Sub-Intimal Tracking and Re-Entry and Investment Procedures: Current Applications and Future Directions

In seeking to improve upon chronic total occlusion (CTO) percutaneous coronary intervention success rates and minimize risk, CTO modification procedures (investment procedures) have been developed and utilized with increasing frequency. Two key techniques have emerged: subintimal tracking and re-entry (STAR) and subintimal plaque modification (SPM). Both require a staged approach with an index procedure for plaque modification and a second procedure weeks later for stenting. Both approaches require entry and wiring with a polymer-jacketed wire in the extra-plaque space, yet unlike SPM, which exclusively requires angioplasty of the extra-plaque space throughout the CTO segment, STAR also involves re-entry into the true luminal distal to the CTO before angioplasty. STAR and SPM, in many ways, represent a paradigm shift in our approach to CTO percutaneous coronary intervention from a 1-step to a 2-step approach in complex cases. In this review, we discuss the technical aspects of the procedures, and controversies and ongoing trials pointing to the future of these techniques. We also highlight non-device-based and intravascular ultrasound-based approaches to anterograde dissection and re-entry, which add to the CTO operator's toolkit for challenging cases.

Dissection and Re-entry Techniques for Chronic Total Occlusion Percutaneous Coronary Intervention

Despite early stagnation in success rates for percutaneous coronary intervention for chronic total occlusion with the traditional antegrade wiring approach, the introduction of dissection/re-entry techniques and the retrograde approach opened new avenues for operators to tackle more complex occlusions. Dissection/re-entry techniques (both antegrade and retrograde) are commonly used in angiographic scenarios characterised by long, tortuous and calcified occlusions, as well as in those with proximal cap ambiguity. Familiarity and comfort using the extraplaque space (with either an antegrade or retrograde approach) have become fundamental to achieving safe and effective recanalisation of complex chronic total occlusions. This review provides an overview of different contemporary antegrade and retrograde dissection re-entry techniques and their acute and longer-term outcomes.

Optimal timing of staged percutaneous coronary intervention after subintimal tracking and re-entry: Rationale and design of the subintimal tracking and re-entry with deferred stenting study

BACKGROUND

Ten to fifteen percent of chronic total occlusion (CTO) percutaneous coronary interventions (PCIs) are unsuccessful in contemporary practice. Subintimal tracking and re-entry (STAR) (one form of "investment procedure") with staged reattempt and stenting may further increase the ultimate success and safety of CTO as a bailout strategy. The optimal timing for staged stenting after STAR is unknown.

METHODS AND RESULTS

We designed a six-center, prospective randomized trial with a planned enrollment of 150 patients where STAR is utilized in case of impending failure. The primary aim is to evaluate the optimal timing of the staged PCI after STAR by randomizing the timing to earlier (5-7 weeks) versus later (12-14 weeks) staged PCI. The primary endpoint of the study is the technical success rate of the staged procedure. The secondary endpoints include: (1) the rate of thrombolysis in myocardial infarction 3 flow at the start of staged intervention, (2) rate of partial technical and procedural success of the staged procedure, (3) rate of in-hospital and 12-month major cardiac and cerebrovascular adverse events, and (4) change in patient-reported quality at 30 days, 6 months, and 12 months assessed by Seattle Angina Questionnaire.

CONCLUSION

This study will ascertain the optimal timing of staged stenting after bail-out STAR approach in contemporary CTO PCI (ClinicalTrials.gov NCT05089864).

Antegrade techniques for chronic total occlusion percutaneous coronary intervention

Antegrade techniques are the foundation of chronic total occlusion (CTO) percutaneous coronary intervention (PCI). Antegrade wiring with the intent to achieve an intraplaque guidewire tracking is not always feasible, and crossing into the extraplaque space with subsequent reentry (antegrade dissection and reentry), might be needed, particularly in more complex occlusions. The present article reviews in detail the antegrade approaches to CTO PCI, focusing on equipment, techniques, and overcoming challenges.

Practice differences and knowledge gaps in complex and high-risk interventions between Japan and the USA: A case-based discussion

Advances in percutaneous coronary intervention (PCI) devices and techniques have expanded the pool of eligible patients for revascularization, including those with comorbidities, reduced left ventricular function, or anatomical complexity (defined as CHIP: complex and high-risk interventions in indicated patients). CHIP interventions are typically performed by selected operators who specialize in complex PCI. This review presents two cases performed in the USA, to discuss the similarities and differences in practice patterns between CHIP operators in Japan and the USA. The first case involves a 58-year-old male presenting with myocardial infarction and cardiogenic shock, and the second case involves a 51-year-old female with a history of coronary artery bypass grafting presenting with a chronic total occlusion and PCI complicated by vessel perforation. The discussion focuses on appropriate patient selection, the role of the heart team approach for decision-making, the use of hemodynamic support devices, and other relevant factors. By comparing practices in Japan and the USA, this review highlights opportunities for knowledge exchange and potential areas for improving patient outcomes.

Comparative Analysis of Polymer Versus Non-Polymer Jacketed Wires in Chronic Total Occlusion Percutaneous Coronary Intervention

There is significant variation in wire utilization patterns for chronic total occlusion (CTO) percutaneous coronary intervention. This study aimed to compare the outcomes of polymer-jacketed wires (PJWs) versus non-PJWs in anterograde procedures. We analyzed clinical and angiographic characteristics, and procedural outcomes of 7,575 anterograde CTO percutaneous coronary interventions that were performed at 47 centers between 2012 and 2023. Cases in which PJWs were exclusively used were classified in the PJW group, whereas cases where at least one non-PJW was employed were classified in the non-PJW group. Study end points were as follows: technical success, coronary perforation, major adverse cardiac event. PJWs were exclusively used in 3,481 cases (46.0%). These cases had lower prevalence of proximal cap ambiguity, blunt stump, and moderate/severe calcification. They also had lower Japanese CTO (J-CTO), Prospective Global Registry for the Study of Chronic Total Occlusion (PROGRESS-CTO), and PROGRESS-CTO complications scores, higher technical success (94.3% vs 85.7%, p <0.001), and lower perforation rates (2.2% vs 3.2%, p = 0.013). Major adverse cardiac event rates did not differ between groups (1.3% vs 1.5%, p = 0.53). Exclusive use of PJWs was independently associated with higher technical success in both the multivariable (odds ratio [OR] 2.66, 95% confidence interval [CI] 2.13 to 3.36, p <0.001) and inverse probability of treatment weight analysis (OR 2.43, 95% CI 2.04 to 2.89, p <0.001). Exclusive use of PJWs was associated with lower risk of perforation in the multivariable analysis (OR 0.69, 95% CI 0.49 to 0.95, p = 0.02), and showed a similar trend in the inverse probability of treatment weight analysis (OR 0.77, 95% CI 0.57 to 1.04, p = 0.09). Exclusive use of PJWs is associated with higher technical success and lower perforation risk in this non-randomized series of patients.

STAR procedure becomes SAFER: First-in-man case series of a new antegrade dissection re-entry technique

INTRODUCTION

Antegrade dissection and re-entry (ADR) is an integral part of the hybrid algorithm, which has allowed for improved outcomes in chronic total occlusion (CTO) coronary intervention (PCI).

METHODS

A new ADR method, Subintimal Antegrade FEnestration and Re-entry (SAFER), is described. The results of a first-in-man series are presented.

RESULTS

SAFER was performed on seven consecutive patients with angiographic and clinical success in all patients.

CONCLUSIONS

This first-in-man study has shown that the SAFER technique is feasible and effective with the possibility of improving the antegrade PCI CTO success rate.

Long term clinical outcome after success re-attempt percutaneous coronary intervention of chronic total occlusion

BACKGROUND

To evaluate the long-term outcome after re-attempt CTO-PCI.

METHODS

This is a retrospective cohort study that included 113 re-attempt CTO-PCI patients who were consecutively registered from January 2019 to December 2020 at Beijing Anzhen Hospital's Center of Coronary Artery Disease. All patients were divided into two groups based on procedural success or failure. The primary endpoint was major adverse cardiac events (MACE), a composite of all-cause mortality, myocardial infarction and target vessel revascularization (TVR). The secondary endpoint was angina after PCI.

RESULTS

Overall, the successful re-attempt CTO-PCI was archived in 77 patients, the failed CTO-PCI was performed in 36 patients. After a median follow-up of 21.7 months (interquartile range: 10.9-26.0), the incidence of the primary outcome was significantly lower in the success group [14.2% vs. 38.9%, adjusted hazard ratio (HR) 0.351, 95% CI 0.134-0.917, P = 0.033], mainly driven by the reduction of TVR (9.1% vs. 30.6%, adjusted HR 0.238, 95% CI: 0.078-0.72, P = 0.011). Furthermore, patients who had successful re-attempt CTO-PCI had a lower risk of angina after PCI (27.3% vs.61.1%, adjusted HR 0.357, 95% CI 0.167-0.76, P = 0.008). The risk factors of TVR in the patients with successful re-attempt CTO-PCI were stent length > 100 mm (adjusted HR 21.805, 95% CI 1.765-269.368, P = 0.016) and J-CTO score > 3(adjusted HR: 9.733, 95% CI:1.533-61.797, P = 0.016).

CONCLUSIONS

For the patients with previous CTO-PCI failure, a successful re-attempt CTO-PCI was associated with significantly lower MACE, which was primarily driven by a lower TVR rate. More complex CTO lesions and longer stents were the independent predictors of TVR after successful CTO-PCI.

Why and How Should We Treat Chronic Total Occlusion? Evolution of State-of-the-Art Methods and Future Directions

Chronic total occlusions are considered the most complex coronary lesion in interventional cardiology. The absence of visible lumen on angiography obscures the vessel course and makes vessel wiring unlikely with conventional techniques. Often a source of severe ischemia, chronic occlusions are also markers of advanced atherosclerosis that brings other complex features including lesion length, bifurcations, calcification, adverse vessel remodelling, distal disease, and anatomic distortion from previous bypass grafting. Often advanced atherosclerosis is associated with patient characteristics like left ventricular dysfunction, previous coronary bypass surgery, or multivessel disease that increase procedural demands and hazards. To accommodate these challenges new techniques and dedicated technologies have been developed. When applied to appropriate patients, these advances have improved procedural success, safety, and outcomes. Our aim is to provide the general cardiologist with an overview of these advances that can serve as a basis for counselling patients considered for revascularization.

Impact of Subintimal Plaque Modification on Reattempted Chronic Total Occlusions Percutaneous Coronary Intervention

BACKGROUND

Predictors of success in reattempted chronic total occlusion (CTO) percutaneous coronary intervention (PCI) procedures remain obscure, mainly owing to the lack of consecutive angiograms and procedural records of initial attempts in the same cohort.

OBJECTIVES

This study sought to investigate the factors predicting the success of reattempted CTO PCI procedures.

METHODS

A total of 208 consecutive patients who underwent a failed CTO PCI attempt and received reattempted procedure at the same cardiac center were retrospectively analyzed. Predictors of the success of reattempted procedures were evaluated.

RESULTS

The overall technical success rate of reattempted CTO PCI procedures was 71.2%. Subintimal plaque modification (SPM) was implemented in 35 (16.8%) procedures in initial attempts. The reattempted technical success rate was 93.3% in cases in which SPM with guidewire (GW) crossing was achieved in the initial attempt; however, the success rate was 55.0% for procedures involving SPM without GW crossing. SPM with GW crossing (OR: 11.21; 95% CI: 1.31-96.16; P = 0.028), referral to high-volume operators (OR: 2.38; 95% CI: 1.14-4.98; P = 0.021), and a bidirectional approach (OR: 2.31; 95% CI: 1.12-4.79; P = 0.024) were positive independent predictors of technical success in the subsequent reattempt. The time interval for reattempt (per 90-day increment) was negatively correlated with the technical success of the reattempted procedures (OR: 0.85; 95% CI: 0.73-0.98; P = 0.030).

CONCLUSIONS

This study identified independent predictors of success in reattempted CTO PCI procedures. SPM with GW crossing achieved in the initial attempt is associated with a higher success rate in the subsequent reattempt.

Contemporary Issues in Chronic Total Occlusion Percutaneous Coronary Intervention

Remarkable progress has been achieved in chronic total occlusion (CTO) percutaneous coronary intervention (PCI) in recent years, with refinement of the indications and technical aspects of the procedure, imaging, and complication management. Randomized controlled trials and rigorous prospective registries have provided high-quality data on the benefits and risks of CTO PCI. Global collaboration has led to an agreement on nomenclature, indications, endpoint definition, and principles of clinical trial design that have been distilled in global consensus documents such as the CTO Academic Research Consortium. Increased use of preprocedural coronary computed tomography angiography and intraprocedural intravascular imaging, as well as development of novel techniques and structured CTO crossing and complication management algorithms, allow a systematic, stepwise approach to this difficult lesion subset. This state-of-the-art review provides a comprehensive discussion about the most recent developments in the indications, preprocedural planning, technical aspects, complication management, and future directions of CTO PCI.

CTO in Contemporary PCI

Percutaneous Coronary Intervention (PCI) of Chronic Total Occlusions (CTO) represents the most challenging procedure in modern endovascular treatments. In recent years, the success rate of CTO PCI has substantially improved, owing to increasing operator expertise and advancements in CTO equipment and algorithms as well as the development of expert consensus documents. In this review, we summarize existing evidence for CTO PCI, its success/ risk prediction scoring tools, procedural principles and complications and provide an insight into the future role of CTO PCI.

Update on chronic total occlusion percutaneous coronary intervention

Chronic total occlusion (CTO) percutaneous coronary interventions (PCI) can be challenging to perform. The main indication for CTO PCI is to improve symptoms. Several contemporary studies have reported high CTO PCI success rates at experienced centers but success rates in all-comer registries remain low. Several scores can estimate the difficulty and the likelihood of success of CTO PCI. Dual arterial access and use of CTO crossing algorithms can improve the success and safety of CTO PCI. Intracoronary imaging can optimize stent expansion and minimize adverse cardiovascular events. While complications are more common in CTO PCI, careful planning and prompt diagnosis and treatment can prevent them or minimize their adverse consequences. In this article, we review contemporary data on the indications, safety and efficacy of CTO PCI.

Chronic total occlusion percutaneous coronary intervention in everyday clinical practice - an expert opinion of the Association of Cardiovascular Interventions of the Polish Cardiac Society

Coronary chronic total occlusions (CTO) are increasingly encountered during invasive and non-invasive coronary angiography and remain the most challenging lesions for percutaneous revascularization. During recent years success rates and safety outcomes of CTO percutaneous coronary intervention (PCI) have substantially improved, particularly due to the introduction of new techniques and dedicated equipment as well as specialized training programs of CTO operators. Significantly, the steady advances in CTO PCI techniques have coincided with the new data from randomized clinical trials supporting the role of percutaneous recanalization of CTO in relieving angina and improving the quality of life. The current expert consensus document outlines the rationale, clinical outcomes as well as technical, safety and reimbursement issues of CTO PCI. In addition, the requirements for achieving and maintaining competency in CTO PCI among interventional cardiologists are discussed. Finally, we present the modified hybrid algorithm (the so-called Polish hybrid algorithm) providing some unique refinements to the contemporary CTO PCI strategies. Continuous efforts (including active engagement with the payer) are urgently needed to increase guideline-recommended referrals to CTO PCI, and thus improve the quality of life of CTO patients in Poland.

Development and validation of a prediction model for angiographic perforation during chronic total occlusion percutaneous coronary intervention: OPEN-CLEAN perforation score

BACKGROUND

Perforation is the most frequent complication of chronic total occlusion (CTO) percutaneous coronary intervention (PCI) and is associated with adverse events including mortality.

METHODS

Among 1,000 consecutive patients enrolled in 12 center prospective CTO PCI study (OPEN CTO), all perforations were reviewed by the angiographic core-lab. Eighty-nine patients (8.9%) with angiographic perforation were compared to 911 patients without perforation. We sought to describe the clinical and angiographic predictors of angiographic perforation during CTO PCI and develop a risk prediction model.

RESULTS

Among eight clinically important candidate variables, independent risk factors for perforation included prior CABG (OR 2.0 [95% CI, 1.2-3.3], p < .01), occlusion length (OR 1.2 per 10 mm increase [95% CI, 1.1-1.3], p < .01), ejection fraction (OR 1.2 per 10% decrease [95% CI, 1.1-1.5], p < .01), age (OR 1.3 per 5 year increase [95%CI, 1.1-1.5], p < .01), and heavy calcification (OR 1.7 [95% CI, 1.0-2.7], p = .04). Three other potential candidate variables, glomerular filtration rate, proximal cap ambiguity, and target vessel, were not independently associated with perforation. The model was internally validated using bootstrapping methods. From the full model, a simplified perforation prediction score (OPEN-CLEAN score: CABG, Length [occlusion], EF < 50%, Age, CalcificatioN) was developed, which discriminated the risk of angiographic perforation well (c-statistics = 0.75) and demonstrated good calibration.

CONCLUSION

This simple 5-variable prediction score may help CTO operators to risk-stratify patients for angiographic perforation using variables available prior to CTO PCI procedures.

Perforation Mechanisms, Risk Stratification, and Management in the Post-Coronary Artery Bypass Grafting Patient

Coronary perforations during chronic total occlusion percutaneous coronary intervention (CTO PCI) is a most frequent major complication and the incidence is significantly higher compared with non-CTO PCI. Patients with prior history of coronary bypass have more major adverse events when perforation occurs compared with patients without prior bypass surgery. In this article, the authors discuss the unique challenges in identification and timely treatment of perforations in patients with prior bypass surgery.

Subintimal Plaque Modification and Subintimal Dissection and Reentry: Strategies to Turn Failure into Success

The success of chronic total occlusion (CTO) percutaneous coronary intervention (PCI) depends on the execution of bailout strategies, like subintimal dissection and reentry (STAR) and subintimal plaque modification (SPM). These are invaluable when traditional techniques fail. SPM is a modification of the STAR technique in which angioplasty is performed of the occluded segment without true lumen access in the distal vessel. Available data on SPM has shown favorable outcomes with a greater than 90% success rate when the failed CTO is reattempted in 8-12 weeks after SPM has been performed. Future studies are needed to better assess its role.

Intermediate procedural and health status outcomes and the clinical care pathways after chronic total occlusion angioplasty: A report from the OPEN-CTO (outcomes, patient health status, and efficiency in chronic total occlusion hybrid procedures) study

BACKGROUND

No previous reports have described the comprehensive care pathways involved in chronic total occlusion percutaneous coronary intervention (CTO PCI).

METHODS

In a study of 1,000 consecutive patients undergoing CTO PCI using hybrid approach, a systematic algorithm of selecting CTO PCI strategies, the procedural characteristics, complication rates, and patient reported health status outcomes through 12 months were assessed.

RESULTS

Technical success of the index CTO PCI was 86%, with 89% of patients having at least one successful CTO PCI within 12 months. A total of 13.8% underwent CTO PCI of another vessel or reattempt of index CTO PCI within 1 year. At 1 year, the unadjusted major adverse cardiac and cerebral event (MACCE) rate was lower in patients with successful index CTO PCI compared to patients with unsuccessful index CTO PCI (9.4% vs. 14.6%, p = .04). The adjusted hazard ratios of myocardial infarction and death at 12 months were numerically lower in patients with successful index CTO PCI, compared to patients with unsuccessful index CTO PCI. Patients with successful index CTO PCI reported significantly greater improvement in health status throughout 12-months compared to patients with unsuccessful index CTO PCI.

CONCLUSION

CTO-PCI in the real-world often require treatment of second CTO, non-CTO PCI or repeat procedures to treat initially unsuccessful lesions. Successful CTO PCI is associated with numerically lower MACCE at 1 year and persistent symptomatic improvement compared to unsuccessful CTO PCI. Understanding the relationship between the care pathways following CTO PCI and health status benefit requires further study.

Modified subintimal plaque modification improving future recanalization of chronic total occlusion percutaneous coronary intervention

BACKGROUND

Subintimal plaque modification (SPM) is often performed to restore antegrade flow and facilitate subsequent lesion recanalization. This study aimed to compare the safety and efficacy of modified SPM with traditional SPM.

METHODS

A total of 1454 consecutive patients who failed a chronic total occlusion percutaneous coronary intervention (CTO PCI) attempt and underwent SPM from January 2015 to December 2019 at our hospital were reviewed retrospectively. Fifty-four patients who underwent SPM finally were included in this study. We analyzed the outcomes of all the patients, and the primary endpoint was recanalization rate, which was defined as Thrombolysis in Myocardial Infarction (TIMI) grades 2-3 flow on angiography 30 to 90 days post-procedure.

RESULTS

The baseline characteristics were similar between the two groups. In the follow-up, the recanalization rate was noticeably higher in the modified SPM group compared with the traditional SPM group (90.9% vs. 62.5%, P < 0.05). The proposed strategy in the modified group was more aggressive, including a larger balloon size (1.83 ± 0.30 vs. 2.48 ± 0.26 mm, P < 0.05) and longer subintimal angioplasty (0.59 ± 0.16 vs. 0.92 ± 0.12 mm, P < 0.05). Also, the common use of a Stingray balloon and guide catheter extension resulted in improvement of patients in the modified SMP group (12.5% vs. 100%, P < 0.05).

CONCLUSION

Modified SPM, which is associated with a high likelihood of successful recanalization, is an effective and safe CTO PCI bail out strategy.

Latest developments in chronic total occlusion percutaneous coronary intervention

INTRODUCTION

Chronic Total Occlusion Percutaneous Coronary Intervention (CTO PCI) is now performed with high success rates and acceptable complication rates.

AREAS COVERED

We describe recent clinical and technological developments in CTO PCI from 2018 to 2020.

EXPERT OPINION

After publication of six randomized controlled trials, improving patient symptoms remains the principal indication for CTO PCI. Although good outcomes can be achieved with CTO PCI at experienced centers, success rates are significantly lower at less experienced centers, despite increased use in CTO crossing algorithms and development of novel and improved equipment and techniques.

Multicenter experience with the antegrade fenestration and reentry technique for chronic total occlusion recanalization

OBJECTIVES

We aimed to evaluate the efficacy and safety of antegrade fenestration and reentry (AFR) for chronic total occlusion (CTO) recanalization in a multicenter registry.

BACKGROUND

Adoption of antegrade dissection/reentry (ADR) for CTO recanalization has been limited, and novel ADR techniques are needed.

METHODS

AFR involves the balloon-induced creation of multiple fenestrations between the false and true lumen. A targeted true lumen reentry is subsequently achieved with a low tip-load polymer-jacketed guidewire. Following the initial description and dissemination of AFR, patients undergoing AFR-based CTO recanalization at nine centers were included in the present registry. Study endpoints were AFR success, procedural success, and target-lesion failure (TLF) on follow-up.

RESULTS

We included 41 patients. Mean J-CTO score was 2.5 ± 1.4. In 80.5% of cases, AFR was performed after failed antegrade wire escalation. Another ADR technique was used before AFR in one-third of cases. AFR achieved distal true lumen reentry in n = 27/41 (65.9%) cases. In n = 14/41 (34.1%) cases with AFR failure, use of alternative techniques led to successful CTO recanalization in eight additional patients. The overall technical and procedural success rates were 85.4% and 82.9%, respectively. No AFR-related complications were observed. One-year TLF rate was 8.3% overall, with no differences between successful and failed AFR.

CONCLUSIONS

We report on AFR feasibility in a multicenter registry of patients undergoing CTO recanalization. We observed a moderate success rate, coupled with the absence of complications. Moreover, even a failed AFR attempt did not preclude the use of alternative techniques to achieve recanalization. Further studies should confirm and extend our findings.

Guiding Principles for Chronic Total Occlusion Percutaneous Coronary Intervention

Outcomes of chronic total occlusion (CTO) percutaneous coronary intervention (PCI) have improved because of advancements in equipment and techniques. With global collaboration and knowledge sharing, we have identified 7 common principles that are widely accepted as best practices for CTO-PCI.  1. Ischemic symptom improvement is the primary indication for CTO-PCI.  2. Dual coronary angiography and in-depth and structured review of the angiogram (and, if available, coronary computed tomography angiography) are key for planning and safely performing CTO-PCI.  3. Use of a microcatheter is essential for optimal guidewire manipulation and exchanges.  4. Antegrade wiring, antegrade dissection and reentry, and the retrograde approach are all complementary and necessary crossing strategies. Antegrade wiring is the most common initial technique, whereas retrograde and antegrade dissection and reentry are often required for more complex CTOs.  5. If the initially selected crossing strategy fails, efficient change to an alternative crossing technique increases the likelihood of eventual PCI success, shortens procedure time, and lowers radiation and contrast use.  6. Specific CTO-PCI expertise and volume and the availability of specialized equipment will increase the likelihood of crossing success and facilitate prevention and management of complications, such as perforation.  7. Meticulous attention to lesion preparation and stenting technique, often requiring intracoronary imaging, is required to ensure optimum stent expansion and minimize the risk of short- and long-term adverse events. These principles have been widely adopted by experienced CTO-PCI operators and centers currently achieving high success and acceptable complication rates. Outcomes are less optimal at less experienced centers, highlighting the need for broader adoption of the aforementioned 7 guiding principles along with the development of additional simple and safe CTO crossing and revascularization strategies through ongoing research, education, and training.