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Table of Contents
EDITORIAL REVIEW
Year : 2018  |  Volume : 1  |  Issue : 1  |  Page : 18-30

Left main stenting: What we have learnt so far?


1 Division of Cardiology, Thumbay Hospital, Ajman, UAE, UAE
2 Division of Cardiology, Nanjing Medical University, Nanjing, China

Date of Web Publication24-Aug-2018

Correspondence Address:
Dr. Debabrata Dash
Division of Cardiology, Interventional Cardiologist,Thumbay Hospital, P.O Box 4184, Ajman
UAE
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IHJI.IHJI_14_18

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  Abstract 

For many decades, coronary artery bypass grafting (CABG) has been considered as the gold standard treatment of unprotected left main (LM) coronary artery disease. However, a large vessel caliber and anatomic accessibility makes percutaneous coronary intervention (PCI) an attractive option for interventional cardiologists. The introduction of drug-eluting stents (DESs) along with rapid advancements in techniques, devices, and adjunctive pharmacotherapies has further extended the application of PCI for this subset. The available current evidence comparing efficacy and safety of PCIs using DES and CABG revealed comparable results in terms of safety and a lower need for repeat revascularization for CABG. Despite recent developments in the field of LM PCI, treatment of distal LM bifurcation lesions continues to pose unique technical challenges to the interventional cardiologists. The provisional one-stent approach has shown more favorable outcome than the two-stent technique, making the former the first-line treatment in most types of LM bifurcation lesions. However, some complex lesions would require two stents from the outset. The complexity of this lesion subset reinforces an integrated approach combining tailored techniques, adjunctive physiological and morphologic evaluation, hemodynamic devices, and pharmacologic agents to improve clinical outcomes.

Keywords: Bifurcation lesions, drug-eluting stent, left main coronary artery, percutaneous coronary interventions


How to cite this article:
Dash D, Chen SL, Zhang JJ. Left main stenting: What we have learnt so far?. Indian Heart J Interv 2018;1:18-30

How to cite this URL:
Dash D, Chen SL, Zhang JJ. Left main stenting: What we have learnt so far?. Indian Heart J Interv [serial online] 2018 [cited 2018 Nov 12];1:18-30. Available from: http://www.ihji.org/text.asp?2018/1/1/18/239777




  Introduction Top


Significant unprotected left main (LM) disease constitutes approximately 5%–7% of the patients undergoing coronary angiography (CAG)[1],[2],[3] and more than 80% involve bifurcation. Until recently, coronary artery bypass grafting (CABG) has been the gold standard therapy for this subset of disease. Randomized clinical trials (RCTs) have shown a higher rate of repeat revascularization after percutaneous coronary intervention (PCI) compared with CABG, but a lower incidence of cerebrovascular events; no differences were reported in the overall major adverse cardiovascular events (MACEs).[4],[5],[6],[7],[8],[9] However, anatomically easy accessibility and large caliber make LM PCI an attractive choice for interventionists.[10] Marked technical innovation in PCI and stent technology have emboldened the interventionists to test the feasibility of LM PCI. Treatment of ostial and mid-shaft has shown excellent outcomes with minimal mortality and long-term complications compared with distal LM bifurcations.[7] Lack of RCTs addressing LM bifurcation has led to uncertainties regarding optimal stenting strategy. Although the provisional one-stent technique has been the default strategy on the basis of nonrandomized studies and extrapolations from the results of non-LM bifurcation trials, two-stent techniques are selected more frequently for LM bifurcation than for non-LM bifurcation.[11]


  Anatomical Complexity and Rheology Top


Severe LM diseases would jeopardize significant areas of the myocardium, as it supplies approximately two-thirds of the blood to the heart and 100% to the left ventricle.[12] Being a large artery, it tends to have a high plaque volume. It is also prone to calcification. Carina shift and incomplete stent expansion are therefore important technical considerations in the stenting of LM.[11]

Greater elastic tissue content of this artery explains the elastic recoil and high restenosis following balloon angioplasty.[12],[13]LM represents the largest coronary bifurcation, and stenting techniques are driven by potential complications to the left circumflex (LCX) coronary artery such as acute occlusion and long-term adverse outcomes of target vessel failure and target lesion revascularization (TLR).[14] Intimal atherosclerosis in this bifurcation location is accelerated primarily in the area of low shear stress along the lateral wall extending distally on the myocardial walls of the left anterior descending (LAD) and LCX arteries. Involvement of the flow divider (carina) is minimal or absent. A long LM artery (≥10mm) has more pressure drop and lower shear stress, contributing to plaque formation.[15] The current trend to treat LM bifurcation by extending the main branch (MB) stent into the proximal LAD is supported by the continuous extension of plaque from LM to proximal LAD artery in 90% of cases.[16] The LM artery typically has a diameter ranging between 4.5 and 6mm in a majority of cases, whereas the LAD and LCX arteries have diameters ranging from 3.5 to 4.5mm and 3.0 to 4.5mm, respectively. This drives the interventionists to be familiar with large diameter stents with expansion properties. The takeoff angulation of LCX is greater than 90° in more than 70% of the patients. The size discrepancy and takeoff angle of LCX have great implications for LM bifurcation stenting.[17] A wide angle between the LAD and the LCX pre-PCI has predicted of worse outcomes after the culotte and classic crush techniques.[18],[19],[20] However, in the DKCRUSH-III (Double Kissing Crush vs. Culotte Stenting for the Treatment of Unprotected Distal Left Main Bifurcation Lesions III) study, double kissing (DK) crush has reported lower rates of MACEs when the bifurcation angle between the LAD and LCX was >70° compared with the culotte stenting technique.[21] Therefore, for wider bifurcation angles or when the LCX is smaller than the LAD (but larger than 2mm), DK crush is the ideal two-stent technique.

If the bifurcation angle is less than 70° and the LCX diameter is equal to or within 0.5mm of the LAD diameter, either the culotte or the DK crush technique can be employed.[14],[22]LM disease tends to be diffuse and may conceal stenosis. The diffuse disease should be suspected if the reference diameter of LM is similar to the reference diameter of LAD.


  Evidence for Percutaneous Coronary Intervention and Major Society Guidelines Top


To date, a large body of data from observational registries to clinical trials supports the feasibility, efficacy, and safety of PCI as compared to CABG for the treatment of unprotected LM disease. Several observational studies revealed that the early clinical events of LM stenting were similar or superior to those of CABG because of significant increase in periprocedural myocardial infarction (MI) or stroke in the patients with CABG, and that the mortality between 30 days and 3 years was similar in both the groups.[23],[24],[25],[26]However, the risk of target vessel revascularization (TVR) was higher with PCI than that with CABG.

The SYNTAX (Synergy between Percutaneous Coronary Intervention with TAXUS and Cardiac Surgery) trial incorporating 705 patients with LM that compares PCI and CABG has revolutionized decision-making in patients with LM disease by introduction of the SYNTAX score, a heart team approach, and evolving a close cooperation between both cardiac surgery and interventional cardiologists.[27] When stratified by score, the 5-year incidence of major adverse cardiac or cerebrovascular events (MACCEs) was similar between the groups with low (<23) and intermediate (23–33) SYNTAX score. In addition, the SYNTAX data show a significantly lower rate of stroke in the PCI group at 1 year and maintain a trend at 5 years.[9],[28]However, the patients with a SYNTAX score >33 had lower mortality and a lower rate of repeat revascularization with CABG compared with PCI, thus establishing CABG as the preferred revascularization method.

The introduction of newer generation drug-eluting stent (DES) with proven improvements in both safety and efficacy has prompted the design of two new dedicated randomized trials comparing CABG and PCI: the NOBLE (Coronary Artery Bypass Grafting vs. Drug-Eluting Stent Percutaneous Coronary Angioplasty in the Treatment of Unprotected Left Main Stenosis)[29] and EXCEL (Evaluation of XIENCE Everolimus-Eluting Stent vs. Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization) trials.[30] In the EXCEL trial, the composite primary end point of all-cause death, stroke, or MI at 3 years occurred in 15.4% of the patients treated with PCI and in 14.7% of the patients undergoing CABG. The difference was significant for non-inferiority, but not for superiority. The patients with low- or intermediate-SYNTAX scores treated with an everolimus-eluting metallic stent (Xience [Abbott Vascular, Santa Clara, CA, USA]) had comparable rates of death, stroke, or MI at 3 years when compared with patients treated with CABG surgery.[30]In contrast, in the NOBLE trial, treatment with PCI using predominantly a biolimus-eluting stent (BioMatrix Flex [Biosensors Inc, Newport Beach, CA, USA]) was associated with a significantly higher rate of MACCEs at 5 years when compared with CABG. Individually, all-cause mortality was comparable between the two treatments, whereas nonprocedural MI and the need for a repeat coronary revascularization were higher among those treated with PCI. Stroke rates were higher among the patients treated with CABG at 30 days. However with extended follow-up the patients with PCI group had higher stroke rate.[29]One must keep in mind that the benefit of CABG is often seen after extended follow-up.[31] Both studies had a median follow-up duration of 3.1 years, which is relatively short; hence, a long-term follow-up is needed before any concrete conclusion is drawn. In the EXCEL trial, by the time one gets out over 3 years, death begins to split in favor of CABG. It may become statistically significant once the median follow-up is extended up to 5 years.[31]

The 2014 European Society of Cardiology (ESC)/European Association for Cardio-Thoracic Surgery (EACTS) guideline statement [Table 1] for myocardial revascularization makes Class I recommendation for PCI in the setting of LM disease with SYNTAX score ≤22 and Class IIa recommendation with SYNTAX score 23–32, whereas CABG is the preferred approach for patients presenting with high SYNTAX scores >32.[5]
Table 1: Major society recommendations for the use of PCI for unprotected left main coronary artery disease

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The American College of Cardiology and the American Heart Association 2014 guidelines give a Class IIa indication for LM PCI in patients with stable ischemic heart disease, low procedural risk, and SYNTAX scores <22 and a Class IIb recommendation for intermediate scores (22–32).[32] Both the American and European guidelines recommend the heart team evaluation in the decision between CABG and PCI.


  Preprocedural Assessment and Planning of Intervention Top


We strongly feel that the LM stenting should be performed by skilled operators who are familiar with various stenting techniques at the facilities having access to intracoronary imaging (intravascular ultrasound [IVUS] or optical coherence tomography [OCT]), coronary physiology, atherectomy, and mechanical circulatory support.

CAG could be ambiguous at times to determine the LM lesion severity, highlighting the need for other imaging modalities or functional assessments. The Medina classification[33],[34],[35] is an angiographic classification of bifurcation lesion complexity, which defines plaque distribution and procedural planning but does not predict PCI outcome. Several parameters (including larger side branch [SB], long SB lesion, wide bifurcation angle, and high risk of hemodynamic deterioration associated with potential SB occlusion) may warrant two-stent techniques. The validity of this classification requires bifurcation-dedicated quantitative coronary angiographic software.

The criteria for LM intervention are the following: LM diameter stenosis ≥70% by CAG, minimum lumen area (MLA) ≤6.0mm2 by IVUS or OCT, and fractional flow reserve (FFR) ≤0.80.


  Intravascular Ultrasound and Optical Coherence Tomography Top


The angiographic assessment of the LM segment is difficult in view of the vessel overlap, ostial angulation and deformity, and foreshortening and streaming of contrast. IVUS or OCT imaging is useful to assess the size, angle, and length of LM and the daughter vessels, plaque distribution, tissue characterization, arc of calcification (270°–360°), and severity of stenosis. The LITRO trial has shown the IVUS-derived cutoff value of 6mm2 (threshold) as a safe MLA at which PCI may be safely deferred.[36]However, an IVUS MLA of <4.5mm2 corresponds to FFR of <0.8 in the Asian population.[37]

OCT offers a more detailed assessment of the lumen and intima than IVUS because of its higher resolution. The limitations of OCT include its difficulty in clearing the LM lumen with adequate flush and reduced depth of penetration compared with IVUS. Power injection of 20mL of contrast over 5s and a pressure of 500 psi can improve the image quality. The preprocedure “spiky” carina or “eyebrow” sign at the origin of the SB observed in both IVUS and OCT is a predictor of carinal shift and restenosis after LM stenting in a single-stent strategy.[38]

Fractional flow reserve

No definite consensus related to exact FFR cutoff is reported. It may be reasonable to defer LM PCI in patients with FFR >0.80. An FFR value between 0.75 and 0.80 should be repeated and supplemented with an IVUS assessment. In the presence of concomitant lesions in both the LAD and LCX without repairing the downstream lesions, the FFR may underestimate the true significance of the LM lesion.[10] One study reports that the need for PCI of the ostial LCX after LM-LAD crossover stenting may be reduced by FFR guidance.[39] Given the nearly identical 1-year MACE rates with both approaches in DKCRUSH-VI trial, either the angiography-guided or the FFR-guided technique may be recommended for provisional SB stenting of true bifurcation lesions.[40] However, further studies are required to validate the efficacy of this strategy.

Hemodynamic support

USpella registry strongly supports the feasibility, safety, and hemodynamic usefulness of Impella (Abiomed, Danvers, MA) device for LM PCI with acceptable in-hospital and 30-day MACE rates.[41]The Impella device is currently recommended for high-risk LM patients with depressed ejection fractions of <35%.


  Stenting of LM Ostial and Mid-Shaft Lesions Top


These lesions can be stented with single-stent strategy with good immediate and long-term outcomes. It is possible to successfully direct stent the mid-shaft, but careful assessment should be made of the vessel diameter, lesion length, and the degree of calcification. The potential for plaque shift should also be considered. Predilatation should be carried out in case of any doubt. It is better to wire both MBs before stenting. If the shaft of LM is too short, the stent can be implanted into the LAD across the ostium of the LCX.

Careful imaging must be performed to ensure adequate visualization of the ostium and adjacent aorta. Usually anteroposterior (AP) cranial and/or slightly left anterior oblique (LAO) cranial projections give the best view. The guide catheter may be occlusive with severe stenosis. It should be disengaged slightly from the ostium by pushing gently on the wire to minimize coronary ischemia. The guide can then be gently moved toward the ostium, by slight traction on the wire, to allow contrast injection and imaging. The guide should be short tipped with side holes. The Amplatz guides should be avoided in ostial lesions. Ostial lesions are often predilated. The stent needs to be placed carefully with 1–2mm protruding into the aorta. After deployment, the balloon should be pulled back slightly into the aorta and proximal part of the stent should be post-dilated to flare it, which ensures good stent apposition at the ostium. IVUS may be used to ensure a satisfactory result.


  Choosing a Stenting Strategy in LM Bifurcation Top


LM bifurcation lesions may be treated by either a provisional one-stent or a two-stent strategy. There is a lack of randomized studies comparing one- and two-stent strategies for this lesion. The DEFINITION (Definitions and Impact of Complex Bifurcation Lesions on Clinical Outcomes After Percutaneous Coronary Intervention Using Drug-Eluting Stents study) trial provides evidence that for complex LM bifurcation lesions, two stents are associated with improved clinical outcomes compared to one-stent strategy.[42] DKCRUSH-V randomized trial shows lower rate of target lesion failure at 1 year with DK crush technique compared to provisional stenting.[43] The ongoing EBC MAIN (European Bifurcation Club Left Main Study; NCT02497014)[44] randomized trial comparing one versus two stents (DK crush or culotte) is expected to further shed light on the optimal technique for LM bifurcation PCI.

The choice of strategy depends not only on vessel and lesion characteristics but also on operator experience and expertise. The provisional stenting is a one-stent strategy, although it allows the placement of a second stent (T, T and protrusion [TAP], culotte technique) whenever required. More complex lesions may require two-stent strategy (T stenting, TAP, mini-crush, DK crush, culotte, V stenting) from the outset.[10] To stratify the best stenting strategy, LM bifurcations are classified as simple or complex on the basis of the criteria in the DEFINITION trial. LM bifurcation is designated as simple if SB diameter stenosis is <70% and lesion length is <10mm. This is observed in 75% of the cases, and a one-stent provisional approach is the treatment of choice. A complex LM bifurcation lesion has SB diameter stenosis >70% and lesion length >10mm. A simple lesion can convert into a complex lesion with the presence of two of the following six minor criteria[42]: 1) moderate to severe calcification, 2) multiple lesions, 3) LAD-LCX bifurcation angle >70°, 4) main vessel reference vessel diameter <2.5mm, 5) thrombus-containing lesion, and 6) main vessel lesion length >25mm. Complex lesions generally require a two-stent strategy even if one-stent provisional approach is easier and more effective in the long term. The decision for specific types of complex two-stent strategy rests on the basis of the vessel size, bifurcation angle, and severity and length of the lesion of the major SB. Even if there is little consensus and a few data on the optimal complex two-stent technique, DK crush stenting can be applied in almost all types of complex LM bifurcation [Figure 1].
Figure 1: Algorithm for left main bifurcation percutaneous coronary intervention.
Abbreviations: LM, left main; SB, side branch; TAP, T and protrusion; DK-crush, double kiss crush; FFR, fractional flow reserve; TIMI, thrombolysis in myocardial infarction; IVUS, intravascular ultrasound; OCT, optical coherence tomography


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Provisional one-stent technique

The provisional stenting with one-stent crossover into the LAD or the MB is the most common strategy in LM bifurcation lesions. LM with nonsignificant (<50%) ostial LCX lesion with a lesion length of <10mm, a non-left dominant coronary system, or LCX with <2mm diameter favors one-stent approach. An inverted provisional approach (provisional one stent from LM to LCX) can be employed if the predominant lesion is in the LCX without ostial disease of LAD. Optimal visualization of the LM bifurcation and the SB ostium is achieved in LAO caudal, AP, or right anterior oblique caudal projections. A stent is deployed from LM to the LAD after sizing with MB reference (LAD). Oversizing of the stent may increase not only the risk of distal dissection but also the risk of carinal shift leading to the SB occlusion. The proximal optimization technique (POT)[34] is then performed, which allows strut protrusion into the SB with a larger strut opening, as well as no or limited carinal shifting for easier guidewire exchange. Three options for the SB are reported. 1) The crossover stenting is followed by the POT with no SB dilatation or kissing balloon inflation (KBI). 2) If the SB needs intervention, the guidewires are then exchanged; the LAD wire can be withdrawn and passed through the most distal cell (closest to carina) to the LCX, thus allowing the projection of struts in the ostial segment of the SB opposite the carina. The “jailed” wire in the LCX is withdrawn and advanced to the LAD. An alternative technique is to form a gentle double curve at the fresh wire tip, crossing LM into the LAD with the tip pointing upward and then pulling back gently with tip rotating downward to enter the LCX. Then POT, KBI, and re-POT are performed [Figure 2], [Figure 3], [Figure 4], [Figure 5] or 3) POT, SB inflation, and re-POT are performed without KBI.[45],[46]This results in optimizing the result of provisional stenting by maintaining circular geometry and reducing strut obstruction of the SB, allowing access to the LCX, the risk for SB occlusion, and global strut malapposition. Optimal control of the guide catheter is critical to avoid deep throating and damage of the stent during pullback of the jailed wire or a partially deflated balloon.
Figure 2: A and B: Baseline CAG showing simple “true” LM bifurcation lesion (Medina 1, 1, 1)

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Figure 3: IVUS pullback from LAD, first diagonal, and LCX

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Figure 4: Step-by-step illustration of provisional ones-stent technique. (A) Predilatation of the LAD with 3.5 x 10 mm cutting balloon at 12 atm (B) Predilatation of the LCX with 3.5 x 10 mm cutting balloon at 12 atm (C) Stenting of the LM-LAD using 3.5 x 30 mm DES at 10atm with jailed guidewire (D) The proximal optimization technique (POT) of the LM using 5 x 8 mm non-complaint balloon at 20 atm (E) Recrossing of the LCX through the distal stent cell (F) Final kissing balloon inflation (KBI) using non-complaint 4 x12 mm balloon in the LAD and 3.5 x 12 mm balloon in the LCX at 8 atm (G) Re-POT of the LMusing 5 x 8 mm non-complaint balloon at 20 atm (H) Final result

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Figure 5: IVUS depiction of the final result

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The POT allows the reconstruction of the initial physiological anatomy of the LM bifurcation. It avoids abluminal wire exchange outside the proximal part of the stent. The stent should be deployed sufficiently proximal to the SB to accommodate a short, large-diameter balloon, sized to the LM, and at least 6–8mm in length. The distal marker of the balloon is positioned in front of the carina and is inflated to optimize the proximal stent segment that allows strut protrusion into the SB with larger strut opening, no or limited carinal shifting, optimization of the stent diameter to the LM diameter, correcting malapposition, and reducing ellipticity of the stented segment.[46]

Routine KBI is not recommended for a single-stent strategy, but it is mandatory for two-stent techniques, including provisional stenting converting into a two-stent technique. Final KBI after provisional stenting has failed to provide clear clinical benefit except for a decrease in the SB stenosis, whereas a significant reduction of MACEs has been documented in the deployment of two stents.[47] In the Korean Coronary Bifurcation Stenting (COBIS) registry, KBI was associated with a higher MACE rate.[48] Five-year follow-up of DKCRUSH-II study demonstrated increased TLR in provisional stenting with KBI group.[49] The short non-complaint balloons with minimal overlap are used to prevent dissection and avoid oval distortion in the LM. Balloon diameters are chosen according to Murray’s law, and the balloon is inflated in the SB first, followed by simultaneous deflation. To reduce proximal deformation, a “modified KBI approach” has been recently proposed, using asymmetric inflation pressures: the SB is first inflated to 12 atm, then partly deflated back to 4 atm with simultaneous inflation of the MB balloon at 12 atm.[50]

Provisional stenting of the SB (conversion to a two-stent strategy)

Usually, the provisional stenting of the SB is indicated by major SB dissections or compromised SB flow. The SB stent may be deployed as T-stenting when the angle between the two vessels is close to 90°. The precise deployment of the SB stent at the ostium is crucial without protrusion inside the MB. The TAP technique is a very simple approach to bail out SB stenting with a narrow bifurcation angle. The LM-LAD stent is sized to the distal vessel, and the POT is performed. The jailed wire is withdrawn, and the LCX is recrossed through the distal cell (closest to the carina). Then the LCX stent is deployed with minimal protrusion (1–2mm inside the LM stent), while maintaining an uninflated balloon in the MB. A slight retraction of the SB stent balloon is followed by final KBI. The kissing balloon deflation should be simultaneous, otherwise the protruded stent in the LM will keep the same position as before KBI. The TAP stenting eliminates the need for a second SB rewiring. An anticipated pitfall of this technique is the creation of a single-layer “neocarina.” The length of neocarina is determined by the takeoff angle of the SB and the site of strut crossing. With a T-shaped takeoff, a small protrusion of the LCX stent inside the LM is required to cover the LCX ostium. In contrast, acute (Y-shaped) SB angles are associated with longer, oval-shaped SB ostia, warranting the need for wider protrusion of the stent. In the BBK (Bifurcations Bad Krozingen) II study, culotte stenting was associated with a significantly lower incidence of angiographic restenosis at 1 year compared with the TAP stenting.[51]

Internal mini-crush involving more protrusion of the SB stent inside the MB stent may also be employed in less angulated LM bifurcation. It is faster and easier to rewire than classic and mini-crush, but has the limitation of the presence of triple-stent layer in the proximal MB. The provisional culotte with proximal overlap of two stents still requires rewiring of the MB.


  Intentional Two-Stent Technique Top


Culotte stenting

The culotte stenting has been evaluated in randomized trials with similar clinical results compared to mini-crush[52] and favorably compared with T-stenting.[53] The more angulated branch, usually the SB (LM-LCX), is stented. The LAD is rewired through the stent struts and dilated. A second stent is advanced through the struts of the first into the LAD. The LM-LAD stent is then deployed. Each limb of the culotte is dilated at high pressure using noncompliant balloon, followed by final KBI at medium pressure. In contemporary culotte stenting, the POT is recommended after the first- and second-stent deployment, as well as a final POT after KBI. It is advisable to avoid a long overlap of stents in the proximal MB, whenever possible (mini-culotte). This technique ensures near-perfect coverage of the carina and the LCX ostium. The main disadvantage of the technique is that rewiring both branches through stent struts can be technically demanding and time-consuming. A bench study reports that a “napkin” or a gap usually exists at the SB ostium after culotte stenting, leading to failure to fully scaffold the ostium and resulting in increased in-stent restenosis (ISR), TLR, and stent thrombosis.[54]

Mini-crush stenting

The SB stent is positioned in the LCX, followed by an advancement of the LAD stent. The LCX stent is pulled back into the LAD approximately 1–2mm and is deployed. The deployment of LAD stent crushes the proximal LCX stent against the LM wall. The LCX is rewired through the proximal stent struts of both LAD and crushed LCX stent to perform final KBI. The mini-crush technique is suitable in narrow-angled LM bifurcation (<70°). The immediate patency of both branches is assured, making this technique useful in conditions of instability or complex anatomy. This technique provides excellent coverage of the LCX ostium. The main disadvantage is that to perform final KBI, there is a need to recross multiple struts with wire and a balloon.[10],[12]

Double kiss (DK) crush stenting

A stent is placed into the LCX, and a balloon placed in the LM-LAD 2–3mm of the LCX stent is positioned in the LM. The LCX stent is deployed, and then the guidewire and balloon from the LCX are removed. The prepositioned balloon in the LM-LAD is inflated to crush the protruding segment of the LCX stent against the LM wall. The LCX is rewired through proximal cell of the stent, followed by first KBI. Then a stent is deployed in the LM-LAD segment, which is followed by POT. The wire is again recrossed into the LCX and final KBI is followed by re-POT [Figure 3]. As a result, the DK crush technique consists of seven steps: the SB stenting with 2–3mm protrusion into the MB, balloon-crush of the SB stent, first SB rewiring through proximal stent cell, first KBI, the MB stenting followed by POT, second rewiring of the SB through proximal stent cell, final KBI, and the POT [Figure 6], [Figure 7], [Figure 8]. First KBI in DK crush stenting can optimize the distorted SB stent and leave only one layer of stent struts at the SB ostium, which facilitates final KBI after the MB stenting. Another advantage of this technique over classical crush is that the first KBI rebuilds the shape of bifurcation anatomy by minimizing repeated distortion of the SB ostial stent. This innovative DK crush technique compared to classical crush is shown to have a significantly shorter procedural time, lower contrast usage, and a higher final KBI rate (100% vs. 70%; P < 0.01) [Table 2], leading to an improved angiographic result with residual stenosis.[55] It is of paramount importance that rewiring of the SB is carried out from the proximal stent cell as distal SB recrossing is likely to navigate the guidewire in the abluminal area between the stent and arterial wall leaving a significant gap at the SB ostium after final KBI. The guidewire position in SB is confirmed by the visual assessment from fluoroscopy (two orthogonal projections) and/or IVUS or OCT guidance from the MB. DKCRUSH-V study shows a lower rate of target lesion failure at 1 year compared with a provisional stenting strategy.[43] DK crush bested the culotte method in the patients with high-risk LM bifurcation in the DKCRUSH-III randomized trial.[21] More than twice the patients in the culotte group experienced MACE at 1 year compared with the DK crush group (16.3% vs. 6.2%, P < 0.05). Even 3 years of clinical outcomes were in favor of DK crush when compared to culotte stenting.[21],[22]Significantly high rates of TVR are the main drivers of the high MACE rate in culotte technique.
Figure 6: Step-by-step illustration of DK crush technique. (A) Baseline CAG revealing significant complex LM bifurcation lesion involving proximal LAD and LCX (Medina 1, 1, 1) (B) Navigation of guidewires into the LAD and LCX followed by stenting of the LCX with 2–3mm protrusion into the LM (C) Crushing of the LCX stent by compliant balloon in the LM-LAD (D) First KBI of LAD and LCX after rewiring of the LCX through the proximal stent cell (E) Stenting from LM to the LAD (F) POT of the LM (G) Final KBI after second rewiring of the LCX through the proximal stent cell (H) Final result

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Figure 7: Post-PCI IVUS of the LM-LAD

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Figure 8: Post-PCI IVUS of the LM-LCX

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Table 2: Comparison of DK crush with classical crush-stenting technique

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V stent and the simultaneous kissing stent

V stenting is performed by placing and deploying two stents together in a narrow-angled bifurcation.[12],[56]Guidewires are placed in both the LAD and LCX, and with or without predilatation, the two stents are placed into LM and the respective branches and deployed by simultaneous inflation. We are not a proponent of simultaneous kissing stent that allows a variable amount of protrusion, creating rather long double barrel. V stenting is relatively easy and fast, and thus an ideal in emergencies. It is indicated in patients with a short LM-free disease and a critical disease of both the LAD and LCX ostia.[12]


  Dedicated Bifurcation Stents Top


Several dedicated bifurcation stents (DBSs) have been adopted recently for LM disease.[57] These devices offer common advantages over conventional DES to cover LM bifurcation segment. Their design conforms to the natural anatomy of the bifurcation and can facilitate more effective SB ostial scaffolding. Furthermore, DBS provides easier and quicker access to MB and SB, thereby lowering the risk of SB closure. A limited experience with DBS for LM bifurcation is available. Most of them are not designed for the specific characteristics of the LM and do not meet extreme variations in the vessel size, ostial SB opening, and bifurcation angle observed in LM. As the anatomy of LM bifurcation varies considerably, further studies are required to define their role in this subset of patients.


  Postprocedure Imaging Top


Postprocedure imaging with IVUS or OCT is strongly recommended for LM bifurcation of PCI. This should be performed from the LAD and LCX to the LM.

IVUS is considered to be a useful modality in selecting treatment strategy [Figure 3] and helpful in optimally expanding the stent [Figure 5], [Figure 7], and [Figure 8], with or without post-stent balloon dilatation, to avoid under- or overstretch of the stent diameter, and might contribute to better long-term outcomes as compared with conventional angiography guidance.[58 Stent underexpansion is the most important cause of DES failure. A minimal stent area (MSA) less than 5.0–5.5mm2 is the best predictor of DES restenosis and early thrombosis.[59],[60]The optimal IVUS-MSA criteria for ISR were assessed in 403 patients undergoing DES implantation for LM PCI. The cutoff values for MSA predicting angiographic restenosis on a segmental basis were 5.0mm2 for LCX ostium, 6.3mm2 for LAD ostium, 7.2mm2 for polygon of confluence (POC), and 8.2mm2 for the proximal LM above POC.[61] Underexpansion was more significantly frequent in the two-stent technique, the LCX ostium being the most common site of underexpansion. A smaller IVUS-MSA predicted angiographic ISR, 9 months after DES implantation to treat LM disease, and post-PCI underexpansion was an independent predictor of 2-year major adverse cardiac events, especially repeat revascularization.[62] A subgroup analysis from the MAIN-COMPARE registry shows reduced mortality with IVUS as compared to angiography guidance.[58] Another recent IVUS study showed that the incidence of the composite of cardiac death, MI, and TLR, and stent thrombosis are lower in IVUS-guided group.[62]

Frequency domain OCT offers superior resolution and can identify stent malapposition, edge dissections, tissue protrusion, and thrombus more clearly than IVUS.[63] It has been observed that OCT-guided optimization of LM PCI is feasible and safe.[64],[65]As blood must be adequately replaced by the contrast for clear image, assessment of LM ostium or a relatively large LM is often problematic. Furthermore, as no standardized OCT criteria for stent optimization are available, this modality may not be quite useful to guide LM bifurcation PCI. Nevertheless, with accumulating experience and data, it is expected that OCT will be an important adjunctive tool for LM PCI.


  LM Trifurcation Top


LM trifurcation encountered in 10% of CAG cases poses real technical challenges. A single-stent strategy is still favorable. If the SBs have limited disease, a triple KBI is associated with favorable early and long-term results. According to the specific anatomy, the SBs of significant sizes and diseases might require two-stent techniques; a minor SB (LCX or ramus) is generally identified and treated with a “keep it open” strategy.[66]


  Conclusion Top


LM stenting is a different animal with its bifurcation as a unique entity in view of a larger myocardium at jeopardy, wider bifurcation angle and almost the similar importance of the SB and MB. Despite impressive advances in the stent technology, revascularization of the LM disease remained the province of the surgeon until recently. LM PCI employing current generation DES is safe and effective with clinical outcomes comparable to CABG. Stenting of ostial and shaft of LM can be achieved without major technical difficulties and with good immediate and long-term results. Distal LM bifurcation and trifurcation lesions continue to pose considerable challenges and require expertise and performance of unique approaches for optimal results. An integrated approach that combines careful case selection, proper preprocedure planning, and specialized techniques with adjunctive intracoronary imaging support is further likely to improve the success rate and long-term clinical outcomes of LM PCI.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

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Abstract
Introduction
Anatomical Compl...
Evidence for Per...
Preprocedural As...
Intravascular Ul...
Stenting of LM O...
Choosing a Stent...
Intentional Two-...
Dedicated Bifurc...
Postprocedure Im...
LM Trifurcation
Conclusion
References
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