Percutaneous coronary interventions (PCI) of chronic total occlusions (CTO) are among the most technically demanding procedures. While CTOs are present in up to 20–30% of patients undergoing coronary angiography, CTO PCI is only attempted in < 10% . The most commonly cited reasons for the low attempt rate are the lower success rates with CTO PCI and higher procedural complication rates. Historical success rates in CTO recanalization ranged between 50 and 60% , but with the advent of the retrograde and hybrid approaches, success rates have increased to as high as 80–90% . Studies have also demonstrated acceptably low complication rates of CTO PCI in the hands of experienced operators .

As a CTO operator progresses, there are advancing drifts in skill sets beginning with basic procedural preparation, including the use of routine dual injections and microcatheters, that translate to higher success rates. Successful recanalization continues to improve with refined antegrade wiring techniques and proper wire choices. These gradual drifts in success rates become shifts as the operator masters utilization of the subintimal space and controlled dissection re-entry with the Stingray system (Boston Scientific). As one continues to become a complete CTO operator, the most powerful addition to one’s quest to achieve a 90% procedural success rate is employment of the retrograde strategy. While necessary for a higher success rate, retrograde CTO PCI has been shown to be associated with higher complication rates than antegrade CTO PCI . A potential reason for the difference has been attributed to the manipulation of collaterals needed to accomplish retrograde CTO PCI.

The only 3 options for retrograde CTO PCI are the use of the septal collaterals, bypass grafts, or epicardial collaterals (EC). While all retrograde approaches can be fraught with potential dangers and pitfalls, septal collaterals have traditionally been viewed as the safest channels to traverse during these procedures. Like the groomed slopes of a ski resort, the cascades of connections between the left anterior descending (LAD) artery and posterior descending artery (PDA) offer a certain degree of assurance of safe traveling with minimal opportunities for disastrous accidents. These avenues have been traveled so frequently during similar procedures, and the familiarity with the forgivingness of these connections confers a degree of comfort and confidence in their safety. When navigating retrograde, these potential avenues should be exhausted first before venturing off piste into the more unpredictable terrain of EC. The heterogeneity of epicardial connections is riddled with unknown hidden hazards of often extreme tortuosity, friability, and hidden side branches that may lead one to undesired location and consequence. While taking this way down the mountain may be successful and necessary in situations where other options do not exist, eventually, if selected frequently enough, collisions with buried rocks, unavoidable trees, or unstable snow will lead even the most expert professionals into perils that are often only recognized after the voyager’s fate has already been determined. Perforation of these vessels is not infrequent, which can result in cardiac tamponade, hemodynamic compromise, and death if not immediately treated. Preparedness to deal with these catastrophic consequences mandates that the operator be facile with and have a full arsenal of equipment, including 0.14 compatible coils, to actively treat and extinguish perforations.

Until recently, the perceived difficulties and dangers in successfully using EC as opposed to the apparent forgivingness of septal collaterals, while accurate, has largely been anecdotal. Previously, there were no studies to objectively perform a head-to-head comparison of retrograde CTO PCI comparing the use of epicardial collaterals (EC) to non-epicardial collaterals (NEC).

In the current issue of Cardiovascular Revascularization Medicine , Benincasa et al. compare the procedural and long-term clinical outcomes of retrograde CTO PCI via EC to NEC . This is the first such study to do so. The main findings of the study are as follows: 1) CTO PCI via EC is associated with lower technical and procedural success rates; 2) numerically higher (although not statistically significant) perforations occur with CTO PCI via EC than NEC; and 3) major adverse cardiac events (MACE) at 2 years are numerically higher (but once again, not statistically significant) with CTO PCI via EC as compared to NEC. The major findings of the study confirm the anecdotal experience of most CTO PCI operators; namely, that technical and procedural outcomes are worse when EC are used (technical success: 35% EC vs. 76% NEC; procedural success: 30% vs. 76%, p < 0.001). While the perforation rates (3% EC vs. 0% NEC) and MACE rates (12.9% EC vs. 5.4% NEC) were not statistically significant between the two types, it is likely due to the small size of the study (75 patients). Given the numerically higher rate of perforations and MACE with EC, a larger patient population would have most likely borne a statistically significant difference.

The authors should be commended for undertaking this worthwhile study. However, it should be noted that the study is single-center, single-operator with a small sample size. A larger, multi-center study is needed to confirm − as well as add to − the findings of this study. It should also be noted that epicardial collaterals are quite heterogeneous in terms of their anatomy and complexity. EC with significant redundancy and tortuosity are markedly more difficult to navigate, whereas larger, straighter-caliber EC vessels are easier to negotiate. Furthermore, it should be mentioned that AV groove collaterals are EC that have been shown to be more prone to vascular injury than traditional EC and, therefore, felt by many to be associated with worse outcomes. While this study performed a basic angiographic assessment of collateral tortuosity, an objective assessment of epicardial vessel features was not performed. Future efforts need to focus on defining anatomical characteristics of EC that can predict which potential channels can be crossed successfully without consequential perforation with wires and microcatheters. Traditional concerning qualities of these connections, such as the number and frequency of redundant omega turns, vessel size, regions of angiographic invisibility, and particular anatomic connections need to be systematically databased with a standardized core lab. When such a study is completed, we can hope to develop a scoring mechanism to allow an operator to choose appropriately when it may be safe to travel off the traditional slopes of septal connections and venture into the out-of-bounds terrain that EC currently are. Without a clearer understanding of which EC are safe to use, off-piste adventures will continue to occasionally result in complications that will challenge even the most expert operators’ abilities to maintain equanimity.