The importance of catheter stability evaluated by Visitag(TM) during pulmonary vein isolation

Characterizing lesion morphology of a novel diamond-tip temperature-controlled irrigated radiofrequency ablation catheter

BACKGROUND

The DiamondTemp ablation (DTA) system is a novel temperature-controlled irrigated radiofrequency (RF) ablation system that accurately measures tip-tissue temperatures for real-time power modulation. Lesion morphologies from longer RF durations with the DTA system have not been previously described. We sought to evaluate lesion characteristics of the DTA system when varying the application durations.

METHODS

A bench model using porcine myocardium was used to deliver discrete lesions in a simulated clinical environment. The DTA system was power-limited at 50 W with temperature set-points of 50 °C and 60 °C (denoted Group_50 and Group_60). Application durations were randomized with a range of 5-120 s.

RESULTS

In total, 280 applications were performed. Steam pops were observed in five applications: two applications at 90 s and three applications at 120 s. Lesion size (depth and maximum width) increased significantly with longer applications, until 60 s for both Group_50 and Group_60 (depth: 4.5 ± 1.2 mm and 5.6 ± 1.3 mm; maximum width: 9.3 ± 2.7mm and 11.2 ± 1.7mm, respectively). As lesions transition from resistive to conductive heating (longer than 10 s), the maximum width progressed in a sub-surface propagation. Using a "Time after Temperature 60 °C" (TaT60) analysis, depths of 2-3 mm occur in 0-5 s and depths plateau at 4.6 ± 0.8 mm between 20 and 30 s.

CONCLUSIONS

The DTA system rapidly creates wide lesions with lesion depth increasing over time with application durations up to 60 s. Using a TaT60 approach is a promising ablation guidance that would benefit from further investigation.

Stabilizing interventional instruments in the cardiovascular system: A classification of mechanisms

Positioning and stabilizing a catheter at the required location inside a vessel or the heart is a complicated task in interventional cardiology. In this review we provide a structured classification of catheter stabilization mechanisms to systematically assess their challenges during cardiac interventions. Commercially available, patented, and experimental prototypes of catheters were classified with respect to their stabilizing mechanisms. Subsequently, the classification was used to define requirements for future cardiac catheters and persisting challenges in catheter stabilization. The classification showed that there are two main stabilization mechanisms: surface-based and volume-based. Surface-based mechanisms apply attachment through surface anchoring, while volume-based mechanisms make use of locking through shape or force against the vessel or cardiac wall. The classification provides insight into existing catheter stabilization mechanisms and can possibly be used as a tool for future design of catheter stabilization mechanisms to keep the catheter at a specific location during an intervention. Additionally, insight into the requirements and challenges for catheter stabilization inside the heart and vasculature can lead to the development of more dedicated systems in the future, allowing for intervention- and patient-specific instrument manipulation.

Design and Evaluation of a Passive Constant Force Mechanism for a Cardiac Ablation Catheter

Contact force management has been proven to have a positive effect on the outcome of cardiac ablation procedures. However, no method exists that allows maintaining a constant contact force within a required and effective range. This work aims to develop and evaluate such a constant force mechanism for use in an ablation catheter. A passive constant force mechanism was designed based on a tape loop. The tape loop consists of two tapered springs that work in parallel. A finite element analysis was carried out to verify the behavior and performance of the design. A design based on requirements for a constant force ablation tip showed an average force of about 7.8×10−2 N±8×10−3 N over 20 mm in simulation. A scaled prototype was built and evaluated to prove the validity of the concept; this prototype provides an average force of 1.3×10−1 N±1.6×10−2 N over 35 mm. The mechanism allows for controlled delivery of contact force within a desired and effective range. Based on these findings, it can be concluded that the approach is successful but needs to be optimized for future applications. Being able to control the delivery of contact force in a constant range may increase the effectivity of cardiac ablation procedures and improve clinical outcomes.

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.

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.

Contact force sensing for ablation of persistent atrial fibrillation: A randomized, multicenter trial

BACKGROUND

Impact of contact force sensing (CFS) on ablation of persistent atrial fibrillation (PeAF) is unknown.

OBJECTIVE

The purpose of the TOUCH AF (Therapeutic Outcomes Using Contact force Handling during Ablation of Persistent Atrial Fibrillation) randomized trial was to compare CFS-guided ablation to a CFS-blinded strategy.

METHODS

Patients (n = 128) undergoing first-time ablation for persistent AF were randomized to a CFS-guided vs CFS-blinded strategy. In the CFS-guided procedure, operators visualized real-time force data. In the blinded procedure, force data were hidden. Wide antral pulmonary vein isolation plus a roof line were performed. Patients were followed at 3, 6, 9, and 12 months with clinical visit, ECG, and 48-hour Holter monitoring. The primary endpoint was cumulative radiofrequency (RF) time for all procedures. Atrial arrhythmia >30 seconds after 3 months was a recurrence.

RESULTS

PeAF was continuous for 26 weeks (interquartile range [IQR] 13-52), and left atrial size was 45 ± 5 mm. Force in the CFS-blinded and CFS-guided arms was 12 g [IQR 6-20] and 14 g [IQR 9-20] (P = .10), respectively. Total RF time did not differ between CFS-guided and CFS-blinded groups (49 ± 14 min vs 50 ± 20 min, respectively; P = .70). Single procedure freedom from atrial arrhythmia was 60% in the CFS-guided arm and 63% in the CFS-blinded arm off drugs. Lesions with gaps were associated with significantly less force (11.4 g [IQR 6-19] vs 13.2 g [IQR 8-20], respectively; P = .0007) and less force-time integral (174 gs [IQR 91-330] vs 210 gs [IQR 113-388], respectively; P <.001).

CONCLUSION

CFS-guided ablation resulted in no difference to RF time or 12-month outcome. Lower force/force-time integral was associated with significantly more gaps.

General anesthesia improves contact force and reduces gap formation in pulmonary vein isolation: a comparison with conscious sedation

Compared to conscious sedation (CS), the use of general anesthesia (GA) in pulmonary vein isolation (PVI) is associated with a lower recurrence rate of atrial fibrillation (AF). GA may improve catheter stability and mapping system accuracy compared to CS, but its influence on contact force (CF) parameters during ipsilateral PVI has not previously been investigated. The study population comprised 176 consecutive patients (107 in GA group and 69 in CS group) with AF who underwent their first PVI procedure. We retrospectively assessed CF parameters, force-time integral (FTI), FTI/wall thickness during anatomical ipsilateral PVI and long-term outcome after ablation. Complete PVI with single continuous circular lesions around the ipsilateral PVs was achieved in 54 patients (50.5%) in the GA group but only 24 patients (34.8%) in the CS group (P = 0.04). The distribution of gaps did not differ between the groups. All CF parameters were significantly higher in the GA group than in the CS group (average CF: 19.4 ± 8.7 vs. 16.7 ± 7.7 g, P < 0.0001; FTI: 399.0 ± 262.5 vs. 293.9 ± 193.4 gs, P < 0.0001; FTI/wall thickness: 155.5 ± 106.1 vs. 115.7 ± 85.5 gs, P < 0.0001). GA was associated with lower AF recurrence rate in patients with paroxysmal AF but not with persistent AF. Compared with CS, GA improves CF parameters, FTI and FTI/wall thickness, and reduced gap formation after ipsilateral PVI.

Clinical utility of automated ablation lesion tagging based on catheter stability information (VisiTag Module of the CARTO 3 System) with contact force-time integral during pulmonary vein isolation for atrial fibrillation

BACKGROUND

The clinical utility of an automated lesion tagging module based on catheter stability information (VisiTag) with the CARTO system during atrial fibrillation (AF) ablation remains to be established. We investigated whether VisiTag-guided extensive encircling pulmonary vein isolation (EEPVI) produces durable lesions.

METHODS

The study involved 54 patients undergoing EEPVI for paroxysmal AF. We performed EEPVI guided by the module-generated ablation tags, i.e., "VisiTags," which are point-by-point ablation tags placed on 3D maps. The patients were divided into two groups: those treated under a moderate catheter stability VisiTag setting, i.e., a 3-mm distance limit for at least 5 s and a minimum contact force (CF) of 8 g over 25 % of the set time period with a target force-time integral (FTI) ≥300 g*s (n = 27), and those treated under a strict catheter stability setting, i.e., a 3-mm distance limit for at least 10 s and a minimum CF of 10 g over 50 % of the set time period with a target FTI ≥400 g*s (n = 27).

RESULTS

After EEPVI, adenosine triphosphate-provoked dormant PV conduction was observed in six (22 %) patients in the moderate catheter stability group and in one (4 %) patient in the strict catheter stability group (p = 0.1003); the 12.9-month success rate was 81 % in both groups.

CONCLUSIONS

The strict catheter stability setting for automated lesion tagging together with a target FTI of >400 g*s, vs. the moderate catheter stability setting with a target FTI of >300 g*s, produces less frequent ATP-provoked PV conduction and yields a comparably high mid-term success rate.

Pharmacological Tests in Atrial Fibrillation Ablation

The invasive management of atrial fibrillation (AF) has been considerably changed by the identification of major sites of AF initiation and/or maintenance within the pulmonary vein antra. Percutaneous catheter ablation of these targets has become the standard of care for sustained maintenance of sinus rhythm. Long-term failure of ablation is related to an inability to create a durable transmural lesion or to identify all of the non-pulmonary vein arrhythmia triggers. Pharmacological challenges during catheter ablation have been suggested to improve outcomes in both paroxysmal and persistent AF. Herein we review the mechanism and evidence for the use of pharmacological adjuncts during the catheter ablation of AF.