Relationship Between Ablation Lesion Size Estimated by Ablation Index and Different Ablation Settings-an Ex Vivo Porcine Heart Study

In Vitro Models for Improved Therapeutic Interventions in Atrial Fibrillation

Atrial fibrillation is the most common type of cardiac arrhythmias in humans, mostly caused by hyper excitation of specific areas in the atrium resulting in dyssynchronous atrial contractions, leading to severe consequences such as heart failure and stroke. Current therapeutics aim to target this condition through both pharmacological and non-pharmacological approaches. To test and validate any of these treatments, an appropriate preclinical model must be carefully chosen to refine and optimise the therapy features to correctly reverse this condition. A broad range of preclinical models have been developed over the years, with specific features and advantages to closely mimic the pathophysiology of atrial fibrillation. In this review, currently available models are described, from traditional animal models and in vitro cell cultures to state-of-the-art organoids and organs-on-a-chip. The advantages, applications and limitations of each model are discussed, providing the information to select the appropriate model for each research application.

Efficiency and safety of high-power ablation guided by Lesion size index: An ex vivo porcine heart study

BACKGROUND

Although Lesion size index (LSI) has been reported to highly predict radiofrequency lesion size in vitro, its accuracy in lesion size and steam pop estimation has not been well investigated for every possible scenario.

METHODS

Initially, radiofrequency ablations were performed on porcine myocardial slabs at various power, CF, and time settings with blinded LSI. Subsequently, radiofrequency power at 20, 30, 40, 50, and 60 W was applied at CF values of 5, 10, 20, and 30 g to reach target LSIs of 4, 5, 6, and 7. Lesion size and steam pops were recorded for each ablation.

RESULTS

Lesion size was positively correlated with LSI regardless of power settings (p < 0.001). The linear correlation coefficients of lesion size and LSI decreased at higher power settings. At high power combined with high CF settings (50 W/20 g), lesion depth and LSI showed an irrelevant correlation (p = 0.7855). High-power ablation shortened ablation time and increased the effect of resistive heating. LSI could predict the risk of steam pops at high-power settings with the optimal threshold of 5.65 (sensitivity, 94.1%; specificity, 46.1%). The ablation depth of the heavy heart was shallower than that of the light heart under similar ablation settings.

CONCLUSIONS

LSI could predict radiofrequency lesion size and steam pops at high power settings in vitro, while synchronous high power and high CF should be avoided. Lighter hearts require relatively lower ablation settings to create appropriate ablation depth.

Integrated Ultrasound and Photoacoustic-Guided Laser Ablation Theranostic Endoscopic System

Advancements in ablation techniques have paved the way towards the development of safer and more effective clinical procedures for treating various maladies such as atrial fibrillation (AF). AF is characterized by rapid, chaotic atrial activation and is commonly treated using radiofrequency applicators or laser ablation catheters. However, the lack of thermal lesion formation and temperature monitoring capabilities in these devices prevents them from measuring the treatment outcome directly. In addition, poor differentiation between healthy and ablated tissues leads to incomplete ablation, which reduces safety and causes complications in patients. Hence, a novel photoacoustic (PA)-guided laser ablation theranostic device was developed around a traditional phased-array endoscope. The proposed technology provides lesion formation, tissue distinguishing, and temperature monitoring capabilities. Our results have validated the lesion monitoring capability of the proposed technology through PA correlation maps. The tissue distinguishing capability of the theranostic device was verified by the measurable differences in the PA signal between pre-and post-ablated mice myocardial tissue. The increase in the PA signal with temperature variations caused by the ablation laser confirmed the ability of the proposed device to provide temperature feedback.

Effects of different ablation settings on lesion dimensions in an ex vivo swine heart model: Baseline impedance, irrigant, and electrode configuration

INTRODUCTION

Intramural or epicardial locations of the arrhythmogenic substrate are regarded as one of the main reasons for radiofrequency (RF) catheter ablation failure. This study aims to conduct a comprehensive analysis of various factors including baseline impedance, irrigant and electrode configuration at similar ablation index (AI) value.

METHODS

In 12 ex vivo swine hearts, RF ablation was performed at a target AI value of 500 and a multistep impedance load (100-180 Ω) in 4 settings: (1) conventional unipolar configuration with an irrigant of normal saline (NS); (2) conventional unipolar configuration with an irrigant of half normal saline (HNS); (3) bipolar configuration with an irrigant of NS; (4) sequential unipolar configuration with an irrigant of NS. The relationships between lesion dimensions and above factors were examined.

RESULTS

Baseline impedance had a strong negative linear correlation with lesion dimensions at a certain AI. The correlation coefficient between baseline impedance and depth, width, and volume were R = -0.890, R = -0.755 and R = -0.813, respectively (p < .01). There were 10 (total: 10/100, 10%; bipolar: 10/25, 40%) transmural lesions during the whole procedure. Bipolar ablation resulted in significantly deeper lesion than other electrode configurations. Other comparisons in our experiment did not achieve statistical significance.

CONCLUSION

There is a strong negative linear correlation between baseline impedance and lesion dimensions at a certain AI value. Baseline impedance has an influence on the overall lesion dimensions among irrigated fluid and ablation configurations. Over a threshold impedance of 150 Ω, the predictive accuracy of AI can be compromised.

Effect of Baseline Impedance in Radiofrequency Delivery on Lesion Characteristics and the Relationship Between Impedance and Steam Pops

Objective

To explore the effects of baseline impedance (R) and power (P) on radiofrequency ablation (RFA) lesion characteristics and their correlation with steam pops using ThermoCool SmartTouch-SF (STSF) catheters in the porcine heart.

Method

A porcine left ventricle was submerged in 37°C saline ex vivo, and the experiment was performed with various P (P = 30, 40, 50, and 60 W) and multiple R loads (R = 80–100, 100–140, 140–180, and 180–220 Ω) to reach the target ablation index (AI; AI = 350, 450, and 500) or reach the target ablation time using a fixed contact force (CF; CF = 10–15 g) and the same saline irrigation (30 W/8 ml/min or 40–60 W/15 ml/min), repeated five times under each condition.

Results

The surface diameter, maximum diameter, depth, and volume of the lesions were strongly correlated with the AI (P = 40 W, R = 100–140 Ω, CF = 10–15 g) (r = 0.5412; r = 0.7889; r = 0.9366; and r = 0.913, respectively; all p < 0.05). As the value of R increased, the maximum diameter, depth, and volume of the lesions significantly increased (AI = 350, P = 30 W). Moreover, the higher the baseline value of R, the greater the absolute value of the R decrease (r = 0.9035, p < 0.05, Y = 0.2759 × X – 18.33). Under high power and high impedance, the occurrence rate of steam pops was high (P = 60 W, R = 180–220 Ω, AI when a steam pop occurred: 480 ± 26.5, ablation time: 11.29 ± 1.04 s).

Conclusion

Radiofrequency catheter ablation (RFCA) in power-controlled mode resulted in various lesion characteristics that were related to diverse baseline Rs. In addition, the incidence of steam pops was strongly correlated with high baseline R and high P.

Catheter contact area strongly correlates with lesion area in radiofrequency cardiac ablation: an ex vivo porcine heart study

PURPOSE

Our previous study confirmed that not only force but also the catheter contact angle substantially impacted the contact area and its morphology. Therefore, in this study, we aimed to further investigate the relationship between the catheter contact area and the dimensions of the ablation lesion area as a function of catheter contact angle and force in radiofrequency catheter ablation.

METHODS

The radiofrequency catheter ablation test was performed for 5 contact angles and 8 contact forces at a fixed ablation time of 30 s. The initial impedance was 92.5 ± 2.5 Ω, the temperature during ablation was 30 °C, and the power was 30 W. The irrigation rate during ablation was set to 17 mL/min. Each experiment was repeated 6 times.

RESULTS

The catheter contact area showed a strong correlation with the ablation lesion area (r = 0.8507). When the contact area was increased, the lesion area also increased linearly in a monotonic manner. The relationships between catheter contact force and ablation lesion area and between catheter contact force and ablation lesion depth are logarithmic functions in which increased contact force was associated with increased lesion area and depth. The catheter contact angle is also an important determinant of the lesion area. The lesion area progressively increased when the contact angle was decreased. In contrast, the lesion depth progressively increased when the contact angle was increased.

CONCLUSIONS

The catheter contact area was strongly correlated with the ablation lesion area. Additionally, catheter contact force and contact angle significantly impacted the dimensions of the lesion in radiofrequency catheter ablation procedures.