Locations of high contact force during left atrial mapping in atrial fibrillation patients: electrogram amplitude and impedance are poor predictors of electrode-tissue contact force for ablation of atrial fibrillation

Evaluation of electrode-tissue contact using multifrequency impedance analysis and Cole-Cole model fitting

Atrial fibrillation (AF) is a common cardiac arrhythmia, and ablation is the primary treatment for patients with drug intolerance. The success of AF ablation depends on the adhesion of the catheter to the tissue. Existing electrical coupling index (ECI) and electrode-interface resistance (IR) methods based on impedance measurement to evaluate the adhesion between catheters and tissues do not explore the internal changes of the tissue during the compression process. This study introduces a new method to understand these internal changes using multi-frequency impedance combined with Cole-Cole model fitting, which is critical for accurate characterization of the contact between catheter and tissue. We used four-electrodes impedance measurement, using customized circuits and compression platform, applying 5-400 g (3.6-228.2 Pa) pressure to the bullfrog thighs to collect impedance data at frequencies of 500-100 kHz. The Cole-Cole model was then used for data fitting and analysis. The customized circuit accurately detects impedance up to 2 kΩ with less than 5% amplitude error, less than 15% phase error, and less than 6% error in model component values. Correlation analysis showed a significant linear relationship between extracellular fluid resistance and applied pressure (Pearson R ≈ 0.9, p < 0.05), indicating that extracellular fluid resistance increases with compression. This suggests that there is a significant linear positive correlation between the extracellular fluid resistance and the applied pressure, meaning that as the pressure increases, the extracellular fluid resistance correspondingly rises. This may provide a new perspective for studying the degree of catheter-tissue contact during atrial fibrillation ablation procedures.

Bioelectrical Impedance Spectroscopy for Monitoring Mammalian Cells and Tissues under Different Frequency Domains: A Review

Bioelectrical impedance analysis and bioelectrical impedance spectroscopy (BIA/BIS) of tissues reveal important information on molecular composition and physical structure that is useful in diagnostics and prognostics. The heterogeneity in structural elements of cells, tissues, organs, and the whole human body, the variability in molecular composition arising from the dynamics of biochemical reactions, and the contributions of inherently electroresponsive components, such as ions, proteins, and polarized membranes, have rendered bioimpedance challenging to interpret but also a powerful evaluation and monitoring technique in biomedicine. BIA/BIS has thus become the basis for a wide range of diagnostic and monitoring systems such as plethysmography and tomography. The use of BIA/BIS arises from (i) being a noninvasive and safe measurement modality, (ii) its ease of miniaturization, and (iii) multiple technological formats for its biomedical implementation. Considering the dependency of the absolute and relative values of impedance on frequency, and the uniqueness of the origins of the α-, β-, δ-, and γ-dispersions, this targeted review discusses biological events and underlying principles that are employed to analyze the impedance data based on the frequency range. The emergence of BIA/BIS in wearable devices and its relevance to the Internet of Medical Things (IoMT) are introduced and discussed.

Improvement in Lesion Formation with Radiofrequency Energy and Utilization of Alternate Energy Sources (Cryoablation and Pulsed Field Ablation) for Ventricular Arrhythmia Ablation

Current ablation systems rely on thermal energy to produce ablation lesions (heating: RF, laser and ultrasound, and cooling: cryo-thermia). While thermal ablation has been proven to be effective, there are several limitations: 1) relatively long procedural times; 2) high recurrence rate of ventricular arrhythmias; and 3) excessive heating potentially leading to serious complications, including steam pop (perforation), coronary arterial injury and thrombo-embolism. Pulsed field ablation (PFA)/irreversible electroporation (IRE) offers a unique non-thermal ablation strategy which has the potential to overcome these limitations. Recent pre-clinical studies suggest that PFA/IRE might be effective and safe for the treatment of cardiac arrhythmias.

Characterization of radiofrequency ablated myocardium with optical coherence tomography

Certain types of cardiac arrhythmias are best treated with radiofrequency (RF) ablation, in which an electrode is inserted into the targeted area of the myocardium and then RF electrical current is applied to heat and destroy surrounding tissue. The resulting ablation lesion usually consists of a coagulative necrotic core surrounded by a rim region of mixed viable and non-viable cells. The characterization of the RF ablated lesion is of potential clinical importance. Here we aim to elaborate optical coherence tomography (OCT) imaging for the characterization of RF-ablated myocardial tissue. In particular, the underlying principles of OCT and its polarization-sensitive counterpart (PS-OCT) are presented, followed by the knowledge needed to interpret their optical images. Studies focused on real-time monitoring of RF lesion formation in the myocardium using OCT systems are summarized. The design and development of various hybrid probes incorporating both OCT guidance and RF ablation catheters are also discussed. Finally, the challenges related to the transmission of OCT imaging systems to cardiac clinics for real-time monitoring of RF lesions are outlined.

In vivo Lesion Index (LSI) validation in percutaneous radiofrequency catheter ablation

INTRODUCTION

Lesion Index (LSI) has been developed to predict lesion efficacy during radiofrequency (RF) catheter ablation. However, its value in predicting lesions size has still to be established. The aim of our study was to assess the lesions size reproducibility for pre-specified values of LSI reached during RF delivery in an in vivo beating heart.

METHODS

Ablation lesions were created with different values of LSI in 7 domestic pigs by means of a contact force sensing catheter (TactiCath^TM , Abbott). Lesions were identified during RF delivery by means of a 3D mapping system (EnSite^TM Precision, Abbott) and measured after heart explantation. Histology was carried out after gross examination on the first 3 lesions to confirm the accuracy of the macroscopic evaluation.

RESULTS

A total of 64 myocardial lesions were created. Thirty-nine lesions were excluded from the analysis for the following reasons: histological confirmation of macroscopic lesion measurement (n=3), transmurality (n=24), unfavorable anatomic position (n=10), not macroscopically identifiable (n=2). In a final set of 25 non-transmural lesions, injury width and depth were respectively 4.6±0.6 mm and 2.6±0.8 mm for LSI=4, 7.3±0.8 mm and 4.7±0.6 mm for LSI=5, and 8.6±1.2 mm and 7.2±1.1 mm for LSI=6. A strong linear correlation was observed between LSI and lesion width (r=0.87, p<0.00001) and depth (r=0.89, p<0.00001). Multiple linear regression analysis identified LSI as the only ablation parameter that significantly predicted lesion width (p<0.001) and depth (p<0.001).

CONCLUSION

In our in vivo study, LSI proved highly predictive of lesion size and depth. This article is protected by copyright. All rights reserved.

A Systematic Review and Meta-Analysis of the Direct Comparison of Second-Generation Cryoballoon Ablation and Contact Force-Sensing Radiofrequency Ablation in Patients with Paroxysmal Atrial Fibrillation

The superiority of second-generation cryoballoon (2G-CB) ablation versus contact force-sensing radiofrequency (CF-RF) ablation in patients with paroxysmal atrial fibrillation (AF) was assessed in this systematic review and meta-analysis. Freedom from atrial tachyarrhythmias (ATAs) (OR = 0.89; 95% confidence interval [CI] = 0.68 to 1.17; p = 0.41), freedom from AF (OR = 0.93; 95% CI = 0.65 to 1.35; p = 0.72), and acute pulmonary vein isolation (PVI) (OR = 1.17; 95% CI = 0.54 to 2.53; p = 0.70) between 2G-CB ablation and CF-RF ablation were not different. The procedure time for the 2G-CB ablation was shorter (MD = −18.78 min; 95% CI = −27.72 to −9.85 min; p < 0.01), while the fluoroscopy time was similar (MD = 2.66 min; 95% CI = −0.52 to 5.83 min; p = 0.10). In the 2G-CB ablation group, phrenic nerve paralysis was more common (OR = 5.74; 95% CI = 1.80 to 18.31; p = < 0.01). Regarding freedom from ATAs, freedom from AF, and acute PVI, these findings imply that 2G-CB ablation is not superior to CF-RF ablation in paroxysmal AF. Although faster than CF-RF ablation, 2G-CB ablation has a greater risk of phrenic nerve paralysis.

Choice of Steerable Sheath Impacts Contact Force Stability During Pulmonary Vein Isolation

A stable contact force (CF) is correlated with more effective radiofrequency (RF) ablation (RFA) lesions and long-term procedural outcomes. Efforts to improve catheter stability include jet ventilation, pacing, steerable sheaths, and CF-sensing ablation catheters. This study compares CF stability and effective RF lesions between two commercially available steerable sheaths. Thirty patients underwent first-time RFA at a single center using the Agilis™ NxT (Abbott, Chicago, IL, USA) or SureFlex™ (Baylis Medical, Montreal, Canada) steerable sheath. High-power short-duration RFA was utilized, targeting a 10-Ω drop. Sheath performance was assessed for the entire procedure and around each pulmonary vein (PV) in terms of mean CF, CF variability, RF time per lesion, and inefficient contact lesions (defined as lesions with a CF of less than 5 g for at least 10% of the RF delivery time). The operator-targeted mean CF was achieved using both sheaths; however, the overall CF variability was 12.8% lower when using the SureFlex™ sheath (p = 0.08). The CF variability was generally 16% greater in the right PVs than the left PVs (p = 0.001) but trended lower with the SureFlex™ sheath. There were 8% more inefficient contact lesions created when using the Agilis™ sheath as compared to the SureFlex™ sheath (p = 0.035), especially in the right inferior PV (p = 0.009). The RF time per lesion was, on average, 12% (1.4 seconds) shorter when using the SureFlex™ sheath than the Agilis™ sheath (p < 0.05). The choice of steerable sheath may affect both catheter stability and lesion quality, especially in the right PVs.

Impact of open-irrigated radiofrequency catheter with contact force measurement on the efficacy and safety of atrial fibrillation ablation: a single-center direct comparison

BACKGROUND

In atrial fibrillation (AF) patients, catheter ablation of pulmonary veins (PVI) is the most effective therapeutic option to maintain sinus rhythm. To improve successful PVI, contact force-sensing (CF) catheters became routinely available. Previous studies did not clearly show superior clinical efficacy in comparison with non-CF catheters.

METHODS

We investigated consecutive patients, who underwent index PVI for AF at our hospital between 2012 and 2018. Three hundred and fifty-four patients were ablated without CF. After availability of CF catheters in 2016, 317 patients were ablated using CF. In case of crossover between the groups, follow-up was censored. The primary endpoint was any documented atrial tachycardia (AT) or atrial fibrillation > 30 s after a 3-month blanking period. Secondary endpoints were procedural characteristics and periprocedural complications.

RESULTS

There was no significant difference between the groups at baseline except hyperlipidemia. After 365 days of follow-up, 67% of patients in the CF group remained free from AF/AT recurrence compared to 59% in non-CF group (P = 0.038). In multivariable Cox regression analysis, non-CF ablation was an independent risk factor for AF recurrence besides age and persistent AF. Total fluoroscopy time (15 ± 7.6 vs. 28 ± 15.9 min) and total procedure time (114 ± 29.6 vs. 136 ± 38.5 min) were significantly lower for CF-guided PVI (P < 0.001). Complication rates did not differ between groups (P = 0.661).

CONCLUSIONS

In our study, the AT/AF recurrence rate and pulmonary vein reconnection rate is lower after CF PVI with a similar complication rate but lower total procedure time and total fluoroscopy time compared to non-CF PVI.

Lesion Sequence and Catheter Spatial Stability Affect Lesion Quality Markers in Atrial Fibrillation Ablation

OBJECTIVES

This study sought to analyze high-frequency catheter excursion in relation to lesion quality markers in 20 consecutive patients undergoing first-time radiofrequency (RF) ablation for paroxysmal atrial fibrillation (AF).

BACKGROUND

Ablation therapy for AF requires the delivery of durable lesions. The extent to which lesion sequence, catheter spatial stability, and anatomic location influence lesion formation during RF ablation of AF is not well understood.

METHODS

Three-dimensional spatial excursion of the ablation catheter sampled at 60 Hz during pre-specified pairs of RF lesions was extracted from the CARTO3 System (Biosense Webster Inc., Irvine, California) and analyzed by using custom-developed MATLAB software (MathWorks, Natick, Massachusetts) to define precise catheter spatial stability during RF ablation. Ablation parameters including bipolar electrogram amplitude reduction, impedance decline and transmurality-associated unipolar electrogram (TUE) as evidence of lesion transmurality during lesion placement were recorded and analyzed.

RESULTS

We collected 437,760 position data points during lesion placement. Ablation catheter spatial stability and lesion formation parameters varied considerably by anatomic location. Lesions placed immediately had similar bipolar electrogram amplitude reduction, smaller impedance decline, but higher likelihood of achieving TUE compared to delayed lesions. Greater catheter spatial stability correlated with lesser impedance decline.

CONCLUSIONS

Lesion sequence, ablation catheter spatial stability, and anatomic location are important modifiers of RF lesion formation. Lesions placed immediately are more likely to exhibit TUE. Greater ablation catheter stability is associated with lesser impedance decline but greater likelihood of TUE.

Updated systematic review and meta-analysis of the impact of contact force sensing on the safety and efficacy of atrial fibrillation ablation: discrepancy between observational studies and randomized control trial data

Aims

Despite widespread adoption of contact force (CF) sensing technology in atrial fibrillation (AF) ablation, randomized data suggests lack of improvement in clinical outcomes. We aimed to assess the safety and efficacy of CF-guided vs. non CF-guided AF ablation.

Methods and results

Electronic databases were searched for randomized controlled trials (RCTs) and controlled observational studies (OS) comparing outcomes of AF ablation performed with vs. without CF guidance. The primary efficacy endpoint was freedom from AF at follow-up. The primary safety endpoint was major peri-procedural complications. Secondary endpoints included procedural, fluoroscopy, and ablation duration. Subgroup analyses were performed by AF type and study design. Nine RCTs (n = 903) and 26 OS (n = 8919) were included. Overall, CF guidance was associated with improved freedom from AF [relative risk (RR) 1.10; 95% confidence interval (CI) 1.02-1.18], and reduced total procedure duration [mean difference (MD) 15.33 min; 95% CI 6.98-23.68], ablation duration (MD 3.07 min; 95% CI 0.29-5.84), and fluoroscopy duration (MD 5.72 min; 95% CI 2.51-8.92). When restricted to RCTs however, CF guidance neither improved freedom from AF (RR 1.03; 95% CI 0.95-1.11), independent of AF type, nor did it reduce procedural, fluoroscopy, or ablation duration. Contact force guidance did not reduce the incidence of major peri-procedural complications (RR 0.89; 95% CI 0.64-1.24).

Conclusion

Meta-analysis of randomized data demonstrated that CF guidance does not improve the safety or efficacy of AF ablation, despite initial observational data showing dramatic improvement. Rigorous evaluation in randomized trials is needed before widespread adoption of new technologies.

Single transseptal puncture technique and contact force catheter: A simplified ablation strategy for paroxysmal atrial fibrillation

The present study aimed to evaluate the safety and efficacy of an optimized single transseptal puncture technique and contact force sensing atrial fibrillation (AF) radiofrequency catheter ablation (RFCA) strategy within a clinical setting. Fast anatomic mapping and contact force sensing ablation was applied to patients with paroxysmal AF (PAF) ablation between September 2014 and December 2016 using a single trans-septal sheath. Pulmonary vein isolation (PVI) and linear ablation were performed in PAF individually with a 10-20 g contact force with minimal fluoroscopy. Stimulation with 10 mA outputs on the lesions without capture was used as endpoint. A total of 419 consecutive patients who underwent first-time RFCA were enrolled in the current study, and acute PVI was achieved in all patients. The average procedure time was 74.5±9.7 min, with an average ablation time of 27.3±7.8 min. The average fluoroscopy time was 4.7±3.3 min and the average radiation dose was 24.3±25.2 mGy. At a mean follow-up time of 14.5 ± 4.1 months, sinus rhythm was maintained at 85.0%. Cardiac tamponade occurred in one case. The results indicated that this simplified technique was a simple, safe and effective approach for PAF ablation therapy.

A novel local impedance algorithm to guide effective pulmonary vein isolation in atrial fibrillation patients: Preliminary experience across different ablation sites from the CHARISMA pilot study

INTRODUCTION

Recently, a novel technology able to measure local impedance (LI) and tissue characteristics has been made available for clinical use. This analysis explores the relationships among LI and generator impedance (GI) parameters in atrial fibrillation (AF) patients. Characterization of LI among different ablation spots and procedural success were also evaluated.

METHODS AND RESULTS

Consecutive patients undergoing AF ablation from the CHARISMA registry at five Italian centers were included. A novel radiofrequency (RF) ablation catheter with a dedicated algorithm (DIRECTSENSE™) was used to measure LI and to guide ablation. The ablation endpoint was pulmonary vein (PV) isolation. We analyzed 2219 ablation spots created around PVs in 46 patients for AF ablation. The mean baseline tissue impedance was 105.8 ± 14 Ω for LI versus 91.8 ± 10 Ω for GI (p < .0001). Baseline impedance was homogenous across the PV sites and proved higher in high-voltage areas than in intermediate- and low-voltage areas and the blood pool (p < .001). Both LI and GI displayed a significant drop after RF delivery, and absolute LI drop values were significantly larger than GI drop values (14 ± 8 vs. 3.7 ± 5 Ω, p < .0001). Every 5-point increment in LI drop was associated with successful ablation (odds ratio = 3.05, 95% confidence interval: 2.3-4.1, p < .0001). Conversely, GI drops were not significantly different comparing successful versus unsuccessful sites (3.7 ± 5 vs. 2.8 ± 4 Ω, p = .1099). No steam pops or major complications occurred during or after the procedures. By the end of the procedures, all PVs had been successfully isolated in all patients.

CONCLUSIONS

The magnitude of the LI drop was more closely associated with effective lesion formation than the GI drop.

Contact Force and Ablation Index

Radiofrequency ablation of arrhythmias depends on durable lesion formation. Catheter tip-tissue contact force (CF) is a key determinant of lesion quality; excessive CF is associated with major complications, whereas insufficient CF increases the risk of electrical reconnection and arrhythmia recurrence. In recent years, CF-sensing catheters have emerged with the ability to directly measure CF and provide operators with real-time feedback. CF-guided ablation has been associated with improved outcomes in observational studies. However, randomized controlled trials have not shown any reduction in procedural durations, fluoroscopy exposure, incidence of major complications, or long-term arrhythmia recurrence with use of CF-sensing catheters.

Role of Contact Force Sensing in Catheter Ablation of Cardiac Arrhythmias: Evolution or History Repeating Itself?

Adequate catheter-tissue contact facilitates efficient heat energy transfer to target tissue. Tissue contact is thus critical to achieving lesion transmurality and success of radiofrequency (RF) ablation procedures, a fact recognized more than 2 decades ago. The availability of real-time contact force (CF)-sensing catheters has reinvigorated the field of ablation biophysics and optimized lesion formation. The ability to measure and display CF came with the promise of dramatic improvement in safety and efficacy; however, CF quality was noted to have just as important an influence on lesion formation as absolute CF quantity. Multiple other factors have emerged as key elements influencing effective lesion formation, including catheter stability, lesion contiguity and continuity, lesion density, contact homogeneity across a line of ablation, spatiotemporal dynamics of contact governed by cardiac and respiratory motion, contact directionality, and anatomic wall thickness, in addition to traditional ablation indices of power and RF duration. There is greater appreciation of surrogate markers as a guide to lesion formation, such as impedance fall, loss of pace capture, and change in unipolar electrogram morphology. In contrast, other surrogates such as tactile feedback, catheter motion, and electrogram amplitude are notably poor predictors of actual contact and lesion formation. This review aims to contextualize the role of CF sensing in lesion formation with respect of the fundamental principles of biophysics of RF ablation and summarize the state-of-the-art evidence behind the role of CF in optimizing lesion formation.

How is Contact Force implemented in routine clinical practice? Results from a French National and Monaco Survey

BACKGROUND

Combination of elementary parameters (force, time, power, impedance drop) has been proposed to optimize radiofrequency (RF) delivery. They have been partially validated in clinical studies.

AIMS

The aim of this study was to assess contact-force (CF) implementation into clinical practice.

METHODS

A 36-question electronic form was sent to 105 electrophysiologists (EP) including some general questions concerning the practice of catheter atrial fibrillation ablation and items concerning the parameters used for CF-guided ablation.

RESULTS

Answers from 98 EP were collected (93% response rate). The CF-catheters used were Smart Touch, Biosense (52%), Tacticath, Saint-Jude Medical (12%), or both (27%) and no CF (9%). The power applied on the left atrial (LA) anterior (LAAW) and posterior (LAPW) wall was, respectively, 26-34 W (for 73% of the EP) and below 25 W (88% of the EP). Forty percent of the Visitag® users mostly used the nominal parameters. Seventy-five percent of the users did not use automatic display of the impedance drop. For the Tacticath users, 57% used a target value of 400 gs on the LAAW and 300 to 400 gs on the LAPW. Lesion Size Index was exceptionally used.

CONCLUSIONS

The parameters used for CF-guided ablation are widely variable among the different operators. Further prospective studies are needed to validate the targets for automatic annotation of the RF applications.

Contact Forces Required to Record Monophasic Action Potentials: A Complement to Catheter Contact Force Measurement

OBJECTIVE

The ability to monitor catheter contact force (CF) plays a major role in assessing radiofrequency ablation, impacting lesion size and arrhythmia recurrence, and dictating ablation duration and/or overall patient safety. Our study sought to determine the relative CFs required to elicit reproducible monophasic action potential (MAP) recordings.

METHODS

The study utilized four swine in which: first, median sternotomies were performed and MAPs were collected from seven ventricular locations on the epicardial surface of each heart; and second, a subset of endocardial signals was recorded from a reanimated heart. In these studies, the initial elicitation and then loss of stable MAP waveforms were recorded, as were their associated catheter CFs (n = 371).

RESULTS

Mean CF at the onset of stable MAP recordings was 14.2 ± 2.9 g for epicardial and 16.6 ± 2.5 g for endocardial locations. Across epicardial locations, no significant differences in CF were required to elicit MAPs. Additionally, endocardial and epicardial CFs for MAPs did not significantly differ for respective locations, i.e., right ventricular septum endocardial versus epicardial. In our study, the catheter CFs required to elicit MAPs were within optimal ranges previously reported for eliciting clinically viable radiofrequency ablations.

CONCLUSION

We believe that MAP recordings could complement CF measurements with electrical data, providing additional clinical feedback for physicians performing cardiac ablation.

SIGNIFICANCE

If applied clinically, MAP recordings could potentially improve ablation outcomes in patients with cardiac arrhythmias.

Targeted ablation of specific electrogram patterns in low-voltage areas after pulmonary vein antral isolation in persistent atrial fibrillation: Termination to an organized rhythm reduces atrial fibrillation recurrence

BACKGROUND

Ablation strategies have been developed to improve outcomes in patients with persistent atrial fibrillation (PsAF). However, the impact of atrial fibrillation (AF) termination on late AF recurrence is not well known. The aim of our study was to evaluate the impact of AF termination to atrial tachycardia (AT) or sinus rhythm (SR) during catheter ablation on late AF recurrence after the 3-month blanking period.

METHODS AND RESULTS

We prospectively recruited 140 patients (mean age: 58.5 ± 12.3 years old, 74.3% males) with uninterrupted PsAF of a mean duration of 3.7 months. Pulmonary vein antral isolation (PVAI) was the first ablation step, and if AF did not terminate (to SR or AT), we ablated low-voltage areas less than 0.4 mV with specific electrogram characteristics. We successfully converted AF to AT or SR in 56 patients (40%) during PVAI (n = 24) or low-voltage ablation ( n = 32). The remaining 84 patients (60%) were electrically cardioverted to SR at the end of the procedure. One hundred patients (71.4%) maintained SR after a single procedure during a mean follow-up of 21.1 ± 0.8 months. Of the 56 patients with AF termination, 46 (82.1%) had no recurrence, while in the group of 84 patients without AF termination, 54 patients (64.3%) remained in SR ( P < 0.02).

CONCLUSION

Ablation of PVAI and specific electrograms in low-voltage areas less than 0.4 mV can lead to encouraging outcomes with a low recurrence rate as well as a lower need for redo procedures.

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.

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.

Relation between denaturation time measured by optical coherence reflectometry and thermal lesion depth during radiofrequency cardiac ablation: Feasibility numerical study

BACKGROUND/OBJECTIVE

Radiofrequency (RF) catheter ablation is a minimally invasive medical procedure used to thermally destroy the focus of cardiac arrhythmias. Novel optical techniques are now being integrated into RF catheters in order to detect the changes in tissue properties. Loss of birefringence due to fiber denaturation at around 70°C is related to changes in accumulated phase retardation and can be measured by polarization-sensitive optical coherence reflectometry (PS-OCR). Since irreversible thermal lesions are produced when the tissue reaches 50°C, our goal was to seek the mathematical relationship between both isotherms.

MATERIALS AND METHODS

A two-dimensional model based on a coupled electric-thermal problem was built and solved using the finite element method. The model consisted of cardiac tissue, blood, and a non-irrigated electrode with a sensor embedded in its tip to maintain a specific target electrode temperature. Computer simulations were conducted by varying the tissue characteristics. Lesion depth was estimated by the 50°C isotherm, while the denaturation time (TD) was taken as the time at which the 70°C isotherm reached a depth of 0.75 mm (which corresponds to the optical depth reached by PS-OCR technology).

RESULTS

A strong correlation (R²  > 0.83) was found between TD and lesion depth and an even stronger correlation (R² > 0.96) was found between TD and the time required to achieve a specific lesion depth. For instance, the ablation time required to ensure a minimum lesion depth of 3 mm was 1.33 × TD + 3.93 × seconds.

CONCLUSIONS

The computer results confirmed the strong relationship between denaturation time and lesion depth and suggest that measuring denaturation time by PS-OCR could provide information on the ablation time required to reach a specific lesion depth. Lasers Surg. Med. 50:222-229, 2018. © 2017 Wiley Periodicals, Inc.

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.

Left atrial remodeling: Regional differences between paroxysmal and persistent atrial fibrillation

BACKGROUND

The mechanisms underlying self-perpetuation of persistent atrial fibrillation (AF) are not well understood. To gain insight into these mechanisms, we conducted a study comparing left atrial (LA) electroanatomic maps obtained during sinus rhythm between patients with paroxysmal AF (PAF) and patients with persistent AF (PerAF).

METHODS

The study included 23 men with PAF (age, 56.3±12.1 years) and 13 men with PerAF (age, 54.3±13.4 years). LA voltage mapping was performed during sinus rhythm. The clinical and electroanatomic characteristics of the two groups were evaluated and analyzed statistically.

RESULTS

The bipolar voltages at the LA septum, roof, and posterior wall, right superior pulmonary vein (PV) and its antrum, right superior PV carina, and right inferior PV antrum were significantly lower in patients with PerAF than in those with PAF. The bipolar voltages in other parts of the LA did not differ statistically between the two groups.

CONCLUSION

PAF and PerAF seem to be characterized by differences in the regional voltage in the LA and PVs. The LA structural remodeling of PerAF may initiate from the right PVs and their antra and LA septum, roof, and posterior wall.

Contact force technology integrated with 3D navigation system for atrial fibrillation ablation: improving results?

INTRODUCTION

Pulmonary veins isolation (PVI) by radiofrequency (RF) ablation is currently an established treatment for symptomatic, drug-resistant paroxysmal atrial fibrillation. Although the effectiveness of the therapy has been clearly demonstrated, success rate after a single procedure is still sub-optimal. The main reason for recurrences after PVI is electrical pulmonary vein-atrium reconnection. In order to increase the likelihood of permanent PVI, the creation of a transmural, durable lesion is mandatory. The main determinants of lesion size and transmurality are power, stability, duration and contact-force during RF application. In recent times, catheters with contact-force sensors have been developed and released for clinical use. Areas covered: The present review summarizes rational and clinical evidences for efficacy and safety of contact force (CF) technology integrated into 3D navigation systems for AF ablation. Expert commentary Although CF technology has a strong rational, clinical data on the superior safety and efficacy of CF technology over traditional non-CF catheters are still conflicting. The reason for that is very likely to rely on the lack of definite data on how to optimize CF parameters and how to integrate CF data with power, duration of RF applications and information on catheter stability.

What Is the Appropriate Lesion Set for Ablation in Patients with Persistent Atrial Fibrillation?

OPINION STATEMENT

Special attention must be paid to detect, diagnose, and optimize management of reversible or treatable causes of long-standing persistent atrial fibrillation (LSPAF) such as obesity, obstructive sleep apnea (OSA), hypertension, hypo or hyperthyroidism, inflammatory and infectious diseases, and stress. Though, we strongly believe that the role of the pulmonary veins (PVs) is more pronounced in paroxysmal atrial fibrillation (AF) than in persistent AF, performing an adequate pulmonary vein isolation is still key in LSPAF. Patients with LSPAF will frequently require a more aggressive mapping and ablative approach. We do not encourage the use of empiric lines or complex fractionated atrial electrograms. Ablation of sites associated with non-PV triggers such as the entire posterior wall, the roof, the anterior part of the left atrium septum, left atrial appendage (LAA), the CS and SVC has been shown to improve the freedom from AF at follow-up when combined with PVs isolation. During the isoproterenol challenge, non-PV triggers are detected in most patients with AF. Mapping non-PV triggers is guided by multiple catheters positioned along both the right and left atriums: a 10-pole circular mapping catheter in the left superior PV recording the far-field LAA activity, the ablation catheter in the right superior PV that records the far-field interatrial septum and a 20-pole catheter with electrodes spanning from the SVC to the CS. With this simple catheter setup, when focal ectopic atrial activity is observed (a single ectopic beat is enough) their activation sequence is compared to that of sinus rhythm, allowing to quickly identify their area of origin. For significant non-PV triggers (repetitive isolated beats, focal atrial tachycardias or beats triggering AF/atrial flutter, a more detailed activation mapping is performed in the area of origin. They are subsequently targeted with focal ablation, exception being the triggers originating from the SVC, LAA or CS, in which cases complete isolation of these structures is the ablation strategy of choice. We truly believe the LAA deserves special consideration when managing patients with persistent AF and LSPAF.

Fiber Optic Force Sensors for MRI-Guided Interventions and Rehabilitation: A Review

Magnetic Resonance Imaging (MRI) provides both anatomical imaging with excellent soft tissue contrast and functional MRI imaging (fMRI) of physiological parameters. The last two decades have witnessed the manifestation of increased interest in MRI-guided minimally invasive intervention procedures and fMRI for rehabilitation and neuroscience research. Accompanying the aspiration to utilize MRI to provide imaging feedback during interventions and brain activity for neuroscience study, there is an accumulated effort to utilize force sensors compatible with the MRI environment to meet the growing demand of these procedures, with the goal of enhanced interventional safety and accuracy, improved efficacy and rehabilitation outcome. This paper summarizes the fundamental principles, the state of the art development and challenges of fiber optic force sensors for MRI-guided interventions and rehabilitation. It provides an overview of MRI-compatible fiber optic force sensors based on different sensing principles, including light intensity modulation, wavelength modulation, and phase modulation. Extensive design prototypes are reviewed to illustrate the detailed implementation of these principles. Advantages and disadvantages of the sensor designs are compared and analyzed. A perspective on the future development of fiber optic sensors is also presented which may have additional broad clinical applications. Future surgical interventions or rehabilitation will rely on intelligent force sensors to provide situational awareness to augment or complement human perception in these procedures.

Is the knowledge of contact force beneficial in pulmonary vein antrum isolation?

OBJECTIVE

To investigate the effect of the operator knowing the real-time contact force (CF) on the efficacy of pulmonary vein antrum isolation (PVAI).

METHODS

Fifty patients with paroxysmal atrial fibrillation (AF) or short lasting persistent AF were randomized to CF guided PVAI (n = 25) or conventional PVAI (n = 25). In the CF guided group, CF between 10 and 40 g was aimed at. Efficacy of PVAI was measured as reduction in AF burden (AFB) and time to AF recurrence detected by implantable cardiac monitor (ICM), inserted three months before PVAI. Blanking period was three months and follow-up 12 months.

RESULTS

All pulmonary veins were isolated in the CF guided group and all but one in the conventional group. Mean CF was 25 g in the CF guided group and 24 g in the conventional group (p = 0.75). Compared to pre-ablation, median [IQR] relative reduction in AFB 3-12 months after ablation was 100 [99-100]% in the CF guided group (p < 0.001) and 99.4 [25-100]% in the conventional group (p < 0.001), not different between groups (p = 0.09). Nine patients (36%) had AF recurrence in the CF guided group and 13 (52%) in the conventional group (p = 0.21, log-rank test). CF differed between operators. When adjusted for operator by regression analysis, patients without recurrent AF had lower proportion of ablation time with CF <10 g than recurrent patients (p = 0.034). No complications occurred.

CONCLUSIONS

Operator knowledge of real-time CF had no significant effect on AFB reduction or time to AF recurrence. Larger trials should be done to study benefit of real-time CF.

Comparison of Left Atrial Bipolar Voltage and Scar Using Multielectrode Fast Automated Mapping versus Point-by-Point Contact Electroanatomic Mapping in Patients With Atrial Fibrillation Undergoing Repeat Ablation

INTRODUCTION

Bipolar voltage criteria to delineate left atrial (LA) scar have been derived using point-by-point (PBP) contact electroanatomical mapping. It remains unclear how PBP-derived LA scar correlates with multielectrode fast automated mapping (ME-FAM) derived scar. We aimed to correlate scar and bipolar voltages from LA maps created using PBP versus ME-FAM.

METHODS AND RESULTS

In consecutive patients undergoing repeat AF ablation, 2 separate LA maps were created using PBP and ME-FAM during sinus rhythm before ablation. Contiguous areas in the LA with a bipolar voltage cutoff of ≤0.2 mV represented dense scar; LA scar percentage was calculated for each map. Each LA shell was divided into 9 regions and each region further subdivided into 4 quadrants for additional analysis; mean voltages of all points obtained using PBP versus ME-FAM in each region were compared. Forty maps (20 PBP: mean 228.5 ± 95.6 points; 20 ME-FAM: 923.0 ± 382.6 points) were created in 20 patients. Mapping time with ME-FAM was shorter compared with PBP (13.3 ± 5.3 vs. 34.4 ± 13.1 minutes; P < 0.001). Mean LA scar percentage was higher with PBP compared with ME-FAM (15.5 ± 17.1% vs. 12.8 ± 17.6%; P = 0.04). Mean PBP voltage distribution was lower (compared with ME-FAM) in the septum (0.95 ± 0.73 vs. 1.46 ± 0.99 mV; P = 0.009), posterior wall (0.84 ± 0.42 vs. 1.40 ± 0.83 mV; P = 0.0008), roof (0.78 ± 0.80 vs. 1.39 ± 1.09 mV; P = 0.0003), and right PV-LA junction (0.34 ± 0.25 vs. 0.59 ± 0.50 mV; P = 0.01) regions, while voltages were similar in all other LA regions (all P > 0.05).

CONCLUSIONS

In AF patients undergoing repeat ablation, bipolar voltage is greater in certain LA segments with ME-FAM compared with PBP mapping.

Remote Magnetic Navigation: A Focus on Catheter Ablation of Ventricular Arrhythmias

VT ablation is based on percutaneous catheter insertion under fluoroscopic guidance to selectively destroy (i.e., ablate) myocardial tissue regions responsible for the initiation or propagation of ventricular arrhythmias. Although the last decade has witnessed a rapid evolution of ablation equipment and techniques, the control over catheter movement during manual ablation has remained largely unchanged. Moreover, the procedures are long, and require ergonomically unfavorable positions, which can lead to operator fatigue. In an attempt to overcome these constraints, several technical advancements, including remote magnetic navigation (RMN), have been developed. RMN utilizes a magnetic field to remotely manipulate specially designed soft-tip ablation catheters anywhere in the x, y, or z plane inside the patient's chest. RMN also facilitates titration of the contact force between the catheter and the myocardial tissue, which may reduce the risk of complications while ensuring adequate lesion formation. There are several non-randomized studies showing that RMN has similar efficacy to manual ablation, while complication rates and total radiation exposure appears to be lower. Although these data are promising, larger randomized studies are needed to prove that RMN is superior to manual ablation of VT.

Relationship Between Catheter Stability and 12-Month Success After Pulmonary Vein Isolation: A Subanalysis of the SMART-AF Trial

OBJECTIVES

This study sought to assess the correlation between catheter and tissue contact force (CF) stability and 12-month clinical success for atrial fibrillation (AF) ablation.

BACKGROUND

The SMART-AF (Thermocool Smarttouch Catheter for the Treatment of Symptomatic Paroxysmal Atrial Fibrillation) multicenter trial provided a robust dataset of AF ablation procedures, using the CF sensing ablation catheter.

METHODS

CF and CF stability were correlated with 12-month success for drug-refractory symptomatic AF ablation. CF stability was assessed by stability of ablation parameters (CF, time, location stability) over 3-dimensional electroanatomic maps of pulmonary veins (PVs) using a new proprietary software module and the percentage of time within investigator-selected CF ranges. Available data for potential "PV gaps" were retrospectively identified when stability criteria were not met and were correlated with 12-month success.

RESULTS

Average CF categories of 0 to 10, 10 to 20, and >20 g were associated with 12-month success rates of 90%, 70%, and 70%, respectively; thus, higher average CF did not correlate with treatment success. An exploratory univariate analysis showed significantly higher success rates with a CF of 6.5 to 10.3 g than with <6.5 g (odds ratio: 2.95; 95% confidence interval: 1.13 to 7.72; p = 0.028) but a CF >10 g did not improve success. When stable CF was applied ≥73% of the time within the preselected CF range, success improved. A receiver operating characteristic curve analysis revealed that PV gaps exceeding 10.6-mm distance significantly correlated with 12-month failure.

CONCLUSIONS

In the SMART-AF trial, CF stability with sufficient CF was most predictive of optimal 12-month success. (Thermocool Smarttouch Catheter for the Treatment of Symptomatic Paroxysmal Atrial Fibrillation [SMART-AF]; NCT01385202).

Automated lesion annotation during pulmonary vein isolation: influence on acute isolation rates and lesion characteristics

PURPOSE

Recovery of pulmonary vein (PV) conduction is a common mechanism of atrial fibrillation recurrence after PV isolation (PVI), underscoring the need for durable lesion formation. We aimed to evaluate the utility of an automated lesion annotation algorithm (ALAA) on acute isolation rates and resulting lesion characteristics.

METHODS

Fifty patients underwent PVI using a contact force (CF) sensing catheter and ALAA. Single antral circles around ipsilateral PVs were performed with ALAA-1 settings including catheter stability (range of motion ≤2 mm, duration >10 s). Target CF was 10-20 g but not part of ALAA-1 settings. If PV conduction persisted after circle completion, force over time was added to automated settings (ALAA-2). Emerging gaps were subsequently ablated, followed by re-assessment for PVI.

RESULTS

ALAA-1 isolated 70 % of the left and 78 % of the right PVs using 756.3 ± 212.3 s (left) and 737.1 ± 145.9 s (right) of energy delivery. ALAA-2 settings identified 29 gaps in previously unisolated PVs, closure significantly increased isolation rates to 88 % of the left and 96 % of the right PVs with additional 325.4 ± 354.1 s (left) and 266.8 ± 279.5 s (right) of energy delivery (p = 0.001). Lesion characteristics significantly differed between ALAA-1 (n = 3521 lesions) and ALAA-2 (n = 3037 lesions) settings, and between isolated and non-isolated PV segments, particularly with respect to CF. Interlesion distances with ALAA-2 were significantly longer in the left superior, left superior-anterior, and right superior-posterior segments when compared to ALAA-1.

CONCLUSIONS

Settings of an ALAA affect lesion characteristics reveal areas of insufficient lesion formation and influence acute effectiveness of PVI. Combination of CF and stability shows superior performance over stability alone.