Segmented nitinol guidewires with stiffness-matched connectors for cardiovascular magnetic resonance catheterization: preserved mechanical performance and freedom from heating

Abstract

BackgroundConventional guidewires are not suitable for use during cardiovascular magnetic resonance (CMR) catheterization. They employ metallic shafts for mechanical performance, but which are conductors subject to radiofrequency (RF) induced heating. To date, non-metallic CMR guidewire designs have provided inadequate mechanical support, trackability, and torquability. We propose a metallic guidewire for CMR that is by design intrinsically safe and that retains mechanical performance of commercial guidewires.MethodsThe NHLBI passive guidewire is a 0.035” CMR-safe, segmented-core nitinol device constructed using short nitinol rod segments. The electrical length of each segment is less than one-quarter wavelength at 1.5 Tesla, which eliminates standing wave formation, and which therefore eliminates RF heating along the shaft. Each of the electrically insulated segments is connected with nitinol tubes for stiffness matching to assure uniform flexion. Iron oxide markers on the distal shaft impart conspicuity.Mechanical integrity was tested according to International Organization for Standardization (ISO) standards. CMR RF heating safety was tested in vitro in a phantom according to American Society for Testing and Materials (ASTM) F-2182 standard, and in vivo in seven swine. Results were compared with a high-performance commercial nitinol guidewire.ResultsThe NHLBI passive guidewire exhibited similar mechanical behavior to the commercial comparator. RF heating was reduced from 13 °C in the commercial guidewire to 1.2 °C in the NHLBI passive guidewire in vitro, using a flip angle of 75°. The maximum temperature increase was 1.1 ± 0.3 °C in vivo, using a flip angle of 45°. The guidewire was conspicuous during left heart catheterization in swine.ConclusionsWe describe a simple and intrinsically safe design of a metallic guidewire for CMR cardiovascular catheterization. The guidewire exhibits negligible heating at high flip angles in conformance with regulatory guidelines, yet mechanically resembles a high-performance commercial guidewire. Iron oxide markers along the length of the guidewire impart passive visibility during real-time CMR. Clinical translation is imminent.

CMR fluoroscopy right heart catheterization for cardiac output and pulmonary vascular resistance: results in 102 patients

“…In all 5 patients, pulmonary artery catheterization under X-ray guidance was also unsuccessful without the aid of a guidewire. CMR-conditional guidewires are in development, which should improve the procedural success rate [ 14 , 15 ]. CMR-conditional guidewires will also permit more complex interventions to be performed under CMR guidance.…”

MR-guided Cardiac Interventions

“…Guidewires with a fiberglass core and non-metallic guidewires made of resin microparticle compound covered by polytetrafluoroethylene have been used for MR-guided interventions in animals 92,93 and successful clinical trials with interventions in congenital heart disease but these have had been difficult to steer and proved to be fragile 94,95 . Consequently, a newer nitinol based guidewire with iron oxide markers along the length to impart visibility has been developed with good preclinical results 96 .…”

MRI use for atrial tissue characterization in arrhythmias and for EP procedure guidance

“…The larger (>2 mm) metallic-shaft devices were replaced with plastic (or polymer) shaft devices, whereas the very thin devices, such as guidewires, were built using low-conductivity and low-susceptibility metals (nitinol) 67, 68 , or were remade of plastic or fiber-glass shafts 69, 70 . In addition, the standard electrodes used on the EP catheters were replaced with higher-cost platinum or gold electrodes 71 , with all high-susceptibility (stainless steel, nickel) metals removed.…”