Linear ablation for atrial fibrillation guided by acoustic imaging: “How does it sound?”

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Despite advances in techniques on catheter ablation of atrial fibrillation (AF), a substantial proportion of patients after ablation had recurrences of AF, and even after multiple repeated procedures. Pulmonary vein isolation remains the cornerstone of most AF ablation procedures, and additional ablation strategies such as creation of lines of conduction block in the left atrium (LA) and right atrium (RA) and ablation targeting onpulmonary vein triggers, the autonomic ganglia, or complex fractionated electrograms have been employed in either the initial or the repeat procedure with variable success. Catheter-based linear atrial ablation attempts to replicate the surgical Maze procedure, in which up to a 90% long-term success rate of maintaining sinus rhythm has been reported. The comparatively lower success rate of catheter vs surgically delivered linear ablation could be explained by multiple factors such as inadequate line continuity and transmurality, difference in line design, and additional effect of surgical procedures on autonomic ganglia. Among these factors, uncertainty in creating a complete line of block is thought to be the main Achilles tendon of catheter-based approach, not only because it is unable to eliminate AF but also because it is potentially proarrhythmogenic. In this issue of HeartRhythm, Eyerly et al report their experience of using intracardiac acoustic radiation force impulse imaging (ARFI) in animals to guide the creation of a complete line of block. This technology is based on the principle that focused and short duration intracardiac ultrasound will create an acoustic force on myocardial tissue. These pulses induce local tissue displacements that are influenced by tissue characteristics. Thus, protein denaturation following catheter blation will result in a “stiffer” myocardium compared with he surrounding untreated myocardium and thus provide an ndicator of the adequacy of catheter ablation, almost like an ndirect “palpation” of the tissue characteristics. The authors have demonstrated previously in an in vitro porcine myocardium model that this technology is capable of “visualizing” radiofrequency ablation (RFA)-induced lesions of dimension within 1 mm (axial) to 2 mm (lateral).