Predictors of Failure of Final Kissing-Balloon Inflation After Mini-Crush Stenting in Non-Left Main Bifurcation Lesions: Importance of the Main-Vessel Angle

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Abstract: Background. The majority of bifurcation lesions are treated with crush stenting. However, the success of crush stenting depends on final kissing-balloon inflation (FKBI), which is potentially difficult. Although mini-crush stenting has a higher rate of successful FKBI, it still cannot be achieved in some patients. The aim of this study was to investigate the factors that contribute to failure of FKBI in mini-crush stenting. Methods and Results. We included 173 consecutive patients who were treated with mini-crush stenting. The patients were divided into FKBI and non-FKBI groups. The bifurcation angles were measured: (1) proximal bifurcation angle (angle A, between proximal main vessel and side branch); (2) distal bifurcation angle (angle B, between distal main branch and side branch); and (3) the main-vessel angle (angle C, between proximal main vessel and distal main branch). FKBI could be performed in 153 patients. Angle C and calcification were significantly lower and angle A and mean stent diameter in the main vessel were significantly higher in the FKBI group. Multivariate logistic regression analysis showed that only Angle C was an independent predictor of FKBI failure. Conclusions. Main-vessel angle was the only independent predictor of FKBI failure in mini-crush stenting. 

J INVASIVE CARDIOL 2013;25(3):118-122

Key words: mini-crush stenting, final kissing balloon inflation, main-vessel angle

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Bifurcation lesions still represent a technical challenge for the interventional cardiologist. Although different techniques have been proposed, percutaneous coronary intervention (PCI) for bifurcation lesions is still associated with lower procedural success rate, higher major adverse cardiac event rate, and poor long-term outcomes compared with non-bifurcation lesions, even in the drug-eluting stent (DES) era.^1-3

The majority of bifurcation lesions are treated with crush stenting in many clinics. However, the success of crush stenting depends on a final kissing-balloon inflation (FKBI), which is potentially difficult, because wire and balloon have to cross double layers of stent at the side-branch (SB) orifice. Early and long-term results after PCI are not satisfactory in patients with FKBI failure.⁴ The rate of FKBI success with this technique varies between 64%-92%.^4-7 To overcome this problem, the mini-crush stent technique was devised. Although mini-crush stenting has a higher rate of FKBI success, it still cannot be achieved in all patients.⁷ The exact causes of FKBI failure during mini-crush stenting are not fully understood. The aim of this study was to investigate the factors that contribute to FKBI failure in mini-crush stenting. 

Methods 

Patients. Of the 4375 PCI procedures performed between January 2010 and May 2012 at Adana Numune Education and Research Hospital in Adana, Turkey, we included 173 consecutive patients (101 males and 72 females; mean age, 58.0 ± 10.5 years) who were treated with the mini-crush stenting technique. Mini-crush stenting cases were identified through cineangiogram and procedural report review. Patients with acute myocardial infarction, left ventricular dysfunction, left main (LM) coronary bifurcation lesion, as well as those treated with crush stenting but had unsatisfactory cineangiograms, were excluded from the study. Demographic, angiographic, and procedural variables were recorded. The Local Ethics Committee approved the study protocol. 

PCI procedure. All patients were previously treated with aspirin and clopidogrel. If patients were not pretreated with clopidogrel, a 600 mg loading dose of clopidogrel was administered just before the index procedure. The mini-crush stenting procedure was performed using the technique described by Galassi et al.⁸ In our laboratory, 2-step FKBI is routinely performed whenever possible for all patients treated with crush or mini-crush stenting. Stepwise balloon inflation, beginning from 1.5 mm in diameter to the optimal SB stent dilatation was followed by FKBI. If the 1.5 mm balloon failed to cross through the stent struts, we then used a 1.25 or 1.5 mm Sprinter balloon to separate struts and allow a larger balloon to pass. If the Sprinter balloon also failed to cross the SB, we then used the proximal optimization technique (POT). In any case with difficulty crossing into the SB, the POT became routine in our clinic by 2010. Procedural time was defined from wiring of both vessels to FKBI. If predilatation was performed, procedure time was started after the predilatation. Based on the success of FKBI, the patients were divided into an FKBI group (n = 153) and a non-FKBI group (n = 20).

In this study, the Liberté bare-metal stent (Boston Scientific) was used in 37 patients for treatment of the main vessel and in 46 patients for the treatment of a side branch. In other patients, PCI was performed with the following DESs: Endeavor stents (Medtronic Inc), Coraxel paclitaxel-eluting stents (Alvi Medica), Coracto sirolimus-eluting stents (Alvi Medica), Xience V stents (Abbott Vascular), and Promus stents (Boston Scientific).

All procedural cineangiograms were acquired digitally and stored in Digital Imaging and Communication in Medicine standard format. Lesion morphology, stent type, and stent size were recorded in all patients. Three-dimensional reconstruction was performed off-line by the same experienced operator (MG), blinded to individual patient data and clinical outcome, using 3-dimensional software (CardiOp-B system, version 2.1.0.151, Paieon Medical, Ltd).^9,10 The software algorithm rendered an image as well as quantitative information, including bifurcation angle measurement. All bifurcation angle evaluations were performed before PCI in the absence of the guidewires in place (as these could modify the angle). All three non-left main bifurcation angles were presented in accordance with the European Bifurcation Club consensus definition (Figures 1 and 2).¹¹ Angle A (proximal bifurcation angle) is defined as the angle between the proximal main vessel and the SB; angle B (distal bifurcation angle) is defined as between the distal main branch and the SB; and angle C (main-vessel angle) is defined as the angle between the proximal main vessel and the distal main branch.

Statistical analysis. All calculations were performed with the SPSS version 13.0 (SPSS Inc). Continuous variables were tested for normality with the Kolmogorov–Smirnov test. Continuous variables were expressed as mean ± standard deviation and compared using independent sample t-tests or analysis of variance (ANOVA) where appropriate. Categorical variables were compared with the chi-square test. Multiple logistic regression analysis with backward elimination process was used to identify predictors of FKBI failure. All significant parameters on univariate analysis, such as lesion calcification, angle A, angle C, and mean stent diameter in the main vessel were selected in the multivariate model. A receiver operator characteristic (ROC) curve analysis was performed to identify the optimal cut-off point of MVA and PBA to predict the failure of FKBI. The area under the curve (AUC) value was calculated. A P-value of <.05 was considered significant.

Results

The index lesion location was the left anterior descending artery/diagonal branch in 159 patients (91.9%), the circumflex artery/obtuse marginal branch in 12 patients (6.9%), and the right coronary artery/posterior descending artery/posterolateral branch in 2 patients (1.2%). Patients underwent PCI due to stable angina pectoris and unstable angina pectoris in 145 (83.8%) and 28 (16.2%), respectively. FKBI could be performed in 153 patients (88.4%). Baseline demographic characteristics of patients with FKBI and non-FKBI were similar (Table 1).

Angiographic and procedural variables of the FKBI and non-FKBI groups were compared in Table 2. Lesion calcification (14.5% vs 35.0%; P=.04) and angle C (148.4 ± 14.7 vs 175.0 ± 10.3; P<.001) were significantly lower in the FKBI group than in the non-FKBI group. Angle A (154.3 ± 14.2 vs 130.7 ± 16.4; P<.001) and the mean stent diameter in the main vessel were significantly higher in the FKBI group than in the non-FKBI group (3.37 ± 0.42 vs 3.16 ± 0.41; P=.04).

As expected, the procedure time and contrast volume were significantly higher in the non-FKBI group. However, there were no significant differences in angle B, the need for predilatation, stent type, or the stent length between the two groups. Multivariate logistic regression analysis showed that only angle C was an independent predictor of FKBI failure (odds ratio [OR], 0.80; 95% confidence interval [CI], 0.73-0.88; P<.001). ROC curve analysis was performed to evaluate the usefulness of angle C for predicting FKBI failure. The AUC was 0.931 (95% CI, 0.874-0.987; P<.001) and the cut-off value of angle C was 167° for predicting FKBI failure, with a sensitivity of 86.7% and a specificity of 89.2% (Figure 3).

The median angle C was 152°. The patients were divided into three groups according to tertiles of angle C, which were defined as angle Clow <141° (n = 57), angle Cmid = 141°-160° (n = 59), and angle Chigh >160° (n = 57). Failure of FKBI, procedure time, and contrast volume increased significantly from the angle Clow group to the Angle Chigh group. Angiographic and procedural characteristics of the patients according to the angle C tertiles are summarized in Table 3.

Discussion

To the best of our knowledge, this is the first article investigating the reasons for FKBI failure during mini-crush stenting. We found that only angle C was an independent predictor of FKBI failure. We also showed that increased angle C is associated with a higher incidence of FKBI failure, longer procedure time, and more contrast volume.

The Achilles’ heel of true bifurcation lesion PCI is restenosis in the SB ostium. One of the most important reasons of SB ostial restenosis is incomplete coverage.¹² Colombo et al¹³ described the crush stenting technique, which offers complete coverage of SB ostium, in 2003. Using this technique, SB restenosis was reduced to about 13%-26%.^7,14-16 However, three stent layers in the proximal part of the bifurcation lesion in crush stenting predisposes to incomplete stent apposition and potentially leads to thrombotic complications. Furthermore, the success of crush stenting depends on achievement of FKBI, which is potentially difficult because the wire and balloon have to cross double layers of stent at the SB orifice.⁴ The rate of FKBI success with this technique varies between 64%-92%.^4-7 The mini-crush stent technique was devised to improve the success rate of FKBI. Although the success rate of FKBI while using the mini-crush stent technique is significantly improved, it still cannot be achieved in approximately 12% of patients.⁷ The exact reasons for FKBI failure remain unknown. In our study, the failure rate of FKBI was 11.6%, which was consistent with the literature. 

Previous studies have researched the effect of bifurcation angles on clinical outcome and the success of FKBI.^2,17 Dzavik et al¹⁶ investigated the effects of bifurcation angle on the performance of FKBI in 133 patients with crush stenting. They divided the patients into four groups according to quartiles of the bifurcation angle and reported that the success rate of FKBI was similar in all groups. In addition, Chen et al² recently showed that there is no influence of angle B on the success of FKBI. In our study, there was also no relation between angle B and FKBI failure, and only angle C was an independent predictor of FKBI failure. We also showed that when angle C was increased, FKBI  failure and procedural difficulty were increased. A possible explanation of these findings is that the stent strut cell at the SB ostium is relatively narrowed in patients with wider angle C and advancement of the balloon into the SB is extremely difficult. However, patients with lower angle C have relatively larger strut cells at the SB ostium with easier advancement of balloons into the SB to facilitate FKBI (Figure 1).

It has been reported that another possible reason for FKBI failure in crush stenting is a long main-vessel stent, which can have a higher probability for malapposition, resulting in the incorrect advancement of the guidewire.¹⁸ In this study, we could not see any relationship between main-vessel stent length and FKBI failure. We think that usage of POT in patients with FKBI failure has decreased malapposition in the bifurcation region. In addition, we found a weak correlation between FKBI failure and both stent diameter in the main vessel and lesion calcification on univariate analysis. However, multivariate logistic regression analysis showed that only angle C was an independent predictor of FKBI failure.

It is well known that bifurcation treatment with two stenting techniques modifies bifurcation angle^19-21 and that modification may influence FKBI performance.²² Importantly, Godino et al¹⁹ reported that change in bifurcation angle is most pronounced after the crush stenting technique. Interestingly, they found no significant difference comparing angle C at baseline and after stenting.¹⁹ This angle appears to be the least affected by the different types of stenting technique. In this study, we measured bifurcation angle only before PCI without the guidewires in place and found that only angle C was an independent predictor of FKBI failure. 

Stent design is another factor that may potentially affect FKBI performance. Open-cell stent designs with a large cell size should be used in the treatment of coronary bifurcation lesions. When the cell size is large, the access to the SB is facilitated. Maximal achievable cell diameters of the studied stent designs differ considerably, with values varying between 3.0 and 6.3 mm.²³ These stent cell sizes play an important role during coronary bifurcation treatment.^24,25 All of the stents used in this study were open-cell design with large cell size. In addition, stent types were similar in the FKBI and non-FKBI groups. Furthermore, the patients who were divided into three groups according to angle C tertile also had similar stent types.

Impact of bifurcation angles on outcomes. It has been known that angle A has an influence on the accessibility of the SB, which is frequently the main reason for selecting a double-stent technique, and that angle B has an impact on the risk of SB occlusion during main-vessel stenting. This angle appears to be the most influenced by the choice of bifurcation stenting technique.¹⁹ Our study suggests that angle C is related to the success rate of FKBI when using the mini-crush stent technique.

Study limitations. We studied the effect of angle C on procedure success only in patients who underwent mini-crush stenting. It can be further investigated in other bifurcation techniques, such as culotte stenting or provisional stenting. In this study, we showed the effect of angle C on the success rate of FKBI during mini-crush stenting. The relationship between angle C and long-term clinical outcomes must be investigated by further research. 

Conclusions

In this study, we found that angle C was the only independent predictor of FKBI failure in patients who underwent mini-crush stenting. Patients with lower angle C have relatively larger strut cells at the SB ostium with easier advancement of balloons into the SB to facilitate FKBI. Increased angle C is associated with difficulty of procedure, FKBI failure, more procedure time, and more contrast used.

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From the Department of Cardiology, Adana Numune Education and Research Hospital, Adana, Turkey.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted August 29, 2012, provisional acceptance given November 13, 2012, final version accepted December 7, 2012.

Address for correspondence: Dr Durmus¸  Y. S¸ahin, MD, Adana Numune Education and Research Hospital, Department of Cardiology, Seyhan Application Center, Çukurova, Adana, 01170, Turkey. Email: dysahin79@hotmail.com