Treating coronary chronic total occlusions

Significant advances in chronic total occlusion treatment have led to technical success rates approaching 90% with an overall complication rate that is no higher than conventional PCI

Joy Shome MRCP

Specialist Trainee in Cardiology

Department of Interventional Cardiology, Freeman Hospital, Newcastle Upon Tyne, UK

Mohaned Egred BSc (Hons) MB ChB MD FRCP FESC

Consultant Interventional Cardiologist & Honorary Senior Lecturer

Department of Interventional Cardiology, Freeman Hospital, Newcastle Upon Tyne, UK

Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK

Chronic total occlusion (CTO) of the coronary arteries is the most difficult of lesion subsets in percutaneous coronary intervention (PCI) for coronary artery disease (CAD). The mid 1990s witnessed the increasing popularity of CTO PCI in centres across the world with coronary stenting becoming a commonplace. 

The initial enthusiasm was offset by problems inherent to contemporary stent implantation, including high rates of in-stent restenosis and occlusion prevalent at the time. Nevertheless, interest in CTO PCI continued, especially in Japan. However, data from the European Registry on Chronic Total Occlusion (ERCTO) 2007 study showed that despite overall burgeoning PCI volumes, attempts at CTO PCI constituted only 9.4% of all PCIs undertaken. This at large reflected the reluctance of the wider interventional cardiology community in dealing with these complex lesions, often due to a multitude of reasons including a low success rate. As a result, patients with single vessel disease (SVD) with a CTO were being managed medically despite having significant symptoms on optimal medical therapy (OMT) or evidence of widespread ischaemia. Patients with multi vessel disease (MVD) were being referred for coronary artery bypass grafting (CABG) even though the non-CTO lesions were amenable to PCI. 

In the last few years, technological advancements in tool kits used for CTO PCI, new and enhanced operator strategies and techniques and increased collaboration and enthusiasm amongst operators (including dedicated CTO operators, ‘CTO days’ and ‘CTO clubs’) have led to a resurgence in CTO PCI with ever increasing numbers and much improved success rates. 

The scope of the problem – the prevalence of CTOs

The prevalence of CTOs in patients undergoing coronary angiography for known or suspected CAD was document in few studies. Kahn et al. and Jeroudi et al. reported about a third of their patients having one or more CTOs, whereas Fefer et al. observed the same in approximately one fifth of their patients although more than half of them had not had a prior myocardial infarction (MI). Again, as mentioned above, PCI to the CTO artery was attempted in only 10% of CTO patients with <70% overall procedural success rates.

Current evidence base and justification for CTO PCI

Observational data suggests that in patients who are symptomatic or have a significant ischaemic burden attributed to a CTO, successful CTO PCI can improve symptoms and perhaps even survival.  Subset analysis from the SYNTAX trial suggests that incomplete revascularisation has a negative impact on clinical outcomes. Currently, two randomised controlled clinical trials – The Drug-Eluting Stent Implantation Versus Optimal Medical Treatment in Patients with Chronic Total Occlusion (DECISION-CTO) trial (NCT01078051) and the European Study on the Utilisation of Revascularisation versus Optimal Medical Therapy for the Treatment of Chronic Total Coronary Occlusions (EURO-CTO) trial (NCT01760083), are underway to help confirm the superiority of CTO PCI in addition to OMT.

Assessment of lesion severity

Although all CTOs are complex by nature, the degree of complexity varies and the J-CTO score helps ascertain this complexity and the anticipated difficulty of opening a CTO lesion. One point each is assigned to five variables (previously failed lesion, blunt proximal cap, CTO calcification, severe vessel tortuosity and occlusion length >20mm). Lesions can be classified as easy, intermediate, difficult and very difficult based on scores of 0, 1, 2, and ≥3 respectively with the success rate decreasing with increasing J-score.

Technical aspects and the ‘Hybrid Approach’ to CTO PCI: The need for and principal components of the hybrid approach

Autopsy studies have provided insight into the pathology of CTOs. Negative remodelling of the occluded segment is common and increases with time. Contrary to popular perception, micro-channels within the occluded segment are rare, and a tapered distal cap is more prevalent than a tapered proximal cap. Thus, resorting to only a “one size fits all” conventional, ante grade, true lumen to true lumen approach in CTO PCI would inevitably be fraught with failure in improving procedural success rates. 

Consequently, there has recently been a paradigm shift in the fundamental approach to the percutaneous treatment of these difficult lesions. The new “hybrid approach” to CTO PCI has, at its heart, the objective of opening the occluded vessel using all available techniques at its disposal in an algorithmic, albeit “mix and match” way, that ensures optimal efficacy and safety of the therapeutic interventions, within the shortest possible duration. The core components of the hybrid interventional strategy consist of (1) wire escalation and/or (2) dissection and re-entry strategies, in either ante grade or retrograde directions, or both, as dictated by angiographic characteristics of the case in question. 

Antegrade and retrograde access and the importance of dual injection

Pivotal to the hybrid strategy is the use of two guiding catheters for synchronised ante grade and retrograde coronary injection. This is indispensable for a meticulous review of the coronary angiogram. It is mandatory in the presence of contralateral collaterals and provides superior delineation of the occluded segment, as well as the proximal and distal caps and the quality of the distal vessel. This forms the first step in deciding the initial and subsequent approaches necessary to achieve successful recanalisation. Rarely, a single guiding catheter may suffice where ipsilateral collaterals exist. During an ante grade dissection re-entry approach, ante grade only contrast injection as in a single catheter setting, can enlarge the subintimal space and reduce chances of successful re-entry, and should ideally be avoided.

Angiographic determinants and the rationale for initial and subsequent strategies

There are four angiographic parameters that need to be studied in minute detail, necessitating dual coronary injection. They include a clear demarcation of the location of the proximal cap using angiography or intravascular ultrasonography, lesion length, presence of branches as well as size and quality of the target vessel at the distal cap, and finally suitability of collaterals for retrograde techniques. The initial strategy of choice is guided by the above characteristics. Should the primary strategy be futile, and then appropriate further secondary and tertiary approaches can be resorted to depending on the above features.

In general, if the CTO segment is short (<20cm) with a good distal vessel target, an ante grade wire escalation approach is preferred. A primary ante grade dissection re-entry approach is selected where the lesion is long and complex, but the proximal cap is well seen and distal target is of reasonable quality.  An initial retrograde approach may be needed in complex lesions with poor distal vessel or where the entry point to the vessel is unclear. The fundamental principle of the hybrid technique is that if the initial or current strategy is not working, the other strategies should be tried, with a low threshold for rotation of strategies if needed for maximum efficiency and to avoid spending too much time on a single approach. This helps avoid the law of diminishing returns and facilitates procedural success within the shortest possible duration.

Optimising hardware and essential ‘CTO tool kit’

Given the complexity of CTO lesions and for optimal implementation of the hybrid strategy, it is recommended that a routine two guiding catheter strategy be employed with a shorter catheter in the retrograde vessel. This enables rapid exchange between ante grade and retrograde approaches where the anatomy is suitable. Dual arterial access can be bi-femoral, radio-femoral or bi-radial. Modification of conventional equipment is often necessary in CTO PCI. Optimising guide catheter support is crucial, and this is aided by using long sheaths and wide bore guiding catheters. Use of child in a mother extension such as GuideLiner catheter, and balloon anchoring manoeuvres can further enhance guiding catheter support.

The “CTO trolley” should be appropriately stocked with a toolkit now routinely used for coronary CTO PCI. This involves an array of wires including (1) hydrophilic and/or polymer-jacket, low gram force, tapered wire such as Fielder XT, (2) hydrophilic, polymer-jacket, non-tapered wire such as Pilot 50, Fielder FC, (3) polymer-jacket, non-tapered, moderately-high gram force wire such as Pilot 200, (4) high gram force wire with tapered, non-jacketed tip such as Confianza Pro 12, and (5) externalisation wires such as RG3. The individual properties of these wires are customised to its anticipated role in the hybrid algorithm.

Microcatheters used in conjunction with wires include Corsair (possibly most frequently used in contemporary practice), Finecross, Tornus, and other over the wire balloon catheters.

Dissection and re-entry devices include the CrossBoss catheter, and Stingray balloon and Stingray guide wire systems.

In addition, safety equipment should also be within instant reach if required. This includes pericardiocentesis kit, covered stents, and embolisation devices.

Technical executions within the hybrid CTO PCI procedure

Wire escalation

An initial wire escalation strategy is chosen where the proximal cap is discernible, the vessel has a suitable distal target and the occlusion is ideally no more than 20mm in length. A tapered, low gram force, polymer jacket wire (Fielder XT) is usually taken first. A Corsair microcatheter is often used in conjunction. Failure to cross the lesion with this wire necessitates the use of an alternative wire which is usually a moderately high gram force, non-tapered, polymer jacket wire (for example, Pilot 200) should the occlusion be long, uncertain or tortuous. On the other hand, a stiff, tapered penetration wire such as Confianza Pro 12 is better suited to trying to cross a shorter lesion with a well-delineated vessel course. Failure to achieve true distal lumen position or inadvertent entry into the subintimal space with wire escalation manoeuvres should prompt immediate consideration of strategy change and conversion to dissection re-entry techniques. 

Dissection and re-entry

This can be broadly classified into ante grade or retrograde dissection re-entry techniques. 

Antegrade

The fundamental principle of the ante grade dissection approach is the subintimal advancement of a guide wire or crossing microcatheter. This is frequently achieved using the knuckle wire technique using a looped polymer jacket wire (Fielder XT, Pilot 200), which is advanced towards the distal CTO segment, or through the use of a tailor made device such as the CrossBoss catheter, which facilitates a more controlled dissection. Once the CTO segment has been crossed subintimally, re-entry techniques to enter the distal lumen are employed. The favoured modality at present is the Stingray system, consisting of the Stingray balloon and Stingray guide wire, to facilitate re-entry into the distal true lumen, especially if the CrossBoss catheter has been used. Alternatively, with the help of a microcatheter near the re-entry point, the knuckle wire can be changed to a stiff, penetrative wire, to perform re-entry into the distal true lumen. Similar examples are the LaST (Limited ante grade Subintimal Tracking) and STAR (Subintimal Tracking And Re-entry) techniques.

Occasionally it may be prudent to leave a large coronary dissection alone as these dissections heal and the failed procedure can be viewed as an “investment” procedure and form the basis for further successful attempt.

Retrograde

When a retrograde approach is being used either as an initial strategy or as part of a hybrid strategy, if wire escalation fails, the next recommended manoeuvre is the reverse CART (Controlled Antegrade and Retrograde Tracking) technique. This is carried out by placing a microcatheter retrogradely through a collateral vessel from the donor artery into the occluded segment over a guide wire, which lies in the subintimal space. An ante grade wire is also placed in the CTO segment (with or without the aid of a crossing catheter or balloon) and an angioplasty balloon is then tracked to the position of the retrograde microcatheter and inflated with the objective of making a connection between these two spaces. The retrograde wire is then advanced through this space into the proximal true lumen. Subsequent wire exchange and externalisation using long wires such as Viper or RG3 enables ante grade stent delivery. Reverse CART can be guided by IVUS if desired. Other modifications to the retrograde approach include the ‘capture’ and the ‘rendezvous’ techniques.

Other miscellaneous techniques 

Novel techniques such as ‘wire cutting’, the “subintimal distal anchor” technique, use of GuideLiner guide catheter extension, and use of excimer laser with or without rotational atherectomy have paved the way for procedural success in certain ‘balloon uncrossable’ lesions.

Conclusions

Significant breakthrough in the way we evaluate and treat CTOs has been achieved and current CTO PCI techniques have been associated with technical success rates in approaching 90%, in experienced hands, with an overall complication rate that is no higher than conventional PCI. There is also increasing evidence that successful recanalisation of CTOs improves prognosis, lowers rates of adverse cardiac events and reduces the need for subsequent bypass surgery. 

Anatomy alone should not be the sole driving factor-influencing referral for PCI. Rather, anatomy should serve to determine the strategy to be used for CTO PCI.

Our message to non-dedicated CTO operators and to the wider cardiology community is that, if revascularisation is appropriate (symptoms or ischaemia), then the presence of a CTO does not preclude PCI and we recommend referral of such cases to a dedicated CTO operator. This would increase the chances of offering patients a percutaneous option for treatment and to achieve complete revascularisation and symptoms 

control.

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