Fast Pathway Effective Refractory Period Research Articles

The prevalence and characteristics of coexisted atrioventricular nodal reentrant tachycardia and idiopathic left fascicular ventricular tachycardia.

Coexistence of idiopathic left fascicular ventricular tachycardia (ILFVT) and atrioventricular nodal reentrant tachycardia (AVNRT) has been rarely reported. The study aimed at elucidating the prevalence of coexisted AVNRT in patients with ILFVT during longitudinal follow-up. The electrophysiological properties and clinical predictors of coexisted ILFVT and AVNRT were investigated. From 1999 to 2017, a total of 108 patients (age: 33.7 ± 14.3, 84 male) with ILFVT from one tertiary center were consecutively enrolled. The prevalence of coexisted arrhythmias was explored during a longitudinal follow-up and the electrophysiological parameters from the index procedure were compared. During a mean follow-up period of 106.8 ± 69.5 months, 21 of 108 patients (19.4%) had coexisted AVNRT. The electrophysiological study demonstrated patients with coexisted ILFVT and AVNRT were characterized by more antegrade dual AV node conduction (52.4%vs. 19.5%, P=0.002; 9.5%), shorter antegrade slow pathway effective refractory period (285.1 ± 34.1ms vs. 329.2 ± 69.2ms, P=0.034), longer retrograde fast pathway effective refractory period (368.9 ± 56.7ms vs. 312.5 ± 95.2, P=0.036), and less VA dissociation (19.0%vs. 60.9%, P=0.001) than those without a coexisted AVNRT. Multivariate logistic analysis showed that presence of antegrade dual AV nodal physiology and retrograde VA conduction could predict a coexisted AVNRT in patients with ILFVT (P=0.005, OR: 4.80, 95% CI: 1.65-14.37 and P=0.002, OR: 0.14, 95% CI: 0.04-0.49, respectively). There was a high prevalence of coexisted AVNRT in patients with ILFVT during longitudinal follow-up. The presence of antegrade dual AV nodal physiology and retrograde VA conduction can predict the coexisted AVNRT in patients with ILFVT.

Analysis of atrioventricular function and its efficacy in patients with AVNRT undergoing atrioventricular junction ablation of slow conduction pathway

Objective The electrophysiological parameters of atrioventricular conduction function in patients with atrioventricular nodal reentry tachycardia (AVNRT) were analyzed, and to explore the effect of different ablation endpoints on atrioventricular conduction function in patients with AVNRT. Methods 96 cases with AVNRT underwent radiofrequency catheter ablation (RFCA) of slow conduction pathway.According to whether the slow pathway eliminated, the patients were divided into the slow pathway disappeared group and slow tracks remaining group.Preoperative and postoperative intracavitary electrophysiological examination and atrioventricular function data were recorded, including before and after radiofrequency ablation of bundle of HIS, PA, AH, HV interval, atrioventricular prequel venturi point(AVN-WKB), ventriculoatrial retrograde venturi point(VAN-WKB), atrioventricular node prequel effective refractory period(AVB-WKB). Patients were followed up by telephone for a year.Then, a comparative analysis of preoperative and postoperative was done. Results RFCA of AVNRT patients with atrioventricular node prequel time effect: RFCA and preoperative ratio, after his bundle electrogram PA, ah, HV interval had no significant changes(P>0.05). Effect of RFCA surgery on patients with AVNRT refractory atrioventricular node prequel: compared with RFCA before surgery, postoperative slow pathway disappear fast pathway shortening of effective refractory period[preoperative(287.5±46.2)ms, postoperative(260.2±55.6)ms, t=2.901, P=0.005], slow pathway effective refractory period[disappear preoperative(243.3±43.2), postoperative(0.0±0.0)ms, t=43.290, P=0.000], AV node Wenckebach point in advance before operation[(261.3±44.3)ms, postoperative(293.2±46.2)ms, t=3.828, P=0.000]; group after slow pathway to improve fast pathway effective refractory period without obvious change(P>0.05), the slow pathway effective refractory period in high concentration[preoperative(242.2±42.8)ms, postoperative(281.2±41.3)ms, t=3.879, P=0.000], atrioventricular node Wenckebach point in advance before operation[(261.5±43.5)ms, postoperative(291.3±46.5)ms, t=2.769, P=0.007]. Comparison between groups, after slow pathway disappeared group fast pathway effective refractory period was significantly shorter in the slow diameter improvement group, but between the two groups in the atrioventricular node Wenckebach point differences was not statistically significant(P>0.05). There was no recurrence in the follow-up after a year of slow path loss and slow pathway. Conclusion RFCA caused by slow pathway to disappear or modified two slow pathway ablation right AVNRT patients atrioventricular time had no effect, but all the atrioventricular junction the prequel's point advance.The atrioventricular node slow pathway disappear fast and effective pathway refractory period shortened, slow pathway improved the slow pathway effective refractory period.RFCA surgery done by the slow pathway disappeared or slow pathway ablation is effective in patients with AVNRT, and there was no significant recurrence rate in both groups within 1 year. Key words: Ablation; Tachycardia; Atrioventricular conduction function

小児の房室結節における速遅伝導路間の電気的相互作用の検討

小児の房室結節における速遅伝導路間の電気的相互作用の検討

Cryoablation of AVNRT When Sustained Tachycardia Cannot be Induced

Inducibility of sustained tachycardia is preferred prior to cryoablation for atrioventricular nodal reentrant tachycardia (AVNRT). The Pediatric Electrophysiology Database of a single institution was retrospectively reviewed for patients with clinical sustained (≥ 30 seconds of symptoms) AVNRT documented by noninvasive means who underwent cryoablation for AVNRT to determine if intermediate-term success with cryoablation for AVNRT can be achieved without inducibility of sustained AVNRT during electrophysiology study (EPS). There were no differences between patients with sustained (≥ 30 seconds of tachycardia) AVNRT (N = 67) and patients with nonsustained (ns, ≥ 3 beats and <30 seconds of tachycardia) AVNRT at EPS (N = 16). Acute success was achieved without PR prolongation in all patients. Although duration of follow-up was shorter for the sustained group than the nonsustained group (2.7 ± 1.6 years vs 3.8 ± 1.4 years, P = 0.008), recurrence rate was similar (6% vs 6.3%, P = 0.6). In patients with only nonsustained AVNRT at EPS, supportive findings for procedural effectiveness seen: (1) Dual atrioventricular node physiology (DAVNP) was eliminated in 14/14, (2) the fast pathway effective refractory period (FPERP) decreased after ablation in 10/11, (3) sustained slow pathway conduction was eliminated in 8/8 including both patients without discrete DAVNP prior to ablation, and (4) FPERP increased during lesion formation in 10/10. Intermediate-term success can be achieved with cryoablation of ns AVNRT. Attention should be paid to supportive indicators of damage to slow pathway.

What Can We Tell by the Fast Pathway Effective Refractory Period?

What Can We Tell by the Fast Pathway Effective Refractory Period?

Gender Differences in the Clinical Characteristics and Atrioventricular Nodal Conduction Properties in Patients With Atrioventricular Nodal Reentrant Tachycardia

The detailed electrophysiological characteristics of the gender differences associated with atrioventricular nodal reentrant tachycardia (AVNRT) have not been clarified. This study investigated the gender-related electrophysiological differences in a large series of patients undergoing radiofrequency catheter ablation. A total of 2,088 consecutive AVNRT patients (men/women 869/1,219) who underwent catheter ablation were enrolled in this study. We evaluated the gender differences in their electrophysiological characteristics. Women had a significantly younger age of onset, higher incidence of multiple jumps, shorter AH interval, atrial effective refractory period (ERP), anterograde fast pathway ERP, anterograde slow pathway ERP, and retrograde slow pathway ERP, and longer ventricular ERP than men. The incidence of baseline ventriculoatrial dissociation was lower in women than in men. Women needed less isoproterenol/atropine to induce AVNRT. No gender differences in the radiation exposure time, procedure time, complication rate, acute success rate, or second procedure rate were noted. Both typical and atypical AVNRT were more predominant in women. In the patients with atypical AVNRT, there was no significant gender difference in incidence of baseline ventriculoatrial dissociation; however, the retrograde slow pathway ERP was significantly shorter in women than in men. Women of premenopausal age (≤50 years old) had a significantly higher incidence of anterograde multiple jumps and a retrograde jump phenomenon, and a shorter anterograde slow pathway ERP and retrograde slow pathway ERP than those of women over 50 years old. Gender differences in the anterograde and retrograde AV nodal electrophysiology were noted in the patients with AVNRT.

Developmental aspects of atrioventricular node reentry tachycardia

Atrioventricular node reentry tachycardia is an incompletely understood substrate for supraventricular tachycardia. Although there is agreement that the mechanism involves functionally separate fast and slow AV node pathways, which are somewhat anatomically discrete, the anatomical basis for the reentrant circuit is not well defined. Furthermore, the nature of the long fast pathway effective refractory period is not known but most likely involves electrotonic interactions between fast and slow AV nodal pathways. The proposition that the mechanism is related to features of cell coupling has been studied in a finite element computer model. Because the calculations rely on assumptions about nodal size and space constants, clinical studies in smaller and younger patients are naturally of interest.

The Different Ablation Effects on Atrioventricular Nodal Reentrant Tachycardia in Children with and without Dual Nodal Pathways

Previous studies in adults have shown a significant shortening of the fast pathway effective refractory period (ERP) after successful slow pathway ablation. However, information on atrioventricular nodal reentrant tachycardia (AVNRT) in children is limited. The purpose of this retrospective study was to investigate the different effects of radiofrequency (RF) catheter ablation in pediatric AVNRT patients between those with and without dual atrioventricular (AV) nodal pathways. From January 1992 to August 2004, a total 67 pediatric patients with AVNRT underwent an electrophysiologic study and RF catheter ablation at our institution. We compared the electrophysiologic characteristics between those obtained before and after ablation in the children with AVNRT with and without dual AV nodal pathways. Dual AV nodal pathways were found in 37 (55%) of 67 children, including 36 (54%) with antegrade and 10 (15%) with retrograde dual AV nodal pathways. The antegrade and retrograde fast pathway ERPs in children with dual AV nodal pathways were both longer than the antegrade and retrograde ERPs in children without dual AV nodal pathways (300 +/- 68 vs 264 +/- 58 ms, P = 0.004; 415 +/- 70 vs 250 +/- 45 ms, P < 0.001) before ablation. In children with antegrade dual AV nodal pathways, the antegrade fast pathway ERP decreased from 300 +/- 68 ms to 258 +/- 62 ms (P = 0.008). The retrograde fast pathway ERP also decreased after successful ablation in the children with retrograde dual AV nodal pathways (415 +/- 70 vs. 358 +/- 72 ms, P = 0.026). The dual AV nodal physiology could not be commonly demonstrated in pediatric patients with inducible AVNRT. After a successful slow pathway ablation, the fast pathway ERP shortened significantly in the children with dual AV nodal pathways.

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.

Prolongation of the fast pathway effective refractory period during cryoablation in children: A marker of slow pathway modification

The fast pathway effective refractory period (ERP) has been reported to decrease after slow pathway modification with radiofrequency (RF) energy. How the fast pathway ERP changes during the ablation application has not been reported with either RF or cryoenergy. Using the unique features of cryotherapy, this study assesses the short-term changes in fast pathway ERP during cryomodification of the slow pathway and examines whether these changes are a useful marker for successful slow pathway modification in children. Nineteen pediatric patients (median age 15.1 years, range 9.6-19.6 years; weight 60.7 kg, range 35.6-130.2 kg) with anterograde dual AV nodal physiology underwent slow pathway modification with catheter-based cryoablation. Programmed stimulation was performed during cryoapplications after reaching -25 degrees C to assess fast pathway and slow pathway conduction. Data were analyzed from 59 of 237 cryoapplications where the fast pathway ERP was measured more than once (n = 13 patients). For 23 of 59 applications where the slow pathway was modified, the fast pathway ERP significantly increased during cryotherapy (Delta = 33.5 ms, P <.0001). The magnitude of fast pathway ERP prolongation during cryotherapy was larger when the slow pathway was modified than when there was no effect on slow pathway conduction (33.5 +/- 30.5 vs 5.8 +/- 18.9 ms, P =.0005). Prolongation of fast pathway ERP by >/=20 ms had 70% sensitivity and 72% specificity for predicting slow pathway modification. Following termination of cryoapplications, which resulted in slow pathway modification, the fast pathway ERP had significantly decreased from baseline (difference 44.5 ms, P <.0001). The effect on fast pathway ERP was not related to changes in cycle length during (R(2) = 0.04, P = .045) or after ablation (R(2) = 0.13, P = .012). The fast pathway ERP prolongs during cryoapplications that result in slow pathway modification and shortens after termination of cryoapplications. The magnitude of fast pathway ERP prolongation during cryoapplication may be useful as a marker for successful slow pathway modification.

Effects of a blocked atrial beat on the atrioventricular nodal recovery property in patients with dual nodal pathways.

Dual AVN physiology can be demonstrated by a variety of maneuvers. To determine whether AVN recovery times following a blocked extrastimulus facilitate or obscure detection of dual AVN physiology, 11 patients (9-17 years) were studied with dual AVN pathways by using single and double atrial extrastimuli. With a single atrial extrastimuli, the premature atrial stimulus (A2) was coupled to basic atrial beats (A1). The fast and slow AVN recovery curves were constructed with plots of the nodal conduction time against the recovery time (A1A2,A2H2). With double atrial extrastimuli, a fixed blocked A2 beat (A2B) was followed by a scanning atrial beat (A3). The nodal recovery property post-A2B was studied by plots of A2BA3,A3H3. In all patients the recovery curve of the fast pathway post-A2B had a leftward shift when compared to that of the pre-A2B curve (i.e., the AH was shortened at the same recovery time). The window of slow pathway conduction post-A2B disappeared totally in five patients and decreased significantly in six patients (post-A2B: 26 +/- 42 ms; pre-A2B: 80 +/- 65 ms, P < 0.05). In the six patients that still had slow pathway conduction post-A2B, the slow pathway effective refractory period post-A2B was significantly less than that of pre-A2B (215 +/- 38 vs 268 +/- 16 ms, P < 0.05). The fast pathway effective refractory period post-A2B was also diminished significantly (235 +/- 62 vs 357 +/- 76 ms, P < 0.0001). The authors conclude that blocked atrial beats decrease the visibility of the slow pathway conduction.

Atrioventricular nodal reentrant tachycardia in children: effect of slow pathway ablation on fast pathway function.

Prior studies in adults have shown significant shortening of the fast pathway effective refractory period after successful slow pathway ablation. As differences between adults and children exist in other characteristics of AV nodal reentrant tachycardia (AVNRT), we sought to characterize the effect of slow pathway ablation or modification in a multicenter study of pediatric patients. Data from procedures in pediatric patients were gathered retrospectively from five institutions. Entry criteria were age <21 years, typical AVNRT inducible with/without isoproterenol infusion, and attempted slow pathway ablation or modification. Dual AV nodal pathways were defined as those with > or =50 msec jump in A2-H2 with a 10-msec decrease in A1-A2. Successful ablation was defined as elimination of AVNRT inducibility. A total of 159 patients (age 4.4 to 21 years, mean 13.1) were studied and had attempted slow pathway ablation. AVNRT was inducible in the baseline state in 74 (47%) of 159 patients and with isoproterenol in the remainder. Dual AV nodal pathways were noted in 98 (62%) of 159 patients in the baseline state. Ablation was successful in 154 (97%) of 159 patients. In patients with dual AV nodal pathways and successful slow pathway ablation, the mean fast pathway effective refractory period was 343+/-68 msec before ablation and 263+/-64 msec after ablation. Mean decrease in the fast pathway effective refractory period was 81+/-82 msec (P < 0.0001) and was not explained by changes in autonomic tone, as measured by changes in sinus cycle length during the ablation procedure. Electrophysiologic measurements were correlated with age. Fast pathway effective refractory period was related to age both before (P = 0.0044) and after ablation (P < 0.0001). AV block cycle length was related to age both before (P = 0.0005) and after ablation (P < 0.0001). However, in dual AV nodal pathway patients, the magnitude of change in the fast pathway effective refractory period after ablation was not related to age. Lack of clear dual AV node physiology is common in pediatric patients with inducible AVNRT (38%). Fast pathway effective refractory period shortens substantially in response to slow pathway ablation. The magnitude of change is large compared with adult reports and is not completely explained by changes in autonomic tone. Prospective studies in children using autonomic blockade are needed.

Atrioventricular node reentrant tachycardia in patients with a long fast pathway effective refractory period: Clinical features, electrophysiologic characteristics, and results of radiofrequency ablation

Twenty-two patients (group 1) with AV node reentrant tachycardia and a baseline fast pathway effective refractory period (ERP) ≥500 msec were compared with 30 consecutive patients (group 2) with AV node reentrant tachycardia and a fast pathway ERP <500 msec. Both groups underwent slow pathway ablation. In the patients with complete elimination of slow pathway, the fast pathway ERP and shortest 1:1 conduction cycle length shortened significantly after ablation but was greater in group 1 ( n = 14) than in group 2 ( n = 21) (125 ± 78 msec vs 48 ± 29 msec, p < 0.001 and 103 ± 72 msec vs 52 ± 30 msec, p < 0.001, respectively). In group 1, the shortening of fast pathway ERP was correlated to baseline difference between anterograde fast and anterograde slow ERP ( r = 0.806, p < 0.001, slope = 1.08), and the shortening of fast pathway shortest 1:1 conduction cycle length was correlated to baseline difference between anterograde fast and anterograde slow shortest 1:1 conduction cycle length ( r = 0.885, p < 0.001, slope = 1.47). During follow-up bradycardia did not develop in any patient and no one required pacing. This shortening of the fast pathway ERP and shortest 1:1 conduction cycle length after complete elimination of slow pathway reduced the concern of subsequent impairment of AV node conduction. (Am Heart J 1997;134:387-94.)

The effect of variable retrograde penetration on dual AV nodal pathways: observations before and after slow pathway ablation LDD.

Retrograde VA conduction is usually over the fast pathway and rarely over the slow pathway in patients with dual AV nodal pathways. It is unknown whether this apparent unidirectional conduction of the slow pathway is due to the lack of its retrograde conducting ability or the result of concealment. The effect of variable retrograde AV nodal penetration on antegrade AV nodal conduction was determined in patients with typical AV nodal reentrant tachycardia before and after the slow pathway ablation. Variable retrograde penetration was produced by delivering a ventricular extrastimulus simultaneously with (VE-0), 50 ms after (VE-50), or 100 ms after (VE-100) the last basic atrial stimulus, while atrial extrastimuli were used to determine changes of anterograde AV nodal effective refractory period (ERP) and A-H interval. The AV nodal functions measured without the ventricular extrastimuli served as the baseline. Although the mean slow pathway ERP was not significantly different among the different stimulation protocols, a significant shortening of the slow pathway conduction time (A-H from 348 +/- 60 to 324 +/- 119 ms, P < 0.05) was observed with upper level retrograde penetration of the AV node (VE-0). This facilitating effect became a prolonging effect when the retrograde penetration level moved to the lower level (VE-100, A-H from 324 +/- 119 to 366 +/- 122 ms, P < 0.05). The fast pathway ERP shortened with an upper level penetration (VE-0) but tended to prolong with a lower level retrograde-penetration (VE-100) both before and after the slow pathway ablation (preablation, from 348 +/- 143 of the baseline to 302 +/- 114 to 360 +/- 143 ms, P < 0.05; postablation, from 314 +/- 101 of the baseline to 274 +/- 118 to 361 +/- 143 ms, P < 0.05). The mean A2-H2 interval of the slow pathway was significantly shorter than the baseline (350 +/- 44 ms) with VE-0 (249 +/- 48 ms, P < 0.05) and VE-50 stimulation (285 +/- 82 ms, P < 0.05) but not with VE-100 stimulation (330 +/- 83 ms, P = NS). Before slow pathway ablation, the A2-H2 interval of the fast pathway at equal coupling intervals was shorter than the baseline (165 +/- 53 ms) with VE-0 (144 +/- 47 ms, P < 0.01) and VE-50 stimulation (152 +/- 43 ms, P < 0.05) but tended to be longer with VE-100 stimulation (175 +/- 47 ms, P = NS). After slow pathway ablation, the mean A2-H2 interval at the same coupling interval was shorter than the baseline (173 +/- 39 ms) with VE-0 (139 +/- 35 ms, P < 0.05), VE-50 (153 +/- 32 ms, P = 0.05) but tended to be longer with VE-100 stimulation (178 +/- 49 ms, P = NS). We conclude that: (1) concealed retrograde conduction can be demonstrated in both the slow and the fast AV nodal pathways; and (2) concealed retrograde conduction may either shorten or prolong anterograde refractoriness and conduction time, depending on the level of retrograde penetration.

Safety of Slow Pathway Ablation in Patients With Atrioventricular Node Reentrant Tachycardia and a Long Fast Pathway Effective Refractory Period

Radiofrequency catheter ablation is an accepted primary therapy for atrioventricular (AV) node reentrant tachycardia (AVNRT). There is concern that slow pathway ablation in patients with a long anterograde fast pathway effective refractory period (ERP) may potentially impair subsequent node conduction. Eighteen patients (14 women; age 53 ± 20 years) with symptomatic AVNRT, whose fast pathway ERP at baseline was ≥500 ms, underwent slow pathway ablation. Their outcome was compared with 24 consecutive control patients (17 women; age 42 ± 17 years) who underwent ablation for AVNRT whose fast pathway ERP at baseline was <500 ms (controls). Slow pathway ablation was successful in 16 patients (90%). One patient had inadvertent fast pathway ablation. In a second patient the slow pathway could not be ablated because of recurrent transient AV block. Ablation was successful in all patients in the control group. Transient AV block related to current application occurred in 4 patients (22%) versus 1 control (4%) (p = 0.07). After ablation, the AV node refractory period increased in patients (368 ± 68 to 428 ± 92 ms, p = 0.02) and in controls (282 ± 35 to 336 ± 55 ms, p <0.0001), but the fast pathway ERP shortened in both groups (patients: 558 ± 63 to 428 ± 92 ms, p = 0.003; controls: 356 ± 53 to 336 ± 55 ms, p = 0.05). Furthermore, the slope of the regression line relating to shortening of the fast pathway ERP to the baseline ERP was markedly steeper in patients compared with controls (1.9 vs 0.4, p <0.0001). The shortening of the fast pathway ERP was greater in patients compared with controls (122 ± 130 vs 21 ± 50 ms, p = 0.001). During a mean follow-up of 18 ± 11 months, 1 patient with severe coronary artery disease died suddenly 2 years after ablation. There was no recurrence of clinical tachycardia, and none of the patients developed symptoms of bradycardia or required permanent pacing. Thus, slow pathway ablation in patients with AVNRT and a long fast pathway ERP is safe and effective.

Evaluation of Fast Pathway Function

There is no consensus oti the effect of slow pathway ablation on the electrophysiologic properties of the fast pathway in patients with AV ncxial reentrant tachycardia. Some investigators have demonstrated that ahlation of the slow pathway results In shortening of the fast pathway effective refractory period, while other investigators have not made this observation.' '^ In the setting of sympathetic stimulation, slow pathway ahlation does not result in shortening of the fast pathway eifective refractory period.' The results from studies not perfonned in the setting of autonomic blockade have been variable.--^-'^-'^ However, the majority of studies perfonned in the setting of autonomic blockade have demonstrated shortening of the fast pathway effective refractory period after complete, but not partial, elimination of slow pathway fimction.** Among the four studies that have included autonomic blockade as part of the study design, three demonstrated that the fast pathway effective refractory period decreases after complete elimination of slow pathway function.**' In one study, shortening of the fast pathway effective refractory period after slow pathway ahlation in the setting of atropine and propranolol was not observed. In this report, complete autonomic blockade was not maintained throughout the study, as evidenced by large changes in the sinus cycle length before and after the ablation procedure. If shortening of the fast pathway effective refractory period can be obscured by alterations in autonotnic lone, then complete autonomic blockade throughout the entire study is required. Given that the changes in fast pathway function occur only after complete elimination of slow pathway function and that sympathetic stimulation can obscure these

A direct midseptal approach to slow atrioventricular nodal pathway ablation.

The purpose of this study was to describe a midseptal approach to selective slow pathway ablation for the treatment of AV nodal reentrant tachycardia (AVNRT). In addition, predictors of success and recurrence were evaluated. Selective ablation of the slow AV nodal pathway utilizing radiofrequency (RF) energy and a midseptal approach was attempted in 60 consecutive patients with inducible AVNRT. Successful slow pathway ablation or modification was achieved in 59 of 60 patients (98%) during a single procedure. One patient developed inadvertent complete AV block (1.6%). A mean of 2.7 +/- 1.4 RF applications were required with mean total procedure, ablation, and fluoroscopic times of 191 +/- 6.3, 22.8 +/- 2.3, and 28.2 +/- 1.8 minutes, respectively. The PR and AH intervals, as well as the antegrade and retrograde AV node block cycle length, were unchanged. However, the fast pathway effective refractory period was significantly shortened following ablation (354 +/- 13 msec vs 298 +/- 12 msec; P = 0.008). The A/V ratio at successful ablation sites were no different than those at unsuccessful sites (0.22 +/- 0.04 vs 0.23 +/- 0.03). Junctional tachycardia was observed during all successful and 60 of 122 (49%) unsuccessful RF applications (P < or = 0.0001). A residual AV nodal reentrant echo was present in 15 of 59 (25%) patients. During a mean follow-up of 20.1 +/- 0.6 months (11.5-28 months) there were four recurrences (5%), 4 of 15 (27%) in patients with and none of 44 patients without residual slow pathway conduction (P = 0.002). A direct midseptal approach to selective ablation of the slow pathway is a safe, efficacious, and efficient technique. Junctional tachycardia during RF energy application was a highly sensitive but not specific predictor of success and residual slow pathway conduction was associated with a high rate of recurrence.

Effects of partial and complete ablation of the slow pathway on fast pathway properties in patients with atrioventricular nodal reentrant tachycardia.

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). 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). 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.

NASPE Young Investigator Awardee-1993. Computer model of the atrioventricular node predicts reentrant arrhythmias.

Following atrial premature beats, the AV node may exhibit sustained reentrant tachyarrhythmias, isolated echo beats, or discontinuities in the recovery curve (the plot of conduction time versus atrial cycle length). A computer model was used to examine the hypothesis that spatial variation of AV nodal passive electrical resistance may account for these phenomena. A computer model of a rectangular lattice of electrotonically linked elements whose ionic kinetics simulated nodal ionic flux was developed. The model showed that there exists a resistance value that minimizes the effective refractory period, because high resistance prevents depolarization of distal elements, while low resistance allows leakage of depolarizing current by electrotonic transmission, preventing activation of proximal elements. High resistances stabilized reentry by slowing conduction. Simulations incorporating equal resistance values between elements predicted increased AV nodal conduction times with increasing prematurity of atrial impulses. A model with a gradual change in resistance between fibers produced discontinuities and tachycardia, but not both simultaneously. Uniform anisotropy produced preferential transverse block, leading to echo beats and "fast-slow" tachycardia, but not recovery curve discontinuities. Nonuniform anisotropy could produce reentry, but tachycardia often occurred without discontinuities. Dividing the lattice into two electrotonically linked parallel pathways with different resistance values ("dual pathway model") predicted recovery curve discontinuities, echo beats, and tachycardia. At critical atrial cycle lengths, only the (high resistance) slow pathway conducted antegradely, while the fast pathway conducted retrogradely, to generate the typical "slow-fast" tachycardia. Responses of the dual pathway model to ablation were consistent with clinical data, including the previous observation of a decrease in fast pathway effective refractory period after slow pathway ablation. Differences in passive electrical resistance of electronically linked dual pathways within the AV node may account for functional longitudinal dissociation, reentrant arrhythmias, and responses to catheter ablation therapy.

Electrophysiologic effects and efficacy of cibenzoline in patients with supraventricular tachycardia.

Electrophysiologic effects of intravenous (i.v.) cibenzoline were evaluated in 18 patients with accessory pathways or dual atrioventricular (AV) nodal pathways (12 men and 6 women with a mean age of 44 +/- 18 years). Twelve patients had accessory AV pathways, including 6 patients with a manifest accessory pathway. Six patients had AV nodal reentrant tachycardia (AVNRT). Electrophysiologic studies were performed before and after cibenzoline (1.4 mg/kg i.v.) infusion for 5 min. Sinus cycle length did not change significantly after cibenzoline administration. Cibenzoline increased both the AH (85 +/- 20 vs. 91 +/- 21 ms, p less than 0.05) and HV intervals (41 +/- 10 ms vs. 53 +/- 11 ms, p less than 0.001). Neither the atrial nor ventricular effective refractory period (ERP) was altered by cibenzoline. Complete block in the accessory pathway occurred antegradely in 4 patients and retrogradely in 1 patient. Cibenzoline prevented induction of AV reentrant tachycardia (AVRT) in 3 of 8 patients with sustained orthodromic AVRT by abolishing retrograde accessory pathway conduction or prolonging the retrograde accessory pathway ERP. Of 5 patients who continued to have inducible AVRT before and after cibenzoline administration, the tachycardia cycle length was increased in 3, mainly due to the increase in retrograde accessory pathway conduction time. Cibenzoline prevented induction of sustained AVNRT in 4 of 5 patients by prolonging the minimum pacing cycle length, maintaining 1:1 ventriculoatrial (VA) conduction through the retrograde fast AVN pathway or shortening the antegrade fast AVN pathway ERP equal to the slow AVN pathway. In one patient who had an uncommon type of AVNRT, sustained tachycardia was induced by cibenzoline.(ABSTRACT TRUNCATED AT 250 WORDS)