Chi Hui Chuang

Catheterization Technique for Laser Photoahlation of Atrioventricular Conduction from the Aortic Root in Dogs

A simple catheterization technique for producing suppression or block of atrioventricular (AV) conduction in dogs by neodymium:YAG (Nd:YAG) laser photocoagulationfrom the aortic root is described. In 14 canines, electrode catheters were percutaneously advanced to the high right atrium, to the His bundle area at the tricuspid valve (right His (RHJ), and the noncoronary cusp of the aortic valve (left His [LH]). A 400μ optical fiber was fed into the lumen of the LH catheter. Continuous wave Nd:YAG lasing at λ= 1,064 nm at 15–20 watts was performed at the site of the largest recorded LH deflection, opposite ta the RH catheter, until complete AV block (CAVB, group I, eight dogs) or persistent A‐H prolongation (AHPr, group 11, four dogs) occurred; in two animaJs, laser photoablation was unsuccessful. CAVB and AHPr were achieved in < 140 seconds of lasing. Mean lasing time was 51 ± 41 seconds, total energy delivered, 776 ± 601 J. There were no complications. Dogs were followed for up to 120 days. In group I, 6/6 dogs followed /or at least I week continued to have CAVB (three AV nodal, five infra‐His). In group II, 1/4 dog progressed to infra‐His CAVB; 3/4 had depressed AV nodal function. AV block was not reversed by isoproterenol. Aortic root angiograms revealed intact valve function in all. Histology showed various degrees of damage and repair of AV functional tissue. There were no valvular perforations. Transcatheter Nd:YAG laser photocoagulation of the AV junction from the aortic root is a fast, simple, and safe method for creating AV conduction block in dogs.

Selective coagulation necrosis of canine adventitia and media induces extracellular matrix accumulation without neointima formation

Endothelial cell injury, the disruption of the internal elastic membrane and medial damage represent important stimuli for the development of a neointima. It is unclear whether selective adventitial and medial injury also induce neointima formation. Incremental argon laser energies (11.4-180 J/cm2) were applied to the external surface of dog femoral arteries to evaluate the vascular repair of acute adventitial or medial necrosis without injury of the intima. The animals were sacrificed either one hour after the initial procedure or after an 8 week follow up period for histologic examination. Acute, and mild to moderate necrosis of the arterial wall was found above 50 J/cm2. Ablation of the internal elastic membrane or mural thrombi was not detected. Eight weeks after photocoagulation with laser energies above 50 J/cm2, a significant increase in mean wall thickness of the media was observed. The medial thickening was characterised by an accumulation of extracellular matrix and a loss of smooth muscle cells. Necrosis of adventitia and media resulted in arterial wall thickening without neointima formation. It is concluded that, in dogs, an acute, selective injury of adventitia and media stimulates the production of extracellular matrix and not the proliferation of cells. Smooth muscle cell migration and subsequently neointima formation are induced by viable smooth muscle cells when blood-borne stimuli are available.

Myocardial temperature distribution under cw Nd:YAG laser irradiation in in vitro and in vivo situations: theory and experiment

Tissue samples ranging from 2 to 16 mm in thickness were irradiated at 1064 nm with energies ranging from 40 to 2400 J. Coagulation lesions of in vitro and in vivo experiments were subjected to temperature profiling and submitted for histology. Irreversible damage was calculated with the damage integral formalism, following the bioheat equation solved with Monte Carlo computer light-distribution simulations. Numerical temperature rise and coagulation depth compared well with the in vitro results. The in vivo data required a change in the optical properties based on integrating sphere measurements for high irradiance to make the experimental and numerical data converge. The computer model has successfully solved several light-tissue interaction situations in which scattering dominates over absorption.

Computer simulated light distributions in myocardial tissues at the Nd-YAG wavelength of 1064 nm

Continuous wave Nd-YAG myocardial laser photocoagulation of ventricular tachycardia at the 1064 nm wavelength is a new investigational procedure in the treatment of arrhythmias. Computer simulated light diffusion patterns, generated by the Monte Carlo technique, are used to illustrate the calculated light distribution in myocardial tissues such as normal, and photocoagulated (canine) myocardium, epicardial fat on myocardium, and aneurysm for the optical properties at the Neodymium-YAG wavelength of 1064 nm.Calculated total reflection from myocardial tissue increased from 16% to 28% as a result of photocoagulation in the Monte Carlo light distribution simulations. The calculated total transmission dropped from 0.8% to 0.1% as a result of coagulation. Transmission reduced from 5% to 0.8% due to an increase in absorption from 0.04 mm−1 to 0.1 mm−1, based on capillary blood absorption. Adding an epicardial fat layer to normal myocardium total reflection and backscatter increased from 16% to 44%.Computer simulations for normal and pathological myocardium showed a wide diversity in light propagation characteristics, indicating the importance of including all myocardial tissues in light dosimetry analyses.

Computerized three-dimensional activation mapping study of spontaneous ventricular arrhythmias during acute myocardial ischemia in dogs: evidence against macroreentrant mechanism

This study was undertaken to investigate the activation patterns of spontaneous ventricular arrhythmias during acute myocardial ischemia in dogs. In 14 open-chest dogs, the left anterior descending coronary artery was occluded for 2 hours. Three-dimensional activation maps were derived from 240 bipolar sites by insertion of 60 plunge needle electrodes into both ventricles and the septum. Global ventricular activation sequences were displayed in five planes in 10 dogs, whereas the high density regional activation maps of the anterior wall were displayed in four layers in 4 dogs. Three-dimensional activation maps of 95 sinus beats, 82 premature ventricular complexes (PVCs), and 210 beats of ventricular tachycardia (VT) were analyzed. Sinus beats had a uniform activation pattern with total ventricular activation times measuring 42 +/- 4 ms and 67 +/- 8 ms during baseline and ischemia, respectively (P < .05). The PVCs and VTs originated from the subendocardial and intramural layers, and activation patterns invariably suggested focal excitation. Macroeentry was not operative because (1) the breakthrough sites were always remote from the latest activation areas; (2) there was no electrical activity bridging the gap between the termination of a beat and initiation of the subsequent beat; and (3) impulse conduction was not sufficiently delayed to reexcite the area of impulse origin even though functional conduction block was frequently present. In high-density regional activation maps, fragmented activity spanning the diastolic interval was never found. In conclusion, spontaneously occurring PVCs and VTs during acute myocardial ischemia in dogs display focal excitation with no evidence of macroreentry.

Current Status of Lasers for Arrhythmia Ablation

Current Status of Lasers for Arrhythmia Ablation. Wavelength specific effects and mode of laser operation allow either photocoagulation or tissue removal as a means of approaching arrhythmia ablation. Successful intraoperative ablation of ventricular tachycardias has been performed with the Nd: YAG laser (photocoagulation) and argon laser (tissue vaporization). The argon laser has been used intraoperatively for transection of accessory pathways. Experimental studies indicate a strong theoretical potential for Nd:YAG laser catheter ablation of ventricular tachycardia. Laser energy has been used experimentally to evaluate the possibility of AV junctional ablation/modification and accessory pathway ablation. Adaption of laser energy to effective catheter systems for arrhythmia ablation requires solutions to problems inherent in all catheter systems and some unique to laser energy. (J Cardiovasc Electrophysiol, Vol. 3, pp. 345–353, August 1992)

Selective elimination of retrograde conduction by intraoperative neodymium: YAG laser photocoagulation in dogs

OBJECTIVES The purpose of this study was to test the feasibility of selective elimination of ventriculoatrial (VA) conduction by limited laser photocoagulation of the atrioventricular (AV) node, and to analyze the histologic substrate of unidirectional retrograde block. BACKGROUND Atrioventricular node reentry requires intact retrograde conduction. METHODS Neodymium:yttrium-aluminum-garnet laser photocoagulation was performed during cardiopulmonary bypass through a right atriotomy in 15 dogs that had intact retrograde conduction before operation. Short laser pulses were delivered to an area between the coronary sinus orifice and the proximal His bundle. The end point of lasing was second-degree AV node block at a paced atrial cycle length of 250 ms. RESULTS Complete retrograde block developed immediately in 11 of the 15 dogs (group I), while AV conduction persisted in all 11. In 4 of the 15 dogs (group II), both AV and VA conduction remained intact. During a 3-month follow-up period, retrograde conduction remained absent in all group I dogs. Retrograde block was not reversed by isoproterenol. Anterograde AV node characteristics (Wenckebach cycle length, functional refractory period, ventricular rate during atrial fibrillation) were unchanged in five dogs and modified in six. Complete AV block did not develop. In four control dogs (group III, sham operation), anterograde and retrograde AV node characteristics were unchanged. The anterograde Wenckebach cycle lengths in groups I, II and III at 3 months measured 192 +/- 15 ms, 195 +/- 6 ms and 170 +/- 22 ms, respectively, whereas the retrograde Wenckebach cycle lengths in groups II and III measured 345 +/- 62 ms and 278 +/- 25 ms, respectively. Histologic study at 3 months in cases with unidirectional VA block showed the compact part of the AV node intact with destruction of the atrial approaches and the superficial layers of the proximal end of the node on the right side. CONCLUSIONS 1) With limited laser photocoagulation of the proximal AV node area, VA conduction can be eliminated and anterograde AV node transmission maintained. 2) Destruction of the atrial approaches on the right side with preservation of the compact part of the AV node may result in unidirectional retrograde block.

Non-linear optical phenomena in contact fiber laser-photocoagulation of myocardium

The rise time of epicardial temperatures on the left ventricular free wall during endocardial transcatbeter delivery of Nd:YAG laser energy, recorded by thermography has sparked interest in anomalous optical phenomena. Transmission measurements on whole blocks of myocardium showed a decrease in the attenuation coefficient at high power densities. The definition of the attenuation coefficient is the natural log of the ratio of the incident and the transmitted beams, divided by the physical thickness of the sample. When Nd:YAG laser light at the 1064 um wavelength irradiated fresh myocardial tissue from the free left ventricular wall, the incident power density increased from 0.0026 W/mm2 to approximately 200 W/mm2, the attenuation coefficient dropped from 0.97 ± 0.11 mm−1 to 0.77 ± 0.07 mm−1. This would indicate a non-linearity in the optical properties of the tissue as a function of the laser irradiation power density.

Laser photoablation of experimental post-infarction ventricular tachycardia guided by three dimensional activation mapping

The purpose of this study was to evaluate the efficacy of epicardially delivered laser energy to ablate induced ventricular tachycardia in a post‐infarction canine model.

Optical Changes In Myocardial Tissue Due To CW ND-YAG Irradiation

Administration of laser energy will be facilitated by a better understanding of the optical properties of the myocardium and the changes in optical properties during laser irradiation. The purpose of this study was (1) tc compare the optical properties of canine myocardium before and after laser irradiation and (2) to compare the optical properties of canine and human myocardium. Measurements were made with the double integrating sphere method. This study shows (1) a 40% increase in scattering coefficient as a result of photocoagulation and (2) that human and canine myocardium have comparable optical characteristics. The optical properties for normal and photocoagulated canine myocardium and for normal human myocardium are presented in Table 1. Photocoagulation resulted in a significant increase in scattering coefficient by 40% (P<O.Ol) and a 3% decrease in scattering anistropy factor (Pt0.01). No significant differences were found between the optical properties of normal canine and human myocardium.