Novel energy modalities for catheter ablation of cardiac arrhythmias: Pitfalls and possibilities of potent power sources

Abstract

The acceptance of catheter ablation as treatment for cardiac arrhythmias is amongst others dependent on its success rate, a high initial success rate will increase physician and patient acceptance. One of the reasons why recurrence of arrhythmia after ablation is substantial is non-transmurality of ablation lesions. Transmurality is essential for conduction block and is depending on many factors, such as tissue ablation duration, thickness of the cardiac wall, ablation technique used, catheter contact force and heat or cold sink effects of surrounding tissue/vessels. Complication rate of a treatment is also an important factor in the acceptance of catheter ablation as a treatment option for cardiac arrhythmias. Most complications occur from vascular access, pericardial effusion or cardiac tamponade. These complications are usually not life-threatening or disabling and can be resolved quickly and effectively. However, although more seldom, severe complications happen too: stroke and myocardial infarction by air or thrombotic embolism, paralysis of the hemidiaphragm by phrenic nerve injury and (lethal) atrial-to-esophageal fistula can occur. On the quest for the “ideal” ablation modality an old and abandoned cardiac ablation technique, direct current ablation, was refurbished. One of the major responsibilities was to make the old technique safe for human use. Therefore, the ablation current was spread out over a larger electrode surface, minimizing the risk of arcing and the subsequent cascade of adverse events. We investigated this in a dose-response finding study, showing that single 6 millisecond 200 joules electroporation ablations could create deep and continuous myocardial lesions. Now that had been demonstrated that safe, fast and effective electroporation ablation was possible, we focused on the traditional downside of potent ablation modalities: complications. Therefore, we initiated two studies in which we gave an “overdose” of electroporation energy inside the pulmonary veins and in the direct vicinity of the phrenic nerve. The pulmonary veins treated with electroporation ablation did not show angiographic narrowing after three months follow-up, in contrast to the pulmonary veins in which circumferential radiofrequency ablation was performed. Also, the function of the phrenic nerve was spared acutely as well as long term, one hour and three months after the electroporation application all phrenic nerves demonstrated normal function during capture-pacing from the superior caval vein. This favorable combination of safe, fast and effective electroporation ablation in the absence of severe complications paved the way for the exploration of potential treatment indications of electroporation ablation. One of the possible treatment indications is epicardial ablation. Currently, epicardial ablation is limited by lesion depth, presence of coronary arteries and phrenic nerve. Therefore, we simulated human epicardial ablation and performed electroporation ablation on the epicardium. We demonstrated that epicardial catheter ablation using electroporation creates extensive and deep myocardial lesions without significant injury to the coronary arteries after a 3-month follow-up period and that there was a significant relationship between the amount of ablation energy delivered and lesion depth. This effective new ablation technique could possibly solve one of the most important current limitations of epicardial catheter ablation: safe ablation on or near main coronary arteries.