Unexpected Complete AV Block Following Transcatheter Ablation of a Left Posteroseptal Accessory Pathway

Radiofrequency catheter ablation is the procedure of choice for the nonpharmacological treatment of AV connections that are responsible for debilitating tachycardia. This article describes a patient with a manifest left posteroseptal accessory pathway and recurrent syncopes in whom a transient complete AV block occurred after transcatheter radiofrequency ablation of the left posteroseptal pathway. Three electrical abnormalities were present in this patient: AV infra-Hisian block, a left posteroseptal accessory pathway, and an AV nodal reentry tachycardia. This case report reminds you that one should be prepared for all fall backs during catheter ablation.     

Radiofrequency Catheter Ablation of Concealed Atrio-His Bypass Tract Involved in Paroxysmal Supraventricular Tachycardia

In a patient with paroxysmal supraventricular tachycardia and without any evidence for preexcitation syndrome or dual atrioventricular (AV) nodal pathways, the tachycardia reentry circuit consisted of the AV node as an antegrade limb of the circuit and a concealed atrio-His bypass tract located in the posterior septum as a retrograde limb. During the tachycardia, the atrial potentials in the septal region and coronary sinus were inscribed in the QRS complex, and the earliest atrial activation site was located in the posterior septum. Ventricular extrastimulation at critically short intervals reproducibly demonstrated a ventriculo-His-atrial activation sequence with the same earliest retrograde atrial activation site as that during the tachycardia. Radiofrequency energy (20 W) was applied to this earliest activation site during ventricular pacing, which resulted in complete ventriculo-atrial block within 2 seconds after energy application. The antegrade AV conduction property was not affected and the tachycardia was no longer induced. The patient has been free from tachycardia attack for a follow-up period of 8 months. Therefore, radiofrequency catheter ablation for an atrio-His bypass tract is feasible without inducing any AV conduction disturbance.     

Radiofrequency Ablation of Pediatric AV Nodal Reentrant Tachycardia during the Ice Age: A Single Center Experience in the Cryoablation Era

Background: Radiofrequency catheter ablation of atrioventricular nodal reentrant tachycardia (AVNRT) has proven to be an effective therapy in the pediatric population. However, concerns of inadvertent permanent AV nodal block have resulted in many pediatric programs adopting cryoablation as their primary ablation approach for AVNRT.
Methods: A retrospective analysis of the results of pediatric radiofrequency catheter ablation at a single institution over the most recent 5 years (January 2004 through December 2008) was performed. Acute, intermediate, and long-term success, along with the incidence of AV block, were determined.
Results: There were 65 patients with a mean age of 12.1 ± 5.2 years and weight of 46.5 ± 17.3 kg who underwent radiofrequency catheter ablation for AVNRT. There was 100% acute success with no recurrences at a mean follow up of 32.5 months. Although two patients had a brief second-degree AV block, there was no permanent AV block of any degree.
Conclusions: The safety and efficacy of radiofrequency catheter ablation for pediatric AVNRT demonstrated in this study support its continued application and should not be abandoned as a method of treatment. (PACE 2010; 6–10)     

Narrow Complex Tachycardia with VA Block: Diagnostic and Therapeutic Implications

To review our experience with cases of narrow complex tachycardia with VA block, highlighting the difficulties in the differential diagnosis, and the therapeutic implications. Prior reports of patients with narrow complex tachycardia with VA block consist of isolated case reports. The differential diagnosis of this disorder includes: automatic junctional tachycardia, AV nodal reentry with final upper common pathway block, concealed nodofascicular (ventricular) pathway, and intra-Hissian reentry. Between June 1994 and January 1996, six patients with narrow complex tachycardia with episodes of ventriculoatrial block were referred for evaluation. All six patients underwent attempted radiofrequency ablation of the putative arrhythmic site. Three of six patients had evidence suggestive of a nodofascicular tract. Intermittent antegrade conduction over a left-sided nodofascicular tract was present in two patients and the diagnosis of a concealed nodofascicular was made in the third patient after ruling out other tachycardia mechanisms. Two patients had automatic junctional tachycardia, and one patient had atroventricular nodal reentry with proximal common pathway block. Attempted ablation in the posterior and mid-septum was unsuccessful in patients with nodofascicular tachycardia. In contrast, those with atrioventricular nodal reentry and automatic junctional tachycardia readily responded to ablation. The presence of a nodofascicular tachycardia should be suspected if: (1) intermittent antegrade preexcitation is recorded, (2) the tachycardia can be initiated with a single atrial premature producing two ventricular complexes, and (3) a single ventricular extrastimulus initiates SVT without a retrograde His deflection. The presence of a nodofascicular pathway is common in patients with narrow complex tachycardia and VA block. Unlike AV nodal reentry and automatic junctional tachycardia, the response to ablation is poor.     

V-A block during atrioventricular nodal reentrant tachycardia: reentry confined to the AV node

Retrograde block during atrioventricular (AV) nodal reentrant tachycardia is considered a rare phenomenon that can potentially occur in the AV node or in the atrium. A patient with slow-fast AV nodal reentrant tachycardia and transient VA block localized in the AV node is presented. Pharmacological and stimulation maneuvers identified the site of block in the AV node and not in the atrium. Thus, AV nodal reentry can be confined to the AV node.     

The Electrocardiographic Manifestation of Combined AV Nodal Wenckebach Periodicity and Reentry

Presented are three patients with Wenckebach type second degree AV block that was complicated with AV nodal reentry producing different arrhythmias. The common presentation of manifest AV nodal reentry is an incomplete Wenckebach periodicity, whereby the retrograde impulse interrupts the Wenckebach cycle; rarely, the retrograde impulse initiates an AV junctional reentrant tachycardia. The documentation of concealed AV nodal reentry is more difficult and should be considered if there is a sudden increase of the PR interval in the Wenckebach cycle.     

Transcoronary Ethanol Ablation of the Atrioventricular Node in a Young Patient with Tricuspid Atresia

Catheter ablation of AV conduction with radiofrequency energy can be challenging in the presence of structural abnormalities of the AV junction, either congenitally or after reconstructive surgery. We used transcoronary ethanol to ablate the AV node in a patient with classic tricuspid atresia and refractory intraatrial reentry tachycardia. This approach provides an alternative means of creating complete heart block with catheter-based techniques, when radiofrequency catheter ablation is technically impossible or ineffective.     

Anatomical perspective on radiofrequency ablation of AV nodal reentry tachycardia after mustard correction for transposition of the great arteries

A case of radiofrequency catheter ablation of atrioventricular (AV) nodal reentry tachycardia, in a patient with transposition of the great arteries after venous rerouting according to Mustard, is described. An electroanatomical map of the His and AV nodal region was created from inside the systemic venous atrium. Retrograde mapping of the pulmonary venous atrium was performed and the arterial catheter retracted to a position in close proximity to the venous catheter inside the intraatrial baffle. This position was chosen to deliver radiofrequency current.     

Reentrant Junctional Tachycardias

AKHTAR, M.: Reentrant Junctional Tachycardias. Most of the tachycardia arising in the atrioventricular (AV) junction are reentrant in nature. The two most common variety are AV nodal reentry and AV reentry utilizing an accessory pathway of the Kent bundle type. Typically these tachycardias have narrow QRS complex and are regular but an associated right or left bundle branch block could result in a wide QRS complex. Other mechanisms for wide QRS in AV junctional tachycardia include: (a) antidromic reentry; (b) preexcited tachycardia using two accessory pathways; (c) AV nodal reentry with incidental accessory pathway participation; and (d) atriofascicular (nodoventricular) Mahaim participation. A variety of surface ECG and intracardiac electrophysiological methods are used to delineate the precise mechanisms which is essential for successful nonpharmacological therapy in these patients.     

Dual AV Nodal Pathway Physiology After Injury with Radiofrequency Energy in a Patient Without a History of Reentrant Tachycardia

PATRAWALA, R.A., et al. : Dual AV Nodal Pathway Physiology After Injury with Radiofrequency Energy in a Patient Without a History of Reentrant Tachycardia. Radiofrequency (RF) atrioventricular (AV) nodal modification has been reported to occasionally produce a proarrhythmic effect. Dual AV nodal pathway physiology in patients without reentrant tachychardia has also been reported. This case describes AV nodal modification with RF energy in an anatomically intermediate area resulting in the appearance of discontinuous antegrade conduction curves and reentry in a patient in which these were previously not present. This suggests that AV nodal injury may be a mechanism for acquired AV nodal reentry.     

Radiofrequency Catheter Ablation for AV Nodal Reentry: A Technique for Rapid Transection of the Slow AV Nodal Pathway

Selective radiofrequency (RF) catheter ablation of the slow AV nodal puthway has shed new light on the anatomy and physiology of the atrioventricular junction. The recording of “slow pathway potentials” facilitates localization of the slow pathway and has led to a concept of multiple pathway components with atrial insertion sites covering a potentially broad region surrounding the coronary sinus os. The critical area for complete interruption of the slow pathway may be larger than lesion size produced by ablation at a single site, resulting in multiple RF applications with lengthy sessions and prolonged radiation exposure. Information from both old and recent literature suggests that the slow AV nodal pathway is represented by a group of fibers originating from the posteroinferior interatrial septum and coursing anterosuperiorly near the tricuspid annulus before converging upon the compact AV node. Based on this anatomical arrangement, the present study was conducted to evaluate a technique designed to transect the slow pathway by producing a linear RF lesion perpendicular to the orientation of the slow pathway within the mid-portion of Koch's triangle. Using this technique, 30 of 30 patients with common AV nodal reentry ivere rendered noninducible using 1 to 3 RF applications. Total procedure time averaged 3.4 ± 1.1 hours and fluoroscopy time averaged 14.8 ± 4.6 minutes. As a marker of efficacy, episodic nonsustained atrial tachycardia (NSAT) during RF delivery occurred in 28 of 30 (93%) successful applications. Three patients experienced tachycardia recurrence and were successfully ablated by repeat procedure. Conduction characteristics and refractoriness of the fast pathway were unchanged in 23 of 23 patients reevaluated at a mean of 7.2 weeks postablation. Two of 30 (6%) patients experienced procedure related complications but there were no instances of AV block. We conclude that the technique of producing a linear lesion by continuous migratory RF application in the manner described safely and effectively eliminates AV nodal reentry, simplifies the procedure, and minimizes radiation exposure to the patient and the physician.     

Dissociation of Atrioventricular Conduction and Refractoriness Following Application of Radiofrequency Energy to the Canine Atrioventricular Node: Acute and Chronic Observations

The electrophysiology of AV nodal modification induced by radiofrequency energy (n = 5) or a sham procedure (n = 5) was studied in ten dogs. The five dogs that received radiofrequency energy had an AH prolongation > 100% from baseline values and this prolongation persisted throughout the 2-month study. The AV nodal functional refractory period was prolonged only acutely. These data indicate a dissociation between the effects on AV nodal conduction and refractoriness that was induced by this procedure. The five sham treated controls showed no acute or chronic electrophysiological changes. In the dogs that received radiofrequency energy, there was fibrosis of the approaches to the AV node and the region of the A V node itself. It is concluded that chronic modification of AV nodal conduction without concomitant changes in refractoriness can be induced by radiofrequency energy delivered in the proximal portion of the AV node. It would be anticipated that this procedure would not decrease the ventricular response to atrial fibrillation or flutter, but may be effective in preventing AV nodal reentrant tachycardia by interfering with conduction either in the AV node or perinodal region. Since the AV node itself suffers at least moderate pathological damage, there may be an appreciable incidence of the late development of complete heart block after this procedure.     

Atrioventricular Electrotonic Interaction in Complete Atrioventricular Block: An Experimental Model Using Radiofrequency Energy in the Rabbit Heart

Provided the conditions for electrotonic transmission exist, an automatic focus surrounded by a block zone may be externally modulated. The atrioventricular (AV) electrotonic interaction was studied in 16 perfused rabbit hearts with supra-Hisian complete AV block induced using low radiofrequency energy doses (2.5 watts; 10 seconds). In nine experiments the sinus node was preserved (group I), whereas in seven it was removed maintaining an AV nodal rhythm (group II). The V-V (ventricular cycle length) and V-A (coupling of the intervening atrial beat) in both groups, and also the A-A (atrial cycle length) and A-V (coupling of the intervening ventricular beat) intervals in group II, were measured beat by beat after current delivery. The phase response curves V-V versus V-A, and A-A versus A-V showed AV interaction in five experiments from group I, and in four from group II, as follows: (1) accelerating phase response curve, characterized by a pacemaker acceleration (V-V or A-A abbreviation) at a critical V-A or A-V coupling interval; maximum acceleration could be progressively (phase response curve without rapid cross-over) or briskly (phase response curve with rapid crossover) reached; from this point onwards acceleration decreased with a further increase in V-A or A-V coupling interval (acceleration slope). (2) Biphasic phase response curve, characterized by initial delaying and late accelerating phases. Maximum acceleration and the acceleration slope were both smaller in accelerating phase response curves without rapid cross-over. On reverting complete block in two experiments, a progressive increase in maximum acceleration and acceleration slope was observed. Conclusions: (1) AV interaction in complete AV block can be manifested as accelerating or biphasic phase response curves; (2) transition from electrotonic interaction to conduction seems to be a continuum.     

Controlled Cryothermal Injury to the AV Node: Feasibility for AV Nodal Modification

Elective subtotal injury to the AV node-His bundle region may create a negative dromotropic effect to provide a therapeutic advantage in some patients with supraventricular tachycardia without creating complete AV block. We examined the effects of cryosurgery to the AV nodal region, varying temperature and time using a 15 mm circular cryoprobe applied directly to the canine AV node-His bundle region. Twelve dogs were anesthetized and the heart was exposed through a right thoracotomy. Electrophysiological data obtained included conduction intervals, incremental pacing, and extrastimulus testing. Under inflow occlusion, the cryoprobe was positioned over the AV node-His bundle region using anatomical landmarks and a single freeze was applied (-15 degrees C to -60 degrees C, 15 to 60 seconds). Dogs were allowed to recover for 1 month, after which time electrophysiological testing was repeated under similar conditions; then the animals were sacrificed. With probe temperatures of -60 degrees C for 15 to 60 seconds, five of six dogs experienced complete heart block with dense fibrosis observed in the AV nodal-His bundle region. After freezing with higher temperatures, the remaining seven dogs had return of atrioventricular conduction postoperatively with prolongation of AH time observed in five and marked prolongation of the Wenckebach cycle length in three of the five. We conclude that controlled cryothermal injury to the AV node-His bundle region may be useful to create a desirable negative dromotropic response without creating complete AV block.     

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.     

Specificity of Retrograde Conduction in Screening for Atrioventricular Nodal Reentrant Tachycardia

Baseline AV conduction properties (antegrade and retrograde) are often used to assess the presence of dual AV nodal physiology or concealed AV accessory pathways. Although retrograde conduction (RET) is assumed to be a prerequisite for AV nodal reentrant tachycardia (AVNRT), its prevalence during baseline measurements has not been evaluated. We reviewed all cases of AVNRT referred for radiofrequency ablation to determine the prevalence of RET at baseline evaluation and after isoproterenol infusion. Results: Seventy-three patients with AVNRT underwent full electrophysiological evaluation. Sixty-six patients had manifest RET and inducible AVNRT during baseline atrial and ventricular stimulation. Seven patients initially demonstrated complete RET block despite antegrade evidence of dual AV nodal physiology. In 3 of these 7 patients AVNRT was inducible at baseline despite the absence of RET. In the other four patients isoproterenol infusion was required for induction of AVNRT, however only 3 of these 4 patients developed RET. One of these remaining patients had persistent VA block after isoproterenol. Conclusions: The induction of AVNRT in the absence of RET suggests that this is not an obligatory feature of this arrhythmia. Therefore, baseline AV conduction properties are unreliable in assessing the presence of AVNRT and isoproterenol infusions should be used routinely to expose RET and reentrant tachycardia.     

Histopathological Study Following Catheter Guided Radiofrequency Current Ablation of the Slow Pathway in a Patient with Atrioventricular Nodal Reentrant Tachycardia

The present study examined histological changes induced by catheter guided radiofrequency current in a patient with AV nodal reentrant tachycardia who underwent cardiac transplantation 1 week after ablation of the slow pathway. During the electrophysiology study AV nodal conduction curves were discontinuous and AV nodal reentry was induced. At the conclusion of the procedure there was no evidence of slow pathway function. Histological sections from the explanted heart demonstrated a sharply demarcated atrial lesion (5 × 5 × 4 mm) extending from the septal portion of the tricuspid annulus to the posterior border of the AV node. The lesion did not encompass the compact AV node. These observations support the hypothesis that the slow pathway is comprised of atrial approaches to the AV node and is distinct from the compact AV node.     

Successful Slow Pathway Ablation in a Patient with Atrioventricular Nodal Reentrant Tachycardia Having a Proximal Common Pathway

Radiofrequency catheter ablation was attempted in a patient with atrioventricular nodal reentrant tachycardia (AVNRT). AVNRT was easily inducible but an intermittent loss of the atrial activation was observed during AVNRT suggesting the presence of a proximal common pathway. During sinus rhythm, a relatively delayed activation that was compatible with a slow potential, was recorded anterior to the ostium of coronary sinus, and radiofrequency catheter ablation application (20 watts) to the site induced junction tachycardia. After an additional radiofrequency catheter ablation application to close the site, AVNRT became noninducible without deterioration of atrioventricular conduction through a fast pathway. This is the first case in which radiofrequency catheter ablation application to the slow potential recording site has been successful, even in AVNRT having a proximal common pathway.     

A Wide QRS Complex Tachycardia with Different Initiation Patterns: What is the Mechanism?

A 47-year-old man with palpitations underwent electrophysiologic testing (EPS). Burst atrial pacing while infusing isoproterenol induced non-reproducible wide QRS tachycardias with an unusual pattern of an H-A-V activation with the same tachycardia cycle length and two different initiation patterns. The tachycardia had the earliest atrial activation at the His bundle region. No dual atrioventricular (AV) nodal physiology was demonstrated by programmed atrial stimulation. Though a definite diagnosis of AV nodal reentrant tachycardia was not obtained, slow pathway ablation was performed in order to avoid inadvertent AV block as a complication. Thereafter, no tachycardias were induced by repeat burst atrial pacing.     

Electrophysiological characteristics of junctional rhythm during ablation of the slow pathway in different types of atrioventricular nodal reentrant tachycardia

BACKGROUND: Junctional rhythm (JR) is commonly observed during radiofrequency (RF) ablation of the slow pathway for atrioventricular (AV) nodal reentrant tachycardia. However, the atrial activation pattern and conduction time from the His-bundle region to the atria recorded during JR in different types of AV nodal reentrant tachycardia have not been fully defined. METHODS: Forty-five patients who underwent RF ablation of the slow pathway for AV nodal reentrant tachycardia were included; 27 patients with slow-fast, 11 patients with slow-intermediate, and 7 patients with fast-slow AV nodal reentrant tachycardia. The atrial activation pattern and HA interval (from the His-bundle potential to the atrial recording of the high right atrial catheter) during AV nodal reentrant tachycardia (HA(SVT)) and JR (HA(JR)) were analyzed. RESULTS: In all patients with slow-fast AV nodal reentrant tachycardia, the atrial activation sequence recorded during JR was similar to that of the retrograde fast pathway, and transient retrograde conduction block during JR was found in 1 (4%) patient. The HA(JR) was significantly shorter than the HA(SVT) (57 +/- 24 vs 68 +/- 21 ms, P < 0.01). In patients with slow-intermediate AV nodal reentrant tachycardia, the atrial activation sequence of the JR was similar to that of the retrograde fast pathway in 5 (45%), and to that of the retrograde intermediate pathway in 6 (55%) patients. Transient retrograde conduction block during JR was noted in 1 (9%) patient. The HA(JR) was also significantly shorter than the HA(SVT) (145 +/- 27 vs 168 +/- 29 ms, P = 0.014). In patients with fast-slow AV nodal reentrant tachycardia, retrograde conduction with block during JR was noted in 7 (100%) patients. The incidence of retrograde conduction block during JR was higher in fast-slow AV nodal reentrant tachycardia than slow-fast (7/7 vs 1/11, P < 0.01) and slow-intermediate AV nodal reentrant tachycardia (7/7 vs 1/27, P < 0.01). CONCLUSIONS: In patients with slow-fast and slow-intermediate AV nodal reentrant tachycardia, the JR during ablation of the slow pathway conducted to the atria through the fast or intermediate pathway. In patients with fast-slow AV nodal reentrant tachycardia, there was no retrograde conduction during JR. These findings suggested there were different characteristics of the JR during slow-pathway ablation of different types of AV nodal reentrant tachycardia.