Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures.

BACKGROUND: One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating. METHODS: A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip. RESULTS: A maximum temperature rise of 22.4°C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2°C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8°C. CONCLUSION: Up to a maximum of 22.4°C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.

Carotid artery stenting using a novel self-expanding braided nickel-titanium stent: feasibility and safety porcine trial.

We studied the deliverability and safety of a braided, self-expanding, closed-cell nickel-titanium (NiTi) stent (E-volution, Jotec GmbH, Hechingen, Germany) especially designed for the endovascular treatment of carotid artery bifurcation stenosis with special regard to in-stent stenosis and thrombosis compared with a laser-cut reference nitinol stent in a porcine model of percutaneous vascular interventions. We aimed to assess histopathologic response in minipig carotid and subclavian arteries. Eight minipigs received a total of 42 stents: 14 reference stents and 28 E-volution stents. Eleven of the E-volution stents were additionally coated with heparin. Control angiography was obtained immediately before and after vascular intervention as well as 4 weeks after the procedure. Primary endpoints were 28 days of angiographic analyses as well as histomorphometric analysis, including injury score, inflammation score, luminal diameter, vessel diameter, maximal neointimal thickness, and area of in-stent stenosis. Secondary end points were procedural success, 28-day mortality, and stent thrombosis. All stents could be delivered successfully without procedural complications, morbidity, or mortality during our observation time. As confirmed by histology, no in-stent thrombosis was observed. Compared with common carotid arteries, subclavian arteries are significantly more vulnerable to developing in-stent stenosis caused by neointima proliferation (p < 0.05). Compared with the use of 1 single stent/artery, serial application of two stents leads to a more excessive but not significantly different neointimal proliferation (p > 0.05). The E-volution stent, especially when heparin coated, is in line with the comparison to the laser-cut reference stent displaying similar results of angiographic, histologic, and histomorphometric analyses (p > 0.05). Compared with the reference laser-cut stent, the self-expanding nitinol stent (E-volution) with its advanced braiding technology is feasible and safe. In our opinion, the high radial resistive force and the advanced braided design with tight stent-strut interstices may be beneficial in terms of plaque stabilization. Further studies are necessary and warranted.

Treatment of wide-necked intracranial aneurysms with a novel self-expanding two-zonal endovascular stent device.

INTRODUCTION: Endovascular treatment of intracerebral wide-necked aneurysms carries the risk of incomplete embolisation and recanalisation of the aneurysm as well as coil protrusion into the parent artery and embolic complications. We present preliminary results with the placement of a novel tightly braided stent across the aneurysm neck which might lead to thrombosis of these aneurysms. METHODS: A bifurcation artery aneurysm was created in a male New Zealand White Rabbit. After 4 weeks, a novel highly flexible stent with a central tightly braided mesh was placed across the aneurysm neck. Diagnostic angiography was performed during the procedure and immediately after stent deployment as well as 2 and 4 weeks following stent placement. Histological analyses, including microscopic investigations for evaluating intra-aneurysmal thrombosis and proliferation of the intima, were performed after 1 month. RESULTS: Intra-aneurysmal flow reduction due to stent placement was achieved as early as 45 min after deployment. Unchanged complete occlusion of the aneurysm could be observed by angiography 2 and 4 weeks post-stent deployment. Histological analysis confirmed angiographical findings of complete aneurysm occlusion and excluded significant neointimal coverage. CONCLUSION: This newly designed flexible stent may offer the potential to expand endovascular treatment of wide-necked intracranial aneurysms.

50 Hz fatigue testing of large diameter stent grafts.

An aortic stent graft has been fatigue tested in a system that operates at a frequency of 50 Hz. The mode of operation and the results that supplement finite element model calculations are described.