Impact of electrode tip shape on catheter performance in cardiac radiofrequency ablation

Background

The role of catheter tip shape on the safety and efficacy of radiofrequency (RF) ablation has been overlooked, although differences have been observed in clinical and research fields.

Objective

The purpose of this study was to analyze the role of electrode tip shape in RF ablation using a computational model.

Methods

We simulated 108 RF ablations through a realistic 3-dimensional computational model considering 2 clinically used, open-irrigated catheters (spherical and cylindrical tip), varying contact force (CF), blood flow, and irrigation. Lesions are defined by the 50°C isotherm contour and evaluated by means of width, depth, depth at maximum width, and volume. Ablations are deemed as safe, critical (tissue temperature >90°C), and pop (tissue temperature >100°C).

Results

Tissue-electrode contact is less for the spherical tip at low CF but the relationship is inverted at high CF. At low CF, the cylindrical tip generates deeper and wider lesions and a 4-fold larger volume. With increasing CF, the lesions generated by the spherical tip become comparable to those generated by the cylindrical tip. The 2 tips feature different safety profiles: CF and power are the main determinants of pops for the spherical tip; power is the main factor for the cylindrical tip; and CF has a marginal effect. The cylindrical tip is more prone to pop generation at higher powers. Saline irrigation and blood flow effect do not depend on tip shape.

Conclusion

Tip shape determines the performance of ablation catheters and has a major impact on their safety profile. The cylindrical tip shows more predictable behavior in a wide range of CF values.

Spatial temperature reconstructions in myocardial tissues undergoing radiofrequency ablations by performing high-resolved temperature measurements

BACKGROUND

Radiofrequency (RF) lesion creation is related to the heat propagation induced by RF application on tissues. Thermocouple embedded in the RF antenna are not able to predict deep tissue temperature at various level.

OBJECTIVES

This study aims to investigate the influence of power delivered on radiofrequency catheter ablation (RFCA) effects by means of high resolved 2D temperature maps.

METHODS

Three trials of four ablations (12 applications) were executed on each specimen of healthy excised swine myocardium in different application points at four RF power values (30 W, 40 W, 50 W, and 60 W) for a fixed treatment time. All the data provided by the fiber Bragg gratings (FBGs) were analyzed. Temperature variations (ΔT) in time recorded in the 28 sites of measurements were reported. Also, temperature maps showing the ΔT spatial distribution reached within the tissue at the end of the RFCA were produced and displayed, together with the representation of the lethal isotherm. Moreover, the time of achievement of the lethal isotherm at different tissue depths (from 1 to 8 mm) was evaluated for the four power settings.

RESULTS

Temperature trends reported comparable profiles across the different power settings. ΔT values and ΔT rising times showed dependence on the sensors' proximity to the RF energy source and on the set RF power. Temperature maps confirmed that heat propagation occurs preferentially along the width of the tissue than in the depth. Also, for the adjusted treatment time, no power setting guarantees lesions thicker than 6 mm.

CONCLUSIONS

ΔT maximal values and ΔT rising time strongly depends on the proximity of the tissues to RF energy source, as well as on the RF power setting. A plateau is reached in lesion size, regardless of the power setting. A first correlation between lesion size, power setting, and time to achieve lethal isotherms has been established.

Systematic Characterization of High-Power Short-Duration Ablation: Insight From an Advanced Virtual Model

Background: High-power short-duration (HPSD) recently emerged as a new approach to radiofrequency (RF) catheter ablation. However, basic and clinical data supporting its effectiveness and safety is still scarce.

Objective: We aim to characterize HPSD with an advanced virtual model, able to assess lesion dimensions and complications in multiple conditions and compare it to standard protocols.

Methods: We evaluate, on both atrium and ventricle, three HPSD protocols (70 W/8 s, 80 W/6 s, and 90 W/4 s) through a realistic 3D computational model of power-controlled RF ablation, varying catheter tip design (spherical/cylindrical), contact force (CF), blood flow, and saline irrigation. Lesions are defined by the 50°C isotherm contour. Ablations are deemed safe or complicated by pop (tissue temperature >97°C) or charring (blood temperature >80°C). We compared HPSD with standards protocols (30–40 W/30 s). We analyzed the effect of a second HPSD application.

Results: We simulated 432 applications. Most (79%) associated a complication, especially in the atrium. The three HPSD protocols performed similarly in the atrium, while 90 W/4 s appeared the safest in the ventricle. Low irrigation rate led frequently to charring (72%). High-power short-duration lesions were 40–60% shallower and smaller in volume compared to standards, although featuring similar width. A second HPSD application increased lesions to a size comparable to standards.

Conclusion: High-power short-duration lesions are smaller in volume and more superficial than standards but comparable in width, which can be advantageous in the atrium. A second application can produce lesions similar to standards in a shorter time. Despite its narrow safety margin, HPSD seems a valuable new clinical approach.

Modeling esophageal protection from radiofrequency ablation via a cooling device: an analysis of the effects of ablation power and heart wall dimensions

BACKGROUND

Esophageal thermal injury can occur after radiofrequency (RF) ablation in the left atrium to treat atrial fibrillation. Existing methods to prevent esophageal injury have various limitations in deployment and uncertainty in efficacy. A new esophageal heat transfer device currently available for whole-body cooling or warming may offer an additional option to prevent esophageal injury. We sought to develop a mathematical model of this process to guide further studies and clinical investigations and compare results to real-world clinical data.

RESULTS

The model predicts that the esophageal cooling device, even with body-temperature water flow (37 °C) provides a reduction in esophageal thermal injury compared to the case of the non-protected esophagus, with a non-linear direct relationship between lesion depth and the cooling water temperature. Ablation power and cooling water temperature have a significant influence on the peak temperature and the esophageal lesion depth, but even at high RF power up to 50 W, over durations up to 20 s, the cooling device can reduce thermal impact on the esophagus. The model concurs with recent clinical data showing an 83% reduction in transmural thermal injury when using typical operating parameters.

CONCLUSIONS

An esophageal cooling device appears effective for esophageal protection during atrial fibrillation, with model output supporting clinical data. Analysis of the impact of ablation power and heart wall dimensions suggests that cooling water temperature can be adjusted for specific ablation parameters to assure the desired myocardial tissue ablation while keeping the esophagus protected.

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

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

Should fluid dynamics be included in computer models of RF cardiac ablation by irrigated-tip electrodes?

Background

Although accurate modeling of the thermal performance of irrigated-tip electrodes in radiofrequency cardiac ablation requires the solution of a triple coupled problem involving simultaneous electrical conduction, heat transfer, and fluid dynamics, in certain cases it is difficult to combine the software with the expertise necessary to solve these coupled problems, so that reduced models have to be considered. We here focus on a reduced model which avoids the fluid dynamics problem by setting a constant temperature at the electrode tip. Our aim was to compare the reduced and full models in terms of predicting lesion dimensions and the temperatures reached in tissue and blood.

Results

The results showed that the reduced model overestimates the lesion surface width by up to 5 mm (i.e. 70%) for any electrode insertion depth and blood flow rate. Likewise, it drastically overestimates the maximum blood temperature by more than 15 °C in all cases. However, the reduced model is able to predict lesion depth reasonably well (within 0.1 mm of the full model), and also the maximum tissue temperature (difference always less than 3 °C). These results were valid throughout the entire ablation time (60 s) and regardless of blood flow rate and electrode insertion depth (ranging from 0.5 to 1.5 mm).

Conclusions

The findings suggest that the reduced model is not able to predict either the lesion surface width or the maximum temperature reached in the blood, and so would not be suitable for the study of issues related to blood temperature, such as the incidence of thrombus formation during ablation. However, it could be used to study issues related to maximum tissue temperature, such as the steam pop phenomenon.