Differential effect of high-frequency electroporation on myocardium vs. non-myocardial tissues

Abstract

Aims: Pulsed-field ablation (PFA) is an emerging non-thermal ablation method based on the biophysical phenomenon of electroporation. Data on PFA cardiac selectivity nature and tissue-specific thresholds are lacking. We aim to compare the in vivo differential effect of high-frequency irreversible electroporation (HF-IRE) protocols on various tissues.

Methods and results: Twenty-three Sprague-Dawle rodents were allocated into three different protocols of 300, 600, and 900 V, respectively, while delivering twenty 100 µs bursts of a 150 kHz biphasic square wave to five tissues; cardiac muscle, skeletal muscle, liver, carotid artery and sciatic nerve. Lesions were evaluated quantitatively by histologic analysis and by morphometric evaluation. There were eight, seven and eight animals in the 300, 600, and 900 V protocols, respectively. High-frequency electroporation protocols showed a graded effect on myocardial tissue with larger lesions in the 900 V protocol compared with the other two protocols as demonstrated by width (P = 0.02), length (P = 0.01) and fibrosis ratio (P = 0.001). This effect was not observed for other tissues with attenuated degree of damage. No damage to the carotid artery was observed in all protocols. Partial damage to the sciatic nerve was observed in only two samples (25%) in the 600 V group and in one sample (14.3%) in the 900 V group.

Conclusion: Electroporation effect is tissue-specific such that myocardium is more prone to electroporation damage compared with neural and vascular tissues. Our results suggest no neural or vascular damage with using a low-amplitude HF-IRE protocol. Further investigation is warranted to better identify other tissue-specific thresholds.

Keywords: Cardiac selectivity; Electroporation; High-frequency electroporation; Pulsed-field ablation.

Graphical Abstract

Figure 1

Equipment description and configuration; (left) a custom-made generator based on an H bridge circuit consisting of four N and P channels MOSFET. The generator enables a maximal output voltage of 1100 V, at a frequency range of 75–150 kHz with burst duration between 100 and 200 µs. (Right) Two needle electrodes (top) with 3 mm in length and with 5 mm distance between them and (bottom) two-clamp electrodes (0.5 mm in diameter) with 0.5 cm inter-electrode distance.

Figure 2

Quantitative evaluation of tissue damage; evaluation of tissue damage by fibrosis measurements as quantified by (A) Fiji software (ImageJ®), showing histological sample (left column) of scarred ablated skeletal muscle tissue (fibrosis is stained with red (left side), from the 900 V and after Fiji software analysis (right column, fibrosis is marked in white (left side)) and (B) direct measurements of length and width using CellSense Imagine software (Olympus®) on scarred ablated liver tissue, from the 900 V.

Figure 3

Histological appearance of tissue damage; histology of (A) cardiac, (B) liver, (C) skeletal muscle (D) nerve tissues and (E) carotid artery. Fibrosis is stained with red after Picrosirius and marked with an asterisk (indicates tissue injury). Scarred ablated tissue from the 900 V protocol group (right column) is compared with the healthy tissue from each organ (left column) showing greater damage to the heart. Carotid artery samples did not demonstrate significant damage in all protocols.

Figure 3

Histological appearance of tissue damage; histology of (A) cardiac, (B) liver, (C) skeletal muscle (D) nerve tissues and (E) carotid artery. Fibrosis is stained with red after Picrosirius and marked with an asterisk (indicates tissue injury). Scarred ablated tissue from the 900 V protocol group (right column) is compared with the healthy tissue from each organ (left column) showing greater damage to the heart. Carotid artery samples did not demonstrate significant damage in all protocols.

Figure 4

Effect of voltage on tissue damage; histology of (A) myocardial tissue and (B) nerve tissue after being treated with 300 V protocol (left column), 600 V protocol (middle column) and 900 V protocol (right column) showing a graded effect of voltage in the heart but not in the Sciatic nerve. Fibrosis is stained with red after Picrosirius and marked with an asterisk (indicates tissue injury).

Figure 5

Evaluation of the degree of fibrosis in the heart for different protocols as quantify be length (µM), width (µM) and fibrosis ratio. A comparison between different protocols (300 V vs. 600 V vs. 900 V) for myocardial damage as evaluated by length (µM), width (µM) and fibrosis ratio, showing a positive correlation between voltage and extent of damage in width and fibrosis ratio.