The incremental value of invasive coronary angiographic characteristics in predicting the success of retrograde chronic total occlusion percutaneous coronary intervention via invisible collateral channels

Introduction

Successful percutaneous coronary chronic total occlusion (CTO) recanalization provides significant clinical benefit (1-3). However, percutaneous coronary intervention (PCI) for CTO remains technically challenging and typically exhibits lower success rates than does non-CTO PCI (4). The retrograde approach has emerged as a valuable technique, being widely adopted for CTO PCI and contributing to improved technical success rates (5). Access to the distal vessel via the retrograde approach is typically achieved through septal or epicardial collateral channels (CCs) (6), with septal CCs being favored due to their greater safety and relative ease of navigation relative to epicardial CCs (7-9).

In retrograde CTO PCI, invasive coronary angiographic (ICA) characteristics, such as CC size and tortuosity, are crucial predictors of successful guidewire and device crossing (8). CC size is often classified according to Werner’s CC grading system, which designates collaterals without a visible connection to the recipient vessel as grade 0 CCs (10). Notably, these invisible connections represent significant predictors of procedural failure in the retrograde approach (6). However, other studies have indicated that crossing invisible septal CCs can be achieved through the surfing technique (11,12).

The introduction of the Guidezilla catheter has provided additional support, and the use of this catheter can serve as a significant independent predictor of initial microcatheter crossing success in retrograde septal PCI for CTO (12,13). Despite its potential, there remains limited data for the application of the Guidezilla catheter for retrograde CTO PCI via invisible septal CCs.

Consequently, this study aimed to assess the incremental value of ICA characteristics when combined with Guidezilla catheter use status in predicting technical success in retrograde CTO PCI through invisible septal CCs. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-135/rc).

Methods

Patient population and outcome definition

This study was approved by the Institutional Review Board of Guangdong Provincial People’s Hospital (Approval No. KY2023-716-01) and was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The requirement for informed consent was waived due to the retrospective nature of the analysis. From January 2019 to December 2022, we prospectively included consecutive retrograde CTO PCI procedures performed via grade 0 septal CCs with or without the Guidezilla catheter (Boston Scientific, Marlborough, MA, USA). The Guidezilla catheter was selected as the representative mother-in-child catheter in this study due to its favorable profile for deliverability through tortuous collaterals, its proven capability in providing strong passive backup support, and its widespread availability and familiarity among the operating physicians at our institution. These procedures were carried out across 40 tertiary hospitals by a high-volume operator (B.Z.), defined as a primary operator who performs at least 50 CTO PCIs annually (14). The Werner classification categorizes coronary CCs as follows: grade 0, no visible connection with the recipient vessel; grade 1, thread-like tiny vessels; and grade 2, small vessel-like channels (Figure 1) (10).

Figure 1 Werner classification of CCs. The categorization of CCs is delineated as follows: grade 0 (yellow arrows) includes CCs traversing septal branches from the left anterior descending artery to the PDA branches, which are not continuously visible and appear interrupted; grade 1 (black arrows) includes continuous thread-like connections; and grade 2 (white arrows) includes side branch-like connections of similar size to the native vessel. CCs, collateral channels; PDA, posterior descending artery.

A CTO is defined as a completely occluded segment with thrombolysis in myocardial infarction (TIMI) flow grade 0 and an estimated duration of at least 3 months (15). A procedure was classified as retrograde if a wire was used to attempt a crossing of a CC regardless of success (11). We compared the clinical data, ICA results, technical characteristics, and procedural outcomes between cases in which the Guidezilla catheter was used and cases in which it was not.

Technical success was defined as successful CTO revascularization with less than 20% residual diameter stenosis in the treated segment and the restoration of antegrade TIMI flow grade 3. We recorded complications related to CTO PCI occurring before hospital discharge for each patient, including death, pericardial tamponade, coronary perforation or dissection, myocardial infarction, stent thrombosis, malignant arrhythmia, no flow or slow flow, retroperitoneal hematoma, stroke, vascular access complications, and the need for emergency surgical intervention or PCI.

ICA assessments

The characteristics analyzed in the ICA included coronary dominance; CTO location [specifically within the left anterior descending artery (LAD) or the right coronary artery (RCA)]; the Japanese-Chronic Total Occlusion (J-CTO) score (including factors such as blunt proximal cap, bending >45°, calcifications, CTO length >20 mm, and previous failed attempts) (16); in-stent CTO; the detailed characteristics of target grade 0 septal CCs [including diameter, tortuosity, donor vessel angle, recipient vessel angle, and length to CTO (LTC)]; and characteristics related to the RCA and posterior descending artery (PDA) [including diameter, length, length of the PDA origin to the apex (LOPA), and RCA-PDA length:LOPA ratio].

Coronary dominance was classified as right dominant, left dominant, or codominant, depending on the PDA supply (17). According to the work by McEntegart et al., tortuosity was defined as the presence of at least one high-frequency curve that remained uncoiled during diastole indicative of reduced channel distensibility (18). A high-frequency curve was defined as one with a >180° within a segment length <3 times the collateral diameter. In-stent CTO was defined as occlusion at the stent site or within 5 mm proximal or distal to the stent (19). LTC was defined as the distance between the end of the septal CCs and the CTO distal cap. PDA length was defined as the distance between the origin of the PDA to its endpoint and was measured during angiography via the right anterior oblique 20°-caudal 20° view. LOPA was defined as the distance from the origin of the PDA to the apex (Figure 2) and identified as the convergence point of the inferior and left heart borders. The maximum diameters of the proximal vessels were measured in reference to both the septal CCs and RCA-PDA.

Figure 2 Invasive coronary angiographic assessment of the PDA length and the LOPA. (A) A patient with LAD artery in-stent occlusion exhibiting numerous CCs from the PDA to the LAD. (B) A patient with RCA occlusion and a collateral supply facilitated through the LAD. The PDA length is measured as the distance between the origin of the PDA (white arrow) and its endpoint (black arrow), while the LOPA is measured from the PDA origin (white arrow) to the apex (yellow arrow). Note that the yellow dots outline the inferior and left heart borders. CCs, collateral channels; LAD, left anterior descending; LOPA, length from the origin of the PDA to the apex; PDA, posterior descending artery; RCA, right coronary artery.

Retrograde strategy

The retrograde approach was used when antegrade crossing attempts failed or in situations in which the anatomy of the CTO was unsuitable for antegrade techniques (e.g., proximal cap ambiguity, bifurcation at the distal cap, diffuse disease, or poorly visible distal vessels) (5). In navigating invisible septal CCs, the septal surfing technique was employed, in which the exploration of the septal CCs is conducted through “trial and error” without the assistance of contrast guidance, with the path of minimal resistance being sought (20). Septal surfing through invisible septal CCs is illustrated in Figure 3. A microcatheter (Corsair, Asahi Intecc, Seto, Japan) was advanced along a guidewire (Sion, Asahi Intecc) into the proximal part of the septal branches (LAD for RCA CTO or RCA-PDA for LAD CTO). Once the retrograde CCs were successfully tracked with the guidewire, techniques such as retrograde wire crossing, kissing wiring, or reverse controlled antegrade-retrograde subintimal tracking were employed to cross the occlusion segment. The Guidezilla catheter was selectively employed based on preprocedural angiographic features and intraprocedural assessments. It was used in cases requiring enhanced backup support, coaxial alignment, or deep intubation due to anatomical challenges such as vessel tortuosity, heavy calcification, long or distal lesions, or difficulty with retrograde wire tracking. The specifics of the procedural methodologies were extensively detailed in our previous work (21), and the procedural steps were as follows: (I) the antegrade wire was advanced from the proximal true lumen into the subintimal space of the CTO, while the retrograde wire, supported by a microcatheter, was navigated through the suitable collaterals to the distal CTO and into the subintimal space; (II) a small balloon was delivered over the antegrade wire and inflated at low pressure to create a dissection that connected the antegrade and retrograde channels; (III) the Guidezilla guide extension was advanced through the antegrade catheter into the subintimal space, providing support, preventing collapse of the dissection plane, and guiding retrograde wire entry; (IV) the retrograde wire and microcatheter were advanced through the created channel from the distal subintimal space into the proximal true lumen and finally into the antegrade catheter; (V) the retrograde wire was exchanged for an antegrade wire, completing the key step of CTO recanalization, and was followed by routine PCI. Intravascular ultrasound was employed to evaluate wire positioning when the connection between retrograde and antegrade wires presented difficulties (22,23).

Figure 3 Visualization of septal surfing through invisible septal CCs. (A) An occluded LAD artery developed collateralized via septal CCs originating from the RCA. Arrows indicate the grade 0 septal CC. (B) A guidewire successfully traversed the grade 0 septal CC (arrows), allowing access to the LAD. (C) Following the recanalization of the LAD, the microcatheter remained positioned in the grade 0 septal CC (arrows). (D) An occluded RCA was collateralized through septal CCs originating from the LAD, with arrows marking grade 0 septal CCs. (E) Microcatheter angiography confirmed the utilization of the grade 0 septal CC. Arrows indicate the grade 0 septal CC. (F) A guidewire traversed the grade 0 septal CC, reaching the RCA (arrows). CCs, collateral channels; LAD, left anterior descending; RCA, right coronary artery.

Statistical analysis

Categorical variables are expressed as percentages and were compared with the Chi-squared test or Fisher’s exact test. Continuous variables are expressed as the mean ± standard deviation or as the median with interquartile range (IQR) and were compared via the Student t-test or Wilcoxon rank-sum test, as appropriate. Logistic regression was performed to identify the clinical, ICA, and procedural factors associated with technical success. Variables yielding a P value <0.10 in the univariate analysis were incorporated into a multivariate model. Host factors, including age and gender, were included as covariates in all analyses. Model discrimination was assessed with receiver operator characteristic (ROC) curves. The areas under the ROC curves (AUCs) were calculated and compared for models predicting technical success based on procedural characteristics alone, ICA characteristics alone, and a combination of procedural and ICA characteristics. To evaluate the incremental value of ICA characteristics when added to retrograde CTO PCI procedural characteristics in predicting technical success, we compared two models: one that included both ICA characteristics and retrograde CTO PCI procedural characteristics and another consisting solely of procedural characteristics. Statistical analyses were performed with SPSS version 19.0 (IBM Corp., Armonk, NY, USA) and MedCalc version 12.1.4.0 (MedCalc Software, Ostend, Belgium). A two-tailed P value of <0.05 was considered statistically significant.

Results

Patient characteristics, procedural outcomes, and ICA characteristics

This study analyzed a total of 166 retrograde CTO PCI attempts via invisible septal CCs performed with or without the Guidezilla catheter. Among these procedures, the Guidezilla catheter was employed in 85 (51.20%) cases. The primary indications included heavy calcification or long/distal lesions requiring deep intubation (n=39, 45.88%), vessel tortuosity requiring coaxial alignment (n=35, 41.17%), and inadequate backup support for delivery of balloons and stents (n=11, 12.94%). Based on Guidezilla utilization, participants were divided into two subgroups: the Guidezilla group (n=85) and the non-Guidezilla group (n=81, 48.80%).

Table 1 summarizes the clinical characteristics of the study population. The mean age of patients was 61.61±10.23 years, with a predominance of males (87.95%). A history of prior myocardial infarction was present in 30.12% of patients, while 2.41% had undergone coronary artery bypass grafting (CABG). Notably, more than half of the cases (57.83%) consisted of reattempts following prior PCI failures. The mean age of the Guidezilla group (63.66±9.30 years) was significantly greater than that of the non-Guidezilla group (59.46±10.77 years; P=0.008). Furthermore, prior CABG was more common in the Guidezilla group than in the non-Guidezilla group (4.71% vs. 0%; P=0.048); additionally, individuals in the Guidezilla group displayed elevated mean levels of creatinine (108.86±81.71 vs. 81.71±29.93 µmol/L; P=0.016) and uric acid (435.42±169.46 vs. 369.91±145.23 µmol/L; P=0.01).

The procedural outcomes are summarized in Table 2. The final technical success rate across all case attempts was 81.33% (135/166). The success rate for the Guidezilla group (88.24%) was significantly higher than that of the non-Guidezilla group (74.07%) (P=0.019). Moreover, the Guidezilla group received a greater median contrast media dose (median 210 mL, IQR 180–260 mL) compared to the non-Guidezilla group (median 200 mL, IQR 150–220 mL) (P=0.025). There were no significant differences noted in crossing time for septal CCs (Guidezilla: median 13 min, IQR 7–29 min; non-Guidezilla: median 10 min, IQR 5.50–29.50 min; P=0.594) or in overall procedure time (Guidezilla: median 168 min, IQR 128.50–223.75 min; non-Guidezilla: median 160 min, IQR 134.50–210 min; P=0.943). The overall rate of major procedural complications was 12.05%, including 9 cases of minor coronary perforation or dissection, 7 cases of cardiac tamponade, 4 cases of no flow or slow flow, and 2 cases of puncture site bleeding. Complication rates did not significantly differ between the subgroups (Guidezilla vs. non-Guidezilla, 10.59% vs. 13.58%; P=0.554).

The ICA characteristics of the lesions in the study population are shown in Table 3. The RCA was more often the target vessel in the Guidezilla group as compared to the non-Guidezilla group (77.65% vs. 58.02%; P=0.007); additionally, lesions with lengths >20 mm were more prevalent in the Guidezilla group (89.41% vs. 77.78%; P=0.042). However, there was no significant difference in the J-CTO score between the Guidezilla group (median 4, IQR 3–4) and non-Guidezilla group (median 3, IQR 3–4) (P=0.34). No other ICA characteristics exhibited significant differences between the groups (all P values >0.05).

Univariate and multivariate analyses

All relevant clinical, procedural, and ICA variables were incorporated into the univariate logistic regression analysis for technical success. The optimal cutoff value for the RCA-PDA length:LOPA ratio was determined to be 0.64 (AUC =0.68; P=0.002). Patients were stratified into two categories based on the high (>0.64) and low (≤0.64) values of this ratio.

Variables significantly associated with technical success at a P value threshold of <0.10 included the lack of moderate/severe tortuosity in the target septal CCs, long RCA-PDA length, an RCA-PDA length:LOPA ratio >0.64, and the use of the Guidezilla catheter (see Table 4). These four variables, along with host factors (age and gender), were subsequently included in the multivariate logistic regression model. Independent predictors of technical success identified were the use of the Guidezilla catheter [hazard ratio (HR) =2.42, 95% confidence interval (CI): 1.01–5.79; P=0.048] and an RCA-PDA length:LOPA ratio >0.64 (HR =6.19, 95% CI: 2.55–14.99; P<0.001). Notably, neither the lack of moderate/severe tortuosity in the target septal CCs nor long RCA-PDA length maintained statistical significance as predictors.

Discrimination of technical success

The discriminative capabilities of the independent predictors for technical success were assessed via ROC analysis (Figure 4). The AUC for Guidezilla use was 0.62 (95% CI: 0.54–0.69), and that of the RCA-PDA length:LOPA ratio was 0.68 (95% CI: 0.60–0.75), and this did not represent a significant difference (P=0.394). The combined model incorporating RCA-PDA length:LOPA ratio and Guidezilla use achieved an AUC of 0.74 (95% CI: 0.67–0.81), superior to that of the RCA-PDA length:LOPA ratio alone (P=0.083). Furthermore, the combined model (RCA-PDA length:LOPA ratio + Guidezilla) demonstrated significant superiority over Guidezilla use only, with a P value of 0.017. In the Guidezilla group, the optimal cutoff value for the RCA-PDA length:LOPA ratio was determined to be 0.65, yielding an AUC of 0.69 (95% CI: 0.58–0.78). This predictive performance was not significantly different from that observed in the overall cohort (P=0.914).

Figure 4 ROC curves for predicting technical success rates. The combined model, including Guidezilla use and the ratio of the PDA length to LOPA, exhibited a markedly enhanced predictive value compared to the Guidezilla-only model (P=0.017). AUC, area under the receiver operator characteristic curve; LOPA, length from the origin of the PDA to the apex; PDA, posterior descending artery; ROC, receiver operating characteristic.

Discussion

To the best of our knowledge, this study represents the largest investigation on the use of the Guidezilla catheter and its capacity to predict technical success in retrograde CTO PCI via invisible septal CCs conducted to date. Our principal findings are as follows: (I) the Guidezilla catheter use and the RCA-PDA length:LOPA ratio serve as independent predictors of procedural success in retrograde CTO PCI via invisible septal CCs, and (II) a combined assessment of RCA-PDA length:LOPA ratio with the application of the Guidezilla catheter may enhance accuracy in predicting the technical success in this context.

Retrograde CTO PCI via invisible septal CCs

Retrograde CTO PCI should be considered for occlusions that feature “interventional” collaterals (24). Several types of CCs are present in patients with CTO lesions, ranging from septal to epicardial and ipsilateral collaterals at various locations in the coronary tree. Septal channels are typically preferred for the retrograde approach due to their superior safety profile, characterized by a lower risk of perforation compared to epicardial channels and enhanced navigability (7-9). Epicardial collaterals should be reserved for consideration by highly experienced operators and regarded as a second-line option. Fortunately, septal CCs are commonly found in both RCA and LAD CTOs and are often described as possessing “interventional capability” (18). Conversely, the utilization of ipsilateral collaterals in retrograde CTO PCI remains rare, being primarily documented in case reports (25).

Invisible (Werner class 0) septal CCs can often be crossed (11) despite larger, nontortuous CCs being easier to navigate (26). Coronary collaterals comprise capillary collaterals in addition to larger, muscular-walled collaterals that develop from pre-existing arterioles through the process of arteriogenesis. Smaller collateral vessels may be stretched or expanded with the passage of microcatheters (27). Grade 0 CCs, although invisible, frequently demonstrate a straighter course, facilitating crossing with success rates comparable to or exceeding those of larger CCs, often in reduced time frames (11).

Although the data on retrograde CTO PCI through invisible septal CCs are limited, our study revealed an impressive final technical success rate of 81.33% for retrograde CTO PCI via these CCs, which improved to 88.24% with the deployment of the Guidezilla catheter. Dautov et al. (11) reported a technical success rate of 81% for both invisible and visible septal CCs, which is consistent with our final success rate observed through invisible septal CCs. Additionally, our findings align closely with the 83% success rate for septal CCs reported by Myat et al. and significantly surpass the 77% success rate associated with epicardial collaterals (6). The results of our study underscore the viability of retrograde PCI for CTOs conducted via invisible septal CCs in clinical practice. Furthermore, the findings emphasize the enhanced success rates attainable through the use of the Guidezilla catheter, which offers a greater variety of optional collateral circulations and subsequently increases the likelihood of procedural success.

Predictive value of the Guidezilla catheter

In this cohort, the use of the Guidezilla catheter was identified as an independent predictor of technical success for retrograde CTO PCI via invisible septal CCs. Despite the relative scarcity of studies exploring the application of the Guidezilla catheter in the management of complex CTOs, our previous research has demonstrated that this device facilitates access to the antegrade catheter during reverse-controlled anterograde and retrograde subintimal tracking, thus providing a convenient and safe approach with a high success rate (21). This rapid-exchange, mother-in-child configuration of the Guidezilla catheter enhances backup support for the guiding catheter, enabling deep coronary intubation and coaxial alignment. Furthermore, it facilitates the delivery of balloons and stents to the target lesion, thereby contributing to an improved success rate of CTO PCI (28). A higher RCA-PDA length:LOPA ratio implies increased distance for retrograde wire traversal, which may compromise guide catheter stability. In such anatomically challenging situations, the Guidezilla catheter provides additional backup support and coaxial alignment, improving the likelihood of successful wire externalization. In this study, the Guidezilla catheter was primarily used in complex CTO cases for which enhanced guide support was necessary for device delivery and wire manipulation. These cases often required multiple angiographic projections for adequate visualization of lesion architecture, wire trajectory, and CCs. Consequently, the observed increase in contrast volume reflects the procedural demands of managing a complex anatomy rather than the use of the Guidezilla itself. Although the use of the Guidezilla was operator-dependent, its application followed predefined angiographic and procedural criteria. The observed association between Guidezilla use and procedural success likely reflects its facilitative role in overcoming anatomic and technical challenges during retrograde CTO PCI.

Predictive and incremental value of RCA-PDA length:LOPA ratio

The RCA-PDA length:LOPA ratio was found to be an additional independent predictor of procedural outcomes, warranting further discussion. Septal collaterals between the LAD and the RCA-PDA are frequently observed and are often interventional in nature. A higher RCA-PDA length:LOPA ratio likely reflects a greater involvement of interventional septal CCs, consequently enhancing the technical success rate for retrograde CTO PCI via grade 0 septal CCs. However, this interpretation remains speculative, as our study did not include a direct morphological assessment of the septal collateral network. Future imaging studies are warranted to validate this speculation and to clarify the relationship between RCA-PDA geometry and septal collateral development.

Multivariate analysis confirmed the use of the Guidezilla catheter and an RCA-PDA length:LOPA ratio >0.64 to be significant predictors. Although these findings alone did not establish the RCA-PDA length:LOPA ratio as a prognostic marker, we further examined its incremental value for predictive accuracy. Comparing a model incorporating RCA-PDA length:LOPA ratio with a model that did not reveal a significant increase in the AUC from 0.62 to 0.74, respectively (P=0.017). These findings underscore the incremental predictive value of this ratio. Information regarding the incremental value of ICA characteristics in predicting the technical success of retrograde CTO PCI via invisible septal CCs is limited. Our results suggest that the evaluation of the RCA-PDA length:LOPA ratio may enhance the predictions of technical success.

The J-CTO score, the inaugural scoring system devised to evaluate CTO lesion complexity and predict procedural outcomes, was not found to be a factor significantly associated with the outcomes in our study. This scoring system was derived and validated through the use of a dataset primarily consisting of antegrade procedures (29), indicating that its predictive performance in the context of retrograde CTO PCI may be limited or inapplicable (30).

Moreover, factors such as the size (6,31) and tortuosity (31,32) of the CCs, as well as lesion calcification (32), which have been identified in other studies as independent predictors of successful retrograde procedures, did not demonstrate a significant association with outcomes in our investigation. This discrepancy may be attributed to the reduced relevance of these factors when invisible septal CCs are being used, when wire manipulation is performed with the surfing technique.

Study limitations

Several limitations to this study should be acknowledged. Although our studies represent the largest series of retrograde CTO PCI attempts via invisible septal CCs with the Guidezilla catheter, the sample size remains relatively limited. This observational and retrospective study predominantly included cases that were referred after previous failures, which might have introduced selection bias in terms of both patients and interventional strategies. Nevertheless, we aimed to enhance the generalization of our findings by including all consecutive patients. Future prospective studies with larger sample sizes are necessary to validate these results. Additionally, all procedures were performed by a high-volume CTO PCI operator, which may restrict the applicability of our findings to less experienced operators and lower-volume centers. Moreover, while we did not use an angiographic core laboratory, it is worth noting that many observational CTO PCI studies also do not report core laboratory assessments. Finally, as we focused exclusively on grade 0 septal CCs, we were unable to compare the efficacy and safety of grade 0 septal CCs with those of non-grade 0 septal CCs.

Conclusions

Our study confirms the clinical feasibility of conducting retrograde CTO PCI via invisible septal CCs via the Guidezilla catheter. The RCA-PDA length:LOPA ratio and the use of the Guidezilla catheter serve as independent predictors of procedural success for retrograde CTO PCI via invisible septal CCs. Moreover, the RCA-PDA length:LOPA ratio adds incremental value to Guidezilla catheter use in terms of predictive capacity. These findings support expanding the options for collateral circulation and may enhance the technical success rates of retrograde CTO PCI.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-135/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-135/dss

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-135/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was approved by the Institutional Review Board of Guangdong Provincial People’s Hospital (No. KY2023-716-01), and the requirement for informed consent was waived due to the retrospective nature of the analysis. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Azzalini L, Karmpaliotis D, Santiago R, Mashayekhi K, Di Mario C, Rinfret S, Nicholson WJ, Carlino M, Yamane M, Tsuchikane E, Brilakis ES. Contemporary Issues in Chronic Total Occlusion Percutaneous Coronary Intervention. JACC Cardiovasc Interv 2022;15:1-21. [Crossref] [PubMed]
2. Kucukseymen S, Iannaccone M, Grantham JA, Sapontis J, Juricic S, Ciardetti N, Mattesini A, Stojkovic S, Strauss BH, Wijeysundera HC, Werner GS, D'Ascenzo F, Di Mario C. Association of Successful Percutaneous Revascularization of Chronic Total Occlusions With Quality of Life: A Systematic Review and Meta-Analysis. JAMA Netw Open 2023;6:e2324522. [Crossref] [PubMed]
3. Kim TO, Kim S, Kim MJ, Kang DY, Lee PH, Kang SJ, Lee CW, Kim YH, Lee JY, Lee SW. Long-term impacts of complete revascularization on clinical outcomes in patients with coronary chronic total occlusion. Heliyon 2024;10:e40326. [Crossref] [PubMed]
4. Soriano K, Jiang GY, Balkan L, Tamez H, Yeh RW. Who Should Undergo Chronic Total Occlusions Percutaneous Coronary Intervention and When?: An Evidence-Based Approach to the Patient Referred for Percutaneous Coronary Intervention of Chronic Total Occlusion. Am J Cardiol 2024;227:18-28. [Crossref] [PubMed]
5. Megaly M, Xenogiannis I, Abi Rafeh N, Karmpaliotis D, Rinfret S, Yamane M, Burke MN, Brilakis ES. Retrograde Approach to Chronic Total Occlusion Percutaneous Coronary Intervention. Circ Cardiovasc Interv 2020;13:e008900. [Crossref] [PubMed]
6. Myat A, Galassi AR, Werner GS, Mashayekhi K, Avran A, Boudou N, Meyer-Gessner M, Reifart N, Lesiak M, Garbo R, Bufe A, Spratt J, Bryniarski L, Christiansen EH, Sianos G, Escaned J, di Mario C, Hildick-Smith D. Retrograde Chronic Total Occlusion Percutaneous Coronary Interventions: Predictors of Procedural Success From the ERCTO Registry. JACC Cardiovasc Interv 2022;15:834-42. [Crossref] [PubMed]
7. Allana SS, Kostantinis S, Rempakos A, Simsek B, Karacsonyi J, Alexandrou M, et al. The Retrograde Approach to Chronic Total Occlusion Percutaneous Coronary Interventions: Technical Analysis and Procedural Outcomes. JACC Cardiovasc Interv 2023;16:2748-62. [Crossref] [PubMed]
8. Chang HY, Huang CC, Hung CS, Meng SW, Lin MS, Chen YH, Yeh CF, Kao HL. Accurate Prediction of Retrograde Collateral Channel Crossing in Coronary Artery Chronic Total Occlusion Intervention. Am J Cardiol 2024;210:93-9. [Crossref] [PubMed]
9. Tajti P, Xenogiannis I, Gargoulas F, Karmpaliotis D, Alaswad K, Jaffer FA, Patel MP, Burke MN, Garcia S, Krestyaninov O, Koutouzis M, Jaber W, Brilakis ES. Technical and procedural outcomes of the retrograde approach to chronic total occlusion interventions. EuroIntervention 2020;16:e891-9. [Crossref] [PubMed]
10. Werner GS, Ferrari M, Heinke S, Kuethe F, Surber R, Richartz BM, Figulla HR. Angiographic assessment of collateral connections in comparison with invasively determined collateral function in chronic coronary occlusions. Circulation 2003;107:1972-7. [Crossref] [PubMed]
11. Dautov R, Urena M, Nguyen CM, Gibrat C, Rinfret S. Safety and effectiveness of the surfing technique to cross septal collateral channels during retrograde chronic total occlusion percutaneous coronary intervention. EuroIntervention 2017;12:e1859-67. [Crossref] [PubMed]
12. Wang CF, Chen BJ, Luan B, Wang Y, Zhang XJ, Qu HB. Incidence, Predictors, and Strategies for Retrograde Wire Tracking Failure via Poor Septal Collateral Channels in Chronic Total Occlusion. Clin Interv Aging 2023;18:1503-12. [Crossref] [PubMed]
13. Zhong X, Ge L, Ma J, Huang D, Yao K, Zhang F, Lu H, Yan Y, Huang Z, Qian J, Ge J. Microcatheter collateral channel tracking failure in retrograde percutaneous coronary intervention for chronic total occlusion: incidence, predictors, and management. EuroIntervention 2019;15:e253-60. [Crossref] [PubMed]
14. Vadalà G, Galassi AR, Werner GS, Sianos G, Boudou N, Garbo R, et al. Contemporary outcomes of chronic total occlusion percutaneous coronary intervention in Europe: the ERCTO registry. EuroIntervention 2024;20:e185-97. [Crossref] [PubMed]
15. Ybarra LF, Rinfret S, Brilakis ES, Karmpaliotis D, Azzalini L, Grantham JA, et al. Definitions and Clinical Trial Design Principles for Coronary Artery Chronic Total Occlusion Therapies: CTO-ARC Consensus Recommendations. Circulation 2021;143:479-500. [Crossref] [PubMed]
16. Morino Y, Abe M, Morimoto T, Kimura T, Hayashi Y, Muramatsu T, Ochiai M, Noguchi Y, Kato K, Shibata Y, Hiasa Y, Doi O, Yamashita T, Hinohara T, Tanaka H, Mitsudo K. Predicting successful guidewire crossing through chronic total occlusion of native coronary lesions within 30 minutes: the J-CTO (Multicenter CTO Registry in Japan) score as a difficulty grading and time assessment tool. JACC Cardiovasc Interv 2011;4:213-21. [Crossref] [PubMed]
17. Wu B, Kheiwa A, Swamy P, Mamas MA, Tedford RJ, Alasnag M, Parwani P, Abramov D. Clinical Significance of Coronary Arterial Dominance: A Review of the Literature. J Am Heart Assoc 2024;13:e032851. [Crossref] [PubMed]
18. McEntegart MB, Badar AA, Ahmad FA, Shaukat A, MacPherson M, Irving J, Strange J, Bagnall AJ, Hanratty CG, Walsh SJ, Werner GS, Spratt JC. The collateral circulation of coronary chronic total occlusions. EuroIntervention 2016;11:e1596-603. [Crossref] [PubMed]
19. Vemmou E, Quadros AS, Dens JA, Rafeh NA, Agostoni P, Alaswad K, et al. In-Stent CTO Percutaneous Coronary Intervention: Individual Patient Data Pooled Analysis of 4 Multicenter Registries. JACC Cardiovasc Interv 2021;14:1308-19. [Crossref] [PubMed]
20. Sianos G, Karlas A. Tools & Techniques: CTO--the retrograde approach. EuroIntervention 2011;7:285-7. [Crossref] [PubMed]
21. Huang Z, Zhang B, Chai W, Ma D, Liao H, Zhong Z, Wang F, Lin J. Usefulness and Safety of a Novel Modification of the Retrograde Approach for the Long Tortuous Chronic Total Occlusion of Coronary Arteries. Int Heart J 2017;58:351-6. [Crossref] [PubMed]
22. Galassi AR, Sumitsuji S, Boukhris M, Brilakis ES, Di Mario C, Garbo R, Spratt JC, Christiansen EH, Gagnor A, Avran A, Sianos G, Werner GS. Utility of Intravascular Ultrasound in Percutaneous Revascularization of Chronic Total Occlusions: An Overview. JACC Cardiovasc Interv 2016;9:1979-91. [Crossref] [PubMed]
23. Fan Y, Maehara A, Yamamoto MH, Hakemi EU, Fall KN, Matsumura M, Ali ZA, Kirtane AJ, Moses JW, Huang H, Mintz GS, Ochiai M, Karmpaliotis D. Outcomes of retrograde approach for chronic total occlusions by guidewire location. EuroIntervention 2021;17:e647-55. [Crossref] [PubMed]
24. Galassi AR, Werner GS, Boukhris M, Azzalini L, Mashayekhi K, Carlino M, Avran A, Konstantinidis NV, Grancini L, Bryniarski L, Garbo R, Bozinovic N, Gershlick AH, Rathore S, Di Mario C, Louvard Y, Reifart N, Sianos G. Percutaneous recanalisation of chronic total occlusions: 2019 consensus document from the EuroCTO Club. EuroIntervention 2019;15:198-208. [Crossref] [PubMed]
25. Azzalini L, Agostoni P, Benincasa S, Knaapen P, Schumacher SP, Dens J, Maeremans J, Kraaijeveld AO, Timmers L, Behnes M, Akin I, Toma A, Neumann FJ, Colombo A, Carlino M, Mashayekhi K. Retrograde Chronic Total Occlusion Percutaneous Coronary Intervention Through Ipsilateral Collateral Channels: A Multicenter Registry. JACC Cardiovasc Interv 2017;10:1489-97. [Crossref] [PubMed]
26. Dash D. Retrograde Coronary Chronic Total Occlusion Intervention: A 2024 Appraisal. J Indian College Cardiology 2024;14:1-10.
27. Choo GH. Collateral Circulation in Chronic Total Occlusions – an interventional perspective. Curr Cardiol Rev 2015;11:277-84. [Crossref] [PubMed]
28. Lei X, Liang Q, Fang Y, Xiao Y, Wang D, Dong M, Li J, Yu T. Guidezilla™ guide extension catheter I for transradial coronary intervention. Front Cardiovasc Med 2022;9:931373. [Crossref] [PubMed]
29. Kalogeropoulos AS, Alsanjari O, Keeble TR, Tang KH, Konstantinou K, Katsikis A, Jagathesan R, Aggarwal RK, Clesham GJ, Kelly PA, Werner GS, Hildick-Smith D, Davies JR, Karamasis G. CASTLE score versus J-CTO score for the prediction of technical success in chronic total occlusion percutaneous revascularisation. EuroIntervention 2020;15:e1615-23. [Crossref] [PubMed]
30. Konstantinidis NV, Werner GS, Deftereos S, Di Mario C, Galassi AR, Buettner JH, et al. Temporal Trends in Chronic Total Occlusion Interventions in Europe. Circ Cardiovasc Interv 2018;11:e006229. [Crossref] [PubMed]
31. Huang CC, Lee CK, Meng SW, Hung CS, Chen YH, Lin MS, Yeh CF, Kao HL. Collateral Channel Size and Tortuosity Predict Retrograde Percutaneous Coronary Intervention Success for Chronic Total Occlusion. Circ Cardiovasc Interv 2018;11:e005124. [Crossref] [PubMed]
32. Tanaka H, Tsuchikane E, Kishi K, Okada H, Oikawa Y, Ito Y, Muramatsu T, Yoshikawa R, Kawasaki T, Okamura A, Sumitsuji S, Muto M, Katoh O. Retrograde Coronary Chronic Total Occlusion Intervention (JR-CTO) Score: From the Japanese CTO-PCI Expert Registry. JACC Cardiovasc Interv 2024;17:1374-84. [Crossref] [PubMed]