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.     

Impaired subsidiary pacemaker function in patients with a right bundle branch block created prior to complete catheter ablation of the AV junction

The impact of a right bundle branch block (RBBB), inadvertentlycreated prior to complete ablation of the atrioventricular (AV)junction, on the intrinsic subsidiary pacemaker function wasinvestigated. In 31 patients suffering from intractable supraventriculartachyarrhythmia, catheter ablation of the AV junction was performedusing direct current (n=13) or radiofrequency (n=18) energy.In 16/31 patients a RBBB was created prior to complete AV ablation.Subsidiary pacemaker function was evaluated after a mean periodof 5 months. Following 5 min of ventricular pacing (70 beats. min^–1) escape interval and spontaneous heart rate weremeasured. In patients with a RBBB there was a trend towardsa longer escape interval (2979±2559 vs 1867±1254ms, P= ns) and a significantly lower intrinsic heart rate (38±14vs 47±8 beats . min^–1, P <0.05). Pacemaker dependencywas only observed among patients with a RBBB (4/16 vs 0/15,P<0.05). HV intervals were shorter in those energy dischargesresulting in a RBBB as compared to those inducing a completeheart block (52±8 vs 66±6 ms, P<0.05). Creationof a RBBB prior to complete ablation of the AV junction resultsin impaired intrinsic subsidiary pacemaker function; the mostproximal catheter position should be carefully sought to minimizethe risk of pacemaker dependency.     

Radiofrequency catheter ablation of the atrioventricular junction from the left ventricle

BACKGROUND. The purpose of this study was to describe a new technique for catheter ablation of the atrioventricular junction using radiofrequency energy delivered in the left ventricle. METHODS AND RESULTS. Catheter ablation of the atrioventricular (AV) junction using a catheter positioned across the tricuspid annulus was unsuccessful in eight patients with a mean +/- SD age of 51 +/- 19 years who had AV nodal reentry tachycardia (three patients), orthodromic tachycardia using a concealed midseptal accessory pathway, atrial tachycardia, atrial flutter (two patients), or atrial fibrillation. Before attempts at catheter ablation of the AV junction, each patient had been refractory to pharmacological therapy, and four had failed attempts at either catheter modification of the AV node using radiofrequency energy or surgical and catheter ablation of the accessory pathway. Conventional right-sided catheter ablation of the AV junction using radiofrequency energy in six patients and both radiofrequency energy and direct current shocks in two patients was ineffective. The mean amplitude of the His bundle potential recorded at the tricuspid annulus at the sites of unsuccessful AV junction ablation was 0.1 +/- 0.08 mV, with a maximum His amplitude of 0.03-0.28 mV. A 7F deflectable-tip quadripolar electrode catheter with a 4-mm distal electrode was positioned against the upper left ventricular septum using a retrograde aortic approach from the femoral artery. Third-degree AV block was induced in each of the eight patients with 20-36 W applied for 15-30 seconds. The His bundle potential at the sites of successful AV junction ablation ranged from 0.06 to 0.99 mV, with a mean of 0.27 +/- 0.32 mV. There was no rise in the creatine kinase-MB fraction and no complications occurred. An intrinsic escape rhythm of 30-60 beats/min was present in seven of the eight patients. Each patient received a permanent pacemaker and has been asymptomatic during 3-13 months of follow-up. CONCLUSIONS. Catheter ablation of the AV junction can be achieved effectively and safely using radiofrequency energy delivered in the left ventricle when the conventional right-sided approach is unsuccessful.     

High success rate of atrioventricular node ablation with radiofrequency energy

Radiofrequency current was introduced as an alternative energy source for transcatheter ablation of cardiac arrhythmias to avoid the complications associated with direct current shocks. Initial use of radiofrequency current for complete ablation of the atrioventricular (AV) node yielded only moderate success rates, presumably because of the small size of electrodes and difficulty in localizing the AV node. The use of a larger 4-mm tip electrode for delivery of radiofrequency current and a method to better localize the AV node were prospectively studied in 32 patients undergoing catheter ablation of the AV node. There were 21 men and 11 women with a mean age of 62 +/- 12 years. Complete AV block was achieved immediately in 31 patients (97%) and it persisted in 28 patients (88%) during a mean follow-up period of 12 +/- 6 months. Three patients who had return of AV condition required no drug therapy for control of ventricular rate during atrial fibrillation. The number of radiofrequency pulses used to achieve complete AV block ranged from 1 to 5 (mean 1.9 +/- 1.1). In greater than 50% of the cases, only one radiofrequency pulse was required. The mean power and duration of radiofrequency pulses were 21.2 +/- 4.5 W and 33 +/- 15 s, respectively. All patients developed a stable junctional escape rhythm within 45 min of successful ablation. The QRS configuration was unchanged in 30 patients. One patient had a new right bundle branch block after ablation. There were no complications related to the ablation procedure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of invasive electrophysiologic testing in the evaluation and management of adult patients with focal junctional tachycardia

Focal junctional tachycardia (FJT) is characterized by a rapid often irregular narrow complex tachycardia with episodes of atrioventricular (AV) dissociation. This uncommon arrhythmia is most likely due to abnormal automaticity or triggered activity. The patients are often quite symptomatic and if left untreated may develop heart failure particularly if their tachycardia is incessant. In patients refractory to medical management, the role of radiofrequency ablation involves either (1) selective ablation of the tachycardia focus while preserving AV conduction or as a last resort (2) AV junction ablation followed by pacemaker implantation. The clinician should first assess whether ventriculoatrial (VA) conduction is present or absent during tachycardia. If present, radiofrequency ablation should be applied at the site of earliest retrograde atrial activation. In the absence of VA conduction and hence an atrial target site, sequential lesions should be applied in the posterior septum (slow pathway region) followed by lesions applied in midseptum and anteroseptum respectively if tachycardia persists. To further minimize the risk of AV nodal block, some authors delivered radiofrequency energy during atrial overdrive pacing to assess AV conduction during ablation. Others recommended mapping the perinodal region and applying radiofrequency ablation at the site where catheter manipulation resulted in tachycardia termination. Using this ablative approach, the risk of AV block is around 5–10%.     

Ablation of the atrioventricular junction with radiofrequency energy using a new electrode catheter

Percutaneous catheter ablation using radiofrequency energy can be used to interrupt atrioventricular (AV) conduction in patients with supraventricular tachycardia refractory to drugs. Results of radiofrequency ablation of the AV junction using a custom-designed catheter with a large, 3-mm-long distal electrode, 2-mm interelectrode spacing, and a shaft with increased torsional rigidity were compared with those using a standard quadripolar electrode catheter (Bard EP). An electrocoagulator (Microvasive Bicap 4005) supplied unmodulated radiofrequency current at 550 kHz, which was applied between the distal electrode of the ablation catheter and a large skin electrode. With use of the modified catheter, 12 of 13 patients (92%) had persistent complete AV block induced with 7 +/- 5 applications of 18 +/- 6 W of radiofrequency power. In contrast, complete AV block was produced in only 9 of 18 (50%) historical control patients treated with the standard catheter, despite a similar number of applications (7 +/- 5) and power output (16 +/- 4 W). A rise in impedance, due to desiccation of tissue and coagulum formation, occurred earlier (28 +/- 18 vs 52 +/- 24 seconds, p less than 0.001) and more frequently (54 vs 40% of applications, p = 0.047) in patients treated with the standard catheter than in patients treated with the modified catheter. The use of a catheter designed to increase the surface area of electrode-tissue contact allows more radiofrequency energy to be delivered before a rise in impedance occurs and appears to increase the effectiveness of radiofrequency ablation of the AV junction.     

Long term results of fast pathway ablation in atrioventricular nodal reentry tachycardia using a modified technique.

OBJECTIVE--To assess immediate and long term success of "fast" pathway catheter ablation with graded use of radiofrequency energy in patients with classic atrioventricular nodal reentrant tachycardia (AVNRT) and evaluate clinical, procedure related, and electrophysiological features affecting long term results. DESIGN--31 consecutive patients with classic AVNRT at electrophysiological study, who were candidates for radiofrequency ablation. Patients were followed for an average of 24 months after ablation. SETTING--All studies and ablations were performed in an electrophysiological laboratory under fluoroscopic guidance using standard electrophysiological techniques. INTERVENTION--Radiofrequency application was performed at the site of proximal His bundle electrogram with A:V ratio of > 1. It was started at 10 W with increment of 5 W to a maximum of 25 W at 60 s. With the onset of junctional rhythm, atrial pacing was begun in order to monitor the PR interval. Application was terminated prematurely with a non-conducted P wave, continued prolongation of the PR interval beyond 50% of the baseline, or a threefold rise in impedance. RESULTS--Successful ablation was possible in 30/31 patients (97%) with an average of seven applications (range 1-10). It was associated with significant prolongation of PR interval (P < 0.001) and AV Wenckebach cycle length (P = 0.01). Ventriculo-atrial conduction was abolished in 24/30 patients (82%) with successful ablation. Two patients developed transient complete heart block (3 and 12 min) and one persistent right branch block. Four patients had late recurrence. Presence of ventriculo-atrial block was the only electrophysiological index predictive of long term success (P = 0.01). CONCLUSIONS--Graded use of radiofrequency energy and atrial pacing to monitor PR interval decreases the risk of atrioventricular block in patients undergoing fast pathway ablation for AVNRT. Ventriculo-atrial block is predictive of long term success and should be a preferred end point for fast pathway ablation.     

Invasive Elektrophysiologie: Komplikationen, Alpträume und deren Management

Most minor side effects of ablation in the right atrium and right ventricle relate to femoral venous catheterization but there is a small risk of severe complications including atrioventricular (AV) block, damage of surrounding structures and thromboembolic events. Impairment of AV conduction can occur during ablation of atrioventricular re-entrant tachycardia, ablation of anteroseptal, mid-septal and parahisian accessory pathways, ablation of ectopic atrial tachycardia originating from the vicinity of the atrioventricular node and when ablating the septal isthmus for typical atrial flutter. Damage of the right coronary artery is a very rare complication after inferior isthmus ablation with high energy. The thromboembolic risk during and after cardioversion and ablation of atrial flutter is higher than previously recognized and anticoagulation therapy decreases this risk. The risk of perforation and tamponade during ablation in the right atrium and right ventricle is very low but particular caution is necessary in thin-walled structures such as the coronary sinus and the upper right ventricular outflow tract. Phrenic nerve injury can be avoided by pacing from the mapping electrode before application of radiofrequency energy at the right atrial free wall. Limitation of power output depending on the site of ablation and titration of energy application with continuous control of temperature and impedance should be considered to minimize the risk of complications.     

Chronic incomplete atrioventricular block induced by radiofrequency catheter ablation

To determine if catheter ablation of the atrioventricular (AV) junction with radiofrequency energy can induce chronic incomplete (first- and second-degree) AV block to avoid the need for a permanent pacemaker, 20 closed-chest dogs were studied. Group 1 (10 dogs) received radiofrequency energy (750 kHz) with a fixed power setting (5 or 10 W) while increasing the pulse duration from 10 to 50 seconds for each application. Group 2 (10 dogs) received energy with a fixed pulse duration (20 or 30 seconds) while increasing the power setting from 5 to 10 W or from 10 to 20 W during each energy delivery. Radiofrequency energy was delivered between a chest-patch electrode and the distal electrode of a regular 7F tripolar His bundle catheter. For each application, the energy delivery was interrupted when 1) the PR interval prolonged (greater than 50%) or 2) second-degree or complete AV block occurred and persisted up to 5 seconds. The ablation procedure ended when there was 1) persistent PR prolongation (greater than 50%) or persistent second-degree AV block (lasting greater than 30 minutes) after ablation, 2) occurrence of two consecutive transient (less than 1 minute) complete AV blocks after each energy delivery, or 3) complete AV block (lasting greater than 2 minutes) after ablation. Of seven dogs in group 1 and five dogs in group 2 in which incomplete AV block was achieved 1 hour after the procedure, six in group 1 and five in group 2 remained in incomplete AV block 2-3 months after ablation. One dog in group 1 progressed into complete AV block. Of the remaining three dogs in group 1 and five dogs in group 2 in which complete AV block was initially achieved 1 hour after ablation, two in group 1 and four in group 2 continued to have complete AV block, whereas one in each group had AV conduction returned to incomplete at 1-2 months of follow-up. Thus, a total of 13 dogs had chronic incomplete AV block induced by radiofrequency catheter ablation. Pathologic examination of the conduction system in two dogs with first-degree AV block, two dogs with second-degree AV block, and one dog with complete AV block showed discrete scars involving the approaches to the AV node and the AV node itself. It is concluded that, in most dogs studied, chronic incomplete AV block could be achieved by careful titration of the dosage of radiofrequency energy and by regulation of the ablation end points.     

Isolated atrial segment pacing: an alternative to His bundle pacing after atrioventricular junctional ablation.

OBJECTIVES: This study was designed to investigate a practical alternative to His bundle pacing after atrioventricular (AV) junctional ablation by pacing a small area of isolated atrial tissue surrounding the AV node. BACKGROUND: His bundle pacing is preferred after AV junctional ablation in patients with refractory atrial fibrillation. However, it is technically difficult and not clinically useful at the present time. METHODS: This study was conducted in an isolated working swine heart model (n = 5), with real-time imaging capabilities. A small area of atrial tissue surrounding the AV node and the His bundle was isolated using sequential radiofrequency ablation lesions. RESULTS: Complete AV block created by segmental atrial isolation was achieved in 5 of 5 experiments. The isolated atrial segment was bordered by the ablation lines, the tricuspid annulus, and the AV node-His bundle. The AV conduction was characterized using a pacing electrode implanted into the isolated atrial segment. Pacing from the atria, the ventricles, and the isolated atrial segment at different rates confirmed complete bidirectional block between the atria and isolated area, whereas antegrade and retrograde AV nodal conduction between the isolated atrial segment and the ventricles remained intact. Pacing from the isolated area produced minimal changes in systolic left ventricular pressure compared with baseline sinus rhythm (mean -2 mm Hg). CONCLUSIONS: Isolation of a small area of atrial tissue surrounding the AV node is feasible by transcatheter radiofrequency ablation. This procedure may be a useful alternative to conventional AV junctional ablation because it can create complete AV block, while in effect permitting the equivalent of His bundle pacing after AV junctional ablation.     

Temperature-controlled slow pathway ablation for treatment of atrioventricular nodal reentrant tachycardia using a combined anatomical and electrogram guided strategy

AIMS: Anatomical and electrogram-guided techniques have been usedseparately for slow pathway ablation in atrioventricular nodalreentrant tachycardia. The aims of the present study were toanalyse electrogram characteristics of target sites and biophysicalparameters using a combined anatomical and electrogram-guidedtechnique for temperature-controlled radiofrequency catheterablation of the slow pathway. METHODS AND RESULTS: Using a temperature-controlled (pre-selected 60 °C) cathetersystem, 53 patients with atrioventricular nodal reentrant tachycardiaunderwent slow pathway radiofrequency ablation. Mapping wasstarted posteroseptally near the coronary sinus ostium and continuedtowards the midseptal area if needed. The longest and latestatrial electrograms with an atrioventricular ratio of 0·5were targeted. After a median of two pulses (mean 2·36± 1·33), atrioventricular nodal reentrant tachycardiawas rendered non-inducible in all patients without complications.Successful sites had longer atrial electrograms (78·8± 9·8 vs 67·6 ± 13·3 ms,P<0·003) and larger ventricular electrogram amplitudes(92·4 ± 51·2 vs 63·1 ± 28·8mV, P<0·05) than the failed sites, but had a similaratrioventricular ratio, P-A interval and atrial electrogramamplitude. Overall, an atrial electrogram duration of 70 mswas associated with effective radiofrequency delivery, with86% sensitivity and 62% specificity. The achieved temperaturemaximum was 62·3 ± 9·8 °C at successfuland 58·8 ± 9·0 °C at unsuccessful sites(ns). There was no significant difference between successfuland unsuccessful applications with respect to power output,impedance and total delivery energy. During a pre-dischargestudy, three patients with inducible atrioventricular nodalreentrant tachycardia underwent a repeat ablation. During 12·3± 2·5 (6–15) months of follow-up, threeothers had a clinical recurrence of atrioventricular nodal reentranttachycardia. CONCLUSIONS: The combined approach for slow pathway ablation is highly effective,requiring a low number of radiofrequency pulses. Long atrialactivation time seems to be the most powerful predictor of success.Similar catheter tip temperature levels during successful andunsuccessful radiofrequency applications indicate that suboptimalselection of target sites rather than ineffective heating dueto poor catheter tissue coupling is responsible for unsuccessfulenergy delivery.     

Slow pathway ablation in patients with atrioventricular node reentrant tachycardia and a prolonged PR interval

Objectives. We sought to assess the safety and efficacy of selective slow pathway ablation using radiofrequency energy and a transcatheter technique in patients with a prolonged PR interval and atrioventricular (AV) node reentrant tachycardia.Background. Although both fast and slow AV node pathways can be ablated in patients with AV node reentrant tachycardia, slow pathway ablation, by obviating the risk of AV block, appears to be safer. However, the safety and efficacy of selective slow pathway ablation using transcatheter radiofrequency energy in patients with a prolonged PR interval during sinus rhythm are unclear.Methods. The seven study patients with a prolonged PR interval (mean ± SD 237 ± 26 ms) comprised three women and four men with a mean age of 31 ± 15 years. The slow pathway was targeted in all seven patients at the posterior/inferior interatrial septal aspect of the tricuspid annulus. Two patients presented with the uncommon variety of AV node reentrant tachycardia after initial fast pathway ablation; in the remaining five patients, the AV node reentrant tachycardia was of the common variety.Results. A single radiofrequency pulse at 30 W successfully abolished the slow pathway in both the anterograde and the retrograde direction in the two patients with uncommon AV node reentrant tachycardia. A mean of 5 ± 3 radiofrequency pulses were required in the remaining five patients with reentrant tachycardia of the common variety. The postablation PR interval and AH interval remained unchanged. The shortest cycle length of 1:1 AV conduction was prolonged significantly (from 327 ± 31 to 440 ± 59 ms, p < 0.01, as was the AV node effective refractory period (from 244 ± 35 to 344 ± 43 ms, p < 0.01). During a mean follow-up interval of 20 ± 6 months, no patient developed symptoms suggestive of AV node reentrant tachycardia or had evidence of second- or third-degree AV block.Conclusions. These data suggest that the AV node slow pathway can be ablated in patients with AV node reentrant tachycardia who demonstrate a prolonged PR interval during sinus rhythm.     

Randomized comparison of bipolar vs unipolar plus bipolar recordings during atrioventricular junction ablation: importance and efficacy of unipolar recording.

BACKGROUND: No prior studies have clarified the utility and efficacy of unipolar recording for identifying successful sites for atrioventricular junction (AVJ) ablation. METHODS AND RESULTS: Thirty-six patients underwent radiofrequency (RF) AVJ ablation for drug-resistant atrial fibrillation (AF) or AF/flutter. AVJ ablation was performed with either bipolar (Bi-group; n=18) or unipolar plus bipolar recording (Uni-group; n=18). In the Uni-group, the primary parameter used to select ablation sites was a QS or rS morphology of the His bundle unipolar recording. There was no significant difference between the 2 groups for the bipolar electrogram characteristics at the successful ablation site. However, in the Uni-group, the procedure time and fluoroscopy duration were shorter (both p<0.05), and the total number of RF energy applications less (p<0.05) than in the Bi-group. In the Uni-group, unipolar His bundle recordings could be assessed in 26 (76%) of 34 RF energy applications: Complete atrioventricular block was obtained at 15 (83%) of 18 sites with QS morphology and in 3 (37%) of 8 sites with rS morphology on the unipolar His bundle recording. CONCLUSIONS: AVJ ablation can be achieved more efficiently and with fewer RF energy applications when guided by unipolar recordings than by bipolar recordings alone.     

Catheter ablation of the atrioventricular junction using radiofrequency energy and a bilateral cardiac approach.

Radiofrequency current catheter ablation was used successfully to create complete atrioventricular (AV) block in 60 of 61 patients (98%) with drug refractory supraventricular tachyarrhythmias. The remaining patient developed Mobitz I AV block and is clinically improved (clinical efficacy 100%). In 54 patients (89%), complete AV block was achieved using a right-sided approach. Patients aged > 60 years needed significantly fewer right-sided radiofrequency applications to produce complete AV block (5.3 +/- 5.3 vs 11.1 +/- 10.0; p = 0.009). In 6 of 7 patients with unsuccessful right-sided ablation, a left ventricular approach was used. In each case, 1 to 4 additional radiofrequency applications produced complete AV block. Patients with unsuccessful right-sided ablation were generally younger than those with successful ablation (50 +/- 16 vs 64 +/- 11; p = 0.007). It is concluded that catheter ablation using radiofrequency current is an extremely effective means of producing complete AV block. Older patients appear to be more susceptible to right-sided radiofrequency approaches. Left ventricular ablation easily produces complete AV block in patients refractory to right-sided attempts.     

射频消融改良房室结控制特发性心房颤动所致快速心室率

采用射频消融改良房室结的方法控制７例特发性心房颤动（简称房颤）病人的快速心室率。５例持续性房颤在房颤时消融，２例阵发性房颤在窦性心律时消融，平均放电６±４次，６例成功，１例失败。成功的病例术后复查动态心电图示静息时房颤的平均最大心室率和平均心室率分别从术前的１６５±１１和１３６±１０ｂｐｍ下降到１１１±１４和８８±１１ｂｐｍ（Ｐ均＜０．００１）。平均随访５±４月患者无明显症状，不服药静息心室率均低于１１０ｂｐｍ，有１例阵发性房颤发作显著减少。结果提示：对于症状明显、药物治疗无效的特发性快速房颤的病例，射频消融改良房室结是控制心室率安全和有效的方法。有关机理和远期疗效有待进一步评价     

Catheter ablation of the atrioventricular junction with radiofrequency energy

Catheter ablation of the atrioventricular junction using direct-current defibrillator discharges requires general anesthesia and may have serious side effects. Sixteen patients with drug-refractory supraventricular tachycardia underwent catheter ablation of the atrioventricular junction using radiofrequency energy. A standard 7F quadripolar electrode catheter was positioned to record the largest unipolar His potential (580 +/- 640 microV) from the distal electrode. An electrocoagulator (Microvasive Bicap 4005) supplied continuous, unmodulated energy at 550 kHz. One to 14 applications of radiofrequency current were delivered between the distal electrode and a large-diameter chest wall electrode. Transient, mild chest discomfort was reported by seven of 16 patients. None had significant arrhythmias or blood pressure changes during radiofrequency ablation. Complete atrioventricular block was produced in nine of 16 patients and high-grade second-degree atrioventricular block was produced in one patient with radiofrequency current. Attenuated His bundle electrograms could still be recorded in the remaining six patients, four of whom underwent successful atrioventricular junctional ablation using direct-current shock during the same session. Atrioventricular block persisted in all 10 patients successfully treated with radiofrequency ablation during a mean follow-up of 4.2 months. Compared with a group of historic control subjects treated with direct-current shock ablation, the 10 patients successfully treated with radiofrequency current had significantly less creatine kinase-MB isoenzyme release (5.7 +/- 5.1 vs. 22 +/- 13 IU, p = 0.006). A junctional escape rhythm was present in all patients after radiofrequency-induced atrioventricular block. In contrast, three of 10 control patients had an idioventricular escape after direct current shock ablation, and four patients had no escape rhythm at all.(ABSTRACT TRUNCATED AT 250 WORDS)     

Catheter ablation of accessory pathways in children

The efficacy and safety of catheter ablation of accessory pathways(AP) was studied in 79 children (age, 4–16 years), usingDC shocks (n=25) or radiofrequency energy (n=54). All patientshad docwnented arrhythimias including ventricular fibrillationin four. Organic heart disease was present in four patients.AP locations were left lateral (n=36), posteroseptal (n=36),right lateral (n=8), Mahaim fibres (n=2) and right anteroseptal(n=6). Seven patients had multiple AP. One patient had a preexcitationwhich appeared secondary to an atrio-infundibular connection(Fontan procedure). The ablation site of concealed or overtAP was identified by retrograde or anterograde conduction mapping,respectively. A mean of 2·6 ± 1 cathodal shocks (80–160J) was delivered to 25 patients over 29 sessions, resultingin initial AP ablation in all. Fulguration was uncomplicatedin all except in one patient (4%) who developed a secondarycomplete AV block post-ablation. During a follow-up period of30–69 months, intermittent preexcitation recurred in twoasymptomatic patients, but no significantly tachycardia wasinducible at late electrophysiological study, including underisoproterenol infusion. Radiofrequency energy was applied to 54 patients during 62 sessions,using 20–40 watts for 30–60 s. AP ablation was initiallyachieved in all patients using a median of three impulses, withoutsignificantly immediate side-effects. Two patients (4%) developeda short episode of blurred vision possibly due to a microembolism.After discharge, the follow-up period was 10 ± 5 months(range 1 to 24). All patients but one (98%) were asymptomaticwithout any drug therapy. AP conduction and tachycardias recurredin one child, within one month after radiofrequency catheterablation. Asymptomatic intermittent preexcitation recurred inanother patient who had had three AP; a late study showed noinducible reciprocating tachycardia even wider isoproterenolinfusion and a minimal preexcited RR interval of 350 ms duringinduced atrial fibrillation. It is concluded that catheter ablation is an effective and relativelysafe method for ablation of AP in children.     

Atrial pacing during radiofrequency ablation of junctional ectopic tachycardia--a useful technique for avoiding atrioventricular bloc

Radiofrequency catheter ablation (RFCA) was performed on a 5-year-old boy with congenital junctional ectopic tachycardia (JET) that was refractory to medical management. Because of the lack of retrograde atrial depolarization during tachycardia, radiofrequency energy was delivered during atrial overdrive pacing to confirm the presence of preserved atrioventricular (AV) conduction. Although the procedure was complicated by complete right bundle branch block after ablation of the para-Hissian region, the patient regained sinus rhythm accompanied by normal AV conduction. Rapid atrial pacing during RFCA of JET may be safely used to avoid AV block.     

Fast pathway ablation in patients with common atrioventricular nodal reentrant tachycardia and prolonged PR interval during sinus rhythm

Aims This study aimed to clarify the safety and efficacy of selectivefast pathway ablation in patients with atrio-ventricular nodalreentrant tachycardia and a prolonged PR interval during sinusrhythm. Such patients have been reported to have an increasedincidence of complete atrioventricular block. Methods and Results In this study, the earliest retrograde atrial activation duringatrioventricular nodal reentrant tachycardia and right ventricularstimulation was localized. Fast pathway ablation was then performedin five patients with the common form of atrioventricular nodalreentrant tachycardia and a prolonged PR interval. Three ofthe five patients had almost incessant atrioventricular nodalre-entrant tachycardia. Radiofrequency catheter ablation induceda complete ventriculo-atrial block during right ventricularstimulation in four patients and a marked prolongation of ventriculo-atrialconduction during right ventricular stimulation in one. Non-inducibilityof common atrioventricular nodal reentrant tachycardia withand without isoproterenol was achieved in all five patients.The PR interval increased from 254±53ms to 276±48msand the atrio-His interval from 172±46ms to 192±45ms.Second- or third-degree atrioventricular block did not occurduring the ablation procedure. During the follow-up of 19±20months none of the patients developed symptoms suggestive ofatrioventricular nodal reentrant tachycardia or evidence ofsecond- or third-degree atrioventricular block. Conclusion These data suggest that atrioventricular node (retrograde) fastpathway ablation can apparently be safely performed in patientswith common atrioventricular nodal reentrant tachycardia anda prolonged PR interval during sinus rhythm.     

Radiofrequency Catheter Ablation Versus Modification of the AV Node for Control of Rapid Ventricular Response in Atrial Fibrillation

AV Node Modification vs Ablation in AF. Atrial fibrillation is a common arrhythmia, which is frequently difficult to control. Symptoms and ventricular dysfunction may be caused by a rapid ventricular response to atrial fibrillation. Radiofrequency catheter ablation techniques for ventricular rate control have been developed, including AV node modification and AV node ablation with pacemaker implantation. For both AV node modification and ablation, radiofrequency energy is applied via a 4-mm tipped electrode catheter. For AV node ablation radiofreqnency energy is applied near the compact AV node or His bundle via the right atrium, or occasionally at the His bundle via the left ventricle. For AV node modification radiofrequency energy is applied in the low middle or posterior septal right atrium near the tricuspid valve annulus. Both techniques can effectively control ventricular response to atrial fibrillation and the associated symptoms, although AV node modification is effective in only about 70% of patients compared to AV node ablation, which is effective in nearly 100%. In patients responding to AV node modification, maximal and mean ventricular response to atrial fibrillation is reduced by 25% to 35% chronically. Inadvertent AV block may occur during attempted AV node modification. It seems appropriate to attempt AV node modification prior to AV node ablation in patients with refractory atrial fibrillation and rapid ventricular response, in order to avoid the need for permanent pacemaker implantation. Although unproven, studies suggest that the mechanism by which AV node modification achieves ventricular rate control may he slow-pathway ablation in the low posterior septal right atrium.