Targeted MRI Biopsy for Non-ischemic Cardiomyopathy with An Active Bioptome in a Canine Model (RF_TH_236)

Background: Nonischemic cardiomyopathy (NICM) can be assessed non-invasively by echocardiography and CMR.  However, endomyocardial biopsy (EMB) is typically performed in the right ventricle with random sampling of the ventricular septum.  Real-time MR-guided EMB could provide targeted sampling and improve accuracy of EMB for targeting in non-diffuse disease, such as NICM.  In this study, we have developed an active MRI EMB-forceps and performed prelimimary testing in animals.

Methods: A prototype 7.5 Fr MRI-EMB forceps catheter (Fig1) comprised of a MoMn  (a refractory metal, selected for hardness properties to impart sharp cutting edge) forceps jaws, an actuation mechanism to facilitate open and close forceps jaws from the handles at the proximal end, and a receive-only MRI antenna to enable active MRI visualization was assembled. The MRI-EMB forceps prototypes were tested on a 1.5T MRI Espree for imaging and RF safety performance in a tissue simulating phantom. For signal profile evaluation, a BEAT-iRTT sequence was used and for RF safety, an high flip angle BEAT-iRTT sequence (TR=3.84 ms; TE-1.39 ms; flip angle = 65) with a WBSAR of 4.0 W/kg was used. All animals studies were approved by the instutional ACUC.  Using real-time navigation, the forceps were guided in vivo to the left ventricle  (LV) of normal dogs, and EMBs were obtained and evaluated for quality, size, and sharpness of cuts.

Results: The distal 15 cm of the MRI-EMB forceps were distinctly conspicuous, and the location of the distal tip of the forceps could be discerned in MRI. The max local temperature rise with the BEAT-iRTT sequence was 3^oC in the phantom.  However, heating was reduced with the real-time BEAT-iRTT to ~1^oC using the expected parameters for in vivo studies.  Successful catheterization of the LV via a carotid approach was possible in dogs with the MRI-EMB forceps, and EMBs of the LV were performed  in acute canine studies without adverse events, e.g.,  perforation, fatal arrhythmias, hemorrhage, gross heating, etc.  Eight-ten samples could be obtained with a single bioptome in each animal with sharp, well-delineated margins (Fig 2).  Average size of the biopsy sample was 1.08±0.08 mm.

Conclusion: The prototype MRI-EMB forceps catheter handled similar to commercial EMB devices.  A steerable sheath is under development that can facilitate directing the forceps to region of interest for targeted biopsies (Fig 3). The forceps cut/sampled myocardium tissue with ease with no tugging. Although potential heating could be seen in the phantom, using pulse parameters expected for in vivo navigation, heating was reduced to an acceptable range.  For acute in vivo studies, no adverse events were noted and all biopsies contained abundant myocytes that could be used for pathological analysis.  The MRI-EMB forceps catheter with active visualization is a potential approach to specifically target diseased myocardium in patients with NICM.