Effect of Baseline Impedance on Ablation Lesion Dimensions

Effect of dispersive electrode position (anterior vs. posterior) in epicardial radiofrequency ablation of ventricular wall: A computer simulation study

An epicardial approach is often used in radiofrequency (RF) catheter ablation to ablate ventricular tachycardia when an endocardial approach fails. Our objective was to analyze the effect of the position of the dispersive patch (DP) on lesion size using computer modeling during epicardial approach. We compared the posterior position (patient's back), commonly used in clinical practice, to the anterior position (patient's chest). The model considered ventricular wall thicknesses between 4 and 8 mm, and electrode insertion depths between .3 and .7 mm. RF pulses were simulated with 20 W of power for 30 s duration. Statistically significant differences (P < .001) were found between both DP positions in terms of baseline impedance, RF current (at 15 s) and thermal lesion size. The anterior position involved lower impedance (130.8 ± 4.7 vs. 146.2 ± 4.9 Ω) and a higher current (401.5 ± 5.6 vs. 377.5 ± 5.1 mA). The anterior position created lesion sizes larger than the posterior position: 8.9 ± 0.4 vs. 8.4 ± 0.4 mm in maximum width, 8.6 ± 0.4 vs. 8.1 ± 0.4 mm in surface width, and 4.5 ± 0.4 vs. 4.3 ± 0.4 mm in depth. Our results suggest that: (1) the redirection of the RF currents due to repositioning the PD has little impact on lesion size and only affects baseline impedance, and (2) the differences in lesion size are only 0.5 mm wider and 0.2 mm deeper for the anterior position, which does not seem to have a clinical impact in the context of VT ablation.

Mapping and Ablation of Premature Ventricular Complexes: State of the Art

Premature ventricular complexes (PVCs) are common arrhythmias in clinical practice. Although benign and asymptomatic in most cases, PVCs may result in disabling symptoms, left ventricular systolic dysfunction, or PVC-induced ventricular fibrillation. Catheter ablation has emerged as a first-line therapy in such cases, with high rates of efficacy and low risk of complications. Significant progress in mapping and ablation technology has been made in the past 2 decades, along with the development of a growing body of knowledge and accumulated experience regarding PVC sites of origin, anatomical relationships, electrocardiographic characterization, and mapping/ablation strategies. This paper provides an overview of the main indications for catheter ablation of PVCs, electrocardiographic features, PVC mapping techniques, and contemporary ablation approaches. The authors also review the most common sites of PVC origin and the main considerations and challenges with ablation in each location.

An optimized approach for increasing lesion size in temperature-controled setting using a catheter with a surface thermocouple and efficient irrigation

Background

We explore an optimized approach for increasing lesion size using a novel ablation catheter with a surface thermocouple and efficient irrigation in a temperature-control setting.

Methods

We conducted radiofrequency applications at various power levels (35 W, 40 W, and 45 W), contact forces (CFs, 10 g/20 g), and durations (60 s/120 s/180 s) in perpendicular/parallel catheter orientations, with normal saline irrigation (NS-irrigation) and Half NS-irrigation (HNS-irrigation) in an ex-vivo model (Step 1). In addition, we performed applications (35 W/40 W/45 W for 60 s/120 s/180 s in NS-irrigation and 35 W/40 W for 60 s/120 s/180 s in HNS-irrigation) in four swine (Step 2), evaluating lesion characteristics and the occurrence of steam pops.

Results

In Step 1, out of 288 lesions, we observed 47 (16.3%) steam pops, with 13 in NS-irrigation and 34 in HNS-irrigation (p = .001). Although steam pops were mostly observed with the most aggressive setting (45 W/180 s, 54%) with NS-irrigation, they happened in less aggressive settings with HNS irrigation. Lesion size significantly increased with longer-duration ablation but not with HNS-irrigation. The optimal %impedance-drop cutoff to predict steam pops was 20% with a negative-predictive-value (NPV) = 95.1% including NS- and HNS-irrigation groups, and 22% with an NPV = 96.1% in NS-irrigation group. In Step 2, similar to the ex-vivo model, lesion size significantly increased with longer-duration ablation but not with HNS-irrigation. Steam pops were absent with NS-irrigation (0/35) even with the largest %impedance-drop reaching 31% at 45 W/180 s. All steam pops were observed with HNS-irrigation (6/21, 29%). The optimal %impedance-drop cutoff predicting steam pops was 24% with an NPV = 96.3% including both NS- and HNS-irrigation groups.

Conclusions

Rather than using HNS-irrigation, very long-duration of radiofrequency applications up to 45 W/180 s may be recommended to safely and effectively increase lesion dimensions using this catheter with NS-irrigation.

"Honey pot"-like lesion formation: Impact of catheter contact angle on lesion formation by novel diamond-embedded temperature-controlled ablation catheter in a porcine experimental model

BACKGROUND

Novel diamond-embedded catheter enables precise temperature-controlled ablation. However, the effects of contact angle on lesion formation of this catheter are poorly understood.

OBJECTIVE

The purpose of this study was to evaluate lesion formation using the temperature-controlled ablation catheter embedded with diamond at different angles in a porcine experimental model.

METHODS

Freshly sacrificed porcine hearts were used. Radiofrequency catheter ablation was performed at 50 W for 15 seconds at an upper temperature setting of 60°C. The contact force (5g, 10g, 30g) and catheter contact angles (30°, 45°, 90°) were changed in each set (n = 13 each). Surface width, maximum lesion width, lesion depth, surface area, distance from the distal edge to the widest area, and impedance drop were evaluated.

RESULTS

Surface width and maximum lesion width were longer at 30° than at 90° (P <.05). There were no significant differences in the lesion depth by catheter angle except at 30g. Surface area was larger at 30° than at 90° (P <.05). Distance from the distal edge to the widest area was longer at 30° than at 90° (P <.05). There were no significant differences in impedance drop according to catheter angle.

CONCLUSION

With diamond-embedded temperature-controlled ablation catheters, lesion width increased at a shallower contact angle, whereas lesion depth did not. Surface area also increased at a shallower contact angle. This catheter created a large ablation lesion on the proximal side of the catheter, which looked like a "honey pot."

Impedance-guided modified CLOSE protocol ablation can reduce ablation index necessary for pulmonary vein isolation in patients with atrial fibrillation

BACKGROUND

Real-time monitoring of generator impedance drop is not considered in CLOSE protocol pulmonary vein (PV) isolation (PVI) in patients with atrial fibrillation (AF). We verified whether additional information of impedance drop could minimize ablation index required for PVI using modified CLOSE protocol (target ablation index ≥ 500 on anterior wall and ≥400 on posterior wall along with inter-lesion distance of 3-6 mm and maximum power of 35 W) without any adverse effect of procedural data and efficacy.

METHODS

Sixty consecutive Japanese AF patients [paroxysmal AF: 43 (72 %) patients] underwent first-time PVI with modified CLOSE protocol with real-time monitoring of impedance drop (impedance-guided modified CLOSE protocol). Ablation tags were colored according to impedance drop and ablation was immediately terminated before reaching target ablation index if impedance drop of ≥10 Ω was confirmed. Ablation index needed for PVI, first-pass PVI rate, other procedural data, and atrial tachyarrhythmia recurrence were evaluated.

RESULTS

Mean ablation index and impedance drop on anterior and posterior walls were 437.6 ± 43.5 Ω and 10.2 ± 2.6 Ω and 393.3 ± 27.4 Ω and 9.3 ± 2.2 Ω, respectively. First-pass PVI per PV pair was accomplished in 90/120 (75 %). No complications occurred. PV gaps after first-pass ablation were locationally most often found on right posterior wall than on the other parts (p < 0.001). There were no differences in mean contact force, impedance drop, and ablation index between walls with and without PV gaps after first-pass PV ablation. During a mean follow-up of 24 ± 9 months, survival from atrial tachyarrhythmia recurrence was 51/60 (85 %) patients.

CONCLUSIONS

Using additional generator impedance drop information may be useful to minimize radiofrequency current application to accomplish PVI with modified CLOSE protocol while maintaining efficacy and safety in Japanese AF population.

Exploring the Full Potential of Radiofrequency Technology: A Practical Guide to Advanced Radiofrequency Ablation for Complex Ventricular Arrhythmias

PURPOSE OF REVIEW

Percutaneous radiofrequency (RF) catheter ablation is an established strategy to prevent ventricular tachycardia (VT) recurrence and ICD shocks. Yet delivery of durable lesion sets by means of traditional unipolar radiofrequency ablation remains challenging, and left ventricular transmurality is rarely achieved. Failure to ablate and eliminate functionally relevant areas is particularly common in deep intramyocardial substrates, e.g. septal VT and cardiomyopathies. Here, we aim to give a practical-orientated overview of advanced and emerging RF ablation technologies to target these complex VT substrates. We summarize recent evidence in support of these technologies and share experiences from a tertiary VT centre to highlight important "hands-on" considerations for operators new to advanced RF ablation strategies.

RECENT FINDINGS

A number of innovative and modified radiofrequency ablation approaches have been proposed to increase energy delivery to the myocardium and maximize RF lesion dimensions and depth. These include measures of impedance modulation, combinations of simultaneous unipolar ablations or true bipolar ablation, intramyocardial RF delivery via wires or extendable RF needles and investigational linear or spherical catheter designs. Recent new clinical evidence for the efficacy and safety of these investigational technologies and strategies merits a re-evaluation of their role and clinic application for percutaneous VT ablations. Complexity of substrates targeted with percutaneous VT ablation is increasing and requires detailed preprocedural imaging to characterize the substrate to inform the procedural approach and selection of ablation technology. Depending on local experience, options for additional and/or complementary interventional treatments should be considered upfront in challenging substrates to improve the success rates of index procedures. Advanced RF technologies available for clinical VT ablations include impedance modulation via hypotonic irrigation or additional dispersive patches and simultaneous unipolar as well as true bipolar ablation. Promising investigational RF technologies involve an extendable needle RF catheter, intramyocardial RF delivery over intentionally perforated wires as well as a variety of innovative ablation catheter designs including multipolar linear, spherical and partially insulated ablation catheters.

Adherence to the CLOSE Protocol and Low Baseline Generator Impedance Are Independent Predictors of Durable Pulmonary Vein Isolation

Background: Atrial fibrillation (AF) recurrence after pulmonary vein isolation (PVI) is predominantly attributed to pulmonary vein reconnection (PVR). Predictors of AF recurrence have been widely studied; however, data are scarce on procedural parameters that predict chronic PVR. We aimed to study PVR rates and predictors of PVR. Methods: We retrospectively included 100 patients who underwent repeated ablation due to AF recurrence after initial PVI with the CARTO system. PVR was determined during the repeated procedure by electrophysiological evaluation, and initial procedural characteristics predicting PVR were studied, including adherence to the CLOSE protocol, use of high power, first-pass isolation (FPI), and baseline generator impedance (BGI). Results: Thirty-eight patients underwent initial CLOSE-guided PVI, and sixty-two underwent initial non-CLOSE PVI. A repeat procedure was performed 23 ± 16 months after the initial procedure. In total, PVR was found in 192 of 373 PVs (51.5%), and all PVs were isolated in 17/100 (17%) patients. Factors associated with all PVs being isolated were adherence to the CLOSE protocol, a higher power setting, the presence of bilateral FPI, and lower BGI (88% vs. 28%, p < 0.0001; 37.5 W vs. 30 W, p = 0.0276; 88.2% vs. 40.4%, p = 0.0007; and 127.6 Ω vs. 136.6 Ω, p = 0.0027, respectively). In initial procedures with adherence to the CLOSE protocol, the FPI rate was significantly higher (73.7% vs. 25%, p < 0.0001), while there were no significant differences in terms of procedure time and left atrial dwell time (81 vs. 85 min, p = 0.83; and 60 vs. 58 min, p = 0.08, respectively). BGI ≥ 130 Ω (AUC = 0.7403, sensitivity: 77.1%, specificity: 68.8%, p = 0.0032) was associated with a significantly higher probability of PVR (OR = 6.757; p < 0.0001). In multivariable analysis, independent predictors for PVR were non-adherence to the CLOSE protocol and BGI ≥ 130 Ω. Conclusions: Our findings indicate that adherence to the CLOSE protocol and baseline generator impedance < 130 Ω during AF ablation are independent predictors of PVI durability.

Efficacy of Pulsed Field vs Radiofrequency for the Reablation of Chronic Radiofrequency Ablation Substrate: Redo Pulsed Field Ablation

BACKGROUND

The efficacy of pulsed field ablation (PFA) for redo procedures is unknown.

OBJECTIVES

In this study, the authors aimed to evaluate the effectiveness of PFA when performing PFA over chronic RFA (redo environment).

METHODS

This was a 3-step in vivo study. In step 1 (creation of redo environment), 6 swine underwent radiofrequency ablation (RFA) with a local impedance measuring catheter and a contact force-enabled catheter in 3 different sites: the right atrium (RA) (intercaval line with intentional gaps), the left atrium (LA) (pulmonary vein isolation [PVI] with intentional gaps and superficial posterior wall ablations), and the left ventricle (LV) (short RFA applications [chronic RFA]). In step 2 (re-ablation), following a survival period of ≈5 weeks, animals were retreated as follows: in the RA, a focal PFA catheter over the prior intercaval line; in the LA, PVI using a pentaspline PFA catheter; and in the LV, animals were randomized to focal PFA or RFA. In each arm, 2 types of lesions were performed: acute or acute over chronic. In step 3 (remapping and euthanization), following an additional 3 to 5 days, all animals were remapped and sacrificed.

RESULTS

In the RA, re-ablation with PFA resulted in a complete intercaval block in all animals, expanding and homogenizing the disparate chronic RFA lesions from a width of 4 to 7 mm (chronic RFA) to a width of 16 to 28 mm (PFA over chronic RFA). In the LA, re-ablation with PFA resulted in complete PVI and transmural ablation of the PW. In the LV, the mean depth for acute RFA (post 2-5 days survival) was 7.6 ± 1.3 mm vs 3.9 ± 1.6 mm in the acute over chronic RFA lesions (P < 0.01). In contrast, the mean depth for acute PFA was 7.0 ± 1.6 mm, similar to when ablating with PFA over RFA (7.1 ± 1.3 mm; P = 0.94).

CONCLUSIONS

PFA is highly efficient for ablation following prior RFA, which may be beneficial in patients presenting for redo procedures. In the ventricle, PFA resulted in lesions that are deeper than RFA when ablating over chronic superficial RFA lesions.

Lower contact force predicts right pulmonary vein carina breakthrough after ablation index-guided pulmonary vein isolation using high-power short-duration

INTRODUCTION

Carina breakthrough (CB) at the right pulmonary vein (RPV) can occur after circumferential pulmonary vein isolation (PVI) due to epicardial bridging or transient tissue edema. High-power short-duration (HPSD) ablation may increase the incidence of RPV CB. Currently, the surrogate of ablation parameters to predict RPV CB is not well established. This study investigated predictors of RPV CB in patients undergoing ablation index (AI)-guided PVI with HPSD.

METHODS

The study included 62 patients with symptomatic atrial fibrillation (AF) who underwent AI-guided PVI using HPSD. Patients were categorized into two groups based on the presence or absence of RPV CB. Lesions adjacent to the RPV carina were assessed, and CB was confirmed through residual voltage, low voltage along the ablation lesions, and activation wavefront propagation.

RESULTS

Out of the 62 patients, 21 (33.87%) experienced RPV CB (Group 1), while 41 (66.13%) achieved first-pass RPV isolation (Group 2). Despite similar AI and HPSD, patients with RPV CB had lower contact force (CF) at lesions adjacent to the RPV carina. Receiver operating characteristic (ROC) curve analysis identified CF < 10.5 g as a predictor of RPV CB, with 75.7% sensitivity and 56.2% specificity (area under the curve: 0.714).

CONCLUSION

In patients undergoing AI-guided PVI with HPSD, lower CF adjacent to the carina was associated with a higher risk of RPV CB. These findings suggest that maintaining higher CF during ablation in this region may reduce the occurrence of RPV CB.

Assessing left atrial intramyocardial fat infiltration from computerized tomography angiography in patients with atrial fibrillation

AIMS

Epicardial adipose tissue might promote atrial fibrillation (AF) in several ways, including infiltrating the underlying atrial myocardium. However, the role of this potential mechanism has been poorly investigated. The aim of this study is to evaluate the presence of left atrial (LA) infiltrated adipose tissue (inFAT) by analysing multi-detector computer tomography (MDCT)-derived three-dimensional (3D) fat infiltration maps and to compare the extent of LA inFAT between patients without AF history, with paroxysmal, and with persistent AF.

METHODS AND RESULTS

Sixty consecutive patients with AF diagnosis (30 persistent and 30 paroxysmal) were enrolled and compared with 20 age-matched control; MDCT-derived images were post-processed to obtain 3D LA inFAT maps for all patients. Volume (mL) and mean signal intensities [(Hounsfield Units (HU)] of inFAT (HU -194; -5), dense inFAT (HU -194; -50), and fat-myocardial admixture (HU -50; -5) were automatically computed by the software. inFAT volume was significantly different across the three groups (P = 0.009), with post-hoc pairwise comparisons showing a significant increase in inFAT volume in persistent AF compared to controls (P = 0.006). Dense inFAT retained a significant difference also after correcting for body mass index (P = 0.028). In addition, more negative inFAT radiodensity values were found in AF patients. Regional distribution analysis showed a significantly higher regional distribution of LA inFAT at left and right superior pulmonary vein antra in AF patients.

CONCLUSION

Persistent forms of AF are associated with greater degree of LA intramyocardial adipose infiltration, independently of body mass index. Compared to controls, AF patients present higher LA inFAT volume at left and right superior pulmonary vein antra.

Evaluation of lesion characteristics and baseline impedance on high-power short-duration radiofrequency catheter ablation using computer simulation

Myocardium baseline impedance (BI) is an important factor in ablation effectiveness. This study examined the performance of low-power and long-duration (LPLD), high-power and short-duration (HPSD) ablation at different BIs by computer simulation. A 3D model of the ablation region was constructed for simulation, and in vitro experiments were performed to validate the simulation. Three ablation power and duration configurations of 30 W/30 s, 50 W/10 s, and 90 W/5 s were used for simulation with BI values of 90, 100, 110, 120, 130, and 140 Ω. Roll-off time and ablation volume were measured to evaluate ablation results. The simulation is consistent with the in vitro experiments. When BI is changed from 90 [Formula: see text] to 140 [Formula: see text], the lesion volume over 50 °C with BI of 140 [Formula: see text] was reduced by 6.3%, 6.7%, and 7.3% for 30 W/30 s, 50 W/10 s, and 90 W/5 s configurations, respectively, and the lesion volume over 100 °C was reduced by 62.8%, 49.7%, and 22.5% under 30 W/30 s, 50 W/10 s, and 90 W/5 s, respectively. Simulation results revealed that HPSD (vHPSD) and LPLD ablation were more affected by changes in BI in the lesion volumes over 50 °C and 100 °C, respectively, and demonstrated that resistive and conductive heating were the main heating effects in HPSD (vHPSD) and LPLD, respectively.

Comparison of Long-Term Clinical Outcomes Between Segmental and Circumferential Pulmonary Vein Isolation in Patients Undergoing Repeat Atrial Fibrillation Ablation

BACKGROUND

Circumferential pulmonary vein isolation (CPVI) has supplanted segmental PVI (SPVI) as standard procedure for atrial fibrillation (AF). However, there is limited evidence examining the efficacy of these strategies in redo ablations. In this study, we investigated the difference in recurrence rates between SPVI and CPVI in redo ablations for PV reconnection.Methods and Results: This study retrospectively enrolled 543 patients who had undergone AF ablation between 2015 and 2017. Among them, 167 patients (30.8%, including 128 male patients and 100 patients with paroxysmal AF) underwent redo ablation for recurrent AF. Excluding 26 patients without PV reconnection, 141 patients [90 patients of SPVI (Group 1) and 51 patients of CPVI (Group 2)] were included. The AF-free survival rates were 53.3% and 56.9% in Group 1 and Group 2, respectively (P=0.700). The atrial flutter (AFL)-free survival rates were 90% and 100% in Group 1 and Group 2, respectively (P=0.036). The ablation time was similar between groups, and there no major complications were observed.

CONCLUSIONS

For redo AF ablation procedures, SPVI and CPVI showed similar outcomes, except for a higher AFL recurrence rate for SPVI after long-term follow-up (>2 years). This may be due to a higher probability of residual PV gaps causing reentrant AFL.

Methods and techniques for increasing the safety and efficacy of pulmonary vein isolation in patients with atrial fibrillation

The most common type of sustained arrhythmia is atrial fibrillation (AF). Pulmonary vein isolation (PVI) is the cornerstone of catheter ablation for atrial fibrillation, which has emerged as the primary therapeutic strategy for atrial fibrillation patients. Unfortunately, about one-third of patients experience recurrent atrial arrhythmias after the procedure.

How to ablate the septo-pulmonary bundle: a case-based review of percutaneous ablation strategies to achieve roof line block

Electrical conduction through cardiac muscle fibres separated from the main myocardial wall by layers of interposed adipose tissue are notoriously difficult to target by endocardial ablation alone. They are a recognised important cause for procedural failure due to the difficulties of delivering sufficient energy via the endocardial radiofrequency catheter to reach the outer epicardial layer without risking adverse events of the otherwise thin walled atria. Left atrial ablations for atrial fibrillation (AF) and tachycardia are commonly affected by the presence of several epicardial structures, with the septo-pulmonary bundle (SPB), Bachmann's bundle, and the ligament of Marshall all posing substantial challenges for endocardial procedures. Delivery of a transmural lesion set is essential for sustained pulmonary vein isolation and for conduction block across linear atrial lines which in turn has been described to translate into a reduced AF/atrial tachycardia recurrence rate. To overcome the limitations of endocardial-only approaches, surgical ablation techniques for epicardial or combined hybrid endo-epicardial ablations have been described to successfully target these connections. Yet, these techniques confer an increase in procedure complexity, duration, cost, and morbidity. Alternatively, coronary venous system ethanol ablation has been successfully employed by sub-selecting the vein of Marshall to facilitate mitral isthmus line block, although this approach is naturally limited to this area by the coronary venous anatomy. Increased awareness of the pathophysiological relevance of these epicardial structures and their intracardiac conduction patterns in the era of high-resolution 3D electro-anatomical mapping technology has allowed greater understanding of their contribution to the persistence of AF as well as failure to achieve transmural block by traditional ablation approaches. This might translate into novel catheter ablation strategies with procedural success rates comparable to surgical 'cut-and-sew' techniques. This review aims to give an overview of percutaneous catheter ablation strategies to target the SPB, an important cause of failed block across the roof line and isolation of the left atrial posterior wall and/or the pulmonary veins. Existing and investigational technologies will be discussed and an outlook of future approaches provided.

Safety of the Radiofrequency Balloon for Pulmonary Vein Isolation: A Focus on Lesion Metric Analysis of Posterior Electrodes

Previous clinical studies on pulmonary vein isolation (PVI) with radiofrequency balloons (RFB) reported safe and effective procedures for a 20 s RF delivery via posterior electrodes. Recent recommendations from the manufacturer suggest reducing the application time to 15 s on the posterior wall (PW) when facing the esophagus region. Here, we retrospectively assess whether 15 s of RF delivery time on posterior electrodes is safe while still ensuring lesion metrics of sufficient quality. This retrospective study included 133 patients with paroxysmal and persistent atrial fibrillation who underwent PVI using an RFB (Heliostar, Biosense Webster, Inc., Irvine, CA, USA) at two European centers. The ablation protocol was set for an RF duration of 20 s/60 s for the posterior/anterior electrodes. A multielectrode temperature probe was systematically used. In the case of an esophageal temperature rise (ETR) above 42 °C (ETR+), an endoscopic evaluation was performed. All posterior electrode lesion metric dynamics (temperature (T) and impedance (Z)) were collected from the RFB generator and analyzed offline. In total, 2435 posterior electrode applications were analyzed. With an RF delivery of 19.8 (19.7-19.8) s, the median impedance drop was 18.4 (12.2-25.2) Ω, while the temperature rise was 11.1 (7.1-14.9) °C. Accordingly, impedance (84.6 (79.3-90.2) Ω) and temperature plateaus (38 (35.3-41.1) °C) were reached at 13.9 (10.6-16) s and 16.4 (12.6-18.5) s, respectively. Overall, 99.6% and 95.8% of electrodes reached 90% (16.6 Ω) and 95% (17.5 Ω) of their impedance drops within 15 s of RF delivery, while 97.2% and 92.8% achieved 90% (34.2 °C) and 95% (36.1 °C) of their temperature rise to reach the plateaus within 15 s of RF delivery. An ETR >42 °C occurred in 37 (30.1%) patients after 17.7 ± 2.3 s of RF delivery. In the ETR+ group, the impedance drop and temperature rise on the posterior electrodes were higher compared to patients where ETR was <42 °C. Two asymptomatic thermal esophageal injuries were observed. In conclusion, 15 s of RF delivery on the posterior electrodes provides a good balance between safety, with no esophageal temperature rise, and efficacy with high-profile lesion metrics.

Innovations in ventricular tachycardia ablation

Catheter ablation of ventricular arrhythmias (VAs) has evolved significantly over the past decade and is currently a well-established therapeutic option. Technological advances and improved understanding of VA mechanisms have led to tremendous innovations in VA ablation. The purpose of this review article is to provide an overview of current innovations in VA ablation. Mapping techniques, such as ultra-high density mapping, isochronal late activation mapping, and ripple mapping, have provided improved arrhythmogenic substrate delineation and potential procedural success while limiting duration of ablation procedure and potential hemodynamic compromise. Besides, more advanced mapping and ablation techniques such as epicardial and intramyocardial ablation approaches have allowed operators to more precisely target arrhythmogenic substrate. Moreover, advances in alternate energy sources, such as electroporation, as well as stereotactic radiation therapy have been proposed to be effective and safe. New catheters, such as the lattice and the saline-enhanced radiofrequency catheters, have been designed to provide deeper and more durable tissue ablation lesions compared to conventional catheters. Contact force optimization and baseline impedance modulation are important tools to optimize VT radiofrequency ablation and improve procedural success. Furthermore, advances in cardiac imaging, specifically cardiac MRI, have great potential in identifying arrhythmogenic substrate and evaluating ablation success. Overall, VA ablation has undergone significant advances over the past years. Innovations in VA mapping techniques, alternate energy source, new catheters, and utilization of cardiac imaging have great potential to improve overall procedural safety, hemodynamic stability, and procedural success.

Impact of baseline pool impedance on lesion metrics and steam pops in catheter ablation

INTRODUCTION

Little is known about the impact of blood-pool local impedance (LI) on lesion characteristics and the incidence of steam pops.

METHODS

Radiofrequency applications at a range of powers (30, 40, and 50 W), contact forces (CF) (5, 15, and 25 g), and durations (15, 30, 45, and 120 s) using perpendicular/parallel catheter orientation were performed in 40 excised porcine preparations, using a catheter capable of monitoring LI (StablePoint©, Boston Scientific). To simulate the variability in blood-pool impedance, the saline-pool LI was modulated by calibrating saline concentrations. Lesion characteristics were compared under three values of saline-pool LI: 120, 160, and 200 Ω.

RESULTS

Of 648 lesions created, steam pops occurred in 175 (27.0%). When power, CF, time, and catheter orientation were adjusted, ablation at a saline-pool impedance of 160 or 200 Ω more than doubled the risk of steam pops compared with a saline-pool impedance of 120 Ω (Odds ratio = 2.31; p = .0002). Lesions in a saline-pool impedance of 120 Ω were significantly larger in surface area (50 [38-62], 45 [34-56], and 41 [34-60] mm2 for 120, 160, and 200 Ω, p < .05), but shallower in depth (4.0 [3-5], 4.4 [3.2-5.3], and 4.5 [3.8-5.5] mmfor 120, 160, and 200 Ω, respectively, p < .05) compared with the other two settings. The correlation between the absolute LI-drop and lesion size weakened as the saline-pool LI became higher (e.g., 120 Ω group (r2  = .30, r2  = .18, and r2  = .16, respectively for 120, 160, and 200 Ω), but the usage of %LI-drop (= absolute LI-drop/initial LI) instead of absolute LI-drop may minimize this effect.

CONCLUSIONS

In an experimental model, baseline saline-pool impedance significantly affects the lesion metrics and the risk of steam pops.

Utility and Limitations of Ablation Index for Guiding Therapy in Ventricular Myocardium

BACKGROUND

Ablation index (AI) is used for guiding therapy during pulmonary vein isolation. However, its potential utility in ventricular myocardium is unknown.

OBJECTIVES

This study sought to examine the correlation between AI and lesion dimensions in healthy and infarcted ventricles.

METHODS

In ex vivo experiments using healthy swine ventricles, the correlation between AI (400-1,200) and lesion dimensions was examined at fixed power (30 W) and contact force (CF) (15 g). To examine the accuracy of AI in predicting lesion dimensions created by different combinations of ablation parameters, applications with a similar prespecified AI value created using different power (30 vs 40 W), CF (15 vs 25 g) or impedance (130-170 Ω) were created. In in vivo experiments, the correlation between AI and lesion dimensions was examined in healthy and infarcted myocardium.

RESULTS

Ex vivo experiments (247 lesions, 36 hearts) showed good correlation between AI and lesion depth (R = 0.93; P < 0.001). However, in vivo experiments (9 healthy swine and 10 infarcted swine) showed moderate correlation in healthy myocardium (R = 0.64; P < 0.01) and poor correlation in infarcted myocardium (R = 0.23; P = 0.61). AI values achieved using different combinations of power, CF, and baseline impedance resulted in different lesion depths: Ablation at 30 W produced deeper lesions compared with 40 W, ablation with CF of 15 g produced deeper lesions compared with CF of 25 g, and ablation at lower impedance produced larger lesions at similar prespecified AI values (P < 0.01 for all).

CONCLUSIONS

AI has limited value for guiding ablation in ventricular myocardium, particularly scar. This may be related to small proportional significance of application duration and complex tissue architecture.

Facilitated Myocardial Ablation Using Heat-Sensitive Liposomes Containing Doxorubicin: A Proof-of-Concept Preclinical Study

The authors sought to evaluate a method for improving radiofrequency (RF) lesion durability using doxorubicin encased in heat-sensitive liposomes (HSL-dox). Using a porcine model, RF ablations were performed in the right atrium after systemic infusion of either HSL-dox or saline control given immediately before mapping and ablation. Lesion geometry was measured with voltage mapping immediately postablation and after 2 weeks of survival. After 2 weeks, lesions demonstrated less regression in scar area in HSL-dox-exposed animals compared with control animals. We demonstrate improved RF lesion durability in animals treated with HSL-dox, and the cardiotoxic effect was more pronounced after RF applications with higher power and longer duration.

Monitoring Spike Potential and Abrupt Impedance Rise with Concomitant Temperature/Contact Force Change for Timely Detection of the Occurrence of “Silent” or “Nonaudible” Steam Pop

Aim. Steam pop (SP) during radiofrequency catheter ablation (RFCA) for pulmonary vein isolation (PVI) may cause cardiac perforation, which may require drainage and emergent thoracotomy or even lead to death. Data investigating the timely detection of the occurrence of “silent” or “nonaudible” SP events are limited. Methods and Results. A total of 516 consecutive atrial fibrillation (AF) patients who underwent index PVI were included in this retrospective observational study. The duration, power, impedance, temperature, and contact force (CF) of RFCA were continually monitored and recorded throughout the procedure. A total of 15 (2.9%) audible SP events occurred in 14 patients; 2 of the patients developed pericardial tamponade, 1 patient underwent drainage, and 1 patient underwent emergent thoracotomy. The time from RFCA initiation to the occurrence of audible SP was 19.4 ± 6.9 s. Abrupt temperature change occurred in 13 (86.7%) of the 15 SP events, of which 8 (53.3%) exhibited an abrupt temperature rise of 2.3 ± 1.0°C, 5 (33.3%) exhibited an abrupt temperature drop of 2.3 ± 1.3°C, and 2 (13.3%) exhibited no discernible temperature change. Conclusions. In conclusion, simultaneously recorded spike potentials and abrupt impedance rise with concomitant temperature and/or CF change could be a feasible method for the timely detection of the occurrence of audible, “silent,” or “nonaudible” SP events, particularly in regions where the risk of perforation may be of concern.

Development of a clinically relevant ex vivo model of cardiac ablation for testing of ablation catheters

INTRODUCTION

Reliable ex vivo cardiac ablation models have the potential to increase catheter testing throughput while minimizing animal usage. The goal of this work was to develop a physiologically relevant ex vivo swine model of cardiac ablation displaying minimal variability and high repeatability and identify and optimize key parameters involved in ablation outcomes.

METHODS AND RESULTS

A root cause analysis was conducted to identify variables affecting ablation outcomes. Parameters associated with the tissue, bath media, and impedance were identified. Variables were defined experimentally and/or from literature sources to best mimic the clinical cardiac ablation setting. The model was validated by performing three independent replicates of ex vivo myocardial ablation and a direct comparison of lesion outcomes of the ex vivo swine myocardial and in vivo canine thigh preparation (TP) models. Replicate experiments on the ex vivo model demonstrated low variance in ablation depth (6.5 ± 0.6, 6.3 ± 0.6, 6.2 ± 0.4 mm) and width (10.4 ± 1.1, 9.7 ± 1.0, 9.9 ± 0.9 mm) and no significant differences between replicates. In a direct comparison of the two models, the ex vivo model demonstrated ablation depths similar to the canine TP model at 35 W (6.9 ± 1.0, and 7.0 ± 0.9 mm) and 50 W (8.0 ± 0.7, and 8.4 ± 0.7 mm), as well as similar power to depth ratios (15% and 19% for the ex vivo cardiac and in vivo TP models, respectively).

CONCLUSION

The ex vivo model exhibited strong lesion reproducibility and power-to-depth ratios comparable to the in vivo TP model. The optimized ex vivo model minimizes animal usage with increased throughput, lesion characteristics similar to the in vivo TP model, and ability to discriminate minor variations between different catheter designs.

Optimal local impedance parameters for successful pulmonary vein isolation in patients with atrial fibrillation

INTRODUCTION

Local impedance (LI) parameters of IntellaNav STABLEPOINT for successful pulmonary vein isolation (PVI) of atrial fibrillation (AF) remain unclear. The purpose of this study was to seek LI data achieving successful PVI.

METHODS

Consecutive AF patients who underwent catheter ablation with STABLEPOINT were prospectively enrolled in two centers. PVI was performed under a constant 35-or 40-watt power, 20-s duration, and >5-g contact force. The operators were blinded to the LI data. The characteristics of all ablation points with/without conduction gaps (Unsuccess or Success tags) after the first-attempt PVI were evaluated for the right/left PVs and anterior/posterior wall (RPV/LPV and AW/PW, respectively), and cutoff values of LI data were calculated for successful lesion formation.

RESULTS

A total of 5257 ablation points in 102 patients (65 [58-72] years old, 65.7% male) were evaluated. The LI drop values were higher in the Success tags than Unsuccess tags on the LPV-AW and RPV-AW/PW (p < .001), except for the LPV-PW (p = .105). The %LI drop values (LI drop/initial LI) were higher for the Success tags in all areas (15.8 [12.2%-19.6%] vs. 11.6 [9.7%-15.6%] in LPV-AW: p < .001, 15.0 [11.5%-19.3%] vs. 11.4 [8.7%-17.3%] in LPV-PW: p = .035, 15.3 [11.5%-19.4%] vs. 9.9 [8.1%-13.7%] in RPV-AW: p < .001, and 13.3 [10.1%-17.4%] vs. 8.1 [6.3%-9.5%] in RPV-PW, p < .001). The LI drop and %LI drop cutoff values were 20.0 ohms and 11.6%, respectively.

CONCLUSIONS

An insufficient LI drop with STABLEPOINT was associated with a gap formation during PVI, and the best cutoff values for the LI drop and %LI drop were 20.0 ohms and 11.6%, respectively.

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.

Multipolar Ablation Using Mapping Electrodes: A Novel Approach to Intramural Arrhythmia Substrates

Intramural ventricular arrhythmias are challenging to treat. Adjunctive techniques such as bipolar ablation, ethanol injection, use of a needle catheter, or surgery have been described. These are often not readily available. This is a case report of a patient with refractory intramural ventricular arrhythmia that was ablated by incorporating electrodes of a mapping catheter into the ablation circuit. The results of ex vivo experiments to determine the characteristics of multipolar ablation lesions using different ablation settings are reported. The feasibility of generating transmural lesions with multipolar ablation in vivo in a porcine model was tested.

Combined contact force and local impedance dynamics during repeat atrial fibrillation catheter ablation

Background: Optimal lesion formation during catheter-based radiofrequency current (RFC) ablation depends on electro-mechanical tip-tissue coupling measurable via contact force (CF) and local impedance (LI) monitoring. We aimed to investigate CF and LI dynamics in patients with previous atrial fibrillation (AF) ablation who frequently present with heterogenous arrhythmia substrate.

Methods: Data from consecutive patients presenting for repeat AF or atrial tachycardia ablation using a novel open-irrigated single-tip ablation catheter were studied. RFC applications were investigated regarding CF, LI and the maximum LI drop (∆LI) for evaluation of ablation efficacy. ∆LI > 20 Ω was defined as a successful RFC application.

Results: A total of 730 RFC applications in 20 patients were analyzed. Baseline CF was not associated with baseline LI (R = 0.06, p = 0.17). A mean CF < 8 g during ablation resulted in lower ∆LI (<8 g: 13 Ω vs. ≥ 8 g: 16 Ω, p < 0.001). Baseline LI showed a better correlation with ∆LI (R = 0.35, p < 0.001) compared to mean CF (R = 0.17, p < 0.001). Mean CF correlated better with ∆LI in regions of low (R = 0.31, p < 0.001) compared to high (R = 0.21, p = 0.02) and intermediate voltage (R = 0.17, p = 0.004). Combined CF and baseline LI predicted ∆LI > 20 Ω (area under the receiver operating characteristic curve (AUC) 0.75) better compared to baseline LI (AUC 0.72), mean CF (AUC 0.60), force-time integral (AUC 0.59) and local bipolar voltage (0.55).

Conclusion: Combination of CF and LI may aid monitoring real-time catheter-tissue electro-mechanical coupling and lesion formation within heterogenous atrial arrhythmia substrate in patients with repeat AF or atrial tachycardia ablation.

Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In silico Modeling

Background: Baseline impedance, radiofrequency current, and impedance drop during radiofrequency catheter ablation are thought to predict effective lesion formation. However, quantifying the contributions of local versus remote impedances provides insights into the limitations of indices using those parameters. Methods: An in silico model of left atrial radiofrequency catheter ablation was used based on human thoracic measurements and solved for (1) initial impedance (Z), (2) percentage of radiofrequency power delivered to the myocardium and blood (3) total radiofrequency current, (4) impedance drop during heating, and (5) lesion size after a 25 W−30 s ablation. Remote impedance was modeled by varying the mixing ratio between skeletal muscle and fat. Local impedance was modeled by varying insertion depth of the electrode (ID). Results: Increasing the remote impedance led to increased baseline impedance, lower system current delivery, and reduced lesion size. For ID = 0.5 mm, Z ranged from 115 to 132 Ω when fat percentage varied from 20 to 80%, resulting in a decrease in the RF current from 472 to 347 mA and a slight decrease in lesion size from 5.6 to 5.1 mm in depth, and from 9.2 to 8.0 mm in maximum width. In contrast, increasing the local impedance led to lower system current but larger lesions. For a 50% fat−muscle mixture, Z ranged from 118 to 138 Ω when ID varied from 0.3 to 1.9 mm, resulting in a decrease in the RF current from 463 to 443 mA and an increase in lesion size, from 5.2 up to 7.5 mm in depth, and from 8.4 up to 11.6 mm in maximum width. In cases of nearly identical Z but different contributions of local and remote impedance, markedly different lesions sizes were observed despite only small differences in RF current. Impedance drop better predicted lesion size (R2 > 0.93) than RF current (R2 < 0.1). Conclusions: Identical baseline impedances and observed RF currents can lead to markedly different lesion sizes with different relative contributions of local and remote impedances to the electrical circuit. These results provide mechanistic insights into the advantage of measuring local impedance and identifies potential limitations of indices incorporating baseline impedance or current to predict lesion quality.

Effect of Baseline Impedance in Radiofrequency Delivery on Lesion Characteristics and the Relationship Between Impedance and Steam Pops

Objective

To explore the effects of baseline impedance (R) and power (P) on radiofrequency ablation (RFA) lesion characteristics and their correlation with steam pops using ThermoCool SmartTouch-SF (STSF) catheters in the porcine heart.

Method

A porcine left ventricle was submerged in 37°C saline ex vivo, and the experiment was performed with various P (P = 30, 40, 50, and 60 W) and multiple R loads (R = 80–100, 100–140, 140–180, and 180–220 Ω) to reach the target ablation index (AI; AI = 350, 450, and 500) or reach the target ablation time using a fixed contact force (CF; CF = 10–15 g) and the same saline irrigation (30 W/8 ml/min or 40–60 W/15 ml/min), repeated five times under each condition.

Results

The surface diameter, maximum diameter, depth, and volume of the lesions were strongly correlated with the AI (P = 40 W, R = 100–140 Ω, CF = 10–15 g) (r = 0.5412; r = 0.7889; r = 0.9366; and r = 0.913, respectively; all p < 0.05). As the value of R increased, the maximum diameter, depth, and volume of the lesions significantly increased (AI = 350, P = 30 W). Moreover, the higher the baseline value of R, the greater the absolute value of the R decrease (r = 0.9035, p < 0.05, Y = 0.2759 × X – 18.33). Under high power and high impedance, the occurrence rate of steam pops was high (P = 60 W, R = 180–220 Ω, AI when a steam pop occurred: 480 ± 26.5, ablation time: 11.29 ± 1.04 s).

Conclusion

Radiofrequency catheter ablation (RFCA) in power-controlled mode resulted in various lesion characteristics that were related to diverse baseline Rs. In addition, the incidence of steam pops was strongly correlated with high baseline R and high P.

Impact of baseline impedance of pulmonary vein antrum on success of catheter ablation for paroxysmal atrial fibrillation guided by ablation index

Objective

Ablation index (AI) is an effective ablation quality marker. Impedance is also an important factor for lesion formation. The present study evaluated the influence of the baseline impedance in the effect of ablation for atrial fibrillation (AF) guided by AI.

Methods

This was a retrospective study. 101 patients with paroxysmal AF (PAF) were enrolled. All patients underwent radiofrequency ablation guided by the same AI strategy. The ablation strategy was pulmonary vein (PV) isolation with non-PV triggers ablation. The baseline impedance of the ablation points was recorded. The patients were followed up every 3 months or so.

Results

During a median follow-up of 12 (4–14) months, freedom from AF/atrial tachycardia recurrence were 82.2%. No difference existed in baseline characteristics between the success group and the recurrence group. The average baseline impedance was 124.3 ± 9.7 Ω. The baseline impedance of the ablation points in success group was lower compared to the recurrence group (122.9 ± 9.4 vs. 130.5 ± 8.8 Ω, P < 0.01). The ratio of impedance drop in the success group was higher than the recurrence group ([8.8 ± 1.4]% vs. [8.1 ± 1.2]%, P = 0.03). Multivariate analysis revealed that baseline impedance, PAF duration and AI were the independent predictors of AF recurrence. The cumulative free of recurrence rate of low-impedance group (≤ 124 Ω, n = 54) was higher than that of high-impedance group.

Conclusion

Baseline impedance correlates with clinical outcome of radiofrequency ablation for PAF guided by AI. Higher impedance in the same AI strategy may result in an ineffective lesion which probably causes recurrence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02530-y.

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.

Computer modeling of radiofrequency cardiac ablation: 30 years of bioengineering research

This review begins with a rationale of the importance of theoretical, mathematical and computational models for radiofrequency (RF) catheter ablation (RFCA). We then describe the historical context in which each model was developed, its contribution to the knowledge of the physics of RFCA and its implications for clinical practice. Next, we review the computer modeling studies intended to improve our knowledge of the biophysics of RFCA and those intended to explore new technologies. We describe the most important technical details of the implementation of mathematical models, including governing equations, tissue properties, boundary conditions, etc. We discuss the utility of lumped element models, which despite their simplicity are widely used by clinical researchers to provide a physical explanation of how RF power is absorbed in different tissues. Computer model verification and validation are also discussed in the context of RFCA. The article ends with a section on the current limitations, i.e. aspects not yet included in state-of-the-art RFCA computer modeling and on future work aimed at covering the current gaps.

Impact of catheter contact angle on lesion formation and durability of pulmonary vein isolation

Purpose

This study is aimed to evaluate the impact of catheter contact angle on lesion formation and durability of pulmonary vein isolation (PVI).

Methods

Both in vitro experiment and retrospective observational study were conducted. For in vitro experiment, radiofrequency lesions were created on explanted swine hearts in three different catheter contact angles (0°, 45°, and 90°). In the retrospective observational study, we assessed patients who had undergone repeat catheter ablation due to atrial fibrillation recurrence after initial PVI. When pulmonary vein (PV) reconnection was observed, we analyzed the previous ablation points within and without the gap area. The gap areas were where ablation had changed the PV activation sequence or eliminated the PV potential in the repeat session.

Results

In the in vitro experiment, lesion width was the smallest (5.3 ± 0.4 mm) in perpendicular contact compared to 0° (vs 5.8 ± 0.5 mm, p = 0.040) and 45° (vs 6.4 ± 0.4 mm, p < 0.001). In the retrospective observational study, we assessed 666 tags of 16 patients with PV reconnections, and 60 tags were in the gap area. Tags in the gap area had longer interlesion distance (odds ratio [OR] 1.49, p < 0.001), greater contact force variability (OR 1.03, p = 0.008), and higher rate of perpendicular contact (OR 3.26, p < 0.001) on multivariate analysis.

Conclusions

Perpendicular contact was associated with a smaller lesion and higher rate of PV reconnection.

Local impedance for the optimization of radiofrequency lesion delivery: A review of bench and clinical data

INTRODUCTION

Radiofrequency catheter ablation is a cornerstone of treatment for many cardiac arrhythmias. Progression in three-dimensional mapping and contact-force sensing technologies have improved our capability to achieve success, but challenges still remain.

METHODS

In this article, we discuss the importance of overall circuit impedance in radiofrequency lesion formation. This is followed by a review of the literature regarding recently developed "local impedance" technology and its current and future potential applications and limitations, in the context of established surrogate markers currently used to infer effective ablation.

RESULTS

We discuss the role of local impedance in assessing myocardial substrate, as well as its role in clinical studies of ablation. We also discuss safety considerations, limitations and ongoing research.

CONCLUSION

Local impedance is a novel tool which has the potential to tailor ablation in a manner distinct from other established metrics.

Ablation of typical atrial flutter using mini electrode measurements for maximum voltage‐guided ablation: A randomized, controlled trial

Background

Novel ablation catheters with mini electrode (ME) sensing have become available but their utility is unclear. We investigated whether ablation of the cavotricuspid isthmus (CTI) for atrial flutter (AFL) would be improved using ME signals.

Methods

Sixty‐one patients (76% male, 63 ± 10 years) with CTI‐dependent AFL underwent ablation using a maximum voltage‐guided approach, randomized to either standard 8 mm non‐irrigated catheter with bipolar signals or IntellaTip MiFi catheter using ME signals alone.

Results

Acute bidirectional block was achieved in 97%. Mean follow‐up was 16.7 ± 10 months. The median number of ablation lesions was 13 in both groups (range 3–62 vs. 1–43, p = .85). No significant differences were observed in AFL recurrences (17% vs. 11%, p = .7), median procedure durations (97 min [interquartile range (IQR), 71–121] vs. 87 min [IQR, 72–107], p = .55) or fluoroscopy times (31 min [IQR, 21–52] vs. 38 min [IQR, 25–70], p = .56). Amplitudes of ME signals were on average 160% greater than blinded bipolar signals. In 23.7% of lesions where bipolar signals were difficult to interpret, 13.6% showed a clear ME signal.

Conclusions

There was no difference in the effectiveness of CTI ablation guided by ME signals, compared with using bipolar signals from a standard 8 mm ablation catheter. While ME signal amplitudes were larger and sometimes present when the bipolar signal was unclear, this did not improve procedural characteristics or outcomes. The results suggest future research should focus on lesion integrity rather than signal sensing.

Short-Time Impedance Spectroscopy Using a Mode-Switching Nonsinusoidal Oscillator: Applicability to Biological Tissues and Continuous Measurement

Herein, we propose an impedance spectroscopy method using a mode-switching nonsinusoidal oscillator and apply this method for measuring the impedance of biological tissues and continuous impedance measurement. To obtain impedance spectra over a wide frequency range, we fabricated a novel nonsinusoidal oscillator incorporating binary counters and analog switches. This oscillator could periodically switch oscillation frequency through the mode switching of the feedback resistor. From the oscillation waveform at each oscillation frequency of this circuit (oscillator), we determined the impedance spectrum of a measured object using the discrete-time Fourier transform. Subsequently, we obtained the broad impedance spectrum of the measured object by merging odd-order harmonic spectral components up to the 19th order for each oscillation frequency. From the measured spectrum, the resistive and capacitive components of the circuit simulating bioimpedance were estimated with high accuracy. Moreover, the proposed method was used to measure the impedance of porcine myocardium; changes in the impedance spectrum of the myocardial tissue due to coagulation could be measured. Furthermore, rapid variations in the resistance value of a CdS photocell could be continuously measured using the proposed method.

Evaluation of different ablation strategies verifying the optimal overlap ratio in point-by-point laser balloon ablation for patients with atrial fibrillation

Background

Optimal overlap ratio remains unclear in point-by-point laser balloon (LB) ablation.

Objective

This study sought to determine the optimal overlap strategy with target energies on the acute and chronic outcomes in LB pulmonary vein (PV) isolation (PVI).

Methods

Consecutive 38 patients (148 PVs) with atrial fibrillation underwent the first-generation LB PVI with the following protocols based on the overlap ratios for each PV anterior/posterior wall: 50%/50% (13 patients [49 PVs], group A), 50%/25% (15 patients [60 PVs], group B), and 25%/25% (10 patients [39 PVs], group C). High energies (240–255 J: 12 W / 20 seconds, 8.5 W / 30 seconds), moderate energies (200–210 J: 10 W / 20 seconds, 7 W / 30 seconds), and low-to-moderate energies (low, 165–170 J: 5.5 W / 30 seconds, 8.5 W / 20 seconds) were targeted for left PV anterior walls, right PV anterior walls, and bilateral PV posterior walls, respectively. First-pass PVI, the other procedure-related data, and atrial tachyarrhythmia recurrences were analyzed.

Results

First-pass PVI rate per PV was higher in group A (94%) than in group B (88%) and group C (62%) (P < .001). All PVs were finally isolated. First-pass time, total LB PVI time, complications, and atrial tachyarrhythmia recurrences during a mean follow-up of 11 ± 5 months did not differ between the groups. A few residual gaps after first-pass LB ablations were found for PV anterior walls even in group A and group B.

Conclusion

Sufficiently overlapped LB ablation promises a high rate of first-pass PVI without adverse outcomes. High energy could be required for PV anterior walls.

Durability of Left Atrial Lesions After Ethanol Infusion in the Vein of Marshall

OBJECTIVES

The aim of this study was to assess the persistence of left atrial (LA) lesions created by ethanol infusion in the vein of Marshall (EIVM) by electroanatomical mapping on repeat catheter ablation for recurrent atrial tachyarrhythmia.

BACKGROUND

Little is known about the durability of LA lesions created by EIVM.

METHODS

The study included consecutive patients who underwent EIVM for persistent atrial fibrillation or perimitral LA flutter (index procedure) and repeat catheter ablation for recurrent atrial tachyarrhythmia or atrial fibrillation at a single center between January 2019 and April 2020. The acute effect of EIVM was assessed at the index procedure by comparing the area of bipolar voltage <0.05 mV in the vein of Marshall (VOM) region before and immediately after EIVM. The long-term effect of EIVM was assessed by comparing this area in the VOM region between the redo procedure and the index procedure.

RESULTS

Twenty-four consecutive patients (mean age 68.6 ± 6.1 years, 58% men) underwent redo procedures after previous EIVM for persistent atrial fibrillation (n = 21 [88%]) or perimitral LA flutter (n = 5 [21%]). In each patient, the EIVM-related lesion persisted, with a chronic scar in the VOM region (median 13.1 cm² [interquartile range: 8.1-15.9 cm²] vs 12.4 cm² [interquartile range: 7.6-15.7 cm²] acutely, respectively). One quarter of patients (9 of 20) had late mitral isthmus reconnection, which was located at the mitral annular edge or in the coronary sinus.

CONCLUSIONS

Atrial lesions created by EIVM are durable, which reinforces the efficacy profile of EIVM. Reconduction sites in the mitral isthmus are located at the edge of the scar and in the coronary sinus.

Novel concepts in atrial fibrillation ablation-breaking the trade-off between efficacy and safety

Despite substantial technological and procedural advances that have improved the efficacy and safety of AF ablation in recent years, the long-term durability of ablation lesions is still not satisfactory. There also remains concern regarding rare but potentially life-threatening procedure-related complications like cardiac tamponade and atrioesophageal fistulae. Current ablation strategies are aiming to optimize the trade-off between efficacy and safety, where more extensive ablation appears to inevitably increase the risk of collateral injury. However, new forms of energy application may have the potential to resolve this quandary. The emerging concept of high power-short duration radiofrequency ablation features a more favorable lesion geometry that appears ideally suited to create contiguous lesions in the thin-walled atrium. Moreover, novel non-thermal ablation methods based on electroporation appear to provide a unique selectivity for cardiomyocytes and to spare surrounding tissues composed of other cell types. Both, high power-short duration and electroporation ablation might have the potential to break the trade-off between effective lesions and collateral damage and to substantially improve risk-benefit ratios in AF ablation. In addition, both approaches lead to considerable reductions in ablation times. However, their putative benefits regarding efficacy, efficiency, and safety remain to be proven in randomized controlled trials.

Feasibility and effectiveness of endoscopic irreversible electroporation for the upper gastrointestinal tract: an experimental animal study

Irreversible electroporation (IRE) is a local non-thermal ablative technique currently used to treat solid tumors. Here, we investigated the clinical potency and safety of IRE with an endoscope in the upper gastrointestinal tract. Pigs were electroporated with recently designed endoscopic IRE catheters in the esophagus, stomach, and duodenum. Two successive strategies were introduced to optimize the electrical energy for the digestive tract. First, each organ was electroporated and the energy upscaled to confirm the upper limit energy inducing improper tissue results, including bleeding and perforation. Excluding the unacceptable energy from the first step, consecutive electroporations were performed with stepwise reductions in energy to identify the energy that damaged each layer. Inceptive research into inappropriate electrical intensity contributed to extensive hemorrhage and bowel perforation for each tissue above a certain energy threshold. However, experiments performed below the precluded energy accompanying hematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays showed that damaged mucosal area and depth significantly decreased with decreased energy. Relevant histopathology showed infiltration of inflammatory cells with pyknotic nuclei at the electroporated lesion. This investigation demonstrated the possibility of endoscopic IRE in mucosal dysplasia or early malignant tumors of the hollow viscus.

Derivation and Verification of the Relationship between Ablation Index and Baseline Impedance

Objective

To explore the quantitative adjustment of ablation index (AI) under different baseline impedance to achieve similar lesion dimensions.

Methods

(1) Keeping the AIs relatively constant, the lesion dimensions in different baseline impedances were studied. (2) According to Joule's law, Q = I²RT, keeping the current (I) unchanged, the powers corresponding to different baseline impedances can be obtained. Under different baseline impedances and corresponding powers, the swine hearts were ablated for 30 s in simulated human circumstances. The baseline impedances, the lesion dimensions, and AIs were recorded. And the derivation of empirical formula was achieved according to the AIs and baseline impedance values in similar lesions dimension. (3) Basic AI and baseline impedance (AI₀/R₀) were set as 400/120 Ω in the common AI groups and 550/120 Ω in the high AI groups, AI values in different baseline impedances were calculated using the empirical formula, and the corresponding lesion dimensions were measured to verify this formula.

Results

(1) Higher baseline impedances were related to smaller lesion dimensions at similar AIs. (2) The lesion dimensions were roughly the same after modulating the baseline impedance and power to keep the electric current relatively constant. The relationship between AI and R fitted with experimental data is AI = 1.9933R + 203.61 (r = 0.9649), and the formula derived is ΔAI = (AI₀ − 203)/R₀ × ΔR. (3) Under the guidance of the empirical formula, there was no significant difference in lesion dimensions between the standard group and the formula guiding groups when AI₀ = 400, but there was a shrinking tendence when AI > 700.

Conclusion

The lesion depths are negatively correlated with baseline impedance at a certain AI. The relationship between baseline impedance and AI is “ΔAI = (AI₀ − 203)/R₀ × ΔR”. It is verified that when the AI is not too high, the empirical formula can be used to guide the quantitative adjustment of AIs at different baseline impedance, and the lesion depths achieved are roughly the same.

Esophageal luminal temperature rise during atrial fibrillation ablation is associated with lower radiofrequency electrode distance and baseline impedance

INTRODUCTION

Esophageal injury during atrial fibrillation (AF) ablation is a life-threatening complication. We sought to measure the association of esophageal temperature attenuation with radiofrequency (RF) electrode impedance, contact force, and distance from the esophagus.

METHODS

The retrospective study cohort included 35 patients with mean age 64 ± 10 years, of whom 74.3% were male, and 40% had persistent AF. All patients had undergone preprocedural cardiac magnetic resonance (CMR) followed by AF ablation with luminal esophageal temperature monitoring. Lesion locations were co-registered with CMR image segmentations of left atrial and esophageal anatomy. Luminal esophageal temperature, time matched RF lesion data, and ablation distance from the nearest esophageal location were collected as panel data.

RESULTS

Luminal esophageal temperature changes corresponding to 3667 distinct lesions, delivered with mean power 27.9 ± 5.5 W over a mean duration of 22.2 ± 10.5 s were analyzed. In multivariable analyses, clustered per patient, examining posterior wall lesions only, and adjusted for lesion power and duration as set by the operator, lesion distance from the esophagus (-0.003°C/mm, p < .001), and baseline impedance (-0.015°C/Ω, p < .001) were associated with changes in luminal esophageal temperature.

CONCLUSION

Esophageal luminal temperature rises are associated with shorter lesion distance from esophagus and lower baseline impedance during RF lesion delivery. When procedural strategy requires RF delivery near the esophagus, selection of sites with higher baseline impedance may improve safety.

Catheter Ablation Using Half-Normal Saline and Dextrose Irrigation in an Ovine Ventricular Model

OBJECTIVES

This study hypothesized that catheter ablation in healthy ovine ventricular myocardium using low ionic 0.45% saline (half-normal saline [HNS]) and nonionic 5% dextrose in water (D5W) would result in larger lesions compared with use of 0.9% saline (normal saline [NS]).

BACKGROUND

Limited data exist regarding the safety and efficacy of catheter ablation using low and nonionic irrigants.

METHODS

Open irrigated ablation was performed on 14 beating ovine hearts (NS, n = 5; HNS, n = 4; D5W, n = 5). Ablation was delivered by using identical parameters (ie, 30 W in power control mode, 60-second duration, contact force of 10-20 g in the endocardial ventricles and 5-10 g in the epicardium). Catheter orientation and tissue contact were optimized by using intracardiac echocardiography. Lesion width, depth, and volume and number of steam pops were compared.

RESULTS

Overall, 196 lesions were analyzed (mean duration: 56.7 ± 8.3 seconds; mean contact force: 15.3 ± 6.1 g; and mean impedance drop: 31 ± 19.1 Ω). Compared with NS, HNS and D5W resulted in larger lesion volumes (NS 349.2 ± 245.1 mm³ vs HNS 645.7 ± 386.4 mm³ vs D5W 633.2 ± 387.1 mm³; HNS vs NS, P < 0.001; D5W vs NS, P < 0.001; D5W vs HNS, P = 0.87). However, D5W was associated with higher steam pop occurrence (NS 5% vs HNS 11% vs D5W 35%; HNS vs NS, P = 0.22; D5W vs NS, P < 0.001; D5W vs HNS, P = 0.002).

CONCLUSIONS

Catheter ablation with HNS and D5W resulted in larger ablation lesions compared with NS but similar lesion dimensions between HNS and D5W. The increase in lesion size with HNS and D5W was associated with a higher incidence of steam pops, especially with D5W, compared with NS.

Optimizing Durability in Radiofrequency Ablation of Atrial Fibrillation

Radiofrequency ablation (RFA) remains a highly effective therapy in the management of paroxysmal atrial fibrillation (PAF) and is an important therapeutic option in the management of persistent atrial fibrillation (PeAF) when clinically indicated. Lesion size is influenced by many parameters, which include those related to energy application (RFA power, temperature, and time), delivery mechanism (electrode size, orientation, and contact force), and the environment (blood flow and local tissue contact, stability, and local impedance). Successful durable RFA is dependent on achieving lesions that are reliably transmural and contiguous, whilst also avoiding injury to the surrounding structures. This review focuses on the variables that can be adjusted in connection with RFA to achieve long-lasting lesions that enable patients to derive the maximum sustained benefit from pulmonary vein isolation and additional lesion sets if utilized.

Comparison of the lesion formation and safety in ex vivo porcine heart study: Using ThermoCool SmartTouch and ThermoCool SmartTouch-SF catheters

BACKGROUND

The study was performed to compare the efficacy and safety during radiofrequency ablation (RFA) using ThermoCool SmartTouch (ST) and ThermoCool SmartTouch-SF (STSF) catheters in the porcine heart.

METHODS AND RESULTS

RFA was performed on the porcine myocardium by using two irrigated ablation catheters. Three groups were divided based on the different contact forces (CFs): low contact force (LCF) (1-3 g), medium contact force (MCF) (5-10 g), and high contact force (HCF) (15-20 g). In each group, RFA was delivered at four power settings of 30, 40, 50, 60 W. At each power, RFA was applied to reach the target ablation index (AI) of 350, 450, and 500. Altogether, 360 RF lesions were created by using 72 ablation conditions. AI value was positively correlated with lesion size using ST and STSF catheters. At a fixed power, lesion dimensions significantly smaller in the LCF group, whereas did not differ between MCF and HCF groups. Furthermore, at a fixed CF, lesion dimensions increased with power set at 40 W compared with 30 W but decreased with high-power RF energy (50 and 60 W). Although the average lesion surface diameter and the maximum diameter was increased using the STSF catheter, there were no significant differences in LV between the two catheters. The steam pop provoked more frequently using ST catheter and showed a negative correlation with CF and positive correlation with high-power energy.

CONCLUSION

The STSF catheter is safer and equally effective in lesion formation compared with the ST catheter. LV was increased along with the early increase of CF and power, whereas a further increase of CF and power significantly reduces the lesion size.

Relationship Between Ablation Lesion Size Estimated by Ablation Index and Different Ablation Settings-an Ex Vivo Porcine Heart Study

This study aimed to verify the reliability of ablation index (AI) for ablation lesion estimating with different settings for radiofrequency (RF) parameters: power, impedance, contact angles, irrigation rate, temperature of irrigation saline, and irrigation solution. RF ablations (N = 66) were performed on ex vivo porcine left ventricle submerged in 37 °C saline. The aforementioned ablation parameters were changed to measure whether the size of the ablation lesion was consistent at a fixed AI value of 500. The maximum lesion diameter (r = - 0.631, P = 0.028), depth (r = - 0.896, P < 0.001), and volume (r = - 0.745, P < 0.005) were significantly reduced with an increase of the impedance. The lesion depth (P < 0.05) and the lesion volume (P < 0.05) were significantly larger with glucose irrigation than saline irrigation. In conclusion, at a fixed AI value, impedance and irrigation solution have impact on the ablation lesions, which could affect the accuracy of AI formula to estimate ablation lesion size. Graphical abstract.