Right heart catheterization using metallic guidewires and low SAR cardiovascular magnetic resonance fluoroscopy at 1.5 Tesla: first in human experience

Abstract

Background: Cardiovascular magnetic resonance (CMR) fluoroscopy allows for simultaneous measurement of cardiac function, flow and chamber pressure during diagnostic heart catheterization. To date, commercial metallic guidewires were considered contraindicated during CMR fluoroscopy due to concerns over radiofrequency (RF)-induced heating. The inability to use metallic guidewires hampers catheter navigation in patients with challenging anatomy. Here we use low specific absorption rate (SAR) imaging from gradient echo spiral acquisitions and a commercial nitinol guidewire for CMR fluoroscopy right heart catheterization in patients.

Methods: The low-SAR imaging protocol used a reduced flip angle gradient echo acquisition (10° vs 45°) and a longer repetition time (TR) spiral readout (10 ms vs 2.98 ms). Temperature was measured in vitro in the ASTM 2182 gel phantom and post-mortem animal experiments to ensure freedom from heating with the selected guidewire (150 cm × 0.035″ angled-tip nitinol Terumo Glidewire). Seven patients underwent CMR fluoroscopy catheterization. Time to enter each chamber (superior vena cava, main pulmonary artery, and each branch pulmonary artery) was recorded and device visibility and confidence in catheter and guidewire position were scored on a Likert-type scale.

Results: Negligible heating (< 0.07°C) was observed under all in vitro conditions using this guidewire and imaging approach. In patients, chamber entry was successful in 100% of attempts with a guidewire compared to 94% without a guidewire, with failures to reach the branch pulmonary arteries. Time-to-enter each chamber was similar (p=NS) for the two approaches. The guidewire imparted useful catheter shaft conspicuity and enabled interactive modification of catheter shaft stiffness, however, the guidewire tip visibility was poor.

Conclusions: Under specific conditions, trained operators can apply low-SAR imaging and using a specific fully-insulated metallic nitinol guidewire (150 cm × 0.035" Terumo Glidewire) to augment clinical CMR fluoroscopy right heart catheterization.

Trial registration: Clinicaltrials.gov NCT03152773 , registered May 15, 2017.

Keywords: Cardiac catheters; Cardiovascular magnetic resonance; Guidewire; Interventional MRI catheterization; Invasive hemodynamics; Medical device heating; Real-time MRI; Right heart catheterization; Spiral MRI.

Fig. 1

Heating of guidewires. Temperature at the tip of the fully insulated guidewire (Terumo Glidewire) (a) and uninsulated tip guidewire (Medtronic Nitrex) (b) during 2 min of continuous scanning (low-SAR and normal-SAR) in the ASTM 2182 phantom with homebuilt positioning system

Fig. 2

Catheter shaft conspicuity imparted by guidewire. Example low-SAR spiral GRE images, with catheter and guidewire (arrowheads) positioned in the superior vena cava (a), main pulmonary artery (b) and left pulmonary artery (c); the guidewire imparts both hypo- and hyper-intense signal along the shaft. The dotted line indicates signal saturation caused by an orthogonal slice plane interleaved during imaging

Fig. 3

Comparator rectilinear bSSFP images. Image orientation comparable to Fig. 2 showing improved blood-tissue contrast with bSSFP rectilinear images (normal-SAR imaging mode) for inferior/superior vena cava view (a), main pulmonary artery view (b) and branched pulmonary arteries view (c). No devices were present during imaging