Electroporation ablation: A new energy modality for ablation of arrhythmogenic cardiac substrate

At the very end of the Direct Current (DC) era, low-energy DC ablation was demonstrated to cause myocardial lesions by non-thermal irreversible electroporation (IRE) (permanent formation of pores in the cell membrane, leading to cell death), without arcing and/or barotrauma. To eliminate rather small cardiac targets, DC ablation was replaced by the much more refined radiofrequency (RF) ablation technique. However, patients with atrial fibrillation (AF) and ventricular tachycardia (VT) require transmural and large myocardial lesions.

At present, AF ablation with RF energy is time consuming, requires significant operator skills and is beset by a high AF recurrence rate, for both pathophysiological reasons and technical imperfections of current thermal catheter techniques. In 10-20% an epicardial catheter-ablation approach is required for VTs related to structural (scar)heart diseases. However, myocardial tissue in close proximity to a coronary artery is not suitable for catheter-ablation with thermal energy, for both reasons of safety (risk on coronary artery injury) and effectivity (heat sink).

The last decade, IRE has been increasingly used as a new, emerging non-thermal ablation modality in the medical field for elimination of specific areas of undesired tissue without destroying surrounding tissues. When incorporated in electroporation lesions, bile ducts, large blood vessels and the urethra are preserved. Therefore, by resolving shortcomings of thermal ablation methods, this energy source may better meet the requirements of current electrophysiological practice. The major challenge was application of low-energy DC shocks (without arcing and/or barotrauma) while still allowing for sufficient (deep) and controlled myocardial lesion formation. We hypothesized that by applying a special catheter design using a circular arrangement of 8-10 connected electrodes, a torus-shaped electric field could be created in which voltage and current density decrease more linearly from the center of the electrodes.

In our first study, circular electroporation ablation at a low energy level was found a feasible and safe method for PV ostial lesion creation. PV electrogram amplitude decreased and stimulation threshold increased significantly. Up to 3.5-mm-deep lesions were found. However, due to the thin atrial wall and the uncertainty where ablations had been performed exactly, lesion size, depth, and continuity could not properly be analyzed in this model. Therefore, subsequent studies were carried out in an epicardial model.

Lesion depth increases linearly with the magnitude of the current density. Acute lesions were mainly characterized by contraction band formation and interstitial edema and did not evolve histologically over the course of 1 hour. Although the electrodes are separated, continuous circular lesions could be created with a single 200 J circular application. The coronary blood flow did not impact on lesion size. Unaffected myocardial tissue was never found right near a coronary artery that was completely embedded in lesion. Coronary arteries did not develop a significant stenosis within 3 months after epicardial electroporation ablation.PV stenosis did not occur as result of an excessive number of electroporation applications (worse case scenario).The function of the porcine right phrenic nerve was preserved after a single circular electroporation application delivered in the superior caval vein.