Thermal effects of laser and electrical discharge on cardiovascular tissue: implications for coronary artery recanalization and endocardial ablation

Excimer laser ablation for valvular angioplasty in pulmonary atresia and intact ventricular septum

BACKGROUND AND OBJECTIVES

The prognosis for infants with pulmonary atresia and intact ventricular septum (PA/IVS) is poor and they present a major management challenge. Mechanical penetration of the atretic pulmonary valve is an applicable option for decompression of the right ventricle and optimization of left ventricular function. The utilization of laser energy for debulking and vaporization of the atretic valve tissue is a relevant approach due to the potential for controlled, precise mode of energy distribution.

STUDY DESIGN/PATIENTS AND METHODS

A 4-month-old female with PA/IVS whose failure to thrive was accompanied by critical hemodynamic abnormalities received successful percutaneous pulmonary valve plate ablation by a 0.9 mm pulsed-wave ultraviolet excimer laser catheter (308 nm wavelength, fluence 50 mJ/mm(2); 30 Hz). A "step-by-step" lasing technique was applied whereby the tip of the emitting laser catheter is advanced ahead of a guide wire that serves mainly as support for positioning of that catheter.

RESULTS

Adequate penetration of the atretic tissue enabled introduction of balloon dilations resulting in patency of the atretic valve, decompression of the right ventricle, improved right and left ventricular hemodynamics, and oxygenation. To further investigate the effect of excimer laser energy on atretic valvular tissue this laser was applied in a specimen of heart from an infant who died because of PA/IVS. Histopathologic examination of the irradiated tissue revealed no laser-induced injury to the pulmonary valve.

CONCLUSIONS

Thus, laser ablation and penetration of an atretic pulmonary valve is feasible and safe. The penetration of the atretic valve with the laser catheter enables subsequent introduction of various sizes balloon dilations. The application of available laser sources for treatment of congenital heart diseases is reviewed.

In vivo effect of coronary laser angioplasty on atherosclerotic plaques: histopathologic analysis

Information from histopathologic examination of coronary arterial atherosclerotic plaques treated with in vivo laser energy is sparse. Directional atherectomy provides biopsies for study of tissue changes (injury) due to coronary arterial debulking devices, including laser. Sixteen patients who presented with acute ischemic coronary syndromes underwent debulking of a total of 17 obstructive intracoronary lesions with pulsed-wave holmium:YAG laser (2.1 microm wavelength). Laser was performed with the "pulse and retreat" technique which incorporates slow catheter advancement (0.5-1 mm/s) with controlled emission of energy. Immediately postlasing, directional atherectomy was utilized to obtain irradiated plaque tissue for pathologic examination. Extent of laser-induced tissue injury to plaques was graded as 0 (no tissue damage), 1 (small foci or charring and vacuoles), 2 (large amount of charring, edge disruption and vacuoles) and 3 (extensive tissue damage). Angiographically and clinically, all 17 lesions were successfully debulked with the laser energy (mean 47+/-25 pulses), with a reduction of target lesion percent diameter stenosis from 92+/-6% to 47+/-25%. Adjunct balloon dilations further reduced the target lesions to a final of 10+/-10% stenosis. The histopathologic examination of the lased specimens demonstrated that 13 lesions (76%) had no evidence of laser-induced injury (Grade 0). Four lesions had low-level injury (Grade 1), and none had evidence of Grade 2 or 3 laser-induced trauma. Therefore, a laser debulking technique, which incorporates slow catheter advancement with controlled emission of pulses, does not cause significant injurious effects to the irradiated plaque.

Comparison of tissue disruption caused by excimer and midinfrared lasers in clinical simulation

Laser coronary angioplasty is a useful therapy for selected complex coronary lesions. Laser-induced acoustic trauma is postulated to be a cause of dissection and acute vessel occlusion. Controversy exists regarding the relative degree of photoacoustic effects of midinfrared and excimer lasers in clinical practice. To date, these systems have not been compared at clinical energy doses and with clinical pulsing strategies. Therefore, we studied the photoacoustic effects of both midinfrared and excimer lasing at clinically accepted doses. Human atherosclerotic iliofemoral artery segments were obtained at autopsy (n = 36) and placed lumen side up in a saline bath. Clinical laser catheters were advanced over an 0.018" guide wire, perpendicular to the tissue. A 10-g down force was applied to the catheter for full-thickness lasing. Pulsing strategies were, for midinfrared laser: 5 pulses, 1-sec pause, 5 pulses, 1-sec pause, 5 pulses, withdraw; for excimer: 5 sec of pulses, wait 10 sec, 5 sec of pulses. Several clinically acceptable energy levels were used; for excimer: 25 mJ/mm2, 40 mJ/mm2, 60 mJ/mm2; for midinfrared: 3 W (400 mJ/mm2), 3.5 W (467 mJ/mm2). Photoacoustic effect was assessed histologically by determining the number of lateral cleavage planes (dissections) arising from the lased crater border and extending into the surrounding tissue. In normal tissue, midinfrared lasing produced less acoustic damage than excimer lasing (2.79 +/- 0.78 vs. 5.27 +/- 0.75 cleavage planes, mean +/- SD, P < 0.05, data for lowest energy for each system). The same was true in noncalcified atheroma (2.48 +/- 0.71 vs. 6.43 +/- 1.09, P < 0.05) and calcified atheroma (2.47 +/- 1.21 vs. 6.27 +/- 1.13, P < 0.05). This effect was similar at all energy levels, with a trend for more damage at higher energies in both systems. This study demonstrates that midinfrared lasing causes less acoustic damage than excimer lasing when using clinical catheters, energy levels, and pulsing strategies. This effect is independent of tissue-type but tends to be dose-related. These findings may explain, in part, the differences in dissection rates seen clinically.

Effects of nimodipine and dexamethasone on low-level CO2 laser-induced release of 51chromium from canine 2C5 gliosarcoma cells

Low-energy penumbral irradiation of surgical lasers may produce undesirable effects on surrounding tissues. This study used a 51Cr cell labeling technique to determine if gliosarcoma cells could be therapeutically protected prior to their exposure to low-power laser irradiation. Canine 2C5 gliosarcoma cells with intracellular 51Cr were treated with nimodipine and/or dexamethasone and then exposed to low-power levels of CO2 laser. The 51Cr was released from the cells in a dose-dependent fashion following exposure to laser energy. Correlative analysis of the data indicated that a strong direct relationship between laser fluence and 51Cr release did exist for controls and drug-treated groups with coefficients of correlation r > or = +0.90 and coefficients of determination r2 > or = 0.82. However, comparison of the data from the drug-treated and control groups found that there was no significant difference between them (P > .05). Therefore, no protective or detrimental effects were observed with the use of nimodipine and/or dexamethasone on the gliosarcoma cells as tested in this system. Further investigation is necessary in order to define the mechanisms by which low-power level lasers affect these cells. These effects do not appear to be mediated through localization of mechanisms to the cell membranes or their constituent Ca2+ channels.

A new, safer lasing technique for laser-facilitated coronary angioplasty

In vitro studies during cold pulsed-wave laser angioplasty have demonstrated production of gas bubbles within the target tissue, creation of shock wave and formation of multi-layer dissections accompanied by an increase in the plaque and vessel wall temperature. These processes account for certain complications of coronary lasing, including acute vessel closure, dissections, spasm, and even perforation. The traditional lasing technique in which a large number of pulses is continually emitted across the lesion, may in fact contribute to the development and acceleration of the above mentioned processes. To overcome the shortcomings we have developed a new, safe lasing technique that consists of multiple trains of a small number of pulses each. Between laser sessions the laser catheter is retracted into the guiding catheter and nitroglycerin is injected intracoronary, thus providing time for dispersion of produced gas bubbles, cooling of the target artery, and adequate coronary vasodilatation. This new technique results in a significant reduction of laser associated complications.

In vivo assessment of vascular pathology resulting from laser irradiation. Analysis of 23 patients studied by directional atherectomy immediately after laser angioplasty

BACKGROUND

The pathological consequences of cardiovascular laser irradiation have been studied extensively in vitro. Previous in vivo studies of laser-induced injury have included analyses of acute and/or chronic findings in experimental animals. Little information, however, is available regarding the acute effects of laser irradiation of human vascular tissues in vivo.

METHODS AND RESULTS

To determine the acute pathology resulting from laser irradiation of human vascular tissue in vivo, specimens retrieved from 23 patients by directional atherectomy immediately after laser angioplasty (19 peripheral and four coronary) were examined by light microscopy. Of the 23 patients, three (13.0%) were treated with a metal-capped ("hot-tip") fiber coupled to a continuous-wave neodymium:yttrium-aluminum-garnet (Nd:YAG) laser using up to 18 W power and 18-305 seconds of cumulative exposure time; in all three patients (100%), thermal injury, including frank charring several cell layers thick, was seen along the luminal borders of the atherectomy specimen. In eight of the 23 patients (34.5%), laser angioplasty was performed using a 250-microseconds holmium:YAG laser at fluences up to 2,300 mJ/mm2, a repetition rate of 5 Hz, and 25-200 seconds of cumulative exposure; in seven of eight patients (85.5%), the atherectomy specimen showed signs of vacuolar injury consisting of central and satellite Alcian-blue-negative vacuoles. In two patients (25.0%), there was a "smudged" or "shredded" edge, whereas in one patient, frank signs of thermal injury were observed. Finally, in 12 of the 23 patients (52.2%), laser angioplasty was performed using a 120-nsec excimer laser at fluences up to 60 mJ/mm2, a repetition rate of 25 Hz, and a cumulative exposure time of 21-315 seconds. Pathological findings among these 12 patients were limited to nine patients (75%) in whom a weakly basophilic, smudged, and/or shredded appearance approximately one cell layer thick was observed along the luminal border of the atherectomy specimen and two patients (16.7%) with small foci of vacuolar injury. None of the atherectomy specimens retrieved after excimer laser angioplasty disclosed signs of thermal injury.

CONCLUSIONS

These findings document that acute pathological alterations resulting from in vivo laser angioplasty are variable, depending on the laser source used, and are similar to that predicted by experimental studies performed previously in vitro. The prognostic implications of these varying pathological features remain to be clarified.

Nd: YAG Laser-Photocoagulation: Acute Electrophysiological, Hemodynamic, and Morphological Effects in Large Irradiated Areas

Laser-photocoagulation (LPC) of arrhythmogenic myocardium has been reported to successfully ablate ventricular tachycardia. The purpose of this study was to investigate the acute hemodynamic and electrophysiological effect of continuous laser energy (Nd:YAG, 1060 nm) applied via a 0.4-mm quartz fiberoptic on the epicardial surface of the heart in nine dogs. A total of 51 +/- 2.3 pulses was delivered in each animal to induce homogeneous tissue necrosis. Applied energy was 12.3 +/- 2.7 J/mm2, irradiated surface measured 12.6 +/- 3.0 cm2, lesion depth was 6.3 +/- 1.2 mm (range: 5.0-8.1 mm), lesion volume was 8.1 +/- 2.8 cm3 (6.8% of left ventricular [LV] mass). After LPC, epicardial stimulation threshold significantly rose from 1.0 +/- 0.3 to 10.2 +/- 4.9 mA in the border zone to nontreated tissue and from 0.9 +/- 0.4 to 32 +/- 15.7 mA in the center of the lesions. Loss of epicardial activation in the irradiated areas could be demonstrated by epicardial mapping. Ventricular extrasystoles during LPC were seen in all dogs, ventricular tachycardia in seven, and ventricular fibrillation in two dogs. After LPC, cardiac output and LV dP/dtmax significantly decreased by 14.2% and 11.2%. LPC induced predictable homogeneous tissue edema, eosinophilic staining, contraction band necrosis, and sharp demarcated hemorrhagic border zones with a sharp electrical border zone to nontreated tissue and loss of epicardial activation. During LPC, various arrhythmogenic effects could be observed. However, no persistent arrhythmic activity developed after LPC. The results confirm the feasibility of epicardial LPC of the myocardium. Although not rested in this study, LPC of arrhythmogenic tissue may also be feasible as a treatment modality of ventricular tachycardia.

Cardiac abnormalities demonstrated postmortem in four cases of accidental electrocution and their potential significance relative to nonfatal electrical injuries of the heart

Death from accidental electrocution is generally thought to be due to an arrhythmia, but little is known of the anatomic changes in the heart and almost nothing is known about the conduction system itself. We have studied the hearts of four men who died from electrical accidents and directed particular attention to the coronary arteries, conduction system, and neural structures of the heart. In every heart there was widespread focal necrosis involving all the myocardium and including the specialized tissue of the sinus and atrioventricular nodes. In all four hearts there was contraction band necrosis of smooth muscle cells in the tunica media of the coronary arteries. Cells in the His bundle and bundle branches were less affected. Neural structures of the heart were minimally involved. We also sought any cardiac changes of a chronic nature that may have predisposed to a fatal arrhythmia. Two of the four hearts were slightly enlarged, and increased myocardial mass predisposes to ventricular fibrillation and makes it more difficult to revert. One heart exhibited focal fibromuscular dysplastic narrowing of small coronary arteries, including that artery supplying the coronary chemoreceptor. Another heart had fatty deposition extensively present within and around the sinus and atrioventricular nodes. Thus numerous abnormalities specifically attributable to the electrocution help explain the pathogenesis of the electrical instability known to occur. But in three of the four hearts there were also chronic abnormalities favoring electrical instability but predating the electrocution.

Carbon dioxide gas as a perfusion medium for the sapphire probe in laser ablation of human atheromatous plaques: comparison study with saline

The effectiveness of CO2 gas as a perfusion medium was compared to that of saline in laser ablation of human atheromatous plaque. In an experimental circulation-occlusion model using flowing whole blood, human cadaveric arterial samples were irradiated by a sapphire probe with the Nd-YAG laser. The following experiments were performed: 1) lasing without perfusion, 2) lasing with saline perfusion of the probe, and 3) lasing with CO2 perfusion. Different perfusion flow rates of saline and CO2 were used. Results showed that the mean ablation area was 1.6-fold larger with CO2 than with saline perfusion (P less than 0.05, Student's t test). The mean lateral injury at the site adjacent to the ablation crater and at the area directly facing the probe was not significantly different with either perfusion medium. The larger ablation area with CO2 was probably due to the fact that CO2 is a good insulator for maintaining a higher probe temperature and keeps the probe free of blood debris. In conclusion, our results show that CO2 perfusion facilitates more effective laser ablation of atheromatous plaque than saline perfusion by the sapphire probe with the continuous wave Nd-YAG laser.

CO2-laser radiation damage of the arterial wall

This study describes the effects of CO2 laser radiation on the histology of the normal rabbit arterial wall, using models that simulate laser angioplasty and anastomosis. Rabbit arteries were exposed to laser treatments similar to those used clinically; 40, 0.5 sec pulses of 40-60 mW, CO2 continuous wavelength laser, or a 1/2-circumferential laser anastomosis with a 60-80 mW continuous pulse. Aneurysms developed in 8 of 22 femoral, 1 of 22 carotid, and no controls at 12 week. There were small breaks in the internal elastic lamina with atrophy, loss of muscularis, "packing" of the elastica, thinning of the muscularis at the damage site, and enlargement of the arterial diameter. Aneurysms developed in one femoral and no carotid anastomosed artery. Laser anastomoses demonstrated more muscle damage and loss, with extensive scarring and a wider area of elastic loss than the controls. The intima was reestablished with focal reduplication of the internal elastic lamina. There were no histologic differences between the arteries which developed aneurysms and those which did not in either series. These results suggest that low power laser damage of the arterial wall consists mainly of destruction of the muscularis propria, with minimal damage to the elastica.

Early experiences with laser-assisted thermal angioplasty for peripheral vascular disease

Laser-assisted angioplasty has been used on 47 occasions in 45 patients for the management of atherosclerosis of the superficial femoral and proximal popliteal arteries. Twenty-four procedures were performed to treat disabling intermittent claudication and 23 procedures were performed for a "threatened limb" (rest pain, ischaemic ulceration or digital gangrene). Technical success was achieved in 40 (85%) cases; the mean length of occluded segment was 7.7 cm. The presence of heavily calcified occlusions contributed significantly (P less than 0.001) to technical failure. In 28 (70%) of the successfully treated cases, the recanalized arteries were patent at one month and in 21 (53%) cases they have remained patent during the follow-up period. In five of nine cases with a nine-month follow-up, the arteries still were patent. The mean length of the occluded segments that were treated initially was 7.1 cm in those that remained patent compared with 8.2 cm in those that reoccluded. Thirty-six (77%) patients were discharged from hospital on the day after the procedure. Laser-assisted angioplasty is a promising new technique that is applied best to short-segment, non-calcified occlusions and should reduce the requirement for femoropopliteal arterial bypass surgery.

Percutaneous Nd:YAG laser coagulation of ventricular myocardium in dogs using a special electrode laser catheter

A novel catheter system was used for intracardiac electrogram recordings, ventricular pacing and continuous-wave Nd:YAG laser (1,064 nm) irradiation of ventricular myocardium in eight dogs. Radiation at a power of 10 W for 3, 5, and 10 seconds was delivered through a 400 microns optical fiber. Power density was 15 W/mm2. A total of 96 laser injuries (12 per dog) were produced in selected sites in both the right and the left normal canine ventricle. Ventricular arrhythmias were noted during 12 of 96 (12.5%) laser pulses. Programmed electrical stimulation performed during control study immediately (all dogs) at 2 days (two dogs), and 4 months (4 dogs) following the experiments showed no episodes of sustained or nonsustained ventricular tachycardia. Radiation energies up to 50 J (10 W over 5 s) caused focal injuries of homogeneous coagulation/fibrosis localized to the target area, without vaporizing tissue and forming craters. Morphometrically and histologically there was a direct relationship between the energy of radiation delivered, and the extent and severity of the injury produced. The maximum size of lesions measured 7/11 mm (diameter/depth). Using a special catheter system laser coagulation of myocardium can be accomplished percutaneously. This method can create controlled subendocardial injuries without major side effects and appears to overcome most disadvantages of transcatheter high energy direct-current shocks when used as a regular course of procedure in ablation of arrhythmogenic tissue in the heart.

Clinical experience with fulguration and antiarrhythmic therapy for the treatment of ventricular tachycardia. Long-term follow-up of 43 patients

Forty-three patients (mean age, 45 +/- 18 years) with drug-refractory VT of varied etiologies, including 15 cases occurring after chronic myocardial infarction, underwent fulguration procedures. With a mean follow-up of 29 +/- 12 months (range, 9 to 55 months), after one to four sessions, VT had been controlled without a need for antiarrhythmic drugs in 22 (56 percent) of the 39 patients surviving the perioperative period and was controlled in 17 patients (44 percent) with the help of drugs. No malignant arrhythmias were observed following fulguration. There were five early deaths, four deaths related to the procedure, and eight late deaths, but no death was thought to be related to the endocardial shock itself. Thus, fulguration appears to be a valuable adjunct to the treatment of drug-resistant VT.

Thermal compression and molding of atherosclerotic vascular tissue with use of radiofrequency energy: implications for radiofrequency balloon angioplasty

The combined delivery of pressure and thermal energy may effectively remodel intraluminal atherosclerotic plaque and fuse intimal tears. To test these hypotheses with use of a non-laser thermal energy source, radiofrequency energy was delivered to postmortem human atherosclerotic vessels from a metal "hot-tip" catheter, block-mounted bipolar electrodes and from a prototype radiofrequency balloon catheter. Sixty-two radiofrequency doses delivered from a metal electrode tip produced dose-dependent ablation of atherosclerotic plaque, ranging from clean and shallow craters with histologic evidence of thermal compression at doses less than 40 J to tissue charring and vaporization at higher (greater than 80 J) doses. Lesion dimensions ranged between 3.14 and 3.79 mm in diameter and 0.20 and 0.47 mm in depth. Tissue perforation was not observed. To test the potential for radiofrequency fusion of intimal tears, 5 atm of pressure and 200 J radiofrequency energy were delivered from block-mounted bipolar electrodes to 48 segments of human atherosclerotic aorta, which had been manually separated into intima-media and media-adventitial layers. Significantly stronger tissue fusion resulted (28.5 +/- 3.3 g) with radiofrequency compared with that with pressure alone (4.8 +/- 0.26 g; p less than 0.0001). A prototype radiofrequency balloon catheter was used to deliver 3 atm of balloon pressure with or without 200 J radiofrequency energy to 20 postmortem human atherosclerotic arterial segments. In 10 of 10 radiofrequency-treated vessels, thermal "molding" of both normal and atherosclerotic vessel wall segments resulted with increased luminal diameter and histologic evidence of medial myocyte damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of CO2 and blood media on laser probe temperature

Blood may limit laser ablation of arterial plaque by decreasing thermal energy transfer from metal-capped probes to arterial occlusions. Since a gas is a good insulator of heat, CO2 may be a better medium for laser recanalization. To study this possibility, a metal-capped fiber was positioned in a segment of blood-filled polyethylene tubing and activated with an argon laser. Probe temperatures were measured in blood and as the blood was displaced by flowing CO2 gas. Probe temperatures were higher at all powers studied in CO2 gas than in blood. Maximum probe temperatures averaged 518 +/- 24 degrees C after CO2 infusion versus 320 +/- 7 degrees C in blood, (P less than 0.0001). Blood aggregate formation was noted on the probe surface in blood but not in CO2 medium. Thus CO2 gas may be a preferable medium for laser recanalization, since higher probe temperatures are achieved, and the probe surface remains free of insulating blood coagulate.

Effects of blood flow on laser probe temperature in human arteries

Laser recanalization using metal capped fibers occurs by thermal vaporization of occluding plaque. However, little is known about the effects of blood and flow on the temperature of the laser probe or the arterial wall during lasing. To study this, probe and arterial wall temperatures were measured while a metal capped fiber, activated by an argon laser, was held stationary in a stenotic human peripheral artery. Arteries were perfused with saline and blood, and flow was varied from 0 to 140 cc/min. Probe temperatures were significantly higher in blood than in saline. However, the increased probe temperature achieved in blood was not transferred to the arterial wall. Increasing flow decreased probe temperature in both media, but again arterial wall temperatures were minimally affected. Thus, the presence of blood and flow may significantly affect heat generation and heat transfer during arterial recanalization using metal capped fibers.

Human percutaneous laser angioplasty. Patient selection criteria and early results

Percutaneous transluminal laser angioplasty is a new method for treating atherosclerotic disease previously not amenable to routine percutaneous transluminal angioplasty techniques. Our results compared favorably with other clinical trials. Patient selection criteria include lesions in the superficial femoral or popliteal system not capable of being treated with routine percutaneous transluminal angioplasty. We think that these lesions include high-grade stenoses or short segmental occlusions. Heavily calcified vessels and long segment occlusions measuring greater than 12 cm in length are probably not amenable to percutaneous transluminal laser angioplasty. The long-term results of this form of therapy for peripheral vascular disease remain unknown.

Laser probe ablation of normal and atherosclerotic human aorta in vitro: a first thermographic and histologic analysis

The metal-tipped optical fiber or "laser probe" has been extensively studied in animal preparations in vivo and in human clinical trials of revascularization. The aim of this study was to evaluate the thermal characteristics of laser probe tissue ablation and to contrast the vascular tissue response to exposure to the laser probe and bare optical fiber. A 2 mm laser probe was heated with up to 4 W of argon-ion laser irradiation and applied to six postmortem strips of human nonatherosclerotic aorta as well as to five atherosclerotic aortic specimens. Surface temperature maps of the laser probe and of the vascular tissue in air were obtained via 8 to 12 micron thermographic imaging. Laser probe temperature was additionally monitored via thermocouples. Two strips each of normal and diseased aorta were irradiated directly with the bare optical fiber. Thus a total of 43 laser probe application sites and 19 bare fiberoptic laser irradiation sites on a total of 15 aortic strips were analyzed both thermographically and histologically. Based on measured temperature rises and histologic findings, the following observations were made: (1) The laser probe heats initially at its tip and attains a uniform surface temperature distribution within 5 sec. The steady-state temperature attained by the probe is inversely related to the thermal conductivity of the surrounding media. In all media studied, probe temperature increases linearly with applied laser energy. (2) Tissue ablation starts at temperatures greater than 100 degrees C, and ablation temperatures typically exceed 180 degrees C. Adventitial temperatures during laser probe application may reach 70 degrees C. Tissue ablation is enhanced both by greater laser energy deposition in the probe and by higher force at which the probe is applied to tissue. (3) Ablation of fibrofatty atheromata is more extensive than of nonatherosclerotic aortic tissue. This may be due to the lower thermal conductivity of atheromatous tissue. (4) In contrast to direct argon-ion laser ablation of aortic tissue, laser probe-mediated ablation occurs in a controlled fashion, is not associated with extensive subintimal dissections, and allows uniform conduction of heat to tissue as reflected by essentially "isothermal" injury lines.

The cellular electrophysiologic changes induced by ablation: comparison between argon laser photoablation and high-energy electrical ablation

The cellular electrophysiologic effects of myocardial ablation performed in vitro with argon laser energy were compared with those of high-energy electrical shocks. A border zone of injured but nonnecrotic tissue surrounding the site of energy delivery was present after tissue ablation by both energy modalities. A decrease in resting membrane potential, action potential amplitude, and maximum rate of upstroke velocity was noted in each tissue sample, was greatest nearest the site of energy delivery, and was of graded severity at increasing distances from the crater edge. The extent of injury, as indexed by changes in action potential variables and necrosis, histologically determined, was greater for tissues exposed to high-energy shocks. The relatively focal injury after argon laser photoablation may explain the lower incidence of arrhythmias and hemodynamic dysfunction noted with the use of this method of ablation in vivo.