Recanalization of Chronic Total Occlusion After Conventional Guidewire Failure: Guided by Optical Coherent Reflectometry and Fac

ABSTRACT: The success rate of percutaneous recanalization of chronic total occlusion remains low. The Safe-Cross wire, which utilizes the principle of optical coherent reflectometry for guidance and has the ability to deliver radiofrequency energy for tissue ablation, was evaluated in 21 patients. This wire was used only after conventional guidewire failure, except in 4 patients who had failed an interventional procedure 3 months to 2 years previously. Conventional guidewires were successful in 9, and the Safe-Cross wire was successful in 10 of the remaining 12, including those 4 with a failed previous attempt. The total success rate was 90% (19/21 patients). Technological improvement in the steerability of the Safe-Cross wire may help to improve the success rate further.

Key words: optical coherent reflectometry

Recent advances in percutaneous coronary intervention (PCI) have resulted in the successful treatment of lesions with very difficult and complex anatomy such as bifurcation and left main stenosis. Chronic total occlusion (CTO), defined as an occlusion of more than three months duration, however, remains a major challenge. Most failures are due to inability to cross the lesion with a guidewire and the remaining are due to failure of a balloon to track along the guidewire through the very hard lesion. Many types of guidewire have been tried, including ball-tipped wires, hydrophilic wires, laser wires, etc., but the recanalization rates remain disappointing at 60–70%. Recently, the new Safe-Steer guidewire system (Intraluminal Therapeutics, Carlsbad, California), which utilizes optical coherent reflectometry (OCR), has been introduced to facilitate guidewire passage safely through CTOs. The system has been described in detail in the literature.^1,2 In brief, the forward-looking fiberoptic system emits near-infrared light, which is reflected to a varying degree by different types of tissue and displayed in real-time on a monitor (Figure 1). Importantly, it is able to recognize the vessel wall and alerts the operator to steer the wire away to prevent subintimal passage or perforation. In August 2002, Safe-Steer wires with the ability to deliver radiofrequency (RF) ablative energy (Safe-Cross wires) were available to us for clinical use. We describe our experience over a five-month period using the Safe-Cross wire to treat CTOs after conventional guidewire failure. Methods From August 2002 through December 2002, twenty-one consecutive symptomatic patients with objective evidence of myocardial ischemia due to single-vessel CTO underwent PCI at out institution. Except for four patients who had failed PCI three months to two years previously, all patients initially underwent intervention with various conventional guidewires, including Hi-torque standard (Guidant Corporation, Temecula, California), Cross-It (Guidant Corporation), Shinobi (Cordis Corporation, Miami, Florida), Crosswire (Terumo Medical Corporation , Somerset, New Jersey), Miracle (Asahi) and Choice PT (Boston Scientific/Scimed, Inc., Maple Grove, Minnesota). The Safe-Cross system was used if conventional guidewires failed to cross the CTO. There were eighteen male and three female patients, ages ranging from 39–75 years old. The CTOs had been present for a period of three months to ten years, estimated either clinically or from previous angiographic studies. Conventional risk factors included diabetes mellitus in ten patients (48%), hypertension in fourteen patients (67%), hypercholesterolemia in nine patients (43%) and cigarette smoking in eight patients (38%). Distribution of diseased vessels is as follows: left anterior descending (LAD) in nine patients (43%), right coronary artery (RCA) in nine patients (43%) and circumflex artery (CX) in three patients (14%). Bilateral coronary injections were liberally used to carefully define the coronary circulation proximal and distal to the CTO, to estimate its length and to provide a roadmap during passage of the guidewire through the occlusion. Conventional guidewires with over-the-wire balloon catheters were initially used, except in the four patients with previous failed PCI. When conventional guidewires failed, they were exchanged for the Safe-Cross wire, which was carefully advanced through the lesion, aided by the OCR signals on the monitor. Only gentle mechanical force was used to advance this wire, and RF energy was applied when resistance was met. There is a built-in safety mechanism in this system such that RF energy cannot be applied whenever the wire is in contact with the arterial wall, in order to reduce the chance of vessel perforation. Successful wiring of the CTO was then followed by balloon dilatation and stenting. Results Of the 21 CTOs, twelve (57%) showed significant fluoroscopic calcification. CTO morphology was deemed favorable in five (tapered stump) and unfavorable in the rest (sidebranch at CTO, eccentrically oriented stump, bridging collaterals). The estimated length of the CTOs varied from 12–51 mm, with a mean of 26.7 ± 9.3 mm. Bilateral coronary injection to visualize the vessel distal to the CTO was utilized in sixteen patients (76%). Nine CTOs were successfully crossed with conventional guidewires, including five in the LAD, two in the RCA and two in the CX. Of the remaining twelve patients, ten were successfully treated with the Safe-Cross wire, including all four patients who had failed a previous PCI attempt. These ten CTOs included four in the LAD, five in the RCA and one in the CX. The two failures were both in the RCA. The overall clinical success rate was therefore 90% (19/21 patients). There were no procedural complications, especially guidewire perforations, in any patient. Figure 2A shows a mid-LAD CTO that had been clinically present for eight years before PCI in September 2000. The distal LAD was filled by ipsilateral collaterals. Attempted recanalization with multiple guidewires resulted in dissection (Figure 2B) and the procedure was abandoned. Angiography in August 2002 showed complete healing of the dissection. The lesion was accessed with a conventional floppy guidewire loaded onto an over-the-wire balloon and then exchanged for the Safe-Cross wire. After advancing for a short distance, it kept entering a small diagonal branch and could not be steered around the vessel bend because of the relatively stiff and straight wire tip (Figure 2C). The over-the-wire balloon catheter was then exchanged for an angled catheter (Figure 1), which provided the necessary deflection for the Safe-Cross wire to advance, with RF energy ablation, into the distal vessel (Figure 2D). After balloon dilatation, a 3.0 x 33 mm Cypher stent (Cordis Corporation) was deployed at high pressure, achieving a very satisfactory result (Figure 2E). This patient has since remained asymptomatic, with a normal stress test at one-year follow-up. Figure 3A is the left coronary angiogram of a 54-year-old man with severe angina, showing significant left main stenosis and total mid-LAD occlusion, with septal-to-septal collaterals filling the distal vessel. Conventional guidewires failed to completely cross the occlusion, and kept entering a small septal branch. The Safe-Cross wire was introduced as a “buddy” wire into the LAD, and finally advanced through the CTO (Figure 3B). After balloon dilatation, the mid-LAD lesion was treated with a 3 x 33 mm Cypher stent and finally the left main stenosis was treated with a 5 x 13 mm Ultra stent (Guidant Corporation) (Figure 3C). This patient has remained symptom-free for eleven months. Discussion CTO remains one of the last major challenges in percutaneous coronary revascularization. This is evident from a recently reported series of 196 patients referred by high-volume interventional cardiologists for coronary artery bypass surgery.³ Even with current techniques and the hypothetical availability of drug-eluting stents with a presumed restenosis rate of near zero, one hundred and fifty-four (79%) of these patients would still be considered for surgery, and the single most important reason for this decision was the presence of a CTO, which occurred in 31.8% of patients. The prerequisite of successful intervention is the passage of a guidewire through the lesion. Although both the proximal and distal ends are angiographically visible, the CTO itself is not, and one has to assume the course of the artery by drawing an imaginary line between these two ends. Unfortunately, there is no way to verify this assumption and one basically has to blindly pass the wire through the lesion, although with experience and different types of guidewire, there is still a reasonable success rate of 60–70%. Another reason for failure to pass the guidewire is related to the hardness of the lesion, which is often fibrotic and calcified, such that the wire cannot be mechanically forced through or is deflected into passages of lesser resistance, such as a sidebranch or the subintimal space, resulting in arterial dissection. The laser wire does provide the required energy for tissue ablation, but due to the lack of directional guidance, has not been found to be superior to conventional guidewires in crossing CTOs.⁴ The Safe-Cross wire is a forward-looking system that utilizes the principle of OCR for guidance. The signals are displayed on a monitor in real time and enable the operator to steer the wire away from the arterial wall and maintain an intraluminal wire position. Coupled with the ability to deliver ablative RF energy, this system would theoretically allow one to navigate safely through the CTO. We therefore set out to investigate whether this system was indeed clinically useful when it became available to us in August 2002. Our objective was not to compare the Safe-Cross wire with conventional guidewires, which were known to yield a reasonable success rate and were much less costly, but to see if this wire could provide additional benefit in the recanalization of CTOs. We therefore started all of our patients with conventional guidewires, unless they had previously failed them. Our success rate with such wires was 43% (9 out of 21 patients), which is comparable to other series. With the Safe-Cross wire, there were ten additional successful patients, including all four previous failures, improving the total success rate to 90% (19 out of 21 patients). In this small series, the age of the CTO did not seem to affect the success of the Safe-Cross wire, as demonstrated by the patient (Figure 2) who had the CTO for ten years and failed an attempt with conventional guidewires two years previously. Several points related to the use of the Safe-Cross wire system are worth mentioning. Interventionists have traditionally used fluoroscopy to facilitate guidewire advancement. One now has to familiarize with and integrate the information from the OCR signals with the information from fluoroscopy for wire navigation. Our previous two years of experience with the Safe-Steer wire, which was an older version of the Safe-Cross wire but without RF energy ability, have been most helpful in this respect. With regard to wire advancement through the CTO, we found two techniques useful. One involves negotiating tortuous arterial bends. Since the angle at the Safe-Cross wire tip is only 20 degrees, it may not be possible to steer the wire through more acute bends. The angled catheter (Figure 1) allows for greater deflection of the wire tip, and this deflection angle can be adjusted to a certain extent by varying the length of the stiff body of the wire that has traversed through the catheter. This is illustrated in the patient shown in Figure 2. Another technique we have found useful is the buddy wire technique (Figure 3). After the conventional guidewire has gone into a subintimal space or into a sidebranch, it is left in place and the Safe-Cross wire is then passed parallel to it. This first wire would help to block the passage of the Safe-Cross wire into this wrong channel and facilitate its further navigation. Despite the theoretical advantages of the Safe-Cross wire system, there are still many technical hurdles to overcome. The wire tip has a very shallow angle of about 20 degrees and cannot be manually shaped or bent; otherwise, the optical fibers inside the wire would be broken. The angled catheter helps to a certain extent, but as the wire is advanced beyond the catheter tip, the stiffer body of the wire will straighten the catheter and the deflection is lost. Also, despite successful wire passage, it is often impossible to track the angled catheter through the CTO because of its large, 2.8 French profile. Exchange for a low-profile balloon catheter is not feasible because of the connectors at the proximal end of the Safe-Cross wire. Our solution is to cut the proximal wire end with a strong pair of scissors to facilitate the exchange with a low-profile balloon catheter. Inability of balloon catheters to track along guidewires through a CTO is the other, albeit less frequent, cause of failure. There was no such instance in all of our patients with successful Safe-Cross wire passage. Although the numbers are too small to draw any conclusions, there is a distinct possibility that RF ablation could have provided a very small channel for easier balloon crossing. In conclusion, we found in our early experience that the Safe-Cross wire system is helpful in improving the success rate in recanalization of CTOs compared to conventional guidewires. With continued innovation in wire technology, we hope that this “last frontier” in interventional cardiology can be approached with greater confidence and success.