Chronic total occlusions: Difference between revisions
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=== Goals of Treatment | ==Background== | ||
Chronic total occlusions (CTO) are often defined as coronary occlusions with TIMI 0 or 1 flow with 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. | |||
== Goals of Treatment == | |||
* Restoration of epicardial & myocardial perfusion in acute total occlusion | * Restoration of epicardial & myocardial perfusion in acute total occlusion | ||
* Improving anginal status: collaterals may maintain viability but collateral insufficiency may lead to [[angina]]l symptoms during times of increased myocardial demand | * Improving anginal status: collaterals may maintain viability but collateral insufficiency may lead to [[angina]]l symptoms during times of increased myocardial demand | ||
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* Promote electrical stability in border/watershed zones | * Promote electrical stability in border/watershed zones | ||
== Patient selection == | |||
Contraindications to treatment include: | Contraindications to treatment include: | ||
* Small area of [[myocardial viability]] | * Small area of [[myocardial viability]] | ||
Revision as of 16:57, 30 July 2010
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Background
Chronic total occlusions (CTO) are often defined as coronary occlusions with TIMI 0 or 1 flow with 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.
Goals of Treatment
- Restoration of epicardial & myocardial perfusion in acute total occlusion
- Improving anginal status: collaterals may maintain viability but collateral insufficiency may lead to anginal symptoms during times of increased myocardial demand
- Increase exercise capacity
- Reduce need for late bypass surgery
- Improve left ventricular remodeling
- Promote electrical stability in border/watershed zones
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 perforations and coronary dissections)
Clincal 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
- Absence of a tapered "beak" at the origin of the total occlusion
- Presence of bridging collaterals
- Tortuosity
- The presnce 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.
Guide Catheter Selection
Good guiding catheter support may facilitate both wire and balloon passage. For the right coronary artery a left Amplatz guide can provide excellent support. A guide with sideholes is often helpful in dilating the right coronary artery. Extra backup (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.
Crossing The Lesion With The Wire
There are several potential choices for crossing a total occlusion and one standard progression in technique might include the following:
- Begin with a conventional guidewire as a first step. A conventional guidewire is crosses > 90% of acute (< 3 month old) total occlusions.
- A standard progression in the selection of more aggressive wires might include the following. It is frequently necessary to use multiple wires to successfully cross a chronic total occlusion.
- Non-hydrophilic wires with an intermediate stiffness are a good first choice as they are less likely to lead to a subintimal position than a hydrophilic wire and may have an additional advantage in crossing 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. Intermediate stiffness hydrophilic wire choices include the Choice PT XS (Extra Support), the Pilot 50, the Pilot 100 or the PT Graphix.
- 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 & 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.
Dilation of the Totally Occluded Lesion
Following initial conventional balloon angioplasty of the lesion, stent placement reduces restenosis, revascularization, & 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.
More tips
- Determine duration of occlusion:
- if duration of occlusion <3 mo, standard PTCA wires usually sufficient
- Laserwires 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 & randomized trials.
- Blunt dissection may be considered if conventional wires fail to cross the occlusion.
- Debulking calcified or rigid lesions w/ 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 (5Fr 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)
- Cotrolled antegrade and retrograde technique (CART)
Outcomes
- Anticipate >90% angiographic success rate if occlusion <3 mo
- Patients w/ total occlusions >3 mo have lower success rate of 70%, & higher acute closure rates
- 80% of failures due to inability to cross lesion; 15% due to inability for balloon to cross; 5% of lesions cannot be dilated adequately (>30% residual stenosis); calcifications are often a major obstacle to crossing the lesion
- Integration of several angiographic factors helps determine likelihood of success (see above); no single factor should preclude revascularization attempt
Long-term outcomes
- Most (70%) patients angina-free 1-4 y after successful PTCA
- Revascularization may prevent ventricular dilation & some studies suggest improvement in global ventricular function
- Successful PTCA reduces need for CABG by 50-75% but does not reduce total mortality or late MI
- Restenosis rates high (40-75%); stents reduce restenosis rates
Trouble-shooting
- Difficult guidewire rotation, difficulty advancing wire or balloon, or guidewire buckling may signify extraluminal position of wire
- Intraluminal position of crossing wire may be verified by distal injection through central lumen of PTCA balloon or distal injection (Ultrafuse) catheter