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Original Contribution
New Concept for CTO Recanalization Using Controlled Antegrade and Retrograde Subintimal Tracking: The CART Technique
July 2006
Percutaneous treatment of coronary chronic total occlusions (CTOs) remains one of the major challenges in interventional cardiology. Recent data have shown that successful percutaneous recanalization of coronary CTOs results in improved survival as well as enhanced left ventricular function, reduced angina and improved exercise tolerance.1–3 However, because of the perceived procedural complexity of angioplasty in CTOs, it still represents the most common reason for referral to bypass surgery, or for choosing medical treatment.4,5 The most common reason for percutaneous coronary intervention (PCI) failure to treat CTOs is the inability to successfully pass a guidewire across the lesion into the true lumen of the distal vessel.6 To date, there is no consensus on how best to treat CTOs after attempts with conventional guidewires have failed. Different strategies and specific devices for CTOs have been developed including subintimal tracking and reentry with the side branch technique,7 the parallel wire technique, the intravascular ultrasound-guided technique, and the retrograde approach.7–10 This paper describes our recently developed strategy for the treatment of CTOs and the initial results of its application in patients.
Material and Methods
Procedural protocol. All patients enrolled in this study were treated with the CART technique either as the primary option, or following a failed antegrade attempt with conventional or dedicated wires during the same or prior procedure. Indications for CTO revascularization were either symptoms of angina or proven stress-induced ischemia. The duration of the occlusion was estimated from previous angiographic data or from clinical information (acute myocardial infarction [MI], sudden change in angina pattern) or electrocardiographic (ECG) changes consistent with the location of the occlusion.
**Surmely1.jpg*Technique description. This technique combines the simultaneous use of the antegrade and retrograde approaches. The retrograde approach means that the occlusion site is approached retrogradely through the best collateral channel from any other patent coronary artery. The retrograde approach requires an intercoronary channel (collateral), which can be an epicardial channel, interatrial channel, intraseptal channel (septal collateral), or a bypass graft. It is uncommon to find an epicardial intercoronary collateral with *a suitable morphology allowing its use as a connecting channel. However, meticulous review of the angiogram of a CTO case will often reveal a septal channel in the left anterior descending artery (LAD) or the right coronary artery (RCA). The basic concept of the CART technique is to create a subintimal dissection with limited extension only at the site of the CTO (Figure 1). First, a wire is advanced antegradely from the proximal true lumen into the CTO, then into the subintimal space at the CTO site. Experienced operators can recognize the wire entering into the subintimal space by a decreased resistance of the wire tip or wire movement. Next, another wire is advanced through the intercoronary collateral using a microcatheter in order to protect the channel from injury, as well as to achieve better wire maneuverability. This wire is placed at the distal end of the CTO, then penetrates retrogradely from the distal true lumen into the CTO, and finally into the subintimal space at the CTO site. After advancing a small balloon (1.5–2.0 mm) over the retrograde wire into the subintima, the balloon should be inflated in the subintima as well as on the course from this subintimal space to the distal end of the CTO. In order to keep this subintimal space open, the deflated balloon should be left in place. As a consequence, the two dissections created by the antegrade wire and the retrograde balloon lie in the subintima at the CTO site, which allows them to be easily connected. Thereafter, the antegrade wire is advanced further along the deflated retrograde balloon that lies from the subintimal space to the distal true lumen. This technique allows limited subintimal tracking only in the portion of the CTO lesion and avoids the difficulty of reentering the distal true lumen. After successful recanalization, dilatation and stent implantation are performed. The steps of the procedure are illustrated in Figure 1, and an example is shown in Figures 2 and 3. The material recommended for the retrograde approach is summarized in Table 1.
Definitions. In our study, coronary CTOs were defined as a true total occlusion if the thrombolysis in myocardial infarction (TIMI) flow was grade 0. Total occlusions of a duration > 3 months were considered chronic. Angiographic success was defined as restoration of antegrade flow, with a TIMI grade 3 flow, and also a final residual stenosis Statistical analysis. Descriptive analyses were used. Results are either quoted as percentages for categorical data or as mean ± standard deviation for continuous variables.
Results
Up to October 2005, 10 patients (9 males, 1 female) with CTO of native coronary arteries were treated with the CART technique. Patient characteristics are summarized in Table 2. Baseline lesion characteristics are shown in Table 3. CTO duration varied from 7 to 84 months. All CTOs were total occlusions with a TIMI 0 flow. Eight of the 10 cases had a previous failed attempt.
Procedural characteristics and results are shown in Table 4. Vessel recanalization with a TIMI 3 flow in the distal true lumen was achieved in all 10 cases. Drug-eluting stents were implanted in all but 2 of the patients. The intercoronary collateral used for the retrograde approach was a septal branch in 4 patients, a collateral between the circumflex artery and the postero-lateral branch (PL) of the distal RCA in 5 patients. In 1 patient, the retrograde approach was performed through a bypass graft (gastro-epiploic artery) to the posterior descending artery of the RCA. The size of the balloon used retrogradely ranged from 1.5–3.0 mm, and the inflation pressure for dilatation of the subintimal space located within the CTOs ranged from 6–18 atmospheres. No complications such as perforation or occlusion occurred in the collateral channel. In all cases, the subintimal dissection was limited to the CTO region. There were no in-hospital deaths, MIs, or emergent TVRs.
Discussion
Despite recent developments in dedicated materials and new strategies for the percutaneous treatment of CTOs, the overall success rate is still not optimal, with a revascularization failure rate of approximately 20%. The most common reason for CTO treatment failure by PCI is the inability to successfully pass a guidewire across the lesion into the true lumen of the distal vessel.6 New strategies using an antegrade approach include the parallel wire technique, the IVUS-guided technique, and the technique involving subintimal tracking and side branch reentry. The retrograde approach for the percutaneous treatment of nonocclusive coronary artery disease is an old concept introduced in the late 1980s.11 Its application for the treatment of CTOs was first performed by one of the authors (O. Katoh) in the early 1990s, and has been regularly presented at international conferences and live demonstrations since 1998. The first retrograde technique introduced used a single wire without a simultaneous antegrade approach. The CTO was crossed only in a retrograde manner. The success rate of this procedure was relatively low. Due to the long access route of the retrograde wire via an intercoronary channel, its maneuverability was poor, and it was difficult to pass it through the CTO lesion. Besides, dissection occurring in the proximal vessel portion can compromise an important side branch. Techniques using antegrade subintimal tracking with distal reentry in the true lumen have been shown to be feasible, with complete recanalization achieved in about 70% of cases.7 However, large, distal subintimal dissections where opacification of the distal true lumen disappears often prevents the wire from re-entering the true lumen.
In this study, we investigated the treatment of CTOs using the new CART technique, which combines the antegrade and retrograde approaches. A subintimal dissection is created antegradely and retrogradely, limiting the extension of the subintimal dissection in the CTO portion. In our small patient population which included difficult CTOs (80% of the patients had a previous failed attempt), we were able to demonstrate the feasibility and safety of this procedure. Successful recanalization was achieved in all of our patients, and no major complications occurred.
The CART technique requires the utilization of an intercoronary channel, which can be either an intercoronary collateral or a bypass graft. Angiographically-demonstrable collaterals are nearly always present in CTOs.12 It is important to carefully check the channel course and tortuosity from multiple angiographic views. The histological structure of those intercoronary collaterals are either capillary-like for the smaller collaterals, or arteriolar-like for the larger ones.13 The concern about causing collateral injury during passage of the retrograde wire and balloon in the collateral channel was not confirmed in our study. It should be emphasized that the clinical consequences resulting from a damaged collateral depends on which type of collateral vessel is used. The risk of damaging a graft can have disastrous consequences. The risk of potentially jeopardizing a functioning graft must be carefully weighed against the benefit of a successful CTO recanalization that cannot be achieved via the antegrade approach. Catheter-induced endothelial damage of the contralateral patent coronary artery with subsequent clinical consequences has been described, although it is an extremely rare event.14 Wire-induced endothelial damage resulting in subsequent clinical consequences seems unlikely, as shown in a 2-year angiographic follow-up study of patients in whom IVUS of non-intervened atherosclerotic coronary arteries was performed.15 Another concern is the use of balloon dilatation in the subintimal space, which is also performed in other approaches such as the IVUS-guided technique.8 In our study, no perforation or extension of the dissection outside of the CTO portion occurred. Although the dissection plane remained confined within the CTO portion in all of our cases, distal and proximal propagation of the dissection plane is a potential complication that could affect the patency of the collateral used. Standard technique should be successful without difficulty in 50–60% of CTO interventions. In our opinion, the two main indications for the CART technique are for difficult cases using standard techniques, or for specific cases with a suitable anatomy for this technique.
Study limitations. This study investigated the feasibility, safety and immediate success rate of the CART technique, however, intermediate and long-term results are still not available. Excellent, immediate success and an absence of MACE were achieved in a small population. It is therefore theoretically possible that in a larger patient series, the rate of complications could be of significance. Furthermore, the procedures in our study were performed by expert CTO-PCI operators. The success and complication rates that can be achieved by different operators on a larger patient population remain to be determined. A multicenter study with angiographic follow up is planned, and should allow for the determination of more precise indications and limitations of this technique.
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