Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus

Novel method for electrode-tissue contact measurement with multi-electrode catheters

Aims

With multi-electrode catheters, measuring contact force (CF) on each electrode is technically challenging. Present electrical methods, like the electrical coupling index (ECI) may yield false positive values in pulmonary veins. We developed a novel method that measures electrode-interface resistance (IR) by applying a very local electrical field between neighbouring catheter electrodes while measuring voltage between each catheter electrode and a skin patch. The aim of this study was to evaluate the new IR method to measure electrode-tissue contact.

Methods and results

In vitro, effects of remote high-impedance structures were studied. In addition, both ECI and IR were directly compared with true electrode-tissue CF. In five pigs, the influence of high-impedance pulmonary tissue on ECI and IR was investigated while navigating the free floating catheter into the caval veins. Inside the left atrium (LA), IR was directly compared with CF. Finally, multi-electrode IR measurements in the LA and inferior pulmonary vein (IPV) were compared. In vitro, IR is much less affected by remote high-impedance structures than ECI (3% vs. 32%). Both IR and ECI strongly relate to electrode-tissue CF (r2 = 0.84). In vivo, and in contrast to ECI, IR was not affected by nearby pulmonary tissue. Inside the LA, a strong relation between IR and CF was found. This finding was confirmed by simultaneous multi-electrode measurements in LA and IPV.

Conclusion

Data of the present study suggest that electrode-tissue contact affects the IR while being highly insensitive to remote structures. This method facilitates electrode-tissue contact measurements with circular multi-electrode ablation catheters.

Identification of Radiofrequency Ablation Catheter Parameters That May Induce Intracardiac Steam Pops: Direct Visualization of Elicitation in Reanimated Swine Hearts

Radiofrequency, a common ablation modality, is used clinically to terminate cardiac arrhythmias. With excessive heating, complications sometimes occur when the applied energy generates steam pops, which cause release of energy in the form of tissue and/or air emboli. In this study, we investigated numerous parameters potentially associated with intracardiac steam pops including (1) wattage, (2) catheter tip temperature, (3) catheter irrigation, (4) anatomic site, and (5) repeat ablations at a given site. Using unique Visible Heart® methodologies in reanimated swine hearts, we visualized 539 ablations; steam pops developed in 140 of these ablations. The incidence of steam pops significantly increased for both nonirrigated and irrigated ablations at 40 W (p < 0.005), and for nonirrigated ablations with catheter contact angles perpendicular to the tissue or that encompassed larger surface areas (p < 0.05). To minimize the incidence of steam pops, clinicians performing radiofrequency ablations must consider catheter parameters.

Ablation of recurrent malignant idiopathic ventricular tachycardia: When proper diagnosis and success is a matter of contact

Effective and stable contact between the catheter tip and the tissue is crucial for both mapping and lesion formation during cardiac ablation procedures. Contact force catheter may be not only a therapeutic approach to arrhythmias, but also a tool for achieving accurate characterization of the arrhythmic substrate.

Benefit of Contact Force Sensing Catheter Technology for Successful Left Atrial Anterior Line Formation: A Prospective Randomized Trial

Introduction

The value of contact force information for ablation of LA anterior line is unknown. In a prospective randomized clinical trial, we investigated if information on contact force during left atrial (LA) anterior line ablation reduces total radiofrequency time and results in higher rates of bidirectional line block in patients undergoing pulmonary vein isolation (PVI) plus substrate modification.

Methods

We included patients with indication for pulmonary vein isolation (PVI) and additional substrate modification. For LA anterior line ablation, patients were randomized to contact force information visible (n=35) or blinded (n=37). Patients received contrast enhanced cardiac magnetic resonance imaging (cMRI) before and 3-6 months after ablation to visualize the LA anterior line. Primary endpoint was radiofrequency time to achieve bidirectional line block. Secondary endpoints were completeness of the LA anterior line on cMRI, distribution of contact force, procedural data, adverse events, and 12 months success rate.

Results

In 72 patients (64±9 years, 68% male), bidirectional LA anterior line block was achieved in 70 (97%) patients. Radiofrequency time to bidirectional block did not differ significantly across groups (contact force information visible 23±18min versus contact force information blinded 21±15min, p=0.50). The LA anterior line was discernable on cMRI in 40 patients (82%) without significant differences across randomization groups (p=0.46). No difference in applied contact force was found depending on cMRI line visibility. Twelve-month success and adverse event rates were comparable across groups.

Conclusion

Information on contact force does not significantly improve the ablation of LA anterior lines.

Clinical Trial Registration

The trial was registered at http://www.clinicaltrials.gov by identifier: NCT02217657.

Contact-Force Guided Pulmonary Vein Isolation does not Improve Success Rate in Persistent Atrial Fibrillation Patients and Severe Left Atrial Enlargement: A 12-month Follow-Up Study

Background

Catheter ablation is a cornerstone treatment strategy in atrial fibrillation (AF). Left atrial (LA) size is one of the contributors in development of AF recurrences. The impact of contact-forced (CF) guided catheter ablation on the success rate of persistent AF patients with severe enlarged LA has not been investigated yet.

Methods

Sixty-six patients with diagnosis of longstanding persistent AF undergoing catheter ablation were enrolled. All patients underwent a standard transthoracic echocardiography according to the guidelines. LA size was considered severely enlarged when LA diameter was ≥ 50 mm. CF catheter ablation with a Tacticath Quartz catheter (St Jude Medical, St. Paul, MN, USA) was used in all patients.

Results

The mean age was 61.9 ± 9.9 years, and LAD 47.8 ± 11.6 mm. Among 66 patients with persistent AF, 32 (48%) patients were diagnosed with AF recurrences. Twenty-eight (42%) patients had severely enlarged LA. The recurrence of AF was comparable in patients with and without severe enlarged LA (47% vs. 42%, p=0.79). The recurrence of AF was lower in patients who underwent CF-guided ablation with a normal LA dimension (36 %, p=0.54). Procedure duration was longer in patients with severely enlarged LA. LA dimension was not significantly different between patients with and without AF recurrence (49.8 ± 7.9 mm vs. 45.9 ± 7.5 mm, p=0.15). LAD and was significantly correlated with the time to recurrence of AF (r:-0.60, p=0.02).

Conclusion

Our preliminary findings have demonstrated that CF guided ablation does not improve the success rate in longstanding persistent AF patients with severe LA enlargement.

Contact force-sensing catheters: performance in an ex vivo porcine heart model

PURPOSE

Contact force (CF) catheters are useful to address proper contact during ablation. However, interactions between the ablation process, or its associated irrigation flow changes, with the CF sensing may translate into unexpected CF value fluctuations. We aimed to test for unintentional CF value variations during radiofrequency applications at a fixed applied force, with two commercially available catheters (TactiCath™ and SmartTouch™), and to evaluate its theoretical clinical significance by correlating CF-derived automatic ablation algorithms (force-time integral and lesion index) and actual lesion size at two standard CF values.

METHODS

Four series of 20 perpendicular epicardial ablations (20 W, 60 s, 17 ml/min) were performed on porcine left ventricle submerged in 37 °C saline. Catheters were mechanically fixed at a constant position and evaluated at 10 and 20 g. CF values were digitally analysed before each application changing irrigation rate (2-17-30 ml/min), and during ablation. Finally, lesions were quantified.

RESULTS

Increasing irrigation before ablation led to a slight but significant CF decrease. During ablation, CF showed a reproducible pattern: fast initial decrease, subsequent increase until higher-than-initial values and final plateau phase (CF variation up to 69% at 10 g). CF variability was significantly higher at 10 g and using TactiCath™. There were no major differences in lesion size between catheters at the same initial CF. CF only correlated mildly to lesion measures, and automatic algorithms globally failed to predict lesion size.

CONCLUSIONS

CF measured values spontaneously vary during ablation following a predictable pattern (initial decrease, subsequent increase and final plateau). This is especially remarkable applying lower CF.

Higher contact force during radiofrequency ablation leads to a much larger increase in edema as compared to chronic lesion size

INTRODUCTION

Reversible edema is a part of any radiofrequency ablation but its relationship with contact force is unknown. The goal of this study was to characterize through histology and MRI, acute and chronic ablation lesions and reversible edema with contact force.

METHODS AND RESULTS

In a canine model (n = 14), chronic ventricular lesions were created with a 3.5-mm tip ThermoCool SmartTouch (Biosense Webster) catheter at 25 W or 40 W for 30 seconds. Repeat ablation was performed after 3 months to create a second set of lesions (acute). Each ablation procedure was followed by in vivo T2-weighted MRI for edema and late-gadolinium enhancement (LGE) MRI for lesion characterization. For chronic lesions, the mean scar volumes at 25 W and 40 W were 77.8 ± 34.5 mm3 (n = 24) and 139.1 ± 69.7 mm3 (n = 12), respectively. The volume of chronic lesions increased (25 W: P < 0.001, 40 W: P < 0.001) with greater contact force. For acute lesions, the mean volumes of the lesion were 286.0 ± 129.8 mm3 (n = 19) and 422.1 ± 113.1 mm3 (n = 16) for 25 W and 40 W, respectively (P < 0.001 compared to chronic scar). On T2-weighted MRI, the acute edema volume was on average 5.6-8.7 times higher than the acute lesion volume and increased with contact force (25 W: P = 0.001, 40 W: P = 0.011).

CONCLUSION

With increasing contact force, there is a marginal increase in lesion size but accompanied with a significantly larger edema. The reversible edema that is much larger than the chronic lesion volume may explain some of the chronic procedure failures.

Effects of Ablation (Radio Frequency, Cryo, Microwave) on Physiologic Properties of the Human Vastus Lateralis

OBJECTIVE

Ablative treatments can sometimes cause collateral injury to surrounding muscular tissue, with important clinical implications. In this study, we investigated the changes in muscle physiology of the human vastus lateralis when exposed to three different ablation modalities: radiofrequency ablation, cryoablation, and microwave ablation.

METHODS

We obtained fresh vastus lateralis tissue biopsy specimens from nine patients (age range: 29-73 years) who were undergoing in vitro contracture testing for malignant hyperthermia. Using leftover waste tissue, we prepared 46 muscle bundles that were utilized in tissue baths before and after ablation.

RESULTS

After ablation with all the three modalities, we noted dose-dependent sustained reductions in peak force (strength of contraction), as well as transient increases in baseline force (resting muscle tension). But, over the subsequent 3-h recovery period, peak force improved and the baseline force consistently recovered to below its preablation levels.

CONCLUSION

The novel in vitro methodologies we developed to investigate changes in muscle physiology after ablation can be used to study a spectrum of ablation modalities and also to make head-to-head comparisons of different ablation modalities.

SIGNIFICANCE

As the role of ablative treatments continues to expand, our findings provide unique insights into the resulting changes in muscle physiology. These insights could enhance the safety and efficacy of ablations and help individuals design and develop novel medical devices.

Contact-force-guided vs. contact-force-blinded catheter ablation of typical atrial flutter: a prospective study

Aims

It remains unknown whether contact force (CF) sensing technology is of value for cavotricuspid isthmus (CTI) ablation. We prospectively evaluated procedural parameters and outcomes of CF-guided vs. CF-blinded CTI ablation for typical atrial flutter (AFL).

Methods and results

A total of 70 consecutive patients (62.5 ± 10.9 years) undergoing CTI ablation for AFL were prospectively enrolled, 35 in CF-blinded and 35 in CF-guided groups. A CF-sensing catheter (power 25-35 W) was used in all. In the CF-guided group, CF target range was 10-25 g, whereas in the CF-blinded group, the operator was blinded to CF. The isthmus was divided into anterior, middle, and posterior segments for region-specific CF analysis. The procedural endpoint of bidirectional isthmus block following a 20-min observation period was achieved in all. A trend towards lower fluoroscopy and procedure duration was observed when the CF-guided group was compared with the CF-blinded group. The total radiofrequency (RF) energy delivery time required to achieve bidirectional block was significantly lower in the CF-guided vs. CF-blinded group [10.0 min (IQR 8.3;15.1) vs. 15.9 min (IQR 9.6;24.7), P= 0.0020], with a significant inverse correlation between CF and total RF delivery time (r = -0.36; P= 0.0027). Mean CF measurements significantly increased from anterior to posterior anatomical zones of CTI in the CF-blinded group (ANOVA P= 0.0466).

Conclusions

Catheter ablation of AFL guided by real-time CF assessment results in a significant reduction in total RF delivery time. Real-time CF measurements facilitate the maintenance of homogenous efficient contact all along the CTI, particularly in the anterior segment where CF is generally lower.

Electrogram characteristics of the coronary sinus in cases requiring epicardial ablation within the coronary sinus for creating a conduction block at the left lateral mitral isthmus

BACKGROUND

Left lateral mitral isthmus (LLMI) linear ablation is a safe and effective technique for treating left mitral flutter. LLMI linear ablation with pulmonary vein isolation may reduce the recurrence of persistent atrial fibrillation. However, epicardial ablation within the coronary sinus (CS) is often required to create the LLMI block line. If the necessity for epicardial ablation is checked before ablation, complications may be reduced.

METHODS

We recruited 135 patients who underwent their first LLMI ablation and divided them into two groups, one group not requiring epicardial ablation for creating a conduction block at the LLMI (Endo group) and another requiring it (Epi group). These two groups were compared in terms of the electrogram characteristics of the CS.

RESULTS

Bidirectional block through the LLMI was achieved in 94.8% of patients. In 42% of these patients, not only the endocardium but also the epicardium was ablated. As for the electrogram, the Endo group had lower atrium voltage and atrioventricular voltage ratios (p = 0.009) than the Epi group before LLMI ablation. By contrast, there were no significant differences in the atrium voltage and the atrioventricular voltage ratio between these two groups after LLMI ablation.

CONCLUSIONS

For creating a conduction block at the LLMI, the atrium voltage and the atrioventricular voltage ratio in the CS before ablation are important. The atrioventricular voltage ratio is a crucial criterion for determining whether epicardial ablation is necessary; furthermore, the atrioventricular voltage ratio in the CS must be reduced with or without epicardial ablation.

Miniaturized Robotic End-Effector with Piezoelectric Actuation and Fiber Optic Sensing for Minimally Invasive Cardiac Procedures

Each year 35,000 cardiac ablation procedures are performed to treat atrial fibrillation through the use of catheter systems. The success rate of this treatment is highly dependent on the force which the catheter applies on the heart wall. If the magnitude of the applied force is much higher than a certain threshold the tissue perforates, whereas if the force is lower than this threshold the lesion size may be too large and is inconsistent. Furthermore, studies have shown large variability in the applied force from trained physicians during treatment, suggesting that physicians are unable to manually regulate the levels of the force at the site of treatment. Current catheter systems do not provide the physicians with active means for contact force control and are only at most aided by visual feedback of the forces measured in situ. This paper discusses a novel design of a robotic end-effector that integrates mechanisms of sensing and actively controlling of the applied forces into a miniaturized compact form. The required specifications for design and integration were derived from the current application under investigation. An off-the-shelf miniature piezoelectric motor was chosen for actuation, and a force sensing solution was developed to meet the specifications. Experimental characterization of the actuator and the force sensor within the integrated setup show compliance with the specifications and pave the way for future experimentation where closed-loop control of the system can be implemented according to the contact force control strategies for the application.

Efficacy of adjunctive measures used to assist pulmonary vein isolation for atrial fibrillation: a systematic review

PURPOSE OF REVIEW

Pulmonary vein reconnection leading to recurrence of atrial arrhythmias after pulmonary vein isolation (PVI) for atrial fibrillation remains a significant challenge. A number of adjunctive measures during PVI have been used to attempt to reduce pulmonary vein reconnection and recurrence of atrial arrhythmias. We performed a systematic review of the literature and meta-analysis of studies evaluating the efficacy of adjunctive measures used during PVI in reducing recurrent atrial arrhythmias.

RECENT FINDINGS

Our literature search found four interventions that met the prespecified definition of adjunctive measure: adenosine testing post-PVI, contact force-guided PVI, pacing inexcitability of the ablation line during PVI and additional ablation based on the computed tomography thickness of the pulmonary vein-left atrial appendage ridge. Sixteen studies enrolling 3507 patients met all inclusion and exclusion criteria. PVI performed with adjunctive measures was shown to reduce the 1-year recurrence rate of atrial arrhythmias. The point estimate for the combined relative risk of atrial arrhythmia recurrence was 0.56 [95% confidence interval (CI): 0.43-0.73; P value <0.001] in the PVI with adjunctive measures group.

SUMMARY

PVI for atrial fibrillation assisted by adjunctive measures results in clinically significant reduction of recurrent atrial arrhythmias. Additional research is required to assess the relative efficacy of individual or combined adjunctive strategies used during PVI for atrial fibrillation.

Impact of impedance decrease during radiofrequency current application for atrial fibrillation ablation on myocardial lesion and gap formation

BACKGROUND

The clinical impact of a decrease in impedance during radiofrequency catheter ablation (RFCA) has not been fully clarified. The aim of the study was to analyze the impact of impedance decrease and to determine its optimal cutoff value during RFCA.

METHODS

We evaluated 34 consecutive patients (total 3264 lesions, mean age 66 ± 8.7 years, 10 females) who underwent their first ablation for atrial fibrillation (AF). The impedance decrease, average contact force (CF), application time, force-time integral (FTI), product of impedance decrease and application time (PIT), and the product of impedance decrease and FTI (PIFT) were measured for all lesions. Levels of cardiac troponin I (TrpI) were measured for assessment of myocardial injury. The incidence of intraprocedural pulmonary vein-left atrium reconnection or dormant conduction (reconnection) was determined. The relationships between the ablation parameters and the increase in TrpI (ΔTrpI) were evaluated. The predictive value of the parameters for reconnection was assessed using receiver operating characteristic (ROC) curve analysis.

RESULTS

Reconnection was detected in 18 patients. Average FTI and PIT were significantly correlated with ΔTrpI (FTI: r2 = .19, P = .0090, PIT: r2 = .21, P = .0058). PIFT was correlated with ΔTrpI and was the best of the three indexes (PIFT: r2 = .29, P = .0010). In ROC curve analysis, the area under the curve for predicting reconnection was 0.71 and the optimal cutoff value was 5200 for PIFT (sensitivity 78%, specificity 63%).

CONCLUSION

The combination of CF and a decrease in impedance could be important in the evaluation of myocardial lesions and reconnection during RFCA.

Comparison of the efficacy between impedance-guided and contact force-guided atrial fibrillation ablation using an automated annotation system

BACKGROUND

This study compared the efficacy of catheter ablation of atrial fibrillation (AF) between impedance (IMP)-guided and contact force (CF)-guided annotation using the automated annotation system (VisiTag™).

METHODS

Fifty patients undergoing pulmonary vein isolation (PVI) for AF were randomized to the IMP-guided or CF-guided groups. The annotation criteria for VisiTag™ were a 10 second minimum ablation time and 2 mm maximum catheter movement range. A minimum CF of 10 g was added to the criteria in the CF-guided group. In the IMP-guided group, a minimum IMP drop of over 5 Ω was added to the criteria.

RESULTS

The rates of successful PVI after an initial ablation line were higher in the CF-guided group (80% vs 48%, P = .018). Although average CF was similar between two groups, the average force-time integral (FTI) was significantly higher in the CF-guided group (298.3 ± 65. 2 g·s vs 255.1 ± 38.3 g·s, P = .007). The atrial arrhythmia-free survival at 1 year demonstrated no difference between the two groups (84.0% in the IMP-guided group vs 80.0% in the CF-guided group, P = .737). If the use of any antiarrhythmic drug beyond the blanking period was considered as a failure, the clinical success rate at 1 year was 52.0% for the CF-guided group vs 56.0% for the IMP-guided group (P = .813).

CONCLUSIONS

Atrial fibrillation ablation using an automated annotation system guided by CF improved the success rate of PVI after the initial circumferential ablation. An IMP-guided annotation combined with catheter stability criteria showed similar clinical outcomes as compared to the CF-guided annotation.

The best of two worlds? Pulmonary vein isolation using a novel radiofrequency ablation catheter incorporating contact force sensing technology and 56-hole porous tip irrigation

AIMS

This study aimed to evaluate feasibility and safety as well as 1-year clinical outcome of pulmonary vein isolation (PVI) using a unique radiofrequency ablation catheter ("Thermocool SmartTouch SurroundFlow"; STSF) incorporating both, contact force (CF) sensing technology and enhanced tip irrigation with 56 holes, in one device.

METHODS

A total of 110 patients suffering from drug-refractory atrial fibrillation underwent wide area circumferential PVI using either the STSF ablation catheter (75 consecutive patients, study group) or a CF catheter with conventional tip irrigation ("Thermocool SmartTouch", 35 consecutive patients, control group). For each ablation lesion, a target CF of ≥ 10-39 g and a force time integral (FTI) of > 400 g s was targeted.

RESULTS

Acute PVI was achieved in all patients with target CF obtained in > 85% of ablation points when using either device. Mean procedure time (131.3 ± 33.7 min in the study group vs. 133.0 ± 42.0 min in the control group; p = 0.99), mean fluoroscopy time (14.0 ± 6 vs. 13.5 ± 6.6 min; p = 0.56) and total ablation time were not significantly different (1751.0 ± 394.0 vs. 1604.6 ± 287.8 s; p = 0.2). However, there was a marked reduction in total irrigation fluid delivery by 51.7% (265.52 ± 64.4 vs. 539.6 ± 118.2 ml; p < 0.01). The Kaplan-Meier estimate 12-month arrhythmia-free survival after the index procedure following a 3-month blanking period was 79.9% (95% CI 70.4%, 90.4%) for the study group and 66.7% for the control group (95% CI 50.2%, 88.5%). This finding did not reach statistical significance (p = 0.18). Major complications occurred in 2/75 patients (2.7%; one pericardial tamponade and one transient ischemic attack) in the study group and no patient in the control group (p = 18).

CONCLUSION

PVI using the STSF catheter is safe and effective and results in beneficial 1-year clinical outcome. The improved tip irrigation leads to a significant reduction in procedural fluid burden.

Prospective Evaluation of Lesion Index-Guided Pulmonary Vein Isolation Technique in Patients with Paroxysmal Atrial Fibrillation: 1-year Follow-Up

Introduction

Pulmonary vein isolation (PVI) using contact force (CF) sensing ablation catheters currently relies on CF and force-time integral (FTI) guidelines. Such measurement of lesion effectiveness still lacks information on current delivery to the tissue, influenced by system impedance and power. Lesion Index (LSI) is a multi-parametric index incorporating CF and radiofrequency current data across time. We aimed to prospectively assess the efficacy of an LSI-guided approach to PVI in patients with paroxysmal atrial fibrillation (PAF).

Methods and Results

The study prospectively enrolled 28 consecutive patients with PAF undergoing PVI with a CF sensing catheter (TactiCathTM, Abbott). LSI-guided ablation target was adapted according to the mean regional thickness of pulmonary vein antra (PVA): LSI range 5.5-6 was pursued in the anterior and septal portions of PVA, 5-5.5 elsewhere. Data from 32 consecutive PAF patients who underwent PVI ablation with a non-CF guided approach (NCF-group) were retrospectively collected for comparison of procedural and clinical outcome.AF-free survival rate at follow-up (17±6 months) was higher for LSI-guided group than NCF-group (89.3% vs 65.6%, p=0.037), with no increase in periprocedural complication rate (no tamponades or other major adverse events reported). Among 1126 lesions with LSI within target range (5-6), average CF was >10g and <30g for 976 lesions (86.7%). Moreover, 1015 lesions (90.1%) had FTI>400gs, but with wide distribution: 30.2% within 400-500gs, 30.0% within 501-600gs, 29.9% over 600gs.

Conclusion

In this first prospective study, LSI-guided PVI improved clinical outcome without any increase in complication rate when compared with standard, non-LSI-guided approach.

Development of an integrated optical contact force monitoring sensor for cardiac ablation catheters

Contact force monitoring technology during cardiac catheter ablation has become a major issue as both appropriate RF delivery and risk-free therapy have been more and more significant. In this study, an elastic waveguide was utilized to detect the contact force of 0 to 40 gF applied at the end of the sensor tip. The sensor showed a hysteresis between the force loading and releasing because of the elasticity of waveguide. The sensing responses were nearly linear and the sensitivity was about 0.2 mV/gF.

Novel Measure of Local Impedance Predicts Catheter–Tissue Contact and Lesion Formation

Background:

Coupling between the ablation catheter and myocardium is critical to resistively heat tissue with radiofrequency ablation. The objective of this study was to evaluate whether a novel local impedance (LI) measurement on an ablation catheter identifies catheter–tissue coupling and is predictive of lesion formation.

Methods and Results:

LI was studied in explanted hearts (n=10 swine) and in vivo (n=10; 50–70 kg swine) using an investigational electroanatomic mapping system that measures impedance from an ablation catheter with mini-electrodes incorporated in the distal electrode (Rhythmia and IntellaNav MiFi OI, Boston Scientific). Explanted tissue was placed in a warmed (37 °C) saline bath mounted on a scale, and LI was measured 15 mm away from tissue to 5 mm of catheter–tissue compression at multiple catheter angles. Lesions were created with 31 and 50 W for 5 to 45 seconds (n=90). During in vivo evaluation of LI, measurements of myocardium (n=90) and blood pool (n=30) were guided by intracardiac ultrasound while operators were blinded to LI data. Lesions were created with 31 and 50 W for 45 seconds in the ventricles (n=72). LI of myocardium (119.7 Ω) was significantly greater than that of blood pool (67.6 Ω; P <0.01). Models that incorporate LI drop (ΔLI) to predict lesion size had better performance than models that incorporate force-time integral ( R 2 =0.75 versus R 2 =0.54) and generator impedance drop ( R 2 =0.82 versus R 2 =0.58). Steam pops displayed a significantly higher starting LI and larger ΔLI compared with successful radiofrequency applications ( P <0.01).

Conclusions:

LI recorded from miniature electrodes provides a valuable measure of catheter–tissue coupling, and ΔLI is predictive of lesion formation during radiofrequency ablation.

Lesion modeling, characterization, and visualization for image-guided cardiac ablation therapy monitoring

In spite of significant efforts to improve image-guided ablation therapy, a large number of patients undergoing ablation therapy to treat cardiac arrhythmic conditions require repeat procedures. The delivery of insufficient thermal dose is a significant contributor to incomplete tissue ablation, in turn leading to the arrhythmia recurrence. Ongoing research efforts aim to better characterize and visualize RF delivery to monitor the induced tissue damage during therapy. Here, we propose a method that entails modeling and visualization of the lesions in real-time. The described image-based ablation model relies on classical heat transfer principles to estimate tissue temperature in response to the ablation parameters, tissue properties, and duration. The ablation lesion quality, geometry, and overall progression are quantified on a voxel-by-voxel basis according to each voxel's cumulative temperature and time exposure. The model was evaluated both numerically under different parameter conditions, as well as experimentally, using ex vivo bovine tissue samples undergoing ex vivo clinically relevant ablation protocols. The studies demonstrated less than 5°C difference between the model-predicted and experimentally measured end-ablation temperatures. The model predicted lesion patterns were within 0.5 to 1 mm from the observed lesion patterns, suggesting sufficiently accurate modeling of the ablation lesions. Lastly, our proposed method enables therapy delivery feedback with no significant workflow latency. This study suggests that the proposed technique provides reasonably accurate and sufficiently fast visualizations of the delivered ablation lesions.

Contact force facilitates the achievement of an unexcitable ablation line during pulmonary vein isolation

AIMS

Contact force (CF) catheters provide catheter-tissue contact information to improve outcome of pulmonary vein isolation (PVI) in paroxysmal atrial fibrillation (PAF). We evaluated different target-CF values for achievement of the additional endpoint of an unexcitable ablation line.

METHODS

A total of 106 patients undergoing PVI were randomized into three groups (G) (G1: target-CF 15 g, G2: target-CF 10 g, G3: CF concealed from operator). The PVI encircling line was divided into predefined sections. Excitable tissue along the PVI-line identified by high output pacing (10 V, 2 ms) was targeted for further ablation.

RESULTS

Mean average CF was 17.4 ± 4.7 g (G1) vs. 12.3 ± 6.0 g (G2) vs. 11.1 ± 6.5 g (G 3) (p < 0.001). Primary unexcitable ablation lines were found in 38.6, 19.4 and 5.7% (G1, G2, G3 respectively; G1 vs. G2 p < 0.05, G1 vs. G3 p < 0.001, G2 vs. G3 ns). Additional radiofrequency (RF)-energy to achieve unexcitability was lowest in G1 (3.6 ± 3.1 kJ vs. 8.6 ± 7.2 kJ (G2) and 10.4 ± 6.7 (G3), p ≤ 0.001, G2 vs. G3 ns) with accordingly lowest additional RF applications in G1 (3.0 ± 2.6 vs. 7.0 ± 5.4 in G2 and 8.4 ± 4.0 in G3; G1 vs. G2 and G3, p < 0.001, G 2 vs. G 3 ns). Sections along ablation lines with low initial CF were most likely to reveal excitability. Single procedure success was 81.9 vs. 73.5 vs. 71.4% (G 1, 2 and 3, p = 0.6) during 437 ± 254 day follow-up.

CONCLUSION

Higher tip-to-tissue CF during PVI facilitates the achievement of an unexcitable ablation line, requiring less additional RF-energy.

Strategy and Outcome of Catheter Ablation for Persistent Atrial Fibrillation - Impact of Progress in the Mapping and Ablation Technologies

Pulmonary vein (PV) antrum isolation (PVAI) is effective in treating paroxysmal atrial fibrillation (AF) but is less so for persistent AF. A recent randomized study on the ablation strategies for persistent AF demonstrated that 2 common atrial substrate modifications, creation of linear lesions in the left atrium and ablation of complex fractionated electrogram sites, in addition to PVAI did not improve the outcome compared with stand-alone PVAI, suggesting the necessity of a more individualized, selective approach to persistent AF. There are emerging technologies, including high-resolution mapping with the use of multi-electrode catheter and auto mapping system and contact force (CF) guide ablation; the former allows rapid and accurate confirmation of the completeness of PVAI, and the latter enhances the achievement of durable ablation lesions more securely. Ablation for fibrotic area(s) has been proposed as a new approach for substrate modification, and high-resolution mapping is useful to define the area with low-voltage electrograms, a surrogate marker for atrial fibrosis. Ablation for non-PV triggers in addition to PVAI improves the outcome of persistent AF. Further, durable isolation of the left atrial posterior wall may reduce AF recurrence. These ablation strategies with concomitant use of the emerging technologies are strongly expected to enhance the effectiveness of catheter ablation for persistent AF.

In Vitro Validation of the Lesion Size Index to Predict Lesion Width and Depth After Irrigated Radiofrequency Ablation in a Porcine Model

OBJECTIVES

In an in vitro model, the authors tested the hypotheses that: 1) lesion dimensions correlate with lesion size index (LSI); and 2) LSI could predict lesion dimensions better than power, contact force (CF), and force-time integral (FTI).

BACKGROUND

When performing radiofrequency (RF) catheter ablation for cardiac arrhythmias, reliable predictors of lesion quality are lacking. The LSI is a multiparametric index incorporating time, power, CF, and impedance recorded during ablation.

METHODS

RF lesions were created on porcine myocardial slabs by using an open-tip irrigated catheter capable of real-time monitoring of catheter-tissue CF. Initially, 3 power settings of 20, 25, and 30 W were used with a fixed CF of 10 g. A fixed power of 20 W was then set with a CF of 20 and 30 g, thereby yielding a total of 5 ablation groups. In each group, LSI values of 5, 6, 7, and 8 were targeted. Sixty RF lesions were created by using 20 ablation protocols (3 lesions for each protocol).

RESULTS

Lesion width and depth were not correlated with power or CF, but the results significantly correlated with FTI (p < 0.01) and LSI (p < 0.0001). Four steam pops occurred with power set at 30 W; no pops were noted with 20 or 25 W even when high LSI values were targeted.

CONCLUSIONS

In this in vitro model, FTI and LSI predicted RF lesion dimensions, whereas power and CF did not. The LSI predictive value was higher than that of FTI. Steam pops occurred only using high ablation power levels, regardless of the targeted LSI.

Reconstruction left atrium and isolation pulmonary veins of paroxysmal atrial fibrillation using single contact force catheter with zero x-ray exposure: A CONSORT Study

BACKGROUND

Conventional ablation of paroxysmal atrial fibrillation (PAF) is associated with radiation risks for patients and laboratory staff. Three-dimensional (3D) mapping system capable of showing contact force (CF) and direction of catheter tip may compensate for nonfluoroscopic safety issues.

OBJECTIVE

The aim of this study was to investigate the feasibility of zero x-ray exposure during reconstruction left atrium (LA) and ablation.

METHODS

Single, CF catheter, and 3D mapping system were used to reconstruct LA and isolate pulmonary veins (PV) in all patients. The patients were randomly divided into 2 groups after LA angiography. In group 1, reconstruction LA and isolation PV was performed with the help of 3D system (without x-ray), whereas in group 2, x-ray and 3D system were utilized to reconstruct LA and ablate PV antrum. After ablation, Lasso catheter was used to confirm the PV isolation. All patients were followed up to 12 months.

RESULTS

A total of 342 PAF patients were continuously enrolled. The basic clinical characteristics between the 2 groups had no significant difference. Parameters related to the procedure, average procedure time, ablation procedure time, average contact force (CF) applied, the percentage of time within CF settings, and average power applied during radiofrequency application showed no significant difference between the 2 groups. In group 1, the average fluoroscopy time before LA reconstruction was similar to that in group 2 (2.8 ± 0.4 vs. 2.4 ± 0.6 minutes, P = .75). The average fluoroscopy time during ablation was significantly lower than that in group 2 (0 vs. 7.6 ± 1.3 minutes, P < .001). The total x-ray exposure dose of the procedure in group 1 was significantly lower than that in group 2 (19.6 ± 9.4 vs. 128.7 ± 62.5 mGy, respectively, P < .001). Kaplan-Meier analysis indicated that there were no statistical differences in the probability of freedom from atrial arrhythmia (AF/AFL/AT) recurrence at 12 months between group 1 and group 2 (P = .152). The success rate after a single ablation procedure and without drugs (Class I/III AAD) at 12 months was not significantly different between the 2 groups (67.6%, 95% confidence interval [CI]: 62%-79.5% in group 1 and 68.9%, 95% CI: 63%-80.7% in group 2, P = .207). Procedural-related adverse events showed no significant different incidence between group 1 and group 2. A multivariate logistic regression analysis of risk factors was performed to evaluate the effectiveness outcome, which demonstrated that the percentage of CF (within the investigator-selected work ranges) during therapy was significantly associated with positive outcomes (odds ratio: 3.68; 95% CI: 1.65-10.6, P = .008), whereas the LA dimension was negatively associated with effectiveness outcomes (odds ratio: 0.72; 95% CI: 0.52-0.84, P = .016).

CONCLUSIONS

Reconstruction LA and isolation PV ablation using single CF-assisted catheter without x-ray exposure was both safe and effective. CF was positively associated with effective outcomes and LA dimensions negatively with effective ones.