Protection & Thrombectomy Devices in PPCI
In limited instances, distal embolization may occur with spontaneous reperfusion or in association with diagnostic angiography; protection devices, in these cases, would be of reduced value. However, the clinical need to limit such phenomena and the fact that distal embolization appears to occur predominantly at the time of intervention in association with a large thrombus burden, has led to the development of dedicated devices to prevent this problem.
These devices, although aimed at reducing the thrombus burden washed downstream, fall into three categories: protection (distal or proximal), thrombectomy devices and mesh-covered stent. Although distal protection devices have demonstrated efficacy in preventing reduced flow following saphenous vein graft interventions, studies, to date, have failed to demonstrate a benefit for these devices in the setting of PPCI. Although not proven, it seems likely to be due to the native coronary artery not being a conduit vessel with a tapered vessel caliber and multiple side branches emerging and escaping protection. This, associated with imperfect vessel-wall apposition by the assessed devices, appears to be the principal cause for their lack of benefit in native coronary occlusion treated by PPCI for STEMI. Potential additional explanations include embolization during passing of the device, embolization prior to device crossing and the possibility that the microvasculature is already dysfunctional prior to use of the device. It should, however, be noted that distal protection devices have not been evaluated by RCTs in PPCI in vein grafts. Proximal protection overcomes some of these limitations, including poor wall apposition, side-branch escape close to the occlusion and intervention site, as well as a small distal vessel. The limitations of these systems are that the vessel needs to be occluded and aspirated during the intervention, possibly causing an even greater ischemic area, as well as the possibility of bringing thrombus to more proximal sites and branches.
To date, evidence appears to be more promising for thrombectomy devices, as recognized by recent international guidelines. Thrombectomy devices vary in design and mechanism of action but can be broadly divided into two groups depending on the presence or absence of a motorized system.