Anterograde slow pathway is not the same as retrograde slow pathway conducted in the reverse direction in patients with uncommon atrioventricular nodal reentrant tachycardia

INTRODUCTION: The aim of this study was to examine the location of anterograde and retrograde slow pathways in 16 patients with uncommon atrioventricular nodal reentrant tachycardia (AVNRT), including the fast-slow form in 10, slow-slow form in 5, and both fast-slow and slow-slow forms in 1. METHODS AND RESULTS: Patients were divided into two groups according to the approach used for slow pathway ablation in the initial radiofrequency catheter ablation (RFCA): one approach used earliest atrial activation during tachycardia (ES group, n = 9), and the other used a slow potential during sinus rhythm (SP group, n = 7). When the initial RFCA failed to eliminate slow pathway conduction in the ES group, an additional RFCA guided by a slow potential was performed. The ratio of lengths from the His-bundle region to the RFCA site and coronary sinus ostium (Abl/His-CS ratio) and the ratio of amplitudes of atrial and ventricular potentials at the RFCA site (A/V ratio) were compared between the two groups. In the initial RFCA, retrograde slow pathway conduction was eliminated without impairment of anterograde slow pathway conduction in 8 (89%) patients from the ES group, and bidirectional slow pathway conduction was eliminated in 6 (86%) patients from the SP group. Residual anterograde slow pathway conduction that was preserved after the initial RFCA in 8 of 9 patients was eliminated by an additional slow potential-guided RFCA. Both the Abl/His-CS ratio (0.86 +/- 0.07 vs 0.73 +/- 0.11, P = 0.01) and A/V ratio (0.80 +/- 0.31 vs. 0.14 +/- 0.01, P < 0.001) were higher in the ES group than the SP group. The ratios for the residual anterograde slow pathway ablation in the ES group were similar to those in the SP group. CONCLUSION: The results of this study suggest that the retrograde slow pathway runs more on the atrial side of the tricuspid valve annulus at the level of the coronary sinus ostium compared with the anterograde slow pathway, although both pathways run parallel or are fused in portions more proximal to the His bundle.     

Persistence of Single Echo Beat Inducibility After Selective Ablation of the Slow Pathway in Patients with Atrioventricular Nodal Reentrant Tachycardia:

Residual Slow Pathway Conduction Effects on AVN Function. Introduction : Residual slow pathway conduction with or without reentrant echo beats has been reported in 25% to 30% of patients undergoing ablation for AV nodal reentrant tachycardia (AVNRT).
Methods and Results : Fifty-eight consecutive patients (aged 45 ± 12 years) with slow-fast AVNRT underwent radiofrequency catheter ablation of the slow AV nodal pathway (SP). Residual slow-fast echo beat was documented in 21 (36%) of 58 patients (group A). The pre-and postablation AH intervals triggering the echo beats were similar (346 ± 8 msec vs 352 ± 6 msec, P = NS), as were the pre-and postablation echo zones (55 ± 6 msec vs 52 ± 5 msec, P = NS) and functional refractory period of the SP. A consistent prolongation of the AV nodal effective refractory period (AVN-ERP; from 265 ± 28 msec to 340 ± 50 msec, P < 0.001) and the Wenckebach cycle length (WBCL; from 298 ± 41 msec to 438 ± 43 msec, P < 0.001) was observed in all patients with abolition of SP conduction (group B). In group A patients, the prolongation of WBCL was less (285 ± 33 msec preablation, and 334 ± 41 msec postablation, P < 0.001). Additional pulses abolished the residual echo in 16 of 21 patients, and further prolongation of the AVN-ERP and WBCL comparable to those found in patients without a residual echo beat was observed. During 19 ± 8 months follow-up, no patient had clinical recurrence of AVNRT.
Conclusion : Residual single echo beat after SP ablation for AVNRT reflects the persistence of some portion of the SP with unchanged functional conduction properties whose prognostic significance is uncertain. A consistent increase of WBCL can be a reliable marker of complete abolition of slow pathway conduction and termination of AVNRT.     

Mechanism of induction of atrioventricular node reentry by simultaneous anterograde conduction over the fast and slow pathways

INTRODUCTION: AV node reentry (AVNRT) is typically induced with anterograde (Ant) block over the fast pathway (FP) and conduction over the slow pathway (SP), with subsequent retrograde (Ret) conduction over the FP. Rarely, a premature atrial complex (PAC) conducts simultaneously over the FP and SP to induce AVNRT (2 for 1). This study investigates the mechanism of 2 for 1 induction. METHODS AND RESULTS: Of 192 consecutive patients (pts) undergoing posteroseptal radiofrequency ablation to treat AVNRT, 4 pts (2%) had 2 for 1 AVNRT induction. All needed isoproterenol for AVNRT initiation, and Ant conduction was over the SP during AVNRT. Controls (n = 15) were randomly selected from the remaining 188 pts and required isoproterenol to induce AVNRT with Ant block over the FP. For 2 for 1 versus control, respectively, there was no difference in mean age (55 vs. 46 yr), AVNRT cycle length (420 vs. 320 ms), or the Ant effective refractory period of the FP (320 vs. 344 ms). Of note, the PAC that induced AVNRT had a significantly longer AH interval over the SP in pts with 2 for 1 versus control (470 vs. 320 ms, P = 0.016), even though the A1A2 interval for induction was longer for 2 for 1 (315 vs. 260 ms, P = 0.003). Ret conduction over the SP was relatively poor in the 2 for 1 group as evidenced by 4/4 pts with induction of AVNRT during incremental ventricular pacing versus only 1/15 control pts (P < 0.001). CONCLUSION: The unique induction of AVNRT by a PAC with simultaneous conduction over the FP and SP is best explained by minimal to no retrograde invasion of the SP from the anterogradely conducted fast pathway impulse, and consistent with this observation is the initiation of slow/fast AVN reentry during incremental RV pacing.     

Clinical and electrophysiological characteristics in patients with atrioventricular reentrant and atrioventricular nodal reentrant tachycardia.

AIM: To compare clinical, electrophysiological characteristics and transcatheter ablation results between two groups of patients, one with atrioventricular reentrant tachycardia (AVRT) and the other with atrioventricular nodal reentrant tachycardia (AVNRT). METHODS: The study population consisted of 94 consecutive patients who underwent endocavitary electrophysiological study and radiofrequency (RF) ablation: 46 patients had AVRT due to an accessory pathway with only retrograde conduction while 48 patients had AVNRT. RESULTS: In relation to general and clinical characteristics, differences between the two groups emerged regarding the age of symptom onset (25+/-16 vs 37+/-17 years, p=0.001), the prevalence of heart disease (8 vs 31%, p=0.001) and the correct diagnosis on surface ECG (50 vs 79%, p=0.001). Clinical presentation was quite similar apart from a higher prevalence of fatigue and sweating in the AVNRT group. Transcatheter RF ablation therapy results were similar. CONCLUSIONS: Patients with AVRT have a lower mean age at arrhythmia symptom onset compared with those with AVNRT and have fewer associated cardiac abnormalities. Clinical presentation is quite similar as well as their outcome after ablation. A correct diagnosis by standard ECG is more frequent in AVNRT.     

Autonomic blockade unmasks maturational differences in rate-dependent atrioventricular nodal conduction and facilitation in the mouse

INTRODUCTION: In large animals, rate-dependent AV nodal (AVN) properties of conduction are modulated by autonomic inputs. In this study, we investigated whether the properties of AVN conduction and facilitation are altered by autonomic blockade in the mouse and whether this effect is age dependent. METHODS AND RESULTS: Young (age 4-6 weeks; n = 11) and adult (age 8-9 months; n = 11) female mice underwent in vivo electrophysiologic testing, before and after autonomic blockade. After autonomic blockade, the adult mice had significantly longer AVN effective refractory period (AVNERP; 67 +/- 14 msec vs 56 +/- 4 msec, P = 0.05) and functional refractory period (AVNFRP; 81 +/- 10 msec vs 72 +/- 4 msec, P = 0.05). With autonomic blockade, the increase from baseline of AVN Wenckebach cycle length (deltaAVW; 1.8 +/- 8.1 msec vs 8.8 +/- 3.3 msec, P = 0.04), as well as of AVNERP (deltaAVNERP; 3.5 +/- 3.5 msec vs 21.4 +/- 12.6 msec, P = 0.002) and AVNFRP (deltaAVNFRP; 2.3 +/- 3.2 msec vs 12.8 +/- 9.0 msec, P = 0.008), was significantly larger in adult than in young mice. Compared with young mice, adult mice were less likely to exhibit AVN facilitation (44% vs 90%, P = 0.03) and had smaller maximal shortening of AVN conduction times after the "test beat" for any coupling of the "facilitating beat" (4 +/- 4 msec vs 7 +/- 3 msec, P = 0.05). CONCLUSION: Complete autonomic blockade significantly increases AVN conduction times and refractory periods in adult but not in young mice. Adult mice also exhibit less AVN facilitation. Our results confirm that, like in larger animals, rate-dependent murine AVN properties of conduction are under autonomic regulation. Adult mice have higher sympathetic AVN inputs at baseline, leading to slower conduction after autonomic blockade.     

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.     

Slow pathway catheter ablation of atrioventricular nodal re-entrant tachycardia guided by electroanatomical mapping: a randomized comparison to the conventional approach.

BACKGROUND: Electroanatomical mapping may be expected to improve safety, efficiency and efficacy of selective slow pathway ablation for atrioventricular nodal re-entrant tachycardia (AVNRT). The goal of this prospective randomized study was to compare the efficiency of conventional fluoroscopic and electroanatomical mapping in guiding catheter ablation of AVNRT. METHODS AND RESULTS: Following induction of typical AVNRT, 20 consecutive patients were randomized to either conventional fluoroscopic or electroanatomical (CARTO) mapping to guide slow pathway ablation using a 4mm electrode. Endpoints for ablation were non-inducibility and no more than a single AV nodal echo on aggressive retesting. Acute procedural success was 100% in both groups, with no complications. Although there were no differences in time taken for pre- and post-ablation electrophysiological evaluations, in the electroanatomical group the ablation portion of the procedure showed a substantial reduction in duration (12.6+/-6.8 vs 35.9+/-18.3 min; P< 0.001) and fluoroscopic exposure (0.7+/-0.5 vs 9.6+/-5.0 min; P< 0.001) compared with the fluoroscopic group, reflected in reduced total procedure time (83.6+/-23.6 vs 114+/-19.3 min; P=0.008) and total fluoroscopic exposure (4.2+/-1.4 vs 15.9+/-6.4 min; P< 0.001). Electroanatomical mapping was associated with a lower number (2.7+/-1.6 vs 5+/-2.8; P=0.018), duration (165.3+/-181.6 vs 341+/-177.7s; P=0.013), and total energy delivery (24.3+/-3.1 vs 28.7+/-4.5 watts; P=0.042) of RF applications. There were no acute or long-term (8.9+/-2.2 month) complications or arrhythmia recurrence in either group. CONCLUSIONS: While both conventional and non-fluoroscopic electroanatomical mapping are associated with excellent results in guiding ablation of typical AVNRT, the latter offers significantly shorter procedure and fluoroscopy times, improving the efficiency of the procedure and reducing X-ray exposure.     

Atrioventricular Nodal Reentry Tachycardia in Patients with Sinus Node Dysfunction: Electrophysiologic Characteristics, Clinical Presentation, and Results of Slow Pathway Ablation

AVNRT and Sinus Node Dysfunction. Introduction: Sinus node dysfunction (SND) is frequently associated with impaired AV conduction. This study investigated the electrophysiologic properties of dual AV nodal pathways in patients suffering from both SND and AV nodal reentrant tachycardia (AVNRT). Methods and Results: Two groups of patients with slow-fast AVNRT underwent invasive electrophysiologic testing and catheter ablation of the slow pathway. Group A comprised 10 patients with SND (age 70 ± 8 years), (Group B included 10 age-matched patients without SND (age 69 ± 7 years; P = NS) who served as controls. Patients of group A exhibited prolongation of the anterograde Wenckebach cycle lengths (WBCLs) of both the fast pathway (559 ± 96 vs 361 ± 38 msec; P < 0.01) and the slow pathway (409 ± 57 vs 339 ± 32 ms; P < 0.01). However, the delta between the WBCLs of the fast and the slow pathways was larger in patients of group A (150 ± 80 vs 22 ± 20 msec; P < 0.01). Retrograde fast pathway conduction was well preserved with no difference in WBCLs (356 ± 42 vs 330 ± 47 msec; P = NS). Cycle lengths of AVNRT were longer in group A (468 ± 46 vs 363 ± 37 msec; P < 0.01). Clinically, all patients of group A suffered from multiple episodes of AVNRT per week, which was not the case in any patient of group B (P < 0.01). Catheter ablation of the slow pathway eliminated AVNRT in all patients without complications. Conclusions: Patients with AVNRT and SND exhibit characteristic electrophysiologic alterations of both AV nodal pathways. Clinically, this results in significantly more frequent episodes of tachycardia. Slow pathway ablation appears to be safe and effective in these patients.     

房室结功能曲线连续性房室结折返性心动过速患者的射频消融终点初探

目的　探讨房室结功能曲线连续性房室结折返性心动过速 (AVNRT)患者的射频消融终点。方法　在AVNRT患者中 ,对心房 A1 A2 和 A1 A2 A3程序刺激房室结功能曲线均呈连续性者为 组 ,A1 A2 刺激房室结功能曲线呈连续性而 A1 A2 A3刺激呈不连续性者为 a组 ,房室结功能曲线均呈不连续性者为 b组。行慢径区域消融后 ,对组间的电生理参数进行比较。结果　 组非典型 AVNRT的诱发率高于 组 (2 7.3 % vs5 .6% ,P<0 .0 5 )。在 I组和 a组 ,消融后最长 A2 H2 间期 (A2 H2 m ax)均比消融前有所缩短 ,但无显著性差异 (P>0 .0 5 ) ,而 b组则显著缩短 (3 76± 73 ms vs2 0 6± 5 6ms,P<0 .0 1)。消融后 组、 a组和 b组的最长 A3H3间期 (A3H3m ax)均比消融前显著缩短 (2 74± 71ms vs 196± 45 ms,P<0 .0 5 ;3 62± 91m s vs 2 2 6± 72 m s,P<0 .0 1;3 85± 88ms vs 2 19± 61ms,P<0 .0 1)。结论　非典型 AVNRT与房室结功能曲线的连续性有关。对于房室结功能曲线连续性的 AVNRT患者 ,消融后 A3H3max的缩短可作为消融终点的指标之一     

房室结折返性心动过速与冠状静脉窦关系的初步研究

为探讨房室结双径路导致折返性心动过速的发病机制，以更准确的选择消融靶点和减少并发症。对经电生理检查诊断的３３例室上性心动过速（ＳＶＴ）病人进行冠状静脉窦（ＣＳ）造影的对比研究。分为两组，其中房室结折返性心动过速（ＡＶＮＲＴ）组１７例，对照组（为其他室上性心动过速）１６例。两组病人均经ＣＳ造影，观察ＣＳ形态、走行及分支情况，测量ＣＳ口（ＣＳＯ）大小、窦体直径、长度及窦口上缘与Ｈｉｓ束之间的距离。结果发现ＡＶＮＲＴ组ＣＳ近端形态多呈漏斗状，占８２．４％，而对照组漏斗状仅占２５．０％，其余多呈管状（Ｐ＜０．０１）。ＡＶＮＲＴ组ＣＳＯ明显扩张，两组ＣＳＯ直径分别为１６．４±４．７和１０．２±３．９ｍｍ（Ｐ＜０．０１）。ＡＶＮＲＴ组窦口上缘到Ｈｉｓ束的距离明显较对照组近（８．０３±６．１２ｍｍｖｓ２１．３±６．４８ｍｍ），Ｐ＜０．００１。结果提示：ＡＶＮＲＴ患者的ＣＳＯ扩张对局部心房肌的压迫和牵拉，使ＣＳＯ周围的心房肌各向异性程度增高，可能是导致各向异性折返的病理机制。由于ＣＳＯ扩张使ＣＳＯ上缘距Ｈｉｓ束距离变近，给射频消融（ＲＦＣＡ）造成困难和危险，对此类ＡＶＮＲＴ病人行ＲＦＣＡ应谨慎从事。     

Radiofrequency Modification for Inducible and Suspected Pediatric Atrioventricular Nodal Reentry Tachycardia

Introduction: AV Node Reentry Tachycardia (AVNRT) is the second most common supraventricular tachycardia (SVT) undergoing pediatric radiofrequency ablation behind accessory pathway reentry tachycardias. AVNRT can be difficult to induce during electrophysiology study (EPS) and dual atrioventricular nodal (AVN) pathways physiology may not be demonstrated in young patients.Purpose: This report is the largest single center long term pediatric experience of radiofrequency modification of slow AVN input fibers for inducible or suspected (non-inducible) AVNRT.Results: One hundred thirty-two patients underwent slow input AVN modification from 1993 to 2002. The mean patient age was 13.7 years (4–20 yrs) with 62M/70F. Outpatient tachycardia was documented by ambulatory monitoring in all patients. AVNRT was induced in 98/132 patients during EPS (group A) with mean SVT cycle length of 324 msec (230–570 msec). Initial AVN modification (group A) was successful in 97/98 patients (99%). During 34/132 EPS, AVNRT was non-inducible; dual AVN physiology was present in 19/34 (group B), and 15/34 did not show evidence for dual AVN physiology (group C). These 34 patients underwent empiric AVN modification following discussion with patients’ families. Freedom of recurrence from SVT at 1 year was 96% for group A (94/98), 89% (17/19) for group B and 93% (14/15) for group C. 1 major and 6 minor complications occurred.Conclusions: AVN modification for AVNRT can be performed safely and effectively in pediatric patients with good long-term results. Empiric slow pathway AVN modification for non-inducible SVT results in a high rate of freedom from recurrence of tachycardia.     

PR/RR Interval Ratio During Rapid Atrial Pacing:

Method for Confirming Slow Pathway Conduction. Introduction: Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysioiogic testing. Methods and Results: The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects ≤ 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 ± 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 ± 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 ± 0.08, P < 0. 00001 vs before ablation: Group 2 = 0.67 ± 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age. Conclusion: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.     

Target Temperatures of 48°C versus 60°C During Slow Pathway Ablation:

INTRODUCTION: The relationship between temperature at the electrode-tissue interface and the loss of AV and ventriculoatrial (VA) conduction is not established, and the optimal target temperature for the slow pathway approach to radiofrequency ablation of AV nodal reentrant tachycardia (AVNRT) is unknown. Therefore, the purpose of this study was to compare target temperatures of 48 degrees C and 60 degrees C during the slow pathway approach to ablation of AVNRT. METHODS AND RESULTS: The study included 138 patients undergoing ablation for AVNRT. Patients undergoing slow pathway ablation using closed-loop temperature monitoring were randomly assigned to a target temperature of either 48 degrees C or 60 degrees C. The primary success rates were 76% in the patients assigned to 48 degrees C and 100% in the patients assigned to 60 degrees C (P < 0.01). The ablation procedure duration (33 +/- 31 min vs 26 +/- 28 min; P = 0.2), fluoroscopic time (25 +/- 15 min vs 24 +/- 16 min; P = 0.5), and mean number of applications (9.3 +/- 6.5 vs 7.8 +/- 8.1; P = 0.3) were similar in patients assigned to 48 degrees and 60 degrees C, respectively. The mean temperature (46.1 degrees +/- 24.8 degrees C vs 48.7 +/- 3.2 degrees C; P < 0.01), the temperature associated with junctional ectopy (48.1 degrees +/- 2.0 degrees C vs 53.5 degrees +/- 3.5 degrees C, P < 0.0001), and the frequency of VA block during junctional ectopy (24.6% vs 37.2%; P < 0.0001) were less in the patients assigned to 48 degrees C compared to 60 degrees C. The frequency of transient or permanent AV block was similar in each group (2.8% vs 3.6%; P = 0.2). In the 60 degrees C group, only 12% of applications achieved an electrode temperature of 60 degrees C. During follow-up of 9.9 +/- 4.2 months, there was one recurrence of AVNRT in the 48 degrees C group and none in the 60 degrees C group. CONCLUSIONS: Compared to 48 degrees C, a target temperature of 60 degrees C during radiofrequency slow pathway ablation is associated with a higher primary success rate and a higher incidence of VA block during junctional ectopy induced by the radiofrequency energy. AV block is not more common with the higher target temperature, but only if VA conduction is aggressively monitored during applications of radiofrequency energy.     

Characterization of subforms of AV nodal reentrant tachycardia.

BACKGROUND: Different subforms of AV nodal reentrant tachycardia (AVNRT) have been described ("Slow/Fast", "Slow/Slow" and "Fast/Slow"). Our aim is to improve definition of these subforms, based on systematic evaluation, in a large cohort of patients, of the site of earliest atrial activation, timing intervals, and evidence for the presence or absence of a lower common pathway (LCP). METHODS AND RESULTS: In 344 patients, AVNRT using a slow pathway (SP) for antegrade conduction and earliest atrial activation at the superior septum (i.e. retrograde fast pathway) was present in 81.4% (Slow/Fast). AVNRT using an SP for antegrade conduction and earliest atrial activation at the inferior septum or proximal coronary sinus (i.e. retrograde slow pathway; Slow/Slow) was present in 13.7%. AVNRT with a short A-H interval and retrograde SP conduction (Fast/Slow) was present in 4.9%. All timing intervals during tachycardia are dependent on autonomic tone. H-A intervals during tachycardia (H-A(t)) overlap in Slow/Slow and Slow/Fast AVNRT: Slow/Slow therefore may mimic Slow/Fast AVNRT. The H-A interval during pacing at the tachycardia cycle length (H-A(p)) better discriminates both subforms. The difference between H-A(p) and H-A(t) (Delta H-A) was significantly longer in Slow/Slow compared with Slow/Fast AVNRT (isoprenaline 0.5 microg/min: 27+/-18 ms vs. 1+/-9 ms; p<0.001). Delta H-A>15 ms had a specificity and sensitivity for Slow/Slow of 94% and 64%, respectively. A Delta H-A>15 ms, combined with other data, pointed to the presence of a long LCP in 36 of 43 evaluable Slow/Slow (84%) and all Fast/Slow, but in only 10% of Slow/Fast (p<0.001). Retrograde conduction during ventricular pacing at the tachycardia cycle length was present in only 6% of Fast/Slow. CONCLUSIONS: AVNRT subforms can be distinguished based on a systematic evaluation of atrial activation sequence, timing intervals and evidence for the presence of an LCP.     

心房起搏法在射频消融房室结折返性心动过速中的应用

将射频消融治疗的９４例房室结折返性心动过速（ＡＶＮＲＴ）病人按心房起搏法和常规法进行分组（分别为３９及５５例），回顾性比较两组病人的消融治疗结果，以评价这两种方法在射频消融治疗ＡＶＮＲＴ中的安全性、成功率和复发率。随访１０．８±４．５个月，总成功率为９６．８％、复发率为２．１％。与常规组相比，起搏组有效放电时间明显延长（１４５±３８ｓｖｓ８２±２６ｓ，Ｐ＜０．０１）、慢径阻断成功率高（６１．５％ｖｓ４０．０％，Ｐ＜０．０１）、一过性房室阻滞发生率低（２．６％ｖｓ１２．７％，Ｐ＜０．０５），但各种类型的永久性房室阻滞发生率和复发率无显著性差异（Ｐ＞０．０５）。表明ＡＶＮ－ＲＴ消融术中采用心房起搏法较常规法更为安全有效。     

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.     

与房室结传导特性有关的RR间期明显不齐的室上性心动过速

目的报道RR间期明显不齐的、与房室结传导特性有关的室上性心动过速。方法分析本院3年期间行射频消融术治疗的4例RR间期明显不齐的室上性心动过速的体表和心内心电图及其电生理特点。结果 4例患者(男女各2例),年龄31~46岁,经心内电生理检查诊断为房室结折返性心动过速(AVNRT)和/或房室结1∶2下传,并经射频消融治疗成功。结论部分AVNRT和/或房室1∶2下传引起的心动过速可表现为RR间期明显不齐。     

Location of the lower turnaround point in typical AV nodal reentrant tachycardia: a quantitative model

INTRODUCTION: Recent observations suggest that the circuit of AV nodal reentrant tachycardia (AVNRT) may extend down to the His bundle. The purpose of this study was to develop a quantitative model indicating the location of the lower turnaround point in AVNRT. METHODS AND RESULTS: Slow pathway modification was performed in 70 patients with typical AVNRT. During sinus rhythm, ventricular pacing was performed with the AVNRT cycle length. During AVNRT, the HinitAinit interval was measured from initial His to the initial atrial deflection recorded in the His-bundle lead. During ventricular pacing, the HendAinit interval was measured from end of the His to the beginning of the atrial deflection. It was hypothesized that x reflects conduction time from the lower turnaround point to Ainit, whereas y reflects conduction time from the lower turnaround point to Hinit. Anterograde conduction during AVNRT and retrograde conduction during ventricular pacing were assumed to be identical if there was 1:1 retrograde conduction at the AVNRT cycle length. The following formulas describe the relation of the measured parameters: x - y = HinitAinit; and x + y = HendAinit. Resolving both formulas yields the unknown x and y: y = (HendAinit - HinitAinit)/2, x = (HendAinit + HinitAinit)/2. These criteria were present in 52 of 70 patients. The mean cycle length of AVNRT was 355 +/- 42 msec, mean HinitAinit was 54 +/- 27 msec, and mean HendAinit was 60 +/- 29 msec. Accordingly, in 20 of 52 patients, the lower turnaround point was located within the His bundle (y = -15.4 +/- 16.1 msec), in 3 of 52 it was in the nodal-His junctional area (y = 0), and in 29 of 52 it was above the His bundle (y = +12.7 +/- 10.3 msec). The HinitAinit interval was significantly longer (66 +/- 32 msec vs 47 +/- 20 msec; P = 0.02) and the HendAinit interval was significantly shorter (45 +/- 30 msec vs 69 +/- 24 msec; P = 0.004) when the first group was compared with the others. CONCLUSION: In about 1 of 3 of patients with typical AVNRT, the lower turnaround point of the circuit is within the His bundle; in more than half of the patients it is above the His bundle. These data do not support the concept that all AVNRTs have an intranodal circuit, but are in accordance with the finding of longitudinal dissociation of the His bundle.     

Evaluation of left ventricular systolic and diastolic function in patients with atrioventricular re-entrant tachycardia treated by radiofrequency current ablation

Little is known about the long-term influence of radiofrequency current ablation (RFCA) on left ventricular (LV) systolic and diastolic function in patients with atrioventricular re-entrant tachycardia (AVRT). METHOD: The study group consisted of 65 patients (33 M, mean age 39 +/- 11 y) with WPW syndrome and recurrent episodes of AVRT without any concomitant diseases. The control group consisted of 50 age-matched healthy volunteers. In both study and control groups transthorasic echocardiography (TTE) and Doppler were performed in order to assess LV systolic and diastolic function. In WPW patients TTE was followed by electrophysiology study and RFCA. TTE was repeated in 6-months time in the study group. RESULTS: At 6-month follow-up a decrease in LV end-systolic diameters (1.77 +/- 0.22 vs. 1.67 +/- 0.22 cm/m2, P < 0.001) and volumes (20 +/- 6 vs. 17 +/- 5 ml, P < 0.001) and an increase in LV FS (33 +/- 6 vs. 37 +/- 5%, P < 0.001), EF (54 +/- 6 vs. 60 +/- 5%, P < 0.001), IVS (44 +/- 13 vs. 49 +/- 14%, P < 0.05) and LV PW thickening (58 +/- 19 vs. 62 +/- 16%, P < 0.05) was found. Doppler analysis revealed an increase in E wave (78 +/- 17 vs. 82 +/- 14 cm/s, P < 0.001), E/A ratio (1.14 +/- 0.37 vs. 1.33 +/- 0.24, P < 0.001) and a decrease in A wave (68 +/- 19 vs. 63 +/- 12 cm/s, P < 0.05), DT (219 +/- 33 vs. 180 +/- 20 ms, P < 0.001 ), IVRT (105 +/- 13 vs. 88 +/- 13 ms, P < 0.001), AR (26 +/- 8 vs. 18 +/- 12 cm/s, P < 0.001 ) and difference between duration of AR and A waves (5 +/- 24 vs. -12 +/- 21 ms, P < 0.001). No significant differences in regard to LV systolic and diastolic variables were found between patients and controls post RFCA. CONCLUSION: RFCA of accessory pathway in patients with WPW syndrome and AVRT is associated with improvement of LV systolic and diastolic function.     

Cryoablation in pediatric atrioventricular nodal reentry: Electrophysiologic effects on atrioventricular nodal conduction

BACKGROUND: Cryoablation for treatment of atrioventricular nodal reentrant tachycardia (AVNRT) is safe and efficacious. Information on the effects of cryoablation on atrioventricular (AV) nodal conduction is limited. OBJECTIVES: The purpose of this study was to evaluate the effects of cryoablation on AV nodal conduction in pediatric patients with AVNRT. METHODS: We retrospectively analyzed electrophysiologic studies before and after successful cryoablation. Patients were divided into two groups: group 1 (n = 22, age 14 +/- 3 years) had baseline discontinuous atrial-to-His interval (AH) conduction curves; and group 2 (n = 13, age 12 +/- 4 years, P = .054) had continuous curves. RESULTS: At baseline, group 1 had longer measurements of maximal AH with A1A2, AV nodal effective refractory period, and AV block cycle length. Postcryoablation, both group 1 and group 2 showed decreases in maximal AH with A1A2 pacing or atrial overdrive pacing and in the finding of PR > or = RR with atrial overdrive pacing (group 1: 55% vs 5%, P < .001; group 2: 69% vs 0%, P < .001). A significant increase in overall AV effective refractory period and a decrease in AV block cycle length were found in group 1 but not group 2. Fifty percent of group 1 patients had complete abolition of slow pathway conduction. CONCLUSION: Successful cryoablation for treatment of AVNRT is associated with a reduction in PR > or = RR and with decreases in maximal AH with A1A2 pacing or atrial overdrive pacing. Further study is needed to determine the usefulness of these parameters for assessment of ablation efficacy or as proxies for AVNRT inducibility.