Retrograde approach is strongly expected to improve the success rate in PCI for CTO lesions. Several reasons can be proposed for increased success rate of retrograde approach. Firstly, previous failed attempts of antegrade approach induce intimal dissection, and as a result the anatomy becomes more difficult on future occasions for further antegrade attempts. Secondly, the distal cap of the CTO lesions is hypothesized to be softer than the proximal cap. Thirdly, the entry point into the CTO lesions, which is inferred from the angiographic appearance, is sometimes wrong.

Septal branch route is considered the most useful among different possible routes irrespective of the target lesion location. Coronary collateral circulation might be present even if no visible collaterals can be detected angiographically. In fact, a hydrophilic guidewire can be passed through such an angiographically invisible septal connection. Thus, as long as the septal artery is chosen for the retrograde route, the attempts to pass a hydrophilic guidewire through invisible routes might be justified. When the visible septal connection cannot be detected, the endhole injection of dye through a microcatheter in the septal branch may show a connection.

Six strategies in a retrograde approach have been proposed according to the CTO lesion characteristics and clinical situation including Just landmark Kissing guidewire CART technique Retrograde proximal true lumen puncture Catching the retrograde guidewire Retrograde true lumen tracking. Thus, a retrograde approach requires a combination of techniques, which have to be chosen on an individual basis according to the patient condition. Retrograde approach is an emerging technique for CTO lesions.

It might potentially be accompanied with several unexpected complications which do not happen during PCI for CTO lesions by using conventional techniques. First, this approach needs the insertion of a guiding catheter into the collateral-donor coronary artery. Diminished flow or occlusion in this artery due to thrombus formation may result in life-threatening ischemic complications. Adequate anti-coagulation therapy during PCI is therefore essential. Second, dissection of the proximal part of the donor artery may be life-threatening, and if it is observed, it should be immediately treated by placing stents across it. Third, there is a risk that ischemia might be induced temporarily because the collateral route might be occluded by catheters during the procedure. Fortunately, ischemia due to this reason has not been observed during the procedures in any of the patients. Fourth, any damage to the collateral routes caused during the procedures may result in the exacerbation of ischemia. There is a case report in which a patient suffered from a complication of septum hematoma and myocardial infarction after successful guidewire passage through the septal artery. In order to reduce this occurrence, excessive forceful attempts to cross a hydrophilic guidewire or a catheter through septal branch should be avoided. This case is a clear warning message not to take the retrograde approach too easily, although septal dilatation with low pressure has been reported to be safe in a small number of patient series. Retrograde approach obviously requires high-class or special devices such as good microcatheters, hydrophilic and CTO guidewires, Tornus, good low-profile OTW balloons, or short guiding catheters. However, it must be emphasized that regular guiding catheters can be used if long-shaft balloons and/or long microcatheters are also employed. This approach should be done exclusively by highly-experienced operators, since it requires a combination of different techniques. Much more sophistication is necessary, before a retrograde approach is widely performed.