Modification of atrioventricular node transmission properties by intraoperative neodymium-YAG laser photocoagulation in dogs.

The purpose of this study was to test the feasibility of neodymium-yttrium-aluminum-garnet (Nd-YAG) laser photocoagulation of the atrioventricular (AV) node to control the ventricular rate during rapid atrial rhythms without creating AV block. In 12 dogs on normothermic cardiopulmonary bypass, short laser pulses were delivered to an area between the coronary sinus orifice and the site of the most proximally recorded His deflection until second degree AV block occurred at a paced atrial rate of 200 beats/min. Long-term effects on AV node function were followed up for 3 months. Three animals developed chronic high grade AV block. In nine animals with preserved 1:1 conduction, the mean (+/- SEM) critical atrial cycle length resulting in AV node Wenckebach periodicity increased from 183 +/- 6 to 261 +/- 24 ms (+43%), the mean RR interval during induced atrial fibrillation increased from 248 +/- 14 to 330 +/- 27 ms (+32%) and the shortest RR interval during atrial fibrillation increased from 215 +/- 11 to 275 +/- 20 ms (+28%). Laser effects were not reversed by isoproterenol infusion. Histologic examination of the irradiated area showed fibrotic changes in the AV node and fatty metamorphosis. This study suggests that 1) graded Nd-YAG laser photocoagulation of the AV node region in dogs results in long-term modification of anterograde AV node transmission properties; 2) 1:1 conduction during sinus rhythm usually remains preserved, but ventricular rate during rapid atrial rhythms is chronically reduced; and 3) progression to high grade AV block occurs in a minority of animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser photoablation of ventricular tachycardia: correlation of diastolic activation times and photoablation effects on cycle length and termination--observations supporting a macroreentrant mechanism.

Neodymium:yttrium-aluminum-garnet (YAG) photocoagulation during ventricular tachycardia allows the electrophysiologic effects of the temporal and spatial sequence of energy delivery to be correlated with local activation times. A retrospective analysis was performed of the termination of 19 episodes of ventricular tachycardia for which the local diastolic activation time was known for all successful ablation sites and for 95% of all ablation sites. The mode of termination was compared with that of 26 episodes of spontaneously terminating ventricular tachycardias. Spontaneous terminations occurred without a change in cycle length (54%) or with a 7 +/- 15% change in cycle length over one to three terminal beats (46%). In contrast, laser ablation-induced terminations resulted in a 39 +/- 55% increase in cycle length over nine or more cycles. The effect of attempted laser ablation was compared with the local presystolic activation time and the local activation time expressed as a percent of the diastolic interval (end of QRS complex = 0%, onset of next QRS complex = 100%). With one exception, no tachycardia terminated at ablation sites activating less than -50 ms before the QRS complex. All 8 successful first ablation attempts and 13 of all 19 successful ablations occurred in the 35% to 50% interval of diastolic activation. All successful ablations at sites activating at greater than 50% of the diastolic interval required multiple ablation attempts. Successful ablation was performed from the epicardium in 6 and from the endocardium in 13 episodes of ventricular tachycardia. These results are most consistent with a macroreentrant mechanism with a region of high vulnerability represented by the 35% to 50% interval of diastolic activation.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Termination of ventricular tachycardia with epicardial laser photocoagulation: a clinical comparison with patients undergoing successful endocardial photocoagulation alone.

Electrical activation-guided laser photocoagulation was used intraoperatively to terminate ventricular tachycardia in patients with ischemic heart disease. During ventricular tachycardia, laser irradiation was delivered to mapped sites with local diastolic activation. In 30 long-term survivors, 85 ventricular tachycardia configurations were terminated by ablation; 72 (84.7%) were terminated by endocardial photocoagulation. Thirteen (15.3%) required epicardial photocoagulation; however, these 13 ventricular tachycardias occurred in 10 (33%) of the 30 patients. An aneurysm was present in 70% of patients with successful endocardial photocoagulation, but in only 10% of patients requiring epicardial photocoagulation for at least one ventricular tachycardia configuration; 90% of all patients requiring epicardial laser photocoagulation had no aneurysm and had either a right or a left circumflex coronary artery-related infarction. In this group, epicardial activation data were similar to those described for ventricular tachycardia with an "endocardial" origin and included 1) delayed potentials during sinus rhythm, 2) presystolic or pandiastolic activation sequences during ventricular tachycardia, and 3) regions of block near the presumed region of reentry during ventricular tachycardia. This study suggests that the critical anatomic substrates supporting reentry in postinfarction ventricular tachycardia may occur at intramural or epicardial sites, particularly in patients with right or circumflex coronary artery-related infarction and no aneurysm.

Aminophylline fails to improve the outcome of cardiopulmonary resuscitation from prolonged ventricular fibrillation: a placebo-controlled, randomized, blinded experimental study.

OBJECTIVES: The purpose of this study was to evaluate systematically the effects of the adenosine antagonist aminophylline on resuscitation outcome in a canine model of postcardioversion nonperfusing rhythm. BACKGROUND: Theoretic considerations and experimental studies indicate that myocardial adenosine accumulation during prolonged ventricular fibrillation might play a significant role in postcardioversion asystole and electromechanical dissociation. A recent uncontrolled clinical trial has suggested that the adenosine antagonist aminophylline might improve the outcome of cardiopulmonary resuscitation from refractory bradyasystolic cardiac arrest. METHODS: Two placebo-controlled, randomized, blinded experimental studies were performed. In protocol 1 (20 dogs), ventricular fibrillation was induced and maintained for 7.5 min. Sixty seconds before cardioversion, dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In protocol 2 (20 dogs), dogs were cardioverted to electromechanical dissociation after 5 min of unsupported ventricular fibrillation. Sixty seconds later, all dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In both experiments, resuscitation efforts were continued until return of spontaneous circulation, or up to 30 min. The primary end point was survival to 1 h. RESULTS: In protocol 1, 4 of 10 dogs survived in the aminophylline group, whereas 7 of 10 dogs survived in the placebo group, a nonsignificant trend toward unfavorable outcome from aminophylline. Pretreatment with aminophylline increased the number of cardioversion applications required to terminate ventricular fibrillation. In protocol 2, 5 of 10 and 6 of 10 dogs survived in the aminophylline and placebo groups, respectively. CONCLUSIONS: The results of this study suggest that aminophylline fails to improve the outcome of resuscitation from prolonged ventricular fibrillation. It does not reverse established electromechanical dissociation and may in fact increase the number of cardioversion applications required to terminate ventricular fibrillation. The rationale for conducting clinical trials with aminophylline during cardiopulmonary resuscitation is questionable.

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.

Atrioventricular alternating Wenckebach periodicity: conduction patterns in multilevel block.

Atrioventricular (A-V) conduction patterns were analyzed in three patients with atrial pacing-induced alternating Wenckebach periodicity. These cases were unique because in each (1) separate levels of block responsible for the conduction disturbance were located above and below the His bundle recording site, and (2) there were several departures from the simple alternating Wenckebach pattern. Apparent supernormal conduction, temporary 1:1 conduction and a specific form of gap in A-V conduction resulted from the interplay of many factors including a simple mathematic relation of the blocking ratio at the two levels, the characteristics of the Wenckebach cycles, and the cycle length-dependent features of refractory periods at the different sites. The findings indicate that (1) delay in proximal impulse transmission is usually the critical factor in overcoming prolonged distal refractoriness and producing variable conduction atterns during the course of alternating Wenckebach periodicity; (2) many irregularities in alternating Wenckebach periodicity can be explained by known electrophysiologic mechanisms; and (3) simple mathematic equations alone are too rigid to reflect properly the dynamic process underlying this conduction disturbance.

Surgical treatment of arrhythmias.

Surgical treatment of arrhythmias is often more expeditious and more cost-effective in the long run than pharmacologic therapy. In the past, surgical treatment of arrhythmias has been reserved for patients with disabling paroxysmal or incessant tachycardia refractory to medical management, severe life-threatening arrhythmia or aborted episodes of sudden death. However, tachyarrhythmias that are refractory to pharmacologic therapy because of drug inefficacy, noncompliance or limiting side effects are not uncommon. Although nonpharmacologic treatment of arrhythmias carries with it a one-time period of higher risk (i.e., when the patient undergoes surgery), it is curative and often preferable to the uncertainty and possibly higher cumulative risk associated with medical management.

Brugada-type electrocardiographic pattern induced by cocaine.

Right bundle branch block with coved ST-segment elevation in leads V1 through V3 is the electrocardiographic (ECG) marker of the Brugada syndrome. We describe a healthy young man with a normal baseline ECG in whom a transient Brugada pattern was observed repeatedly after recreational cocaine use. Intravenous administration of procainamide and subsequent intravenous propranolol followed by noradrenaline failed to reproduce the Brugada sign. An electrophysiologic study performed in the presence of the Brugada ECG pattern showed no inducible arrhythmias. This case illustrates that, in susceptible individuals, cocaine may provoke the Brugada sign. The clinical importance of this cocaine-induced ECG abnormality is currently unknown.

Two-to-one sinoatrial block. Normalization by carotid massage.

In a clinical case of 2:1 sinoatrial block, carotid massage, paradoxically, released the sinoatrial block and doubled the manifest sinus rate. This resulted from a deceleration of the sinus discharge rate which allowed consecutive sinus impulses to traverse the sinoatrial junction.

Comparison of the hemodynamic effects of Hexabrix and Renografin-76 following left ventriculography and coronary arteriography.

A crossover comparison of 41 patients studied by standard percutaneous transfemoral catheterization examined the electrocardiographic effects of Hexabrix and Renografin-76. Following both the right and left coronary angiograms, Renografin-76 caused significantly longer increases in the RR interval than did Hexabrix. Following left ventriculography, Renografin-76 shortened the RR interval more significantly than Hexabrix. Changes in aortic diastolic, systolic and mean pressures, as well as, cardiac index changes and systemic resistance following left ventriculograms were all much less using Hexabrix. Hemodynamic function was routinely affected less following the administration of Hexabrix as compared with Renografin-76. Both contrast agents provided good or excellent diagnostic studies. No observable difference in opacification was noted.

The application of thermography in the study of coronary blood flow.

The technique presented in this paper is based on the authors' previous observations in which they found that artificial decrease of blood flow to a portion of the heart muscle leads to an immediate and proportional drop in the regional myocardial temperature. It appeared to the authors as a logical next step to apply the thermographic camera to a monitor and to record such changes in the human patient during coronary surgery and to use the data to draw conclusions applicable to regional blood supply and to blood flow through surgically inserted vein grafts. They found that, on the normothermic heart, there were well-identifiable "cold" patches corresponding with areas of impaired coronary circulation. By infusion of blood to the ischemic myocardium through individual release of the bypass grafts, the thermogram responded by immediate appearance of "warm" spots corresponding with the areas supplied by the grafts. Even more dramatic demonstration of graft patency and outline of the area supplied by the graft could be performed by injecting cold saline solution into the grafted saphenous veins. In the author's experience this most interesting new method proved to be a useful tool in coronary surgery both as an adjunct in delineating ischemic areas and in proving the patency and efficiency of the grafts inserted.

Technical considerations in the surgical approach to multiple accessory pathways in the Wolff-Parkinson-White syndrome.

Surgical techniques for the approach to and division of atrioventricular accessory pathways have been designed and perfected during the past 18 years. The standard method of exposure of a single left free wall accessory pathway is by a left atriotomy. All other single accessory pathways are exposed through a right atriotomy. Up to twenty percent of patients with Wolff-Parkinson-White (WPW) syndrome harbor multiple atrioventricular accessory pathways. In this subgroup, classic operative techniques, especially the methods of approach, must be combined or modified depending on the specific locations of the accessory pathways encountered. Eighteen of 90 patients operated on for WPW syndrome at Charlotte Memorial Hospital from August, 1983, through September, 1986, had multiple accessory pathways. Thirty-eight of thirty-nine pathways were successfully divided. One posterior septal accessory pathway reappeared 2 months postoperatively and was catheter ablated. The most frequent combination of atrioventricular accessory pathways included a right free wall and a posterior septal accessory pathway (10 patients). This combination is approached by a right atriotomy. The posterior septal space dissection is extended onto the right free wall area. Technically the most difficult combination includes a left free wall and a posterior septal accessory pathway (3 patients in the present series). Our preferred approach is begun with a right atriotomy for the posterior septal space dissection, followed by an atrial septotomy to expose the left free wall area. There are other methods, however, that may be advantageous depending on the exact locations of the accessory pathways encountered.

Successful clinical laser ablation of ventricular tachycardia: a promising new therapeutic method.

This preliminary report describes 5 consecutive patients operated on for drug-resistant ventricular tachycardia (VT). All were successfully treated with laser photocoagulation ablation alone. The continuous-wave neodymium:yttrium-aluminum garnet (Nd:YAG) laser (wavelength, 1.06 micron) was chosen because of its capability for controlled deep tissue penetration, which can be adjusted by manipulating the power and exposure time of the beam. All patients had severe coronary artery disease. Preoperative left ventricular ejection fractions were low (0.18 to 0.29). Risk factors associated with increased failure rates by conventional surgical approaches were frequent: absence of discrete left ventricular aneurysm (5 patients) and multiple VT morphologies with disparate sites of origin (4 patients). All patients recovered fully. VT was not inducible prior to discharge, and no patient was placed on a regimen of antiarrhythmic drugs. Current direct surgical approaches to drug-resistant VT have markedly improved operative results compared with indirect procedures. However, failures and mortality remain high. Laser photocoagulation obviates some of the problems associated with conventional methods. It is similar to cryotherapy in that the structural integrity of affected tissues is maintained. In contrast to cryosurgery, however, laser photocoagulation is achieved more rapidly and with more precise myocardial destruction. One of the most promising features of laser coagulation is that it is administered to the perfused normothermic heart. Consequently, each morphological form of induced VT is observed to disappear as its area of origin is systematically located by mapping and then ablated.

Computational modeling of three-dimensional microwave tomography of breast cancer.

Microwave tomographic approach is proposed to detect and image breast cancers. Taking into account the big difference in dielectrical properties between normal and malignant tissues, we have proposed using the microwave tomographic method to image a human breast. Because of the anatomical features of the objects, this case has to be referred to the tomography with a limited angle of observation. As a result of computer experiments we have established that multiview cylindrical configurations are able to provide microwave tomograms of the breast with a small size tumor inside. Using the gradient method, we have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies.

Microwave tomography: two-dimensional system for biological imaging.

Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to "slice" three-dimensional (3-D) object reconstruction, we still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%.

Three-dimensional microwave tomography: experimental prototype of the system and vector born reconstruction method.

A method of image reconstruction in three-dimensional (3-D) microwave tomography in a weak dielectric contrast case has been developed. By utilizing only one component of the vector electromagnetic field this method allows successful reconstruction of images of 3-D mathematical phantoms. A prototype of the 3-D microwave tomographic system capable of imaging 3-D objects has been constructed. The system operates at a frequency of 2.36 GHz and utilizes a code-division technique. With dimensions of the cylindrical working chamber z = 40 cm and d = 60 cm, the system allows measurement of an attenuation up to 120 dB having signal-to-noise ratio about 30 dB. The direct problem solutions for different mathematical approaches were compared with an experimentally measured field distribution inside the working chamber. The tomographic system and the reconstruction method were tested in simple experimental imaging.

Thermal laser arterial injury and prostacyclin administration in dogs: thrombotic and hyperplastic consequences.

Angioplasty is considered as an alternative to surgical reconstruction of arteriosclerotic vessels especially since lasers and atherectomy devices have become clinically available. However, the resulting arterial injury may lead to acute thrombotic occlusion and chronic restenosis because of hyperplastic vascular repair. The purpose of this experimental study was to evaluate the consequences of thermal laser arterial injury on platelet deposition and myointimal hyperplasia in dog femoral arteries. An intraarterial, short-term prostacyclin (PGI2) infusion was given to evaluate the antithrombotic and antiproliferative effects of this drug. Severe arterial necrosis, partly carbonized and vacuolized, extending to the adventitia was induced by a transluminal heated laser probe motion. The platelet deposition after one hour was 33.62 +/- 6.56 (x 10(6)/cm2.) (mean +/- SEM) without prostacyclin, after 40 ng/kg/min prostacyclin (PGI2) 24.70 +/- 5.45 and after 400 ng/kg/min 9.3 +/- 2.26 (p less than 0.005 no PGI2 vs 400 ng/kg/min PGI2). Myointimal hyperplasia was present eight weeks after thermal laser vascular injury independent of the initially administered prostacyclin. In conclusion, acutely thrombotic and chronically hyperplastic femoral arteries were found following transluminal thermal arterial injury in dogs. Prostacyclin administration could be clinically beneficial in reducing acute vascular thrombosis following thermal angioplasty. Short-term use of this substance, however, may not prevent a hyperplastic response to angioplasty.