Bipolar catheter ablation with dedicated radiofrequency system for highly refractory ventricular arrhythmia-Does the rate of success depend on arrhythmia origin?

INTRODUCTION

Despite rapid technological progress, some arrhythmias are still resistant to standard unipolar ablation. These include arrhythmias arising from the base of the heart, cardiac crux, or epicardium. Bipolar radiofrequency ablation (B-RFA) may be useful in some cases, however, data on the efficacy of this approach in various arrhythmia localizations are scarce. The aim of this study was to assess the efficacy of B-RFA in patients with ventricular arrhythmias originating from various locations, occurring refractory to standard unipolar ablation approaches.

METHODS

An observational, single center study was conducted over a 30-month period. B-RFA were performed using dedicated radio frequency (RF) generator and electroanatomic mapping system.

RESULTS

Twenty-four procedures, in 23 patients with a median (range) of 1 (1-2) previously failed unipolar ablation procedures, were included in the final analysis. There were 12 ablations of ventricular arrhythmias originating from interventricular septum with an acute success rate of 75%, and 12 from left ventricular (LV) summit with an acute success rate of 58%. The midterm success rate (median interquartile range follow-up of 205 days [188-338]) was 66% and 50%, respectively.

CONCLUSIONS

B-RFA is a promising method of catheter ablation for refractory cardiac arrhythmias. A higher success rate was observed in ablation for difficult ventricular arrhythmias originating from interventricular septal region than LV summit.

Bipolar radiofrequency ablation between middle cardiac vein and left ventricular endocardium for intramural ventricular tachycardia originating from the left ventricular inferobasal septum

Ventricular tachycardia ablation in the post-surgical patients is complicated by difficult epicardial access. Endocardial-only ablation may lead to failure which can be prevented by mapping and ablating inside the coronary venous system. Radiofrequency ablation inside the coronary venous system is dependent on anatomical and biophysical factors. Herein we report a ventricular tachycardia case necessitating bipolar ablation between the middle cardiac vein and the left ventricular endocardium.

Bipolar Endo-Epicardial Radiofrequency Ablation of Therapy-Resistant Ventricular Arrhythmias: A Brief Case Series

Despite extensive conventional endoepicardial ablation, significant intramural arrhythmogenic substrate may remain out of reach of unipolar radiofrequency ablation (RFA). The authors present clinical findings and procedural workflow for bipolar radiofrequency ablation (B-RFA) with 1 catheter placed against the endocardium and the other in the pericardial sac to ablate refractory ventricular arrhythmias. No serious adverse events occurred during B-RFA procedures, and the short-term and midterm clinical results were satisfactory. Optimal catheter choice and ablation parameters settings for B-RFA remain to be determined.

Effects of different ablation settings on lesion dimensions in an ex vivo swine heart model: Baseline impedance, irrigant, and electrode configuration

INTRODUCTION

Intramural or epicardial locations of the arrhythmogenic substrate are regarded as one of the main reasons for radiofrequency (RF) catheter ablation failure. This study aims to conduct a comprehensive analysis of various factors including baseline impedance, irrigant and electrode configuration at similar ablation index (AI) value.

METHODS

In 12 ex vivo swine hearts, RF ablation was performed at a target AI value of 500 and a multistep impedance load (100-180 Ω) in 4 settings: (1) conventional unipolar configuration with an irrigant of normal saline (NS); (2) conventional unipolar configuration with an irrigant of half normal saline (HNS); (3) bipolar configuration with an irrigant of NS; (4) sequential unipolar configuration with an irrigant of NS. The relationships between lesion dimensions and above factors were examined.

RESULTS

Baseline impedance had a strong negative linear correlation with lesion dimensions at a certain AI. The correlation coefficient between baseline impedance and depth, width, and volume were R = -0.890, R = -0.755 and R = -0.813, respectively (p < .01). There were 10 (total: 10/100, 10%; bipolar: 10/25, 40%) transmural lesions during the whole procedure. Bipolar ablation resulted in significantly deeper lesion than other electrode configurations. Other comparisons in our experiment did not achieve statistical significance.

CONCLUSION

There is a strong negative linear correlation between baseline impedance and lesion dimensions at a certain AI value. Baseline impedance has an influence on the overall lesion dimensions among irrigated fluid and ablation configurations. Over a threshold impedance of 150 Ω, the predictive accuracy of AI can be compromised.

Increasing Lesion Dimensions of Bipolar Ablation by Modulating the Surface Area of the Return Electrode

OBJECTIVES

This study sought to examine the effect of the return electrode's surface area on bipolar RFA lesion size.

BACKGROUND

Bipolar radiofrequency ablation (RFA) is typically performed between 2 3.5-mm tip catheters serving as active and return electrodes. We hypothesized that increasing the surface area of the return electrode would increase lesion dimensions by reducing the circuit impedance, thus increasing the current into a larger tissue volume enclosed between the electrodes.

METHODS

In step 1, ex vivo bipolar RFA was performed between 3.5-mm and custom-made return electrodes with increasing surface areas (20, 80, 180 mm²). In step 2, ex vivo bipolar RFA was performed between 3.5-mm and 3.5-mm or 8-mm electrode catheters positioned perpendicular or parallel to the tissue. In step 3, in vivo bipolar RFA was performed between 3.5-mm and either 3.5-mm or 8-mm parallel electrode at the: 1) left ventricular summit; 2) interventricular septum; and 3) healed anterior infarction.

RESULTS

In step 1, increasing the surface area of the return electrode resulted in lower circuit impedance (R = -0.65; P < 0.001), higher current (R = +0.80; P < 0.001), and larger lesion volume (R = +0.88; P < 0.001). In step 2, an 8-mm return electrode parallel to tissue produced larger and deeper lesions compared with a 3.5-mm return electrode (P = 0.014 and P = 0.02). Similarly, in step 3, compared with a 3.5-mm, bipolar RFA with an 8-mm return electrode produced larger (volume: 1,525 ± 871 mm³ vs 306 ± 310 mm³, respectively; P < 0.001) and more transmural lesions (88% vs 0%; P < 0.001).

CONCLUSIONS

Bipolar RFA using an 8-mm return electrode positioned parallel to the tissue produces larger lesions in comparison with a 3.5-mm return electrode.

Bipolar Radiofrequency Ablation of Septal Ventricular Tachycardia Facilitated by an Intramural Catheter

Intramural septal substrate presents a challenge in patients undergoing ventricular tachycardia ablation, in terms of both accurate mapping and ablation with unipolar radiofrequency energy. We present the first use of the novel 2-F octapolar catheter in accurately defining intramural septal scar and facilitating bipolar ablation. (Level of Difficulty: Advanced.).

Long-term results of monopolar versus bipolar radiofrequency ablation procedure for atrial fibrillation

Background

In this study, we aimed to evaluate the long-term outcomes of monopolar or bipolar radiofrequency ablation concomitant to mitral valve surgery in patients with atrial fibrillation.

Methods

We retrospectively evaluated a total of 167 patients (67 males, 100 females; mean age 56.8±6.9 years; range, 48 to 65 years) with atrial fibrillation who underwent monopolar or bipolar radiofrequency ablation concomitant to mitral valve surgery between September 2001 and January 2015. The patients were divided into two groups according to the procedure applied as those undergoing monopolar ablation (group 1, n=68) and those undergoing bipolar ablation (group 2, n=99). All patients were followed by electrocardiogram and 24-h Holter monitoring. Echocardiography was performed before discharge, at three and 12 months postoperatively, and annually thereafter. Left atrial volume index, left atrial diameter, and left ventricular ejection fraction were recorded.

Results

There was no significant correlation between the procedure applied and hypertension, hyperlipidemia, diabetes mellitus, chronic obstructive pulmonary disease, history of the cerebrovascular events (p>0.05). The mean preoperative left atrial diameter decreased from 5.3±0.5 cm to 4.9±0.5 cm postoperatively in all patients (p=0.0001). The mean preoperative left atrial volume index decreased from 53.8±0.4 mL/m2 t o 43.7±6.2 m L/m2 i n t he postoperative period (p=0.0001). During follow-up, 61.8% (n=42) of the patients in group 1 and 62.6% (n=62) of the patients in group 2 remained in sinus rhythm. One patient (1.5%) in group 1 and two patients (2.0%) in group 2 developed early postoperative cerebrovascular accident.

Conclusion

Monopolar and bipolar ablation methods are safe and effective methods to ensure long-term sinus rhythm. Both procedures do not increase the morbidity risk with very low thromboembolic complication rates.

Impact of epicardial adipose tissue and catheter ablation strategy on biophysical parameters and ablation lesion characteristics

BACKGROUND

Epicardial adipose (EA) tissue may limit effective radiofrequency ablation (RFA).

OBJECTIVES

We sought to evaluate the lesion formation of different ablation strategies on ventricular myocardium with overlying EA.

METHODS

Bovine myocardium with EA was placed in a circulating saline bath in an ex vivo model. Open-irrigated (OI) RFA was performed, parallel to the myocardium, over fat at 50 W for variable RF durations, variable contact force, catheter configurations (unipolar RF vs bipolar RF), and catheter irrigants (normal saline vs half-normal saline). Ablation was also performed with a needle-tipped ablation catheter (NTAC), perpendicular to the myocardium.

RESULTS

Increasingly thick EA attenuated lesion size regardless of ablation strategy. RF applied with longer durations and increasing CF produced larger lesion volumes and deeper lesions with ablation over EA more than 3 mm but was unable to produce measurable lesions when EA less than 3 mm. Similarly, ablation with half normal saline irrigant created slightly deeper lesions than bipolar RF and unipolar RF with normal saline as EA thickness increased, but was unable to produce measurable lesions when EA more than 3 mm. Of all ablation strategies, only NTAC produced effective lesion volumes when ablating over thick (>3 mm) EA.

CONCLUSIONS

While EA attenuates lesion depth and size, relatively larger, and deeper lesions can be achieved with longer RFA duration, higher CF, half normal saline irrigant, and, to a greater extent, by utilizing bipolar RF or NTAC, but only over thin adipose (<3 mm). Of those catheters/strategies tested, only NTAC was able to effectively deliver RF over thick (>3 mm) EA with this model.

Right atrial position of a return electrode for bipolar ablation of the left posterosuperior process ventricular tachycardia

INTRODUCTION

Radiofrequency (RF) catheter ablation (RFCA) of ventricular tachycardia (VT) is an effective method of treatment. However, when arrhythmia has ischemic etiology and originates from the posterosuperior process (PSP) of the left ventricular (LV) base, ablation performed with conventional unipolar energy sources may be challenging or impossible.

METHOD AND RESULT

A 67-year-old male after six unsuccessful RFCA for highly symptomatic VT originating from PSP of LV base underwent successful RFCA using multiple bipolar RF applications delivered between two electrodes located at LV endocardium and adjacent right atrial sites.

CONCLUSION

This case report shows that bipolar RFCA can be used for safe and successful treatment of VT originating from deep PSP of LV base.

Successful bipolar ablation for ventricular tachycardia with potential substrate identification by pre-procedural cardiac magnetic resonance imaging

Cardiac magnetic resonance imaging (MRI) is a useful tool for detecting the arrhythmogenic substrate in cardiac sarcoidosis. We herein present a case of bipolar radiofrequency catheter ablation for ventricular tachycardia (VT) complicated with cardiac sarcoidosis, guided by pre-procedural cardiac MRI. Neither echocardiography nor endocardial voltage mapping suggested a septal VT substrate. However, MRI alone detected intramural lesions in the septum. Although application of endocardial energy failed to treat the VT, bipolar ablation targeting the potential substrate identified by MRI successfully eliminated the VT. Even when no abnormalities are depicted on echocardiography and endocardial voltage mapping, intramural scar tissue identified by cardiac MRI could be critical for VT.