Radiofrequency catheter ablation for supraventricular tachycardias: blazing paths or burning bridges?

The role of electrolyte in lesion size using an irrigated radiofrequency electrode

Multiple attempts have been made to eliminate atrial fibrillation by performing the surgical maze procedure with radiofrequency energy. Currently, this is limited because of the risk of atrial perforation and the lack of transmural penetration. Saline irrigation has been investigated as a method of radiofrequency cautery tip cooling to prevent rapid temperature and impedance rises, which have been shown to lead to perforation or decreased radiofrequency penetration after eschar formation. There are few data on the influence that different types of electrolyte irrigation solutions have on lesion depth. Using a novel hollow cautery pen, we infused either an electrolyte solution (0.9%, 3%, 14.6%, or 23.4% sodium chloride), a nonelectrolyte solution (1.5% glycine), or no irrigation to produce 819 lesions on 14 left ventricles in swine using radiofrequency energy (450+/-10 kHz) applied at two output settings (20 and 75 watts). The nonelectrolyte solution increased lesion depth compared with no infusion at 20 watts but produced shallower lesion depths compared with electrolyte solutions at 75 watts. Compared with the other electrolyte solutions, the 0.9% sodium chloride solution produced the deepest lesions (3.34+/-0.06 mm) at 75 watts (p < 0.001). As the concentration of electrolyte increased, lesion depth decreased unless generator output increased. Formation of eschar and tissue destruction was seen in the noninfusion and nonelectrolyte groups but not in the electrolyte group. A conductive media coupled with radiofrequency energy allowed for greater lesion depth than irrigated cooling with a nonelectrolyte solution or no irrigation. There was an inverse relationship between electrolyte concentration and lesion depth. We conclude that the concentration of electrolyte irrigant is an important consideration when choosing a solution to improve transmural penetration and decrease the risk of tissue destruction from radiofrequency energy.

Insights into the electrophysiology of accessory pathway-mediated arrhythmias provided by the catheter ablation experience: "learning while burning, part III"

The success of catheter ablation has greatly improved the care of patients with paroxysmal tachycardias and has caused a revolution in the practice of electrophysiology. Some investigators have expressed that concern over procedural success in an increasingly interventional specialty threatens to eclipse attempts to understand the physiology of arrhythmia syndromes. Alternatively, due to the precise and directed nature of the lesions created with radiofrequency energy, catheter ablation procedures have allowed investigation to continue at a more focused level. In this article, the insights provided by the catheter ablation experience into the physiology of arrhythmias mediated by accessory AV pathways will be reviewed. Although the learning process was sometimes delayed by the nearly immediate success of radiofrequency catheter ablation, difficult situations have continued to renew efforts for understanding at a deeper level. Conscious attempts at "learning while burning" will provide the opportunity to investigate aspects of bypass tract physiology that remain incompletely characterized, such as partial response to therapy and late recurrence.

Insights into the electrophysiology of atrial arrhythmias gained by the catheter ablation experience: "learning while burning, Part II"

Although the development and wide-scale application of catheter ablative techniques has drastically changed the practice of electrophysiology, catheter ablation does not preclude physiologic investigation. On the contrary, given the precise and directed nature of this technique and the increased attention to detailed cardiac mapping that it requires, catheter ablation may be viewed as a tool to provide unique information about arrhythmia substrates. In this article, the insights provided by the catheter ablation experience into the pathophysiology of the focal atrial arrhythmias, atrial tachycardia, sinus node reentrant tachycardia, and inappropriate sinus tachycardia will be reviewed. Atrial arrhythmias were initially difficult to treat with ablative therapy, particularly because they can occur anywhere within the atria and the experience with mapping for surgical ablation was quite limited. A number of novel approaches to atrial mapping have been developed in response to this challenge, and presently, catheter ablation provides effective therapy for the majority of patients with focal atrial arrhythmias. In addition, deliberate attempts at "learning while burning" have already begun to enhance our understanding of the interaction of the structural and electrophysiologic aspects of the substrate for atrial arrhythmias.

Insights into the electrophysiology of ventricular tachycardia gained by the catheter ablation experience: "learning while burning"

The success of catheter ablation has significantly improved the treatment of patients with cardiac arrhythmias and has established electrophysiology as an increasingly interventional subspecialty. Some members of the electrophysiology community have expressed concern that this success has been purchased at the cost of undermining what had been our primary concern: understanding the anatomic and physiologic basis of arrhythmia syndromes. In many laboratories, endpoints such as case load and primary success have eclipsed physiologic investigation. Despite these trends, however, catheter ablation is not inherently at odds with investigation and education. On the contrary, because the lesions delivered with current techniques are much more discrete than the effects of antiarrhythmic agents or surgical ablation, catheter ablation can be used as a research tool directed toward a more precise understanding of arrhythmia substrates. Conscious attempts at "learning while burning" have already provided important and unique information about arrhythmia pathogenesis.