Patient, Technique, and Device Selection for Coronary CTO Therapy: Clinical and Angiographic Considerations

Introduction

Over the last decade, there has been remarkable progress in the percutaneous management of coronary artery disease (CAD) as an established alternative to coronary artery bypass surgery. When compared to dilatation of coronary lesions with balloons, the scaffolding properties of stents have resulted in increased safety and predictable results, with reduced rates of acute closure and late restenosis. Recently, the addition of antiproliferative agents on the surface of the metal stents (drug-eluting stents) has been shown to markedly attenuate the vascular responses of neointimal hyperplasia, resulting in a marked reduction in the rate of restenosis.^1–5 Successful recanalization and percutaneous revascularization of coronary arteries with chronic total occlusion (CTO) is one of the “last frontiers” in coronary interventions. Conquering this objective will enable complete percutaneous revascularization in an increasing number of patients. Revascularization of CTOs carries multiple theoretical advantages, such as improvement in abnormal wall motion and left ventricular function and ultimately, increased long-term survival. In the long term, when the coronary disease may progress, having an open artery may increase tolerance to future coronary events. Reducing or abolishing myocardial ischemia improves electrical stability and reduces the predisposition to arrhythmic events. A recent review of the definitions, clinical relevance, indication for treatment, and results were recently summarized in a three-part consensus document.^6–8 The histopathology of the chronically occluded coronary artery has been comprehensively described.^9,10 Chronic coronary occlusion most often arises from thrombotic occlusion, followed by thrombus organization and fibrosis. Approximately half of all CTOs are < 99% stenotic when observed by histopathology, despite the angiographic appearance of total occlusion. The typical atherosclerotic plaques of CTO consist of intracellular and extracellular lipids, smooth muscle cells, extracellular matrix, and calcium. Collagens are the major structural components of the extracellular matrix. Another hallmark of CTOs is the extensive neovascularization, which occurs throughout the vessel wall. Learning and mastering the skills to recanalize CTO is an advanced stage procedure that is best suited to an experienced operator. The variety of CTO cases is wide, and special expertise is needed to differentiate between different anatomic situations, to select the appropriate devices, to change strategies as the cases progress, and to keep it safe — avoiding and treating potential complications. The success rate of CTO treatment is related to the accumulative general percutaneous coronary intervention (PCI) experience of the operator, in general, and CTO cases, in particular. The operator who takes on CTOs should approach cases of increasing difficulty by progressing gradually from tapered to flush occlusions, from short occlusions to longer ones, from straight segments to more tortuous vessels, and with time, to being able to tackle longstanding complete CTOs.

Patient selection. The prevalence of CTO in the general population is not clear. It has been reported in the early nineties that a chronically occluded coronary artery has been found in around one third of patients undergoing angiography.¹¹ Despite this high prevalence, recanalization of CTO has been reported to be attempted in only 8–15% of the patients undergoing PCI.^12–14 The disparity between the frequency of CTO and percutaneous treatment underscores not only the technical and procedural complexities of this lesion subtype, but also the clinical uncertainties with regard to which patients benefit from CTO revascularization.⁶ CTO, usually in the setting of multivessel disease is one of the common causes for referral to bypass surgery.^14–16 Many other patients are treated conservatively, without revascularization. An operator’s decision on whether or not to attempt a CTO recanalization and to send the patient for surgical revascularization or medical treatment is dependent on many clinical and anatomical parameters. Clinically, the patient’s age, the setting, symptom severity and frequency, overall functional status, and associated comorbidities that may affect the procedural outcomes (like renal insufficiency or diabetes mellitus) are all important determinants in selecting the treatment strategy. The extent and complexity of the CAD is one of the major determinants in the decision making. In a recent consensus document, Stone et al distinguished between single vessel CTO and CTO in the setting of multivessel disease.⁸ When the CTO represents the only significant lesion, a PCI attempt is recommended when the following conditions are present: 1) the occlusion is responsible for the symptoms; 2) the myocardial territory supplied by the occluded artery is viable; 3) there is reasonable likelihood of success. In patients with multivessel disease and 1 or more CTOs, the relative risks and benefits of each of the coronary lesions should be considered and weighed against surgical revascularization. Emphasis was put on the following parameters in which surgery should be considered as an alternative to PCI: 1) left main artery disease; 2) complex triple-vessel disease, especially in patients with insulin-dependent diabetes mellitus, severe left ventricular function, or renal insufficiency; 3) occluded proximal LAD; and 4) multiple CTOs with low anticipated success. Multiple noninvasive and angiographic modalities can be used to verify the viability of the myocardial segment supplied by the occluded coronary artery. One of the forgotten, most simple ways to detect viability is the ECG, displaying R waves when electrically viable myocardium exist. During the angiography, the left ventriculogram may show mobility of the corresponding ventricular wall. It should be remembered, though, that akinesis does not necessarily mean nonviability, and severe prolonged hibernation may be the reason for the lack of contractility. In such cases, viability can be demonstrated by rest nuclear techniques like single photon computed tomography (SPECT) or positron emission tomography (PET). Viability can also be demonstrated by echocardiography, at rest or during a provoked stress test. Novel techniques like tissue magnetic resonance imaging (MRI) or Doppler may be also useful. Multiple studies have shown the benefit from the treatment of CTO with PCI. Successful PCI for CTO treatment was associated with high rates of freedom from angina at long-term follow-up,^17–22 reduced need for subsequent surgical revascularization,^{17,19,22–25} and survival advantage.²⁶ In a recent multicenter, prospective, observational study, the Total Occlusion Angioplasty Study (TOAST-GISE), the clinical outcome of PCI for CTO in the contemporary era was studied. By treating 390 occlusions in 376 patients, technical and procedural success was obtained in 77% and 73% of lesions, respectively. In-hospital major adverse cardiac events (MACE) occurred in 5.1% of patients. At 12 months, patients with a successful procedure experienced a lower incidence of cardiac deaths or myocardial infarction (MI) (1% vs. 7%, P = 0.005), a reduced need for coronary artery bypass surgery (2.5% vs. 16%, P < 0.0001), and were more frequently free of angina (89% vs. 75%, P = 0.008), compared with patients who had an unsuccessful procedure. A large series of over 2,000 consecutive patients who underwent PCI for a CTO, a 10-year follow up showed a distinct 10-year survival advantage for successful CTO treatment, compared with failed CTO treatment (74% vs. 65%, P = 0.001). Diabetics in the CTO cohort had a lower 10-year survival compared with nondiabetics (58% vs. 74%, P < 0.0001). Similarly, in patients with multivessel CAD, incomplete revascularization because of non treatment of a CTO has been shown to be associated with increased mortality.²⁷

Angiography and Anatomical Considerations

The first and fundamental step is meticulous angiography. It is critical to have a correct evaluation of the occluded segment, vessel course, CTO morphology, edges, and bifurcations. These will enable the operator to select the appropriate strategy and devices, leading to higher success rates. Features that are considered favorable (increased success rate of recanalization) include occlusion of less than 3 months, occlusion segment less than 1.5 cm, some antegrade blood flow, and visible stump (dimple). Unfavorable features are long-standing occlusion, long segment, TIMI 0 flow, and bifurcating branches at either the proximal or distal edge of the occlusion segment.^22,28–30 Our practice experience has taught us that current angiographic predictors of unsuccessful recanalization of a CTO include long occlusion, vessel tortuosity, heavy calcification, and poor distal vessel visibility. Although the duration of occlusion may be unknown, some parameters can help the operator determine how long the artery has been occluded. Clues from the clinical history and reviewing old angiograms are very helpful. The presence of bridging collaterals is generally an indication of long-standing occlusion. Important anatomical characteristics that should be noticed by the operator include the vessel shape and tortuousity, the proximity of the lesion to the ostium, and the CTO morphology. One of the most important features is the existence or absence of a dimple (tapering CTO). This has significant impact on the success rate. It is important not to overlook the dimple, and multiple projections should be examined to avoid side-branch overlap. Careful investigation of the cine runs, sometimes going frame by frame, may yield additional important information, such as small channels inside the CTO. In cases of bridging collaterals, it is important to distinguish between inside channels and out-of-the-vessel collaterals. Bends or tortuousity inside the occluded segment is important but hard to appreciate, especially in long CTOs. Here, experience with the coronary anatomy plays a major role, and some clues may be helpful: calcification, as seen during fluoroscopy prior to contrast injection is the best way to understand the vessel course. Another potential clue is the movements of the proximal and distal segments of the vessel. If they move in different directions, this is a sign of tortuousity in the occluded segment. New, innovative strategies using computed tomography (CT) angiography to follow the epicardial vessel anatomy have been met with increasing success. Dual injection. The documentation of collaterals serves to evaluate the segments of the artery distal to the occlusion, which is essential to CTO success. In addition to valuable information like the size of the ischemic territory, the operator can evaluate the length of the occluded segment and the size and location of the run-off. One should never blindly cross an occlusion without clearly knowing where the wire should be directed, and whether it is inside the lumen or in a dissection plane. Having a simultaneous contralateral injection can simplify the procedure and increase the chances of successful and safer procedure if ipsilateral collaterals are insufficient. The contralateral injection is done by inserting a 4–5 Fr diagnostic catheter through an additional arterial access, (usually the contralateral groin). The retrograde injection is done a few heart beats before the antegrade injection to allow optimal documentation of both sides of the occluded segments, and adjacent branches, evaluating its actual length and occasionally demonstrating an unsuspected lumen. The best view is one that with the least foreshortening of the occlusive segment and its immediate distal.

IVUS of the entry point. Sometimes, despite multiple view angiography, it is still difficult to assess the exact entry point of the proximal edge of the CTO. This is typical of any flush occlusion at a bifurcating branch. In such cases, intravascular ultrasound guidance allows identification of origin of the true lumen.³¹ The location of the entry point can be obtained by wiring the side branch and performing a thorough IVUS interrogation by pulling back from the side branch to the main branch origin and directing the wire to the spot of vessel occlusion identified by the IVUS image. The IVUS will be less useful in cases of severe calcification in the vessel wall ostium or side branch.

CT angiography. CT angiography has made significant progress in coronary imaging with the introduction of the 64-slice CT. This improved technology allows rapid acquisition of superior studies, in terms of temporal resolution and image quality compared to previous generations. In the evaluation of a CTO, the CT angiogram is able to provide complementary data to that of conventional angiography that may be relevant to the success of the CTO recanalization. Such information may include precise quantification of the length of the occlusion, defining the composition of the plaque, identification of the amount and depth of calcification, and evaluation of the distal vessel beyond the occlusion. In addition to these lesion characteristics, the CT angiogram can also define bends and angles inside the occluded segment, important features that help the operator to safely, and successfully navigate the wire through the occlusion to the distal vessel. Mollete et al performed multislice computed tomographic coronary angiography in 45 patients who had CTOs and were scheduled for percutaneous recanalization.³² Using this new technology imaging technique, they were able to identify the predictors of procedural failure: blunt stump (as by conventional angiography), occlusion length > 15 mm, and severe calcification (by multislice computed tomographic coronary angiography).

Magnetic-assisted navigation. Another novel imaging system that may be helpful in the treatment if CTOs is the magnetic assisted navigation system, Niobe (Stereotaxis, St. Louis, Missouri). The system utilizes two permanent magnets mounted on articulating or pivoting arms that are enclosed within a stationary housing, with one magnet on either side of the patient table, These magnets generate magnetic navigation fields that are less than 10% of the strength of fields typically generated by MRI equipment, and therefore, require significantly less shielding, and cause significantly less interference, than MRI equipment. The NIOBE magnets precisely steer the working tip of the dedicated guidewires, using the 3D reconstruction of the coronary arteries. Coregistration of the 3D map with CT angiography data may assist the operator in navigating the wire through tortuosity inside the occluded segment, keeping it coaxially along the vessel throughout its course. If it can be effectively coupled with a radiofrequency (RF) source at the wire tip, such a system could conceivably evolve into a remote-controlled, semi-automated method.

Selection of Guiding Catheters

As is true in regular interventions, the guiding catheter is of paramount importance in providing safe access of interventional tools to the treatment area, while providing support. In CTO cases, extra support is usually needed to produce greater force for delivery of devices. This is especially important after crossing with the wire. Many times there is significant resistance to cross the lesion, even with a very low profile balloon, and having an extra support guiding catheter can be of help. When the support of the guiding catheter is insufficient, the success rate is lower, especially in cases with unusual anatomic variability, calcified vessel, and additional complexities. The transfemoral approach usually leads for better support than the transradial approach, along with the option of larger caliber catheters. In the left coronary artery, good guiding catheter support can be achieved with a broad transition guiding catheter that has a secondary curve that leans against the opposite wall of the aorta (passive backup), usually EBU (Medtronic, Inc., Minneapolis, Minnesota), XB (Cordis Corp., Miami, Florida) or Voda (Boston Scientific, Natick, Massachusetts) will be sufficient, with rare cases requiring an Amplatz curve catheters. In the right coronary artery, excellent support can be achieved with the Amplatz left family of catheters, usually AL1, with AL 0.75 for small aortas, and AL 1.5 or 2.0 for dilated roots. The operator should remember that these are relatively aggressive catheters with a higher risk of having a dissection. Having a stiff catheter also gives an additional support for the system, with the limitation of reducing the ability for deep engagement, and higher rate of ostial/proximal risk of dissection from the tip. Using a (softer) 6 Fr guiding catheter may allow for additional support by a relatively safe engagement of the catheter deep into the coronary artery (active backup), but 7–8 Fr are generally preferred. The selection of the guiding catheter is also influenced by the location of the occlusion. With very proximal occlusions, having an AL1 catheter may be counterproductive. Judkins right-shaped guiding catheter may be superior, despite having less support. Taking a larger caliber catheter will compensate for the lack of the support, with the option of having additional tricks, like anchoring wire and balloon.

Selection of Guidewires and Related Techniques

Guidewires have remained the most commonly used technology for CTO revascularization. Two groups of wires are usually used for CTOs. Polymer coated and coil wires. The polymer-coated wires have a hydrophilic coating that markedly lowers the friction, helping it to move very easily through the vessel lumen. This feature may also increase the risk of advancing the wire into subluminal planes and create a false lumen, long dissections, or perforations. The coil wires maintain good torquability even inside the fibrosed CTO segment while retaining excellent pushability. The stiffer the wire tip, the higher the torquability of the wire, but the less resistance at the tip felt by the operator, the higher the risk of entering a false channel. With tapered tip wires (e.g., Confienza (Asahi) 0.014–0.009 in or Crossit 0.014–0.010 inches), there is a better chance to enter microchannels than normal 0 .014" tip coil wires.³³ With stiffer coil wires like the Crossit 300–400 (Abbott Vascular, Inc., Redwood City, California), Miracle 9, 12 g (Asahi Devices, Redwood, California, Inc./Abbott Vascular, Inc.), or Persuader (Medtronic), the stiffer tips can increase penetration ability, but run the risk of ending up in a false lumen. Using these specific wires requires close attention by the operator to the 3D wire orientation at all times to reduce the likelihood of perforations. These wires should be used only by experienced operators after attempting more conventional wires. In a registry of 214, CTO revascularization initially attempted with tapered guidewires, achieved overall technical success in 82% of patients. In the presence of a visible microchannel, however, the success rates ranged from 81% (incomplete microchannel) to 100% (microchannel with distal filling).³⁴ Another series comparing multiple techniques underscored the improved recanalization success with the used of tapered-tip wires (a positive predictor of success, P = 0.002).³⁵ Which wire to choose is a difficult question with no straightforward answer. Our practice is to go from the light to the heavy, always starting with a soft tip, changing to a harder and stiffer wire if the lighter and softer wires do not work. For occlusions that are less than 6 months old, an intermediate wire will usually work. The Miracle Bro 3g that has excellent torquability and often will be good choice. For harder lesions, (older than 6 months), wires with stiffer tips will often be needed. Usually, the procedure is starting with a standard, relatively soft-tip guidewire that is used first to deliver the delivery system (small balloon or support catheter) closer to the lesion, and also to try first with a safer wire. Failure to cross with the standard wire is followed with stiffer wires in escalating tip stiffness (usually measured in weight scale, signifying the weight force that is needed to buckle the tip). The last step is usually to use stiff tapered and/or hydrophilic tips. This step is left for the highly experienced operator, since it involves a higher risk of complications. In cases in which a wire is repeatedly advanced into the wrong plane, it can be left in place (subintimal) as a marker of the incorrect path, while a new wire is used and directed to the proper exit point. In the modification of this technique, the “seesaw wiring method,” the parallel wires use two support catheters. This enables the wires to easily alternate their roles as the “marking wire” and the “advancing wire” through the occluded segment.

STAR technique. A promising, but potentially treacherous, wire-based technique is using the “re-entry” approach (STAR). This approach is similar to the one utilized in treating peripheral artery occlusions and aimed to create a subintimal dissection with distal reentry. A 0.014'' hydrophilic wire with a J-configuration is utilized for this purpose. The hydrophilic wire is pushed through the subintimal dissection plane. When pushed distal to the occlusion, the J tip is directed toward the true lumen, attempting to reenter. In a report of 31 patients with CTO, most of whom had a previously failed attempt, recanalization with this technique was successful in 21 patients.³⁶ However, this technique carries a higher potential for perforation than most others.

Retrograde wire technique. An exciting new wire-based approach has recently been introduced in Japan and gaining increasing popularity by top-of-the-line operators is the retrograde approach.^37,38 When antegrade crossing of a CTO fails, the retrograde approach may be considered. In this technique, the operator generally utilizes transeptal from L to R or R to L collaterals, as demonstrated by the bilateral injection angiography. And with subselective injection, the selection of the guiding catheter should be thoughtful: A supportive (at least 7 Fr) short guide (85–90 cm) should be used to enable a longer coronary segment to pass through. A hydrophilic soft wire, supported by a 1.25–1.5 mm over the wire balloon is advanced through the collateral for retrograde approach to the CTO. Frequently, a gentle dilatation of the septal branch with the balloon is needed to facilitate the further delivery of the support balloon. After advancing the supporting balloon close to the occlusion, the wire can be exchanged to one with a stiffer tip to cross the occlusion. In some cases, especially in those when the antegrade wire went into a false lumen, a retrograde wire can be used to give an idea about the location of the true lumen, thus helping the operator to correctly direct forward the antegrade wire, or further subintimal retrograde dilatation can be performed to widen the target for the antegrade wire.

Selection of Novel Technologies

Laser technology. In the previous decade, laser-based wire technology attracted interest. This .018" guidewire technology has made use of the unique debulking properties of excimer laser light. Despite an initial report that suggested its feasibility and safety,^39–41 the TOTAL study demonstrated no superiority of this technique over, and by today’s standards, is inferior to conventional wire-based technology.⁴² However, in cases in which the stenosis has been crossed with a guidewire but a balloon cannot cross, the laser-based catheter can be used for initial debulking. In contrast to rotational atherectomy, the use of an excimer laser does not require wire exchange, and can be used with high power (80J/80Hz), crossing the lesion and creating a lumen that enables delivery balloons and stents. The “point 9” X-80 catheter (Spectranetics Corp., Colorado Springs, Colorado) can cross even heavily calcified lesions. The “point 7” will also be available soon.

OCR and radiofrequency. The Safe-Cross system (IntraLuminal Therapeutics Inc., Carlsbad, California) has further extended the platform of wire-based technology. This system uses forward-looking optical coherence reflectometry, coupled with a radiofrequency energy source at the distal end of the guidewire.⁴³ The optical character recognition (OCR) technology uses low coherence (near-infrared) light transmission through an optical fiber within a 0.014-inch guidewire. The back-scattered light (reflection time and intensity) from tissue in front of the guidewire is measured, and an algorithm analyzes the back-scattered light to identify the interface between normal arterial wall and diseased plaques. A visible and audible signal warns the operator when the tip approaches within 1 mm of the outer vessel wall, allowing the operator to redirect the wire before dissecting or perforating. The safe-Cross RF system combines the OCR technology with a controlled RF energy that the operator can discharge through the wire tip, when he gets an OCR “green” signal, i.e., the tip of the wire is facing an intraluminal plaque, not the vessel wall. Delivery of a train of radiofrequency energy pulses can facilitate crossing hard fibrotic material within the occluded vessel, minimizing the risk of perforation. Recent evaluations in both coronary and peripheral interventions have demonstrated the potential of this technology, particularly following guidewire failures. The Guided Radio Frequency Energy Ablation of Total Occlusions Registry was a prospective, nonrandomized, multicenter registry that enrolled 116 patients who had long-term coronary total occlusions and in whom a > 10-minute good-faith attempt to cross the occlusion using conventional guidewires had failed.⁴⁴ Device success was achieved in 63 of 116 patients (54.3%). Clinical perforation occurred in 2.6% of patients; of these, perforation in only 1 patient (0.9%) was adjudicated to the Safe-Cross radiofrequency wire rather than to the stiff and/or hydrophilic wires used after an inability to advance with the Safe-Cross. Based on these encouraging data, the device has been approved in Europe and was recently (January 2004) granted 510(k) clearance by the FDA.

Vibration and ultrasound. Another ablative novel strategy is the use of vibration energy. The tip of the CROSSER catheter (FlowCardia, Sunnnyvale, California) mechanically vibrates against the face of the CTO at 20,000 cycles per second (20kHz) at a stroke depth of approximately 20 microns. This high frequency, low amplitude longitudinal stroke pulverizes the CTO by mechanical impact creating a channel through the CTO. In addition, high frequency vibration can create vapor-filled micro-bubbles in the fluid (blood & saline) at the tip of the CROSSER catheter. As the CROSSER catheter is activated, these micro-bubbles expand and implode producing liquid jets that can break the molecular bonds and erode the solid surface of the CTO. The vibrating energy is transmitted to the catheter from a generator that converts AC line power into high frequency current. Initial reports from Europe have demonstrated the safety and feasibility of this system.^45,46 In the pivotal US study, FACTOR, the use of this device was successful in 76/125 (61%) of patients with “wire refractory CTO,” without serious complications.

Frontrunner catheter. A second line device to attempt recanalization of CTO is the Frontrunner (LuMend). It is usually used when the wire-based attempts were exhausted and failed.47 This device is designed to create intraluminal blunt microdissection to facilitate penetration of the fibrous cap. The frontrunner catheter is steered and delivered through the coronary artery, just proximal to the occlusion so the blunt tip engages the proximal cap of the CTO. The actuation of jaws on the distal end of a 0.039" diameter catheter creates a 2.3 mm excursion that separates tissue planes within the occluded segment. The tip is pushed forward gently to displace the plaque, and remotely opening the small forceps separates atherosclerotic plaque in various tissue planes by inducing a blunt dissection. Repetitive opening and steering of the catheter creates a microchannel through the occlusion, facilitating the placement of a guidewire across the occlusion. The blunt dissection strategy takes advantage of the elastic properties of the adventitia, as compared to the inelastic characteristics of the fibroblastic plaque, to create the fracture planes. This device may have a special role in refractory in-stent CTO, wherein the stent serves to confine the device as it passes through the occlusion. Currently, this device is rarely used in de novo coronary occlusions. In single-center experiences of patients with CTOs, most of them with prior failure to recanalize the occlusion, the use of the Frontrunner device helped to achieve successful recanalization in 42–77% of patients.^48,49 In a registry of over 900 patients, the company reports 56% success in previously failed CTOs and the perforation rate was 0.9%.⁶

Tornus

The Tornus device (Asahi) is a catheter made of 8 stainless steel strands woven together to enhance flexibility and strength in exchanging wires, delivering balloons and providing support for CTO procedures. It is used after a wire has crossed a chronic occlusion, when a balloon will not cross. The Tornus is advanced into the CTO by up to 20 counter-clockwise rotations without strong back-up support once the tip is encroached. The device can make a smooth channel without dissection, allowing for passage of a low profile balloon.⁵⁰ In addition it can also be “screwed in” to an occlusion to provide excellent backup for guidewire crossing. With the introduction of coronary stents, multiple randomized trials have demonstrated that stents are superior to plain balloon angioplasty in CTO intervention in terms of angiographic restenosis. Overall, the rate of angiographic restenosis with bare-metal stents for CTOs has been reported to vary from 32–55%.⁵¹ Since the introduction of drug-eluting stents (DES) into the United States, there has been a dramatic change in the interventional treatment paradigm such that greater than 90% of current patients receive DES during percutaneous coronary interventional procedures. Studies examining angiographic, intravascular ultrasound, and clinical endpoints have demonstrated safety and efficacy of these devices during the first year after therapy. Several registries have reported high success rate swith DES, with significant lower rates of restenosis, need for repeat revascularization and long-term MACE, when compared to parallel or historical registries of bare-metal stents.^52–59 In a recent prospective, randomized, single-blind, 2-center trial, In patients with CTOs, use of the sirolimus-eluting stents are superior to the bare-metal stents.⁶⁰ Total of 200 patients with total coronary occlusions were randomly assigned to receive bare-metal BxVelocity (Boston Scientific) stents, Cypher stents, or both. The Cypher stent group showed a significantly lower rate of instent binary restenosis (7% vs. 36%, P < 0.001) and lower rate of target lesion revascularization of (4% vs. 19%, P < 0.001). A nonrandomized study from South Korea compared the clinical and angiographic effectiveness of cypher stent and Taxus stents (n = 136), and showed more favorable results regarding restenosis and clinical outcomes with the Cypher stent.⁵⁸ At 6-month angiographic follow up, the restenosis rate was significantly higher in the Taxus group (28.6% vs. 9.4%; P = 0.020). At one-year follow up, the MACE-free survival rate was also significantly higher in the Taxus group (95.8% vs. 85.8%; P = 0.049). Thus, in this nonrandomized report, the implantation of SES in the treatment of CTO lesions showed more favorable results regarding restenosis and clinical outcomes compared with Taxus stent.

Reasons to abort the procedure. The most common reason to bring the procedure to an end is failure to recanalize the occlusion. With more experience, the expert operator learns how to escalate with a thoughtful selection of guidewires and other devices, and getting the insight into the point when further attempt has low yield and carries more risk than benefit. Avoiding complications has major importance in mastering the technique of CTO treatment, and the skilled operator should have the tools and knowledge to take care of them when they occur. Of course, when a complication occurs, the operator should stop the procedure, take care of the complication, stabilize the hemodynamic status, if needed, and avoid the temptation to go on with the procedure. An additional attempt may take place few weeks later when the patient is stable and willing to give another chance. In rare cases, when the occlusion was crossed with the wire predilated but could not be crossed with a stent, it makes sense to conclude the session with partial success, with an option for a reattempt a few weeks later. When the vessel recovers, small dissections heal and a further attempt to deliver a stent can be enhanced by more aggressive predilatation or rotational aterectomy. Special consideration should be given to the volume of contrast media used and the amount of radiation. With prolonged cases, these two may get to toxic levels. Contrast-induced nephropathy (CIN) occurs in as many as 30% of patients who receive iodine-based dye. CIN is associated with extended length of hospital stay, increased cost of hospitalization, and increased co-morbidity and long-term mortality.⁶¹ The operator should pay special attention to risk factors for CIN, like pre-existing renal insufficiency, diabetes mellitus, congestive heart failure, anemia, and dehydration.⁶² Except for adequate hydration, no specific therapy has been proven to have a protective effect in preventing CIN. Complex interventional procedures like the treatment of CTO, may require significant amounts of radiation for their completion.⁶³ It is recommended that operators be aware and document the radiation dose during the procedure. In cases with increased use of radiation dose (> 5 Gy cumulative dose), the patient should be advised to report any new skin redness or ulcers.