Morphologic study of cardiac cells in sheep before and after electric shock

A combined electrophysiological and histopathological study was conducted on sheep myocardium fragments rich in easily identifiable conduction cells subjected to electric shocks of varying intensity. Tissue fragments were immersed in a thermostatically-controlled bath at 37 degrees C, perfused with a carbonated standard tyrode solution at the rate of 30 ml/min and stimulated at a constant bipolar 1 C/sec tension twice as high as the threshold of diastolic excitability. After measurement of reference values, electric shocks of 2 to 80 joules were delivered between two electrodes placed on both sides of the tissue fragment. The electrophysiological part of the study showed disorders of conduction which, depending on the energy delivered, were more or less complete and reversible. The histopathological part of the study showed that conduction tissue was extremely fragile, even to low-energy shocks. This fragility was in glaring contrast with the relatively modest damage suffered by myocytes. Liquefaction and/or coagulation of Purkinje's cells was also striking, as it extended over an area much wider than that subjected to the shock. Thus, with medium intensity shocks destroyed conduction bundles were seen to creep between myocytes that often were perfectly normal or showed rare hypercontraction bands. Some myocytes were in the process of degeneration or even eosinophilic necrosis, but except in case of violent shock these were more or less isolated elements in the vicinity of the stimulated area. The fragility of conduction tissue and its selective damage by low-intensity shocks may be explained partly by its low impedance which allows preferential passage of the electric current.(ABSTRACT TRUNCATED AT 250 WORDS)     

Termination of ventricular tachycardia by single extrastimulation during the ventricular effective refractory period

Termination of ventricular tachycardia by low-energy shocks delivered during the ventricular refractory period has been reported. We describe a case of reproducible termination of multiple episodes of sustained ventricular tachycardia by a low-current extrastimulus delivered during the effective refractory period of the right ventricle, from the distal bipole of a quadripolar electrode catheter.     

Efficacy and safety of catheter electrical ablation for ventricular tachycardia--experimental and clinical studies

We studied the factors determining the extent of myocardial damage induced by catheter electrical ablation in 23 mongrel dogs and evaluated the efficacy and safety of catheter electrical ablation in 6 patients with medically refractory ventricular tachycardias (VT). Electrical shocks were delivered on the epicardium (EPI) and endocardium (END) of the ventricular wall of open-chest anesthetized dogs through a 6F USCI electrode catheter. Effect of the extent of electrode contact pressure was examined by the presence or absence of monophasic action potential using the contact electrode technique. The former was defined as the hard touch condition and the latter was defined as the soft touch condition. The myocardial lesion induced by EPI fulguration was larger than that by END fulguration (EPI-100 J soft touch: 10.2 +/- 2.9 mm in diameter, 6.6 +/- 1.6 mm in depth vs END-100 J soft touch: 7.7 +/- 1.7 mm in diameter, 5.0 +/- 1.2 mm in depth; p less than 0.05, p less than 0.05). The lesion diameter and lesion depth were enlarged by increasing the amount of delivered energy. The lesion depth by the hard touch condition was significantly greater than by the soft touch condition. The transmural perforation was observed in all EPI fulguration in the hard touch condition of the right ventricular wall. In the clinical study, one to three shocks (mean 1.8 +/- 0.7) of 60 to 200 J (mean 151 +/- 48 J) were delivered per session in 6 patients with medically refractory VT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical efficacy of dual electrode systems for endocardial cardioversion of ventricular tachycardia: a prospective randomized crossover trial

In order to eliminate the need for epicardial electrodes, two large transvenous catheter electrodes or one catheter and one extrathoracic patch electrode have been proposed as alternative electrode configurations for defibrillation and ventricular tachycardia cardioversion by implantable cardioverter/defibrillators. We compared the efficacy and safety of endocardial shocks delivered through these two electrode systems in man in a prospective randomized crossover study. Twelve patients with sustained ventricular tachycardia and heart disease undergoing electrophysiologic study were evaluated. A transvenous tripolar cardioversion electrode catheter with a large distal defibrillation electrode (surface area, 400 mm2) and proximal defibrillation electrode (surface area, 800 mm2) was positioned in the right ventricular apex with a cutaneous patch electrode placed on the cardiac apex. Sustained ventricular tachycardia was induced at electrophysiologic study. Shocks were delivered using two catheter electrodes only (right ventricular cathode and right atrial anode = method I), and one catheter electrode and cutaneous patch (right ventricular cathode and cutaneous apical patch anode = method II). Synchronized monophasic shocks were delivered using three preselected protocols based on ventricular tachycardia cycle length and morphology. Initial shock energies were 25 joules for polymorphic ventricular tachycardia and ventricular fibrillation, 15 joules for monomorphic rapid ventricular tachycardia (cycle length less than or equal to 300 msec), and 5 joules for monomorphic slow ventricular tachycardia (cycle length greater than 300 msec). Ventricular tachycardia was reinduced and shock energies titrated until cardioversion threshold was obtained. Identical ventricular tachycardia episodes were treated with both methods at each energy level.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms of ventricular tachycardia termination and acceleration during transvenous cardioversion as determined by cardiac mapping in man

We examined the EP mechanisms underlying efficacy and inefficacy of transvenous cardioversion shocks in 13 patients with coronary artery disease and sustained VT during preoperative and intraoperative cardiac mapping procedures. Shocks were delivered at the right ventricular apex with a Medtronic 6880 catheter and a Model 5350 external cardioverter/defibrillator with two or three electrode configurations, resulting in unidirectional or bidirectional shocks, respectively. Single transvenous shocks with incremental energies ranging from 0.03 to 25 J were delivered in sinus rhythm and VT, and simultaneous right and left ventricular electrograms were obtained. Transvenous cardioversion shocks of 0.03 J in sinus rhythm and VT produced immediate local right ventricular depolarization and subsequently conducted to distant right ventricular and left ventricular sites after 30 to 100 msec. Shocks of 0.05 to 0.5 J produced immediate depolarization of progressively larger right ventricular and left ventricular regions, with shocks greater than or equal to 0.5 J producing immediate depolarization of distant left ventricular sites in sinus rhythm. High energy (greater than 5 J) shocks produced instantaneous depolarization of multiple right ventricular and left ventricular sites in VT. VT termination occurred due to either delay or interruption of conduction in the tachycardia circuit, despite prior depolarization of the early sites of ventricular activation during the QRS complex. This could be due to instantaneous or paced depolarization of critical "excitable" components of the VT circuit, resulting either in immediate conduction block or in instability followed by termination. VT acceleration with transvenous cardioversion was due to modification of the "excitable," slowly conducting components of the VT circuit with the development of new areas of conduction block, along with altered intraventricular conduction. Similar EP mechanisms were observed with unidirectional and bidirectional transvenous shock patterns. We conclude that transvenous shocks alter conduction in human ventricle, and clinical effects of QRS synchronized shocks are related to conduction changes induced in the excitable components of the VT circuit.     

New catheter technique for recording left free-wall accessory atrioventricular pathway activation. Identification of pathway fiber orientation

The ability to record accessory atrioventricular (AV) pathway activation consistently may be uniquely beneficial in improving pathway localization, identifying anatomic relations, and providing insight into unusual conduction properties. For the purpose of recording left AV accessory pathway activation, an electrode catheter was specially designed for use in the coronary sinus. The orthogonal catheter has three sets of four electrodes spaced evenly around the circumference. Electrograms were recorded at low gain (less than 1 cm/mV) between adjacent electrodes on the same set (interelectrode distance, 1.5 mm, center to center). This provides a recording dipole perpendicular to the atrioventricular groove to enhance recording of accessory pathway activation while minimizing overlapping atrial or ventricular potentials. The orthogonal electrode catheter was used in the electrophysiological study of 48 consecutive patients with 59 left AV accessory pathways. The catheter could be advanced along the coronary sinus beyond the site of earliest retrograde atrial activation in 49 of the 59 accessory pathways. Activation potentials were recorded from 45 of the 49 (92%) accessory pathways accessible to the catheter (5 of 5 anterior, 8 of 8 anterolateral, 15 of 16 lateral, 5 of 5 posterolateral, 5 of 5 posterior, and 7 of 10 posteroseptal). Accessory pathway potentials were validated by dissociating them from both atrial and ventricular activation by programmed-stimulation techniques. During surgery, accessory pathway potentials were identified from orthogonal catheter electrodes in the coronary sinus in 14 of 16 accessory pathways (12 patients). Epicardial mapping confirmed the location of the accessory pathway, and direct pressure over the orthogonal catheter electrode that recorded the accessory pathway potential resulted in transient conduction block in nine of the 14 accessory pathways. Orthogonal electrode maps of the coronary sinus identified an oblique course in 39 of 45 recorded accessory pathways. Thirty-two of 38 left free-wall accessory pathways were oriented with atrial insertion 4-30 mm (median, 14 mm) proximal (posterior) to the ventricular insertion. In the remaining six free-wall accessory pathways, the lateral excursion could not be determined because either only the atrial end of the accessory pathway was recorded or activation of multiple pathway fibers prevented tracking of individual strands. The seven recorded posteroseptal pathways exhibited accessory pathway potentials throughout an 8-18-mm (median, 10 mm) length of the proximal coronary sinus, but fiber orientation was difficult to determine.(ABSTRACT TRUNCATED AT 400 WORDS)     

Efficacy and safety of transcatheter ablation of posteroseptal accessory pathways

Eight patients with a posteroseptal accessory pathway and symptomatic atrial fibrillation and/or orthodromic reciprocating tachycardia underwent attempted transcatheter ablation of the accessory pathway. A quadripolar electrode catheter was positioned within the coronary sinus such that the proximal pair of electrodes straddled the os. This proximal pair of electrodes was made electrically common and connected to the cathodal output of a defibrillator. A patch electrode placed over the midthoracic spine was connected to the anodal sink of the defibrillator. Two to three transcatheter shocks were delivered, with a cumulative energy of 600 to 900 J. Immediately after the shocks were delivered, retrograde accessory pathway conduction was absent in each patient. Anterograde conduction through the posteroseptal accessory pathway was absent in six patients. In one patient, retrograde accessory pathway conduction was absent and anterograde conduction was present but was slower than at baseline. In this patient, orthodromic tachycardia was no longer inducible and the ventricular rate during induced atrial fibrillation was 150 beats/min, compared with 220 beats/min before the attempted ablation. He has remained asymptomatic without antiarrhythmic drug therapy for 18 months. In one patient, the transcatheter shocks had no long-term effect on accessory pathway conduction. The shocks delivered at the os of the coronary sinus were well tolerated.(ABSTRACT TRUNCATED AT 250 WORDS)     

High frequency alternating current ablation of an accessory pathway in humans

High frequency alternating current ablation of an accessory pathway was performed in a patient with incessant circus movement tachycardia using a right-sided, free wall accessory pathway. Antiarrhythmic drugs, antitachycardia pacing and transvenous catheter ablation using high energy direct current shocks could not control the supraventricular tachycardia. A 7F bipolar electrode catheter with an interelectrode distance of 1.2 cm was positioned at the site of earliest retrograde activation during circus movement tachycardia. At this area, two alternating current high frequency impulses were delivered with an energy output of 50 W through the distal tip of the bipolar catheter, while the patient was awake. After the first shock supraventricular tachycardia terminated and accessory pathway conduction was absent without altering anterograde conduction in the normal atrioventricular (AV) conduction system. No reports of pain or other complications were noted. In short-term follow-up of 5 months, the patient had been free of arrhythmias without antiarrhythmic medication. Thus, high frequency alternating current ablation was performed for the first time in the treatment of an arrhythmia incorporating an accessory pathway in a human. This technique may be an attractive alternative to the available transcatheter ablation techniques and to antitachycardia surgery.     

Low-energy transvenous ablation of the canine atrioventricular conduction system with a suction electrode catheter

A single suction electrode catheter was used for His bundle electrogram recording. His bundle pacing, and low-energy (20 or 30 J) His bundle ablation in seven dogs. The suction electrode catheter was actively fixed to the atrial endocardium at the His bundle level. Electrophysiologic studies were performed in the control state, immediately after, and late (greater than 40 days) after His bundle ablation and results were correlated with histologic findings in the conduction system. Unipolar His bundle recording and pacing were successfully performed in all dogs with the suction electrode catheter before and after ablation. Complete heart block developed after a single 20 J shock delivered via the suction electrode catheter in all dogs immediately, but reverted to 1:1 atrioventricular conduction with first-degree atrioventricular block in two dogs in which one or two additional shocks (20 or 30 J) produced complete heart block. Mean ablation energy per shock was 22 +/- 4 J. The mean total delivered energy per dog was 31 +/- 20 J. Late electrophysiologic study in all dogs showed persistent complete heart block in five dogs and paroxysmal second-degree or third-degree atrioventricular block in two dogs. Gross examination of the ablation site showed a white plaque above the medial tricuspid leaflet (1.4 to 2.0 cm long and 0.4 to 0.6 cm wide). Microscopically, fibrosis of the penetrating and branching His bundle was seen in all dogs, with minimal atrioventricular node and atrial involvement. Significant proximal right bundle branch fibrosis was observed in the two dogs receiving one or two additional shocks. We conclude that the suction electrode catheter permits repeated His bundle recording, pacing, and ablation with a single catheter. Permanent and safe low-energy ablation of the canine His bundle is feasible. Focal injury localized to the target area in the conduction system can be obtained.     

Transvenous ablation of atrioventricular conduction with a low energy power source.

A power source modified to increase voltage delivery and minimise arcing (for a given energy) was used for transvenous ablation of atrioventricular conduction to control refractory supraventricular arrhythmias in 14 patients. Twelve had atrial fibrillation or flutter, one had atrioventricular nodal reentry tachycardia, and the other had permanent junctional reentry tachycardia. Despite treatment with 5-7 (median 6) antiarrhythmic drugs symptoms had persisted in all the patients. Cathodal discharges of 0.5-39.5 J were delivered to the distal electrode (in one case in parallel with the middle electrode). In all patients shocks produced complete atrioventricular block; this was permanent in eleven (79%). Four patients required a second procedure. In one patient, only a transient atrioventricular block could be produced and catheter ablation with a conventional power source also failed. In the other two atrioventricular conduction was modified such that previously ineffective treatment produced satisfactory control of heart rate. The cumulative energy delivered to those in whom permanent complete heart block resulted ranged from 3.6 to 97.8 (mean 38.3) J with a mean of three shocks (range 1-7) delivered per patient. During follow up of 1-28 (mean 14) months 11 patients remained in complete heart block and free of arrhythmia.     

Transvenous ablation of atrioventricular conduction with a low energy power source

A power source modified to increase voltage delivery and minimise arcing (for a given energy) was used for transvenous ablation of atrioventricular conduction to control refractory supraventricular arrhythmias in 14 patients. Twelve had atrial fibrillation or flutter, one had atrioventricular nodal reentry tachycardia, and the other had permanent junctional reentry tachycardia. Despite treatment with 5-7 (median 6) antiarrhythmic drugs symptoms had persisted in all the patients. Cathodal discharges of 0.5-39.5 J were delivered to the distal electrode (in one case in parallel with the middle electrode). In all patients shocks produced complete atrioventricular block; this was permanent in eleven (79%). Four patients required a second procedure. In one patient, only a transient atrioventricular block could be produced and catheter ablation with a conventional power source also failed. In the other two atrioventricular conduction was modified such that previously ineffective treatment produced satisfactory control of heart rate. The cumulative energy delivered to those in whom permanent complete heart block resulted ranged from 3.6 to 97.8 (mean 38.3) J with a mean of three shocks (range 1-7) delivered per patient. During follow up of 1-28 (mean 14) months 11 patients remained in complete heart block and free of arrhythmia.     

Transmembrane Voltage Changes Produced by Real and Virtual Electrodes During Monophasic Defibrillation Shock Delivered by an Implantable Electrode

Defibrillation Shock-Induced Virtual Electrodes. Introduction: Epicardial point stimulation produces nonuniform changes in the trans membrane voltage of surrounding cells with simultaneous occurrence of areas of transient positive and negative polarization. This is the phenomenon of virtual electrode. We sought to characterize the responses of epicardial ventricular tissue to the application of monophasic electric shocks from an internal transvenous implantable cardioverter defibrillator (ICD) lead.
Methods and Results: Langendorff-perfused rabbit hearts (n = 12) were stained with di-4-ANEPPS. A 9-mm-long distal electrode was placed in the right ventricle. A 6-cm proximal electrode was positioned horizontally 3 cm posteriorly and 1 cm superiorly with respect to the heart. Monophasic anodal and cathodal pulses were produced by discharging a 150-μF capacitor. Shocks were applied either during the plateau phase of an action potential (AP) or during ventricular fibrillation. Leading-edge voltage of the pulse was 50 to 150 V, and the pulse duration was 10 msec. Transmembrane voltage was optically recorded during application of the shock, simultaneously from 256 sites on a 11 × 11 mm area of the anterior right ventricular epicardium directly transmural to the distal electrode. The shock effect was evaluated by determining the difference between the AP affected by the shock and the normal AP. During cathodal stimulation an area of depolarization near the electrode was observed, surrounded by areas of hyperpolarization. The amplitude of polarization gradually decreased in areas far from the electrode. Inverting shock polarity reversed this effect.
Conclusion: ICD monophasic defibrillation shocks create large dynamically interacting areas of both negative and positive polarization.     

Reappraisal of electrical cure of atrioventricular nodal reentrant tachycardia--lessons from a modified catheter ablation technique.

A modified catheter ablation technique was studied prospectively in 29 patients with atrioventricular (AV) nodal reentrant tachycardia. A His bundle electrode catheter was used for mapping and ablation. Cathodic electroshocks (100-250 J) were delivered from the distal two electrodes (connected in common) of the His bundle catheter to the site selected for ablation. The optimal ablation site recorded the earliest retrograde atrial depolarization, simultaneous or earlier than the QRS complex, with absence of a His bundle deflection during AV nodal reentrant tachycardia. One additional electrical shock was delivered if complete abolition of retrograde VA conduction persisted for more than 30 min and AV nodal reentrant tachycardia was not inducible during isoproterenol and/or atropine administration. With a cumulative energy of 323 +/- 27 J and a mean of 2.3 +/- 0.5 shocks interruption or impairment of retrograde nodal conduction was achieved. Antegrade conduction, although modified, was preserved in 27 patients, with persistence of complete AV block in 2 patients. Two of the 27 patients still need antiarrhythmic agents to control tachycardia, the other 25 patients were free of tachycardia within a mean follow-up period of 13 +/- 2 months (range 7 to 20 months). Twenty-three patients received late follow-up electrophysiological studies (3-6 months after the ablation procedures), and the AV nodal function curves were classified into 4 types. The majority of the patients (15/23) had loss of retrograde conduction. Among the 8 patients with prolongation of retrograde conduction, 4 patients still had antegrade dual AV nodal property but all without inducible tachycardia. In conclusion, preferential interruption or impairment of retrograde conduction was the major, but not the sole, mechanism of electrical cure of AV nodal reentrant tachycardia.     

Rhythm and conduction disorders immediately after ventricular fulguration

Forty-four patients with ventricular tachycardias (VT) refractory to medical treatment underwent 73 sessions of endocavitary electrode catheter ablation. The clinical series included 16 cases of post-infarction VT, 14 cases of arrhythmogenic right ventricular dysplasia, 6 cases of dilated cardiomyopathy, 6 cases of idiopathic VT, 1 case of sequela of myocarditis and 1 case of VT consecutive to surgical repair of a congenital cardiopathy. Cardiomegaly was present in 30 patients, and 16 patients had an ejection fraction of less than 30 p. 100. None of the patients were receiving digitalis or class I antiarrhythmic drugs when ablation was performed. A total of 235 shocks of 100 to 320 J (mean 221 +/- 42 J) were delivered. 115 shocks (49 p. 100) were complicated by dysrhythmia and/or disorders of conduction; 29 shocks (12 p. 100) induced 13 ventricular fibrillations and 16 ventricular tachycardias. No relation was found between energy delivered, shock synchronization, haemodynamic status, heart cavity treated, underlying heart disease, CK MB levels and these arrhythmias. On the other hand, ablations performed while the patients were experiencing VT increased the risk of arrhythmia (p less than 0.02). 36 AV blocks, 21 left bundle branch blocks, 12 right bundle branch blocks and 11 sinus bradycardia were observed. With the exception of one right bundle branch block and one left posterior hemi-block, all blocks were transient. In practice: (1) electrode catheter ablation may be complicated by disorders of cardiac rhythm or conduction in 50 p. 100 of the cases; (2) these disorders can easily be corrected by stimulation or defibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Self-adhesive monitor/defibrillation pads improve prehospital defibrillation success

We compared self-adhesive, dual-function monitor/defibrillation electrode pads to standard chest monitoring leads and hand-held electrode paddles in the management of prehospital ventricular fibrillation in a single urban paramedic service. Shocks were delivered more quickly following paramedic arrival with self-adhesive pads than with hand-held paddles (1.6 vs 2.5 min; P less than .001). Ventricular fibrillation was terminated more frequently when shocks were delivered using the self-adhesive pads (55 of 58 patients, 95%) than when shocks were delivered using hand-held paddles (49 of 69 patients, 71%; P less than .005). Initial shocks delivered with self-adhesive pads were especially effective, converting 40 of 58 (69%) patients to an organized rhythm on the first or second shock; this was true of only 24 of 69 (35%) patients shocked with hand-held paddles (P less than .001). Patient survival to hospital admission improved when self-adhesive pads were used: 30 of the 58 (52%) patients shocked with self-adhesive pads achieved hospital admission, while only 21 of 69 patients (30%; P less than .025) survived to admission when hand-held paddles were used. In addition, electrical artifact that interfered with accurate rhythm interpretation was far more prevalent when standard monitoring electrodes were used, including artifact that resulted in inappropriate shock delivery (23% of patients monitored with standard electrodes vs 3% of patients monitored with self-adhesive pads; P less than .005). Self-adhesive monitor/defibrillation pads are superior to standard monitoring leads and hand-held electrode paddles in the management of prehospital ventricular fibrillation.     

Efficacy criteria in the fulguration of the bundle of His

The authors have endeavoured to determine which of the parameters commonly used for His bundle ablation are likely to predict that ablation will be effective in altering the atrioventricular (AV) conduction system durability. His bundle ablation was performed in 18 patients (9 men, 9 women; mean age 47 years) presenting with supraventricular tachycardia refractory to all medical treatments. A total of 29 shocks were delivered with an Odam fulgurator, using a distal electrode connected to the positive pole of a selected catheter. Fifteen shocks were effective, resulting in a complete and permanent AV block (group I); the remaining 14 shocks failed to modify permanently the AV conduction system (group II). The parameters which differed between these two groups were the amplitude and the stability of the His bundle potential, the energy per kg bodyweight delivered with the shock and the possibility to shock the potential with the greatest amplitude in case of instability. A discriminant linear analysis showed that 3 interrelated criteria could be used to classify 83% of the shocks into one or the other group. In order of importance these criteria were: (1) amplitude of the His bundle potential; (2)energy delivered per kg bodyweight, and (3) stability of the potential. The corresponding discriminant values for successful results were more than 300 mV for parameter 1, more than 3 J/kg bodyweight for parameter 2 and very good stability of His bundle potential.     

Electrocoagulation of the His bundle node junction in dogs by a high-frequency current delivered by suction catheter

High-frequency currents constitute an attractive form of energy for transcutaneous myocardial destruction, but their potential for creating lesions varies with the nature of contact between electrode and skin. The adequacy of a suction catheter for electrocoagulation of the AV node-His bundle junction was assessed in 7 dogs. The high-frequency current (1.2 MHz) was delivered as bursts of 6 watts lasting 30 seconds, between the distal electrode of a bipolar catheter containing a central lumen (USCI 8F) and a wide skin electrode. During firing, an 80 kPa depression was applied to the lumen. Electrophysiological testing was performed before and immediately after firing. Continuous 24-hour Holter recording was carried out before, immediately after, then between the 2nd and 20th days post-firing. Following another electrophysiological study, the animals were killed on the 15th or 21st day for anatomical study. Complete atrioventricular block was obtained in all dogs during the first (n = 4) or second (n = 3) firing and persisted in 6 dogs up to the time of anatomical study. The atrial and right ventricular electrophysiological parameters remained unmodified after firing, and no severe ventricular arrhythmia was recorded during the study. The histological lesions were 4.7 +/- 0.7 mm in mean diameter and 3.1 +/- 0.6 mm in mean depth. It is concluded that electrocoagulation of the AV node-His bundle junction performed with high-frequency currents is a safe and selective technique. Using suction catheters makes this technique well reproducible with moderate amounts of energy. The development of preformed catheters should reduce the duration of the procedure.     

Microtransection of the His bundle with laser radiation through a pervenous catheter: Correlation of histologic and electrophysiologic data

This study describes microtransection of the His bundle with a pervenous laser catheter in a live dog. In an adult mongrel dog anesthetized with Nembutol®, administered intravenously, electrode catheters (No. 5Fr and 6Fr) were inserted through a femoral vein and positioned in the high right atrium for atrial pacing and in the His bundle region for recording of His bundle electrograms. The AH and HV intervals were measured during normal sinus rhythm and atrial pacing. Through another femoral vein, a laser fiber was inserted through a lumen catheter (No. 7Fr) with a preformed curved tip. Under fluoroscopic control, the laser fiber tip was positioned immediately next to the His bundle electrode catheter. During continuous His bundle recordings and fluoroscopic monitoring, short bursts (10 to 60 seconds) of argon laser were delivered (2.5 W) in order to produce His bundle interruption and complete heart block. Escape of a His bundle rhythm (cycle length = 1,100 ms) with QRS morphologic characteristics and duration similar to that of normal sinus rhythm was noted. “Split” His bundle potentials were recorded with an unchanged AH (50 ms) and an H'V interval of 20 ms. After the dog was killed, serial sections of the conduction system of the heart were analyzed. Histologic findings showed excellent correlation with electrophysiologic observations and validated “split” His bundle potentials. The laser radiation produced microtransection of the His bundle with a channel of tissue dissolution 0.2 to 0.3 mm wide in diameter. The latter passed through the His bundle at the junction of penetrating and branching segments, dividing it into superior and inferior portions that retained continuity with proximal and distal His bundle. Histologically, the atrioventricular node, proximal and distal His bundle segments and bundle branches were uninjured with laser radiation, and are consistent with an unchanged AH time, QRS duration and morphology. This study demonstrates that the His bundle can be precisely transected with a pervenous laser catheter technique.     

Permanent intra-hisian atrioventricular block induced during right intraventricular exploration]

A 47 year old patient underwent endocavitary electrophysiological investigation for recurrent syncopal episodes occuring three years after an inaugural enterior myocardial infarction. Syncopal ventricular tachycardia was induced during the investigation when the bipolar catheter was in contact with the Bundle of His and several external electric shocks were required for its reduction. During cardioversion a complete intra-hisian atrio venticular block was observed and remained permanently although the values of the conduction intervals had previously been normal. This complication of defibrillation is thought to be the result of an induction phenomenon.     

Catheter ablation of left posteroseptal accessory pathways and of long RP' tachycardias with a right endocardial approach

Fifty-four patients with a posteroseptal accessory connection and symptomatic tachycardias underwent catheter ablation of the anomalous pathway. Eight had the permanent form of reciprocating tachycardias (long RP' tachycardia) and 46 had a left posteroseptal preexcitation marked by a prominent R wave in lead VI. In 14 of 19 patients, ventriculoatrial conduction time during tachycardia lengthened in conjunction with functional left bundle branch block; this behaviour was significantly different from a series of patients with right posteroseptal preexcitation in which functional left bundle branch block lengthened the ventriculoatrial time in only one of 12 patients. A quadripolar electrode catheter was left within the proximal coronary sinus in order to locate the earliest atrial or ventricular activation site. The appropriate bipole was used as the radiographic and electrophysiological reference of the insertion of the accessory pathway. A catheter was then positioned on the septal side of the right atrium, outside the coronary sinus, so that atrial activity during reciprocating tachycardia and ventricular activity during preexcitation were synchronous with or earlier than that recorded within the proximal coronary sinus. Accessory pathway potential was not recorded in any patient. Early ventricular potential occurring --1.5 +/- 8 ms relative to delta wave onset was present at that site. In 38 patients, including 5 with permanent junctional tachycardia, high current (14 mA) pacing yielded direct ventricular paced QRS complexes (no delay spike-QRS) with a morphology similar to left posteroseptal maximal preexcitation. Slight movements of catheter position yielded significantly different pace-maps. One to eight 160 J cathodal shocks (510 +/- 213 J cumulative per patient) were delivered at this site in 61 sessions. Following fulguration, tachycardia recurred without drugs in only one patient over a follow-up period of 20 +/- 13 months. Asymptomatic intermittent preexcitation recurred in two patients. In all patients with long RP' tachycardia, the ablation procedure was successful without the need for drugs or permanent cardiac pacing. A long-term follow-up electrophysiological study in 18 patients demonstrated that conduction through the anomalous pathway was absent in 16 and deeply altered in the two patients with intermittent preexcitation; no tachycardia was inducible in any patient. In conclusion, catheter ablation of left posteroseptal accessory pathways is a feasible procedure using a right atrial approach outside the coronary sinus. This technique is also effective for the treatment of the permanent form of reciprocating tachycardia.