Armin Heinze

Laser versus radiofrequency catheter ablation of ventricular myocardium in dogs : A comparative test

To compare the effects of laser light with those of radiofrequency (RF) current on ventricular myocardium, a total of 36 lesions (endocardial approach n = 10 each and epicardial approach n = 8 each) were produced by either transcatheter laser (Nd:YAG, 1,064 nm, 30 W, 30 s) or RF (70 degrees C, 30 s) catheter applications in the beating hearts of 4 dogs. Volumes of coagulated myocardium in endo-/epicardial approaches were 996 +/- 73/1,075 +/- 82 (laser) and 111 +/- 38/44 +/- 5 mm3 (RF). RF lesions showed intramural bleeding, rupture and dissociation of myocardial fibers, tissue vaporization with crater and thrombus formation. Transcatheter application of laser light produced significantly larger and better reproducible lesions than RF current, without undesirable effects on the ventricular walls.

Laser catheter coagulation of normal and scarred ventricular myocardium in dogs

Larger lesions would increase success rates of catheter ablation of ventricular arrhythmias. Therefore, improved radio frequency current application techniques, but also alternative energy sources, are being investigated. The purpose of this study was to determine morphology and dimensions of ventricular lesions induced by transcatheter application of laser energy.

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.

In vivo temperature measurement during transcatheter endomyocardial Nd-YAG laser irradiation in dogs

Intramural temperatures were monitored during catheter-directed endomyocardial non-contact laser irradiation by means of an array of thermocouples inserted epicardially. Via a novel electrode-laser catheter, a total of 30 Nd-YAG laser pulses, 1064 nm, 25 W/15 s, 20 W/30 s, 15 W/45 s,n = 10 each, were aimed at various endocardial sites in the ventricles of four dogs. Temperatures increased gradually after the onset of the laser pulses. Maximum values were measured in the central area of the irradiated spots: 100 ± 15 ‡C at 25 W, 78± 23 ‡C at 20 W and 80 ± 13 ‡C at 15 W. Application of 300 J of laser energy induced significantly higher temperatures at 25 W (p< 0.02) than at 20 or 15 W (20vs 15 W: p> 0.05). Initial temperature rise and lesion formation was accompanied by dwindling of local electrical potentials. There was no crater formation. Transcatheter non-contact Nd-YAG laser coagulation of healthy ventricular myocardium can be performed in a safe and controllable manner at power settings up to 20 W and laser energies up to 675 J.

Uniform light distribution in hollow organs by means of backscattering layers

The uniform distribution of light over the area to be photodynamically treated is one of the prerequisites for a successful tumor therapy. For homogenization of laser light distributions especially in hollow organs a new method has been developed. It applies fiber coupled emitters in combination with a highly backscattering layer deposited on the inner wall of the organ to be irradiated. The effect of homogenization by means of this layer has been calculated for spherical and cylindrical hollow organs and compared with experimental results. This method also seems to be applicable for organs with irregular geometry. Laser light applications for different medical fields will be described. Applying the same method, isotropic light detectors with diameters of less than 1 mm have been developed for irradiation control during photodynamic treatment or for determination of light distributions in tissue.

Irradiation modalities for photodynamic therapy

For photodynamic therapy of tumors in hollow organs a homogeneous distribution of the applied laser light is desirable but often difficult to be achieved. Different irradiation modalities are compared in this paper. A method for homogenization of light using a layer of a highly backscattering medium deposited on the wall of the organ is described. The homogenization effect is studied theoretically for spherical and cylindrical hollow organs and, in part, compared with experimental results. An irradiation efficiency of more than 90% of the applied light dose is expected, i.e. losses can be reduced to 10% only.

Laser recanalization of peripheral arteries

The aim of this study was to assess safety and efficacy of excimer laser (XeCl, 308 nm) recanalization of diseased peripheral arteries not amenable to conventional balloon dilatation. In 21 patients (ages 44–77) with multiple vascular lesions, laser recanalization of 43 calcified occlusions (2–5 per patient) of 0.5–17.5 cm in length; iliac (21 iliac lesions in 9 patients: group I, 31 femoropopliteal lesions in 12 patients: group II) was attempted. Laser irradiation (60–80 mJ io:/mm2 and 120 ns per pulse, 20 Hz) was applied via concentric and excentric multifiber 4.5–9.0 Fr catheters. In group I, perforation of the aortic wall occurred in one, long-term patency, and normal pain-free walking distances were achieved in all nine patients. In group II, perforation/dissection occurred in four, successful recanalization resulted in peripheral embolization in three, and late reocclusion occurred in two patients. However, clinical improvement (Fontaine class 0–II) could be verified in 7 (60%) of the 12 patients in a follow-up of 9–34 months. Excimer laser recanalization is an alternative to surgical revascularization in patients with peripheral artery occlusions not amenable to conventional percutaneous angioplasty procedures.

Simulation of heat generation for transcatheter Nd-YAG laser photocoagulation of myocardium

Nd-YAG laser photocoagulation is a successful technique for the intraoperative treatment of arrhythmia. Experimental endocardial transcatheter laser application, however, occasionally causes tissue vaporization and perforation. Intramural heat generation was simulated in a Monte Carlo model as a function of laser beam profile and divergence versus individually varying tissue properties. Heat generation at the tissue surface was dominated both by the beam profile and the individual tissue properties. High beam divergence may help to reduce heat accumulation in subsurface regions. Heat distribution in depth as well as backscattering are not substantially influenced by beam parameters but are mainly determined by the optical tissue properties. Surface colling can help to avoid overheating. A catheter, concept for safe endocardial photocoagulation is presented including a highly divergent beam of maximized, spot size, an effective catheter flushing, and shielding of blood.