Unipolar Ablation Research Articles

Out-of-phase Vs. Unipolar Ablation using Multiple Electrode Cardiac Catheters for Creating Continuous Lesions

Background: Unipolar RF energy delivery has been attempted with multiple electrode catheters to create continuous lesions. A pitfall of this method is the lack of uniformity in the lesion dimensions (width, length and depth). Out-of-phase (OOP) RF energy delivery can optimize lesion uniformity by preferentially delivering energy between adjacent electrodes. Unipolar ablation directs energy towards the reference electrode.

Comparison of unipolar versus bipolar ablation and single electrode control versus simultaneous multielectrode temperature control

Creation of linear lesions using multielectrode catheters may be effective at treating cardiac arrhythmias. We compared unipolar versus bipolar ablation, evaluated the effects of varying effective electrode areas, and compared single electrode versus multielectrode temperature control during multielectrode radiofrequency ablation. Intramural radiofrequency ablation was performed on five greyhounds at thoracotomy, from an epicardial approach using a 0.8 mm diameter bipolar electrode needle. Fifteen left ventricular ablations were performed per animal. Intramural ablation was performed to maintain a constant electrode-tissue interface. The distal and proximal electrodes measured 1.5 and 1.0 mm in length respectively with an interelectrode distance of 4 mm. Radiofrequency energy was applied to both electrodes simultaneously for 60 s using a target temperature of 80 degrees C. During bipolar ablation, the temperature was regulated from either the distal (BPA1.5) or proximal (BPA1.0) electrode only. During unipolar ablation (UPA), the temperature at both electrodes were simultaneously controlled. Lesions were assessed histologically. During UPA, consistent target temperatures were achieved at both electrodes. In comparison to UPA, the temperature at both electrodes were significantly decreased during BPA1.0. During BPA1.5 a significant (p < 0.001) temperature increase (94.7 +/- 2.1 degrees C) was observed at the 1.0 mm electrode. BPA1.0 resulted in reduced (p = 0.008) lesion width at the 1.5 mm electrode and no change in lesion depth (p = 0.064) at both electrodes compared to UPA. Conversely, lesion dimensions increase significantly at both electrodes during BPA1.5. Unipolar multielectrode ablation with simultaneous temperature control at both electrodes is more predictable and hence likely to be safer than bipolar ablation.

A possible surgical technique to avoid esophageal and circumflex artery injuries using radiofrequency ablation to treat atrial fibrillation

A surgical technique using unipolar radiofrequency ablation is described, which minimizes the risk of damaging adjacent cardiac structures. The left atrium was fully mobilized. Linear, non-thrombogenic, white blistering lesions were created with a hand-held malleable pen-catheter, making oscillating movements, while preserving a stable endocardium contact, without pressing the atrial wall to adjacent mediastinal structures. The ablated atrial tissue was lifted up with forceps. Each pulmonary vein orifice was circumferentially ablated and interconnected on the ipsi- and to the contra-lateral side, and to the left auricle and mitral valve annulus. No esophageal or circumflex artery injuries were observed.

Modeling bipolar phase-shifted multielectrode catheter ablation.

Atrial fibrillation (AFIB) is a common clinical problem affecting approximately 0.5-1% of the United States population. Radio-frequency (RF) multielectrode catheter (MEC) ablation has successes in curing AFIB. We utilized finite-element method analysis to determine the myocardial temperature distribution after 30 s, 80 degrees C temperature-controlled unipolar ablation using three 7F 12.5-mm electrodes with 2-mm interelectrode spacing MEC. Numerical results demonstrated that cold spots occurred at the edges of the middle electrode and hot spots at the side electrodes. We introduced the bipolar phase-shifted technique for RF energy delivery of MEC ablation. We determined the optimal phase-shift (phi) between the two sinusoidal voltage sources of a simplified two-dimensional finite-element model. At the optimal phi, we can achieve a temperature distribution that minimizes the difference between temperatures at electrode edges. We also studied the effects of myocardial electric conductivity (sigma), thermal conductivity (k), and the electrode spacing on the optimal phi. When we varied sigma and kappa from 50% to 150%, optimal phi ranged from 29.5 degrees to 23.5 degrees, and in the vicinity of 26.5 degrees, respectively. The optimal phi for 3-mm spacing MEC was 30.5 degrees. We show the design of a simplified bipolar phase-shifted MEC ablation system.

Radiofrequency Catheter Ablation of the Left and Right Ventricles: Anatomic and Electrophysiologic Observations

Certain untoward effects associated with the use of direct-current electrical catheter ablation of the ventricular endomyocardium have been noted. We assessed the efficacy and safety of closed-chest catheter ablation of the left and right ventricles using radiofrequency (RF) energy (750 kHz) in six dogs. Mean RF energies between 93 and 123 joules (J) were randomly delivered to three left ventricular (LV) sites via two distal adjacent electrodes (bipolar configuration) using 6-7F USCI tripolar or quadripolar catheters with an interelectrode distance of 5-10 mm. Another 90-143 J were given to two right ventricular (RV) sites in single or multiple divided applications between a distal electrode and an external patch electrode (unipolar configuration). Ventricular arrhythmias were not observed during application of RF energy. Programmed ventricular stimulation before and after the procedure did not induce ventricular tachycardia (VT) or fibrillation except in one dog who had inducible VT prior to ablation. There were no significant changes in LV and RV effective refractory periods after the procedures. Occasional premature ventricular beats and rare episodes of non-sustained VT (3-12 beats) were observed in ambulatory electrocardiographic recordings (13-24 hrs) done immediately after ablation. Dogs were sacrificed after 4-5 days. Pathology showed well-demarcated round or ovoid lesions of varying sizes. Mural thrombus was found in one dog. Microscopic findings consisted of circumscribed areas of coagulation necrosis with a peripheral zone of cellular infiltration. Transmural necrosis without perforation was occasionally seen in the thin RV wall when higher energies were delivered. In conclusion, discrete areas of desiccation injury in the ventricles can be achieved by transcatheter bipolar or unipolar ablation using RF energy. The complications associated with this method appear to be minimal. Further experiments are needed to evaluate its potential for catheter ablation of ventricular tachycardia.

Closed chest catheter desiccation of the atrioventricular junction using radiofrequency energy—A new method of catheter ablation

Closed chest catheter ablation of the atrioventricular (AV) junction has been performed with direct current or laser energy. The effect of 750 kHz radiofrequency energy on ablation of the AV junction was evaluated in 13 dogs. The radiofrequency energy was generated from an electrosurgical generator in the bipolar mode. The radiofrequency output was delivered between two distal electrodes (bipolar ablation) in eight dogs, and between the distal electrode and an external patch electrode (unipolar ablation) in another five dogs at varying power (watts) but with a constant pulse duration of 10 seconds. Complete AV block was achieved in 11 dogs and second degree AV block in 2. During the 4 to 7 day follow-up period, complete AV block persisted in 9 of the 11 dogs with initial complete heart block. The other two had return of AV conduction; one had persistent 2:1 AV block and the other had persistent first degree AV block. Of the two dogs with initial second degree AV block, one developed complete AV block, the other had resumption of 1:1 AV conduction with a normal PR interval. Energy was delivered in 1 to 13 applications per dog. One hundred to 700 J per application was delivered with bipolar ablation and 10 to 100 J with unipolar ablation. There was no damage to the catheter unless the catheter was repeatedly used in excess of 1,500 J of total energy. Ventricular arrhythmias were not observed. Pathologic examination showed well delineated coagulation necrosis at the AV junction without surrounding hemorrhage or mural thrombus. Microscopic findings consisted of necrosis with cell infiltration in the periphery of necrosis. Most injuries involved the AV node, the approaches to the AV node and the penetrating bundle. In conclusion, catheter ablation of the AV junction with radiofrequency energy is safe. It can effectively induce discrete areas of necrosis and produce various degrees of AV block. In addition, ablation by radiofrequency energy has distinct advantages as compared with catheter ablation with direct current or laser energy.