Author + information
- †Department of Cardiology, York Hospital, York, Pennsylvania
- ‡Division of Cardiology, Emory University, Atlanta, Georgia
- §Medizinische Klinik (Cardiology & Intensive Care), Klinikum Darmstadt GmbH, Darmstadt, Germany
- ↵∗Reprint requests and correspondence:
Dr. William J. Nicholson, Department of Cardiology, York Hospital, 1001 South George Street, York, Pennsylvania 17403.
Percutaneous coronary intervention (PCI) for chronic total occlusions (CTOs) remains a challenging procedure with heterogeneous success rates depending upon multiple factors, including lesion characteristics and operator skillsets. Lesion evaluation to establish pre-procedural strategies leads to improved efficiency and success rates (1). Although the dual injection coronary angiogram remains the conventional standard for guiding the operator’s approach, adjunctive imaging modalities including coronary computed tomography angiography (CTA) may offer additional value (2).
In this issue of JACC: Cardiovascular Interventions, Choi et al. (3) present an approach on the basis of CTA criteria to help discriminate between subtotal coronary occlusions (STOs) (those with very high grade but not completely occlusive stenosis, with persisting antegrade perfusion of the distal vessel) and total occlusions (those with complete occlusion of the epicardial vessel lumen and distal vessel perfusion via collateral connections). Distinguishing between these 2 dramatically different lesions is difficult with coronary CTA due to the inherent limitation of the spatial resolution of computed tomography datasets (approximately 0.4 mm) (4). Furthermore, the visualization of the residual channel within such an STO often requires high injection force during coronary angiography and may even be missed when using small-diameter diagnostic catheters. The visualization of the lumen during CTA is made on the basis of passive filling of contrast during a peripheral contrast injection, so no additional injection force is present to fill up the STO. This may be 1 of the reasons why 25% of lesions considered to be CTOs actually were just subtotal occlusions on angiographic evaluation.
In the past, vessel occlusion length was the only CTA parameter useful in differentiating these lesions. This current paper adds to the previous work (5,6) by factoring in additional lesion morphological characteristics and the transluminal attenuation gradient (TAG). The premise of TAG is determined by measuring radiological attenuation in Hounsfield units (HU) beginning at the occluded segment of the vessel and then serially at set intervals distal to the occlusion. With increasing lesion severity (STO) short of complete occlusion, the HU should, in theory, gradually diminish distally as coronary perfusion and contrast penetration dissipates. In contrast, when complete occlusion has occurred, filling of the distal vessel is expected to occur via collateral vessels, thus creating a situation in which the distal vessel enjoys greater perfusion than the region adjacent to the completely occluded segment. This retrograde filling of the vessel creates what has been referred to in the past as a reverse attenuation gradient.
The authors put forth a predictive model using a combination of lesion characteristics (occlusion length ≥15 mm, side branches, blunt stump, visualized collateral vessel, cross-sectional calcification ≥50%, and TAG with the distal vessel ≥0.9 HU/10 mm) to discriminate between STO and complete occlusions with a sensitivity of 85% and a specificity of 75%. Such an approach might be very useful in patients in whom an occlusion is found after undergoing a CTA as a diagnostic approach to detect coronary artery disease without previous angiography. On the basis of the suggested criteria, an STO can be discriminated from a CTO. An STO might be dealt with in an ad-hoc approach when the angiographic procedure is scheduled, whereas a CTO should be referred to an expert for such lesions, and recanalization should not be attempted impromptu at the time of diagnostic angiography. Unfortunately, the authors attempt to take their model and findings 1 step further and put forth the suggestion that this model can also predict procedural success during PCI. The anatomic qualities of the lesions assessed in the current study, including a blunt stump, lesion length, and calcification, are variables included in the J-CTO (Multicenter CTO Registry in Japan) score (7) that may predict likelihood of success in CTO PCI. However, modern CTO PCI and the ability to predictably recanalize these vessels has evolved dramatically over the past several years. Improved wire technology, employment of the retrograde approach, and the more liberal utilization of the subintimal space with antegrade and retrograde dissection re-entry have led to high PCI success rates (8). A CTO operator’s volume of experience and the plenitude of skills required to offer the patient the complete array of recanalization strategies is paramount.
The current study supplies limited lesion characteristics to correctly put the complexity of the occluded vessels in proper context. Growing data supports the premise that accomplished CTO operators can achieve >90% success rates independent of the traditional J-CTO score parameters. The relatively short average complete occlusion length of only 17 mm and the lack of calcium in nearly two-thirds of the complete occlusions in the current study would lead one to believe that most cases would have a J-CTO score <2, which should portend a favorable PCI success rate. The 95% PCI recanalization rate in STO lesions is surprisingly low, as these vessels are open by definition, and one should expect CTO operators to have near 100% success rates in such cases. Additionally, only 57% of completely occluded vessels underwent attempted PCI, with a success rate of only 75%. This is likely attributed to the long patient enrollment period of this trial from 2006 to 2013, during which the technical approach to CTO PCI improved success rates considerably. We are not supplied with the procedural information from these attempts with regard to the presence of and utilization of interventional collaterals or attempted antegrade or retrograde dissection re-entry. One can likely conclude that the predictive value of the model put forth in this study might apply to the rudimentary CTO techniques available at the time that the study was conducted, but may not reflect the expected high success rates demonstrated with modern comprehensive CTO PCI skills.
The authors should be congratulated on their contribution to improve the ability of noninvasive imaging to distinguish between complete and subtotal occlusions before subsequent conventional angiography. It is important to remember that the presence of a complete occlusion does not define it as a chronic occlusion. Additionally, 25% of the patients predicted to have a complete occlusion in the current study were found to have only STO at the time of conventional angiography. Although the predictive value of the current model may lead the physician to expect a complete occlusion, it does not obviate the need for conventional confirmatory angiography. The effort to put forth a model to encourage or discourage attempting PCI on the basis of anatomy falls short of the modern universally adopted strategy of clinically driven revascularization. Experienced CTO operators in the modern era can offer a very large majority of patients, with appropriate clinical indicators, a successful percutaneous strategy for revascularization.
Rather than focusing on the presence of a complete occlusion as a predictor of PCI failure, emphasis should be placed on continuing to understand how to apply the information obtained from CTA to guide and assist the interventional approach. Continued evaluation of the computed tomography data before PCI may help the operator to better understand the course of the occluded segment, assess the quality of the distal vessel as a potential re-entry zone, and identify the presence of interventional collaterals to plan a more efficient percutaneous strategy.
↵∗ Editorials published in JACC: Cardiovascular Interventions reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Interventions or the American College of Cardiology.
Both authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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