Improvement of atrioventricular conduction following catheter ablation of atrioventricular nodal reentry tachycardia in a patient with a prolonged PR interval

We herein present the case of a 60-year-old male with narrow QRS tachycardia who had a remarkable PR prolongation during sinus rhythm. The tachycardia was diagnosed as a slow–fast atrioventricular nodal reentry tachycardia. Slow pathway ablation was performed after the confirmation of the presence of an antegrade fast pathway. Following the elimination of the slow pathway, the PR and atrio-His intervals became shortened from 470 and 420 to 170 and 120 ms, respectively. Moreover, the improvement of atrioventricular conduction after the slow pathway ablation lasted for at least 34 months.     

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.     

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.     

房室结内折返性心动过速慢径路消融中房室传导阻滞的预防

目的 探讨房室结内折返性心动过速(AVNRT)慢径路消融中房室传导阻滞的预防措施。方法 72例AVNRT患者从小功率(5W)开始放电，逐步增加放电功率，根据放电时的反应，及时改换安全的放电部位；放电过程中不苛求房室交接区心律从有到无的规律；慢径路改良，不苟求慢径路消失，以不诱发心动过速为宗旨。结果 72例慢径路消融均成功，无一例发生房室传导阻滞的并发症，无一例远期复发。结论 从小功率开始放电，慢径路改良等措施，可有效预防房室传导阻滞，且对远期复发无影响。     

Cryosurgical ablation of atrioventricular nodal reentry: histologic localization of the proximal common pathway

A method using cryosurgery has been previously described to selectively ablate atrioventricular nodal reentry tachycardia while preserving intact atrioventricular conduction. The purpose of the present study was to define the histologic features of the cryolesions in relationship to the specialized conduction system. In 12 adult dogs a series of nine discrete cryolesions was placed along the perimeter of the triangle of Koch while continuously monitoring the His bundle electrogram. All animals survived the operation and maintained intact atrioventricular conduction. At 14 weeks after surgery the hearts were sectioned and examined. In all 12 animals there was a confluent mass of dense fibrous tissue present in the lower atrial septum that was in immediate proximity to but did not involve the atrioventricular node-His bundle. The ablation of perinodal tissue with preservation of the specialized conduction system with the use of this cryosurgical technique was confirmed. It is likely that the cryoablated perinodal tissue represents the proximal common pathway of the circuit for atrioventricular nodal reentry tachycardia.     

Long-term safety and efficacy of slow pathway ablation in patients with atrioventricular nodal re-entrant tachycardia and pre-existing prolonged PR interval.

The association of atrioventricular nodal re-entrant tachycardia (AVNRT) and pre-existing prolonged PR interval is unusual. Radiofrequency (RF) ablation in such patients may be associated with an increased risk of immediate and delayed AV block. The aim of our study is to assess the long-term efficacy and safety of slow pathway ablation in this population. We studied 10 patients (4 males and 6 females) with pre-existing prolonged PR interval of 68 consecutive patients with AVNRT. All had slow-fast subtype of AVNRT. The mean PR interval was 222 +/- 15 ms before RF. The patients with pre-existing prolonged PR were older (69 +/- 15 vs. 54 +/- 17, P = 0.008) and their tachycardias were slower (387 +/- 102 vs. 323 +/- 73 ms; P < 0.05). Transient complete AV block (<5 s) occurred in two patients. None had permanent complete AV block. One patient had a significant increase in PR interval (from 220 to 320 ms). The mean post-RF PR interval was 232+/-37 ms (P = n.s.). Over a mean follow-up of 39 +/- 21 months, none had a recurrence of tachycardia nor developed higher degree AV block. In conclusion, in patients with AVNRT and pre-existing prolonged PR interval, a slow pathway ablation appeared efficient and safe. From our data, no delayed AV block developed on a long follow-up. Most of the patients with periprocedural transient AV block had no evidence of dual AV node physiology, suggesting that, in this population, absence of dual AV node physiology may be associated with a higher risk of AV block during slow pathway ablation.     

Slow atrioventricular nodal pathway affecting fast pathway conduction

A 15‐year‐old girl with a history of paroxysmal supraventricular tachycardia underwent an electrophysiology study (EPS) for diagnosis and ablation. Her baseline electrocardiogram and echocardiogram were normal. At EPS, she had dual atrioventricular nodal (AVN) conduction, but isoproterenol was needed to initiate the slow‐fast form of AVN reentry. Before ablation without any isoproterenol, she began to have a spontaneous block in the fast pathway with continuous conduction over the slow pathway. After ablation of the slow pathway, all complexes conducted over the fast pathway during a 25‐year follow‐up. Possible electrotonic interaction between the slow and fast pathways is proposed as the mechanism for this phenomenon.     

Differential effects of adenosine on antegrade fast pathway,antegrade slow pathway,and retrograde fast pathway in atrioventricular nodal reentry

Adenosine has a potent negative dromotropic effect. However, comparative effects of adenosine on the three pathways of atrioventricular (AV) nodal reentry remain unclear. In this study, we sought to determine the effects of adenosine on the antegrade fast, antegrade slow, and retrograde fast pathway conduction in patients with AV nodal reentrant tachycardia (AVNRT). Twenty patients with common slow-fast AVNRT (mean cycle length 360 +/- 49 ms) were studied. The effects of adenosine on the antegrade slow pathway and on the retrograde fast pathway conduction were determined during sustained AVNRT and constant right ventricular pacing at identical cycle lengths (mean 360 +/- 49 ms), respectively. Incremental doses of adenosine were rapidly administered: initial dose of 0.5 mg, followed by stepwise increases of 0.5 or 1.0 mg given at 5-min intervals until termination of AVNRT or second-degree ventriculoatrial block occurred. After the antegrade slow pathway conduction was selectively and completely ablated by radiofrequency catheter ablation, the effect of adenosine on the antegrade fast pathway conduction was evaluated. The dose-response curve of adenosine and the dose of adenosine required to produce AV or ventriculoatrial block among the representative three conduction pathways were compared. The dose-response curve for the effect of adenosine on the antegrade fast pathway lies to the left and upward to that of the effect of adenosine on the antegrade slow pathway which in turn lies to the left and upward to that of the retrograde fast pathway. The mean dose of adenosine required to produce conduction block at antegrade fast, antegrade slow, and retrograde fast pathways were 1.4 +/- 0.5, 4.2 +/- 1.6, and 8.5 +/- 2.6 mg, respectively (p < 0.01). Adenosine has a differential potency to depress antegrade fast, antegrade slow, and retrograde fast pathway conduction in patients with AVNRT. The depressant effect of adenosine on the antegrade fast pathway is more potent than that on the antegrade slow pathway which in turn is more potent than that on the retrograde fast pathway conduction.     

Catheter ablation of accessory pathways and atrioventricular nodal reentry tachycardia

Radiofrequency current catheter ablation has gained acceptance as primary long-term therapy for patients with symptomatic accessory pathways and symptomatic atrioventricular nodal reentrant tachycardia (AVNRT) with frequent recurrences. In both arrhythmias, curative treatment is possible in more than 90% of cases at a low complication rate although an incidence of about 1% complete AV block after slow pathway ablation has to be taken into account when this therapy is considered. The recurrence rate is 3-10% for accessory pathways and 0-15% for AVNRT. The high success rate of catheter ablation has already led to a shift in the indications for the procedure where the percentage of patients with accessory pathways is decreasing and there is an increase of patients with AVNRT and newer indications (atrial flutter, focal atrial tachycardias).     

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.     

Catheter ablation of retrograde fast pathway in patients with atrioventricular nodal reentrant supraventricular tachycardia.

Atrioventricular (AV) nodal reentrant tachycardia is a common cause of supraventricular tachycardia. The present study describes catheter ablation of this form of tachycardia in 23 patients using direct current shocks. The aim of ablation was to abolish conduction through the retrograde pathway while preserving the anterograde conduction. All patients had symptomatic, drug resistant, slow-fast variety of dual atrioventricular nodal reentrant tachycardia. Using the retrograde atrial activation in the His bundle catheter as the reference, the optimal ablation site was selected by positioning an electrode catheter to obtain atrial activation synchronous with or earlier than the atrial activation at the reference electrode. Shocks of 100-300 joules were delivered at this site resulting in blockade of retrograde conduction in all patients. Ventriculo-atrial conduction studied 24 hours after the procedure was still absent in 16, modified in 2 and resumed in 3 patients. Two patients developed permanent complete heart block and were given pacemakers. At repeat electrophysiologic study performed after 2-4 months in 10 patients, the supraventricular tachycardia could not be induced. The AH interval was 67 +/- 10 msec during control study and to 115 +/- 39 msec at restudy (p < 0.001). The ventriculo-atrial conduction was absent in 7 cases and had been modified in 1 case. Over a follow up period of 1-30 months (mean 10.8 +/- 7.1 mo) 17 patients (73%) remained free of the arrhythmia without medication or pacemaker. Three other patients were easily controlled with digoxin. Thus, catheter modification of AV node results in permanent cure of the AV nodal tachycardia in majority of patients.     

中位法射频消蚀慢径路治疗房室结折返性心动过速

导管射频消蚀术（ＲＦＣＡ）治疗房室结折返性心动过速４３例，采用＂中位法＂选择性阻断慢径路，该技术的关键是：①在Ｘ线右前斜位３０度下，将消蚀电极置于冠状窦口和希氏束连线的中点附近；②消蚀电极双极记录到小Ａ大Ｖ波；③放电时有交界性心律（包括快交界律、慢交界律、交界性早搏）；④以间断放电和时间递增的方法控制消蚀过程；⑤消蚀终点为放电总累积时间达６０～９０秒，重复电生理检查证实慢径阻断或心动过速不能诱发。经１～３个部位的消蚀彻底阻断慢道３６例，遗留慢径传导７例（有心房回波２例）。除１例术后第二天发生一过性Ⅲ°ＡＶＢ，二周恢复正常外，余无并发症发生，随访３～２４个月（平均１４±６），停用任何抗心律失常药，无心动过速发作。消蚀成功率１００％。认为“中位法”是消蚀房室结慢径路治疗房室结折返性心动过速的安全、简便和有效的方法，部分病例保留慢传导并不增加复发率。     

Radiofrequency catheter ablation of the slow pathway for atrioventricular nodal reentry in a patient with an obstructed inferior vena cava

A 51-year-old man with an obstructed inferior vena cava underwent successful slow pathway catheter ablation using a superior venous approach. Two central venous sheaths were introduced into the right internal jugular vein using different approaches (anterior and posterior), so the two sheaths located away from each other could prevent the catheters from 'sticking' to one another. The transseptal long sheath enabled a stable positioning of the ablation catheter. A nonfluoroscopic mapping system could reduce radiation exposure to the ablator. These techniques may be useful to overcome the disadvantages of the superior venous approach compared to the inferior venous approach.     

房室结折返性心动过速慢径消融终点与复发的关系

目的:观察房室结折返性心动过速(AVNRT)的慢径消融终点与复发的联系。方法:534个慢-快型AVNRT患者行慢径消融治疗,观察A型终点(彻底消融慢径,房室结无跳无折)和B型终点(残留慢径有或无1～3心房回波,不能诱发AVNRT)与AVNRT复发的联系及对房室结传导的影响。结果:①A型复发5例(1.2%),B型复发11例(9.4%),差异有统计学意义(P0.05)。②A型终点房室结前传文氏周期(Wen-AVN)、快径前传有效不应期和房室结双径路(DAVNP)的跳跃增值缩短,B型快径前传有效不应期和房室结双径路的跳跃增值缩短,A型有效不应期的缩短明显大于B型。结论:A型终点的复发率明显低于B型终点;只要改变房室传导功能,不能诱发心动过速,B型终点仍然是有效、可靠的消融终点。     

Retrograde block during dual pathway atrioventricular nodal reentrant paroxysmal tachycardia

There are limited reported data regarding the occurrence of retrograde block during dual pathway atrioventricular (A-V) nodal reentrant paroxysmal tachycardia. This study describes two patients with this phenomenon. The first patient had 2:1 and type 1 retrograde ventriculoatrial block during the common variety of A-V nodal reentrance (slow pathway for anterograde and fast pathway for retrograde conduction). Fractionated atrial electrograms suggested that the site of block was within the atria. The second patient had type 1 retrograde block (between the A-V node and the low septal right atrium) during the unusual variety of A-V nodal reentrance (stow pathway for retrograde and fast pathway for anterograde conduction). The abolition of retrograde block by atropine suggested that the site of block was within A-V nodal tissue. Both cases demonstrate that intact retrograde conduction is not necessary for the continuation of A-V nodal reentrant paroxysymal tachycardia. Case 2 supports the hypothesis that the atria are not a requisite part of the A-V nodal reentrant pathway.