Application repetition and electrode-tissue contact result in deeper lesions using a pulsed-field ablation circular variable loop catheter

Abstract

Aims: Pulsed-field ablation (PFA) is a novel, myocardial-selective, non-thermal ablation modality used to target cardiac arrhythmias. Although prompt electrogram (EGM) signal disappearance is observed immediately after PFA application in the pulmonary veins, whether this finding results in adequate transmural lesions is unknown. The aim of this study is to check whether application repetition and catheter-tissue contact impact lesion formation during PFA.

Methods and results: A circular loop PFA catheter was used to deliver repeated energy applications with various levels of contact force. A benchtop vegetal potato model and a beating heart ventricular myocardial model were utilized to evaluate the impact of application repetition, contact force, and catheter repositioning on contiguity and lesion depth. Lesion development occurred over 18 h in the vegetal model and over 6 h in the porcine model. Lesion formation was found to be dependent on application repetition and contact. In porcine ventricles, single and multiple stacked applications led to a lesion depth of 3.5 ± 0.7 and 4.4 ± 1.3 mm, respectively (P = 0.002). Furthermore, the greater the catheter-tissue contact, the more contiguous and deeper the lesions in the vegetal model (1.0 ± 0.9 mm with no contact vs. 5.4 ± 1.4 mm with 30 g of force; P = 0.0001).

Conclusion: Pulsed-field ablation delivered via a circular catheter showed that both repetition and catheter contact led independently to deeper lesion formation. These findings indicate that endpoints for effective PFA are related more to PFA biophysics than to mere EGM attenuation.

Keywords: Catheter ablation; Irreversible electroporation; Pre-clinical model; Pulmonary vein isolation; Pulsed-field ablation.

Graphical Abstract

Figure 1

Single applications of pulsed-field ablation can silence electrogram activity in a pulmonary vein, but make shallow lesions. (A) A CARTO display of a porcine right inferior pulmonary vein. Left: A pre-ablation voltage map are shown. Middle: A single application of pulsed-field ablation is delivered, and noise depicts the moment of energy delivery. Right: After just 1 application of energy at the right inferior pulmonary vein, electrogram signal attenuation of the vein isolation is noted (1 application, 0.33 ablations). A post-voltage map is shown. As depicted by the number of purple ablation tags, the porcine subject was ultimately treated with two applications at the right inferior pulmonary vein and one application at the right superior pulmonary vein. In both cases, an increase in low-voltage area is observed relative to the pre-voltage map. Images courtesy of © Biosense Webster, Inc. All rights reserved. (B) A scatter plot of lesion depth in a vegetal model when 1–3 applications (0.33–1 ablation) are delivered. As observed in the panel, the greater the number of applications, the deeper the lesion.

Figure 2

Lesion contiguity is achieved between the inter-electrode spaces. (A) A vegetal model sample of one ablation. In the vegetal model, the cross section displays a fully contiguous lesion profile, represented by the convex area below the line. Natural discolouration of the potato has resulted in a dark area in the middle of the potato slice above the lesion region. (B, top) A porcine model sample of one ablation. (B, bottom) Representative intracardiac echocardiography and CARTO images demonstrate the study methodology in the ventricle; contact was confirmed with intracardiac echocardiography before energy application. Images courtesy of © Biosense Webster, Inc. All rights reserved. (C, top) A high-magnification photomicrograph of ventricle ablation from B. The majority of the myocardial cells has smooth, eosinophilic cytoplasm with wavy hyper-eosinophilic bands (their cytoplasm has lost its cross striations), and their nuclei exhibit pyknosis (nuclear condensation). Haematoxylin and eosin staining; the scale bar equals 50 µm. (C, bottom) A high-magnification photomicrograph of ventricle ablation from B. Myocardial cells in the lower portion of the image have fragmented and finely vacuolated cytoplasm (their cytoplasm has lost its cross striations). Haematoxylin and eosin staining; the scale bar equals 20 µm.

Figure 3

Application repetition results in increased lesion depth in a vegetal (A) model and porcine (B) model. (B) A bar graph comparing lesion depths in both vegetal and porcine ventricle tissue when either three or six applications are stacked.

Figure 4

Contact force results in increased lesion depth. (A) An interval plot of lesion depth vs. catheter contact in a vegetal model (P < 0.001). (B) Images of potato lesions corresponding to one application up to six ablations with 0, 15, and 30 g of contact force. The terms ‘low’, ‘nominal’, and ‘high’ refer to the number of energy applications delivered before moving or rotating the catheter. Low dose entails one application, nominal dose entails three applications/one ablation, and high dose entails six applications/two ablations without moving the catheter. (C) An interval plot of lesion depth vs. contact force (P < 0.001) and ablation dosage (P < 0.001). (D) An interval plot of lesion width vs. contact force (P = 0.228) and ablation dosage (P < 0.001).

Figure 5

Tissue proximity indication corresponds to contact and lesion contiguity. Images of potato lesions corresponding to one ablation with 0, 15, and 30 g of contact force. Electrodes with white border rings indicate positive tissue proximity indication. Circled are corresponding areas on the tissue proximity indication and the lesion itself. In areas where there was negative tissue proximity indication, a lack of lesion contiguity is noted. Images courtesy of © Biosense Webster, Inc. All rights reserved.

Figure 6

Variable loop circular catheter repositioning produces similar lesion depths as application stacking. (A) An interval plot of lesion depth vs. catheter workflow (P = 0.444). (B, left) An illustrative depiction of catheter workflows; the variable loop circular catheter is repositioned to obtain a rotation of the loop. (B, right) The variable loop circular catheter is held in place while delivering two ablations. A comparison of vegetal model samples with two ablations with repositioning (right) and two stacked ablations (left). Notice that the gap between Electrodes 1 and 10 where no lesion forms has been filled by loop rotation in the repositioning workflow. Images courtesy of © Biosense Webster, Inc. All rights reserved.

Figure 7

Variable loop circular catheter repositioning resulting in an angular rotation of 120° or more closes the 1–10 electrode gap. Images are of two stacked ablations on a potato model. (A) The degree measures indicate the angle to which the tip of the variable loop circular catheter is rotated (0–180°) around the centre point of the loop from the position of the first ablation to the position of the second stacked ablation. (B) A plot of the width of the gap (where present) on the surface of the potato core slice after two stacked ablations with the indicated rotation angle in between energy deliveries. (C) A comparison of the occurrence of subsurface gaps in the vegetal model after the two stacked ablations with the indicated rotation angle.