Bipolar radiofrequency catheter ablation between the left ventricular endocardium and great cardiac vein for refractory ventricular premature complexes originating from the left ventricular summit

Abstract Ablation for ventricular arrhythmias originating from the left ventricular (LV) summit is sometimes challenging. Bipolar radiofrequency catheter ablation (RFCA) is effective for refractory arrhythmias; little is known about bipolar RFCA from the coronary venous system and the appropriate settings. We experienced three cases of ventricular premature complexes (VPCs) originating from the LV summit successfully treated by bipolar RFCA between the LV endocardium (irrigated catheters as active electrodes) and coronary venous system (8‐mm‐tip catheters as return electrodes). These cases showed that bipolar RFCA was effective for the VPCs originating from the LV summit; 8‐mm‐tip catheters were useful as return electrodes.


| INTRODUC TI ON
Ablation for ventricular arrhythmias (VAs) originating from the left ventricular (LV) summit is sometimes challenging because of intramural origins. 1,2 Bipolar radiofrequency catheter ablation (RFCA) can reportedly create transmural lesions by using 2 ablation catheter tips as active electrodes (AEs) and return electrodes (REs). 3 Previous reports have shown the effectiveness of bipolar RFCA for VAs originating from the LV summit. 4 There are several bipolar RFCA settings and we have recently reported a case of successful bipolar ablation involving changing an irrigated catheter to an 8-mm-tip catheter to reduce the impedance. 5 However, the effectiveness and safety of bipolar RFCA from the coronary venous system for VAs originating from the LV summit and the appropriate settings of bipolar RFCA remain unclear.
Here, we describe 3 cases of successful bipolar RFCA between the LV endocardium and great cardiac vein (GCV) for the treatment of the ventricular premature complexes (VPCs) originating from the LV summit.

| ME THOD
Bipolar RFCA was eligible for cases of VAs for which unipolar RFCA in the prior sessions failed or VA recurred, and the study was approved by the institutional ethics committee. Written informed consent was obtained from all patients. Electrophysiological studies (EPS) and catheter ablation were performed using a 3-dimensional electro-anatomical mapping system (Ensite; Abbott or CARTO; Received: 22 August 2019 | Revised: 9 January 2020 | Accepted: 27 January 2020 DOI: 10.1002/joa3.12312

C A S E R E P O R T
Bipolar radiofrequency catheter ablation between the left ventricular endocardium and great cardiac vein for refractory ventricular premature complexes originating from the left ventricular summit Abstract Ablation for ventricular arrhythmias originating from the left ventricular (LV) summit is sometimes challenging. Bipolar radiofrequency catheter ablation (RFCA) is effective for refractory arrhythmias; little is known about bipolar RFCA from the coronary venous system and the appropriate settings. We experienced three cases of ventricular premature complexes (VPCs) originating from the LV summit successfully treated by bipolar RFCA between the LV endocardium (irrigated catheters as active electrodes) and coronary venous system (8-mm-tip catheters as return electrodes).
These cases showed that bipolar RFCA was effective for the VPCs originating from the LV summit; 8-mm-tip catheters were useful as return electrodes.

K E Y W O R D S
coronary sinus, dilated cardiomyopathy, electric impedance, radiofrequency catheter ablation, ventricular premature complexes Biosense Webster). Bipolar RFCA between the LV endocardium and GCV was performed using irrigated catheters (TactiCath TM ; Abbott or THERMOCOOL SMARTTOUCH® SF; Biosense Webster) in the LV endocardium as AEs, and 8-mm-tip catheters (Dual-8 TM one Ablation Catheter; Abbott) in the GCV via the subclavian vein as REs with cardiac effusion monitoring by intracardiac echo (SOUNDSTAR; Biosense Webster). Impedance was carefully monitored during ablation, and ablation was stopped instantly when impedance increased or it decreased by more than 30 Ω.

| C A S E REP ORT
We experienced 3 cases of VPCs originating from the LV summit successfully treated by bipolar RFCA (Table 1).

| Case 1
A 61-year-old man with dilated cardiomyopathy (DCM) and a history of ventricular tachycardia (VT) ablation for the ventricular septum and epicardium and double valve replacement (DVR) was admitted to our hospital for heart failure. He had a cardiac resynchronization therapy defibrillator generator, and his biventricular pacing rate decreased to 86% because of frequent VPCs ( Figure 1A). The morphology of the VPCs was similar to that of VT, which had been treated in the previous session. In EPS, a good pace-map was obtained for the GCV. A prepotential preceding the surface QRS at 54 ms and a QS pattern were recorded by the unipolar electrogram in the GCV when the VPCs were present.
After unsuccessful unipolar RFCA from the GCV, bipolar RFCA performed between the LV endocardium (an irrigated catheter;

| Case 2
A 58-year-old man who previously underwent unipolar RFCA for VPCs originating from the LVOT experienced recurrent VPCs

| Case 3
A 60-year-old man with DCM was admitted to our hospital owing to frequent VPCs ( Figure 1C)

| D ISCUSS I ON
In this case series, we identified two important clinical issues. First, bipolar RFCA between the LV endocardium and GCV was effective for refractory VPCs originating from the LV summit. In general, unipolar RFCA from the GCV and anterior intraventricular vein was attempted for VAs originating from the LV summit; however, it is sometimes unsuccessful because of intramural origin of the VAs. 1 There are some reports on bipolar ablation for VAs originating from the LV summit; 4 however, the methods are not established. This report showed the effectiveness of bipolar ablation from the coronary venous system.
Second, an 8-mm-tip catheter was shown to be useful as an RE in the GCV. There are various bipolar RFCA settings. 3 In the cases presented in this report, an 8-mm-tip catheter was used as an RE to avoid high impedance, whereas an irrigated catheter was used as an AE in the LV endocardium to reduce the risk of thrombosis in the LV. RFCA from the GCV was sometimes discontinued because of high impedance. Moreover, higher impedance is expected in bipolar RFCA than in unipolar RFCA. A previous study reported that bipolar RFCA using an 8-mm-tip catheter as RE recorded significant lower impedance and lower temperature compared with a 4-mm-tip catheter. 6 This observation was consistent with the previous ex vivo study. 3 This may be related to the current density; the size of the 2 catheters and the distance between them may regulate current density, which produces lesions.
In these cases, bipolar RFCA was performed without high impedance.
An 8-mm-tip catheter can be suitable for use as an RE in the GCV. AEs and REs simultaneously using two RF generators. 6 Technical advancement and further studies are needed to achieve better outcomes and to ensure safety of the procedure.

| CON CLUS ION
Bipolar RFCA between the LV endocardium and GCV was effective for the VPCs originating from the LV summit. An 8-mm-tip catheter may be useful as an RE in the GCV to reduce impedance.

ACK N OWLED G M ENTS
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CO N FLI C T S O F I NTE R E S T S
Authors declare no conflict of interests for this article.