Epicardium

EF is the fat deposit located between the visceral pericardium and the myocardium. EF density decreases with fat gain and increases with fat loss.^{[16 (link),21 (link)]} In addition, EF density increases with inflammatory cell infiltration and metabolic dysfunction.^{[14 (link),16 (link),22 (link)]} Therefore, the higher the density, the more metabolically active the fat deposition might be.^{[13 (link),23 (link)]}EF density and volume were both assessed using non-contrast CT images and a semi-automated software (Aquarius Intuition version 4.4.11; TeraRecon Headquarters, Forster City, CA). The pericardium was manually traced on axial slices from the pulmonary artery bifurcation to the apex of the heart. A CT density between −190 and −30 HU was used to select the EF and exclude any other tissue. Mean EF density and volume were calculated using the software based on the adipose tissue area, the number of slices, slice thickness, and intersection gaps, and reported as a continuous value, expressed in HU and cm³.
Two observers both blinded to HIV status and clinical data measured EF volume and density using the semi-automated software. Inter-observer and intra-observer agreement for EF volume and density measurement were highly reproducible (intraclass correlation coefficient for inter-observer agreement 0.75 for EF volume and 0.99 for density; Intra-observer agreement 0.97 for EF volume and 0.97 for density).^{[24 (link)]}

The monophasic pulse voltage $V_a=P(t)$ was applied on the left electrode, and the zero voltage $V_b=0$ was applied on the right electrode. The boundary of the plastic catheter and the epicardium represents the zero electric flux condition and is expressed as: $$n\cdot \sigma \nabla V=0$$
where $n$ is the normal unit vector to the epicardium surface.
As shown in Figure 4, a typical monophasic PFA waveform usually contains parameters such as pulse width, pulse amplitude, pulse interval, pulse number, etc. The ranges of PFA parameters used in this study were derived from the PFA in AF treatment [20 (link)] or animal experiences [21 (link),22 (link)], as shown in the following:
The pulse width of $P(t)$ is fixed at 100 μs as used in most studies; the pulse amplitude ranges from 1000 V to 2000 V [20 (link)]; the pulse interval ranges from 250 ms to 1000 ms [21 (link)]; and the pulse number ranges from 10 to 60 [22 (link)].
In order to highlight the influence of a single PFA parameter on the temperature rise and myocardial ablation volume of the model, this study took the remaining PFA parameters as the minimum influence on the temperature rise during PFA when investigating a single PFA parameter (minimum pulse amplitude: 1000 V, maximum pulse interval: 1000 ms, and minimum pulse number: 10). The details of the PFA parameter setting are listed in Table 1.
It can be seen from Table 1 that the influence of different PFA parameters on the temperature rise and ablation volume of the model was investigated in each of the three consecutive groups, including group 1 to 3 for pulse amplitude, group 4 to 6 for pulse interval, and group 7 to 9 for pulse number.