Factors Affecting Catheter Contact in the Human Left Atrium and Their Impact on Ablation Efficacy

Role of impedance drop and lesion size index (LSI) to guide catheter ablation for atrial fibrillation

BACKGROUND

When using lesion size index (LSI) to guide catheter ablation, it is unclear what combination of power, contact force and time would be preferable to use and what LSI target value to aim for. This study aimed at identifying desirable ablation settings and LSI targets by using tissue impedance drop as indicator of lesion formation.

METHODS

Consecutive patients, undergoing their first left atrial (LA) catheter ablation for atrial fibrillation, with radiofrequency energy (RF) powers of 20, 30 and 40 W were enrolled. Tissue impedance, contact force (CF), Force Time Integral (FTI) and LSI values were continuously recorded during ablation and sampled at 100 Hz. Mean CF and Contact Force Variability (CFV) were calculated for every lesion. The effect of RF power, ablation time, CF and CFV on impedance drop and LSI were assessed.

RESULTS

A total of 3258 lesions were included in the analysis. For any target LSI value, use of higher RF powers translated into progressively higher impedance drops. The impact of lower CF and higher CFV on impedance drop was more relevant when using lower powers. Target LSI values corresponding to maximum impedance drop were identified depending on RF power, mean CF and CFV used.

CONCLUSIONS

Even in the context of an LSI-guided ablation strategy, use of lower or higher powers might lead to different lesion sizes. Different LSI targets might be needed depending on the combination of RF power, CF and CFV used for ablation. Incorporating indicators of catheter stability, like CFV, in the LSI formula could improve the predictive value of LSI for lesion size. Studies with clinical outcomes are required to confirm the clinical relevance of these findings.

Difference in radiofrequency ablation profile between during sinus rhythm and atrial fibrillation: Considerations in this era of high-power short-duration strategy

Background

The concept of ablation index (AI) was introduced to evaluate radiofrequency (RF) ablation lesions. It is calculated from power, contact force (CF), and RF duration. However, other factors may also affect the quality of ablation lesions. To examine the difference in RF lesions made during sinus rhythm (SR) and atrial fibrillation (AF).

Methods

Sixty patients underwent index pulmonary vein isolation during SR (n = 30, SR group) or AF (n = 30, AF group). All ablations were performed with a power of 50 W, a targeted CF of 5-15 g, and AI of 400-450 using Thermocool Smarttouch SF. The CF, AI, RF duration, temperature rise (Δtemp), impedance drop (Δimp), and the CF stability of each ablation point quantified as the standard deviation of the CF (CF-SD) were compared between the two groups.

Results

A total of 3579 ablation points were analyzed, which included 1618 and 1961 points in the SR and the AF groups, respectively. Power, average CF, RF duration per point, and the resultant AI (389 ± 59 vs. 388 ± 57) were similar for the two rhythms. However, differences were seen in the CF-SD (3.5 ± 2.2 vs. 3.8 ± 2.1 g, p < .01), Δtemp (3.8 ± 1.3 vs. 4.0 ± 1.3°C, p < .005), and Δimp (10.3 ± 5.8 vs. 9.4 ± 5.4 Ω, p < .005).

Conclusions

Despite similar AI, various RF parameters differed according to the underlying atrial rhythm. Ablation delivered during SR demonstrated less CF variability and temperature increase and greater impedance drop than during AF.

Determinants of left atrial local impedance: Relationships with contact force, atrial fibrosis, and rhythm

INTRODUCTION

The relationships between baseline tissue local impedance (LI), contact force (CF), atrial fibrosis, and atrial rhythm are uninvestigated in a clinical setting. We compared the relationship of LI and CF between atrial fibrillation (AF) and sinus rhythm (SR) accounting for the effects of atrial fibrosis as assessed by bipolar voltage and LI.

METHODS

Patients undergoing persistent AF ablation were recruited. LI was recorded referenced to patient blood pool (LIr) and concurrent to changes in CF, with data collected at the same locations in AF and SR.

RESULTS

Twenty patients were recruited. 109 locations were sampled obtaining 1903 data points (SR: 966, AF: 937). CF correlated strongly with LI (repeated measures correlation = 0.64). The relationship between CF and LIr was logarithmic. Rhythm and CF had a significant main (both p < .0005) and interaction effect (p = .022) on tissue LI: AF demonstrated higher LIr values than SR for similar CF. Bipolar voltage had no effect on the relationship of CF to LIr in either rhythm. Assessing fibrosis using LIr showed an interaction effect with CF for LIr in SR and AF, (SR: p < .0005, AF: p = .01), with increased fibrosis showing lesser change in LIr per gram of CF.

CONCLUSIONS

CF and rhythm significantly affect the measured LIr of LA myocardium. Optimal catheter-tissue coupling may be better achieved with higher levels of CF and in AF rather than SR. Atrial fibrosis, as assessed by LIr but not bipolar voltage, affected the CF-LI relationship.

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.

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.

Radiofrequency ablation to achieve durable pulmonary vein isolation

Pulmonary vein isolation (PVI) by radiofrequency (RF) ablation is an important alternative to antiarrhythmic drugs in the treatment of symptomatic atrial fibrillation. However, the inability to consistently achieve durable isolation of the pulmonary veins hampers the long-term efficacy of PVI procedures. The large number of factors involved in RF lesion formation and the complex interplay of these factors complicate reliable creation of durable and transmural ablation lesions. Various surrogate markers of ablation lesion formation have been proposed that may provide information on RF lesion completeness. Real-time assessment of these surrogates may aid in the creation of transmural ablation lesions, and therefore, holds potential to decrease the risk of PV reconnection and consequent post-PVI arrhythmia recurrence. Moreover, titration of energy delivery until lesions is transmural may prevent unnecessary ablation and subsequent adverse events. Whereas several surrogate markers of ablation lesion formation have been described over the past decades, a 'gold standard' is currently lacking. This review provides a state-of-the-art overview of ablation strategies that aim to enhance durability of RF-PVI, with special focus on real-time available surrogates of RF lesion formation in light of the biophysical basis of RF ablation.

Ablation catheter orientation: In vitro effects on lesion size and in vivo analysis during PVI for atrial fibrillation

BACKGROUND

Catheter-delivered radiofrequency (RF) lesion formation is a complex phenomenon, and few studies have explored the effect of catheter orientation on lesion size and catheter orientation behavior during pulmonary vein isolation (PVI) procedures. We evaluated the influence of catheter orientation on lesion dimensions in an in vitro experimental setting and investigated the catheter orientation behavior during PVI.

METHODS AND RESULTS

72 lesions were created in vitro on a porcine heart using a contact force catheter in a parallel, oblique, and perpendicular tip to tissue orientation. The superficial lesion length (SLL) increased shifting the catheter from perpendicular to parallel orientation. The intratissue absolute maximal lesion length (AML) was greater with an oblique catheter orientation. The lesion depth (LD) and the superficial lesion width (SLW) resulted similar with any orientation. Data from 21 PVI procedures in patients with paroxysmal atrial fibrillation using the "wide antral circumferential RF ablation" (WACA) technique were retrospectively analyzed. The mean contact angle among 1130 RF lesions was 28 ± 20°. A prevalent parallel orientation was noted in the anterior WACA segments, whereas it resulted more perpendicular in the posterior segments. Significant differences in catheter orientation between the three operators were found only in few WACA segments.

CONCLUSIONS

In an in vitro setting, catheter orientation affects SLL and AML, but not LD and SLW. During PVI procedures, catheter orientation resulted mostly parallel to the endocardium. Catheter orientation varied among different WACA segments, but only small differences were found between three operators when considering similar WACA segments.

Rapid pacing and high-frequency jet ventilation additively improve catheter stability during atrial fibrillation ablation

INTRODUCTION

Catheter stability during atrial fibrillation ablation is associated with higher ablation success rates. Rapid cardiac pacing and high-frequency jet ventilation (HFJV) independently improve catheter stability. Simultaneous modulation of cardiac and respiratory motion has not been previously studied. The objective of this study was to determine the effect of simultaneous heart rate and respiratory rate modulation on catheter stability.

METHODS

Forty patients undergoing paroxysmal atrial fibrillation ablation received ablation lesions at 15 prespecified locations (12 left atria, 3 right atria). Patients were randomly assigned to undergo rapid atrial pacing for either the first or the second half of each lesion. Within each group, half of the patients received HFJV and the other half standard ventilation. Contact force and ablation data for all lesions were compared among the study groups. Standard deviation of contact force was the primary endpoint defined to examine contact force variability.

RESULTS

Lesions with no pacing and standard ventilation had the greatest contact force standard deviation (5.86 ± 3.08 g), compared to lesions with pacing and standard ventilation (5.45 ± 3.28 g; P < .01) or to lesions with no pacing and HFJV (4.92 ± 3.00 g; P < .01). Lesions with both pacing and HFJV had the greatest reduction in contact force standard deviation (4.35 ± 2.81 g; P < .01), confirming an additive benefit of each maneuver. Pacing and HFJV together was also associated with a reduction in the proportion of lesions with excessive maximum contact force (P < .001).

DISCUSSION

Rapid pacing and HFJV additively improve catheter stability. Simultaneous pacing with HFJV further improves catheter stability over pacing or HFJV alone to optimize ablation lesions.

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.

A Pilot Study on Parameter Setting of VisiTag™ Module during Pulmonary Vein Isolation

Objectives

To identify optimal predefined criteria (OPC) for filters of the VisiTag™ module in the CARTO 3 system during pulmonary vein isolation (PVI).

Methods

Thirty patients with atrial fibrillation (AF) who experienced PVI first were enrolled. PVI was accomplished by using a Thermocool SmartTouch catheter. Ablation lesions were tagged automatically as soon as predefined criteria of the VisiTag™ module were met. OPC should be that ablation with the setting resulting in the conduction gap (CG) as few as possible, while contiguous encircling ablation line (CEAL) without the tag gap (TG) on the 3D anatomic model as much as possible.

Result(s)

When ablation with parameter setting is being catheter movement with a 3 mm distance limit for at least 20 s and force over time (FOT) being off, there were 60 CEAL without TG on the 3D anatomic model. However, 26 CGs were found. After changing FOT setting to be a minimal force of 5 g with 50% stability time, 22 TGs were displayed. Of them, 20 TGs were accompanied by CGs. On reablation at sites of TG with changed parameter setting, 18 CGs were eliminated when 20 TGs disappeared. When reablation with FOT is being a minimal force of 10 g with 50% stability time, 6 remaining CGs were eliminated. However, there was no CEAL. With a mean of follow-up 10.93 months, 2 patients with persistent AF suffered AF recurrence.

Conclusion

A 3 mm distance limit for at least 20 s and FOT being a minimal force of 5 g with 50% stability time might be OPC for the VisiTag™ module.

Ablation Index and Surround Flow Catheter Irrigation: Impedance-Based Appraisal in Clinical Ablation

OBJECTIVES

This study sought to assess the impact of ablation power and catheter irrigation during clinical radiofrequency ablation using impedance drop.

BACKGROUND

In preclinical studies, ablation power and catheter irrigation are determinants of ablation efficacy.

METHODS

Static 30-s left atrial ablations were delivered in patients undergoing their first atrial fibrillation ablation. Impedance drop during ablation (as a measure of efficacy) was compared using the following: the force time integral (FTI); the FTI-P (a cumulative multiple FTI and ablation power), and ablation index (AI), a weighted algorithm including contact force, power, and duration. Comparison was also made between a conventionally irrigated (SmartTouch [ST]) versus surround flow (STSF) contact force-sensing catheter.

RESULTS

We analyzed 1,013 ablations. For both catheters, the Spearman correlation was higher between impedance drop and AI (rho = 0.89 ST, 0.84 STSF) than FTI-P (rho = 0.71 ST, 0.53 STSF) or FTI (rho = 0.77 ST, 0.52 STSF); p < 0.0005 for each. STSF ablations had lower minimum catheter tip temperatures (25°C [interquartile range (IQR): 25°C to 27°C] vs. 35°C [IQR: 34°C to 36°C]; p < 0.005), and lesser impedance drop per FTI or AI (p < 0.005 for both). For STSF, impedance drop plateaued sooner than for ST with respect to FTI (184g.s vs. 463g.s) and AI (370 AI vs. 430 AI).

CONCLUSIONS

AI is a more complete ablation descriptor than is FTI or FTI-P, reflected by a stronger correlation with impedance drop. STSF ablations have lower impedance drop per AI or FTI than ST ablations do, suggesting different targets should be used if ablating guided by impedance drop with STSF. With ST, ablation beyond 430 AI provides minimal additional biophysical efficacy, suggesting an upper limit to use for clinical ablation.

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.

Contact Force and Atrial Fibrillation Ablation

Catheters able to measure the force and vector of contact between the catheter tip and myocardium are now available. Pre-clinical work has established that the degree of contact between the radiofrequency ablation catheter and myocardium correlates with the size of the delivered lesion. Excess contact is associated with steam pops and perforation. Catheter contact varies within the left atrium secondary to factors including respiration, location, atrial rhythm and the trans-septal catheter delivery technology used. Compared with procedures performed without contact force (CF)-sensing, the use of this technology has, in some studies, been found to improve complication rates, procedure and fluoroscopy times, and success rates. However, for each of these parameters there are also studies suggesting a lack of difference from the availability of CF data. Nevertheless, CF-sensing technology has been adopted as a standard of care in many institutions. It is likely that use of CF-sensing technology will allow for the optimization of each individual radiofrequency application to maximize efficacy and procedural safety. Recent work has attempted to define what these optimal targets should be, and approaches to do this include assessing for sites of pulmonary vein reconnection after ablation, or comparing the impedance response to ablation. Based on such work, it is apparent that factors including mean CF, force time integral (the area under the force-time curve) and contact stability are important determinants of ablation efficacy. Multicenter prospective randomized data are lacking in this field and required to define the CF parameters required to produce optimal ablation.

Randomized trial comparing pulmonary vein isolation using the SmartTouch catheter with or without real-time contact force data

BACKGROUND

Contact force (CF) information may improve the safety and efficacy of ablation for paroxysmal atrial fibrillation (PAF).

OBJECTIVE

The purpose of this study was to assess the impact of CF data on ablation for PAF.

METHODS

Patients undergoing first-time PAF ablation were randomized at 7 UK centers to ablation with (CF-on) or without (CF-off) CF data available to the operator, using the same ablation catheter and mapping system. An ablation CF of 5-40g was targeted. Pulmonary vein (PV) reconnection was assessed with adenosine at 60 minutes. Follow-up for arrhythmia recurrence was for 1 year with 7-day Holter recordings at 6 and 12 months.

RESULTS

One hundred seventeen patients were studied (59 CF-on, 58 CF-off). In the CF-on group, a reduction in acute PV reconnection rates (22% vs 32%, P = .03) but no significant difference in 1-year success rates off antiarrhythmic drugs (49% vs 52%, P = .9) was observed. There was no difference in major complication rates: 2 of 59 (3%) CF-on, 3 of 58 (5%) CF-off (P = .7). Procedural and fluoroscopy times were not significantly different (P>.5). Overall mean CFs per ablation were not different between groups (13.4 [9.1-19.6]g CF-on, 13.4 [7.4-22.4]g CF-off, P = .5), but a greater proportion of readings in the CF-on group were in the target range (80% vs 68%, P<.001).

CONCLUSION

This randomized multicenter study demonstrated that CF data availability was associated with reduced acute PV reconnection but not improved 1-year success rates, procedural and fluoroscopy times, or complication rates. There was a reduction in extremes of CF, above and below the study target range, suggesting greater CF control during ablation.

Contact forces during hybrid atrial fibrillation ablation: an in vitro evaluation

PURPOSE

Data on epicardial contact force efficacy in dual epicardial-endocardial atrial fibrillation ablation procedures are lacking. We present an in vitro study on the importance of epicardial and endocardial contact forces during this procedure.

METHODS

The in vitro setup consists of two separate chambers, mimicking the endocardial and epicardial sides of the heart. A circuit, including a pump and a heat exchanger, circulates porcine blood through the endocardial chamber. A septum, with a cut out, allows the placement of a magnetically fixed tissue holder, securing porcine atrial tissue, in the middle of both chambers. Two trocars provide access to the epicardium and endocardium. Force transducers mounted on both catheter holders allow real-time contact force monitoring, while a railing system allows controlled contact force adjustment. We histologically assessed different combinations of epi-endocardial radiofrequency ablation contact forces using porcine atria, evaluating the ablation's diameters, area, and volume.

RESULTS

An epicardial ablation with forces of 100 or 300 g, followed by an endocardial ablation with a force of 20 g did not achieve transmurality. Increasing endocardial forces to 30 and 40 g combined with an epicardial force ranging from 100 to 300 and 500 g led to transmurality with significant increases in lesion's diameters, area, and volumes.

CONCLUSIONS

Increased endocardial contact forces led to larger ablation lesions regardless of standard epicardial pressure forces. In order to gain transmurality in a model of a combined epicardial-endocardial procedure, a minimal endocardial force of 30 g combined with an epicardial force of 100 g is necessary.