Using Cardiac Magnetic Resonance Tomography for Assessment of Aortic Valve Area in Aortic Valve Stenosis

The past, present and future of minimally invasive therapy in endovascular interventions: a review and speculative outlook

Cardiovascular disease is a leading cause of death in all developed countries. In response to this need, endovascular management techniques have been developed across a large range of medical specialties. Minimally invasive percutaneous interventions were initially complex and challenging, but with the continued development of equipment and expertise their use has become routine in many fields. With routine use, it has become important to establish the safety and efficacy of endovascular treatments against the respective "gold standard" procedures, especially in light of their initial intended use for the management of patients at unacceptably high risk for standard therapy only. Such evaluation has to take into account the variety and diversity of devices and techniques, as well as the effects of operator dependability. Endovascular techniques are increasingly recognised as valid alternative management options for a variety of conditions, and it is anticipated that the current trend towards minimally invasive techniques will continue in the future, with moves towards increasingly complex endovascular techniques and hybrid interventions.

Towards real-time cardiovascular magnetic resonance-guided transarterial aortic valve implantation: in vitro evaluation and modification of existing devices

BACKGROUND

Cardiovascular magnetic resonance (CMR) is considered an attractive alternative for guiding transarterial aortic valve implantation (TAVI) featuring unlimited scan plane orientation and unsurpassed soft-tissue contrast with simultaneous device visualization. We sought to evaluate the CMR characteristics of both currently commercially available transcatheter heart valves (Edwards SAPIEN™, Medtronic CoreValve®) including their dedicated delivery devices and of a custom-built, CMR-compatible delivery device for the Medtronic CoreValve® prosthesis as an initial step towards real-time CMR-guided TAVI.

METHODS

The devices were systematically examined in phantom models on a 1.5-Tesla scanner using high-resolution T1-weighted 3D FLASH, real-time TrueFISP and flow-sensitive phase-contrast sequences. Images were analyzed for device visualization quality, device-related susceptibility artifacts, and radiofrequency signal shielding.

RESULTS

CMR revealed major susceptibility artifacts for the two commercial delivery devices caused by considerable metal braiding and precluding in vivo application. The stainless steel-based Edwards SAPIEN™ prosthesis was also regarded not suitable for CMR-guided TAVI due to susceptibility artifacts exceeding the valve's dimensions and hindering an exact placement. In contrast, the nitinol-based Medtronic CoreValve® prosthesis was excellently visualized with delineation even of small details and, thus, regarded suitable for CMR-guided TAVI, particularly since reengineering of its delivery device toward CMR-compatibility resulted in artifact elimination and excellent visualization during catheter movement and valve deployment on real-time TrueFISP imaging. Reliable flow measurements could be performed for both stent-valves after deployment using phase-contrast sequences.

CONCLUSIONS

The present study shows that the Medtronic CoreValve® prosthesis is potentially suited for real-time CMR-guided placement in vivo after suggested design modifications of the delivery system.

The in vivo diagnosis of early-stage aortic valve sclerosis using magnetic resonance imaging in a rabbit model

PURPOSE

To use magnetic resonance imaging (MRI) to identify and monitor early aortic valve sclerosis (AVS) induced by cholesterol feeding in rabbits. AVS is a highly prevalent disease process, affecting more than 25% of the population over age 65. A major obstacle to early stage medical management of AVS has been the lack of an objective noninvasive technique to identify its presence and monitor its progress.

MATERIALS AND METHODS

Retrospectively gated CINE fast spoiled gradient echo (fSPGR) images of aortic valve cusps were collected at 3-month intervals starting at 6 months using a 1.5 T MR scanner interfaced with a customized surface radiofrequency coil. At 16 months a subset of animals was sacrificed and excised cusps were examined with both high frequency ultrasound (US) and histopathological techniques to validate the MRI method.

RESULTS

MR and US analysis identified significant thickening of diseased AV cusps when compared to control (P < 0.05). Histopathological analysis confirmed the presence of human-like AVS in diseased rabbit valves.

CONCLUSION

Early AVS, exemplified by increased valve thickness, can be identified in vivo using high-resolution MRI.