Effect of Sequential, Colocalized Radiofrequency and Pulsed Field Ablation on Cardiac Lesion Size and Histology

Abstract

Background: Sequential application of radiofrequency with pulsed field (PF) ablation may increase lesion depth while preserving the advantages of PF. The study's aim was to determine lesion dimensions of sequential, colocalized radiofrequency and PF ablation.

Methods: A preclinical study using swine (n=4) performed lesions in the right/left ventricles. Ablations were performed with a force-sensing 3.5-mm irrigated-tip ablation catheter using a generator delivering both radiofrequency and PF. PF was delivered using unipolar, biphasic pulses at a standard dose (PF index, 300) with 4-mL/min irrigation. Radiofrequency was delivered at 50 W for 10 s (15 mL/min). Lesions were created by applying colocalized radiofrequency followed by sequential application of PF on the same location, PF followed by sequential application of radiofrequency on the same location, PF alone, or radiofrequency alone. Tissue was collected after 2 hours for lesion assessment. Results are mean±SD.

Results: Forty-five lesions were analyzed. The lesion depth of radiofrequency alone was 4.9±0.8 mm. The mean lesion depth and width for PF alone were 3.5±0.6 and 5.1±1.8 mm. Lesion depths for combined applications were significantly greater versus PF alone (6.2±1.8 mm radiofrequency followed by sequential application of PF on the same location; 5.7±1.3 mm PF followed by sequential application of radiofrequency on the same location; P<0.0001 for both). Lesion widths were also significantly greater with combined therapy versus PF alone (8.6±1.8 mm radiofrequency followed by sequential application of PF on the same location; 8.9±2.1 mm PF followed by sequential application of radiofrequency on the same location; P<0.0001 for both). Histology for both combined lesions showed central thermal necrosis surrounded by a hemorrhagic and transitional PF zone.

Conclusions: Combined, colocalized radiofrequency and PF, irrespective of order, show significantly increased lesion size compared with the same dose of PF or radiofrequency alone.

Keywords: ablation; catheters; heart atria; heart ventricles; irreversible electroporation therapy; models, animal; technology.

Figure 1.

Triphenyl tetrazolium chloride staining of ablated tissue. Vertical and horizontal arrows represent lesion depth and width, respectively.

Figure 2.

Correlation of lesion depth and width to applied ablation mode. Left, Depths. Right, Widths. PF indicates pulsed field-only; PFrf, pulsed field followed by sequential application of radiofrequency on the same location; RF, radiofrequency-only; and RFpf, radiofrequency followed by sequential application of pulsed field on the same location.

Figure 3.

Gross pathology of various types of lesions. Gross sections of triphenyl tetrazolium chloride stained ventricular tissue depicting radiofrequency-only (A), pulsed field (PF)-only (B), radiofrequency followed by sequential application of PF on the same location (C), and PF followed by sequential application of radiofrequency on the same location (D) ablations. A thin hyperstained zone is outlined in A. The central pale zone (1), surrounding dark zone (2), and thin hyperstained zone (3) are depicted in B.

Figure 4.

Hematoxylin and eosin slide of pulsed field ablation. Higher magnification of black boxed area demonstrating contraction band morphology of myocardial tissue (*) with nuclear pyknosis (single arrow) of the treatment site on the left white dotted line. Notice dark, contracted, vacuolated nuclei seen in ablated tissue (double arrows). Normal myocardium on the right of the white dotted line.

Figure 5.

Hematoxylin and eosin slide of pulsed field followed by sequential application of radiofrequency on the same location with colored boxes indicating the location of each figure. A (white box), Disruption of subendocardium myofibers (double arrow) with small fibrin thrombus on the surface (single arrow). B (yellow box), Melted collagen around small blood vessels (single arrow) and coagulative necrosed myofibrils demonstrating loss of normal striations (double arrows). C (blue box), Contraction bands (single arrow) merging into normal myocardium (*).

Figure 6.

Hematoxylin and eosin slide of radiofrequency followed by sequential application of pulsed field on the same location with colored boxes indicating the location of each figure. A (white box), Endocardium demonstrating melted collagen on endocardium (white arrow) and surface thrombus (black arrow). B (black box), Pale zone demonstrating coagulative necrosis with loss of muscle fiber striations (*), and the dark zone demonstrating pyknotic nuclei (arrow) and significant hemorrhage (double arrow). C (cyan box), Contraction bands (*) into normal myocardium (arrow).