Introduction
MRI based ablation provides an attractive capability of seeing ablation related tissue changes in real-time. Here we describe a real time MRI based cardiac cryo-ablation system.
Methods
Studies were performed in canine model (n=4) using MR-compatible cryo-ablation devices built for animal use: focal cryo-catheter with 8 mm tip and 28 mm diameter cryo-balloon. The main steps of MRI guided cardiac cryo-ablation procedure (real-time navigation, confirmation of tip–tissue contact, confirmation of vessel occlusion, real-time monitoring of a freeze zone formation, and intra-procedural assessment of lesions) were validated in a 3 Tesla clinical MRI scanner.
Results
The MRI compatible cryo devices were advanced to the right atrium (RA) and right ventricle (RV) and their position was confirmed by real-time MRI. Specifically, contact between catheter tip and myocardium and occlusion of superior vena cava (SVC) by the balloon was visually validated. Focal cryo lesions were created in the RV septum. Circumferential ablation of SVC-RA junction with no gaps was achieved using the cryo-balloon. Real-time visualization of freeze zone formation was achieved in all studies when lesions were successfully created. The ablations and presence of collateral damage were confirmed by T1-weighted and late gadolinium enhancement MRI and gross pathological examination.
Conclusion
This study confirms the feasibility of a MRI based cryo-ablation system in performing cardiac ablation procedures. The system allows real-time catheter navigation, confirmation of catheter tip–tissue contact, validation of vessel occlusion by cryo-balloon, real-time monitoring of a freeze zone formation, and intra-procedural assessment of ablations including collateral damage.
Difficulty was encountered with the insertion of a right atrial pacing lead via the left jugular vein during lead and pacemaker implantation in a clinically normal goat as part of an ongoing rapid atrial pacing - induced atrial fibrillation research project. Fluoroscopic visualization of an abnormal lead advancement path prompted angiographic assessment which revealed a persistent left cranial vena cava (PLCVC) and prominent coronary sinus communicating with the right atrium. Angiography facilitated successful advancement and securing of the pacing lead into the right side of the interatrial septum. Cardiac magnetic resonance imaging/magnetic resonance angiography (MRI/MRA) allowed further characterization of this rare venous anomaly. Even though PLCVC has been reported once in a goat, to the authors’ knowledge this is the first report to include MRI/MRA characterization of PLCVC and prominent coronary sinus with successful cardiac pacemaker implantation using the PLCVC.
Introduction:
Balloon cryoablation is being increasingly used for pulmonary vein isolation. Acute determination of lesion permanency cannot be ascertained directly, but is inferred by PV occlusion and acute PV isolation. We aimed to determine if direct confirmation of vessel occlusion and lesion formation could be visualized in real time in a MRI system using a novel MRI compatible cryo balloon catheter.
Methods:
We used a canine model (n=3) and a MRI compatible cryo balloon catheter built for animal use (Medtronic CryoCath, Montreal, Canada). The procedure was performed in a 3T (Verio, Siemens) MR scanner. The MRI compatible 28 mm cryo balloon was advanced into the right atrium (RA) via the femoral vein under MRI guidance. Gadolinium based contrast (Multihance) was injected to confirm vessel occlusion. The superior vena cava (SVC) - RA junction was frozen for 3 mins. Post ablation, late gadolinium enhancement MRI (LGE-MRI) was obtained acutely to confirm the ablation. The heart was excised to confirm the tissue changes.
Results:
Panel A shows the inflated balloon at the SVC ostium. Panel B shows contrast injected in the SVC confirming its occlusion. Panel C is an MR image taken during the freeze cycle. Panel D is an LGE-MRI showing enhancement along the SVC wall confirming ablation. Panel E is an axial view of the SVC confirming circumferential ablation with no apparent gaps. The ablation completeness was confirmed in pathology.
Conclusion:
A real time MR-based balloon cryo ablation system was implemented. It allows real time confirmation of vessel occlusion, visualization of a freeze zone and visual confirmation of tissue changes from ablation in the pre-clinical setting.
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