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Oral Abstract

Oral Abstract Translation #1- Integrating Basic Science Insights into Clinical Cardiac MRI Applications

Detecting Elevated LV Filling Pressure on a Commercially Available 0.55T Platform Using a Modified Off-the-shelf Pigtail Catheter: Feasibility Results in a Porcine Model with iCMR-guided Infusion of Microspheres

Friday, January 31, 2025
10:00 AM – 10:10 AM East Coast USA Time
Location: Blue Room
Background: The radiation burden in X-ray fluoroscopy, which is the gold standard imaging modality for cardiac catheterization, is a significant consideration especially in pediatric studies. Interventional CMR (iCMR) has the potential to be the modality of choice for right heart and left heart catheterization (LHC) without ionizing radiation.1-3 LHC enables direct measurement of left ventricular end-diastolic pressure (LVEDP) which is a key hemodynamic marker of LV performance and coronary microvascular health. Prior work on iCMR-enabled LHC has successfully used clinical 1.5T systems1-3 and, recently, on a high-performance ramped-down 0.55T which is not commercially available.4 Here we show the feasibility of iCMR-guided LHC using a modified off-the-shelf pigtail catheter on a commercially available 0.55T platform and a widely available MR-compatible invasive pressure monitoring hardware. We further demonstrate the feasibility of detecting dynamic changes in left ventricular (LV) end diastolic pressure during the iCMR procedure in a preclinical setting using fully iCMR-guided pig model of cardiogenic shock (CS)5-7 with intra-LV infusion of microspheres.

Methods: Non-survival experiments were performed on anesthetized domestic swine (n=22; weight: 45 ± 6 kg) under a protocol approved by the local Institutional Animal Care and Use Committee. Animals were positioned supine head-first within the bore of a Free.Max 0.55T scanner (Siemens Healthineers, Erlangen, Germany). iCMR guidance was used to navigate multiple interventional devices in the arterial circulation (Fig 1a-c). A pigtail catheter was advanced over a guidewire from left femoral artery into LV (details in Fig 1). In 12 animals, the pigtail catheter was then connected to an MR-compatible physiological monitoring system (Biopac Systems, Goleta, CA) for high-fidelity sampling of LV filling pressure. For a subset of animals (n=4), a second pigtail catheter was advanced into the LV cavity for intra-LV infusion of microspheres to induce CS: ≈11 x 106 compressible microspheres (40-μm Embozene, Varian Medical Systems, Palo Alto, CA). As shown in Fig 1d, LVEDP was measured at baseline and after induction of CS. A complete video/audio capture of the study was retrospectively analyzed to measure the “LHC procedure time,” defined as the time it takes for retrograde advancement of the guidewire followed by the pigtail catheter into the LV and subsequent removal of guidewire to enable LVEDP measurement using the catheter.

Results: The iCMR procedure was successfully completed in all studies (n=22 animals) with average LHC procedure time of 1.8 ± 0.5 minutes. A representative case is described in Fig 2. As shown in Fig 3, the mean LVEDP measured at baseline was 8.9 ± 2.1 mmHg (n=12), and notably increased after microsphere infusion to 18.6 ± 5.2 mmHg (n=4). Both measurements are within the range previously reported in anesthetized domestic pigs at baseline and CS.6,7

Conclusion: This study shows that iCMR-guided LHC is feasible using a modified off-the-shelf pigtail catheter, a commercially available 0.55T scanner platform and a widely available pressure measurement system (100% success rate in 22 studies). Furthermore, the feasibility of detecting dynamic LVEDP changes before/after inducing CS using iCMR-guided infusion of microspheres was demonstrated. Our results suggest that the reduced field strength and gradient performance of the 0.55T scanner may have a minimal impact on the iCMR procedure time when compared to high-performance1.5T systems.2


Figure 1: (a) An off-the-shelf, non-braided pigtail catheter (Cook Medical, Bloomington, IN) was modified with MR-conditional markers (the marker locations are shown with red dots) to create negative contrast during interventional MRI on a commercially available 0.55T scanner (Siemens Free.Max). All side-ports located proximally to the most proximal marker were plugged (green arrows). The nitinol-based guidewire used in the experiments is shown on the right with the red dots showing the approximate location of the MR markers. (b,c) Experiments on a 3D-printed heart phantom showed the feasibility of using the MR-markers for left heart catheterization (LHC): red arrows in (b) show the MR markers of the guidewire in the aortic arch and the red arrow in (c) points to the pigtail catheter inside the LV cavity. (d) The protocol diagram for the conducted LHC studies. For LHC, a guidewire was positioned retrograde in the femoral artery and advanced to the ascending aorta. The guidewire was then used to cross the aortic valve. Next, a pigtail catheter was advanced over the guidewire through the ascending aorta and into the LV. Finally, the guidewire was removed to enable fluid-filled pressure measurements by connecting the pigtail catheter to an MR-compatible physiological monitoring system (BioPac). Same LHC procedure was applied to place a second pigtail in LV for microsphere infusion. High-fidelity LV pressure waveforms were recorded at 2 kHz to measure the LVEDP at baseline and after microsphere infusion.

Figure 2: A representative case for LHC from the in-vivo studies. (a) The guidewire (shown with arrows) was advanced retrogradely through femoral artery, descending aorta and ascending aorta. (b) The pigtail catheter (arrows) was then advanced over the guidewire through the ascending aorta to the LV. (c) Image showing the moment the pigtail catheter is fully placed inside the LV chamber and guidewire is pulled back. (d) Free-breathing compressed-sensing short-axis cine scan with reduced flip angle further confirms the positioning of the pigtail inside the LV cavity.

Figure 3: (a) Representative LV pressure waveform at baseline and after intra-LV infusion of compressible microspheres under iCMR guidance to induce cardiogenic shock (CS) in the same animal. In this case example, the LVEDP increases from 8.8 mmHg at baseline to 28.7 mmHg during CS, and heart rate increases from 84 bpm to 114 bpm. (b) Short-axis cine images at baseline vs. CS state: the systolic frame shows septal wall-motion abnormality (red arrows) during CS compared to baseline. (c) Overall comparison of LVEDP at baseline vs CS: mean LVEDP was 8.9 ± 2.1 mmHg at baseline (n=12 animals) and increased 18.6 ± 5.2 mmHg during CS (n=4 animals). The red arrows overlaid in the bar plot highlight the dynamic change in LVEDP before/after intra-LV infusion of microspheres in the 4 animals that developed CS (mean LVEDP before infusion: 10.7 ± 1.9 mmHg vs 18.6 ± 5.2 mmHg after infusion in the same 4 animals, p < 0.05).