Target vessel injury can cause ischemic complications when side branches or dominant ipsilateral collaterals are compromised. For example, if the chronically occluded segment is distal to major side branches and dominant ipsilateral collaterals, injury to the proximal vessel such as dissection will compromise blood flow to these vessels resulting in ischemia. Common causes of proximal vessel injury include coronary and aortocoronary dissection [3]. Coronary dissection can result from aggressive guide catheter engagement, hydraulic dissection from aggressive contrast injection, guidewire manipulation, and advancement of mother-and-child catheters. Prevention of this type of injury is important in order to avoid potentially lethal ischemic complications. Upon engagement, the guide catheter may occlude the vessel and cause hydraulic dissection with aggressive injections. The use of side-hole catheters may prevent ischemia but may also give a false sense of security. It is best to adjust guide catheter engagement to prevent pressure damping and avoid aggressive injections especially with non-coaxial or occlusive engagement. The use of less aggressive guide catheters can also reduce the risk of catheter-induced dissection.

When wiring a proximal vessel, especially a tortuous proximal vessel, use a low-tip load workhorse guidewire to avoid proximal injury. Once the distal cap of the CTO is reached, an over-the-wire device such as a microcatheter and an over-the-wire (OTW) balloon can then be advanced over the workhorse wire. The workhorse wire is then removed and exchanged for a more aggressive, higher tip load CTO guidewire for proximal cap puncture. If insertion of a mother-and-child catheter is required, preparation may be needed with proximal vessel ballooning and advance it over a balloon to prevent mechanical injury.

Aortocoronary dissection, similar to coronary dissection, may cause ischemia by acutely occluding the proximal target vessel (Fig. 17.2). This type of complication may occur from guide catheter hydraulic dissection, aggressive guide engagement, or balloon rupture. More commonly, this type of dissection occurs from retrograde crossing attempts especially of the right coronary artery (RCA) [3]. Aortocoronary dissections may involve only the coronary sinus or extension into the ascending aorta and more distally. Prevention includes strategies described above for coronary dissection such as meticulous engagement of aggressive guide catheters or use of less aggressive guide catheters, and avoiding high balloon pressure inflation at the aortocoronary ostium. When performing dissection reentry techniques, limit subintimal space wiring and dissection to the occluded segments in order to prevent aortocoronary dissections and proximal vessel injury. This allows sparing of important side branches and dominant ipsilateral collaterals. If there are side branches at the proximal or distal cap, avoid using dissection re-entry techniques and if necessary, limit the dissection as mentioned and if possible, protect the side branch with a wire. Once proximal vessel injury or aortocoronary dissections occur with resultant significant ischemia, treatment includes urgent revascularization, mainly with stenting of the injured segment and ensuring full coverage of the ostium in the case of aortocoronary dissection. Urgent bail-out retrograde techniques may be required to revascularize the target vessel [4].

With retrograde approaches, donor vessel compromise is a serious and potentially lethal complication due to global ischemia [5], especially when the donor vessel is the last remaining vessel (commonly seen in patients with prior coronary artery bypass surgery). Main causes of donor artery injury include thrombosis, dissection, and ischemia from presence of retrograde devices, especially in a moderate to severe diffusely diseased vessel. Donor artery thrombosis may occur due to prolonged procedure time and with inadequate anticoagulation [5, 6]. Prevention includes keeping procedure time short and meticulous monitoring of activated clotting time (ACT). We recommend keeping ACT above 350 seconds for retrograde approach and to check ACTs every 30 min. Flush catheters routinely to prevent catheter thrombosis. If thrombosis occurs, standard treatments are utilized such as additional heparin bolus to achieve target ACT, additional glycoprotein IIbIIIa inhibitor may be required, thrombus aspiration, and prolonged balloon inflations. Stenting may be necessary if significant amounts of thrombus persist. Retrograde devices in the donor vessel poses a major problem for emergent stenting. Multiple options exist: (1) stenting on the externalized wire if anatomically feasible, (2) withdrawing the retrograde OTW device back into the donor vessel and using it to exchange the externalized wire for a workhorse wire which can be used for stent delivery, or (3) advancing a second wire for stenting which would jail the externalized wire (and therefore, should be done with great caution) [7].

Similar to donor vessel thrombosis, donor vessel dissection, although rare, can be catastrophic [2, 8]. It can be caused by guide catheters, retrograde equipment especially during removal (Fig. 17.3), and guidewire manipulation [6]. Prevention is the key treatment. When wiring the donor vessel to access the appropriate collaterals for retrograde approach, use a soft tip workhorse wire with appropriate bends to prevent injury. Once collaterals have been crossed and the wire has been externalized, the donor vessel along with collaterals should be protected with a microcatheter or an OTW balloon to prevent injury. If snaring is required to achieve externalization, the wire should be pushed from the retrograde limb rather than being pulled from the antegrade limb to prevent tension and sheer stress, which may cause transection of the vessels involved [5]. Pulling on any intracoronary equipment, especially retrograde devices and externalized wires causes unintentional advancement of guide catheters, especially retrograde guides which can cause dissection of donor vessel. Therefore, careful manipulation and being vigilant of guide catheter position at all times is mandatory. For example, during removal of an externalized wire, aggressive pulling will cause the retrograde guide catheter to dive deep into the donor vessel and cause dissection. Therefore, it is recommended that the retrograde guide is disengaged and the externalized wire is pulled with just enough force during diastole to slowly remove the wire. If donor vessel dissection occurs, prompt treatment with stenting is usually needed to prevent global ischemia and hemodynamic collapse [6]. Emergent stenting of the donor vessel can be problematic due to the presence of retrograde equipment but there are multiple options as discussed above.