Chronic total occlusions

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Duane Pinto, M.D.; Brian C. Bigelow, M.D.; Roger J. Laham, M.D.; Randall K. Harada, M.D.

Overview

Chronic total occlusions (CTO) are often defined as coronary occlusions that have had TIMI 0 or 1 flow for an estimated duration of at least one month. Collateral flow to the distal territory maintains viability, but may be insufficient at times of increased oxygen demand, resulting in chronic stable angina or reduced exercise capacity. The tissue composition of the CTO is a variable mix of collagen-rich plaque, layered thrombus, calcium, and inflammatory cells with fibro-calcific caps at both ends. Neovascularization channels may form a neo-lumen or connect with adventitial vasa vasorum. The latter type of channels and bridging collaterals reduce the likelihood of successful guidewire advancement. Percutaneous interventions of CTO remain a technical challenge.

Goals of Treatment

Restoration of epicardial and myocardial perfusion in acute total occlusion
Improvement of functional status
Improving anginal status: collaterals may maintain viability but collateral insufficiency may lead to angina symptoms during times of increased myocardial demand
Increasing exercise capacity
Reduced need for late bypass surgery
Improved left ventricular remodeling
Promotion of electrical stability in border/watershed zones
Possible benefit of PCI on heart failure, ventricular function, and long-term survival

Treatment Choices

There are three main treatment choices for CTO:

Medical Therapy

All patients should receive optimal medical therapies to reduce angina and cardiovascular (CV) event risk. Revascularization attempts may be considered for patients refractory to antianginal agents.

Percutaneous Revascularization

Observational studies, including TOAST-GISE, showed an association between successful PCI of CTO and higher freedom from angina, exercise testing performance, and adjusted survival-free rates from adverse cardiovascular events.^[1]
Successful PCI of CTO have resulted in improved left ventricular ejection fraction on serial examinations, though parallel groups of medically treated only patients were not included in these studies. Long-term patency of successful angioplasty alone is poor; it is improved with the use of drug-eluting stents (DES).
The randomized trial, PRISON II, showed a superiority of a DES over a bare-metal stent for CTO interventions in adverse clinical events, in-stent late loss, and re-occlusion.^[2]

Surgical Revascularization

Coronary artery bypass surgery (CABG) may be preferable for occluded vessels in patients with higher risk features, such as low LV ejection fraction, diabetes mellitus, or multi-vessel, left main, or high-complexity disease.

Patient selection

Contraindications to treatment include:

Small area of myocardial viability

Techniques to assess viability prior to the procedure include:

Low dose Dobutamine echocardiography
Delayed-enhancement cardiac magnetic resonance
Thalium/Myoview PET scanning

Absence of ischemia
Low likelihood of procedural success based on angiographic predictors (failed intervention patients tend to have higher mortality but also higher procedural complication rate such as coronary artery perforations and coronary dissections)

Clinical predictors of success are very poor. Angiographic predictors of failure include:

Occlusion length > 15 mm (CT may be helpful in defining the length)
Moderate to severe coronary calcification
A flush, rounded or blunt (absence of a tapered "beak" at the origin ) occlusion
Presence of bridging collaterals
Higher age of the occlusion
Tortuosity
Small vessel size
Non-visualization of the distal vessel bed
The presence of a side branch at the occlusion site (the wire may selectively want to enter this rather than the total occlusion)

These predictors may also be assessed with CT, especially occlusion length. CT angiography may aid in choosing retrograde approach via collaterals (CART and reverse CART technique) rather than the traditional antegrade approach.

PCI Techniques

The potential for vessel perforation during the procedure should be kept in mind in selecting antiplatelet agents. Pre-treatment with aspirin may be used in preparation for possible stent implantation. Some operators wait to administer a thienopyridine until the procedure is completed without vessel perforation. Heparin and a short-acting glycoprotein IIb/IIIa inhibitors are favored in case of severe arterial injury requiring anticoagulation reversal. A strategy of heparin with a low target activated clotting time (ACT), followed by supplemental heparin, and glycoprotein IIb/IIIa inhibitor to be administered only after successful guidewire crossing, may be employed.

Arterial Access and Guide Catheter Selection

Contralateral/ double coronary injection from a second catheter, and arterial access to fill the distal vessel bed via collaterals, may be useful for angiographic guidance of the distal wire.

Greater support is often required for CTO interventions, and good guiding catheter support may facilitate both wire and balloon passage. For the right coronary artery, a left or right Amplatz guiding catheter can provide excellent coaxial support. A guide with sideholes is often helpful in dilating the right coronary artery. Extra backup (EBU or XB) guides are useful for the left coronary system. Consideration should be given to the use of 7-8 Fr guide sizes to accommodate extra equipment that may be needed. Further back-up support could be provided by larger caliber guide catheters (7 or 8 French).

Crossing The Lesion With The Wire

There are several potential choices for crossing a total occlusion. One standard progression in technique might include the following:

Begin with a conventional softer tipped, less traumatic guidewire as a first step, before progressing to stiffer wires for occlusions with tougher caps. A conventional guidewire crosses > 90% of acute (< 3 month old) total occlusions.
Several dedicated wires of graded stiffness were developed for CTO crossing, and a successful crossing frequently requires trials of multiple different wires.

Non-hydrophilic or hydrophobic wires with an intermediate stiffness are a good first choice as they have a better tactile response, are less likely to lead to a subintimal position than a hydrophilic wire, and may have an additional advantage in their ability to cross the proximal cap of the occlusion. Choices in this class include the Miracle Bros 3 and the Asahi intermediate wires.
Hydrophilic wires may track better after the proximal cap of the occlusion has been crossed. Hydrophilic/coated wires have better maneuverability in tortuous or calcified vessels. Intermediate stiffness hydrophilic wire choices include the Choice PT XS (Extra Support), the Pilot 50, the Pilot 100 or the PT Graphix.
Shaping the wire tip using a modest angulation is better for blunted stump occlusions.
A low-profile balloon or exchange catheter adds back-up support for wire penetration of fibro-calcific caps and may also be used cautiously for balloon-assisted progression within the occlusion.
Intra-luminal position of the wire distal to the occlusion is suggested by a freely rotating wire tip or angiography in different views by distal catheter or contralateral injections.
Stiffer wire tips will allow for a greater chance of crossing the proximal cap of the occlusion at the cost of an increased risk of vessel dissection or perforation.

Stiff non-hydrophilic wires: The Miracle Bros 6, 9 and 12, Cross-IT, Confienza, Persuader
Stiff and hydrophilic (most aggressive): Pilot 200 and Shinobi

Crossing Lesions That Cannot Be Crossed With A Conventional Wire

Tapered-tip wires are occasionally better at navigating into a smaller channel than on 0.014” wire. Lasers, vibrational energy, blunt dissection (e.g. Lumend Frontrunner) and ultrasound catheters have been used with variable success to recanalize chronic total occlusions resistant to standard wires. Fixed wire-balloon systems do not offer the ability to switch out wires and perform distal injection.

Crossing The Lesion With A Balloon

Once the wire crossed the lesion, the next step is to perform angiography to confirm that you are intraluminal (i.e. that no dissection is present) and that wire perforation is not present. If dissection and wire perforation are not present, then an attempt is made to cross the lesion with a balloon. Fixed wire-balloon systems lack track ability and steer ability therefore over-the-wire systems are usually favored. Fixed wire systems may, however, occasionally be useful because their very low profile which may allow passage in some cases in which a conventional over-the-wire system will not cross. Monorail systems inferior to over-the-wire systems in this setting, because of their inferior balloon tracking characteristics, the inability to exchange guidewires, and the inability to make a distal injection through the central lumen of the balloon to confirm your position. Often a low profile short over the wire balloon is a good first choice. An example would be a 1.5 mm X 6 mm balloon. Many investigators will remove the wire from the central lumen of the balloon and perform a distal injection at this point to confirm an intraluminal location of the balloon. If intraluminal guidewire position cannot be confirmed, balloon inflation should not be performed. If balloon cannot be inserted all the way across lesion, an inflation in proximal part of lesion can be performed to favorably alter anatomy and potentially facilitate eventual crossing. Consider aborting procedure if, despite multiple attempts with various guidewires, lesion cannot be crossed or successfully dilated; the risk of dissection or perforation may outweigh benefit.

Special Techniques

If a wire enters a dissection plane, then a second wire may be used (parallel wire technique) to find a different pathway with the first wire serving as a reference or blocking repeat entry into the false lumen. Also, if a wire favors entering a side-branch near the site of occlusion, then a balloon may be inflated in that side-branch effecting a block to further wire entry.

After failed attempts of recanalizing the true lumen, a subintimal tracking and re-entry (STAR) technique may be considered. This is more safely performed in the RCA where major side branches are absent. Retrograde approaches through robust collaterals from the contralateral vessel have been employed with variable success rates.

Special Crossing Devices

Blunt micro-dissection catheters
Optical coherence reflectometry guidance of the wire
Radiofrequency ablation, ultrasonic energy, or microscopic oscillations delivered by special catheter/wire systems to penetrate fibro-calcific caps

Dilation of the Totally Occluded Lesion

Following initial conventional balloon angioplasty of the lesion, stent placement reduces restenosis, revascularization, and reocclusion rates. Placement of a drug eluting stent is a rational choice given the high risk of restenosis with this lesion type. Given that the lesion was totally occluded, the occurrence of stent thrombosis and complete reocclusion, while unfavorable, may not be as dangerous as it would be in an artery that was patent prior to placement of the stent. Other dilation techniques include rotational atherectomy and laser debulking.

More Tips

Determine duration of occlusion:
- If duration of occlusion <3 months, standard PTCA wires are usually sufficient.
Laserwires are rarely used because they are limited to short lesions where distal vessel can be visualized via collaterals.
Ball-tipped guidewires have not demonstrated clear superiority over conventional wires in observational and randomized trials.
Blunt dissection may be considered if conventional wires fail to cross the occlusion.
Debulking calcified or rigid lesions with rotational atherectomy can facilitate distal delivery of stents or PTCA balloons.
If there is good collateral flow to the vessel distal to the stenosis, the use of two catheters for dual injections may be considered.

Advanced approaches to chronic total occlusions include

Anchor balloon technique Mother-child catheter (5 Fr within an 8 Fr guide)
Parallel wire and seesaw wiring
IVUS guidance to look for the true lumen
Retrograde approach (especially in previous antegrade failures)
Controlled antegrade and retrograde technique (CART)

Outcomes

Success rates of 50-80% have been reported, but may be affected by selection or publication biases. If the occlusion is less than 3 months old, the angiographic success rate is >90%, while patients with occlusions greater than 3 months old have a success rate of 70% and higher acute closure rates. The most common reason for failure is the inability to cross the occlusion with a guidewire (80-90%). Other common reasons for failure are the inability for the balloon to cross the lesion (15%), and lesions cannot be dilated adequately (5%) (>30% residual stenosis). Calcifications are often a major obstacle to crossing the lesion.

Restenosis and reocclusion rates following successful PCI are higher in CTO compared to non-occlusive stenoses. These rates are improved with the use of DES. Successful PCI of CTO is associated with a 50-70% rate reduction of future CABG. The salient complication of CTO PCI is perforation, which requires a rapid response: proximal balloon inflation, protamine administration for heparin reversal, consideration of a covered stent placement, and pericardiocentesis, if indicated.

Integration of several angiographic factors helps determine likelihood of success (see above). No single factor should preclude a revascularization attempt.

Long-term outcomes

Most patients (70%) are angina-free 1-4 years after successful PTCA.
Revascularization may prevent ventricular dilation, and some studies suggest improvement in global ventricular function.
Successful PTCA reduces the need for CABG by 50-75% but does not reduce total mortality or late MI.
Restenosis rates are high (40-75%); stents reduce restenosis rates.

Trouble-shooting

Difficult guidewire rotation, difficulty advancing wire or balloon, or guidewire buckling may signify an extraluminal position of the wire.
Intraluminal positioning of the crossing wire may be verified by distal injection through the central lumen of PTCA balloon or distal injection (Ultrafuse) catheter.

Other Concerns

The decision to terminate the procedure if guidewires fail to cross the occlusion is based on the severity of symptoms (i.e. angina) weighted against the risk of more aggressive techniques/devices, fluoroscopy time, and contrast load.

2011 ACCF/AHA/SCAI Guidelines for Percutaneous Coronary Intervention (DO NOT EDIT)^[3]