Biophysics and clinical utility of irrigated-tip radiofrequency catheter ablation

Fast-Response Variable-Stiffness Magnetic Catheters for Minimally Invasive Surgery

In minimally invasive surgery, such as cardiac ablation, magnetically steered catheters made of variable-stiffness materials can enable higher dexterity and higher force application to human tissue. However, the long transition time between soft and rigid states leads to a significant increase in procedure duration. Here, a fast-response, multisegmented catheter is described for minimally invasive surgery made of variable-stiffness thread (FRVST) that encapsulates a helical cooling channel. The rapid stiffness change in the FRVST, composed of a nontoxic shape memory polymer, is achieved by an active cooling system that pumps water through the helical channel. The FRVST displays a 66 times stiffness change and a 26 times transition enhancement compare with the noncooled version. The catheter allows for selective bending of each segment up to 127° in air and up to 76° in water under an 80 mT external magnetic field. The inner working channel can be used for cooling an ablation tip during a procedure and for information exchange via the deployment of wires or surgical tools.

Comparative Study of Lesions Obtained through Radiofrequency between the Irrigated Ablation Catheter with a Flexible Tip and the Non-Irrigated Catheter in Ex Vivo Porcine Hearts

BACKGROUND

At the same conditions of delivered power and contact force, open-irrigated radiofrequency ablation catheters are believed to create deeper lesions, while non-irrigated ones produce shallower lesions. This ex vivo study aims to directly compare the lesion dimensions and characteristics of an irrigated ablation catheter with a flexible tip and a non-irrigated solid-tip catheter.

METHODS

Radiofrequency lesions were induced on porcine myocardial slabs using both open-tip irrigated and non-irrigated standard 4 mm catheters at three power settings (20 W, 30 W, and 40 W), maintaining a fixed contact force of 10 gr. A lesion assessment was conducted including the lesion depth, depth at the maximum diameter, and lesion surface diameters, with the subsequent calculation of the lesion volume and area being undertaken.

RESULTS

Irrigated catheters produced lesions with significantly higher superficial widths at all power levels (3.8 vs. 4.4 mm at 20 W; 3.9 mm vs. 4.4 mm at 30 W; 3.8 mm vs. 4.5 mm at 40 W; p = 0.001, p = 0.019, p = 0.003, respectively). Non-irrigated catheters resulted in significantly higher superficial areas at all power levels (23 mm2 vs. 18 mm2 at 20 W; 25 mm2 vs. 19 mm2 at 30 W; 26 mm2 vs. 19 mm2 at 40 W; p = 0.001, p = 0.005, p = 0.001, respectively). Irrigated catheters showed significantly higher values of lesion maximum depth at 40 W (4.6 mm vs. 5.5 mm; p = 0.007), while non-irrigated catheters had a significantly higher calculated volume at 20 W (202 µL vs. 134 µL; p = 0.002).

CONCLUSIONS

Radiofrequency ablation using an irrigated catheter with a flexible tip has the potential to generate smaller superficial lesion areas compared with those obtained using a non-irrigated catheter.

Comparative Effectiveness of Various Radiofrequency Ablation Catheters in the Ablation of Typical Atrial Flutter

INTRODUCTION

Although ablation of typical atrial flutter (AFL) can be easily achieved with radiofrequency energy (RF), no studies compare the effectiveness of different ablation catheters. Our study aimed to compare the efficacy of various types of ablation catheters in treating typical AFL.

METHODS

We analyzed patients with AFL who underwent RF ablation by a single operator at our institution. Successful ablation was evidenced by a bidirectional conduction block (trans-isthmus conduction time ≥ 130 ms or double potentials ≥ 90 ms). Logistic regression was used to compare success rate and linear regression to compare lesion time.

RESULTS

Out of 222 patients, only six did not meet the success criteria (2.7%). The catheters used were non-irrigated, large-tip, internally irrigated (Chili II Boston Scientific), and externally irrigated (non-force-sensing) catheters (Cool Path, Abbott). An externally irrigated force-sensing catheter (TactiCath, Abbott) was used with > 10 gm of force and (LPLD) setting (30 W- 45 °C- 60 s), and high-power short-duration (HPSD) setting (50 W- 43 °C - 12 s). No complications were encountered. The catheter type had no statistically significant association with ablation success. With the use of externally irrigated catheter with contract force-sensing and HPSD settings, statistically significantly shortening of lesion time was achieved 758.3 s, [CI - 1128.29, - 388.35 s] followed by LPLD by 419.0 s [CI - 808.49, - 29.47 s].

CONCLUSIONS

The typical atrial flutter radiofrequency ablation procedure had a high success rate, which was not influenced by the type of ablation catheter. Contact force ablation catheter and HPSD are associated with shorter total lesion time.

Effect of esophageal cooling on ablation lesion formation in the left atrium: Insights from Ablation Index data in the IMPACT trial and clinical outcomes

INTRODUCTION

The IMPACT study established the role of controlled esophageal cooling in preventing esophageal thermal injury during radiofrequency (RF) ablation for atrial fibrillation (AF). The effect of esophageal cooling on ablation lesion delivery and procedural and patient outcomes had not been previously studied. The objective was to determine the effect of esophageal cooling on the formation of RF lesions, the ability to achieve procedural endpoints, and clinical outcomes.

METHODS

Participants in the IMPACT trial underwent AF ablation guided by Ablation Index (30 W at 350-400 AI posteriorly, 40 W at ≥450 AI anteriorly). A blinded 1:1 randomization assigned patients to the use of the ensoETM® device to keep esophageal temperature at 4°C during ablation or standard practice using a single-sensor temperature probe. Ablation parameters and clinical outcomes were analyzed.

RESULTS

Procedural data from 188 patients were analyzed. Procedure and fluoroscopy times were similar, and all pulmonary veins were isolated. First-pass pulmonary vein isolation and reconnection at the end of the waiting period were similar in both randomized groups (51/64 vs. 51/68; p = 0.54 and 5/64 vs. 7/68; p = 0.76, respectively). Posterior wall isolation was also similar: 24/33 versus 27/38; p = 0.88. Ablation effect on tissue, measured in impedance drop, was no different between the two randomized groups: 8.6Ω (IQR: 6-11.8) versus 8.76Ω (IQR: 6-12.2; p = 0.25). Arrhythmia recurrence was similar after 12 months (21.1% vs. 24.1%; 95% CI: 0.38-1.84; HR: 0.83; p = 0.66).

CONCLUSIONS

Esophageal cooling has been shown to be effective in reducing ablation-related thermal injury during RF ablation. This protection does not compromise standard procedural endpoints or clinical success at 12 months.

Ablation of Atrioventricular Nodal Re-Entrant Tachycardia Combining Irrigated Flexible-Tip Catheters and Three-Dimensional Electroanatomic Mapping: Long-Term Outcomes

Background: Transcatheter ablation is the standasrd treatment for atrioventricular nodal re-entrant tachycardia (AVNRT). However, different techniques are available. Data about the use of irrigated flexible-tip catheters and three-dimensional electroanatomical mapping (3D EAM) for AVNRT ablation are scant. The aim of this study was to evaluate in long-term follow-up efficacy and safety of a novel approach for AVNRT treatment. Methods: This is a cohort single arm study with long-term follow-up. Patients with AVNRT were treated with catheter ablation by means of irrigated flexible-tip catheters combined with 3D EAM. Results: One-hundred-and-fifty patients were enrolled and followed-up for a median of 38 months (minimum 12, maximum 74). Acute procedural success rate was 96.7% (145/150 patients). During follow-up, 11 patients had arrhythmia recurrences (7.3%). No patient developed atrioventricular conduction block with need for pacemaker implantation (0%). Fourteen patients died during follow-up (9.3%). Conclusions: Acute procedural success and long-term follow-up show that AVNRT could be safely and effectively treated with irrigated flexible-tip catheters and 3D EAM.

Catheter ablation of focal atrial tachycardia in children using three-dimensional electroanatomic mapping system: a 6-year single-centre experience

OBJECTIVE

This study demonstrates the clinical and electrophysiological details of catheter ablation conducted in children with focal atrial tachycardia using three-dimensional electroanatomic mapping systems.

PATIENTS AND METHODS

Electrophysiological procedures were performed using the EnSite™ system.

RESULTS

Between 2014 and 2020, 60 children (median age 12.01 years [16 days-18 years]; median weight 41.5 kg [3-98 kg]) with focal atrial tachycardia and treated with catheter ablation were evaluated retrospectively. Tachycardia-induced cardiomyopathy was developed in 15 patients (25%). Most of the focal atrial tachycardia foci were right-sided (75%), and more than one focus was found in four patients. Radiofrequency ablation was performed in 47 patients (irrigated radiofrequency ablation in seven cases), cryoablation in 9, and radiofrequency ablation and cryoablation in the same session in 4 patients. The median procedural time was 163.5 minutes (82-473 minutes). Fluoroscopy was used in 29 of (48.3%) patients (especially for left-side substrate) with a mean time of 8.6 ± 6.2 minutes. The acute success rate was 95%. The procedure failed in three patients, and recurrence was observed in 3.5% of patients (2/57) during a median follow-up of 17 months (2-69 months). The second ablation was performed in four cases, of which three were successful. Overall success rate was 96.6% with no major complications observed, except in one patient with minimal pericardial effusion.

CONCLUSION

Catheter ablation seems to be an effective and safe treatment in focal atrial tachycardia. Electroanatomic mapping system can facilitate the ablation procedure and minimise radiation exposure.

Bipolar ablation with contact force-sensing of swine ventricles shows improved acute lesion features compared to sequential unipolar ablation

INTRODUCTION

Despite technical progress, ventricular tachycardia (VT) recurrence after unipolar ablation remains relatively high (12%-47%). Bipolar ablation has been proposed as an appealing solution that may overcome limitations associated with unipolar ablation settings. We designed an animal study to compare bipolar (BPA) vs sequential unipolar ablation (UPA) using contact force-sensing technology on both ablation catheters.

METHODS

Twenty large white female pigs (6-months-old, 50-60 kg) underwent multiple RF ablations (30 W, 60 seconds, 30 mL/min irrigation) on the ventricular myocardium from the epicardial and endocardial sides. The hearts were fixed and scanned with high-resolution cardiac magnetic resonance imaging. Thermal lesions were located and characterized in volume, depth, width, and transmurality.

RESULTS

Lesion volume was calculated as the sum of epicardial or endocardial conjoined/isolated lesions at one location. Linear dimensions (width and depth) were measured twice for each location, on the endocardial and epicardial side. We evaluated 35 lesions across the intraventricular septum (UPA, N = 17 vs BPA, N = 18). No difference in volume, linear dimensions or impedance drop was observed in this area between UPA and BPA. However, BPA required half RF time and showed an increased transmurality trend. We then analyzed 73 lesions from the endocardial side (UPA, N = 35 vs BPA, N = 38) and 50 from the epicardial side (UPA, N = 11 vs BPA N = 39) of the ventricular free walls. Lesion transmurality was markedly improved by BPA (P = .030, odds ratio, 23.73 [4.71,31.96]). Ventricular BPA lesions were significantly deeper on the epicardial side (P < .0001) and endocardial side (P = .015).

CONCLUSION

Bipolar ablation is more likely to create transmural and epicardial lesions in the ventricle wall. Half the time is needed for the creation of comparably deep and large lesions.

Ablation of Refractory Papillary Muscle Ventricular Tachycardia Warranting Multiple Adjunctive Ablation Techniques: A Combined Approach for Success

A 27-year-old male presented to our institution with recurrent unifocal premature ventricular contraction/nonsustained ventricular tachycardia (VT) with associated cardiomyopathy. The patient had undergone three prior ablation procedures with continued arrhythmia. Mapping led to identification of the VT arising from the basal aspect of the left ventricular anterolateral papillary muscle. Conventional ablation techniques were unsuccessful. We incorporated adjunctive ablation techniques in this case that ultimately led to a successful outcome. The present discussion covers the roles of intracardiac echocardiography, induced apnea, and low-ionic irrigation.

[Catheter ablation of cardiac arrhythmias : Forms of energy and biophysical principles]

Catheter ablation of cardiac arrhythmias has evolved over the years and has become a cornerstone in the modern treatment of various supraventricular and ventricular arrhythmias. The goal of ablation is to permanently damage myocardium that is critically involved in the individual arrhythmia mechanism. Different catheters and forms of energy are available. Radiofrequency (RF) ablation is most common. Application of an alternating current at the catheter tip induces heating of tissue and, thus, leads to ablation of a targeted arrhythmogenic substrate. High temperatures (>70 °C at the catheter tip and >95 °C within the tissue) bear the risk of coagulum formation and steam pops and should be avoided, which limits power application. The evolution of irrigated RF ablation catheters enables the transfer of more power to the tissue and thereby increases the dimensions of the lesions. Cryoablation represents a valuable alternative. Cooling of tissue to -80 °C causes the intra- and extracellular formation of ice crystals, finally resulting in a dense circumscribed scar. The cryomapping procedure grants improved surveillance of the safety of ablation. Cryoenergy is very popular for pulmonary vein isolation (PVI) using the cryoballoon. In addition to the laser balloon that is established for PVI, ultrasound, microwaves, and stereotactic irradiation complete the arsenal.

Radiofrequency Ablation Using an Open Irrigated Electrode Cooled With Half-Normal Saline

OBJECTIVES

This study evaluated the use of half-normal saline (HNS) as the radiofrequency ablation (RFA) cooling irrigant.

BACKGROUND

Some instances of ventricular arrhythmia may originate deep within myocardium and can be refractory to standard ablation using open irrigated RFA. Recent data suggest that deeper ablation lesions can be created by decreasing the irrigant ionic concentration delivered through open irrigated RFA than by using normal saline (NS).

METHODS

Bovine myocardium was placed in a circulating saline bath. Two RFA catheters were oriented across from each other, with myocardium in between. Sequential unipolar HNS-irrigated RFA was performed and compared to bipolar ablation by using NS or HNS. Unipolar HNS ablation of the ventricles in a porcine model was performed and compared to ablation using NS.

RESULTS

Sequential ex vivo unipolar RFA with HNS produced larger lesions than sequential unipolar RFA with NS and produced lesions of similar size to those created with bipolar RFA using NS. Ex vivo bipolar RFA using HNS created the largest lesions. In vivo unipolar HNS ablation in porcine endocardium created larger lesion volumes, 152.9 ± 29.2 μl, compared to 94.7 ± 33.4 μl for unipolar ablation using NS.

CONCLUSIONS

By decreasing ionic concentration and charge density in RFA using HNS instead of NS irrigant, larger ablation lesions can be created and are similar in size to lesions created using bipolar ablation. This may be a useful ablation strategy for deep myocardial circuits refractory to standard ablation. Further studies are needed to evaluate this novel RFA strategy.

Catheter ablation for supraventricular tachycardias: contemporary issues

The treatment of cardiac arrhythmias has evolved significantly over the last 30 years. Understanding of arrhythmia mechanisms has led to pharmacologic therapies, surgical interventions and the widely used percutaneous catheter ablation techniques. The focus of this review is centered on the current catheter ablation therapies available for supraventricular tachycardia. We will discuss current management strategies including challenges when considering catheter ablation therapy for management of supraventricular tachycardias: atrioventricular nodal reentrant tachycardia, atrioventricular reentrant tachycardia utilizing an accessory pathway, atrial tachycardia and atrial flutter. Selected contemporary issues related to supraventricular tachycardia physiology, ablation approaches and ablation outcomes and complications will be discussed. Future goals for electrophysiologists are to continue to improve procedural safety and efficiency, while maintaining the impressive success rates that have been achieved.