DK Crush (Double-Kissing and Double-Crush) Technique for Treatment of True Coronary Bifurcation Lesions: Illustration and Compar

Bifurcation lesions are still technically challenging, even in the era of modern drug-eluting stents (DES).¹ Data on bare-metal stenting (BMS) did not demonstrate any advantages of the double-stent technique over single stenting because of a high incidence of restenosis in both the main vessel and the side branches. However, several kinds of double-stent techniques, including “T”, “V”, “Y”, “culotte” and “SKS (simultaneous kissing stents)” have been identified as being successful immediately after percutaneous coronary interventional (PCI) procedures.^2–5 DES dramatically decrease the in-stent restenosis rate after BMS. However, studies on DES have documented that the mechanisms contributing to a higher incidence of restenosis at the ostial side branch after double DES may be due to gaps in metal coverage and drug application at the bifurcated level.^6–9 Thus, a new technique ensuring complete vessel scaffolding without gaps in drug delivery at the bifurcation has been developed: the classic (or standard) crush technique proposed by Dr. Antonio Colombo in 2002. From the clinical and geographic standpoint, final kissing balloon inflation (FKBI) is necessary to completely expand the stents and to prevent stent distortion in both the main vessel and the side branch, whichever technique is used.¹⁰
Unfortunately, FKBI immediately after the classic crush technique is difficult or sometimes impossible to do, resulting in worse outcomes during follow up. In order to increase the success rate of FKBI, we propose our double-kissing (DK) crush stenting technique,¹¹ a modified crush technique combining both double-crushing and double-kissing. This report illustrates the procedure of DK crush and provides the 30-day clinical results in 88 patients with true bifurcation coronary lesions treated by either the classic crush or the DK crush technique.

Methods

Patient population. This study describes a consecutive, nonrandomized, open-label study. Eighty-eight consecutive patients from Nanjing First Hospital and Nanjing Heart Center of Nanjing Medical University with single, true (type I and type IV) coronary bifurcation lesions according to the Lefevre Classification² and a side branch diameter >2.0 mm were enrolled in the present study. The first 44 patients (from August 2004 to January 2005) and the later 44 patients (from February 2005 to June 2005) were assigned either to the classic crush or the DK crush technique arm, respectively. The operator is the first author of this study.
Percutaneous coronary intervention (PCI). A PCI procedure was performed immediately after transvenous bolus injection of 10,000 U of heparin. An additional dose of heparin was needed if the PCI procedure required >1 hour to maintain an activated clotting time (ACT) > 280 seconds. Both the main vessels and side branches were stented with Taxus™ Express (Boston Scientific Corp., Natick, Massachusetts) stents.
The ratio of stent-to-artery was 1.1:1. Postdilatation with noncompliant high-pressure balloons with a balloon/stent ratio of 1:1 was recommended for every stent. The criteria for angiographic success included a residual stenosis of <20%, without acute closure and the need for emergency surgical bypass. The diameter of balloons for kissing inflation was equal to or larger than the previous stenting balloon, and stepwise balloon inflation beginning from 1.5 mm in diameter was required if the target balloon failed to access the side branch. The number and average diameter of balloons used for single and kissing inflation were recorded. PCI procedural times, defined as from guidewire-in to guiding-catheter-out, and total volume of contrast used were recorded.
Classic crush has been described previously.¹⁰ Briefly, two stents were loaded in both vessels successively. First, the side stent with its proximal 3–5 mm protruding into the main vessel was inflated and the guidewire and stenting balloon were removed. The stent loaded previously in the main vessel was deployed and crushed the protruded side stent in the main vessel against the main vessel wall (first crush). The final kissing balloon inflation (FKBI, first kissing) was undertaken if rewiring and reballooning of the side branch were successful. Therefore, the classic crush technique consists of three steps: side-stenting, first-crush and FKBI. The outer diameter of the guiding catheter used was 7 Fr or 8 Fr (if the main vessel or side branch stent was >3.0mm in diameter).
The DK crush technique has been described elsewhere¹¹ and is illustrated schematically in Figure 1. A balloon with a target diameter and length is used in the main vessel, and a stent is loaded into the main vessel and the side branch simultaneously. The side stent is inflated first. Next, a balloon in the main vessel is inflated and the protruded side stent is crushed against the main vessel wall after removing the wire and the stenting balloon (balloon crush). The first kissing balloon inflation is undertaken immediately after successfully rewiring the side branch (first kissing). The stent in the main vessel is inflated to further crush the side stent (second or stent crush) after repeatedly removing the side wire and stent. FKBI is repeated after successfully rewiring the side branch. As a result, the DK crush technique consists of five steps: side-stenting, balloon-crush, first-kissing, second-crush, and FKBI. The outer diameter of the guiding catheter is 6 Fr.
A loading dose of 300 mg aspirin and 300 mg clopidogrel was administered at least 6 hours before the PCI procedure. An oral dose of 300 mg/day of aspirin was sustained for 1 month, and 100 mg/day of aspirin and 75 mg/day of clopidogrel was continued thereafter during the study period.
Thirty-day follow up. Patients were monitored for 24 hours in the coronary care unit (CCU). The plasma level of creatine was evaluated before, at 24 hours, and again at 48 hours after the procedure. Definitions of Q-wave and non-Q-wave myocardial infarction have been described.12 Repeat angiography within 30 days was not scheduled unless clinical signs indicated earlier ischemia. Major adverse cardiac events (MACE) were defined as either myocardial infarction, cardiogenic death, or revascularization including PCI or coronary artery bypass grafts (CABG).
Statistical analysis. The SPSS 10.1 statistical software program was used (SPSS, Inc., Chicgao, Illinois) to perform all statistical calculations. Continuous variables were expressed as mean ± standard deviation (SD) and compared using the Student’s paired t-test. The comparison of nonparametric data between two groups was expressed by percentage and examined using Chi-square analysis and Wilcoxon and Mann-Whitney tests. For all tests, a p-value <0.05 was considered statistically significant.

Results

The clinical follow-up rate within 30 days was 100%. Characteristics of all patients at baseline and within 30 days are illustrated in Table 1. Patients in the DK crush group, compared to those in the classic crush group, were characterized by longer lesion length in the side branch (13.5 ± 3.4 mm vs 7.8 ± 3.1 mm; p <0.05), shorter procedural time (44 ± 12 minutes vs 68 ± 17 minutes; p <0.05), a higher success rate of FKBI (100% vs 70%; p <0.01), and lower volume of contrast (102 ± 38 mm vs 176 ± 46 mm; p <0.05). In the DK crush group there was a trend toward larger distal angle between the main vessel and the side branch (57 ± 18° vs 47 ± 15°) and longer lesion length in the main vessel (24.3 ± 8.6 mm vs 21.1 ± 7.3 mm), though without significant differences (p >0.05, respectively). There was no significant difference in postprocedure serum creatine between the two groups.
Subacute stent thrombosis was detected in 2 patients with failure of FKBI in the classic crush group (Table 1). The first patient complained of severe chest pain followed by typical ST-segment elevation from V1 to V5 leads in the morning of day-23 following the classic crush-stenting procedure for Type IV bifurcations involving the left anterior descending artery (LAD) and the first diagonal (D1). The second patient was awoken in the middle of the night by severe chest pain. Electrocardiography confirmed the diagnosis of extensive anterior wall infarction. No patients in the DK crush group had stent thrombosis.
Angiographic parameters by quantitative coronary angiography (QCA) are illustrated in Table 2. There was no difference in preprocedural parameters including reference vessel diameter, minimum lumen diameter, and diameter stenosis between the two groups. Patients in the classic crush group, compared to patients in the DK crush group, were characterized by smaller minimum lumen diameter (MLD) at the side branch ostium (2.74 ± 0.12 mm vs 3.01 ± 0.13 mm; p <0.01) and a higher degree of residual stenosis at the ostial side branch (17.4 ± 11.2% vs 7.3 ± 8.6%; p <0.05).

Discussion

With or without DES, the complexity of bifurcation lesion treatment is dependent on the side branch. Side branch access is facilitated by the jailed wire technique. In false bifurcation lesions there is no rationale for using 2 stents systematically, and the strategy of “provisional stenting” seems to be the simplest among the validated strategies. In true bifurcation lesions, because the side branch lesion is usually short, the same strategy can be applied in the majority of cases. Nakamura et al¹² reported that T- or Y-stenting with BMS did not offer greater advantages in terms of immediate and long-term results over single stenting because of the high incidence of restenosis and target lesion revascularization compared to the single stent subgroup. Interestingly, DES did not change anything at all. Colombo et al⁶ identified the considerable potential of DES for the treatment of bifurcation lesions and reported a total incidence of stent thrombosis and restenosis at the ostia l side branch of up to 3.5% and 28.7%, respectively, within a 6-month follow-up period. Thereafter, single stenting was accepted as an option for the treatment of bifurcation lesions. However, the drawback of this method was a major limitation for lesions at the distal left main involving both the ostial left anterior descending and the left circumflex arteries. In fact, the strategy of PCI for bifurcation lesions is characterized by contradictory views, with very little intention-to-treat usage of 2 stents versus the more dominant strategy of 2-stent implantation.^4,13 In clinical practice, the decision to implant 2 stents from the beginning of the procedure depends on various factors such as the size and extent of myocardium supplied by the side branch.
Potential reasons for primary or secondary failure when stenting the side branch are: a gap between the 2 stents; plaque shifting from the main branch when stenting over the ostium of the side branch; plaque shifting from the main branch when stenting in the proximal side branch through the first strut; crushing of the proximal segment of the side branch stent without, or even after, kissing balloon inflation which may result in malapposition and inefficiency of the DES; and significant injury to the side branch ostium caused by an excessive balloon-to-artery ratio or by the ostium location within the main branch wall.¹
To overcome these shortcomings, especially incomplete coverage of side branch ostium, the crush technique,¹⁰ proposed first by Colombo and coworkers and justified by several reports, met the need to fully cover the orifice of the side branch. Ormiston et al¹⁴ concluded that there was still unsatisfactory results if final kissing was undertaken with a more narrow (smaller diameter) balloon than the previous stenting balloon. As a result, correct FKBI was a useful adjunct and served to repair stent distortion and cover the orifice of the side branch. However, no prospective trials have been conducted to report the real success rate of FKBI. Lim et al¹⁵ reported 70% success with FKBI by step-crush in 7 patients. Step crush, without differentiating from classic crush, is an option that uses the transradial approach with a 6 Fr guiding catheter because it is difficult for many operators to deliver two stents simultaneously with a 6 Fr guiding catheter. Ge et al¹⁶ failed to show a difference in the incidence of thrombus and MACE between the two groups (with and without the use of FKBI). However, they reported a success rate of about 67% with FKBI. The question of whether failed FKBI impacts post-PCI outcome is still unresolved by these nonprospective, nonrandomized studies. Importantly, we still need to understand why classic crush appears to have a lower success rate than FKBI.
Studies have documented that the mechanisms contributing to the failure of FKBI include a crushed portion at the orifice of the side branch with at least two layers of stent strut in the origin of the side branch, geographic distortion of the stent in the side branch, irregular overlapping of the two stents struts at the level of the carina, bifurcation at the bend, and stent design (although Lim¹⁵ et al reported similar distortion for different types of stents). Therefore, with this information, an operator can avoid crushing at the orifice of the side branch and choose the most suitable stent design, but cannot select the type of bifurcation lesion. From our analysis, we conclude that for the repair of a distorted stent in the side branch, keeping the wire or balloon in the true lumen of the side stent and irregular stent strut overlapping at the level of the carina, and keeping only one layer of stent strut at the ostial side branch, facilitates access to the side branch and the successful performance of FKBI. The only way to meet these needs is with kissing balloon inflation. Accordingly, we designed double kissing and double crush (DK crush technique) and compared it with the classic crush technique. First, kissing inflation allowed the full expansion of the side branch orifice, and no stent struts obstructed the side branch ostium immediately after this first kissing.¹¹ And most importantly, only one layer stent strut homogeneously covered the orifice of the side branch at the level of the carina after stenting the main vessel. These characteristics of DK crush allowed the success of FKBI. We reported our pilot study results comparing DK crush and classic crush at the CCT in September 2005 in Japan, and published the report in 2005.¹¹ Our preliminary results from two operators from a single center (Nanjing First Hospital of Nanjing Medical University) confirmed the superiority of DK crush to classic crush in improving FKBI.
The present study clearly demonstrates that DK crush has several advantages over classic crush such as shorter procedural time, less contrast use, and most importantly, 100% success with FKBI. Jim et al¹⁷ in 2006 described the same technique (sleeve technique) as DK crush and reported 100% success with FKBI in 6 patients. Otherwise, 2 patients who did not have successful FKBI in the classic crush group (4.5%) suffered from subacute stent thrombosis, which was consistent with reports by Ge¹⁶ et al. Therefore, the safety of the classic crush technique in terms of stent thrombosis should be reevaluated.
It is difficult or impossible to improve a suboptimal result in the side branch ostium even when FKBI is performed. This phenomenon, characterized by optimal expansion of the side branch balloon without inflation of the main vessel balloon and underexpansion of the main vessel balloon, indicated that FKBI in this situation was unable to repair the stent distortion at the ostial side branch, which contributes to a higher degree of residual stenosis at the side branch ostium. The reasons responsible for this failure in the classic crush arm can be answered by the slogan “kissing is not just kissing” by Dr. Colombo.¹⁸ Figure 2 helps illustrate the difference between the classic and DK crush techniques. Two layers of stents struts, overlapped irregularly at the ostium of the side branch, would allow smaller openings of each main stent cell if classic crush was performed. On the other hand, only one layer of stent struts after first kissing balloon inflation covers the ostial side branch, which would lead to easier FKBI using a larger-diameter stent cell. Notably, 6 Fr guide catheters allowed for DK crush because they avoided 2 stents advanced simultaneously as in the classic crush technique. As a result, DK crush using a 6 Fr guiding catheter increased the success and safety of PCI. Compared with classic crush, DK crush significantly decreased the residual stenosis at the ostium of the side branch immediately after PCI, and subacute stent thrombosis within 30-day follow up, although at the time of these procedures, we did not know the effect the DK crush might have on the restenosis rate in both the main vessel and side branch. In terms of procedural time, the main factor contributing to a shorter PCI time in DK crush was that DK crush facilitated FKBI compared with classic crush, in which FKBI was impossible or difficult, despite the fact that several balloon exchanges and stepwise inflation were performed.
Study limitations. This study has several limitations. First, the sample of patients is small. Second, data on angiographic follow up are necessary to identify the differences in restenosis rates between the two groups. Third, intravascular ultrasound might be a better tool for understanding the mechanisms of both the classic and DK crush techniques. Fourth, distal left main coronary (LMCA) disease often involves the bifurcation, therefore, the stenting of LMCA lesions is a significant issue. Only 3 patients with LMCA lesions were enrolled in each group. Finally, with the development of dedicated bifurcation stents, the overall approach would be changed. As a result, further study is required to establish the ideal approach for treatment of coronary bifurcation lesions.
In conclusion, compared with classic crush, DK crush has the potential to improve the clinical outcome in patients with coronary bifurcation lesions. Further randomized, prospective, multicenter studies are required to confirm the differences between the classic crush and DK crush techniques.

References

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