Catheterization technique for laser photoablation of atrioventricular conduction from the aortic root in dogs

Monitoring of laser effects on the conduction system by using an open-irrigated electrode-laser mapping and ablation catheter: laser catheter mapping

AIMS

To assess the laser effects on the conduction system in dog hearts by monitoring potential amplitudes (PA) in the focused local electrograms (LEG) recorded via pin electrodes (PEs) from the tip of an open-irrigated electrode-laser mapping and ablation (ELMA) catheter.

METHODS AND RESULTS

A total of 54 mapping guided laser impacts (continuous wave Nd:YAG 1064 nm), at 15 W, irrigation rate 30 mL/min, one per dog, were aimed at the sinus nodal (SN) (n = 20) and atrioventricular (AV) nodal (n = 24) areas, and at the His bundle and fascicles (n = 5, each). Laser effects were assessed by monitoring of PA in the bipolar focused LEGs. Electrophysiological and electropharmacological tests were performed prior to, immediately following, and 3-11 months after the experiments. Lesions were evaluated morphometrically and histopathologically. During laser application PA gradually dwindled. Radiation times limited to 3-5 s were allowed for recovery of PA without affecting functions of the conduction system. Graded laser application modulated SN and AV nodal functions permanently, or caused stable complete AV conduction block with a mapping-dependent escape rhythm and electrical axis deviation after radiation aimed at a fascicle.

CONCLUSIONS

Monitoring of PAs recorded in the LEG via PE of the ELMA catheter during laser application is a unique claim of the laser method that enhances the assessment of local electrical activity and ablation efficacy. It allows the assessment of laser effects on the conduction system during ablation. By using the ELMA catheter described, long-term modulation of SN and AV nodal functions are achievable and unwanted complete heart block or fascicular block can be avoided.

What is the most appropriate energy source for aortic cusp ablation? A comparison of standard RF, cooled-tip RF and cryothermal ablation

BACKGROUND

Certain tachycardias can be eliminated by catheter ablation from within the base of the aortic valve (AV) cusps but the high blood flow and proximity to the coronary arteries create unique challenges. Standard radiofrequency (RF) energy, cooled-tip RF energy or cryothermal energy were compared to determine the optimal ablation modality.

MATERIALS AND METHODS

Experiments were conducted using adult swine or goats (15 animals). Ablation lesions were placed using either: temperature-controlled RF (4 mm-tip catheter; 60 degrees C/60 s), cooled-tip RF (4 mm-tip catheter with internal saline circulation at 0.6 ml/s; 40 degrees C/60 s), or cryoablation (6 mm-tip spot cryocatheter; <-75 degrees C/4 min). Animals were sacrificed 1 h after the last application and lesions were subject to pathological analysis.

RESULTS

Standard RF and cryoablation created similar depth lesions in the right coronary cusp (4.2+/-1.3 and 3.4+/-0.5 mm, respectively) but cryoablation was unable to create any visible lesions in the non-coronary cusp. Cooled tip ablation created larger ablation lesions in the right coronary cusp (5.25+/-0.5) and fully transmural left atrial ablation lesions after ablation in the noncoronary cusp. Acute damage to the cusps was not noted with any ablation modality. Disruption of elastic fibers in the aortic media was seen after standard and cooled tip radiofrequency ablation but not cryoablation.

CONCLUSION

Cryoablation within the AV cusps created similar sized lesions to standard RF ablation without evidence of elastic fibre disruption and may therefore be an appropriate first line ablation modality. Cooled-tip ablation created larger ablation lesions and therefore may be required if cryoablation is ineffective.

Transcatheter neodymium-yttrium-aluminum-garnet laser coagulation of canine ventricle using a balloon-tipped cardioscope

The feasibility of transcatheter laser ablation of the canine left ventricle (LV) was tested using a newly developed cardioscope. In 17 anesthetized dogs, a combined laser-endoscope catheter, consisting of an endoscope encased in a 7-French flexible catheter with an inflatable and transparent balloon at the distal end, was introduced into the LV via the carotid artery. A 1064-nm neodymium-yttrium-aluminum-garnet (Nd:YAG) laser was delivered by laser optic fiber, which was introduced through the transport channel and positioned inside the saline-filled balloon. In 16 of 17 dogs, the endocardial surface of the LV was clearly observed. Laser energy totaling 500-5,000 J was applied sequentially in 13 dogs and laser irradiation was completed in all but 2 of the dogs. The excised hearts revealed well-demarcated oval-shaped lesions 2.5-9.5 mm deep in 7 of 11 dogs. Histologic sections revealed coagulation necrosis surrounded by a rim of contraction band necrosis. Thus, transballoon laser photocoagulation of the beating LV is feasible. The newly combined laser-endoscope catheter, which is still in its preliminary stages and needs to be improved to increase the success rate of photocoagulation, appears to be a promising alternative modality for catheter ablative therapy for ventricular tachycardia.

Myocardial temperatures during in vivo endocardial Nd:YAG laser irradiation

To determine safety and efficacy of neodymium:YAG laser irradiation of the endocardium, temperatures at both the epicardium and the endocardium were recorded for thermal damage evaluation. A total of 48 coagulation lesions were created at power settings of 20 and 30 W in 20 open chest dogs by transcatheter endocardial laser irradiation. Tissue temperatures were monitored by epicardial thermography (Tepi), and by endocardial thermocouples at the catheter tip (Tprox) and 4 mm below the endocardial surface (Tdist). In group I the optical fiber extended 1 mm from the catheter and irradiation times ranged from 3 to 60 sec. Tepi reached > or = 57 degrees after a weighted average of 5 sec of laser irradiation (n = 44). In group II the fiber was retracted 1 mm from the catheter tip, and irradiation times were 100 to 150 sec. Tepi reached > or = 57 degrees C after a weighted average of 30 sec (n = 4). Blood vessels were recognized as heat sinks until coagulation occurred. Lesion volume showed a proportional increase with total delivered energy. From the observed timeframes in epicardial temperature rise it is suggested that total direct light absorption at the epicardium was the main contribution to Tepi, and the Nd:YAG laser can efficiently create transmural lesions. The epicardial temperatures remained below 80 degrees C in combination with the constant movement of the epicardial wall suggested safety from thermal damage to the ambient organs.

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.