The Electrophysiologic Characteristics in Patients with Only Ventricular-Pacing Inducible Slow–Fast Form Atrioventricular Nodal Reentrant Tachycardia

Background: Atrioventricular nodal reentrant tachycardia (AVNRT) can be usually induced by atrial pacing or extrastimulation. However, it is less commonly induced only by ventricular pacing or extrastimulation. Objective: The purpose of this retrospective study was to investigate the electrophysiologic characteristics in patients with slow–fast form AVNRT that could be induced only by ventricular pacing or extrastimulation. Methods: The total population was 1497 patients associated with AVNRT. There were 1373 (91.7%) patients who had slow–fast form AVNRT included in our study. Group 1 (n = 45) could be induced only by ventricular pacing or extrastimulation, and Group 2 (n = 1328) could be induced by only atrial stimulation or both atrial and ventricular stimulation. The electrophysiologic characteristics of the group 1 and group 2 patients were compared. Results: Group 1 patients had a significantly lower incidence of both antegrade and retrograde dual AV nodal pathways. The pacing cycle length (CL) of the antegrade 1:1 fast pathway (FP) and antegrade ERP of the FP were both significantly shorter in Group 1 patients. Mean antegrade FRP of the fast and slow pathways were significantly shorter in Group 1 patients. The differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP were much longer in Group 2 patients. Conclusion: This study demonstrated the patients with slow–fast form AVNRT that could be induced only by ventricular stimulation had a lower incidence of dual AV nodal pathways and the different electrophysiologic characteristics (shorter pacing CL of the antegrade 1:1 FP, antegrade ERP of the FP and the differences of pacing CL of 1:1 antegrade conduction, antegrade ERP and FRP) from the other patients. The specific electrophysiologic characteristics in such patients could be the reason that could be induced only by ventricular stimulation.     

Gender-related differences in patients with atrioventricular nodal reentry tachycardia

The present study sought to assess the extent of gender differences in electrophysiologic parameters in patients with atrioventricular nodal reentrant tachycardia (AVNRT). The study population consisted of 203 patients (women/men ratio 2:1) who underwent slow pathway ablation. Patients with associated heart disease experienced the first episode of tachycardia at a significantly older age than patients with lone AVNRT (women 50 +/- 18 vs 29 +/- 15 years, p < 0.0001; men 45 +/- 20 vs 31 +/- 17 years, p = 0.01). Sinus cycle length (797 +/- 142 vs 870 +/- 161 ms, p = 0.0001), HV interval (41 +/- 7 vs 45 +/- 8 ms, p = 0.0001), atrioventricular (AV) block cycle length (348 +/- 53 vs 371 +/- 75 ms, p = 0.01), slow pathway effective refractory period (ERP) (258 +/- 46 vs 287 +/- 62 ms, p = 0.006), and tachycardia cycle length (354 +/- 58 vs 383 +/- 60 ms, p = 0.001) were shorter in women. No gender differences were noted in fast pathway ERP and ventriculoatrial (VA) block cycle length. In women, an AV block cycle length <350 ms along with a VA block cycle length <400 ms predicted tachycardia induction without the need for autonomic intervention, with a positive predictive value of 93% (sensitivity 71%, specificity 82%). No such cut-off values could be found in men. The acute success rate (100% vs 98%) and the recurrence rate (3% vs 6%) were similar for the 2 genders. In conclusion, in patients with lone AVNRT, the onset of symptoms occurred at a younger age than in patients with concomitant heart disease. Women had shorter slow pathway refractory periods, AV block cycle lengths, and tachycardia cycle lengths. No gender differences were noted in the fast pathway ERP. Therefore, women have a wider "tachycardia window" (i.e., the difference between the fast and slow pathway refractory periods), a finding that may explain their greater incidence of AVNRT.     

房室结折返性心动过速患者房室结功能曲线连续性的电生理分析

分析房室结折返性心动过速 (AVNRT)中房室结功能曲线呈连续性者的电生理特点。将AVNRT分为房室结功能曲线连续组 (Ⅰ组 )及房室结功能曲线不连续组 (Ⅱ组 ) ,行慢径消融 ,进行消融前后和组间的电生理比较 ,分析房室结功能曲线呈连续性者的特点。结果 :I组心房程序刺激对AVNRT的诱发率仅 42 % (5 / 12 ) ,低于Ⅱ组的 6 6 %(2 3/ 35 )。Ⅰ组房室结前传有效不应期 (ERP AVN)消融前后无显著变化 (2 18.2± 2 9.3msvs 2 5 3.3± 80 .3ms,P >0 .0 5 ) ;心房程序刺激最长A2 H2 间期 (AHmax)消融前后无显著变化 (2 2 5 .8± 71.8msvs 175 .4± 41.9ms,P >0 .0 5 )。Ⅱ组ERP AVN消融后显著延长 (2 78.9± 5 8.9msvs 2 35 .8± 39.6ms,P <0 .0 5 ) ;AHmax消融后显著缩短 (172 .0± 6 7.1msvs 331.6± 86 .6ms ,P <0 .0 5 ) ;消融后房室结快径前传有效不应期 (ERP FP)显著缩短 (2 78.9± 5 8.9msvs 330 .0±5 5 .3ms,P <0 .0 5 )。消融前Ⅰ组AHmax短于Ⅱ组 (P <0 .0 5 ) ,Ⅰ组心动过速时A2 H2 间期 (AHSVT)与消融前AHmax比较差异无显著性 (P >0 .0 5 ) ;Ⅱ组AHSVT短于消融前AHmax(P <0 .0 5 )。结论 :房室结功能曲线连续性者较难经常规心房程序刺激诱发心动过速 ;慢径消融后曲线“尾巴”消失可作为消融终点的一项指     

Differential Effects of Atropine and Isoproterenol on Inducibility of Atrioventricular Nodal Reentrant Tachycardia

Background: Radiofrequency ablation of the slow pathway in atrioventricular nodal reentrant tachycardia (AVNRT) relies on tachycardia non-inducibility after ablation as success criterion. However, AVNRT is frequently non-inducible at baseline. Thus, autonomic enhancement using either atropine or isoproterenol is frequently used for arrhythmia induction before ablation. Methods: 80 patients (57 women, 23 men, age 50±14 years) undergoing slow pathway ablation for recurrent AVNRT were randomized to receive either 0.01mg/kg atropine or 0.5-1.0g/kg/min isoproterenol before ablation after baseline assessment of AV conduction. The effects of either drug on ante- and retrograde conduction was assessed by measuring sinus cycle length, PR and AH interval, antegrade and retrograde Wenckebach cycle length (WBCL), antegrade effective refractory period (ERP) of slow and fast pathway and maximal stimulus-to-H interval during slow and fast pathway conduction. Results: Inducibility of AVNRT at baseline was not different between patients randomized to atropine (73%) and isoproterenol (58%) but was reduced after atropine (45%) compared to isoproterenol (93%, P<0.001). Of the 28 patients non-inducible at baseline isoproterenol rendered AVNRT inducible in 21, atropine in 4 patients. Dual AV nodal pathway physiology was present in 88% before and 50% after atropine compared to 83% before and 73% after isoproterenol. Whereas both drugs exerted similar effects on ante- and retrograde fast pathway conduction maximal SH interval during slow pathway conduction was significantly shorter after isoproterenol (300±48ms vs. 374±113ms, P=0.012). Conclusion: Isoproterenol yields higher AVNRT inducibility than atropine in patients non-inducible at baseline. This may be caused by a more pronounced effect on antegrade slow pathway conduction.     

Differential Effect of Esmolol on the Fast and Slow AV Nodal Pathways in Patients with AV Nodal Reentrant Tachycardia

Esmolol Effect on AV Nodal Pathways. Introduction: AV nodal reentrant tachycardia (AVNRT) usually involves anterograde conduction over a slowly conducting (“slow”) pathway and retrograde conduction over a rapidly conducting (“fast”) pathway. A variety of drugs, such as beta blockers, digitalis, and calcium channel blockers, have been reported to prolong AV nodal refractoriness in both the anterograde and retrograde limbs of the circuit. However, few data are available that address whether the fast and slow pathways respond in a quantitatively different manner to drugs such as beta-adrenergic antagonists. In addition, it is not known whether the effects of these agents on refractoriness parallel the effects on conduction in the fast and slow pathways. The present study was performed to measure the effect of the intravenous beta-adrenergic agent, esmolol, on refractoriness and conduction in both the fast and slow AV nodal pathways in patients with AVNRT. Methods and Results: Thirteen patients with discontinuous AV nodal conduction properties and typical AVNRT were studied. Anterograde and retrograde AV nodal functional assessment was performed at baseline and following steady-state drug infusion of intravenous esmolol at a dose of 500 μg/kg for 1 minute, 150 /μg/kg per minute for the next 4 minutes, followed by a continuous maintenance infusion of 50 to 100 μg/kg per minute. The anterograde effective refractory period of the fast pathway increased from 381 ± 75 msec at baseline to 453 ± 92 msec during the infusion of esmolol (P = 0.003). The anterograde effective refractory period of the slow pathway was also prolonged by esmolol, from 289 ± 26 msec to 310 ± 17 msec (P = 0.005). However, the absolute magnitude of the change in the anterograde effective refractory period of the fast pathway (+72 ± 59 msec) was significantly greater than the change in anterograde effective refractory period of the slow pathway (+21 ± 16 msec, P = 0.01). The mean retrograde effective refractory period of the fast pathway increased from 276 ± 46 msec to 376 ± 61 msec during esmolol infusion (P = 0.03). Retrograde slow pathway conduction that could not be demonstrated at baseline became manifest in three patients during esmolol infusion. In contrast to the effects of esmolol on refractoriness, the AH interval during anterograde slow pathway conduction prolonged to a far greater extent (+84 msec) than the HA interval associated with retrograde fast pathway conduction (+5 msec, P = 0.04). Conclusion: The beta-adrenergic antagonist, esmolol, has a quantitatively greater effect on anterograde refractoriness of the fast than the slow AV nodal pathway. However, the effects on conduction intervals during AVNRT are greater in the anterograde slow pathway than in the retrograde fast pathway. These observations suggest that the fast and slow pathways may have differential sensitivities to autonomic influences. This difference in the response to beta-adrenergic antagonists may be exploited as a clinically useful method for demonstrating slow pathway conduction in some individuals with AVNRT.     

特殊类型房室结折返性心动过速的电生理机制及其射频消融

报道２例特殊类型的房室结折返性心动过速（ＡＶＮＲＴ），１例为慢－慢型ＡＶＮＲＴ伴起始部多径路逆传；１例为两种不同电生理特性的慢径交替前传、快径逆传构成的ＡＶＮＲＴ。电生理检查均提示房室结三径路。２例病人均于冠状静脉窦口上方消融慢径改良房室结成功，心动过速不再被诱发。随访２个月心动过速均无复发。提示房室结多径路形成的特殊类型ＡＶＮＲＴ，需详细的电生理检查并仔细鉴别方能予以诊断。射频导管消融方法同典型ＡＶＮ－ＲＴ，且安全、有效。     

Atrioventricular Nodal Reentrant Tachycardia with Multiple Discontinuities in the Atrioventricular Node Conduction Curve: Immediate Success Rates of Radiofrequency Ablation and Long-Term Clinical Follow-up Results as Compared to Patients with Single or No AH-Jumps

Background: Some patients with atrioventricular nodal reentrant tachycardia (AVNRT) demonstrate multiple discontinuities (AH jump) in their antegrade AV node conduction curves. We evaluated and compared the immediate success rates, procedure-related complications, long-term clinical follow-up results and recurrence rates after slow pathway ablation in patients with multiple versus single or no AH jumps. Methods: The study group consists of 278 consecutive patients (mean age 36.6 ± 15.7) who underwent ablation for typical AVNRT, divided into three categories according to the number of AH jumps (50 ms) before ablation: Group-1 consisted of 63 patients (23%) with continuous AV node function curves; Group-2 of 183 patients (66%) with a single jump and Group-3 of 32 (12%) patients showing more than one AH jumps. Results: Age was significantly higher in Group-3 as compared to Group-1 (43 ± 18 years vs. 34 ± 16 years, p = 0.020). The electrophysiological features of AVNRT did not differ among groups. Before ablation, the maximum AH interval was significantly longer in Group-3 as compared to Groups-1 and -2 (p < 0.001 for both). AV node antegrade ERP was significantly shorter in Group-3 than in Group-2, both before and after ablation (p < 0.050 for both). AV node Wenckebach cycle length (WCL) was shorter in Group-3 as compared to both Groups-1 and -2, before and after ablation (p < 0.050 for all). AV node WCL was prolonged significantly in all groups after ablation (p < 0.001 for all). Residual dual pathways were present in 37 of 278 patients (13%) after ablation and were significantly more frequent in Group-3 than Group-2 (31% vs. 15%, p = 0.023). Conclusions: Patients with multiple AH jumps are older and more often have residual dual atrioventricular nodal pathway physiology after successful ablation but these features do not affect the immediate and long-term success rates of slow pathway ablation as compared to patients with single or no AH jumps.     

快径间断逆传是房室结折返性心动过速的少见电生理表现

报道 4例房室结折返性心动过速 (AVNRT)的少见电生理表现———快径间断逆传。 4例经心电图和食管电生理检查证实为AVNRT的病人 ,心内电生理检查中心室刺激无快径逆传 ,遂静脉注射异丙肾上腺素和消融阻断慢径后观察室房 (VA)传导特点。结果 :4例病人基础电生理检查均无快径逆传。静脉注射异丙肾上腺素后心室刺激 ,3例显示快径逆传并诱发AVNRT ,1例仍不显示快径逆传。消融阻断慢径后 ,4例病人均显示良好的快径逆传。结论 :快径间断逆传是AVNRT的少见电生理特点 ,慢径和快径相互干扰是其产生的重要机制之一。     

从射频消融探讨房室结双径路的本质和房室结改良的机制

采用两种方法对142例房室结折返性心动过速(AVNRT)患者进行房室结改良。128例慢—快型AVNRT中,83例单纯慢径改良,33例慢径前传和快径逆传同时改良,3例单纯快径逆传改良,7例快径前传和慢径或快径逆传同时改良,2例失败。1例发生永久性Ⅲ度房室传导阻滞;10例快—慢型和4例慢—慢型AVNRT患者均慢径改良成功。总成功率98.6％。平均随访6±4月,4例(2.8％)复发,均再次消融成功。慢径改良后,快径前传有效不应期、维持1:1快径前传最短的心房刺激周期明显缩短(P<0.05),而逆向快径有效不应期、维持1:1快径逆传最短的心室刺激周期无明显变化(P>O.05)。本研究提示:快径和慢径可能是解剖上不同的纤维。慢径前传和逆传可以是同一条纤维,也可以是不同的纤维;快径亦然。     

Effects of Partial and Complete Ablation of the Slow Pathway on Fast Pathway Properties in Patients with Atrioventricular Nodal Reentrant Tachycardia

Fast Pathway Properties. Introduction: The purpose of this study was to prospectively compare the effects of complete and partial ablation of slow pathway function on the fast pathway effective refractory period (ERP).
Methods and Results: The subjects were 20 patients (mean age 43 ± 13 years) with atrioventricular nodal reentrant tachycardia (AVNRT), no structural heart disease, and easily inducible AVNRT. Autonomic blockade was achieved with propranolol (0.2 mg/kg) and atropine (0.04 mg/kg). After elimination of AVNRT and during autonomic blockade, the presence of residual slow pathway function was determined by the presence of a single AV nodal echo and/or dual AV nodal physiology. After autonomic blockade and before ablation, the mean fast pathway ERP was 319 ± 44 msec and the mean slow pathway ERP was 251 ± 31 msec. After slow pathway ablation and during autonomic blockade, 7 patients had residual slow pathway function and 13 did not. Complete loss of slow pathway function was associated with a shortening of the fast pathway ERP from 334 ± 35 msec to 300 ± 62 msec (P < 0.01), while the fast pathway ERP did not change significantly in patients with residual slow pathway function (291 ± 29 msec vs 303 ± 38 msec, respectively; P = 0.08). A shortening of 30 msec or more in the fast pathway ERP was observed in 11 of 13 patients who did not have residual slow pathway function, compared to 0 of 7 patients with residual slow pathway function (P < 0.001).
Conclusion: Shortening of the fast pathway ERP after successful ablation of AVNRT is dependent upon complete loss of slow pathway function. This observation is consistent with electrotonic inhibition of the fast pathway by the slow pathway.     

Radiofrequency Catheter Ablation of AtypicalAtrioventricular Nodal Reentrant Tachycardia

Ablation of Atypical Atrioventricular Nodal Reentrant Tachycardia, Introduction: Published reports of radiofrequency ablation of atypical atrioventricular nodal reentranttacbycardia (AVNRT) have been limited. We present our experience in 10 consecutive patientswith atypical AVNRT wbo underwent radiofrequency ablation of the "slow" AV nodal pathway.
Methods and Resttlts: there were 9 females and 1 male; their mean age was 44 ± 19 years (± SD), the mean AVNRT cycle length and ventriculoatrial (VA) interval at the His positionduring AVNRT were 340 ± 50 msec and 200 ± 70 msec, respectively. the slow pathway wassuccessfully ablated in all patients with a mean of 10 ± 7 radiofrequency energy applications inthe posteroseptal right atritim near the coronary sinus os. The mean procedure duration was 100 ± 35 minutes. There were no complications. In 4 patients, target sites were identified during sinus rhythm by mapping for possible slow pathway potentials, In the other 6 patients, target sites were identified by mapping retrograde atrial activation during AVNRT or ventricularpacing, The VA times at successful target sites were a mean of 45 ± 30 msec less tban the VAtime at the His cathetcr during AVNRT, There were no differences in success rate, number ofradiofrequency energy applications, or procedure duration between patients in whom mappingwas guided by possible slow pathway potentials or by retrograde atrial activation, During 6 ± 3 months of followup, 1 patient bad a recurrence of atypical AVNRT and underwent a secondablation procedure, which was successful.
Conclusion: Radiofrequency ablation of atypical AVNRT can be safely and effectivelyaccomplisbed when target sites are identified based either on possible slow pathway potentialsduring sinus rbytbm or retrograde atrial activation times during tachycardia.     

Electrophysiologic Spectrum of Atrioventricular Nodal Behavior in Patients with Atrioventricular Nodal Reentrant Tachycardia Undergoing Selective Fast or Slow Pathway Ablation

AV Nodal Behavior After Ablation. Introduction; The objective of this report is to delineate the atrioventricular (AV) nodal electrophysiologic behavior in patients undergoing fast or slow pathway ablation for control of their AV nodal reentrant tachycardia (AVNRT).
Methods and Results: One hundred sixteen consecutive patients with symptomatic AVNRT were included. Twenty-two patients underwent fast pathway ablation with complete abolition of AVNRT in all and development of complete AV block in five patients. Of 17 patients with intact AV conduction postablation, 12 had demonstrated antegrade dual pathway physiology during baseline study, which was maintained in three and lost in nine patients postablation. Two patients with successful fast pathway ablation developed uncommon AVNRT necessitating a slow pathway ablation. Twenty-one patients demonstrated both common and uncommon forms of AV nodal reentry during baseline study. The earliest site of atrial activation was close to the His-bundle recording site (anterior interatrial septum) during common variety and the coronary sinus ostium (posterior interatrial septum) during the uncommon AV nodal reentry in all 21 patients. Ninety-six patients underwent successful slow pathway ablation. Among these, the antegrade dual pathway physiology demonstrable during baseline study (60 patients) was maintained in 25 and lost in 35 patients postablation.
Conclusion: These data suggest that: (1) dual pathway physiology may persist after successful ablation, which might be a reflection of multiple reentrant pathways in patients with AVNRT: and (2) the retrograde pathways during common and uncommon AVNRT have anatomically separate atrial breakthroughs. These findings have important electrophysiologic implications regarding the prevailing concept of the AV nodal physiology in patients with AVNRT.     

Utilization of Retrograde Right Bundle Branch Block to Differentiate Atrioventricular Nodal from Accessory Pathway Conduction

Introduction: Defining whether retrograde ventriculoatrial (V-A) conduction is via the AV node (AVN) or an accessory pathway (AP) is important during ablation procedures for supraventricular tachycardia (SVT). With the introduction of ventricular extrastimuli (VEST), retrograde right bundle branch block (RBBB) may occur, prolonging the V-H interval, but only when AV node conduction is present. We hypothesized that when AP conduction was present, the V-A interval would increase less than the V-H interval, whereas with retrograde nodal conduction, the V-A interval would increase at least as much as the V-H interval.
Methods and Results: We retrospectively reviewed the electrophysiological studies of patients undergoing ablation for AVN reentrant tachycardia (AVNRT) (55) or AVRT (50), for induction of retrograde RBBB during the introduction of VEST, and the change in the measured V-H and V-A intervals. Results were found to be reproducible between independent observers. Out of 105 patients, 84 had evidence of induced retrograde RBBB. The average V-H interval increase with induction of RBBB was 53.7 ms for patients with AVRT and 54.4 ms for patients with AVNRT (P = NS). The average V-A interval increase with induction of RBBB was 13.6 ms with AVRT and 70.1 ms with AVNRT (P < 0.001). All patients with a greater V-H than V-A interval change had AVRT, and those with a smaller had AVNRT.
Conclusions: Induction of retrograde RBBB during VEST is common during an electrophysiological study for SVT. The relative change in the intervals during induction of RBBB accurately differentiates between retrograde AVN and AP conduction.     

Atrioventricular Nodal Response to Retrograde Activation in Atrial Fibrillation

Atrioventricular Nodal Reset. Retrograde (ventriculoatrial) conduction that reaches the atrioventricular node simultaneous with, or just before an atrial impulse ean facilitate subsequent anterograde conduction. However, a spontaneous or programmed ventricular extrasystule during atrial nbrillation is generally followed by a compensatory pause indicating subsequent delayed anterograde transmission. This characteristic response was used as a model to study the mechanism of atrioventricular nodal behavior during atrial fibrillation. In eight medically-treated patients with chronic atrial fibrillation and a relatively slow but random ventricular response, single premature right ventricular stimuli were delivered after every eighth spontaneous R wave during at least 1 hour. A fixed coupling interval of the ex-trastimulus, considerably shorter than the shortest spontaneous RR interval, was used. The histograms of the postextrasystolic intervals were compared with those of the spontaneous noninterrupted RR intervals. The average postextrasystolic interval was 180 to 300 msec longer than the mean control RR interval, and in six of eight patients, the shape of the histogram of the postextrasystolic cycles was insignificantly different from that of the spontaneous RR intervals. This suggests that In those six patients, the retrograde impulse had reset the random timing cycle of atrioventricular nodal discharge during atrial fibrillation. This observation is compatible with the hypothesis that electrotonically-mediated propagation across a weakly coupled junctional area within the atrioventricular node, rather than decremental conduction and extinction of anterograde atrial impulses at different levels within the node, may be the mechanism of atrioventricular transmission in atrial fibrillation. (J Curdiovasc Electrophysiol, Vol. 1, pp. 437–447, October 1990)     

从慢径消融发生的交界区心律试探房室结双径的本质

７６例慢－快型房室结折返性心动过速（ＡＶＮＲＴ）患者接受房室结慢径消融术。６５例慢径阻断、９例双径存在但ＡＶＮＲＴ不能诱发、２例快径阻断。慢径阻断后，除快径的前传有效不应期（ＥＲＰ）缩短（２８７．０±７９．０ｍｓｖｓ３４４．０±８７．０ｍｓ，Ｐ＜０．０１）外，房室传导的文氏点、２１阻滞点、室房传导的１１点、快径逆传ＥＲＰ、前传和逆传功能不应期均无明显改变。共放电８４１次，其中无交界区心律的３１７次放电，无一次消融成功。６５例慢径阻断者，交界区心律减少或消失。以上结果提示快径和慢径可能是两条各具电生理特性的传导纤维。     

Differential Effect of Adenosine on Anterograde and Retrograde Fast Pathway Conduction in Patients with Atrioventricular Nodal Reentrant Tachycardia

Adenosine and Retrograde Fast Pathway Conduction . Introduction : Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction.
Methods and Results : The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 ± 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients ( P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 ± 78 vs 333 ± 74 msec, P < 0.01), a shorter VA block cycle length (383 ± 121 vs 307 ± 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 ± 23 vs 41 ± 17 msec, P < 0.01).
Conclusion : Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.     

选择性消融逆传快径治疗典型房室结折返性心动过速

设计一种新的射频消融方法（选择性消融逆传快径）对25例反复发作的典型房室结折返性心动过速（AVN－RT）进行消融治疗。经股静脉插入1～2很大头电极至Koch氏三角区,于旁His束心室起搏下寻找还传A’最早的靶点,靶点图上不能有或仅有极小H波,大头电极用力压向靶点出现：①VA分离或H’A’间期延长,说明逆传快径已被机械刺激所阻断,立即放电15～25W,持续30～90S;②AH间期延长,说明前传快径已被机械刺激所阻断,移开大头电极待AH间期恢复正常,再重新标测;③反复数次操作,大头电极的机械刺激仍不能阻断逆传快径,则选择逆传A’最早的靶点试放电30S,出现VA分离或H’A’间期延长,则放电至60～90s,否则重新标测靶点。消融终点为VA分离或H’A’间或延长,用异丙肾上腺素仍不能诱发典型和非典型AVNRT。25例均一次消融成功,逆传快径被阻断、前传慢径均保留;23例VA分离、2例仅有H’A’间期延长;6例前传快径阻断;4例病人术中大头电极的机械刺激阻断了逆传快径。1倒成功靶点位于His束电极后上方,24例位于His束电极与冠状窦电极之间的区域。结论：在仔细精确的电生理标测下可实现选择性消融逆传快径,保留前传快慢径。此方法安全有效。     

快-慢型房室结折返性心动过速的电生理特征和射频消融治疗

报道８例快－慢型房室结折返性心动过速（ＡＶＮＲＴ）的电生理特征及射频消融治疗。其中３例为慢－快型ＡＶＮ－ＲＴ射频消融改良慢径后出现的快－慢型ＡＶＮＲＴ。８例均经消融慢径而成功终止心动过速。平均放电次数３±１．１次、平均放电时间１２０±３０．４ｓ、平均放电功率３０±１１Ｗ。随访６～２４个月，无复发。快－慢型ＡＶＮＲＴ具有以下临床电生理特征：①快径不应期短、慢径不应期长。②心内电刺激无房室结双径路现象。③心动过速能由心房刺激诱发。④心动过速时ＡＨ间期＜ＨＡ间期，冠状窦近端Ａ波最提前。熟悉快－慢型ＡＶＮＲＴ的电生理特征，对于鉴别房性心动过速及右后间隔旁道参与的房室折返性心动过速十分重要，也是指导快－慢型ＡＶＮＲＴ射频消融成功的关键。     

Atrioventricular nodal reentrant tachycardia with retrograde block induced by aprindine.

Two patients are described who had atrioventricular nodal reentrant tachycardia (AVNRT) with 1:1 relationship in the control state, but in whom a varying degree of VA block during AVNRT was observed during therapy with aprindine. Aprindine, however, did not cause anterograde blockade of conduction over the slow AV nodal pathway during tachycardia. These observations support the conclusion that the bulk of atrial muscle is not a requisite part of the tachycardia circuit in AVNRT and that antiarrhythmic drugs may have disparate effects on conduction in the retrograde and anterograde limbs of the circuit.     

Electrophysiologic Characteristics and Radiofrequency Catheter Ablation in Atrioventricular Node Reentrant Tachycardia with Second-Degree Atrioventricular Block

Second-Degree AV Block During AVNRT. Introduction : Detailed electrophysiologic study of AV nodal reentrant tachycardia (AVNRT) with 2:1 AV block has been limited.
Methods and Results : Six hundred nine consecutive patients with AVNRT underwent electrophysiologic study and radiofrequency catheter ablation of the slow pathway. Twenty-six patients with 2:1 AV block during AVNRT were designated as group I, und those without this particular finding were designated as group II. The major findings of the present study were: (1) group I patients had better anterograde and retrograde AV nodal function, shorter tachycardia cycle length (during tachycardia with 1:1 conduction) (307 ± 30 vs 360 ± 58 msec, P < 0.001), and higher incidence of transient bundle branch block during tachycardia (18/26 vs 43/609, P < 0.001) than group II patients: (2) 21 (80.8%) group I patients had alternans of AA intervals during AVNRT with 2:1 AV block. Longer AH intervals (264 ± 26 vs 253 ± 27 msec, P = 0.031) were associated with the blocked beats. However, similar HA intervals (51 ± 12 vs 50 ± 12 msec, P = 0.363) and similar HV intervals (53 ± 11 vs 52 ± 12, P = 0.834) were found in the blocked and conducted beats; (3) ventricular extrastimulation before or during the His-bundle refractory period bundle could convert 2:1 AV block to 1:1 AV conduction.
Conclusions : Fast reentrant circuit, rather than underlying impaired conduction of the distal AV node or infranodal area, might account for second-degree AV block during AVNRT. Slow pathway ablation is safe and effective in patients who have AVNRT with 2:1 AV block.