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November/December 2007
Retrograde Approach for Coronary CTO
A promising strategy for successful revascularization.
Although percutaneous coronary intervention (PCI) is now widely attempted for revascularization of coronary chronic total occlusions (CTO), procedural success still depends highly on successful wiring through CTO lesions. In many cases, antegrade wiring fails to cross CTO lesions. However, the retrograde approach to wiring can overcome the limitations of the conventional antegrade approach and helps to achieve a successful recanalization via a collateral vessel that connects with the distal target vessel.
Retrograde wiring was first performed via a bypass graft and was initially reported in 1990.1 This approach is basically a combination of using the retrograde collateral route combined with retrograde wire-crossing techniques. A wire is advanced in a retrograde fashion through the collateral channel of an appropriate opened artery to the distal end of the total occlusion. The retrograde wiring requires the use of collateral channels that can be performed via one of the following routes: a bypass graft, an epicardial channel, or an intraseptal channel (septal collateral). After successful passage of the wire through a collateral channel, one of several techniques must be utilized to finally lead the antegrade wire to the distal true lumen: the retrograde wire-crossing technique, kissing-wire technique, knuckle-wire technique, or CART (controlled antegrade and retrograde subintimal tracking) technique.
COLLATERAL ROUTE
Bypass Grafts
Even in the drug-eluting stent era, we sometimes encounter an untreatable diseased bypass graft, such as a severely degenerated saphenous vein graft. In such cases, it is necessary to open a native coronary artery (usually completely obstructed) to improve long-term outcome. Despite the poor suitability of the graft for PCI, it can be used as a channel for wire passage using the retrograde approach. A completely blocked vein graft should not be used for this technique. In some cases, an arterial graft could also be used for the retrograde conduit.
Epicardial Collaterals
CTOs of RCAs often receive collaterals from the LCx via epicardial channels. Also, in cases of RCA or LAD CTO, anterior and posterior descending arteries are sometimes connected directly by collateral channels. When an epicardial collateral channel is large enough to receive a balloon or microcatheter, it can be used as a channel for the retrograde approach (Figure 1). These epicardial channels commonly comprise challenging anatomy, such as a corkscrew or highly tortuous configuration, so that the wire crossing is difficult and has a risk of causing perforation. However, careful wire handling associated with the use of a microcatheter to stretch and straighten the proximal tortuosity of the channel may make it possible to achieve a successful retrograde wire passage. The most important issue is vessel diameter of the epicardial channel. Also, stenoses in these channels should never be dilated because this can cause severe perforation. When the channel is the only donor artery to a viable CTO region, the wiring procedure may transiently occlude this collateral and cause an ischemic event.
Septal Perforator
More recently, the retrograde approach using septal collateral channels has been introduced to treat CTOs of the RCA or LAD.2 In CTOs of the RCA or LAD, the anatomical course of the principal collateral is predominantly a septal connection (between septal perforators of anterior and posterior descending arteries). Also, a continuous septal connection is found in more than 80% of cases (Figure 2).3 Compared to epicardial collaterals, the septal channel is a shorter route to the recipient vessel and has a less-tortuous anatomy. Furthermore, although it looks like a tiny channel, the septal channel can be dilated using a small balloon (1.25 mm to 1.5 mm) with very low pressure (up to 2 atm) to advance a catheter through it with no major adverse clinical events.2 Although overdilatation of septal branches may cause perforation into the ventricles, these connections rarely require additional treatment. However, the conflict between the catheter and septal vessel wall during advancement of the catheter sometimes causes a hematoma inside the septum. To reduce this conflict, dilatation of the entire septal channel should be conducted after successful wire passage.
In all collateral routes, a hydrophilic soft wire (eg, Asahi Fielder, Abbott Vascular, Redwood City, CA; or Whisper Wire, Abbott Vascular) should be used to negotiate the collateral channel with the support of a microcatheter (eg, Transit, Cordis Corporation, a Johnson & Johnson company, Warren, NJ) or a small (1.25 mm or 1.5 mm) over-the-wire balloon. The retrograde wire is then often changed to a stiffer wire to be advanced into CTO lesions after the successful passage of a catheter through the collateral channel into the target vessel. At this point, there are several options of wiring technique for subsequent successful antegrade wire crossing.
WIRING TECHNIQUE
Retrograde Wire-Crossing Technique
Sometimes, the retrograde wire is easily advanced through the entire CTO lesion to the proximal true lumen of the CTO target vessel (Figure 1). By using the current wires dedicated for CTO (eg, Asahi Miraclebros, Abbott Vascular), this technique is successful in approximately 30% of cases with the retrograde approach. Because this technique is the simplest, it should be the first technique attempted in all retrograde approaches. When it is successful, the wire should be advanced deeply into the antegrade guiding catheter or aorta. In the former situation, the retrograde wire can be trapped inside the guiding catheter by a percutanerous transluminal coronary angioplasty balloon to provide super extra back-up force to advance a 1.5-mm balloon retrogradely and dilate the CTO lesion (Figure 3). Usually, the antegrade wire is then easily negotiated through the lesion. However, when this is unsuccessful, there is some risk of creating a subintimal space extending from the distal CTO vessel to the proximal true lumen of the CTO, which may cause dissection and an adverse event when the CTO is located in the proximal part of the left coronary artery. In such instances, a bilateral wiring approach must be used.
Kissing-Wire Technique
In the kissing-wire technique (one of the bilateral approaches), the antegrade wire must be advanced forward into the CTO to reach the retrogradely advanced wire.4 However, it is not easy to align each inside the true channel because the true channel has multiple layers due to both plaque and neovascular channels.
Knuckle-Wire Technique
To make a crack inside the CTO lesion, the retrograde wire is advanced into the CTO as a knuckle wire. Usually, this knuckle wire can be advanced into the subintimal space so that the antegrade wire inside the subintimal space can be advanced and aligned to the retrograde wire (Figure 4). However, in this technique, the created subintimal space cannot be controlled, and sometimes an expanded subintimal dilatation occurs beyond the CTO lesion.
CART Technique
To minimize enlargement of the subintimal space at the CTO site, the CART technique has been recently introduced.5 Figure 5 illustrates the concept and sequential steps of the CART technique. The retrograde wire penetrates from the distal true lumen into the CTO and then into the subintimal space at the CTO site. After advancing a small balloon (1.5 mm to 2 mm) over the retrograde wire into the subintima, the balloon should be inflated in the subintima to make a large crack. To keep this subintimal space open, the deflated balloon should be left in place. As a consequence, the antegrade wire advancing into the subintimal space is easily led into the crack created by retrograde balloon. The main advantage of this technique is the minimization of subintimal tracking only at the location of the CTO lesion. Hence, this technique is completely different from the STAR (subintimal tracking and re-entry) technique,6 and a better long-term outcome after implantation of a drug-eluting stent can be expected. Figure 6 shows a representative case successfully treated by a retrograde approach combined with the CART technique.
Reverse-CART Technique
To conduct the CART technique, a retrograde balloon must be advanced into the CTO lesion to make a crack. However, this is not always possible because sometimes the complex morphology of the distal true lumen (ie, calcification or bending) obstructs the passage of the retrograde balloon. In such cases, the last alternative is the reverse-CART technique. In the reverse-CART technique, the creation of a subintimal crack is conducted by an antegrade balloon at the proximal part of the CTO lesion advanced through the antegrade wire inside the subintima. The retrograde wire then comes to the proximal true lumen. In other words, this technique is a retrograde wire-crossing technique through the subintima. There is some risk of unexpected subintimal dilatation antegradely beyond the CTO lesion caused by antegrade wiring through the subintima and/or antegrade balloon dilation.
In every kind of bilateral wiring technique, a tapered stiff wire should not be used as a retrograde wire because this kind of wire sometimes causes wire perforation retrogradely. Once successful antegrade wiring is achieved, ballooning and stent implantation should be performed antegradely.
CLINICAL IMPLICATIONS
It is acceptable to approach the CTO antegradely because the target vessel is already closed. However, the retrograde approach does pose a risk of serious or fatal adverse events because a relatively nondiseased donor artery will be instrumented using many devices (guide catheter, wire, balloon, etc). If thrombus formation or coronary artery dissection occurs in the donor artery, it could be disastrous. Therefore, during the retrograde approach, very careful attention and care to the condition of the donor artery is mandatory. In my opinion, the first attempt for recanalization of a CTO should be conducted by the antegrade approach. If this method fails, the retrograde approach may be justified as the second attempt. However, in the CTO case having a diffused narrowing distal true lumen, it is very difficult to penetrate antegradely. In such cases, a retrograde approach may be considered as the first attempt when a reliable collateral route can be detected.
CONCLUSION
The retrograde approach has definitely increased the recanalization success rate in CTO PCI procedures. Now, top Japanese operators have an approximately 95% success rate in all CTO PCI procedures. However, to minimize procedural risk, it is still important to perform the procedure carefully and correctly. For this purpose, devices dedicated for a retrograde approach have been, and are being, developed. To negotiate a tricky collateral channel, a tapered hydrophilic soft tip wire has already been introduced. To advance through a septal channel without septal dilatation, a special microcatheter is currently under development but has not yet been made commercially available. In the near future, these new technologies will ensure and facilitate the procedural success of the retrograde approach.
Etsuo Tsuchikane, MD, PhD, is from the Department of Cardiology, Toyohashi Heart Center, Toyohashi, Aichi, Japan. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Tsuchikane may be reached at +81 532 37 3377; dokincha@aioros.ocn.ne.jp.
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