© 2004 by European Society of Cardiology
REVIEW
Paraseptal accessory connections in the proximity of the atrioventricular node and the His bundle. Additional observations in relation to the ablation technique in a high risk area
University Cardiac Department, Hippokration General Hospital Athens, Greece
Manuscript submitted 21 January 2003. Accepted after revision 1 October 2003.
*Corresponding author. Fragogianni 34, Papagos 156 69, Athens, Greece. Tel.: +30-1-6513158; fax: +30-1-7784590. E-mail address: kgatzoulis{at}med.uoa.gr
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Abstract |
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INTRODUCTION: Paraseptal pathways, namely, accessory connections (AC) in the vicinity of the atrioventricular node (AVN) and the bundle of His, are associated with a high risk of complete atrioventricular block (AVB) during transcatheter radiofrequency ablation (RFA) in the Electrophysiology Laboratory. In previously reported series of ablation of paraseptal ACs, the coexistence of multiple ACs in this high-risk region has rarely been mentioned.
METHODS AND RESULTS: We studied 15 patients undergoing RFA of paraseptal ACs 2 of whom had dual pathways with an additional midseptal pathway revealed after the elimination of the anteroseptal target AC. The fundamental goal of the pre-ablation electrophysiological mapping was the clear-cut determination of anatomical site with His bundle recording activity. This required unique pharmacological and programmed electrical stimulation manipulations in 8 patients in whom His bundle recording activity was only temporarily possible. After identifying the corresponding His bundle site, special attention was given to the ablation catheter being situated at least 3 mm away, thus recording minimal or no His bundle activity. Additional precautions were taken so that the delivered therapy was of minimal duration and powered by temperature regulation with immediate interruption in case of AVB or nodal rhythm appearance. With this therapeutic approach, 16 of the 17 paraseptal ACs were ablated successfully with the inadvertent induction of AVB in only 1 patient. In the patient with persistent ventricular preexcitation after the ablation session, modification of both the AC and the AVN was noted so that the previously easily induced reciprocating atrioventricular tachycardia was no longer so, using programmed stimulation.
CONCLUSION: Transcatheter radiofrequency ablation is a feasible and effective radical therapy for patients with paraseptal ACs, provided the His bundle site has first been clearly defined and the coexistence of other nearby tracts has been excluded.
Key Words: paraseptal pathways, transcatheter radiofrequency ablation, ventricular preexcitation
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Introduction |
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Paraseptal accessory connections (AC) are located close to the atrioventricular node and the His bundle. These ACs are associated with the risk of inducing complete atrioventricular block (AVB) during surgical or transcatheter radiofrequency ablation [1
–3]. This latest therapeutic approach has been established as the treatment of choice for symptomatic patients with the Wolff–Parkinson–White syndrome offering, uniquely in Interventional Cardiology, an opportunity for a radical cure [4,5]. However, the probability of inducing AVB, which could result in a lifelong pacemaker-dependent patient, renders these ACs of "high risk" during radiofrequency catheter ablation in the Electrophysiology Laboratory. Thus, it is not uncommon to postpone the scheduled ablation session when the invasive electrophysiological mapping discloses an AC in the proximity of the atrioventricular junction. Nevertheless, not uncommonly, we do encounter patients with drug refractory recurrent supraventricular tachycardias or with a very short antegrade effective refractory period of the AC, at risk for fast preexcited atrial fibrillation, who are definite candidates for nonpharmacological radical therapy. Unlike other atrioventricular ring sites that may harbour more than a single AC as a result of multiple developmental atrioventricular node remnants, the paraseptal region has rarely been mentioned as an area where more than one AC may be found. In this paper, we present the clinical and electrophysiological characteristics of 15 patients with 17 paraseptal ACs who underwent transcatheter radiofrequency ablation in the Electrophysiology Laboratory of our hospital. Particular attention is given to the precautions taken during the ablative procedure to avoid the induction of complete AVB, while the unexpected coexistence of anteroseptal and midseptal pathways in 2 of our 15 patients is further discussed.
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Material and methods |
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Patients
Over the last 7 years, 15 patients with 17 ACs localized close to the His bundle, namely, anteroseptal or midseptal pathways, underwent radiofrequency catheter ablation in the Electrophysiology Laboratory of our hospital. The patients' clinical characteristics are presented in Table 1. Fourteen patients presented with recurrent episodes of either narrow (n=14) and/or wide (n=1) QRS complex reciprocating atrioventricular tachycardia, while in 2 patients, episodes of rapid preexcited atrial fibrillation were also documented. In a middle-aged patient, arterial hypertension and one vessel coronary artery disease with well-preserved left ventricular function was concurrently present. In 2 patients, after the ablation of an anteroseptal pathway, a second manifest midseptal pathway between the His bundle and the coronary sinus os was found. Thirteen of the 17 ACs were manifest with ventricular preexcitation while in 4 patients the pathways were concealed and were revealed during the baseline electrophysiological study (EPS).
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Electrophysiological study
This was performed after informed written consent was obtained and while any previously given antiarrhythmic drugs were discontinued for at least 4 drug half-lives. The probability of inducing complete AVB with the need for permanent dual chamber pacing was seriously discussed and only when the patient and the family accepted the associated risk, the ablation procedure followed during the same session. Under local anaesthesia, 3 transvenous introducers were placed in the right and/or the left femoral vein, with an additional introducer placed in the left subclavian vein in 12 patients, including the 4 patients with concealed ACs. Usually, 3 quadripolar electrode catheters were advanced through the femoral vein into the right heart and placed in the high right atrium, the tricuspid ring to record the His bundle activation and in the right ventricular apex. A multipolar, most commonly an octapolar orthogonal catheter, was advanced through the left subclavian or the femoral vein into the coronary sinus in 12 patients. Programmed atrial and ventricular stimulation according to a standard protocol was applied in all cases through a programmed stimulator (Medtronic SP 05034 or Biotronik-Era-S-His) in order to determine the anatomical and functional properties of the AC. Mapping of the area surrounding the His bundle was performed using gentle movements of the mapping catheter after the His bundle recording site was identified and marked in right and left oblique fluoroscopic views. In case such activity could not be identified, due to coexisting preexcitation during sinus rhythm, a further attempt to record His bundle activity followed using programmed atrial stimulation or the intravenous administration of ajmaline (Fig. 1). If these attempts failed, His bundle activity was sought after induction of orthodromic atrioventricular tachycardia. The EP mapping was completed during ventricular pacing or after induction of reciprocating atrioventricular tachycardia in the concealed ACs as well as during sinus rhythm or atrial pacing in the manifest pathways.
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Ablation technique
After the AC site was identified in the anteroseptal or the midseptal space, the high right atrial recording catheter was replaced by a steerable quadripolar ablation catheter (Cordis Webster Inc.) advanced to the identified AC site in close proximity to the His bundle recording catheter. A new mapping attempt followed with minimal movements of the steerable ablation catheter around the distal pole of the His bundle recording catheter. Special attention was given to the His bundle recording catheter in order to keep it in a stable position during the movements of the ablation catheter around it. The selection of the target site was based on the presence of either continuous atrioventricular activity during sinus rhythm or closely coupled local ventriculoatrial activity (VA interval
30 ms) during orthodromic atrioventricular tachycardia or ventricular pacing (Fig. 1). Care was taken that the target site be at least 3 mm away from the His bundle recording site (Fig. 2). The RFA was considered successful at the selected target site when preexcitation was abolished within 10 s or when retrograde conduction was blocked in the concealed pathway during ventricular pacing or orthodromic atrioventricular tachycardia. In case of an unsuccessful transvenous ablation approach, a retrograde transaortic approach seeking a probable superficial course of the ventricular aspect of the pathway on the left side of the intraventricular septum completed the intervention session.
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The radiofrequency energy was delivered from an RF device (Osypka HAT 200 or 300) between the distal pole of the ablation catheter and a large skin patch electrode on the left posterior thoracic wall. The delivered power was set between 15 and 20 W in temperature modulated mode at 70 °C (T-mode, 70 °C). Continuous attention was given to the earliest recognition of developing atrioventricular block or accelerated nodal rhythm during energy delivery. In case of a successful result within 10 s, the RF energy application was continued to a total of 30–60 s depending on the proximity of the His bundle and following the above-mentioned precautions.
After the intracardiac catheter placement and before the application of the electrical therapy, intravenous heparin at a loading dose of 10,000 units followed by a maintenance dose of 1000 units/h was administered in the majority of the procedures.
After a successful ablation result, the patient remained in the EP Laboratory for half an hour when the EP study, including measurements of intracardiac intervals, was repeated.
With all procedures, the possible need for dual chamber pacemaker placement was monitored in case of induced irreversible complete AVB before the patient left the EP Laboratory. The patient was discharged home the 2nd or 3rd postinterventional day after repeat echocardiograms and electrocardiograms were obtained. Long-term follow-up included visits at 15 days and every 6 months thereafter.
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Results |
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Baseline electrophysiological study (EPS)
Orthodromic atrioventricular tachycardia (AVRT) at a mean CL of 290±40 ms was induced in 13 patients. In 1 patient, episodes of antidromic AVRT at 240 bpm were also induced. Aberrantly conducted AVRT was observed in 3 patients (2 with right and 1 with left bundle branch block). Fast preexcited atrial fibrillation was induced in 2 patients (Fig. 3). The mean antegrade effective refractory period of the manifest ACs was 260±50 ms. During the baseline EPS, His bundle activity recording was not possible with sinus rhythm in 8 patients. The His bundle site was identified in all 8 patients after programmed atrial stimulation, intravenous ajmaline administration or the induction of orthodromic AVRT (Figs. 1 and 4).
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Ablation results
Sixteen of the 17 ACs were successfully ablated in the area surrounding the His bundle. Ten were ablated in front of the distal pole of the His bundle recording catheter (anteroseptal). The other 7 ACs were localized in a midseptal site inferior and posterior to the His bundle site between this and the coronary sinus os. In a young male patient, despite the application of 22 therapies in a midseptal pathway from both sides of the interventricular septum, using a retrograde transaortic approach, permanent elimination of the ventricular preexcitation was not achieved. In this patient, before the ablation and during the baseline EPS, multiple episodes of both orthodromic and antidromic AVRT were easily induced. After the attempted ablation and despite the persistence of ventricular preexcitation, the reciprocating tachycardia was no longer induced even after intravenous isoprenaline provocation while the antegrade bypass tract ERP was significantly prolonged from 220 to 270 ms. It should also be noticed that a significant modification of the atrioventricular node was also observed with prolongation of its ERP and the earlier appearance of Weckenbach and 2:1 AV block on atrial stimulation. Taking into account the inability to reinduce AVRT along with the modification of the atrioventricular node, we decided to avoid the risk of AVB with further therapies. In another young male patient, after the ablation of an anteroseptal pathway, a second manifest pathway was revealed on the 12 lead ECG (Fig. 5). The ensuing electrophysiological mapping localized this pathway in the midseptal area, approximately 2.5 cm inferior and posterior to the initially ablated anteroseptal tract (Fig. 6). Two additional lesions in this area normalized the ECG in this patient. Similar coexistence of an anteroseptal with a midseptal pathway was encountered in another middle-aged male patient. After ablating an anteroseptal pathway with a long antegrade ERP, an intermittent delta wave pattern appeared. Subsequent EP mapping localized this second pathway in front and medial to the coronary sinus os. Two more RFA applications were also required to eliminate this pathway. First-degree AV block with an unchanged HV interval of 40 ms and no evidence of infra-nodal block was present after the ablation of the dual paraseptal pathways in this patient. Thus, all except one of the paraseptal pathways we encountered were successfully ablated via a transvenous approach. Complete nonreversible AVB with a wide QRS complex escape rhythm at 55 bpm was induced during ablation of an anteroseptal tract in a young female patient. A dual chamber pacemaker was implanted during the same session. Temporary nodal rhythm after the ablation of a midseptal pathway was also observed in another young female patient.
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Procedure data
The mean number of the required RF therapies to achieve the desired result was 7.1±3.2 (1–22) with a mean procedural duration of 105±50 (30–440) min and fluoroscopy of 30±10 (5–100) min. No patient required a repeat session for reappearance of the bypass tract.
Long-term follow-up
During a mean follow-up period of 3.6±4 years (6 months to 7 years), all patients remained asymptomatic without antiarrhythmic medication. However, early recurrence of the ventricular preexcitation was confirmed in the young patient with the 2 paraseptal pathways, after the 15 day visit. This patient has remained asymptomatic for the subsequent 8 months and with mutual agreement, we decided to repeat the ablation session only in case of recurrence of tachycardia. It is noteworthy that the other patient also remains asymptomatic, after the modification of the midseptal pathway and the atrioventricular node, despite the persistence of the ventricular preexcitation. Both of these patients presented with multiple, drug refractory tachycardia episodes. The paced patient returned with normal atrioventricular conduction after 6 months when a repeat EP study demonstrated no pathway activity recurrence. Based on her own desire and after confirming the integrity of infra-nodal conduction, the pacemaker was explanted.
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Discussion |
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In our series of 15 patients with the 17 paraseptal pathways in Koch's triangle in close proximity to the atrioventricular node and the His bundle, we had a highly successful transvenous radiofrequency catheter ablation result with the inadvertent induction of complete AVB in one young female patient. In the patient in whom permanent block of the midseptal pathway was not possible, a favourable modification of the AC was achieved as shown by the repeat EPS and the long-term outcome. Thus, it is evident that RFA application is an effective and radical treatment modality even for patients with "high risk" pathways close to the atrioventricular junction. Because of their location, the approach to these ACs requires particular attention and experience in order to avoid the induction of complete AVB during transcatheter radiofrequency energy delivery [2,
3,6]. Difficulties in this approach with the frequent induction of complete AVB are known since the era of surgical management of the Wolff–Parkinson–White syndrome [1]. As in our series, highly successful ablation results of such pathways, ranging from 71 to 100%, have been published over the last 9 years from large volume EP centre [3–10]. The corresponding proportion of patients developing AVB during transvenous catheter RFA of these fibres ranged from 0 to 36% [3–9,11]. It appears that the methodology of approaching these difficult atrioventricular pathways is crucial in order to achieve success with acceptable complication rates. In our patients, particular attention was initially given to the clear-cut site determination of His bundle activity. This was not possible during sinus rhythm in 8 patients with manifest paraseptal pathways because of the coexistence of continuous atrioventricular electrogram activity in all assessed sites. It has been reported and proposed as a criterion for the existence of a paraHisian pathway, the concurrent presence of His bundle activity with that of the accessory connection [7–9]. Unfortunately, questions are frequently raised when such electrical activity is found, due to the presence of continuous atrioventricular activity (Fig. 1). In order initially to record discrete His bundle activity, we employed a number of pharmacological and programmed stimulation manipulations during sinus rhythm aiming at temporary loss of preexcitation (Fig. 1). In case of failure or when a concealed paraseptal pathway was encountered, the His bundle site was unmasked by induction of orthodromic AVRT. Care was taken that the target site be at least 3 mm away from the dipole of the His bundle recording catheter with the ablation catheter recording minimal or no His bundle activity (Figs. 2,4, and 5). Furthermore, the RF energy was delivered gradually starting from a low power setting, at 15 W, in order to achieve the smallest possible lesion. Even lower power settings have been proposed to obtain safely the desired result [6]. Whether other modes of energy delivery, such as cryoablation, may be better and safer for destroying paraseptal pathways has not so far been explored. It is remarkable that these pathways are frequently destroyed with minimal RF energy and not uncommonly their activity is temporarily interrupted during catheter manipulation because of their superficial subendocardial course [9]. In contrast, the bundle of His is a structure more deeply situated, surrounded by the central fibrous body, thus requiring higher RF energy power settings for ablation [12]. Such observations most likely explain the unexpectedly low incidence of complete AV block induction despite the high ablation success rate for septal pathways in most published series. However, the possibility of inducing AVB even at AV nodal sites without recording His bundle activity should always be kept in mind especially when delivering the RF energy during ventricular pacing with concurrent retrograde conduction through a concealed paraseptal pathway. As in one of our patients, preexcitation recurrence is usually observed early, during the first 2 months, and frequently during the first few hours or the day after the successful ablation session [11]. The paraseptal AC site together with a prolonged time interval from the energy delivery onset to the interruption of the pathway are variables correlating with recurrences [13].
The 12 lead electrocardiographic characteristics of paraseptal pathways have been studied in patients undergoing surgical or transcatheter ablation [2,3,8,12,14–17]. In contrast to ACs of the left ventricular free wall or the posteroseptal space, the proposed algorithms have a lower predictive value for correctly identifying the site of the paraseptal pathway. An overlap between their ECG appearance has been found in anteroseptal and midseptal pathways with even those localized in the right ventricular free wall [12]. Furthermore, the terminology referring to paraseptal pathways is somewhat confusing. Paraseptal pathways in close proximity to the compact atrioventricular node (paranodal) or to the His bundle (paraHisian) have been termed intermediate septal accessory pathways [1–3]. Their electrocardiographic appearance is frequently similar to those termed anteroseptal or midseptal pathways and not uncommonly all these ACs are included in one group, the so-called septal pathways within the Koch's triangle [6]. In our patients' series, we surprisingly encountered 2 patients with the coexistence of an anteroseptal and a midseptal pathway. The unusual 12 lead ECG picture in the first patient (Fig. 6) was probably due to a fused preexcited pattern from two closely localized but different septal atrioventricular pathways (Fig. 7). In the second patient, after the ablation of the presenting anteroseptal pathway, a preexcitation pattern consistent with either a right posteroseptal or a midseptal tract was intermittently present. The second pathway was also successfully ablated in the lower midseptal region. Both pathways had long antegrade ERPs with intermittent preexcitation patterns not giving a fused preexcitation morphology like in the previous patient. Similar cases of coexistence of different paraseptal pathways have been previously mentioned [9,10]. An unusual feature is also the presentation of antidromic AVRT through a manifest septal pathway as was observed in one of our patients [18].
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Approaching paraseptal pathways through the superior vena cava has been previously proposed [12]
. In our experience, all successfully ablated paraseptal pathways were approached through the femoral vein. It is likely that the femoral venous approach is effective and reduces the total procedure time. We conclude that the majority of paraseptal pathways can be successfully ablated through the transvenous radiofrequency catheter approach in the Electrophysiology Laboratory. Complete AVB induction can be avoided in the majority of the cases after applying a strict protocol of low power electrical therapies in sites of even minimal distance from the His bundle recording site. This requires not only precise localization of the AC but also of the His bundle recording site together with a number of pharmacological or/and programmed electrical stimulation manoeuvres. Although not being previously highly recognised, dual paraseptal pathways may occasionally be encountered in the same patient, giving rise to unique electrocardiographic patterns or early recurrences after a successful ablation session.
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References |
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