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Subintimal space: The final frontier?

As a program director, sometimes I have to remind myself that our current fellows in interventional cardiology have little insight into the challenges we faced in the 1980–1990s, before the availability of moveable guidewire systems, stents, rotational atherectomy, low profile angioplasty equipment, and a wide array of devices to assess lesions and guide decision-making. The original limitations of angioplasty, including dissection, abrupt closure, lesion rigidity, acute thrombosis, and late restenosis, have been nearly eliminated by contemporary technology and pharmacotherapy. However, the final frontier of percutaneous coronary intervention (PCI) remains the recanalization of chronic total occlusions (CTOs), and the most common mode of PCI failure of CTOs is the inability to cross the occlusion with any guidewire. It would certainly be a mistake to assume that failure to cross a CTO is a reflection of a lack of technology on the part of medical device companies or on a lack of determination by interventional cardiologists. Older approaches to antegrade recanalization included ball-tipped guidewires with and without powered rotation, laser guidewires with and without ‘‘smart’’ optical coherence technology, and ultrasound and vibrational approaches, many of which did not withstand the test of time and were discarded. Tremendous improvements in technology have led to the availability of numerous hydrophilic, polymer jacket, tapered tip, and high gram force guidewires, as well as lowprofile over-the-wire microcatheters for supporting guidewire passage and confirming intraluminal position. Although some operators rely exclusively on single injection from a guiding catheter for antegrade crossing of CTOs, many operators routinely use dual injection to enhance their ability to visualize contralateral collaterals, with and without retrograde techniques for crossing CTOs. Whether using single or dual injection, or antegrade or retrograde crossing techniques, most operators try to maintain intraluminal position of their guidewires. In contrast to intraluminal approaches to crossing CTOs, re-entry approaches allow subintimal passage of the guidewire, followed by re-entry into the true lumen. Re-entry can be achieved with combinations of guidewires and microcatheters or with dedicated re-entry devices. Several re-entry devices are commercially available for patients with peripheral CTOs and are guided by intravascular ultrasound or radiographic markers on the devices. In this issue of Catheterization and Cardiovascular Intervention, Whitlow et al. [1] report their observations in 19 consecutive patients treated with a dedicated coronary re-entry device at four institutions in Chile and Japan. Clinical inclusion criteria were medically refractory angina and/or a large ischemic territory by stress test. All patients failed prior PCI or were turned town for PCI and were scheduled for elective coronary artery bypass grafting (CABG). No patients were excluded on the basis of perceived adverse angiographic characteristics. After confirming subintimal position of the guidewire, re-entry was successfully accomplished in 16 patients (84.2%) using a dedicated re-entry balloon (Stingray Orienting Balloon Catheter, BridgePoint Medical, Plymouth, MN) and a dedicated re-entry guidewire or high-gram-force guidewire. Outcomes included successful drug-eluting stenting (DES) in 16 patients with successful re-entry, successful DES after retrograde recanalization of the CTO after failed re-entry, and elective CABG in two patients after failure to cross their CTOs. Although small, this observational study complements an earlier study by some of the same authors using the same re-entry system [2] and expands the interventional toolbox for recanalizing CTOs. Although interventional cardiologists do not yet have a large experience with coronary re-entry techni-