Chronic total occlusions (CTOs) are defined as completely occluded coronary arteries with Thrombolysis In Myocardial Infarction (TIMI) 0 flow with an estimated duration of at least 3 months . CTOs can be challenging to recanalize, requiring specialized equipment and techniques , which is covered in detail in the Manual of Chronic Total Occlusion Interventions . A global consensus document on the key principles underlying CTO PCI was recently published and will be briefly discussed in this chapter .
21.1
Planning
Planning is key for the success and safety of CTO PCI. The key indication for CTO PCI is symptom improvement . To allow adequate time for procedural planning and preparation and for proper counseling of patients, ad hoc CTO PCI is discouraged in most cases . CTO PCI preplanning can also help minimize contrast and radiation dose, reduce patient and operator fatigue, allow additional evaluation (such as myocardial viability) to be performed, and enable detailed discussion with the patient about all aspects of the CTO PCI procedure.
Coronary computed tomography angiography (CCTA) can be useful for evaluating the CTO segment and planning PCI. Several CCTA-based scores have been developed, such as the CT-RECTOR multicenter registry (Computed Tomography Registry of CTO revascularization) score and the Korean Multicenter CTO CT Registry score . CCTA can also help identify the optimal fluoroscopic projection angles with the least foreshortening to use during CTO crossing attempts ( Fig. 21.1 ).
In selected cases, however, ad hoc PCI may be the best option, such as in patients who present with an acute coronary syndrome due to failure of a highly diseased saphenous vein graft. In such patients treatment of the native coronary artery CTO is preferred, if feasible ( Section 18.7 ) . Another possible scenario is patients in whom obtaining arterial access is very challenging.
21.2
Monitoring
CTO PCI can be technically challenging and time consuming, and may require high radiation and contrast doses. Careful attention to the patient’s ECG and hemodynamics, as well as radiation and contrast use, is needed throughout the case. Moreover, the operators should be ready to manage any complication that may occur, such as perforation.
21.3
Medications
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Unfractionated heparin is the preferred agent, because it can be reversed in case of severe perforation. The recommended activated clotting times (ACT) are:
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>300 seconds (Hemochron) for antegrade CTO PCI (some operators use >250 s).
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>350 seconds (Hemochron) for retrograde CTO PCI (some operators use >300 s but check ACT very frequently if it is in the low 300s range).
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The ACT should be checked every 20–30 minutes once therapeutic.
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Bivalirudin is best avoided because its anticoagulant effect cannot be reversed. Moreover, there are unpublished cases in which guide thrombosis occurred during long procedures.
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Glycoprotein IIb/IIIa inhibitors and cangrelor should NOT be given, even after successful crossing and stenting of the CTO, because minor wire perforations could reopen and cause delayed pericardial effusion and tamponade.
21.4
Arterial access
CTO PCI is unique in that dual (or sometimes triple) arterial access is commonly required to allow dual angiography (see angiography section below). Both femoral and wrist access (proximal radial, distal radial , and ulnar) can be used, with use of radial access, including biradial access , significantly increasing in recent years . Use of distal radial access ( Section 4.3.2 ) or use of long radial artery sheaths may facilitate use of the left radial artery for CTO PCI. However, many operators still utilize at least one femoral access (often with 45 cm long sheaths) to increase guide catheter support.
21.5
Engagement
Vessel engagement is performed as outlined in Chapter 5: Coronary and Graft Engagement . Use of large (7 or 8 French) guide catheters with supportive shapes (AL for the right coronary artery and EBU or XB for the left main) are particularly important in CTO PCI, since strong support is often required to cross the CTO. Using 6 French guide catheters may limit the option of using IVUS-guided cap penetration or management of subsequent complications.
21.6
Angiography
A key difference of CTO PCI compared with non-CTO PCI is that in most cases it requires dual injection for better understanding of the CTO anatomy and guiding CTO crossing attempts. Dual injection angiography is the simplest and most effective technique for increasing CTO PCI success rates and should be performed in all patients with contralateral collaterals . It also improves procedural safety by elucidating the guidewire location during crossing attempts and facilitating management of periprocedural complications, such as perforation .
The following four characteristics need to be assessed for every CTO: (1) proximal cap morphology, (2) occlusion length, course, and composition (e.g., calcium), (3) quality of the distal vessel, and (4) characteristics of the collateral circulation ( Fig. 21.2 ).
21.6.1
Proximal cap morphology
Understanding the location and morphology of the proximal cap is critical for selecting an optimal CTO crossing strategy, because trying to cross an ambiguous proximal cap may lead to perforation. Several techniques can be used to clarify the location of the proximal cap and allow safe antegrade crossing, such as:
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Additional angiographic projections.
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Selective contrast injection through a microcatheter located near the proximal cap.
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Use of intravascular ultrasound (IVUS) .
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Preprocedural CCTA or real-time CCTA coregistration .
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Use of dissection/reentry techniques (move the cap techniques) .
If the location of the proximal cap cannot be resolved, a primary retrograde approach or move the cap techniques are often recommended, if technically feasible.
21.6.2
Lesion length, course, and composition
Lesion length is often overestimated with antegrade only injections due to underfilling and poor opacification of the distal vessel from competing antegrade and retrograde coronary flow, leaving uncertainty about the location and morphology of the distal cap. Dual injection or preprocedural CCTA allows more accurate estimation of the CTO proximal cap location, length, and distal cap anatomy.
Severe calcification and tortuosity of the occluded segment can adversely affect CTO crossing and increase the likelihood of subintimal (also called extraplaque) guidewire entry. Advancing a knuckled (J-shaped) guidewire or changing to the retrograde approach is often preferred when the vessel course is unclear or highly tortuous , since a knuckled guidewire can facilitate advancement within the vessel architecture with low risk of perforation .
21.6.3
Distal vessel
The quality of the distal vessel can significantly impact the likelihood of CTO crossing: distal vessels of large caliber (>2.0 mm) that fill well, do not have significant disease and are free from major branches may facilitate CTO recanalization . Conversely, small, diffusely diseased distal vessels are more challenging to recanalize, especially following subintimal guidewire entry. In some cases, however, distal vessels are small due to hypoperfusion, leading to negative remodeling and will increase in size after recanalization . Distal CTO caps in native coronary artery CTOs are more likely to be calcified and resistant to guidewire penetration in vessels previously bypassed distal to the CTO . Moreover, distal vessel calcification may hinder wire reentry in case of subintimal guidewire entry. The presence of a bifurcation at the distal cap (as well as at the proximal cap or within the occluded segment) may hinder antegrade wiring of the main branch and also increases the likelihood of side branch loss. The retrograde approach is favored in cases of CTOs with a bifurcation at the distal cap because antegrade techniques often lead to occlusion of one of the two branches .
21.6.4
Collateral circulation
Evaluation of the collateral circulation is critical for determining the feasibility of the retrograde approach . High-quality angiography (ideally obtained on low magnification during breath hold and without panning) allowing complete opacification of collateral vessels and obtained in optimal angiographic projections, should, therefore, be encouraged as part of the routine diagnostic studies when a CTO is discovered.
Retrograde access to the distal vessel can be achieved via septal collaterals, epicardial collaterals, or (patent or occluded) coronary bypass grafts. When assessing collateral channels it is important to consider size, tortuosity, bifurcations, angle of entry to and exit from the collateral, jailing of entry or exit by a previously deployed stent, which may hinder guidewire crossing, and distance between the collateral exit and the distal cap. The most important predictor of successful guidewire and device crossing is lack of tortuosity, followed by size . The size of the collaterals is often assessed using the Werner classification (CC0: no continuous connection; CC1: threadlike connection; CC2: side branch-like connection) . Crossing invisible septal collateral channels is often possible with the surfing technique, letting the wire find the path of least resistance . It is important to carefully study previous angiograms for multiple potential collateral pathways, as the predominant collateral may change over time prior to the procedure or during the course of PCI (“shifting collaterals”). Previously visualized collaterals that disappear at the time of the procedure may still be crossable. Whenever required, and after ensuring adequate blood backflow to prevent barotrauma, selective contrast tip injections through the microcatheter can be safely performed to outline collateral anatomy. Patent bypass grafts represent an ideal retrograde conduit due to the absence of side branches, predictable course and large caliber, although the angle of the distal bypass graft anastomosis can sometimes be unfavorable to obtain retrograde access. Even occluded grafts can be used as retrograde pathways. In cases where the collateral circulation originates from the left anterior descending artery that is supplied by a mammary artery graft, access through the IMA graft increases the risk of global ischemia and should be avoided whenever possible .
Septal collaterals are usually safer and easier to navigate compared with epicardial collaterals . In contrast to epicardial collaterals, septal collaterals can be safely dilated with small (≤1.5 mm) balloons at low pressure (2–4 atm) to facilitate microcatheter or device crossing, if required. The donor vessel proximal to the collateral origin, as well as collateral dominance (i.e., presence of a single large visible collateral), should also be assessed during retrograde procedures to determine the risk of ischemia during retrograde crossing attempts. Careful review of collaterals prior to the procedure can reduce contrast and radiation dose as well as the duration of the procedure. In cases where the collateral anatomy is unclear or ambiguous, it can be helpful to perform selective contrast injection into the collateral through the central lumen of a microcatheter placed into the collateral using a 2–3 cc luer lock syringe, such as the Medallion syringe (Merit Medical). In cases where unfavorable or non-interventional epicardial collaterals provide the dominant blood flow to the CTO, gentle balloon occlusion of the epicardial collateral for 2–4 minutes may allow recruitment of more favorable interventional collaterals that can be used for retrograde crossing .
21.7
Determine target lesion(s)
This step is performed as discussed in Chapter 7: Selecting Target Lesion(s) .
21.8
Wiring
Advancing a guidewire through the CTO is the most challenging part of CTO PCI. There are four CTO crossing strategies, classified according to wiring direction (antegrade and retrograde) and whether or not the subintimal space is utilized (wiring vs dissection and reentry) ( Fig. 21.3 ) .
21.8.1
Antegrade wiring
Antegrade wiring (also called antegrade wire escalation) is the most widely used CTO crossing technique . Various guidewires are advanced in the antegrade direction (original direction of blood flow). The choice of guidewire depends on CTO characteristics. If there is a tapered proximal cap or a functional occlusion with a visible channel, a polymer jacketed, low penetration force, tapered guidewire is used initially with subsequent escalation to intermediate and high penetration force guidewires, as required. If there is a blunt proximal cap, antegrade wiring is usually started with an intermediate penetration force polymer-jacketed guidewire or a composite core guidewire. Stiff, high penetration force guidewires may be required in highly resistant proximal caps or when areas of resistance are encountered within the body of the occlusion. After proximal cap crossing of 1–2 mm, however, deescalation to less penetrating guidewires should follow to safely navigate through the CTO segment (“step-up/step-down” technique).
Contralateral injection and orthogonal angiographic projections help determine the guidewire position during crossing attempts. If the guidewire enters into the distal true lumen, the microcatheter is advanced into the distal true lumen and the dedicated CTO guidewire is exchanged for a workhorse guidewire through the microcatheter to minimize the risk of distal vessel injury and perforation during subsequent balloon angioplasty and stenting. If the guidewire exits the vessel structure it should be withdrawn and redirected without advancing microcatheters, balloons, or stents over it to prevent enlarging (or creating) a perforation. If the guidewire enters the subintimal space it can be redirected, but if this maneuver fails, the wire can be left in place to aid directing a second guidewire into the distal true lumen (parallel wire technique), which can be assisted by a dual lumen microcatheter, or facilitated by the use of IVUS . Alternatively, antegrade dissection/reentry techniques can be used to reenter into the distal true lumen, as described below. Subintimal guidewire advancement significantly distal to the distal cap should be avoided, as it can lead to hematoma formation, causing luminal compression and reducing the likelihood of success. Antegrade vessel reentry can be guided by IVUS, although this approach requires 8 French guide catheters and expertise in IVUS interpretation and may be hindered by limited wire maneuverability in the presence of the subintimal IVUS catheter.
21.8.2
Antegrade dissection and reentry
Antegrade dissection and reentry involves entering the subintimal space, followed by subintimal crossing of the CTO with subsequent reentry into the distal true lumen. Antegrade dissection may be intentional or unintentional during antegrade wiring attempts. The initially developed dissection reentry technique was named STAR (subintimal tracking and reentry) and used uncontrollable reentry into the distal lumen . This frequently necessitated stenting long coronary segments with occlusion of numerous side branches, with extensive vascular injury and high rates of in-stent restenosis and reocclusion . As such, the STAR technique has evolved to a bailout strategy without stent implantation after ballooning, in preparation for a repeat CTO PCI attempt (subintimal plaque modification, also called “investment” procedure) after 2–3 months . The development of limited dissection/reentry techniques (using dedicated reentry systems or wire-based strategies ) was an important advancement, as they minimize vascular injury, limit the length of dissection and subsequent stent length, and increase the likelihood of side branch preservation . Such approaches have been associated with favorable clinical outcomes .
21.8.3
The retrograde approach
The retrograde technique differs from the antegrade approach in that the occlusion is approached from the distal vessel with guidewire advancement against the original direction of blood flow . A guidewire is advanced into the artery distal to the occlusion through a collateral channel or through a bypass graft, followed by placement of a microcatheter at the distal CTO cap. Retrograde CTO crossing is then attempted either with retrograde wiring (usually for short occlusions, especially when the distal cap is tapered ) or using retrograde dissection/reentry techniques.
The most commonly used retrograde crossing technique is the reverse controlled antegrade and retrograde tracking (reverse CART), in which a balloon is inflated over the antegrade guidewire which is usually located in the subintimal space, followed by retrograde guidewire advancement into the space created by the deflated antegrade balloon. In challenging reverse CART cases, intravascular ultrasound can clarify the mechanism of failure and increase the likelihood of success . Guide catheter extensions can also facilitate reverse CART .
21.8.4
Crossing strategy selection
Selecting the initial and subsequent crossing strategies depends on the CTO lesion characteristics and local equipment availability and expertise.
Several algorithms have been developed to facilitate crossing strategy selection, such as the hybrid and Asia Pacific algorithm. Antegrade crossing is generally preferred over retrograde crossing as the initial crossing strategy, given the higher risk of complications, longer procedure time and more radiation with the retrograde approach and need for antegrade lesion preparation even when the retrograde approach is used. Some retrograde CTO PCI complications, however, are caused by antegrade crossing attempts. The retrograde approach remains critical for achieving high success rates, especially in more complex CTOs and has been associated with favorable long-term outcomes .
CTOs with proximal cap ambiguity or flush aorto-ostial CTOs are often approached with a primary retrograde strategy. Alternatively, CTOs with ambiguous proximal caps can be approached in the antegrade direction, especially when no collateral or graft is available by using: (1) intravascular ultrasound or preprocedural CCTA for determining the location of the proximal cap and vessel course or (2) techniques to facilitate entry into the subintimal space proximal to the occlusion (move the cap techniques) .
21.8.5
Change of crossing strategy
If the initial or subsequent crossing strategy fails to achieve progress, small changes (such as modifying the guidewire tip angulation or changing guidewire) or more significant changes (such as converting from an antegrade to a retrograde approach) should be made, based on pre-procedural planning and the case progression .
Similar to selection of the initial crossing strategy, the timing and choice of subsequent crossing strategies depends on lesion characteristics, challenges encountered with the original technique, and equipment availability and expertise. Strategy selection can be guided by various crossing algorithms, such as the hybrid algorithm ( Fig. 21.4 ) .
