Introduction
Coronary bifurcations are commonly encountered and remain a challenge to many interventionalists. Bifurcation differ in terms of anatomical configuration, pathological disease, and severity. Various strategies and techniques have been developed for bifurcation percutaneous coronary intervention (PCI). The appropriate technique may be selected according to the lesion characteristics and complexity of the bifurcation.
The provisional stenting strategy is suitable for most bifurcation lesions. It is a stepwise layered approach to intervention for bifurcation. This strategy is highly successful and associated with a low risk for adverse events.
The aim of this review is to analyze the contemporary approach to provisional stenting, while highlighting specific key points relevant to the optimal performance of this stenting technique. Lingering gaps and controversies of provisional stenting are also discussed.
When to choose provisional stenting strategy?
The importance of a bifurcating coronary segment is defined by the significance of its side branch (SB). If the SB is one which the operator should avoid losing, then appropriate procedural strategy should be adopted to achieve this intention. The early randomized bifurcation stenting trials (eg, the British Bifurcation Coronary Study (BBC ONE) and Nordic Bifurcation Study (NORDIC ONE)) did not associate a systematic 2-stent strategy with a significant advantage.[1,2]
A meta-analysis of 6961 patients from 5 randomized controlled trials and 7 observations trials showed an increased risk of myocardial infarction with a double-stent strategy versus a single-stent strategy, likely related to drug-eluting stent thrombosis.[3] However, it may be inappropriate to extrapolate these findings to all scenarios, as the studies are limited by patient selection biases. Also, there have been subsequent advancements in newer generation drug-eluting stents, refinement of bifurcation techniques (eg, proximal optimization technique (POT), kissing balloon inflations (KBIs), intravascular imaging, etc), which may invalidate some of these early observations.
In its latest consensus document, the European Bifurcation Club (EBC) reaffirms the provisional stenting strategy as the default plan for most bifurcations. This is because the strategy retains the flexibility to escalate treatment options to 2-stent techniques, for example, T-stenting, T and small protrusion (TAP), and Culotte.[4] It must be emphasized that provisional stenting should be understood as a treatment philosophy rather than a technique, that is, a plan for a “simple” approach to bifurcation PCI, with escalation to SB dilatation or stenting should the need arise.
This endorsement does not support the use of provisional stenting as the default approach to all bifurcations. Categorization of bifurcation disease (simple vs. complex) using tools (eg, the DEFINITION Criteria) enables an educated approach to bifurcation PCI.[5] The DEFINITION and DEFINITION II trials showed that the provisional stenting strategy results in better outcomes for simple bifurcations, whereas a systematic 2-stent strategy is more effective for complex bifurcations.[6]
How to perform provisional stenting?
The sequential steps for provisional stenting include [Figure 1][7]: (1) wiring of the main branch and SB; (2) pre-dilation of the main branch up to the operator’s discretion; (3) stenting of the main vessel (MV) across the bifurcation with a stent of appropriate size according to the diameter of the distal MV, followed by mandatory POT application to the proximal MV; (4) removal of the SB wire and rewiring into the SB via the distal stent strut, if treatment of the SB is considered; (5) treatment of the SB through balloon angioplasty; (6) KBI and POT; (7) Stenting into the SB according to the T, TAP, or Culotte techniques; and (8) KBI and final POT.[4]
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Figure 1:: Procedure of
provisional stenting. (1) Wiring of both the main branch and SB. (2) Stenting of the MV according to the size of the distal MV. (3) POT to the proximal MV. (4) Post-POT. (5) and (6) Switching wires between the MV and SB. Distal strut wire crossing into the SB. (7)
Kissing balloon inflation. (8) Final results after final POT/re-POT of the proximal MV. If an SB stent is necessary, T-stenting, T-stenting and small protrusion, or a Culotte technique may be used. MV: Main vessel; POT:
Proximal optimization technique; SB: Side branch. Adapted from Sawaya et al.
[ 7 ]This strategy may be performed with a 6-Fr or 7-Fr system. Larger guiding catheters may be considered in situations such as the use of rotational atherectomy with burr sizes ≥1.75 mm or for the facilitation of simultaneous use of 2 stents or balloons.
Wiring into the more difficult SB should be attempted first. Inserting a wire into the SB protects against loss of the SB, improves the SB angulation which will facilitate the rewiring, and serves as a landmark for rewiring in the event of SB occlusion after MV stenting. Appropriate preparation of the MV prior to stenting is necessary. The operator determines the need for pre-dilation or other lesion preparations (eg, atherectomy) based on the anatomy and lesion characteristics.
Routine dilation of the SB before MV stenting is not recommended to reduce the risk of dissection, which would then necessitate the placement of a stent. Balloon injury may also increase the risk of SB restenosis. Nevertheless, use of a smaller balloon for SB pre-dilation may be considered if the SB ostium is severely stenosed, difficulty in rewiring into the SB is anticipated, or the ostium is heavily calcified.
The results of a small series conducted by Pan et al[8] suggested that pre-dilation into the SB improves thrombolysis in myocardial infarction (TIMI) flow post-MV stenting and reduces the need for SB treatment. Stenting of the MV is performed with a stent of appropriate size according to the diameter of the distal MV. This is followed by systematic POT utilizing a balloon of the same size as the diameter of the proximal MV.
When SB intervention is deemed necessary (see below), the SB is rewired with the “pullback rewiring technique” aiming at a distal strut. One may use a new wire or exchange the MB and trapped SB wire. The SB is subsequently treated with balloon dilatation. The procedure must be finalized with KBI and a final POT (also termed re-POT).
If the SB yields a suboptimal result, further stenting using the T, TAP, or Culotte techniques is recommended. Ideally, the SB is wired through the distal strut. If SB stenting is planned, T-stenting would be adequate for complete SB ostial coverage. However, if the SB is wired through proximal struts, there will be a gap in SB ostial stent coverage after KBI. If there is no plan to attempt a distal SB rewiring or the patient’s instability demands urgent stent implantation, then the TAP or Culotte techniques can be selected [Figure 2].
Figure 2:: Provisional side branch (SB) stenting according to the location of side branch wire crossing. POT:
Proximal optimization technique; TAP: T-stenting and small protrusion. Adapted from Sawaya et al.
[ 7 ]The jailed balloon technique is a modification of guidewire jailing for protecting the SB.[9] SB compromise occurs after MV stenting owing to plaque or carina shift. Spatial occupation of the SB ostium with an uninflated balloon during MV stenting prevents the occurrence of SB compromise. If the SB flow is preserved, the jailed balloon may be removed uninflated. In the presence of SB compromise, the jailed balloon functions as a visible marker of the SB and bifurcation-angle modifier to facilitate SB rewiring. If the SB flow is compromised, thereby affecting hemodynamic and electrical stability, the jailed balloon may be inflated to re-establish flow before attempting the rewiring. POT of the proximal MV, SB rewiring, KBI, and final POT are important subsequent steps for the correction of stent deformation and malapposition.
Intravascular imaging with intravascular ultrasound (IVUS) or optical coherence tomography (OCT) are useful aids in bifurcation PCI. It enables good PCI planning through a more comprehensive assessment of plaque characteristics, for example, calcification. This approach allows proper vessel sizing, lesion length estimation, etc.
Imaging guidance optimizes PCI outcomes by allowing proper lesion preparation (eg, atherectomy), ensuring stent expansion and apposition, and detecting complications (eg, edge dissection and stent deformation). Owing to its high resolution, 3-dimensional OCT also allows the confirmation of guidewire distal strut crossing; this is an important step in cases requiring SB stenting.[10]
Under specific circumstances (ie, when the distal MV is not significantly diseased), an “inverted provisional” approach may be used. This technique involves stent implantation from the proximal MV into the SB, across the distal MV.
Key technical steps in provisional stenting
For optimal provisional stenting results, the following steps are crucial: (1) POT; (2) optimal SB rewiring; and (3) KBI.
POT
POT was first introduced by Dr. Olivier Darremount at the EBC Meeting held in 2007. Stenting of the MV according to the size of the distal MV avoids overexpansion of the distal MV and carina shift at the bifurcation. Subsequently, a short balloon with a size determined according to the proximal MV is used to dilate the proximal MV stent. It is important to ensure adequate length of stent landing (≥6–8 mm) in the proximal MV to permit POT with the shortest available balloon without risking injury to the proximal peri-stent segment.
A non-compliant balloon is preferred if the stent is under-expanded and the reference diameter of the proximal MV is ascertained. In the absence of disease in the proximal MV segment, use of a semi-compliant balloon may be feasible. This step optimizes the stent expansion and apposition at the proximal MV and restores the fractal geometry of the bifurcation. It also opens the stent struts, thereby facilitating SB rewiring (especially through the distal struts) while avoiding accidental wiring outside the proximal part of the stent.
The position of the POT balloon markedly affects the procedural outcome.[11] It is placed immediately proximal to the carina, and the dilation should cover the length until the proximal edge of the stent.
It has been shown that the POT technique improves clinical outcomes.[12] Following KBI, a final POT/re-POT is needed to correct oval/elliptical stent deformation (“bottle-neck” deformation) at the proximal MV.[13]
After SB stenting (eg, with the TAP technique), there is a new metal carina. Placing the final POT balloon immediately proximal to this carina is crucial for the prevention of “jailing” in the SB ostia through deflection of the overhanging struts towards the SB ostia [Figure 3].[14]
Figure 3:: Final POT balloon position and assessment of the cell opening area (yellow) through 3-dimensional micro-CT. CT: Computed tomography; POT:
Proximal optimization technique; SB: Side branch. Adapted from Andreasen et al.
[ 14 ]The operator should be familiar with the balloons used for POT, as they are manufactured with different cone angles and positions of the shoulder in relation to the balloon markers. Dedicated short length balloons for POT with short shoulders are available in certain countries.
Distal strut guidewire crossing
Following POT, the operator determines if further intervention is required for the SB. If so, rewiring into the SB is performed. Distal strut crossing allows better strut clearance from the SB ostia and permits stent scaffold of the SB ostia opposite to the carina.[7]
SB rewiring may be performed with the MV guidewire “pullback” technique or the insertion of a new guidewire. The jailed SB guidewire is pulled back completely out of the stent at the proximal MV. Subsequently, it is rewired into the MV, preferably in a loop. During the jailed SB wire pullback, one needs to be careful to avoid deep intubation of the guiding catheter, which may cause proximal vessel dissection or longitudinal stent deformation.
KBI
In provisional stenting, the performance of KBI is optional. However, if any instrumentation (eg, balloon dilatation) has been utilized across the stent struts into the SB, KBI is necessary for the correction of MV stent deformation. SB distal strut crossing is important for a good KBI result.
The use of non-compliant short balloons with short overlap is recommended during KBI. The size of the balloons is determined according to the reference diameters of the MV and SB. In KBI, it is recommended to inflate the SB balloon prior to the simultaneous inflation of both balloons and subsequent simultaneous deflation. KBI may cause proximal MV stent deformation, particularly with long balloon overlaps. As mentioned earlier, this complication must be corrected by performing a final POT/re-POT.
Mortier et al[15] proposed a “modified KBI approach” which uses asymmetric inflation pressures. The SB is inflated to 12 atm and, subsequently, partly deflated back to 4 atm. Next, simultaneous inflation of the both balloons at 12 atm is performed. This approach resulted in less proximal elliptical stent deformation, no increase of malposed struts, and reduced risk of SB ostial stenosis.
Bench tests have proposed a simpler alternative to KBI, namely the POT-Side-POT technique.[16] It involves sequential dilation of a single balloon in the proximal MV, SB, and finally the proximal MV again. This approach maintains the circular geometry without arterial overstretch whilst reducing the obstruction of SB ostium struts and minimizing strut malapposition.
When should the SB be treated when using a provisional strategy?
Currently, there are no consistent definitions of a suboptimal SB result or definite recommendations on the application of provisional stenting to the SB. Various clinical trials have used different metrics. Examples include:
- Angiographic criteria (eg, degree of stenosis (DS) of the SB ostium, SB TIMI flow, significant dissection): (1) SIRIUS Bifurcation trial: SB DS >50%.[17] (2) Pan et al[18]: SB DS >50% and TIMI flow <3. (3) Nordic Bifurcation study: TIMI flow = 0 after balloon dilatation.[2] (4) SMART-STRATEGY trial: DS >50% for left main (LM) bifurcation; DS >75% for non-LM bifurcation.[19]
- Intravascular imaging criteria (OCT): OCTOBER trial: SB minimal diameter <50% of the SB reference diameter.[20]
- Physiological indices: (1) Fractional flow reserve (FFR): Koo et al[21]: FFR < 0.75; Lee et al[22]: FFR ≤ 0.80. (2) Instantaneous wave-free ratio ≤ 0.89.[23]
The significance of SB compromise that warrants further intervention is at the discretion of the operator.
Use of routine final KBI for provisional stenting?
Generally, the use of routine KBI following stenting of the MV is not recommended.[24] Research has yielded conflicting data regarding routine KBI. Computational flow dynamics showed improved laminar flow after clearing of the struts across the SB ostia.[25]
The Nordic-Baltic Bifurcation III Study showed that final KBI in a single-stent bifurcation PCI strategy reduced angiographic SB ostial stenosis.[26] However, the major adverse cardiac event rates were similar regardless of whether final KBI was performed. The COBIS I Registry reported higher target lesion revascularization (TLR) with routine final KBI after MV stenting in single-stent bifurcation PCI.[27]
However, the COBIS II Registry showed better survival from major adverse cardiac events (cardiac death, myocardial infarction, and TLR) after routine final KBI.[28] This difference derived from a large registry could be related to the increased use of second-generation drug-eluting stents and large SB sizes. Hence, there is an ongoing debate regarding the need to clear overhanging/“floating” stent struts across the SB ostia as a systematic practice in single-stent PCI strategy.
Provisional stenting for LM bifurcation
The details of LM bifurcation PCI are outside the purview of this article. However, the challenge concerning LM PCI relates mainly to the large and important SB, the left circumflex (LCx) artery.
The EBC MAIN study did not show differences in the triple primary endpoints (ie, death, myocardial infarction, TLR) between a provisional stenting approach and a systematic 2-stent approach for left main coronary artery (LMCA) bifurcation PCI.[29] Hence, the investigators concluded that the simpler stepwise layered provisional approach should be the preferred choice for most LMCA bifurcations. The Double Kissing Crush (DK-CRUSH) V study showed that the upfront 2-stent strategy using the DK-Crush technique produced better results than a provisional strategy.[30] The 1-year composite primary endpoint of cardiac death, target vessel myocardial infarction, or clinically driven TLR was 5% in the DK-Crush arm and 10.7% in the provisional strategy arm. The divergent results of the EBC MAIN and DK-CRUSH V studies could be related to the more complex bifurcations treated in the latter trial. The very low utility of the DK-Crush technique (only 5% of cases) and high usage of the Culotte technique (53%) in the EBC MAIN trial could also be a technical explanation. The DK-CRUSH III trial demonstrated that the Culotte technique was inferior to the DK-Crush technique for LM bifurcation PCI.[31] The provisional stenting strategy is generally recommended for the treatment of simple LM bifurcations. However, one should not hesitate to consider the upfront 2-stent technique for complex LM bifurcations, and the DK-Crush technique should be the technique of choice.
Intravascular imaging, especially IVUS, is important for stent optimization and the prevention of major adverse cardiac events in LMCA PCI.[32] Moreover, it may improve patient survival.[33] The presence of a large final minimum stent area (MSA) is associated with improved outcomes. MSA thresholds based on IVUS that predicts event-free survival and TLR were defined in an Asian single-center study.[31] The thresholds were 5, 6, 7, and 8 mm2 for the proximal LCx, proximal left anterior descending (LAD) artery, polygon of confluence, and LMCA, respectively. However, a larger multi-center trial with a predominantly Caucasian population with larger body sizes from the Americas and Europe suggested higher MSA thresholds for the proximal LCx, proximal LAD and LMCA (6, 7, and 10 mm2, respectively).[34] Maehara et al[35] presented “How to Use IVUS to Guide LM Stenting: Evidence and Case Examples” at the 2018 Transcatheter Cardiovascular Therapeutics meeting held in San Diego (California, USA).
OCT may be helpful for distal LMCA bifurcation PCI. Owing to its enhanced resolution, it allows better assessment of the plaque morphology, especially calcification, vessel sizing, and lesion length planning. Also, 3-dimensional OCT can assist in the confirmation of distal stent strut crossing into the SB.
Owing to the large discrepant sizes of the proximal and distal MV, POT is critical for LMCA stenting.
Conclusions
Coronary bifurcation remains a common technical challenge in PCI. The provisional stenting approach is the default strategy for most bifurcations. This article describes the stepwise technique, which is easy to perform and provides the flexibility to escalate therapeutic options (eg, balloon dilatation or stenting) for a compromised SB. Technical tip for optimal performance of key steps in this strategy (eg, POT and KBIs) ensure high procedural success with minimal complications.
Based on the findings of the randomized EBC MAIN trial, provisional stenting for LM bifurcation is an appropriate strategy. However, equally robust clinical data were obtained with the DK-Crush stenting technique in the DK-CRUSH V trial. The divergent results should not be interpreted as favoring a specific strategy but instead considered complementary, that is, the appropriate strategy is selected according to the anatomy and complexity of the LM bifurcation.
Certain controversies pertaining to provisional stenting remain, such as the definition of a SB requiring further intervention and the role of systematic KBI in single-stent bifurcation PCI. The proposed alternative to KBI (ie, the POT-Side-POT technique) also warrants further validation.
Funding
None.
Conflicts of interest
None.
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