Permanent AV Block or Modification of AV Nodal Function by Selective AV Nodal Artery Ethanol Infusion

The acute and chronic effects of selective AV nodal artery ethanol infusion on AV nodal function was studied in 9 closed chest anesthetized dogs. Using standard percutaneous techniques of arterial catheterization, a 2.2 French infusion catheter was positioned in the AV nodal artery. Ten minute infusions into the AV nodal artery of 25%, 50%, or 100% ethanol in normal saline at rates of 0.5 mL/min acutely resulted in complete AV nodal block (AVB) in 5 dogs, 2:1 AV nodal block in 1 dog, and prolongation of AV nodal effective refractory period and/or Wenckebach cycle length in the remaining 3 dogs. One dog died with persistent complete AV block 1 week after the ethanol infusion. When restudied 4 weeks later, 7 of the 8 surviving dogs had persistent modification of AV nodal function, including complete AV block in 5 dogs and lengthening of AV nodal effective refractory period and/or Wenckebach cycle length without AV block in 2 dogs. Pathologic examination of the animals exhibiting chronic modification or ablation of AV nodal function revealed healing infarction of the AV node or its approaches. Distant myocardial necrosis was not observed and left ventricular function was normal. Slow infusion of low concentrations of ethanol into the AV nodal artery results in AV nodal modification or ablation due to localized necrosis in or around the AV node. This technique may have a role in AV nodal modification or ablation, particularly in patients who have failed DC shock or radiofrequency ablation.     

Modification of Atrioventricular Conduction Using a Combined Laser-Electrode Catheter

Ablation of the AV junction is an accepted technique for the management of selected supraventricular tachyarrhythmias. Radiofrequency ablation appears to be safe and effective for AV junction ablation in most patients, but the need for firm tissue contact may make it less effective for ventricular tachycardia and certain ectopic atrial tachycardias. Laser energy can also be delivered through a catheter, and thus it may be an attractive alternative energy source for ablation. A new laser-electrode catheter was developed for modification of conduction through the AV node as a model for ablation of an arrhythmia substrate. A window for delivery of continuous-wave Nd:YAG laser energy was placed between the two electrodes of a bipolar electrode catheter. In vitro studies using a matrix of power versus time were performed to determine the energy that would create lesions of the appropriate size in vivo. Using this information, advanced AV block was successfully created in 16 of 17 dogs (94%) with the laser-electrode catheter. Advanced AV block was successfully created in all four dogs in the chronic study, and it persisted for 1-24 weeks of follow-up until sacrifice of the animals. Histologic examination demonstrated discrete thermal damage at the AV junction with no instances of septal perforation in the acute studies or progressive necrosis in chronically maintained dogs. Advanced AV block may be produced consistently and safely in dogs using a combined laser-electrode catheter.     

Mapping Guided Laser Catheter Ablation of the Atrioventricular Conduction in Dogs

Safety and efficacy of mapping guided laser catheter ablation of the AV junction was tested in a canine model. A total of 43 laser pulses (continuous wave, Nd:YAG, 1,064 nm, 30 W, irradiated spot diameter 2.0–2.5 mm) were delivered in 15 dogs (2–5 per dog) via a novel laser catheter system. Pulses were selectively aimed at: (1) the AV node: (2) the His bundle; and (3) the bundle branches. Laser pulses of 9.7 ± 1.1 seconds (n = 31) produced reversible conduction disturbances in the targeted segment of the AV conduction system, while pulses of 28.6 ± 7.9 seconds (n = 9) resulted in chronic block. The dogs survived the procedure without complications. Follow-up was 6.5–10.5 months. Histopathologically, lesions showed clear-cut oval-shaped areas of fibrosis of 0.5–18.0 mm in diameter and 0.5–3.5 mm (transmural) in depth, depending on the irradiation time. Pervenous mapping guided laser catheter irradiation of the AV junction can produce AV block consistently and selectively in the targeted segment of the right ventricular conduction system in dogs. The method is safe and can be performed in a controllable manner by using the catheter system presented.     

Electrophysiologic and Histologic Observations of Chronic Atrioventricular Block Induced by Closed-Chest Catheter Desiccation with Radiofrequency Energy

Direct-current or laser energy has been used to induce atrioventricular (AV) block, but certain complications associated with this type of energy have been reported. We have previously documented that radiofrequency (RF) energy can effectively and safely induce acute AV block in ciosed-chest dogs during the 4–7 days of follow-up. This study was undertaken Io determine if the ablation was permanent and to define the chronic pafhoiogy and site of AV block. Gomplete AV block was successfully achieved in four dogs immediately after ablation with a bipolar "standard" RF output (750 kHz) delivered between the tip electrode of a standard 7F USCI catheter and an external patch electrode on the left iateral chest wall. During 2 months of follow-up, three dogs had persistent complete AV block with a stable escape rhythm; the other had persistent 2:1 AV block. Repeat His bundle recordings were performed at 2 months prior to sacrifice of the dogs. Supra-His AV block was noted in two dogs; His bundle potential could not be recorded in another two. Histologically, the damaged area was well delineated. In all animals, the AV node and, in some dogs, part of the His bundle were completely replaced by granulation tissue and/or cartilage. There was fatty infiltration and also chronic inflammatory cells around the lesions. Neither perforation, hemorrhage nor vacuolation was seen in the adjacent area. Thrombus was not present. It is concluded that RF energy can effectively achieve chronic AV block and produce well-circumscribod pathological lesions.     

Closed Chest Radiofrequency Ablation of the Sinoatrial Node in Dogs

Transcatheter ablation of the sinoatrial node with radiofrequency energy (0.6 MHZ, 2.5-5 watts) was performed in 10 dogs under fluoroscopic monitoring and autonomic blockade. Sinus function was previously studied in terms of cycle length, recovery time and atrial activation pattern by catheter mapping. Several discharges (8-22) were applied for variable periods of time (maximum 1 minute). Sinus tachycardia and/or sinus arrest during ablation confirmed correct catheter position. Sinus rhythm was abolished in eight dogs. The ectopic rhythm was atrial in six and AV nodal in two dogs. Ectopic atrial cycle length and recovery time were longer than the baseline sinus values: 724 +/- 321 versus 509 +/- 147, P less than 0.05; 1103 +/- 775 versus 618 +/- 151, P less than 0.05 (values in msec). The study was repeated 10-14 days later in six dogs; three maintained the same atrial rhythm, one persisted in sinus rhythm, and one dog changed from atrial to sinus rhythm, whereas another changed from sinus to atrial rhythm. Gross findings revealed transmural lesions in all dogs, without perforation. Histology in chronic dogs showed sinus cell necrosis and its replacement by granulation tissue. In conclusion: sinus function may be abolished by closed chest radiofrequency ablation.     

Impact of duration of cryothermal application on clinical efficacy of pulmonary vein isolation using transvenous cryoablation

BACKGROUND: Recent studies have demonstrated that transvenous cryoablation is a safe and feasible method for pulmonary vein (PV) isolation for treatment of atrial fibrillation (AF). However, this technique is limited by a much longer ablation time than conventional radiofrequency ablation. The aim of this study was to determine the effect of duration of cryoablation application with double freeze-thaw cycles on clinical efficacy for PV isolation for treatment of AF. MATERIALS AND RESULTS: We compared the clinical efficacy and procedural time of cryoablation (CryoCorTM, San Diego, CA, USA) for segmental PV isolation in 30 patients (mean age 51 +/- 13, 20 men) with paroxysmal AF using either double 5-minute (n = 15) or double 2.5-minute (n = 15) freeze-thaw cycle delivered with a 10 F deflectable transvenous catheter. Clinical recurrence of AF and the occurrence of PV stenosis as determined by computer tomography of the thorax were performed at 3- and 12-month follow-up. Acute successful electrical isolation of PV was achieved with cryoablation in 96 of 98 (98%) targeted PVs in 30 patients (mean: 3.2 +/- 0.8 PVs per patient). There were no significant differences between the baseline characteristics, the number of PV isolated per patient, the total number and percentage of effective cryoablation and the acute clinical efficacy between using double 5-minute and double 2.5-minute freezes (P > 0.05). However, the fluoroscopy time (107 +/- 43 vs 138 +/- 113 minutes, P = 0.06) and the procedural time (360 +/- 113 vs 510 +/- 115 minutes, P = 0.01) of using double 2.5-minute freezes was reduced by approximately 30% compared with double 5-minute freezes. At a mean of 20 +/- 8 month follow-up, there was no significant difference in the chronic clinical efficacy of cryoablation in terms of freedom from AF in the absence of antiarrhythmic drug therapy between using double 5-minute (6/15, 40%) and double 2.5-minute freezes (7/15, 46%, P = 0.98). CONCLUSION: As compared with double 5-minute freeze, the use of a shorter double 2.5-minute freeze protocol significantly reduces the procedural time without affecting the acute and long-term clinical efficacy of cryoablation to isolate PV for treatment of AF.     

In Vitro and In Vivo Results of Transcatheter Microwave Ablation Using Forward-Firing Tip Antenna Design

This study was designed to test a microwave (MW) ablation system using approximately 2,450 MHz of energy and a deflectable catheter with forward-firing tip antenna, an early clinical prototype system. In vitro three-dimensional thermal mapping of single and double helix antenna designs was performed. Quantitative measurements of antenna radiation were recorded on tissue phantoms equipped with temperature sensors distributed radially and outwardly. In vivo testing consisted of closed-chest AV junction ablation in three dogs. Thermal mapping showed hemispherical heat distribution from the tip antenna. For the double helix design, this distribution was measured at 8,4-mm diameter with a maximum temperature of 61.62°C. As expected, the single helix design produced less heating with a measured diameter of 6.4 mm and maximum temperature of 55.90°C. The in vivo study produced lesions of geometry and size concordant with these heating patterns. MW ablation produced bundle branch block in one dog and complete AV nodal block in the remalning two, without transvalvular or other structural damage. The histopathology of the lesions was typical of a thermal burn showing hemorrhage and coagulative necrosis with clearly demarcated borders. We conclude that, using this early clinical prototype system with a deflectable catheter and a forward-firing tip antenna design, MW heating can produce a moderate-size lesion and is safe and effective for cardiac ablation.     

Radiofrequency Ablation of Pediatric AV Nodal Reentrant Tachycardia during the Ice Age: A Single Center Experience in the Cryoablation Era

Background: Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia (AVNRT) has proven to be an effective therapy in the pediatric population. However, concerns of inadvertent permanent AV nodal block have resulted in many pediatric programs adopting cryoablation as their primary ablation approach for AVNRT.
Methods: A retrospective analysis of the results of pediatric radiofrequency catheter ablation at a single institution over the most recent 5 years (January 2004 through December 2008) was performed. Acute, intermediate, and long-term success, along with the incidence of AV block, were determined.
Results: There were 65 patients with a mean age of 12.1 ± 5.2 years and weight of 46.5 ± 17.3 kg who underwent radiofrequency catheter ablation for AVNRT. There was 100% acute success with no recurrences at a mean follow up of 32.5 months. Although two patients had a brief second-degree AV block, there was no permanent AV block of any degree.
Conclusions: The safety and efficacy of radiofrequency catheter ablation for pediatric AVNRT demonstrated in this study support its continued application and should not be abandoned as a method of treatment. (PACE 2010; 6–10)     

Effects on Cardiac Performance of Atrioventricular Node Catheter Ablation Using Radiofrequency Current for Drug-Refractory Atrial Arrhythmias

Patients with atrial fibrillation or atrial flutter (AF) are candidates for radiofrequency (RF) catheter ablation of the atrioventricular (AV) node with the aim being to control heart rate. As patients wilh AF can have markedly impaired ventricular function, information concerning the hemodynamic effects of AV node ablation using RF current would be valuable. Fourteen consecutive patients (mean age 65 ± 3 years) with drug-resistant AF underwent AV node catheter ablation with RF current and had permanent pacemaker implantation. The mean left ventricular ejection fraction (FFJ by two-dimensional echoeardiography immediately before ablation was 42 ± 3% (range 14%–54%) and their mean exercise time was 4.4 ± 0.4 minutes. Complete AV block was achieved in all 14 patients with 6 ± 2 RF applications (range 1–18). There was no evidence of any acute cardiodepressant effect associated with delivery of RF current, and EF 3 days after ablation was 44 ± 4%. By 6 weeks after ablation, the left ventricular EF was significantly improved compared to baseline (47 ± 4% postablation vs 42 ± 3% preahlation; P < 0.05), and this modest increase in EF was accompanied by an improvement in exercise time (5.4 ± 0.4 min). In conclusion, delivery of RF current for AV node catheter ablation in patients with AF and reduced ventricular function is not associated with any acute cardiodepressant effect. On the contrary, improved control of rapid heart rate following successful AV node ablation is associated with a modest and progressive improvement in cardiac performance.     

Modification of Atrioventricular Conduction by Selective AV Nodal Artery Catheterization

The effects of selective AV nodal artery embolization on AV nodal function was investigated in six closed-chest adult dogs. Programmed atrial stimulation was performed to determine control values for AV nodal effective refractory period (AVN-ERP) and the paced cycle length at which AV nodal Wenckebach conduction occurred (WCL). Using standard percutaneous femoral techniques of coronary artery catheterization, a flexible infusion catheter was positioned selectively in the AV nodal artery. Proper positioning of the catheter was confirmed angiographically and by selective acetylcholine (ACH) infusion into the AV nodal artery, which caused transient complete AV nodal block in three dogs, and for the group, caused lengthening of both AVN-ERP and WCL. Following cessation of ACH infusion and autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg, denervated recontrol values for AVN-ERP and WCL were 192 msec and 243 msec, respectively. The AV nodal artery was then embolized with a suspension of cross-linked collagen fibrils in either normal saline or absolute ethanol. Successful embolization of the AV nodal artery, confirmed angiographically, caused an acute increase in AVN-ERP (243 msec, P less than 0.05 compared to denervated control) and WCL (287 msec, P = 0.058 compared to denervated control). However, at a mean follow-up of 37 days, only one animal exhibited a chronic increase in AVN-ERP and WCL. Selective AV nodal artery catheterization can be performed using standard percutaneous catheterization techniques. Selective administration of agents with direct cidal effects on the AV node using this technique may provide an alternative to conventional methods of catheter ablation of AV conduction in patients with drug-resistant supraventricular arrhythmias.