Direct Current Ablation Research Articles

Radio-frequency catheter ablation of cardiac arrhythmias: Appraisal of an evolving therapeutic modality

Since its introduction in 1985, there have been numerous reports of the use of radio-frequency (RF) current as an alternative energy source for catheter ablation. RF current (frequency range 150 kHz to 1 MHz), when delivered in bipolar mode, causes desiccation of tissue by creating a localized area of heat that results in discrete coagulation necrosis. An equivalent energy source such as direct current (DC) shock can be delivered at lower power (5 to 30 W) and lower voltage (30 to 80 V) for a longer pulse duration (10 to 60 seconds), thus eliminating barotraumatic effects. Because of its high frequency, RF current does not stimulate neuromuscular fibers, and general anesthesia during ablation is not needed. Studies in animals have shown that catheter-delivered RF energy can safely produce permanent complete or partial AV block, necrosis of atrial and ventricular myocardium adjacent to the mitral and tricuspid anuli potentially suitable for ablation of accessory pathways, and discrete lesions in the left and right ventricular myocardium. Recently, investigators from several centers have reported successful ablation of the AV junction (either complete or partial AV block) in patients with refractory supraventricular tachyarrhythmias, ablation of accessory pathways, and ablation of focal ventricular myocardium or a segment of a bundle branch in patients with drug-resistant ventricular tachycardia. Specific modification of AV conduction to cure AV nodal reentrant tachycardia has been successfully attempted. In all studies the application of RF current has not caused any serious complications. However, the size of lesions is generally smaller as compared with DC ablation when the conventional electrode catheter is used. Delivery of higher power (> 30 W) and longer pulse duration (> 40 seconds) is often limited due to a sudden impedance rise as a result of coagulum formation around the electrode. Increase in lesion size and decrease in impedance rise may be achieved by using a larger electrode or a cooled porous electrode with saline infusion or by the use of a thermistortipped temperature-guided electrode. In conclusion, RF catheter ablation is a safe and useful technique in selected patients with cardiac arrhythmias. It may prove to be a better energy source for modification of AV conduction and for ablation in patients with poor ventricular function.

Catheter ablation of the atrioventricular junction with radiofrequency energy.

Catheter ablation of the atrioventricular junction using direct-current defibrillator discharges requires general anesthesia and may have serious side effects. Sixteen patients with drug-refractory supraventricular tachycardia underwent catheter ablation of the atrioventricular junction using radiofrequency energy. A standard 7F quadripolar electrode catheter was positioned to record the largest unipolar His potential (580 +/- 640 microV) from the distal electrode. An electrocoagulator (Microvasive Bicap 4005) supplied continuous, unmodulated energy at 550 kHz. One to 14 applications of radiofrequency current were delivered between the distal electrode and a large-diameter chest wall electrode. Transient, mild chest discomfort was reported by seven of 16 patients. None had significant arrhythmias or blood pressure changes during radiofrequency ablation. Complete atrioventricular block was produced in nine of 16 patients and high-grade second-degree atrioventricular block was produced in one patient with radiofrequency current. Attenuated His bundle electrograms could still be recorded in the remaining six patients, four of whom underwent successful atrioventricular junctional ablation using direct-current shock during the same session. Atrioventricular block persisted in all 10 patients successfully treated with radiofrequency ablation during a mean follow-up of 4.2 months. Compared with a group of historic control subjects treated with direct-current shock ablation, the 10 patients successfully treated with radiofrequency current had significantly less creatine kinase-MB isoenzyme release (5.7 +/- 5.1 vs. 22 +/- 13 IU, p = 0.006). A junctional escape rhythm was present in all patients after radiofrequency-induced atrioventricular block. In contrast, three of 10 control patients had an idioventricular escape after direct current shock ablation, and four patients had no escape rhythm at all.(ABSTRACT TRUNCATED AT 250 WORDS)

Catheter Ablation for Recurrent Tachyarrhythmias. Clinical Experience with Two Different Techniques of Ablation in 21 Patients

Between 1984 and 1988, 21 patients underwent catheter ablation for drug refractory arrhythmias. Nine patients presented atrial flutter, atrial fibrillation or atrial tachycardia, nine had supraventricular tachycardia (one AV nodal reentrant tachycardia, one reciprocating tachycardia due to concealed accessory pathway and seven WPW syndrome). Three had ventricular tachycardia. Fourteen patients were treated with direct current shock ablation (DC) and seven patients with radiofrequency ablation (RF). Eight patients underwent ablation of the His bundle. In six patients permanent AV block could be induced and in two first-degree AV block. All became asymptomatic (two with additional antiarrhythmic drug therapy). In four patients with WPW syndrome DC ablation of the accessory pathway was attempted. In one patient a permanent block in the accessory pathway and in another an intermittent block were obtained. In the two remaining patients with accessory pathways the ablation failed to interrupt the retrograde conduction: in one the retrograde conduction was modified; however, in the other no change could be demonstrated. Two patients underwent ventricular foci ablation, with one partial success (arrhythmia controlled with associated drug therapy) and one failure. Three patients had RF His bundle ablation (two for atrial flutter and one for atrial fibrillation). One complete atrioventricular block, one first degree AV block and one first degree AV block associated with right bundle branch block were induced. Recurrence of tachyarrhythmias was prevented only in the patient with complete atrioventricular block. RF ablation of accessory pathway was performed in three patients.(ABSTRACT TRUNCATED AT 250 WORDS)