During RF ablation for atrial fibrillation, undesired tissue conductivity is interrupted by inducing lesions through applying RF current. Feedback on lesions formed is currently indirect, leading to unpredictable outcomes for patients. Previously we have shown that two-wavelengths photoacoustic imaging can distinguish between scarred and healthy tissue (Iskander-Rizk et al. BOE 2018). This principle may be translated to clinical imaging by integrating an optical fiber in the ablation catheter to generate photoacoustic signals of lesions using commonly present intracardiac echo (ICE) probe as a receiver.
We modified a commercially available ablation catheter to fit a 400µm, 0.39 NA multi-mode optical fiber through the flushing channel. In a porcine passive beating heart model (Lifetec, Eindhoven), we inserted the modified ablation catheter and a St Jude ViewFlex ICE probe through the jointly tied pulmonary vein into the left atrium. We ablated around the mitral valve, and we used a 100Hz laser source (Innolas Spitlight EVO-OPO) constantly toggling between 790 and 930 nm to generate photoacoustic signals at the ablation site. The signals were digitized and processed with a Verasonics vantage 256 system. One acquisition frame consisted of 5 tilted diverging wave ultrasound acquisitions and 1 photoacoustic acquisitions per wavelength.
We monitored lesion progression and continuity in a beating heart addressing motion artefacts concerns. In addition to that, the dual wavelength photoacoustic images successfully eliminate undesirable signals from the catheter tip, blood and healthy tissue, leaving only signals from lesions, enabling real-time intracardiac ablation monitoring that is readily translatable to an in vivo setting.