Outcomes of simultaneous unipolar radiofrequency catheter ablation for intramural septal ventricular tachycardia in nonischemic cardiomyopathy

Accepted Manuscript Outcomes of Simultaneous Unipolar Radiofrequency Catheter Ablation for Intramural Septal Ventricular Tachycardia in Non-Ischemic Cardiomyopathy Jiandu Yang, MD, Jackson Liang, DO, Yasuhiro Shirai, MD, Daniele Muser, MD, Fermin C. Garcia, MD, David J. Callans, MD, Francis E. Marchlinski, MD, Pasquale Santangeli, MD, PhD PII:

S1547-5271(18)31284-0

DOI:

https://doi.org/10.1016/j.hrthm.2018.12.018

Reference:

HRTHM 7853

To appear in:

Heart Rhythm

Received Date: 17 September 2018

Please cite this article as: Yang J, Liang J, Shirai Y, Muser D, Garcia FC, Callans DJ, Marchlinski FE, Santangeli P, Outcomes of Simultaneous Unipolar Radiofrequency Catheter Ablation for Intramural Septal Ventricular Tachycardia in Non-Ischemic Cardiomyopathy, Heart Rhythm (2019), doi: https:// doi.org/10.1016/j.hrthm.2018.12.018. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Outcomes of Simultaneous Unipolar Radiofrequency Catheter Ablation for Intramural Septal

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Ventricular Tachycardia in Non-Ischemic Cardiomyopathy

Running title: Simultaneous Unipolar RF for Intraseptal VT in NICM

§

Jiandu Yang,* MD; Jackson Liang,* DO; Yasuhiro Shirai,* MD;

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Daniele Muser,* MD; Fermin C. Garcia,* MD; David J. Callans,* MD;

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Francis E. Marchlinski,* MD; Pasquale Santangeli,* MD, PhD

*Cardiac Electrophysiology, Hospital of the University of Pennsylvania, Philadelphia, PA §State Key Laboratory of Cardiovascular Disease, Arrhythmia Center, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Total word count: 4642.

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Corresponding author:

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Conflict of Interest Disclosures: None related to this topic.

Pasquale Santangeli, MD, PhD

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Hospital of the University of Pennsylvania 9 Founders Pavilion – Cardiology 3400 Spruce St.

Philadelphia, PA, 19104 Tel: 215-662-6005

Fax: 215-662-2879 E-mail: [email protected]

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Abstract Background. Radiofrequency (RF) ablation of intramural septal ventricular tachycardia (VT) in patients with non-ischemic cardiomyopathy (NICM) is challenging.

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Objective. This study investigated the outcomes of simultaneous unipolar RF ablation for intramural septal VT in NICM.

Methods. We included patients with NICM and mid-myocardial septal substrate referred for VT ablation. Following failed prolonged sequential unipolar RF lesions, simultaneous unipolar RF was delivered using

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two open-irrigated catheters at the site of earliest activation and/or best entrainment or pace-mapping and at an anatomically adjacent/opposite site (up to 40W for up to 3 min; RF energy independently titrated for

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each catheter to achieve an impedance drop of at least 15% from baseline values).

Results. A total of 6 patients (age 62±13 years, ejection fraction 38%±17%) were included. The clinical VT(s) were mapped at the anterior interventricular septum in 2 patients, and at the inferior septum in 4. In all patients, prolonged sequential unipolar RF at the best activation/entrainment/pace-mapping site and at an anatomically opposite/adjacent site failed to eliminate VT. In 3 (50%) cases, late VT termination with VT re-inducibility was observed following sequential unipolar RF. Simultaneous unipolar ablation was

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then delivered resulting in VT elimination and non-inducibility in all patients. No procedural complications and no steam pops were observed. After 20 months (13-20 months) follow-up, 4 (67%) patients remained free of VT recurrence.

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Conclusions. In patients with NICM and intramural septal VT refractory to conventional RF ablation, simultaneous unipolar RF ablation is a safe and effective alternative ablation approach to improve long-

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term VT control.

Key Words: catheter ablation; non-ischemic cardiomyopathy; septal substrate; ventricular tachycardia; simultaneous unipolar ablation.

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INTRODUCTION The management of recurrent ventricular tachycardia (VT) in patients with nonischemic cardiomyopathy (NICM) is problematic, owing to the complexity of the underlying substrates which frequently involve the

distribution.

1-3

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basal perivalvular regions and the interventricular septum, with a high prevalence of mid-myocardial The latter represents a unique challenge, as conventional unipolar radiofrequency (RF)

ablation delivered from the endocardial aspects of the interventricular septum may be inadequate to reach intramural substrates responsible for VT. Several alternative ablation strategies have been

4

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proposed to target intramural substrates when conventional RF ablation fails; these include bipolar RF 5

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ablation, transcoronary ethanol ablation, use of half-normal saline irrigation, and needle catheter 7, 8

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ablation.

Simultaneous unipolar RF ablation has been reported to increase the lesion size and depth compared to 9

standard sequential unipolar RF ablation in pre-clinical studies, and has been recently described as a safe and effective approach to improve procedural success for idiopathic intramural ventricular arrhythmias refractory to conventional sequential unipolar RF.

10

No previous study has investigated the

role of simultaneous unipolar RF ablation to target intramural substrates in patients with NICM. The

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purpose of this study is to evaluate the safety and efficacy of simultaneous unipolar RF ablation for treatment of VT in NICM patients with intraseptal substrate who have failed conventional sequential RF

METHODS

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ablation.

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Patients characteristics

We included consecutive patients with NICM and intramural septal substrate referred for VT ablation to the University of Pennsylvania between December 2015 and September 2017 and in whom simultaneous unipolar RF ablation was attempted following failure of sequential unipolar RF ablation. All patients underwent pre-procedural contrast-enhanced cardiac magnetic resonance imaging (MRI) and all demonstrated evidence of intramural septal substrate (see below). All patients gave written informed consent prior the procedure and data were entered in a VT registry approved by the University’s

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investigational review board. Procedures were performed according to the institutional guidelines of the University of Pennsylvania Health System.

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Electrophysiology study and catheter ablation All patients underwent the procedure in the fasting state. Whenever possible, AADs were discontinued ≥5 half-lives before the procedure, with the exception of amiodarone, which was discontinued for at least 3 days. Catheters were placed into position in the heart using fluoroscopic guidance. A 6-Fr quadripolar

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catheter with 5-mm interelectrode distance (Bard Inc., Delran, New Jersey) was placed at the right

ventricular (RV) apex. A decapolar catheter was placed in the CS and advanced into the CS into the

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anterior interventricular vein/great cardiac vein junction in 2 patients. An 8-Fr intracardiac echocardiography (ICE) catheter was advanced into the heart and images were integrated into a 3dimensional electroanatomic map using CartoSound to create a detailed anatomic shell. Intravenous heparin was administered to maintain an activated clotting time above 300 seconds and endocardial access was obtained to the LV using retrograde transaortic or trans-septal approach, and to the right ventricle using a transvenous approach. An electroanatomic map (CARTO, Biosense Webster, Diamond

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Bar, California) was created during sinus or paced rhythm to identify areas of low voltage and abnormal electrograms. Signals with a peak-to-peak bipolar signal amplitude of >1.5 mV were categorized as normal voltages. As previously reported, we defined normal RV endocardial unipolar electrograms as

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having an amplitude ≥5.5 mV11 and normal LV unipolar electrograms as ≥8.3 mV.1, 12 As mentioned, all patients underwent pre-procedural CMR that showed evidence of intramural septal

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substrate. At the time of the procedure, the presence of abnormal intramural septal substrate was further corroborated by the following findings: 1) presence of confluent septal areas of low unipolar voltage in the presence of no or minimal bipolar voltage abnormality, 2) presence of abnormal electrograms in the septum characterized by fragmented, late, and split potentials regardless of the absolute peak-to-peak voltage amplitude, 3) evidence of disrupted transmural activation (>40 ms) coupled with long (>95 ms) duration electrograms with transseptal pacing, as previously described.

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All spontaneous and induced VTs with cycle length >250 ms were targeted. For hemodynamically stable VTs, entrainment mapping was performed to identify the best sites to target for ablation. For unmappable

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VTs, substrate modification was performed with cluster lesions targeting sites identified by pace mapping and encompassing abnormal/prolonged duration electrograms recorded with sinus/paced rhythm mapping or at sites indicating presence of intramural substrate characterized by long transseptal

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conduction times. Radiofrequency lesions were delivered with an open-irrigated ablation catheter (ThermoCool or ThermoCool SF, Biosense Webster, Diamond Bar, California) with a power of 30 to 50W (maximum electrode tip temperature 45 degrees Celsius) and titrated to an impedance drop of at least 10% from baseline values (typically 12 to 18 Ohms). Lesions were routinely prolonged for at least 3 min

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duration and extended to up to 5 min at sites where VT suppression was observed. Sequential

biventricular unipolar RF ablation from both sides of the septum was performed at sites identified with the

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approaches described above. If VT remained inducible despite sequential unipolar RF ablation delivered from both sides of the septum, irrigated unipolar RF was simultaneously applied from 2 separate openirrigated catheters (ThermoCool or ThermoCool SF, Biosense Webster, Diamond Bar, California) and using 2 RF generators (SmartAblate and Stockert, Biosense Webster, Diamond Bar, California) at the same sites that were targeted with initial sequential unipolar RF configuration (Figure 1). To allow for RF delivery in the simultaneous configuration without error messages from the RF generators, power had to

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be manually titrated from 0W to up to 40W at both RF generators while carefully observing the impedance trend and impedance drops at both RF generators for a total duration of up to 3 min. Following ablation, programmed stimulation was repeated with up to 3 ventricular extrastimuli delivered from 2 different sites

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and at 2 pacing cycle lengths (600ms and 400ms) down to refractoriness. Acute procedural success was defined as lack of inducibility of the clinical VT(s) and of all the mappable and unmappable nonclinical

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induced VT(s) with cycle length of >250 ms. Repeat noninvasive programmed stimulation (NIPS) before discharge was performed in 3 patients.

Cardiac MRI Acquisition Protocol Cardiac MRI was performed on a 1.5T scanner (Avanto, Siemens Medical Solutions, Erlangen, Germany) with a cardiac phased-array receiver surface coil and ECG-gating. Cine imaging was performed using a steady state free precession sequence in long axis slices and in a stack of contiguous 6mm-thick short axis slices encompassing the whole ventricles. LGE images were acquired using the same slice coverage

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as long-axis and short-axis cine images 15 minutes after intravenous injection of 0.2mmol/Kg gadobenate dimeglumine contrast agent (MultiHance, Bracco Diagnostics, Princeton, N J, USA) using an inversionrecovery gradient-echo pulse sequence, individually adjusting inversion time to optimize nulling of 14

In subjects with ICDs, for which strict institutional safety procedures

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apparently normal myocardium.

were followed, a wideband LGE sequence was used to minimize artifacts from the battery pack.

Clinical follow-up

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Patients were evaluated clinically and with ICD interrogation at scheduled outpatient appointments 4 to 8 weeks after ablation and every 3 to 6 months thereafter. For patients not followed at the University of

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Pennsylvania, referring cardiologists were contacted and records reviewed. VT recurrences included any episode of sustained VT/VF leading to appropriate ICD interventions (ATP or shocks) or any documented symptomatic VT. All VT recurrences were adjudicated by review of ICD electrograms and/or 12-lead electrocardiograms.

Statistical analysis

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Continuous variables are expressed as means ± standard deviations if normally distributed or medians (25th-75th percentile) if not normally distributed. Categorical data are expressed as counts and percentages. Survival curves were generated by the Kaplan–Meier method. Analyses were performed

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RESULTS

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using STATA version 14.2 statistical package (Stata Corporation, College Station, TX).

Patients characteristics

The baseline characteristics of patients included in the study are described in Table 1. During the study period, a total of 63 patients with NICM and septal substrate underwent catheter ablation of VT at our Institution, with 30/63 (48%) patients presenting with recurrent VT after a prior failed ablation procedure. Of these, 20/30 (67%) underwent a single repeat conventional RF ablation procedure, 6/30 (20%) more than one repeat conventional RF ablation procedure, and 4/30 (13%) a repeat procedure in which simultaneous unipolar RF ablation was performed. An additional 2/63 (3%) patients crossed over to

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simultaneous unipolar RF during their first ablation procedure after failure of prolonged sequential unipolar RF. Therefore, the final study population consisted of 6 patients (9% of the total NICM with septal substrate group, mean age 62±13 years, 5 males, average left ventricular ejection fraction 38%±17%)

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(Table 1). All patients had recurrent VT despite treatment with at least one antiarrhythmic drug, with 5 (83%) patients who failed ≥2 drugs. Before the ablation, 5 (83%) patients were receiving treatment with amiodarone, with an average daily dose of 360±167 mg. The ECG characteristics of the clinical VTs which were targeted with simultaneous unipolar ablation are described in Table 1 and presented in

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Figure 2. The targeted clinical VT had a left bundle branch block (LBBB) configuration in 5 patients (3 with superior axis and 2 with inferior axis) and a right bundle branch block (RBBB) configuration with

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superior axis in one patient.

Acute procedural outcomes

Pre-procedural CMR demonstrated mid-myocardial septal late gadolinium enhancement in all patients (Table 1), which corresponded to regions of abnormal septal substrate detected with intraprocedural mapping using the criteria described above. In particular, an endocardial septal bipolar voltage

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abnormality was detected in 4/6 (67%) patients, and all patients had evidence of low unipolar voltage coupled with abnormal EGM recordings and long transseptal conduction times.

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Limited activation and entrainment mapping was possible in 4/6 (67%) patients. Sequential biventricular

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prolonged unipolar RF was delivered during ongoing VT in these 4 patients and resulted in late VT termination during RF application in 3 cases (no effect in the remaining 1 patient) followed by VT re-

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inducibility with repeat programmed stimulation. Simultaneous unipolar RF was then applied at the same sites resulting in VT termination in all 4 cases, with no further VT re-inducibility (Figures 3 and 4). In the remaining 2/6 (33%) patients, the induced VTs were hemodynamically unstable or rapidly degenerated to faster polymorphic VT. In these cases, the optimal ablation sites were determined by pace-mapping within the abnormal septal substrate. Prolonged sequential unipolar RF ablation was performed from both sides of the interventricular septum; in particular, ablation was delivered first at the site(s) of best pacemapping match within the abnormal septal substrate followed by anatomically opposite/adjacent septal site(s). In all cases, VT remained inducible with programmed stimulation after

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sequential unipolar septal RF ablation. Simultaneous unipolar RF ablation was then performed at the same selected sites with no further VT inducibility at repeat programmed stimulation. The average distance between the two catheters at the selected sites during simultaneous unipolar RF was 13.3±4mm

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(range 7.8-20.1mm) (Table 1). No complications were observed during the procedure. In particular, no steam pops occurred during both prolonged sequential and simultaneous unipolar RF.

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Follow-up

A total of 3 (50%) patients underwent NIPS before hospital discharge a mean of 4±1.5 days following the

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procedure. Non-inducibility of any VT at NIPS was observed in 2 cases; in the remaining 1 case, a nonclinical VT different from the targeted septal VT was induced. Five (83%) patients were discharged on a reduced dose of a single previously ineffective antiarrhythmic drug agent, with 4 (67%) patients being maintained on amiodarone (average dose 250±100 mg/d).

After a median follow-up of 20 months (range 13-20 months), 2 (33%) patients had recurrent VT. One of these patients (patient #3, Table 1) had acute recurrence of the targeted VT before hospital discharge

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and underwent a repeat ablation procedure during which the infero-septal substrate was targeted again with simultaneous unipolar RF resulting in acute VT non-inducibility. One month following the repeat ablation procedure, the same VT recurred and it was further managed with escalation of antiarrhythmic

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procedure.

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drug therapy. The second patient had a VT recurrence 20 months following the simultaneous unipolar RF

DISCUSSION

The present study describes the outcomes of simultaneous unipolar RF ablation to target intramural septal substrates in patients with NICM and VT refractory to conventional sequential unipolar RF. Overall, this ablation approach was demonstrated feasible, safe, and had acceptable long-term outcomes with a cumulative VT-free survival at a median follow-up of 20 months of 67% in a particularly challenging patient population.

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Prior studies have consistently documented poor outcomes with a high rate of acute and long-term procedural failure in patients with NICM and intramural septal substrate,

2, 3, 16

which reflect the limitations

of standard techniques to target intramural VT sources. From a mapping perspective, an isolated

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intramural circuit cannot be entirely defined with surface LV/RV mapping, which poses significant challenges in the definition of the optimal endocardial sites (i.e., anatomically closer to the critical parts of the intramural circuit) to apply RF energy. In the absence of uniform and reproducible approaches to obtain direct intramural recording from multiple sites, activation and entrainment mapping (when possible)

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or analysis of pace-mapping information from the mappable surface adjacent to the abnormal intramural substrate have been used to determine the optimal sites to deliver RF energy.

1, 13, 16

Termination of VT

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during RF application at selected sites and/or lack of VT re-inducibility following septal substrate modification ultimately validate the adequacy of the selected septal ablation sites. In our series, sequential unipolar RF could be applied during ongoing VT in 4/6 (67%) cases and resulted in VT termination in 3/4 (75%) patients. This finding suggests that the septal VT circuits were indeed affected by ablation at the selected sites, although only temporarily as VT could be re-induced with programmed stimulation following ablation in all cases. These results are in line with prior experiences

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from different groups of investigators, and support the notion that standard unipolar RF ablation is greatly limited by the inability to reach deep substrates and eliminate septal circuits.

2, 4, 6

In order to overcome the

limitations of conventional unipolar RF, different alternative ablation approaches have been described.

needle catheter,

7, 8

5, 17

4

bipolar RF ablation, ablation with a dedicated

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These include coronary arterial or venous embolization,

or unipolar ablation using irrigation with half-normal saline.

6, 18

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Simultaneous unipolar RF has been suggested as a potential alternative strategy to increase lesion size compared to standard sequential unipolar RF in pre-clinical studies,

9, 19

and recently described as an

effective approach to improve procedural success in patients with focal intramural outflow tract ventricular arrhythmias.10 The incremental benefit of simultaneous unipolar RF compared to standard sequential RF is likely due to increased temperature at intramural sites, which results in improved RF lesions.

9, 20

In

patients with septal substrates, simultaneous unipolar RF also minimizes the effect of convective cooling from the high-flow of endocardial blood at the opposite RV/LV septum. The application of a separate

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source of resistive heating on the opposite site of the septum may ultimately result in increased intramural tissue temperature and more effective RF lesion. It is important to emphasize that simultaneous unipolar RF uses commonly available RF generators and

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catheters and, as such, can be easily implemented in any EP laboratory. In this regard, with the important exception of ablation using half-normal saline irrigation, which has been described only recently,

6, 18

all

the other approaches above mentioned either utilize tools that are not yet available for routine clinical use,

4, 7, 8

or require special expertise in coronary arterial-venous catheterization, balloon occlusion and 5, 17

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injection/embolization.

Furthermore, simultaneous unipolar RF may offer additional advantages compared to other approaches

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such as bipolar ablation. For instance, with bipolar ablation the current is delivered from one catheter to the other regardless of the local tissue impedance, electrode contact and orientation. As such, in regions of impedance mismatch or when there are differences in tissue-catheter contact affecting the electrode surface in contact with the myocardium, bipolar RF may result in uneven tissue heating at either catheter 4

and steam pops. Simultaneous unipolar RF allows for independent titration of RF power at the individual catheters, as well as independent assessment of the impedance trends during ablation at each location.

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In this regard, to avoid error messages from the two RF generators preventing RF delivery, we found that RF energy had to be started at 0 Watts and manually titrated to the desired output. Careful monitoring of the impedance trends at the individual RF generators during the simultaneous unipolar RF application

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Study limitations

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appeared safe, and we didn't observe any steam pops during the procedures.

This study included a small number of patients, which is linked to the inclusion of a selected population of patients with NICM and septal VT refractory to conventional sequential unipolar RF. However, the clinical and procedural characteristics of the included patients were homogeneous, with proven intramural septal substrate at both pre-procedural imaging and intraprocedural mapping. In addition, the sample size is comparable to that of prior investigations evaluating alternative ablation approaches for ventricular arrhythmias refractory to conventional unipolar RF ablation.

4, 5, 8, 17

Direct intramural mapping utilizing

septal coronary venous/arterial septal perforator branches was not attempted,

5, 17, 22, 23

and

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intraprocedural integration of CMR reconstruction of the intramural scar not performed;

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these

techniques may have improved the definition of the optimal LV/RV septal sites for RF ablation. In the simultaneous unipolar RF configuration, power was titrated to a maximum of 40W while observing the

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impedance trend and impedance drops at both RF generators. With these settings we could consistently achieve adequate impedance drops at both RF generators while being able to maintain the power

application for the entire duration of the lesion without incurring in steam pops. However, it is possible that our RF parameters in the simultaneous configuration may have been too conservative and a higher

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power application of up to 50W would have resulted in larger and deeper lesions, possibly increasing the likelihood of achieving long-term success in the 2 patients experiencing VT recurrence over follow-up.

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Finally, the reported outcome results were obtained while maintaining most patients on a reduced dose of a single previously ineffective antiarrhythmic drug agent, which included amiodarone in 67% of cases.

Conclusions

In patients with NICM and intramural septal VT refractory to conventional sequential unipolar RF,

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control.

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simultaneous unipolar RF ablation is a safe and effective adjunctive strategy to enhance long-term VT

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Table 1. Clinical and procedural characteristics of the subjects included in the study. Pt #2

Pt #3

Age

64

72

63

Sex

M

M

F

25%

15%

60%

Basal-septal mid-myocardial LGE

Antero-septal mid-myocardial LGE

Basal-septal midmyocardial and infero-lateral LGE

Yes (DC-ICD)

No*

No

Procedural Data

Prior procedure mapping/ablation sites

36

63

M

M

M

50%

30%

55%

Basal-septal midmyocardial and inferior LGE

Basal-septal midmyocardial and infero-lateral LGE

Basal-septal mid-myocardial LGE

No

Yes (CRT-D)

Yes (CRT-D)

Yes (DC-ICD)

Yes

Yes

Yes

No

Yes

-

LVOT; RVOT; coronary cusps; CS

RV; MCV

LV; RV

-

LV; RV

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Prior procedure

75

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ICD prior to ablation

Pt #6

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MRI

Pt #5

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LVEF

Pt #4

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Pt #1

Mapping/ablation during simultaneous unipolar RF procedure

LVOT; coronary cusp; RVOT

LVOT; RVOT; coronary cusp; AIV

LV; RV; MCV; Epi

LV; RV

LV; RV; MCV; Epi

LV; RV; MCV; Epi

Simultaneous unipolar RF sites

Anterior septum

Anterior septum

Basal inferior septum

Mid septum

Basal inferior septum

Inferior septum

Distance between the two

14.4

13.8

15.7

7.8

8.2

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catheters (mm) No

No

No

No

No

No

Duration of follow-up, months

20

24

19

20

12

13

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Complications

AC C

EP

TE D

M AN U

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DC-ICD=dual chamber implantable cardioverter-defibrillator; CRT-D=cardiac resynchronization therapy-defibrillator; LVEF=left ventricular ejection fraction; RF=radiofrequency; MRI=magnetic resonance imaging; LGE=late gadolinium enhancement; LV=left ventricle; RV=right ventricle; LVOT=left ventricular outflow tract; RVOT=right ventricular outflow tract; AIV=anterior interventricular vein; MCV=middle cardiac vein; Epi=direct epicardial via percutaneous subxiphoid approach. *ICD implanted after the procedure before hospital discharge.

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Figure 1. Diagram showing the simultaneous unipolar RF configuration. Ablation is delivered from 2 separate open-irrigated ablation catheters using 2 separate RF generators. Power can be titrated

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independently at each ablation catheter under continuous impedance trend monitoring.

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Patch 1

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RF generator 1

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Patch 2

RF generator 2

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Figure 2. 12-lead ECG of the clinical VTs targeted with simultaneous unipolar RF ablation in the patients included in the study.

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I II

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III

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aVR aVL

V2

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V3

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V1

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aVF

V4 V5

V6

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Figure 3. Example of simultaneous unipolar RF ablation from patient #2. Panel A: right anterior oblique view and cranial view of the activation maps of the right and left ventricular outflow tracts. The earliest activation during VT was recorded at the antero-septal right ventricular outflow tract. Panels B and C:

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right and left anterior oblique fluoroscopic view showing the position of the two ablation catheters, one at the earliest activation site in the antero-septal right ventricular outflow tract and another at the

anatomically opposite left ventricular outflow tract. Panel D: Simultaneous unipolar RF delivered during

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ongoing VT results in VT termination.

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Figure 4. Example of simultaneous unipolar RF ablation from patient #4. Panel A: inferior view of the bipolar voltage maps of the left and right ventricles. Red tags indicate ablation sites. Panel B: right anterior oblique fluoroscopic view showing the position of the two ablation catheters at the right and left

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ventricular aspects of the basal inferior septum. Panel C: Simultaneous unipolar RF delivered during

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ongoing VT results in VT termination.

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AC C

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AC C

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