Catheter ablation of right ventricular outflow tract tachycardia: a simplified remote-controlled approach

Abstract

Aims

Manual mapping and ablation of right ventricular outflow tract (RVOT) tachycardia may be associated with cardiac perforation and complicated by mechanically induced ventricular extrasystoles (VESs). The aim of this study was to assess remote-controlled magnetic (RCM) mapping and ablation of RVOT ventricular tachycardia (VT)/VES utilizing a soft magnetic catheter.

Methods and results

Mapping and ablation of RVOT VT/VES were performed using the magnetic navigation system (MNS, Niobe II, Stereotaxis, St Louis, MO) in conjunction with a cardiodrive motor unit (Stereotaxis). A soft magnetic catheter (Celsius RMT, 4 mm solid tip, Biosense Webster, Diamond Bar, CA) was navigated to the RVOT using a sequence of pre-installed magnetic vectors. The primary endpoint was defined as successful RCM VT/VES ablation. Other parameters observed included RCM RVOT accessibility, mapping-induced mechanical VES, fluoroscopy time, complications, and arrhythmia recurrence. Thirteen consecutive patients (mean age: 50 ± 14 years; 10 females, 6 RVOT VT) underwent RCM mapping and ablation. The RVOT was reached in all patients utilizing solely the MNS. Successful RCM RVOT ablation was achieved in {12 of 13} (92.3%) patients. Mean procedure and fluoroscopy times were 116.5 ± 48.9 and 7.5 ± 4.3 min, respectively. Catheter-induced VES during RVOT mapping were observed in {1 in 13} patients (7.7%, three VES). No complications occurred. During a mean follow-up of 252 ± 211 days, clinical arrhythmia recurrence was observed in {1 in 13} (7.7%) patients.

Conclusions

Automatic RCM RVOT access is feasible, while RVOT mapping and ablation appear to be safe, fast, and effective. The soft magnetic catheter rarely induces mechanical VES.

Introduction

Right ventricular outflow tract (RVOT) ventricular tachycardia (VT) or ventricular extrasystoles (VES) is amenable to catheter ablation requiring precise catheter movement within the RVOT.^1–4 Manual mapping and ablation utilizing a conventional stiff catheter may result in frequent mechanically induced VES and bear the potential risk for cardiac perforation.^5,6 In order to facilitate manual RVOT mapping and ablation, the use of three-dimensional electro-anatomical reconstruction (3D-EAR) has been suggested.^7,8 Initial experience using the remote-controlled (RCM) magnetic navigation system (MNS) for RVOT tachycardia/VES ablation required a 64-polar basket catheter within the RVOT.⁹ In contrast, the aim of our study was to assess the feasibility of fully automated RVOT access and ablation using the MNS without additional mapping tools (i.e. basket catheter, 3D-EAR).

Methods

Inclusion and exclusion criteria

Between April 2008 and August 2009, 13 patients presenting with VT/VES suggestive of RVOT origin¹⁰ were included in this study and provided written informed consent. Patients were excluded if contraindications existed for the use of the MNS (e.g. implantable cardioverter-defibrillator or pacemaker devices, metallic implants, claustrophobia, etc.).

Magnetic navigation

The concept of magnetic navigation has recently been described.^11–14 Briefly, the MNS Niobe II incorporates two computer-controlled permanent magnets located in parallel to the fluoroscopy table, generating a magnetic field (0.08 T) allowing remote steerable mapping and ablation within the heart. The novel mapping and ablation catheter is equipped with three permanent magnets within its distal shaft aligning in parallel to the remotely controlled magnetic field. Altering the orientation of the outer magnets results in a magnetic field change and corresponding deflection of the catheter. Magnetic field vectors can be stored and, if necessary, recalled to facilitate automated navigation of the magnetic catheter. A computer-controlled catheter advancer system (Cardiodrive, Stereotaxis, Inc., St Louis, MO) and a video workstation (Navigant 2.11, Stereotaxis, Inc.) are required to assist precise remote catheter manipulation. Compared {with} the first generation, the second-generation Niobe II MNS permits tilting of both magnets to right anterior oblique (RAO) 30° and left anterior oblique (LAO) 40° projections.

Electrophysiological study

All patients were studied in a fasting state. During the initial diagnosis, sedation was not administered to avoid a potential suppression of clinical VES or VT. Once VES/VT were documented [electrocardiogram (ECG) recording system AXIOM Sensis, Siemens], intravenous sedation was started (fentanyl, midazolam, and continuous infusion of 1% propofol). A His bundle recording catheter (PerryHis, Biosense Webster, Diamond Bar, CA) was advanced via the femoral vein and a multipolar catheter (PerryHis, Biosense Webster) was positioned within the distal coronary sinus via the left subclavian vein. In case of RCM ablation failure, crossover to manual ablation was performed guided by a 3D mapping system (CARTO, Biosense Webster).

Automatic navigation to the right ventricular outflow tract and magnetic mapping

Automated navigation to the RVOT was performed utilizing a 4 mm solid tip soft magnetic catheter (Celsius RMT, Biosense Webster). Pre-installed magnetic vectors were applied as follows: placement of the magnetic catheter at the His bundle (pre-selected vector: tricuspid 3° clock area; Step 1), followed by the right ventricular (RV) apex (pre-selected vector: RV apex; Step 2), and finally the RVOT (pre-selected vector: central RVOT; Step 3). Catheter positions were confirmed by local electrograms and fluoroscopic views in standard angulations (RAO 30°, LAO 40°) (Figure 1). Detailed mapping within the RVOT was performed by step-by-step RCM catheter movement guided by gradual changes {in} the magnetic field vector. Interesting sites according to pace map and activation map criteria together with the presence of a QS pattern in the unipolar signal were stored as selected vectors. All catheter-induced VES observed during RVOT mapping were counted. Notably, no 3D-EAR was utilized in conjunction with RCM mapping.

Ablation

Radiofrequency current (RFC) ablation (maximum temperature: 55C°; maximum energy: 20–40 W; duration: 60 s) was performed at the site of earliest local bipolar activation (≥30 ms from the onset of the QRS), presence of a QS pattern in the unipolar signal, and/or a perfect pace map (≥11/12 leads) according to established criteria^4,15–18 (Figure 2). A waiting period of 30 min was applied to all patients. Ablation endpoints were the elimination of spontaneous clinical VT/VES and non-inducibility after burst stimulation and orciprenalin administration (5 mg/250 ml NaCl 0.9%) post-ablation while the patient was awake. Total fluoroscopy time (examination room plus control room) was measured. Post-ablation heparin i.v. (50 IU/kg) was administrated to the patients.

Endpoint

In the study, the primary endpoints were defined as feasibility of automatic RCM RVOT accessibility, successful acute RCM VT/VES ablation, and recurrence of clinical VES; also, procedural data including procedure duration, fluoroscopy time, complications, and catheter-induced VES during RVOT mapping were evaluated.

Follow-up

In all patients, pneumothorax and pericardial effusion were ruled out the day after the procedure. All patients underwent a 24 h Holter ECG monitoring post-ablation and were scheduled for a 3-month follow-up visit at our outpatient clinic and/or regularly contacted via the referring doctor and/or via telephone.

Statistical analysis

Data analysis was performed. Data mean ± standard deviation (SD) was used to describe continuous variables with approximately normal distribution. Otherwise, the median and range are presented.

Results

Patients

A total of 13 patients with a mean age of 50 ± 14 years (10 females, 6 VT, 7 VES) underwent RCM mapping and ablation for drug-refractory suspected RVOT VT/VES according to the baseline 12-lead ECG. Two patients had coronary artery disease and six patients had arterial hypertension. In {6 of 13} (46.2%) patients, sustained VT was present during the procedure. The remaining seven patients (53.8%) were in sinus rhythm interrupted by spontaneous VES and non-sustained VT.

Automatic navigation to the right ventricular outflow tract and magnetic mapping

Stepwise automated access to the RVOT was successfully obtained in all 13 (100%) patients, utilizing the above-described sequence of pre-installed vectors. Catheter-induced VES during RVOT mapping were observed only in 1 in 13 patients (7.7%, three VES). The RVOT was identified as the origin of the VES/VT in {12 of 13} (92.3%) patients. A left-sided VES focus origin was suspected by an earliest ventricular activation recorded from the distal coronary sinus in the remaining patients. Successful RVOT ablation sites were identified in antero-septal ({11 of 13} patients, 84.6%) and mid-septal ({1 in 13} patient, 7.7%) positions in these 12 patients.

Ablation data

Remote-controlled magnetic RFC ablation acutely abolished VT/VES in {12 of 13} (92.3%) patients requiring a mean of 4 ± 2 RFC applications. Total mean RFC duration was 225 ± 183 s. During RFC ablation, VT acceleration was observed in {3 of 13} (23.1%) patients. After RCM ablation, VT/VES was not inducible in {12 of 13} (92.3%) patients during a 30 min waiting period. In the patient with suspected left-sided origin, transient suppression of VES was achieved in the RVOT using RCM. However, no ablation was performed in the left ventricular outflow tract.

Procedural data

Mean procedure time was 116.5 ± 48.9 min. Mean total fluoroscopy time was 7.5 ± 4.3 min.

Mean fluoroscopy time from the control room was 1.7 ± 1.1 min, resulting in a 22.7% reduction in fluoroscopy exposure to the investigator (Table 1).

Follow-up

No complications were observed. During a mean follow-up of 252 ± 211 days, in the 12 patients with successful ablation in the RVOT, palpitation occurred without evidence of VES or/and VT in 2 patients. The remaining 10 patients were free of symptoms and evidence of VES on Holter ECG.

Discussion

This study describes a fully automated stepwise approach to catheter mapping and ablation of RVOT VT/VES using the RCM MNS. The main findings are as follows: (i) stepwise fully automated accessibility to the RVOT is feasible, (ii) mapping and ablation within the RVOT are safe, fast, and effective, and (iii) low numbers of catheter-induced VES were observed.

Automated navigation to the right ventricular outflow tract

The concept of RCM catheter manipulation represents a platform technology. Pre-installed magnetic vectors allow targeting specific regions within the heart.¹⁴ In our study, the RVOT was accessed solely by sequential application of pre-installed magnetic vectors. Automation of catheter navigation is one potential application for the MNS. Further software refinements may allow for automation of precise catheter movements, even in more complex anatomic regions, such as the left atrium.

Remote-controlled magnetic mapping and ablation

The soft magnetic catheter allows for safe RCM mapping from the control room.^13,14,19 Manipulation within the RVOT using a stiff manual ablation catheter may result in cardiac perforation as a known but rare complication.^5,6 More frequently, mechanically induced VES are seen during manual mapping and ablation. In order to improve manual mapping and ablation, 3D-EAR of the RVOT has been suggested.^7,8 In a previous study using the MNS, an additional basket catheter was placed in the RVOT to facilitate RCM mapping and ablation.⁹ In our simplified approach, we used only a single magnetic mapping catheter to perform pace and/or activation mapping. Reduction in radiation exposure to the investigator is in line with previous reports.^13,14 It is well established that 12-lead ECG morphology of left-sided outflow tract VES/VT can resemble RVOT VES/VT.⁴ In one patient only transient VES elimination was achieved despite crossover to an irrigated tip catheter in conjunction with 3D-EAR of the RVOT suggesting a non-RVOT focus.

Low number of catheter-induced ventricular extrasystoles by the magnetic navigation system

It has been demonstrated that conventional mapping can be easily performed in the RVOT. However, frequent catheter-induced VES occur during mapping with the stiff conventional catheter. In the present study, mechanically induced VES were observed in 1 out of these 13 patients using the soft magnetic catheter for mapping and ablation. Furthermore, in clinical practice, pace mapping is generally used to identify the VES/VT origin in the RVOT. On the contrary, near the left Purkinje system, pace mapping has limitation in identifying the focus origin.²⁰ Therefore, activation mapping is commonly used for mapping the origin. On the other hand, 3D activation mapping is time consuming due to catheter-induced VES in the LV. This finding of low incidence of mechanical VES may provide a potential advantage using MNS to identify the LV focal origin.

Limitations

The study has several limitations. First, the patients’ population with clinical VES from the RVOT was small. Secondly, this is a non-randomized study. However, using this simplified approach, RCM ablation was easily and successfully performed in the RVOT area, leading to VES/VT elimination in these 12 patients. Further investigation is needed to evaluate whether MNS is superior to the manual approach in patients with RVOT VT/VES.

Conclusions

Automated RCM access to the RVOT is feasible. In addition, RCM RVOT mapping and ablation appear to be safe, fast, and effective. The soft magnetic catheter rarely induces mechanical VES.

Conflict of interest: K.-H.K. received consultant fees from Stereotaxis.

Funding

M.K. was funded by EHRA (Basic training fellowship programme).

References