Methods and results
The study was performed in six pigs (weight 60–75 kg). After median sternotomy and opening of the pericardium, a pericardial cradle was formed and filled with blood. A linear seven polar 7-Fr electrode catheter with 2.5 mm electrodes and 2.5 mm inter-electrode spacing was placed in good contact with epicardial tissue. A single IRE application was delivered using 50 J at one site and 100 J at two other sites, in random sequence, using a standard monophasic defibrillator connected to all seven electrodes connected in parallel. The pericardium and thorax were closed and after 3 weeks survival animals were euthanized. A total of 82 histological sections from all 18 electroporation lesions were analysed. A total of seven 50 J and fourteen 100 J epicardial IRE applications were performed. Mean peak voltages at 50 and 100 J were 1079.2 V ± 81.1 and 1609.5 V ± 56.8, with a mean peak current of 15.4 A ± 2.3 and 20.2 A ± 1.7, respectively. Median depth of the 50 and 100 J lesions were 3.2 mm [interquartile range (IQR) 3.1–3.6] and 5.5 mm (IQR 4.6–6.6) (P < 0.001), respectively. Median lesion width of the 50 and 100 J lesions was 3.9 mm (IQR 3.7–4.8) and 5.4 mm (IQR 5.0–6.3), respectively (P < 0.001). Longitudinal sections showed continuous lesions for 100 J applications.