Interventions in chronic total coronary occlusion (CTO)

Interventions in chronic total coronary occlusion (CTO)

Interventions in chronic total coronary occlusion (CTO): A total occlusion (TIMI 0 flow) of a coronary artery which is beyond three months of duration is considered as a chronic total occlusion (CTO). Re opening of a CTO has several concerns. If it is a large artery and supplies a large territory, it is useful to open that occluded vessel. The reasons for which CTOs are opened up may be for the relief of angina, for freedom from future coronary artery bypass grafting, improved left ventricular function (in cases where the CTO territory has a preserved left ventricular wall thickness of 75%) and finally for improving the survival. Those with medically refractory angina and having significant viable myocardium are good candidates for attempting CTO interventions. The down side of CTO interventions are the lower success rates, higher radiation rates and a higher risk with about 1.6% mortality rates in some studies. CTO interventions are not attempted if there is a long and tortuous CTO segment, if there is severe calcification or there is no visualization of the distal vessel even by contralateral injection.

Bridging collaterals
Bridging collaterals

Bridging collaterals may make crossing the lesion difficult because the guide wire tends to pass through the collaterals rather than through the true lumen. Since there is no antegrade flow it is difficult to know whether the wire crossing the CTO is passing through the lumen or subintimally. Contralateral contrast injection simultaneous with ipsilateral injection will visualize the track and guide the process. After crossing, if the guide wire passes down easily, it is more likely to be in the true lumen. Close observation to rule out perforation is needed at this stage. This can be achieved by watching the hemodynamic status as well by looking for dye staining and collection of the dye in the pericardial space. Another supportive evidence for a true track is the ease by which the guide wire can be passed into multiple side branches beyond the CTO. This is unlikely if the wire is passing subintimally. Special techniques in CTO include subintimal angioplasty and retrograde approach. In subintimal angioplasty, the guide wire tracks subintimally and later re-enters the true lumen. In retrograde approach guide wire is threaded from the contralateral vessel through the collaterals into the distal end of the CTO. It may be possible to cross the lesion retrogradely in some cases in which antegrade crossing is not possible. Another approach is the use of multiple guide wires. In this technique, when the guide wire is seen repeatedly tracking a false passage, that wire is kept there, occluding that track and another wire is used to enter the true lumen (parallel wire technique). Side branches can also be kept occluded by a balloon inflation. Anchor balloons and anchor wires help crossing the CTOs. Anchor balloons are occluded in the side branch proximal to the CTO. Use of balloon support and stiffer guide wires are methods of crossing CTOs. Both these approaches do increase the risk of perforation. If at all perforation occurs, it can be tackled by deploying a  covered stent. If that is not feasible, balloon tamponade by keeping a balloon inflated will prevent further oozing and cardiac tamponade while preparations are being made for surgical bail out. Balloon tamponade is unlikely to cause any ischemia in a CTO territory. While giving contralateral injections for track visualization, prolonged simultaneous injection should be avoided to prevent global ischemia. Contralateral catheter may be removed once the guide wire access has been obtained. This is more important in case of contra lateral trans radial access as prolonged presence of catheter within the radial artery may increase the chance of vasospasm. Retrograde angioplasty may use CART (controlled antegrade and retrograde subintimal tracking) or reverse CART. Kissing wires are used in CART. Dilatation is with the antegrade balloon in reverse CART and vice versa. Micro catheters are also useful crossing CTOs. Tornus is useful for calcific lesions. 1.25 mm balloons are needed for CTO angioplasty. Problems during CTO interventions could be retrograde dissection, perforation, failure to cross and spasm of collaterals causing ischemia.