Aortic Stenosis: Assessment of the Patient at Risk

Early identification of aortic valve sclerosis using iron oxide enhanced MRI

PURPOSE

To test the ability of MION-47 enhanced MRI to identify tissue macrophage infiltration in a rabbit model of aortic valve sclerosis (AVS).

MATERIALS AND METHODS

The aortic valves of control and cholesterol-fed New Zealand White rabbits were imaged in vivo pre- and 48 h post-intravenous administration of MION-47 using a 1.5 Tesla (T) MR clinical scanner and a CINE fSPGR sequence. MION-47 aortic valve cusps were imaged ex vivo on a 3.0T whole-body MR system with a custom gradient insert coil and a three-dimensional (3D) FIESTA sequence and compared with aortic valve cusps from control and cholesterol-fed contrast-free rabbits. Histopathological analysis was performed to determine the site of iron oxide uptake.

RESULTS

MION-47 enhanced the visibility of both control and cholesterol-fed rabbit valves in in vivo images. Ex vivo image analysis confirmed the presence of significant signal voids in contrast-administered aortic valves. Signal voids were not observed in contrast-free valve cusps. In MION-47 administered rabbits, histopathological analysis revealed iron staining not only in fibrosal macrophages of cholesterol-fed valves but also in myofibroblasts from control and cholesterol-fed valves.

CONCLUSION

Although iron oxide labeling of macrophage infiltration in AVS has the potential to detect the disease process early, a macrophage-specific iron compound rather than passive targeting may be required.

A new tool for the resection of aortic valves: In-vitro results for turning moments and forces using Nitinol cutting edges

The use of minimally invasive techniques for aortic valve replacement (AVR) may be limited for severely calcified and degenerated stenotic aortic valves. A quick resection leaving a defined geometry would be advantageous. Therefore, a new minimally invasive resection tool was developed, using rotating foldable cutting edges. This report describes the first experimental in-vitro results of measuring turning moment and forces during cutting of test specimens. Nitinol cutting edges were mounted on a simplified version of the resection instrument. The instrument shaft was combined with an exchangeable gear (1:3.71 vs. 1:5.0), and an exchangeable screw thread for accurate feed motion (0.35 mm or 0.5 mm) was implemented. Furthermore, the option of an added stabilisation body (SB) to prevent strut-torsion during cutting was tested. Tests were performed upon specially designed test specimens, imitating native calcified aortic valves. Resection was successful in all 60 samples (12 samples for each of the five configurations). Mean resection time ranged from 18.7+/-1.0 s (gear 1:3.71, screw thread 0.5, with SB) to 29.3+/-4.6 s (gear 1:5, screw thread 0.35, with SB), mean maximum turning moment ranged from 2.1+/-0.2 Nm (gear 1:3.71, screw thread 0.35, with SB) to 2.8+/-0.4 (gear 1:5, screw thread 0.35, with SB), mean maximum force from 36.0+/-11.3 N (gear 1:3.71, screw thread 0.35, with SB) to 56.3+/-10.5 N (gear 1:3.71, screw thread 0.5, without SB) and mean number of required rotations from 41.3+/-2.9 (gear 1:3.71, screw thread 0.5, with SB) to 59.1+/-3.7 (gear 1:3.71, screw thread 0.35, without SB). In summary, the positive influence of the stabilisation body could be shown. Combining the right parameters, it is possible to limit maximum cutting forces to F(max)<50 N and maximum turning moments to M(max)< 3.0 N.