Is Magnetic Resonance Image Guidance the Key to Opening Chronic Total Occlusions?

Abstract

T hrough progressive plaque growth or fibrotic organization of occlusive thrombus, atherosclerosis may result in chronic total occlusion (CTO) of a major arterial conduit. If CTO develops slowly, collateral pathways may supply sufficient perfusion to retain tissue viability despite occlusion of the major inflow conduit. However, such collateral-mediated perfusion rarely matches that provided by an open main conduit, particularly during the peak demand of regional muscular activity. Although strategies to limit regional oxygen demand (eg, ␤-blockers for the treatment of angina pectoris) or to enhance collateral function (eg, a walking program for superficial femoral occlusion, experimental angiogenesis) may be of some benefit, these approaches generally offer less complete return of normal physiology and relief of ischemic symptoms than does direct revascularization of the occluded vessel. With surgical bypass, the nature of the occlusion (its length, duration, tortuosity, calcification) is less important than the presence of a suitable distal anastomotic target. On the other hand, with catheter-based techniques, success depends heavily on these lesion characteristics. In fact, crossing such occluded segments with a guidewire remains the dominant barrier to catheter-based treatments of occluded arterial segments. Once the guidewire has been passed successfully into the distal true lumen, the process of dilating and stenting the segment is usually straightforward and durable, at least with the use of drug-eluting stents in coronary CTOs. 1,2 Article p 1101Devices designed to cross CTOs should have 3 key features: an ability to distinguish a true luminal path from one created within (dissection) or through (perforation) the vessel wall of the occluded segment, an ability to change direction (steer) to correct deviations from the desired path through the occlusion, and an ability to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, radiofrequency, ultrasound, blunt microdissection).Despite these seemingly simple requirements, devices that have emphasized only the third feature-penetrating powerhave generally failed to deliver significant enhancements in their ability to cross the occluded segment and reenter the distal true lumen, because they can easily enter a vessel wall dissection plane (the path of least resistance) within the occlusion and then remain next to (rather than within) the distal true lumen. 3 Fluoroscopic or intravascular ultrasoundguided devices can then be used to attempt puncture back into the distal true lumen to augment the success of such devices. Secondary success for crossing lesions that are uncrossable with conventional guidewire, however, is only 50% to 60%. On the other hand, if the energy source leads to frank perforation of the vessel wall, safe conclusion of the procedure may be difficult (except in the superficial femoral, where it may be possible to negotiate alo...

MRI endoscopy using intrinsically localized probes

“…Magnetic resonance imaging ͑MRI͒ employing tiny intravascular detectors 7,8 might offer performance advantages for plaque imaging compared to IVUS, 9 and moreover, would provide access to the entire range of high-contrast, multifunctional, high-speed, and three-dimensional ͑3D͒ visualization capabilities afforded by MRI in the same exam. Yet, as a recent editorial notes, 10 for MRI to be competitive with x-ray guided coronary procedures, better spatial resolution and efficiency or speed is essential.…”

The revascular active percutaneous interventional device for coronary total occlusions study

“…Ideally, these devices should combine three key features: (1) ability to distinguish a true luminal path from the one created within (dissection) or through (perforation) the vessel wall of the occluded segment; (2) capacity to change direction to correct deviations from the desired path through the occlusion, and (3) facility to penetrate the frequently fibrotic and focally calcific substance of the occlusion through the use of either mechanical stiffness or an alternative energy modality (laser, radiofrequency, ultrasound, blunt micro dissection) [22]. In the past decade some of these new devices have been developed and tested in human.…”

High‐resolution 3D arteriography of chronic total peripheral occlusions using a T1‐W turbo spin‐echo sequence with inner‐volume imaging

“…A recent study successfully demonstrated catheter navigation and CTO recanalization wholly under real‐time MRI guidance (17), which has been recognized as an important development in the field (25). Advances in registration techniques using the hybrid XMR imaging systems (26, 27) now also make it possible to overlay MR images on real‐time X‐ray images during catheterization procedures.…”