Abstract 1078: Non-Invasive Assessment of Tissue Heating during Cardiac Radiofrequency Ablation Using MRI Thermography
Introduction: Arrhythmias often recur after ablation because of incomplete lesion generation. Permanent lesions are created by tissue heating greater than 50°C. This study evaluates myocardial heating during radiofrequency (RF) ablation using proton resonance frequency shift thermography which has previously not been possible due to cardiac motion.
Methods: An MRI compatible electrode catheter was inserted into the left ventricle (LV) in 6 dogs. Gradient recalled echo (GRE) imaging with motion artifact reduction by reducing echo time and image registration was performed before and during RF power application in 1 to 3W increments until high impedance was reached. In 4 animals, imaging was also performed 60 seconds after stopping RF power. Delayed gadolinium-enhanced images (DEMRI) of the lesions were collected and gross pathology was obtained. Thermography images were computed from the phase component of the GRE images using standard methods. Thermography lesion extent was defined by a tissue temperature above 50°C.
Results: An expanding thermal lesion was noted as RF power was increased in all animals (Figure A–C⇓ [yellow, red]) and was no longer visible by 60 seconds after stopping RF power (D). The heating location (Figure C⇓) corresponded to the lesion location on DEMRI (E) and pathology (F). The transmural lesion extent by thermography was within 20% of that obtained by pathology and DEMRI. 50°C tissue heating could be detected with a signal to noise ratio above 5.
Conclusion: Non-invasive imaging of tissue heating during RF ablation is possible using MRI thermography and may allow more accurate placement and titration of ablation, possibly reducing arrhythmia recurrences.