Catheter-Free Arrhythmia Ablation Using Scanned Proton Beams: Electrophysiologic Outcomes, Biophysics, and Characterization of Lesion Formation in a Porcine Model.

BACKGROUND: Proton beam therapy offers radiophysical properties that are appealing for noninvasive arrhythmia elimination. This study was conducted to use scanned proton beams for ablation of cardiac tissue, investigate electrophysiological outcomes, and characterize the process of lesion formation in a porcine model using particle therapy. METHODS: Twenty-five animals received scanned proton beam irradiation. ECG-gated computed tomography scans were acquired at end-expiration breath hold. Structures (atrioventricular junction or left ventricular myocardium) and organs at risk were contoured. Doses of 30, 40, and 55 Gy were delivered during expiration to the atrioventricular junction (n=5) and left ventricular myocardium (n=20) of intact animals. RESULTS: In this study, procedural success was tracked by pacemaker interrogation in the atrioventricular junction group, time-course magnetic resonance imaging in the left ventricular group, and correlation of lesion outcomes displayed in gross and microscopic pathology. Protein extraction (active caspase-3) was performed to investigate tissue apoptosis. Doses of 40 and 55 Gy caused slowing and interruption of cardiac impulse propagation at the atrioventricular junction. In 40 left ventricular irradiated targets, all lesions were identified on magnetic resonance after 12 weeks, being consistent with outcomes from gross pathology. In the majority of cases, lesion size plateaued between 12 and 16 weeks. Active caspase-3 was seen in lesions 12 and 16 weeks after irradiation but not after 20 weeks. CONCLUSIONS: Scanned proton beams can be used as a tool for catheter-free ablation, and time-course of tissue apoptosis was consistent with lesion maturation.

Atrioventricular node ablation in Langendorff-perfused porcine hearts using carbon ion particle therapy: methods and an in vivo feasibility investigation for catheter-free ablation of cardiac arrhythmias.

BACKGROUND: Particle therapy, with heavy ions such as carbon-12 ((12)C), delivered to arrhythmogenic locations of the heart could be a promising new means for catheter-free ablation. As a first investigation, we tested the feasibility of in vivo atrioventricular node ablation, in Langendorff-perfused porcine hearts, using a scanned 12C beam. METHODS AND RESULTS: Intact hearts were explanted from 4 (30-40 kg) pigs and were perfused in a Langendorff organ bath. Computed tomographic scans (1 mm voxel and slice spacing) were acquired and (12)C ion beam treatment planning (optimal accelerator energies, beam positions, and particle numbers) for atrioventricular node ablation was conducted. Orthogonal x-rays with matching of 4 implanted clips were used for positioning. Ten Gray treatment plans were repeatedly administered, using pencil beam scanning. After delivery, positron emission tomography-computed tomographic scans for detection of ß(+) ((11)C) activity were obtained. A (12)C beam with a full width at half maximum of 10 mm was delivered to the atrioventricular node. Delivery of 130 Gy caused disturbance of atrioventricular conduction with transition into complete heart block after 160 Gy. Positron emission computed tomography demonstrated dose delivery into the intended area. Application did not induce arrhythmias. Macroscopic inspection did not reveal damage to myocardium. Immunostaining revealed strong γH2AX signals in the target region, whereas no γH2AX signals were detected in the unirradiated control heart. CONCLUSIONS: This is the first report of the application of a (12)C beam for ablation of cardiac tissue to treat arrhythmias. Catheter-free ablation using 12C beams is feasible and merits exploration in intact animal studies as an energy source for arrhythmia elimination.

[Echocardiographic parameters in patients with Wolf-Parkinson-White syndrome before and during one year after radiofrequency catheter ablation of accessory atrioventricular junction].

We present in this paper results of assessment of morphofunctional state of myocardium in patients with the Wolf-Parkinson-White syndrome before and during one year after radiofrequency catheter ablation (RFA) of accessory atrioventricular junction (AAVJ) and comparison of them with analogous parameters of the group of healthy volunteers as well as in dependence on electrophysiological properties of AAVJ and its localization. One hundred sixty patients took part in the conducted study: main group comprised 160 patients (80.7%) with WPW syndrome (114 men [81.4%], 26 women [18.6%], mean age 39.5+/-15.3 years), comparison group comprised 20 practically healthy persons (15 men [75.0%], 5 women [25%], mean age 41.9+/-5.3 years). All main group patients were subjected to endocardial electrophysiological investigation and RFA of AAVJ. Transthoracic echocardiography (EchoCG) was carried out in patients of main group before and in 2, 6, and 12 months after operation of RFA of AAVJ, and once in control group. Analysis of parameters of central hemodynamics according to data of transthoracic EchoCG in patients with WPW syndrome before RFA of AAVJ demonstrated that before conduct of operative intervention no significant differences were revealed in the studied parameters compared with analogous characteristics of the clinical comparison group. During whole period of dynamic observation (2, 6, and 12 months after fulfilled RFA of AAVJ) in patients with WPW syndrome the studied parameters of central hemodynamics did not undergo substantial changes compared with initial characteristics. We failed to establish significant differences of EchoCG parameters in patients with WPW syndrome in dependence on electrophysiological properties of AAVJ (concealed, manifest) and on AAVJ localization (right, left, septal). According to EchoCG data in patients with WPW syndrome so called "minor" anomalies of development of connective tissue of the heart were diagnosed in 69 (49.3%) patients while in control group - in 2 (10%) patients.

[Parameters of central hemodynamics in patients with paroxysmal atrioventricular nodal reciprocal tachycardia before and after radiofrequency catheter ablation].

We present in this article results of assessment of morphofunctional state of the myocardium in patients with typical form of paroxysmal atrioventricular nodal reciprocal tachycardia (AVNRT) before and during one year after radiofrequency catheter ablation of slow part of atrioventricular junction and their comparison with analogous parameters of control group. Participants of this study (n=81) were divided into 2 groups: main (study group) and control group. Main group comprised 61 (75.3%) patients with AVNRT in variant of typical course, mean age 45.3+/-15.1 years. All patients of study group were subjected to endocardial electrophysiological investigation and radiofrequency ablation (RFA) - modification of slow part of atrioventricular junction. Control group comprised 20 practically healthy persons aged 41.9+/-5.3 years in whom no structural pathology of cardiovascular system was found. Transthoracic echocardiography (EchoCG) was carried out before and in 2, 6, and 12 months after operation in patients of main group and once in control group. Analysis of parameters of central hemodynamics studied with the Echo method in patients of main group before and in 2, 6, 12 months after RFA demonstrated that before conduct of surgical intervention there were no significant differences between the parameters studied and analogous characteristics of the control group. It was established in the course of dynamic observation of patients of the study group that in 2, 6 and 12 months after RFA the studied parameters of central hemodynamics did not undergo substantial changes compared with initial values. According to EchoCG data so called minor anomalies of development of cardiac connective tissue were diagnosed in 28 cases (45%) among patients of study group and in 2 cases (10%) in control group.

Estimulación cardiaca temporal. Estimulación tras cirugía cardiaca / Temporary cardiac pacing. Pacing after cardiac surgery

La estimulación cardiaca temporal transvenosa es la modalidad de elección cuando se precisa estimulación cardiaca temporal continua, ya como puente a la resolución de la bradiarritmia o al implante del marcapasos definitivo. Generalmente es suficiente estimular el ventrículo derecho, salvo en situaciones hemodinámicas muy especiales como son el shock en el infarto de ventrículo derecho o la miocardiopatía hipertrófica obstructiva con bloqueo auriculoventricular. La estimulación cardiaca transcutánea es la más adecuada para solventar las situaciones de emergencia que requieren un soporte de estimulación cardiaca y en la mayoría de las profilácticas, con lo que en estas últimas se evita las potenciales complicaciones de la endovenosa. La estimulación epicárdica temporal tras la cirugía cardiaca, además de la contribución al tratamiento de las frecuentes alteraciones posquirúrgicas de la conducción, tiene un importante papel en la contribución al gasto cardiaco dependiente de la frecuencia y en la reducción o prevención de la fibrilación auricular postoperatoria. En los pacientes con disfunción ventricular izquierda y complejo QRS ancho preoperatorio, es deseable dejar implantados unos electrodos temporales en el ventrículo izquierdo, para poder realizar estimulación biventricular si fuese necesario. La decisión del momento más adecuado para la implantación de un marcapasos definitivo tras cirugía cardiaca es materia de controversia y debería ser individualizado para cada paciente (AU)

Temporary transvenous cardiac pacing is the treatment of choice when continuous temporary cardiac pacing is required, for example, as a bridge until a bradyarrhythmia has resolved or until permanent pacemaker implantation. Generally, right ventricular pacing is sufficient except under very special hemodynamic conditions, such as cardiogenic shock due to right ventricular myocardial infarction or obstructive hypertrophic cardiomyopathy with atrioventricular block. Transcutaneous cardiac pacing is the most appropriate technique for use in emergencies that require the support of cardiac pacing and for the majority of prophylactic applications, thereby avoiding, in these latter cases, the potential complications associated with the intravenous approach. In addition to contributing to the treatment of the conduction abnormalities that frequently occur after cardiac surgery, temporary post-surgery cardiac pacing also plays an important role in helping to increase heart rate-dependent cardiac output and in reducing or preventing postoperative atrial fibrillation. In patients who have left ventricular dysfunction and a wide QRS complex before surgery, it is advantageous to implant temporary leads in the left ventricle so that biventricular pacing can be implemented if necessary. There is some controversy about when is the most appropriate time for deciding to implant a permanent pacemaker, and this decision has to be taken individually for each patient (AU)

Selección del modo de estimulación en las bradiarritmias. Controversias sobre la indicación del modo AAI o el modo DDD en la enfermedad del nódulo sinusal y sobre la utilización del modo VDD en el bloqueo auriculoventricular / Pacing mode selection for bradyarrhythmias. Controversies concerning indications for the AAI mode versus the ddd mode in sick sinus syndrome and on the use of the VDD mode for atrioventricular block

Desde que en los años cincuenta se introdujo la estimulación cardiaca como tratamiento de las bradiarritmias cardiacas, el marcapasos cardiaco implantable ha sufrido una progresiva sofisticación y un continuo intento de aproximación, en su funcionamiento, a la fisiología normal del corazón. Al mismo tiempo, las indicaciones para implantación de un marcapasos han ido variando durante los últimos años y se han consensuado por expertos en documentos (Guías de Actuación Clínica) basados en la experiencia y en el índice de evidencia existente para cada indicación. A pesar de ello, siguen evidenciándose discrepancias entre estas indicaciones claramente establecidas y el modo de estimulación utilizado para el tratamiento de las bradiarritmias sintomáticas. Probablemente, los dos modos que ofrecen más discrepancia en su utilización sean los modos AAI y VDD. En este capítulo se realiza una revisión de las indicaciones de estimulación cardiaca, resaltando las nuevas evidencias existentes en cuanto al modo de estimulación, lugar de estimulación y efectos indeseables de la estimulación cardiaca. Asimismo, se analiza la controversia existente sobre la estimulación AAI y la estimulación DDD en la enfermedad del nódulo sinusal y la utilización del modo VDD en el bloqueo auriculoventricular (AU)

Since cardiac pacing was introduced for the treatment of cardiac bradyarrhythmias in the 1950s, implantable cardiac pacemakers have become increasingly sophisticated and there have been continuous attempts to enable them to approximate more closely the normal physiologic functioning of the heart. At the same time, indications for pacemaker implantation have been changing in recent years and a number of expert consensuses have been reached. These are contained in documents (i.e., clinical practice guidelines) based on clinical trails and on the current level of evidence for each indication. Nevertheless, there continue to be demonstrable differences between clearly established recommendations and the pacing modes used for treating symptomatic bradyarrhythmias. Probably, the two pacing modes exhibiting the greatest difference in practice are the AAI and VDD modes. This article contains a review of indications for cardiac pacing, with an emphasis on newly revealed data on pacing modes, pacing sites, and the undesirable side effects of cardiac pacing. In addition, there is a discussion of current controversies about the AAI mode versus the DDD mode in sick sinus syndrome and about use of the VDD mode for atrioventricular block (AU)

Catheter ablation using very high frequency current: effects on the atrioventricular junction and ventricular myocardium in sheep.

BACKGROUND: Radiofrequency ablation is currently used in the treatment of various cardiac arrhythmias. However, this technique is limited by impedance rise, leading to coagulum formation and desiccation of tissue. We developed a new generator, providing very high frequency (27 MHz) current, which is in the intermediate range between radiofrequency and microwave energy. The aim of this study was to evaluate the results for catheter ablation of the atrioventricular junction and characteristics of the lesions obtained at ventricular sites. METHODS AND RESULTS: The generator was coupled to a specially designed 7-French coaxial catheter. The study included experiments performed on 10 sheep (Wt. 31- 42 kg). In seven sheep, the catheter was introduced into the femoral vein and advanced across the tricuspid annulus to record the largest possible His electrogram. VHF current was applied for 25 s, with increasing energies. The energy needed to obtain complete atrioventricular (AV) block ranged from 60 to 100 Watts. Six animals were observed for 6 to 21 days. Complete AV block was found to be persistent. In those seven sheep in whom AV junction was ablated and in three additional sheep, the ablation catheter was positioned toward the right ventricular apex using the same approach and into the left ventricle via the femoral artery, and 20 to 90 Watts energy was delivered in order to assess the size of the induced lesions. Side effects included ventricular tachycardia degenerating into ventricular fibrillation in six cases, but the same effect was observed in this animal model with radiofrequency energy. No cardiac perforation was noted. No thrombus was observed at the catheter tip. The size of the lesion ranged from 3 to 45 mm in width and 1 to 15 mm in depth. CONCLUSIONS: Catheter ablation using VHF current is feasible and appears effective in producing stable AV block when applied at the AV junction and results in substantial myocardial lesions. Further studies are needed to define its clinical interest and side effects.

Extracardiac ablation of the canine atrioventricular junction by use of high-intensity focused ultrasound.

BACKGROUND: High-intensity focused ultrasound has been applied to internal organs from outside the body to ablate tissue. No published study has assessed the feasibility of ablating cardiac tissue within the beating heart by use of this type of therapeutic ultrasound. The purpose of this study was to determine whether high-intensity focused ultrasound can be used to ablate the atrioventricular (AV) junction within the beating heart. METHODS AND RESULTS: Ten dogs were anesthetized and underwent a thoracotomy. The heart was covered with a polyvinyl chloride membrane. The thorax above the membrane was perfused with degassed water, which functioned as a coupling medium for the ultrasound. A 7.0-MHz diagnostic ultrasound probe was affixed to a spherically focused 1.4-MHz high-intensity focused ultrasound transducer with a 1.1x8.3-mm focal zone 63.5 mm from the ablation transducer. The diagnostic ultrasound probe was calibrated such that the location of the focal zone of the ablation transducer was identifiable on the 2-dimensional ultrasound image. Target sites were identified with the diagnostic ultrasound. The maximum ultrasound intensity for ablation (2.8 kW/cm2) was delivered to the AV junction only during electrical diastole and for a total of 30 seconds. Complete AV block was achieved in each of the 10 dogs with 6.5+/-5.6 (range, 3 to 21) 30-second applications of therapeutic ultrasound. Gross inspection showed that the mean lesion volume was 124+/-143 mm3, with a depth of 6.7+/-3.6 mm, a length of 5.7+/-2.5 mm, and a width of 4.7+/-1.8 mm. Four hours after the dogs were killed, histopathological study demonstrated a well-demarcated area of necrosis and early inflammation. CONCLUSIONS: High-intensity focused ultrasound produces well-demarcated lesions and appears to be a feasible energy source to create complete AV block within the beating heart without damaging the overlying or underlying cardiac tissue. This energy source may allow for a noninvasive approach to ablation of cardiac arrhythmias.

Associated cardiac lesions in patients with radiation-induced complete heart block.

We investigated the clinical, electrophysiological, haemodynamic and angiographic aspects of four patients (two men and two women, aged 31-46 years) who developed complete heart block 13-20 years after therapeutic irradiation of the chest for Hodgkin's disease. The initial cardiac symptom was syncope in three, effort intolerance in one. The electrocardiogram recorded third-degree atrioventricular block in three patients, right bundle branch block and posterior fascicular block in one. The electrophysiological study, performed in three cases, showed that the block was infranodal in two. Three patients had significant coronary arterial stenoses, that involved the ostia in two. All patients had mild-to-moderate aortic and mitral regurgitation. One patient had haemodynamic signs of constriction. Another patient had recurrent pericardial effusions. All had echocardiographic evidence of a thickened pericardium. Cardiac involvement can be extensive in patient with radiation-induced heart block. Because coronary artery disease can be particularly severe, coronary angiography appears to be warranted in such patients.

Radiofrequency versus pharmacologic modification of the atrioventricular node.

Although transcatheter radiofrequency modification of the atrioventricular (AV) node has been proposed as curative treatment in AV nodal reentry tachycardias, its role for the control of the ventricular rate in atrial tachyarrhythmias remains unclear. The aim of this study was to analyze the acute effect of radiofrequency current on AV nodal conduction and refractoriness, and to compare it with the effects of two antiarrhythmic drugs such as amiodarone (class III) and flecainide (class I). Twenty-one dogs were studied: (1) radiofrequency group (5 W for less than 45 seconds; 2 to 12 discharges; seven dogs); (2) amiodarone group (5 mg/kg intravenously; seven dogs); and (3) flecainide group (2 mg/kg intravenously; seven dogs). The following parameters were measured under basal conditions and after each procedure: AH interval, AV nodal functional refractory period, Wenckebach cycle length, minimum R-R interval during atrial fibrillation, and fitting of AV nodal function curve to a hyperbolic equation using its linear transformation. The AV nodal effective refractory period could not be calculated in any dog in the basal study because it was shorter than the atrial functional refractory period.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiofrequency endocardial catheter ablation of accessory atrioventricular pathway atrial insertion sites.

BACKGROUND: High rates of success using radiofrequency ablation energy have rapidly transformed catheter ablation from an investigational procedure to the nonpharmacological therapy of choice for symptomatic Wolff-Parkinson-White syndrome. Prior studies of radiofrequency accessory pathway ablation were based on a ventricular approach. Risks associated with prolonged arterial catheter manipulation, retrograde left ventricular catheterization, and production of ventricular lesions required for successful ventricular insertion ablation can be avoided using atrial insertion ablation procedures. The purpose of the present study was to define the safety and efficacy of accessory pathway ablation using radiofrequency energy delivered solely to accessory atrioventricular pathway atrial insertion sites. METHODS AND RESULTS: One hundred fourteen patients with accessory pathway-mediated tachycardia underwent attempted radiofrequency current ablation at the accessory pathway atrial insertion site. All catheters were introduced transvenously. Left-sided accessory pathways were approached using transseptal left atrial catheterization techniques. Retrograde localization of the atrial insertion site during reentrant tachycardia was characterized by 40 +/- 15-msec local ventriculoatrial and 79 +/- 17-msec surface QRS to local atrial electrogram intervals. Presumed accessory pathway potentials were present in only 30% of ablation site electrograms. Successful ablation required 6.2 +/- 5.3 radiofrequency energy applications. Cumulative energy dose required for success was 2,341 +/- 2,233 J. There were no complications associated with transseptal catheterization. Energy delivery to accessory pathway atrial insertion sites was associated with non-life-threatening complications in two patients. Recurrent conduction requiring repeat ablation occurred in 10 of 115 (9%) successfully ablated accessory pathways, all within 1 month of the ablation procedure. After 21.2 +/- 4.6 months of follow-up, 108 of 114 (95%) patients are asymptomatic and without evidence of accessory pathway conduction. CONCLUSIONS: The atrial insertion approach to accessory pathway ablation is safe and highly effective. This approach compares favorably with the retrograde ventricular insertion ablation technique. Atrial insertion ablation eliminates the need to produce ventricular lesions and avoids the risks of prolonged arterial catheter manipulation and retrograde left ventricular catheterization.

Reappraisal of intermediate-term follow-up of radiofrequency ablation of accessory atrioventricular pathways for treatment of Wolff-Parkinson-White syndrome.

To evaluate the safety and efficacy of catheter mediated radiofrequency (RF) ablation in patients with Wolff-Parkinson-White syndrome, 125 patients with accessory pathway (AP) mediated tachyarrhythmias underwent RF ablation. Right-sided APs were ablated from the atrial aspect of the tricuspid annulus (all from the femoral vein approach) and the left-sided APs were ablated from the atrial or ventricular aspect of the mitral annulus. Immediately after ablation, 3 of 8 APs (38%) and 131 of 137 APs (95%) were ablated successfully with RF through a small-tip (2 mm) and a large-tip (4 mm) electrode catheter, respectively. Seven of the 11 APs where RF ablation failed had a later successful DC ablation. During follow-up (3 to 22 months), 11 of the 114 patients (10%) with successful ablation had return of accessory pathway conduction (2 had recurrence of tachycardia (2%)). Complications included transient myocardial injury (peak CK-MB 15 +/- 3 IU/l), transient proarrhythmic effects (more atrial and ventricular premature beats), accidental AV block (1 patient), cardiac tamponade (1 patient) and suspicion of aortic dissection (1 patient). In successful sessions, procedure and radiation exposure time were 3.8 +/- 0.2 h and 45 +/- 4 min, respectively. This study confirms that RF ablation with a large-tip electrode catheter is an effective and relatively safe nonsurgical method for treatment of Wolff-Parkinson-White syndrome.

An anatomically guided approach to atrioventricular node slow pathway ablation.

Radiofrequency ablation of the "slow" pathway of the atrioventricular (AV) node reentrant circuit may be guided by electrophysiologic ("slow pathway potential") or anatomic landmarks. Experience with a systematic, anatomically guided approach in 25 patients (20 women and 5 men, aged 38 +/- 15 years) with typical AV node reentry is described. The slow pathway is assumed to be the posterior input to the AV node, approaching the nodal region in the corridor between the tricuspid annulus and the orifice of the coronary sinus. A series of radiofrequency lesions are given to interrupt this corridor at its entrance to Koch's triangle. If this is unsuccessful, the series of lesions are repeated progressively at higher levels approaching the AV node. The major end point for success is elimination of the slow pathway as determined by extrastimulus testing. A mean of 1.2 +/- 0.2 ablative sessions (20 +/- 12 applications of energy) achieved clinical success in 24 of 25 patients (96%) at a follow-up of 8.6 +/- 2.2 months. Anterograde Wenckebach cycle length increased from 361 +/- 67 ms to 398 +/- 70 ms (p = 0.01), yet the atrio-Hisian interval in sinus rhythm did not change (69 +/- 17 ms before vs 65 +/- 15 ms after ablation), p = 0.22. Retrograde Wenckebach cycle length was not affected (348 +/- 78 ms before vs 366 +/- 82 ms after ablation). During ablation, transient third-degree AV block occurred in 6 patients with no permanent sequelae. This approach provides a systematic, expedient technique to eliminate slow pathway conduction based on anatomic landmarks.

Closed chest catheter desiccation of the atrioventricular junction using radiofrequency energy--a new method of catheter ablation.

Closed chest catheter ablation of the atrioventricular (AV) junction has been performed with direct current or laser energy. The effect of 750 kHz radiofrequency energy on ablation of the AV junction was evaluated in 13 dogs. The radiofrequency energy was generated from an electrosurgical generator in the bipolar mode. The radiofrequency output was delivered between two distal electrodes (bipolar ablation) in eight dogs, and between the distal electrode and an external patch electrode (unipolar ablation) in another five dogs at varying power (watts) but with a constant pulse duration of 10 seconds. Complete AV block was achieved in 11 dogs and second degree AV block in 2. During the 4 to 7 day follow-up period, complete AV block persisted in 9 of the 11 dogs with initial complete heart block. The other two had return of AV conduction; one had persistent 2:1 AV block and the other had persistent first degree AV block. Of the two dogs with initial second degree AV block, one developed complete AV block, the other had resumption of 1:1 AV conduction with a normal PR interval. Energy was delivered in 1 to 13 applications per dog. One hundred to 700 J per application was delivered with bipolar ablation and 10 to 100 J with unipolar ablation. There was no damage to the catheter unless the catheter was repeatedly used in excess of 1,500 J of total energy. Ventricular arrhythmias were not observed. Pathologic examination showed well delineated coagulation necrosis at the AV junction without surrounding hemorrhage or mural thrombus. Microscopic findings consisted of necrosis with cell infiltration in the periphery of necrosis. Most injuries involved the AV node, the approaches to the AV node and the penetrating bundle. In conclusion, catheter ablation of the AV junction with radiofrequency energy is safe. It can effectively induce discrete areas of necrosis and produce various degrees of AV block. In addition, ablation by radiofrequency energy has distinct advantages as compared with catheter ablation with direct current or laser energy.

Laser catheter-induced atrioventricular nodal delays and atrioventricular block in dogs: acute and chronic observations.

Selective modification of atrioventricular (AV) nodal conduction, that is, induction of varying degrees of AV nodal delays or block (second or third degree), or both, was achieved with a pervenous laser catheter technique. In six adult mongrel dogs anesthetized with pentobarbital (Nembutal), 5F leads were placed through femoral and external jugular veins and placed into the right atrium and His bundle region. Through another femoral vein, a 200 micron optical fiber was inserted by way of a 7F catheter with a preformed curved tip. Guided by fluoroscopy and His bundle electrograms, the fiber's tip was positioned in the AV nodal region. After autonomic blockade was achieved with intravenous propranolol (5 mg) and atropine (1 mg), AV conduction was analyzed. An argon laser delivered 3 to 4 watts into the fiber in bursts of 10 seconds' duration until the desired degree of AV nodal delay or block (second or third degree) was manifested. Monitoring of His bundle electrograms was continued for 2 hours. Four weekly serial electrocardiograms were recorded, after which electrophysiologic studies were repeated. Acute post-lasing studies showed that: in all six dogs, the mean PR interval was prolonged from 116 ms (range 100 to 135) to 153 ms (range 120 to 185), with the prolongation being caused exclusively by AH lengthening from 68 ms (range 50 to 90) to 105 ms (range 65 to 140); the mean effective refractory period of the AV node increased from less than 185 ms (range less than 150 to less than 200) to 215 ms (range 190 to 280); and the mean atrial pacing cycle length, at which second degree AV nodal block was manifested, increased from 210 ms (range 160 to 260) to 261 ms (range 205 to 320).(ABSTRACT TRUNCATED AT 250 WORDS)