Ho Chae, MD†,
- Young-Seok Cho, MD†,⁎ (, )
- Seong-Wook Kim, BS†,
- Han-Mo Yang, MD⁎,
- Jae-Bin Seo, MD‡,
- Song-Yi Kim, MD§,
- Il-Young Oh, MD†,
- Chang-Hwan Yoon, MD†,
- Jung-Won Suh, MD†,
- Kyung-Woo Park, MD⁎,
- Woo-Young Chung, MD‡,
- Tae-Jin Youn, MD†,
- Dong-Ju Choi, MD† and
- Hyo-Soo Kim, MD⁎
- ↵⁎Reprint requests and correspondence
: Dr. Young-Seok Cho, Internal Medicine, Seoul National University Bundang Hospital, 166 Gumi-ro, Bundang, Seongnam 463-707, South Korea
Objectives This study sought to investigate the extent of and factors related to lumen and vessel area change in coronary arteries after total occlusion (TO) recanalization.
Background TO of a coronary artery promotes negative remodeling in distal reference segments. Recanalization can restore blood flow, potentially leading to positive vascular remodeling.
Methods From March 2005 to June 2008, 58 consecutive patients with de novo TO lesions of at least 1-month duration were enrolled. We performed intravascular ultrasound after successful percutaneous coronary intervention and at the 6-month follow-up, and we quantified changes in the distal reference segments.
Results At the 6-month follow-up, there was a significant increase in the mean lumen diameter (+0.21 mm, p = 0.001), the mean external elastic membrane diameter (+0.13 mm, p = 0.010), the lumen area (+0.87 mm2, p < 0.001), and the external elastic membrane area (+0.85 mm2, p = 0.001) in the distal reference segments and an increase in the left ventricular ejection fraction (+2.77%, p = 0.010). Overall, 40 of 58 patients (69%) showed lumen area increase; these patients had increase in lumen diameter by 0.40 ± 0.34 mm (p < 0.001) and increase in incomplete stent apposition rate (p = 0.006). A TO duration of longer than 3 months (odds ratio [OR]: 14.8; 95% confidence interval [CI]: 1.28 to 172.8, p = 0.032), a poor collateral flow (OR: 12.0; 95% CI: 1.92 to 74.2, p = 0.008), and statin use (OR: 7.4; 95% CI: 1.03 to 53.6, p = 0.047) were independent predictors of lumen area increase.
Conclusions Recanalization of TO led to lumen area increase in two-thirds of the patients. Independent predictors of lumen area increase were occlusion duration, a poor collateral flow, and statin use. These factors could be used as guides in choosing the optimal stent size during percutaneous coronary intervention to TO lesions and optimal medical therapy during follow-up.
- collateral circulation
- coronary occlusion
- coronary vessels
- interventional ultrasonography
- myocardial revascularization
Vascular remodeling is a homeostatic response to changes in flow and circumferential stretch to maintain or restore normal shear stress and wall tension (1). In the presence of stable atherosclerotic lesions, the remodeling process primarily causes luminal narrowing of the lesional and extra-lesional vessel segments (2). Blood vessels can enlarge to accommodate increasing flow to the organs downstream, and it is known that luminal stenosis correlates more closely with the direction and magnitude of remodeling than with plaque size (3). In patients with a total occlusion (TO) of a coronary artery, reduced blood flow in distal reference segments might promote both negative vascular wall remodeling and plaque growth, as shown in animal models with carotid arteries (4).
TO, including chronic total occlusion (CTO), occurs frequently, with a reported incidence of 30% to 50% among patients with significant coronary artery disease (5). Despite the development of novel techniques and devices in the field of percutaneous coronary intervention (PCI), the recanalization of TO still remains complex and challenging (6,7). Successful TO recanalization has been associated with a significant improvement in angina symptoms (8–10). The recanalization of TO may improve distal blood flow. But, it is unknown whether the flow restoration can influence the remodeling process in the distal reference segments in humans.
Hence, we sought to determine the degree of remodeling of distal reference segments after successful recanalization of TO by intravascular ultrasound (IVUS) and the factors that influence the remodeling process in a prospective TO-IVUS cohort at our institution.
From March 2005 to June 2008, we consecutively enrolled patients with de novo TO who were successfully recanalized at our institution. TO was defined as a lesion exhibiting a TIMI (Thrombolysis In Myocardial Infarction) flow grade of 0 to 1 for more than 1 month. All patients had at least 1 occlusion within a major epicardial coronary artery. Immediately after successful recanalization, the patients underwent an IVUS exam for the measurement of vessel and lumen size. Patients with acute myocardial infarction within 1 month were excluded in addition to those with total occlusion of the left main coronary artery or arterial or vein graft lesions. All patients underwent follow-up coronary angiography, and those without significant in-stent restenosis (diameter stenosis >50%) of previously recanalized TO underwent follow-up IVUS examination for evaluation of the distal reference segments.
Hence, 58 patients with successfully recanalized TO, an IVUS exam at the index PCI and 6-month follow-up coronary angiography were enrolled. End-diastolic and end-systolic left ventricular (LV) volumes were measured in the apical 4- and 2-chamber view with a modified Simpson method. The LV ejection fraction was subsequently calculated. Written informed consent for study participation was obtained from each patient before enrollment. The study complied with the Declaration of Helsinki and was approved by the Institutional Review Board of Seoul National University Bundang Hospital.
The duration of the occlusion was determined by the interval from the last episode of acute coronary syndrome, from the first episode of effort angina consistent with the location of the occlusion in patients without a history of acute coronary syndrome, or by a previous coronary angiography. In patients without a history of angina, the changes in noninvasive tests (i.e., electrocardiography or echocardiography) and stress tests (i.e., exercise electrocardiography, myocardial perfusion imaging, or dobutamine-stress echocardiography) were considered. CTO was defined as TO with a duration longer than 3 months (6,7). Positive vascular remodeling was defined as external elastic membrane (EEM) area increase at the follow-up (11). Successful recanalization was defined as a restoration of TIMI flow grade 3 with residual stenosis <30%.
Calcification was identified as readily apparent radiopacities within the vascular wall at the site of the occlusion and was classified as none/mild, moderate (radiopacities noted only during the cardiac cycle before contrast injection), and severe (radiopacities noted without cardiac motion before contrast injection generally compromising both sides of the arterial lumen) (12).
After successful TO recanalization, IVUS was carried out in all patients 2 min after intracoronary injection of 200 μg of nitroglycerin. The imaging catheter (Eagle Eye, Volcano Corp., Rancho Cordova, California) with a 20-MHz phased-array transducer was advanced at least 20 mm beyond the stent, and a mechanical pullback was performed at 0.5 mm/s. The point of measurement was 10 mm distal from the stent distal edge to exclude the effect of the stenting procedure. To assess exactly the same segment between the index and the 6-month follow-up, we used geometric markers, such as the distance to stent edge and relationship to side branches during the IVUS analysis. The following measurements were obtained: the mean lumen diameter, the mean EEM diameter, the lumen area, the plaque and media area, and the EEM area. Lumen area increase was defined as any lumen area increase at the 6-month follow-up. The IVUS analysis was performed by 2 independent experienced observers who were blinded to the angiographic results.
Qualitative analysis included incomplete stent apposition (blood speckle behind stent struts), stent fracture (absence of struts over more than one-third of the stent circumference), aneurysm (lumen >50% larger than the proximal reference), and edge dissection. Incomplete stent apposition was defined as at least 1 stent strut clearly separated from the vessel wall with evidence of blood speckles behind the strut not associated with any side branches.
The data were presented as numbers and frequencies for categorical variables and as the mean ± SD for continuous variables. For comparison between groups, the chi-square test (or Fisher exact test when any expected cell count was <5 for a 2 × 2 table) was used for categorical variables, and the Mann-Whitney U test and the Kruskal-Wallis test were applied for continuous variables. For changes between the index and the 6-month follow-up, a paired t test and the McNemar test were used. A multivariate logistic regression analysis was performed to determine the independent predictors of lumen area increase. Factors entered into the multivariate model included those with p values <0.10 from the univariate analysis along with common cardiovascular risk factors. Two-sided p values <0.05 were considered statistically significant. Statistical tests were performed using SPSS software (version 17, SPSS Inc., Chicago, Illinois).
A total of 105 patients were initially enrolled in the TO-IVUS cohort. Six patients turned out not to have TO as defined by the definition. At the 6-month follow-up, 1 patient had died; 4 patients became lost to follow-up; and 15 patients refused hospital admissions for the follow-up coronary angiography. Among the 79 patients who underwent follow-up coronary angiography, 5 patients had in-stent restenosis >50%; 7 patients refused the IVUS exam; and 1 patient had an unsuccessful IVUS exam due to passage failure of the IVUS catheter. In 5 patients, the distal reference segment was too thin and/or tortuous to fully advance the transducer at least 20 mm beyond the stent edge, and in 3 patients, the quality of IVUS recording was too poor to perform an accurate measurement, leaving 58 patients available for the final analysis (Online Fig. 1). The clinical and angiographic characteristics along with qualitative IVUS analysis of the study patients are summarized in Tables 1 and 2.⇓ Overall, the mean age was 59.9 years, and most patients were men (82.8%). Thirty-seven (63.8%) patients initially presented with stable angina, and 21 (36.2%) presented with acute coronary syndrome. Twenty-four percent of the patients had 1-vessel disease, whereas 76% had multivessel disease. TO was most frequently localized in the left anterior descending artery. Rentrop's grade 3 collateral flow to the distal reference segments was present only in 11.5%.
The IVUS exam of the distal reference segments at the 6-month follow-up revealed that there was a significant increase in the mean lumen diameter by +0.21 mm (10.4 ± 19.9%) (2.24 ± 0.48 mm → 2.45 ± 0.59 mm, p = 0.001), in the mean EEM diameter by +0.13 mm (5.8 ± 14.9%) (2.91 ± 0.70 mm → 3.05 ± 0.69 mm, p = 0.010), in the lumen area by +0.87 mm2 (29.6 ± 50.8%) (4.00 ± 1.90 mm2 → 4.87 ± 2.38 mm2, p < 0.001), and in the EEM area by +0.85 mm2 (17.3 ± 36.2%) (6.80 ± 3.21 mm2 → 7.65 ± 3.41 mm2, p = 0.001), but not in the plaque and media area (−0.05 mm2 [24.5 ± 124.6%]) (2.83 ± 2.35 mm2 → 2.78 ± 2.30 mm2, p = 0.768) (Fig. 1).
Only 40 patients (69%) had increases in lumen areas, whereas 31% had unchanged or decreased lumen areas (Fig. 2). Among those with lumen area increase, the mean lumen diameter increased by 0.40 ± 0.34 mm (18.9 ± 17.3%) (2.19 ± 0.41 mm → 2.59 ± 0.53 mm, p < 0.001). As for the heart function change during the follow-up period, there was a significant increase in the left ventricular ejection fraction (LVEF) of +2.77% (57.3 ± 9.9% → 60.1 ± 8.3%, p = 0.010) (Online Fig. 2). When defining EEM area increase as positive remodeling (11), only patients with positive vascular remodeling showed a significant increase in LVEF of 3.6% (56.3 ± 8.8% → 60.0 ± 8.8%, p = 0.014), whereas those without positive remodeling did not show any change in LVEF (60.0 ± 6.7% → 60.3 ± 7.3%, p = 0.460).
We also investigated whether changes in lumen area are associated with the incidence of incomplete stent apposition (ISA). In general, 12 patients (20.7%) had ISA at baseline; and after 6 months, the number of patients with ISA increased significantly to 25 patients (43.1%) (p = 0.002). When stratifying the patients according to the lumen area change, the proportion of patients with ISA increased significantly in patients with lumen area increase during the follow-up period (8 patients [20%] at baseline →18 patients [45%] at 6-month follow-up, p = 0.006), but not in those without lumen area increase (4 patients [22.2%] at baseline →7 patients [38.9%] at 6-month follow-up, p = 0.375) (Tables 2 and 3).⇓
As for drug-eluting stent types, both first- (sirolimus-eluting stent + paclitaxel-eluting stent) and second-generation drug-eluting stents (zotarolimus-eluting stent [ZES]) showed a significant increase in lumen area in the distal reference segments (3.84 ± 0.72 mm2 → 4.78 ± 2.35 mm2, p = 0.001 for sirolimus-eluting stent + paclitaxel-eluting stent, 3.68 ± 0.72 → 4.56 ± 1.11, p = 0.044 for ZES). There was no difference in the degree of lumen area increase between both stent generations (0.94 ± 1.80 mm2 for sirolimus-eluting stent + paclitaxel-eluting stent vs. 0.88 ± 1.10 mm2 for ZES, p = 0.922).
During clinical follow-up, only 1 patient with lumen area increase had a myocardial infarction 5 months after TO recanalization. To be more precise, the patient underwent right coronary artery TO recanalization at the index PCI, but the culprit artery of the myocardial infarction at 5 months was the left main artery. Cardiac death, myocardial infarction, or stent thrombosis was not observed in the remaining 57 patients.
Patients with lumen area increase had a significantly longer TO duration (4.5 months, [interquartile range (IQR): 2 to 23 months] vs. 1.5 months [IQR: 1 to 8 months], p = 0.020) and had more frequent poor collateral flow (grade 0 to 2, 95% vs. 73%, p = 0.050), compared with those without lumen area increase. The rates for left anterior descending artery TO (58% vs. 33%, p = 0.089) and single-vessel disease (30% vs. 11%, p = 0.062) tended to be higher in the lumen area increase group than in those without lumen area increase. There was a positive correlation between the TO duration and the lumen area change (r = 0.293, Spearman rho, p = 0.026). When classifying the distal reference segment according to its location—mid- versus distal vessel location according to the CASS (Coronary Artery Surgery Study) system—the location of the distal reference segment was not associated with lumen area change (p = 0.113), although the distal reference segment was more likely to be located in mid-vessel in patients with lumen area increase (37.5% vs. 16.7%), and in distal vessel in those without lumen area increase (62.5% vs. 83.3%). The degree of calcification was not associated with lumen area change (the proportion of patients with none/mild calcification: 87.5% vs. 83.3%; the proportion of patients with moderate calcification: 10.0% vs. 16.7%; the proportion of patients with severe calcification: 2.5% vs. 0.0%, in lumen area increase group vs. in no lumen area increase group, respectively, p = 0.627).
The concomitant medications did not differ between patients with and without lumen area increase, although the proportion of patients with statin use seemed to be higher in patients with lumen area increase than in those without lumen area increase (90.0% vs. 66.7%, p = 0.055).
The clinical factors in Table 1 with p < 0.10, such as a TO duration >3 months, a poor collateral flow (grade 0 to 2), the coronary artery disease extent, and the TO location, and statin use were entered into a multivariate analysis along with common cardiovascular risk factors, such as age (in decades), sex, diabetes mellitus, hypertension, and smoking status to determine the independent predictors of lumen area increase. In the multivariate analysis, independent predictors of lumen area increase were a poor collateral flow (odds ratio [OR]: 14.8, 95% confidence interval [CI]: 1.28 to 172.8, p = 0.032), a TO duration of longer than 3 months, that is, CTO (OR: 12.0, 95% CI: 1.92 to 74.2, p = 0.008) at TO recanalization, and statin use (OR: 7.4, 95% CI: 1.03 to 53.6, p = 0.047) (Table 4).
In this study, we found evidence of a flow-dependent vascular remodeling process in human coronary arteries after successful TO recanalization that was associated with increases in lumen diameter, EEM diameter, lumen area, EEM area, and LVEF. Overall, 69% of the patients with successful TO recanalization showed lumen area increase with a mean lumen diameter increase of 0.40 ± 0.34 mm at the 6-month follow-up. In patients with lumen area increase, the frequency of ISA increased significantly during the 6-month follow-up period, but not in those without lumen area increase. Furthermore, we discovered that a poor collateral flow to the distal reference segments, a TO duration of longer than 3 months, and statin use were strong independent predictors of lumen area increase. With the help of IVUS, which permitted detailed, high-quality, cross-sectional imaging of the coronary arteries in vivo, we were able to precisely quantify vascular changes in reference segments between the index PCI and the 6-month follow-up after TO recanalization rather than relying on quantitative coronary angiography—to the best of our knowledge—for the first time.
Clinical implication of CTO recanalization
On the role of CTO recanalization, several retrospective analyses and meta-analyses of CTO studies have shown mortality reduction in patients successfully treated with CTO recanalization compared with those treated medically (8,13,14). A possible explanation for the clinical benefit of CTO recanalization includes an improvement in LV function, a decrease in the rate of ventricular remodeling, and a decrease in electrical instability and its associated risk for fatal arrhythmic events (6,15,16).
When recanalizing CTO segments, the distal reference segments in coronary angiograms usually appear very thin, inviting the question of whether flow restoration of these tiny vessels will lead to any substantial improvement in cardiac function and justify the risk of this complex procedure at all, because CTO recanalization is more frequently associated with various complications during PCI (17). We showed that more than two-thirds of the patients after TO recanalization showed lumen area increase in the distal reference segments along with improved LVEF 6 months after PCI. This vascular remodeling process with better coronary flow might contribute to improved myocardial function and clinical outcomes. This is consistent with the finding that a significant improvement in LVEF was observed only in patients with positive vascular remodeling. Therefore, in selected patients with TO, the long-term benefits of recanalization might outweigh the risk of the procedure-related complications.
Vascular remodeling and its clinical predictors
Hemodynamic stimuli and intact endothelial function are 2 important factors that influence vascular remodeling. Hemodynamic stimuli, such as flow and circumferential stress, induce arterial remodeling to achieve homeostasis of shear stress and wall tension (1). In an animal experiment, a reduction in blood flow caused a decrease in vessel diameter (4), whereas elevated flow tended to increase it. In de novo atherosclerosis, remodeling is a major determinant of luminal narrowing. As initial plaque growth narrowed the lumen significantly, local shear stress increased (18). In a rabbit model, the endothelium reacted to increasing flow with nitric oxide production that led to chronic vasodilation (19). But, whether this flow-dependent remodeling process also takes place in human coronary arteries has not been answered yet.
In our study, a TO duration of longer than 3 months, a poor collateral flow, and statin use were independent predictors of lumen area increase after recanalization. The degree of collateral flow might reflect the magnitude of hemodynamic stimuli deprivation, whereas the TO duration correlates with the time in which vessels undergo a negative remodeling process. Therefore, patients with long TO durations and severely compromised collateral flow would have already undergone more extensive negative remodeling compared with those with short TO durations and good collateral flow (20). By contrast, these patients would react more intensively to flow restoration with lumen area increase, given that we showed a positive correlation between the duration of TO and changes in lumen area. By contrast, patients with good collateral flow would have preserved their lumen size due to the maintenance of hemodynamic stimuli. Those patients would not necessarily undergo lumen area increase after recanalization. Furthermore, statin use was also a strong independent predictor of lumen area increase. This is consistent with previous reports: Treasure et al. (21) showed that statins improved endothelium-mediated responses in the coronary arteries of patients with atherosclerosis. Furthermore, statins have been associated with reduced progression and even regression of coronary atherosclerosis (22).
Choosing the optimal stent size
Another interesting clinical perspective involves the question of whether these clinical predictors can be used for selection of the optimal stent size during PCI for a TO. The distal reference vessels appear to be very “thin” in coronary angiography after successful wiring and balloon dilation, so that many operators tend to choose stents with small diameters. As shown in our study, more than two-thirds of the patients showed lumen area increase in the distal reference segments at the 6-month follow-up. We showed that the mean increase in the lumen diameter was 0.21 mm in all patients, and among those with lumen area increase, this was an even higher 0.40 mm. It is also important to note that patients with lumen area increases would be more likely to experience incomplete stent apposition during the follow-up period. Therefore, choosing a stent size only according to the distal reference vessel seen on angiography during index PCI might lead to choosing a stent that is too small if the vascular remodeling is not considered (Fig. 3). By contrast, if a stent that is too large is chosen in expectation of excessive vascular remodeling, as some operators practice according to their intuition, it might cause vessel injury. Therefore, clinical predictors of lumen area increase would guide the operators in choosing the optimal stent size. As such, in patients with a long TO duration and a poor collateral flow, a larger stent size could be considered, whereas oversized stent implantation could be avoided in TO without those predictors.
First, although the data were collected prospectively, the precise duration of the occlusion was not angiographically documented, which means that the duration had to be assumed based on the patients' history and noninvasive test results. We believe that this limitation is applicable to all observational studies with CTO. Second, we did not evaluate the ischemia and viability in the area subject of recanalization in all patients before PCI. Vessels supplying areas without viability may be less prone to show lumen area increase. However, 72% of the study patients had positive results in at least 1 of the functional tests, including electrocardiography, echocardiography, treadmill test, and myocardial perfusion imaging (Table 1), and the rest of the study patients had typical symptoms of myocardial ischemia. Third, vascular remodeling implies an actual change in the arterial structure at the cellular levels. Because biopsy of the human coronary artery is impossible, our data relied on “surrogate markers,” such as the lumen and EEM area change, derived from IVUS examination. Further studies with virtual histology might answer some part of this question. Fourth, because we measured vascular change over a 6-month period, it is unknown whether it is safe to implant an oversized stent during initial PCI based on the expectation that over the next 6 months, the vessel might grow into the appropriate size. The result of the current study is hypothesis-generating rather than definitive. Therefore, further prospective trials addressing this question should follow. Fifth, the results of this study may be prone to type II error due to small sample size. In patients with lumen area increase, the coronary artery disease extent seemed to be smaller, the TO vessels were more likely localized in left anterior descending artery, the proportion of patients with diabetes mellitus was lower, and the distal reference segment was more likely to be localized in the mid-vessels. Therefore, if more patients were enrolled, these parameters might have been revealed as significant predictors of vascular remodeling. Nonetheless, the occlusion duration, a poor collateral flow, and statin use were strong independent predictors of lumen area increase despite the small size, suggesting that these parameters might be powerful predictors of vascular remodeling. Further studies with enough sample size are warranted.
Our study is the first that prospectively quantified vascular changes of distal reference segments after TO recanalization with IVUS. The distal reference vessels underwent lumen area increase after successful TO recanalization in only two-thirds of the cases, and the clinical predictors of lumen area increase included a TO duration of longer than 3 months, a poor collateral flow, and statin use. These predictors could be considered for the selection of the optimal stent size during PCI to TO lesions and optimal medical therapy during follow-up.
For supplemental figures, please see the online version of this article.
All authors have reported that they have no relationships relevant to the contents of this paper to disclose. Drs. Jin Joo Park and Chae contributed equally to this paper.
- Abbreviations and Acronyms
- confidence interval
- chronic total occlusion
- external elastic membrane
- interquartile range
- incomplete stent apposition
- intravascular ultrasound
- left ventricular
- left ventricular ejection fraction
- odds ratio
- percutaneous coronary intervention
- Thrombolysis In Myocardial Infarction
- total occlusion of a coronary artery
- zotarolimus-eluting stent(s)
- Received February 6, 2012.
- Revision received March 26, 2012.
- Accepted May 12, 2012.
- American College of Cardiology Foundation
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