Intravascular-Ultrasound Assisted Localization and Revascularization of an Ostial Chronic Total Occlusion: Utility of Near-Field and Far-Field Imaging

Abstract: Percutaneous coronary interventions (PCI) of chronic total occlusions (CTOs) can be technically challenging, but are valuable in patients with severe angina. Recently, algorithms for CTO-PCI have been proposed to facilitate the selection of the PCI approach that can best achieve procedural success. When the ostium of the occluded vessel is ambiguous or not well visualized, the success rate of antegrade approaches is significantly diminished. In our case, we demonstrate the utility of intravascular ultrasound imaging in the localization of an ambiguous or “stump-less” ostial CTO in addition to providing real-time far-field imaging, which is helpful in tracking wire progress through the occluded segment. Adjunctive imaging was instrumental in achieving procedural success using the antegrade approach. 

J INVASIVE CARDIOL 2015;27(3):E37-E39

Key words: chronic total occlusion, percutaneous coronary intervention, intravascular ultrasound

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Chronic total occlusions (CTOs) are frequently encountered in patients undergoing coronary angiography.^1,2 Due to the challenging nature of CTO percutaneous coronary interventions (PCI), medical therapy or surgical revascularization options are commonly considered, with many not even offered the option of PCI. CTO-PCI can be beneficial to patients with severe or lifestyle-limiting angina. Algorithms have been proposed that aid in the selection of the best approach to CTO-PCI by assessing four key variables that influence procedural success. These include: CTO cap, lesion length, quality of the distal target, and presence and location of collaterals.³ The procedural success of an antegrade approach is predicated on a clear understanding of the proximal cap location and characteristics. One of the most important predictors of antegrade approach procedural failure is the presence of a large branch in close proximity to the CTO cap. We present a case where we were able to overcome the limitations of a ”stump-less” or ambiguous ostial CTO with the use of intravascular ultrasound (IVUS) imaging. IVUS played a key role in achieving procedural success by locating the ostium of the occluded vessel, assisting in guidewire crossing, and confirming the intraluminal wire position once the lesion was crossed.

Case Report

A 65-year-old male with known coronary artery disease and Canadian class III angina was referred for PCI of a large obtuse marginal (OM) branch CTO. The CTO was initially discovered 7 years previously, when the patient presented with an acute coronary syndrome caused by a right coronary artery (RCA) lesion. At that time, the culprit RCA lesion was treated percutaneously and coronary angiography demonstrated well-developed left-to-left and right-to-left collaterals. Over the last several years, and despite the use of beta-blockers, long-acting nitrates, and ranolazine, his angina progressed. During a recent nuclear stress test, the patient was only able to exercise for 5 minutes on a standard Bruce protocol before developing limiting angina. SPECT imaging revealed a large, moderate-severity, reversible, inferolateral defect with normal left ventricular function. 

At the time of diagnostic angiography for procedural planning, several lesion challenges were noted (Figure 1). First, the ostium of the OM vessel was not visualized, even though the well-developed collaterals adequately filled the distal segment of the OM branch. The anatomic pattern (and vessel size) favored a more proximal location of the ostium, while the collateral filling seemed directed to a more distal take-off. Both possible locations are noted (Figure 1, arrows). Second, the lesion chronicity, calcification, and length portended a lower procedural success rate. 

The decision was made to attempt PCI using the antegrade approach, with use of IVUS imaging to assist in defining the location of the occluded ostium. An 8 Fr extra back-up guiding catheter was used to provide support and dual injections of right and left coronaries provided adequate visualization of the distal target vessel via the well-developed contralateral collaterals. With the IVUS catheter in the mid circumflex artery, the occluded OM branch ostium was located as shown in Figure 2 and Video 1 (available online at www.invasivecardiology.com). An angiogram was performed to document the location of the transducer, and clearly demonstrated a more proximal origin of the occluded OM branch. Additionally, severe ostial calcification was noted. 

After crossing the CTO cap, the 3 g tip wire could not be advanced further due to lesion chronicity, length, and heavy calcification despite adequate guide support and the assistance of a balloon catheter. Additional IVUS imaging confirmed the intraluminal wire position (Figure 3, Video 1), which allowed the exchange for a heavier 12 g tip penetrating wire to facilitate crossing the CTO segment. With the help of far-field IVUS imaging and contralateral RCA injections, the 12 g wire was advanced across the entire occluded segment and into the distal marginal branch without complications. 

The initial attempt to pass a low-profile microcatheter was unsuccessful due to lesion resistance. Additional support was obtained using an anchoring balloon in the distal main circumflex artery, until the microcatheter and eventually a balloon catheter were delivered to the distal target vessel. Following balloon angioplasty, the lesion was stented using a single 3.0 x 33 mm drug-eluting stent. The final angiogram demonstrates a good result, with the CTO stented area highlighted (Figure 4). The patient returned to clinic 1 week later with complete resolution of his angina. 

Discussion

Over the last several years, advances in interventional techniques, wires, and devices have led to improvements in CTO-PCI outcomes. Challenges in CTO-PCI are determined by lesion characteristics, length, quality of the distal target, and the presence and location of collaterals. Ostial “stump-less” CTO lesions are associated with blunt or vague stumps and subsequent lower revascularization success rates. Procedural failure is driven primarily by the inability to locate the ostium with conventional angiographic images and the frequent deflection of the crossing wire into the patent branch or mother vessel rather than penetrating the rigid proximal CTO cap.⁴ 

Recent CTO crossing algorithms have highlighted the utility of IVUS to detect the side-branch ostium and improve revascularization rates in stump-less CTO lesions.³ Rare case reports have demonstrated the usefulness of this approach, and a recent case series of consecutive stump-less CTO cases achieved a success rate in excess of 80%.⁵ Although these rates should be interpreted with caution, since they were performed by experienced operators, the high success rates in this population are encouraging, and may lead to increased adoption of IVUS for this unique subset of CTO lesions. This IVUS-assisted antegrade approach is particularly important when retrograde approaches are not optimal, eg, when collaterals are poorly developed, small, or tortuous, or if only epicardial collaterals are available (with known higher risk of perforation). 

In addition to successful ostium identification and demonstration of cap characteristics, IVUS also provides far-field imaging, which may be helpful in assessing wire location and rule out subintimal entry.⁶ Far-field imaging is not conventional or standard practice with the use of coronary IVUS imaging. In this case, IVUS provided real-time far-field imaging that allowed the operators to track the course of the wire from proximal to distal, clearly demonstrating the intraluminal wire position. With the reassurance of the intraluminal position, wire exchanges and more aggressive back-up support using the anchoring technique were employed to provide the necessary force for the catheter to cross the lesion and achieve procedural success.⁷

The use of IVUS imaging may have several limitations in CTO-PCI. First, the parent vessel needs to be of adequate caliber to accommodate the IVUS catheter. Lower-profile catheters are now available to overcome this limitation in CTO cases. Second, image quality is affected by near-field calcification, which can lead to shadowing. Lastly, far-field IVUS takes advantage of the structures adjacent to the catheter. The viewing distance from the parent vessel may be limited in cases with large side-branch angles, where the branch quickly distances itself from the transducer. 

Conclusion

Intravascular ultrasound imaging during CTO-PCI can identify and characterize ambiguous proximal caps, allowing antegrade revascularization, which might otherwise may not be feasible. In addition, our images demonstrate the usefulness of intravascular imaging for complicated interventions, including providing real-time far-field imaging to assist in CTO lesion crossing and to document wire position.  

Acknowledgment. The authors acknowledge the valuable contribution of Wael El Mallah, MD, PhD, in preparation of the video clips accompanying the manuscript.

References

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From the  Gill Heart Institute, University of Kentucky, Lexington, Kentucky.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted May 19, 2014 and accepted June 30, 2014.

Address for correspondence: Khaled M. Ziada, MD, FACC, FSCAI, Division of Cardiovascular Medicine, Gill Heart Institute, 900 South Limestone, 326 Wethington Building, Lexington, KY 40536-0200. Email: khaled.ziada@uky.edu