A Direct Midseptal Approach to Slow Atrioventricular Nodal Pathway Ablation

Objectives: 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. Methods: 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. Results: 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 < 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). Conclusions: 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.     

Is Vagal Innervation to the Atrioventricular Node Impaired After Radiofrequency Ablation of the Slow Atrioventricular Nodal Pathway?

To assess the potentially adverse effects of RF catheter ablation (RFCA) of the slow AV nodal pathway on the parasympathetic innervation to the AV node in patients with AV nodal reentrant tachycardia (AVNRT), AV nodal conduction was evaluated following vagal stimulation by means of a phenylephrine bolus injection (200 μg) before and after RFCA in ten patients (mean age, 37 ± 14 years). Nine patients with AV reentrant tachycardia (AVRT) due to a left free wall accessory pathway served as a control group (mean age of 37 ± 12 years). Whereas no prolongation of the AH interval was observed in the AVNRT group following the phenylephrine bolus during sinus rhythm, despite a significant slowing in sinus rate, phenylephrine administration in AVRT patients was associated with both slowing of the sinus rate and prolongation of the AH interval. Following successful RFCA, the same responses were observed. To delineate the indirect effect of heart rate on AV conduction in response to the phenylephrine bolus, the AH interval was also measured during fixed atrial pacing. A marked prolongation of the AH interval occurred in both groups following phenylephrine administration. This prolongation was biphasic in 50% of A VNRT patients before ablation, suggesting a predominant effect of vagal stimulation on the fast AV nodal pathway. RFCA was associated with disappearance of discontinuous AV conduction in all but one patient with AVNRT. Vagal stimulation caused the same amount of AH interval prolongation as before RFCA in both study groups. In conclusion, patients with AVNRT have a preserved modulation of AV nodal conduction in response to vagal stimulation during sinus rhythm. In addition, vagal stimulation seems to exert a predominant effect on the fast A V nodal pathway. RFCA of the slow AV nodal pathway in patients with A VNRT does not cause detectable damage to the vagal innervation to the AV node.     

Changes in AV Node Conduction Curves Following Slow Pathway Modification

GELLER, J.C., et al. : Changes in AV Node Conduction Curves Following Slow Pathway Modification. Dual AV node physiology often persists after successful slow pathway (SP) ablation, and the mechanism of tachycardia elimination is unresolved. Therefore, AV node conduction curves were analyzed following successful ablation (  4 ± 1  energy applications) in 85 consecutive patients (58 women, age  50 ± 2  years) with typical AVNRT. Twenty-seven patients (32%) had complete elimination (group 1) whereas 58 (68%) patients had persistence (group 2) of dual AV node physiology. A significant increase in the AV node Wenckebach cycle length (WB-CL) was observed in both groups (  310 ± 9 to 351 ± 15 ms  in group 1, and  325 ± 8 to 369 ± 9 ms  in group  2, P < 0.05  ). A decrease in the fast pathway (FP) ERP (  339 ± 15 to 279 ± 12 ms  ) and an increase in the maximum FP AH interval (  141 ± 5 to 171 ± 7  ) were observed only in group 1 (P < 0.05). In group 2, no change in the SP ERP (  267 ± 7 to 280 ± 10 ms  ) was observed, and the change in the maximum SP-AH following ablation showed a significant inverse relation to the maximum SP-AH at baseline in group 2. In conclusion, (1) an increase in the WB-CL is observed independent of the persistence or elimination of dual physiology after successful ablation; (2) when dual physiology is eliminated, significant changes in the FP ERP and the maximum FP-AH occur; (3) when dual physiology persists, FP physiology and the SP ERP remain unchanged, and a significant inverse relation between the change in the maximum SP-AH following ablation and the maximum baseline SP-AH is observed.     

Shortcut Link Between the Fast and Slow Pathways and the Mechanism of Cure in Atrioventricular Nodal Reentrant Tachycardia by Catheter Ablation

The mechanism of cure in AV nodal reentrant tachycardia (AVNRT) by catheter ablation has not been fully clarified. We hypothesized that disruption of a shortcut link between the fast and slow pathways is responsible for the elimination of tachycardia. Results: AVNRT was eliminated in 20 patients by catheter ablation. In five patients (25%; group 1) slow pathway conduction disappeared 1 week after ablation. In six patients (30%; group II), the effective refractory period of the slow pathway was prolonged by more than 50 ms (212 ± 81 ms vs 340 ± 81 ms; P < 0.05). In the remaining nine patients (45%; group III), there was no change in the refractory period (270 ± 65 ms vs 273 ± 74 ms), although tachycardia was not inducible. A shortcut link between the fast and slow pathways was examined by comparing the A-H intervals over the slow pathway during the tachycardia and during atrial pacing at the tachycardia cycle length. Prior to ablation, a shortcut link was assumed in 1 of group I patients, 2 of group II patients, and 8 of group III patients. Of the 9 patients in whom the slow pathway was not impaired after ablation (group III), 8 patients were found to have a shortcut link, while 8 of 11 patients with impairment of the slow pathway after ablation (groups I and II) had no shortcut link between the fast and slow pathways (P < 0.05). Conclusion: In patients with a shortcut link between the fast and slow pathways, slow pathway conduction itself does not need to be impaired to eliminate the AVNRT, whereas in patients without this shortcut link, slow pathway conduction must be impaired.     

Effects of Pharmacological Autonomic Blockade on Dual Atrioventricular Nodal Pathways Physiology in Patients with Slow-Fast Atrioventricular Nodal Reentrant Tachycardia

The purpose of this study was to investigate the atrioventricular AV nodal physiology and the inducibility of AV nodal reentrant tachycardia (AVNRT) under pharmacological autonomic blockade (AB). Seventeen consecutive patients (6 men and 11 women, mean age 39 ± 17 years) with clinical recurrent slow-fast AVNRT received electrophysiological study before and after pharmacological AB with atropine (0.04 mg/kg) and propranolol (0.2 mg/kg). In baseline, all 17 patients could be induced with AVNRT, 5 were isoproterenol-dependent. After pharmacological AB, 12 (71 %) of 17 patients still demonstrated AV nodal duality. AVNRT became noninducible in 7 of 12 nonisoproterenol dependent patients and remained noninducible in all 5 isoproterenol dependent patients. The sinus cycle length (801 ± 105 ms vs 630 ± 80 ms, P < 0.005) and AV blocking cycle length (365 ± 64 ms vs 338 ± 61 ms, P < 0.005) became shorter after AB. The antegrade effective refractory period and functional refractory period of the fast pathway (369 ± 67 ms vs 305 ± 73 ms, P < 0.005; 408 ± 56 ms vs 350 ± 62 ms, P < 0.005) and the slow pathway (271 ± 30 ms vs 258 ± 27 ms, P < 0.01; 344 ± 60 ms vs 295 ± 50 ms, P < 0.005) likewise became significantly shortened. However, the ventriculoatrial blocking cycle length (349 ± 94 ms vs 326 ± 89 ms, NS) and effective refractory period of retrograde fast pathway (228 ± 38 ms vs 240 ± 80 ms, NS) remained unchanged after autonomic blockade. Pharmacological AB unveiling the intrinsic AV nodal physiology could result in the masking of AV nodal duality and the decreased inducibility of clinical AVNRT.     

Relation between the AH interval and the ablation site in patients with atrioventricular nodal reentrant tachycardia

The determinants of slow pathway conduction in patients with AV nodal reentrant tachycardia (AVNRT) are still unknown, and great differences in the AH interval during slow pathway conduction are observed between patients. In 35 patients with typical AVNRT who underwent successful slow pathway ablation (defined as complete elimination of dual pathway physiology), the A2H2 interval at the "jump" during programmed atrial stimulation and the AH interval during AVNRT (as a reflection of slow pathway conduction time) and the fluoroscopic distance between the successful ablation site and the His-bundle recording site and between the coronary sinus ostium (CSO) and the His-bundle recording site were determined. The mean (+/- SEM) AH interval during slow pathway conduction was 323 +/- 12 ms with programmed stimulation and 310 +/- 10 ms during AVNRT. The mean number of energy applications was 8 +/- 1 (range 1-21). The mean distances between (1) the successful ablation site and the His bundle recording site and (2) between the CSO and the His-bundle recording site were 24 +/- 1 and 28 +/- 1 mm in the RAO and 23 +/- 1 and 28 +/- 1 mm in the LAO projections, respectively. The AH interval during slow pathway conduction correlated significantly with the distance between the successful ablation site and the His-bundle (P < 0.001) but not with the distance between CSO and His-bundle recording site. There is a significant correlation between the AH interval during slow pathway conduction and the distance of the successful ablation site from the His bundle. This relationship (1) suggests that, in addition to functional factors, anatomic factors influence slow pathway conduction and (2) may be helpful in determining the initial energy application site during slow pathway ablation.     

Spontaneous Accelerated Junctional Rhythm: An Unusual but Useful Observation Prior to Radiofrequency Catheter Ablation for Atrioventricular Node Reentrant Tachycardia in Young Patients

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2–25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500–750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6–31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.     

Abnormal Atrioventricular Node Conduction and Atrioventricular Nodal Reentrant Tachycardia in Patients Older Versus Younger Than 65 Years of Age

Study Objective: We examined the possible role of atrioventricular node (AVN) conduction abnormalities as a cause of AVN reentrant tachycardia (RT) in patients >65 years of age.
Study Population: Slow pathway radiofrequency catheter ablation (RFCA) was performed in 104 patients. Patients in group 1 (n = 14) were >65 years of age and had AV conduction abnormalities associated with structural heart disease. Patients in group 2 (n = 90) were <65 years of age and had lone AVNRT.
Results: Patients in group 1 versus group 2 (66% vs. 46% men) had a first episode of tachycardia at an older age than in group 2 (68 ± 16.8 vs 32.5 ± 18.8 years, P = 0.007). The history of arrhythmia was shorter in group 1 (5.4 ± 3.8 vs 17.5 ± 14, P = 0.05) and was associated with a higher proportion of patients with underlying heart disease than in group 2 (79% vs 3%, P < 0.001). The electrophysiological measurements were significantly shorter in group 2: atrial-His interval (74 ± 17 vs 144 ± 44 ms, P = 0.005), His-ventricular (HV) interval (41 ± 5 vs 57 ± 7 ms, P = 0.001), Wenckebach cycle length (329 ± 38 vs 436 ± 90 ms, P = 0.001), slow pathway effective refractory period (268 ± 7 vs 344 ± 94 ms, P = 0.005), and tachycardia cycle length (332 ± 53 vs 426 ± 56 ms, P = 0.001). The ventriculoatrial block cycle length was similar in both groups. The immediate procedural success rate was 100% in both groups, and no complication was observed in either group. One patient in group 2 had recurrence of AVNRT. One patient with a 98-ms HV interval underwent permanent VVI pacemaker implantation before RFCA procedure.
Conclusion: In patients undergoing RFCA for AVNRT at >65 years of age had a shorter history of tachycardia-related symptoms than patients with lone AVNRT. The longer AVN conduction intervals and refractory period might explain the late development of AVNRT in group 1.     

Electrophysiological Behavior of Atrioventricular Node After Selective Fast or Slow Pathway Ablation in Patients with Atrioventricular Nodal Reentrant Tachycardia

One hundred twenty consecutive patients with symptomatic atrioventricular nodal reentrant tachycardia (AVNRT) underwent catheter ablation using radiofrequency energy. Fast pathway ablation was attempted in the first 16 consecutive patients by application of radiofrequency current in the anterior and superior aspect of the tricuspid annulus. Successful results were accomplished in 13 patients, complete atrioventricular (AV) block occurred in three. One hundred four patients underwent ablation of the slow pathway in the posterior and inferior aspect of the tricuspid annulus, which was successful in 98 patients. The remaining six patients subsequently underwent a fast pathway ablation with successful results in four and AV block in two. Therefore. 102 (98%) of the last 104 patients became free of AVNRT while maintaining intact AV conduction. This study characterizes the electrophysiological properties of the residual AV node following a selective fast or slow pathway ablation.     

The different ablation effects on atrioventricular nodal reentrant tachycardia in children with and without dual nodal pathways

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSION: 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.     

Pacemapping of the triangle of Koch: a simple method to reduce the risk of atrioventricular block during radiofrequency ablation of atrioventricular node reentrant tachycardia

Slow pathway ablation in common AVNRT can be complicated by total AV block. When radiofrequency energy is delivered to the posterior aspect of the triangle of Koch, total AV block may be the consequence of the absence of anterograde conduction along the fast pathway or of inadvertent damage to a fast pathway abnormally located close to the slow pathway. To localize the anterogradely conducting fast pathway, the triangle of Koch was pacemapped in 72 patients who underwent the ablation of common AVNRT. In all cases, before ablation the St-H interval was calculated by stimulating the anteroseptal (AS), mid-septal (MS), and posteroseptal (PS) aspect of the triangle of Koch at a rate slightly faster than the sinus rate. In all patients, common AVNRT was induced. In 64 (89%) of 72 patients (group A) the shortest St-H interval was recorded on stimulating the AS region. In six (8%) patients (group B) the shortest St-H interval was recorded on stimulating the MS region. Finally, in two (3%) patients (group C) the shortest St-H interval was recorded stimulating in the PS region. In group C, AH interval, calculated on stimulating in the AS region, was significantly longer than in patients of groups A and B (200 +/- 99 ms vs 64 +/- 18 and 62 +/- 3, respectively). In group A, on stimulating in the AS, MS, and PS regions, the AH interval remained constant in all patients. In contrast, in groups B and C on stimulation in the MS and PS regions, AH interval shortened (in group B from 56 +/- 8 to 27 +/- 37 and 37 +/- 14, respectively; in group C from 200 +/- 99 to 170 +/- 100 and to 137 +/- 109, respectively). In groups A and B, a posteroseptal slow pathway, and in group C, an anteroseptal retrograde fast pathway were successfully ablated without AV block. Pacemapping of the triangle of Koch can help to recognize patients in whom the anterograde conducting fast pathway is abnormally located far from the anteroseptal region or in whom anterograde conduction of the fast pathway is absent. In these cases the risk of AV block can be reduced by performing slow pathway ablation in a site sufficiently far from the site of the anterograde fast pathway or ablating the retrogradely conducting fast pathway.     

Single Physician Approach to Radiofrequency Catheter Ahlation in Patients with Supraventricuiar Tachycardia

The minimal requirements for safe and effective performance of catheter ablation using radio/requency current are still unclear. To determine the feasibility and safety of single physician approach to catheter ablation of supraventricuiar tachycardia substrate using radio-frequency energy, the results of the ablation procedure in 52 consecutive patients were evaluated. The procedures were performed during 1 year by the same physician and nurse. Twenty-one patients had selective atrioventricuJar (AV) nodal pathway ablation and 31 patients had accessory AV pathway ablation. Forty-eight patients (89%) had the diagnostic and the ablative procedure during the same electrophysiological test. In the 21 patients with AV nodal reentrant tachycardia, all had successful selective ablation of the fast (13) or the slow (8) pathways. Eight patients had recurrence of the clinical tachycardia and had a successful reablation. No patient developed complete AV block or other significant complications. The mean fluoroscopy time during the procedure was 16.0 ± 8.6 minutes. In the eight patients with Wolff-Parkinson-White syndrome, all concealed accessory pathways were successfully ablated with a mean fluoroscopy time of 30.0 ± 27.9 minutes. Two patients had recurrence of the conduction through the accessory pathway and had a successful reablation. Eighteen of 19 patients with a single overt accessory pathway had successful ablation, with a fluoroscopy time of 22.7 ± 20.6 minutes. Three patients had an early recurrence of the conduction through the accessory pathway, reablation was successful in two of them. Ten accessory pathways were ablated in four patients with multiple pathways during nine procedures. Only two patients developed minor peripheral vascular complications. Radiofrequency ablation of supraventricular tachycardia substrates may be performed effectively and safely by a small team just of one physician and one nurse.     

Modification of antegrade slow pathway is not crucial for successful catheter ablation of common atrioventricular nodal reentrant tachycardia

We tested the hypothesis that in some patients affected by typical AVNRT, successful catheter ablation treatment may be achieved independently of specific measurable electrophysiological modifications of antegrade AV node conducting properties. Standard electrophysiological parameters and comparable antegrade AV node function curves were obtained, before and after successful ablation, in 104 patients (mean age 52 +/- 16 years; 69 women and 35 men) affected by the common form of AVNRT. The end point of the ablation procedure was noninducibility of AVNRT and of no more than one echo beat. For the purpose of this study, AV node duality was defined as an increase of > or = 50 ms in the A2H2 interval in response to a 10 ms decrease of the A1A2 coupling interval. Before ablation, AV node duality was present in 65 patients (62%) and absent in 39 patients (37%). Ablation caused measurable modifications of electrophysiological properties of the AV node in most patients with elicited AV node duality, but not in most patients without demonstrable AV node duality. After ablation, AV node duality persisted in 20 patients who had it before, whereas a new duality that could not be elicited before appeared in 5 patients. During 19 +/- 6 months of follow-up, clinical AVNRT recurred in 1 of 45 patients who had disappearance of AV node duality after ablation, in 1 of 34 patients who did not show AV node duality before and after ablation, and in 1 of 20 patients who had persistence of AV node duality after ablation. In conclusion, modifications of antegrade conduction properties of the AV node are not crucial for the cure of AVNRT in many patients.     

Safety of Slow Pathway Ablation in Patients with Long PR Interval: Further Evidence of Fast and Slow Pathway Interaction

Whether the presence of abnormal PR before selective slow pathway ablation for AV node reentrant tachycardia increased the risk of complete heart block remains controversial. We report our experience in seven patients with prolonged PR intervals undergoing catheter ablation for AV reentry tachycardia. Their mean age was 66 ± 12 years; four patients were female and three were male. RF ablation was performed using an anatomically guided stepwise approach. In six patients, common type AV node reentry was induced and uncommon type was observed in the remaining patient. In all seven patients, successful selective slow pathway ablation was associated with no occurrence of complete heart block and was followed by shortening of the AH interval in five patients. In all seven patients, successful ablation was achieved at anterior sites (M₁ in two patients and M₂ in five patients). Despite AH shortening after ablation, the 1:1 AV conduction was prolonged after elimination of the slow pathway, excluding either sympathetic tone activation or parasympathetic denervation. In conclusion, selective slow pathway ablation can be performed safely in the majority of patients with prolonged PR interval before the procedure. Because successful ablation is achieved at anterior sites in most patients, careful selection and monitoring of catheter position is required.     

Delayed Effects of Radiofrequency Energy on Accessory Atrioventricular Connections

The purpose of this study was to determine the incidence and characteristics of delayed effects on conduction through accessory atrioventricular (AV) connections after apparently successful attempts at radiofrequency catheter ablation. Among 450 patients who had 471 accessory AV connections, the ablation procedure was unsuccessful in 26 patients (6%), as defined by persistent conduction through the accessory AV connection 60 minutes after the final application of radiofrequency energy. In 6/26 unsuccesfully treated patients (24%), conduction through the accessory AV connection disappeared on a delayed basis. At least once during the ablation procedure, conduction through each of these 6 accessory AV connections was transiently eliminated for 10 seconds to 60 minutes. Five of these accessory AV connections were left-sided and one was posteroseptal; one was concealed and five were manifest. Conduction through the accessory AV connection disappeared on a delayed basis 6–18 hours after the ablation procedure in 4 patients, and at some time between 1–5 days or 1–60 days in the other 2 patients. In 2 patients, the delayed effect was only transient, while in 4 patients, conduction through the accessory AV connections did not return during 5–23 months of follow-up. In conclusion, up to 15% of patients who undergo an apparently unsuccessful attempt at radiofrequency ablation of an accessory AV connection may later manifest a permanent loss of conduction through the accessory AV connection.     

Role of Specialized Conducting Fibers in the Genesis of "AV Nodal" Re-entry Tachycardia

Recent reports have suggested that an accessory bypass tract connecting the His bundle to the atrium (His-atrial fiber) may form the retrograde limb of "AV nodal" re-entry tachycardia (AVNRT). We studied 12 patients with AVNRT in whom the presence of an accessory atrioventricular fiber (Kent fiber) was excluded. We investigated the possibility of a His-atrial (H-A) fiber by examining the nature of retrograde conduction and by assessing the necessity of the atrium as a part of the re-entry pathway. Retrograde conduction through the A V node had characteristics similar to retrograde conduction over a Kent bundle; that is, retrograde conduction times were short and did not vary. With echo beats (Ae) evoked during antegrade refractory period determination early premature beats resulted in prolongation of the AH interval with no change in HA_e interval. During AVNRT the A'H':H'A' ratios ranged from 2.0–8.0 (mean 4.0 ± 1.8) and with changes in tachycardia cycle length the H'A interval remained constant. During retrograde refractory period determination, delay occurred below the AV node without change in the H-A interval. Estimations of retrograde conduction times by all 3 methods were not significantly different (p > 0.2). The pattern of retrograde conduction suggests anatomical or functional specialized fibers as the retrograde limb of the tachycardia. The necessity of the atria as a part of the re-entry circuit was assessed by the introduction of atrial premature beats (APBs) in the region of the atrial septum during AVNRT in 10 patients. APBs pre-excited the atria by 40–140 ms without changing the cycle length of the tachycardia, providing strong evidence against the participation of an extranodal His-atrial fiber in AVNRT, In conclusion, retrograde conduction during AVNRT appears to take place over a functional or anatomical specialized fiber within the AV node and not over an extranodal H-A fiber.     

Slow AV Nodal Pathway Ablation Utilizing a Unique Temperature Controlled Radiofrequency Energy System

Thirty-nine consecutive patients with symptomatic AV nodal reentrant tachycardia (AVNRT) underwent temperature guided slow AV nodal pathway ablation (group 1). Forty-three consecutive patients undergoing nontemperature guided slow AV nodal pathway ablation late in our experience compose the control population (group 2). Slow pathway ablation was achieved in all patients of both groups. The mean fluoroscopy and ablation times for group 1 were significantly shorter than for group 2 (26.1 ± 14.9 vs 33.9 ± 18.9 min, P < 0.05; 19.9 ± 12.1 vs 30.9 ± 23.3 min, P ≤ 0.02). There were no episodes of coagulum formation in group 1, while there were 15 episodes (7.1 % of energy applications) in group 2 (P = 0.0006) despite a significantly higher applied power in group 1 (53.4 ± 25.1 vs 35.6 ± 9.5W, P = 0.0001). Successful energy applications were associated with significantly higher temperatures than unsuccessful applications in group 1 (55.6 ± 5.8 C vs. 52.9 ± 6.8 C, P ≤ 0.03). The minimum temperature required for successful ablation was 48 C for two patients (5%) and was > 50 C for the remainder of patients (37/39 [95%]). The catheter ablation system used in this study was safe, effective, and prevented coagulum formation while delivering relatively high power. In addition, shorter ablation times and radiation exposure were seen with this system. Although successful energy applications and the production of junctional rhythm were associated with higher achieved temperatures, temperature alone did not predict either endpoint. Future prospective, randomized trials are needed to confirm these findings and further evaluate the value of temperature monitoring.     

Superior type of atypical AV nodal reentrant tachycardia: incidence, characteristics, and effect of slow pathway ablation

Background: Atypical atrioventricular (AV) nodal reentrant tachycardias (AVNRT) usually exhibit the earliest retrograde atrial activation (ERAA) at the right inferoseptum (Rt-IS) or proximal coronary sinus (PCS). The purpose of this study was to characterize atypical AVNRT with the ERAA at the right superoseptum (Rt-SS).
Methods: Seventy-three atypical AVNRTs induced in 63 cases were classified into the superior type with the ERAA at the Rt-SS and inferior type with the ERAA at the Rt-IS or PCS.
Results: There were nine superior (12%) and 64 inferior types of atypical AVNRT (88%) in seven and 56 cases, respectively. The superior type exhibited a short atrial-His interval during the tachycardia (166 ± 41 ms), long His-atrial interval during the tachycardia (H-At:156 ± 38 ms), and ventricular pacing at the tachycardia cycle length (TCL) (H-Ap:201 ± 36 ms), and evidence for a lower common pathway, including second-degree AV block (four tachycardias) and an H-Ap being longer than the H-At (nine tachycardias). The TCL was shorter in the superior type than in the inferior type (322 ± 35 vs 404 ± 110 ms; P < 0.02). In the inferior type, all tachycardias were eliminated after the ablation at the Rt-IS (44 tachycardias) or PCS (20 tachycardias) where an ERAA was recorded. In the superior type, ablation at the Rt-IS was ineffective; however, ablation at the right midseptum eliminated seven (78%) of the nine tachycardias.
Conclusions: The tachycardia circuit of the superior type might have deviated to a more superior part of Koch's triangle than that of the inferior type.     

Radiofrequency Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia in Children

Radiofrequency (RF) catheter ablation has been widely used in the treatment of cardiac arrhythmias. In atrioventricular nodal reentrant tachycardia (AVNRT), the experience has been predominantly in adults. The cardiac electrophysiological records of 18 consecutive children undergoing RF catheter AV node modification for AVNRT were reviewed. The patients (10 females, 8 males) were 8.2–17.9 years of age (mean 13.6 ± 3.0), weight 15.2–88.1 kg (mean 52.2 ± 20.8), and height 103–190 cm (mean 157.1 ± 21.7). Thirteen were on antiarrhythmic medications (1–3, average 1.5 drugs/day). All drugs were discontinued 48 hours prior to the ablations. The procedures were performed under sedation and local anesthesia. Pre- and post-AV node modification electrophysiological studies were performed in all procedures. The 18 patients underwent a total of 25 procedures (1.39 ± 0.61 per patient): the anterior approach aimed at the antegrade fast pathway in the first four patients and the posterior approach aimed at the slow pathway in the remainder. Thenumber of energy applications was 8–54 (19.8 ± 10.7) per procedure. The maximum energy used in each procedure was 30–50 watts (33.8 ± 8.4). The average energy was 24–50 watts (33.0 ± 6.8). The fluoroscopy time was 7.1–73.4 minutes (29.9 ± 20.0) per procedure, for a total catheterization time of 228–480 minutes (300.3 ± 59.1). Preablation spontaneous or induced AVNRT (cycle length 310.4 ± 55.0 msec) was seen in all except one who had the arrhythmia (cycle length 270 msec) on surface ECG. In 22 of 25 studies, the AH interval measured 67.4 ± 13.2 msec pre- and 98.7 ± 58.4 msec post-AV node modification (P < 0.02). Procedures were initially successful in 16 (89%) of 18 patients. One patient developed complete AV block requiring DDD pacemaker and has since recovered normal AV conduction. Transient third- or second-degree block was seen in four. Other complications included airway obstruction in one and excessive emesis in another. In follow-up of 2–26 months (13.0 ± 7.3), one patient underwent surgical ablation for failed initial RF catheter ablation, and two underwent successful RF procedures for recurrences. RF catheter AV node modification for AVNRT in children is a useful technique. Under ideal circumstances, it is safe and efficacious. Follow-up to determine the potential long-term complications is necessary.     

Fast pathway ablation in a patient with PR prolongation

The classical form of typical atrioventricular node reentrant tachycardia (AVNRT) is a “slow-fast” pathways tachycardia, and the usual therapy is an ablation of the slow pathway since it carries a low risk of atrioventricular (AV) block. In patients with long PR interval and/or living on the anterograde slow pathway, an alternative technique is required. We report a case of a 42-year-old lady with idiopathic restrictive cardiomyopathy, persistent atrial fibrillation status post pulmonary vein isolation, and premature ventricular complex ablation with a systolic dysfunction, who presented with incessant slow narrow complex tachycardia of 110 bpm that appeared to be an AVNRT. Her baseline EKG revealed a first-degree AV block with a PR of 320 ms. EP study showed no evidence of anterograde fast pathway conduction. Given this fact, the decision was to attempt an ablation of the retrograde fast pathway. The fast pathway was mapped during tachycardia to its usual location into the anteroseptal region, then radiofrequency ablation in this location terminated tachycardia. After ablation, she continued to have her usual anterograde conduction through slow pathway and the tachycardia became uninducible. In special populations with prolonged PR interval or poor anterograde fast pathway conduction, fast pathway ablation is the required ablation for typical AVNRT.