Correction to: Rapid, Full-Scale Change to Virtual PCIT During the COVID-19 Pandemic: Implementation and Clinical Implications

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Optimization of Irreversible Electroporation Protocols for In-vivo Myocardial Decellularization

<div><p>Background</p><p>Irreversible electroporation (IRE) is a non-thermal cell ablation approach that induces selective damage to cell membranes only. The purpose of the current study was to evaluate and optimize its use for in-vivo myocardial decellularization.</p><p>Methods</p><p>Forty-two Sprague-Dawley rats were used to compare myocardial damage of seven different IRE protocols with anterior myocardial infarction damage. An in-vivo open thoracotomy model was used, with two-needle electrodes in the anterior ventricular wall. IRE protocols included different combinations of pulse lengths (70 vs. 100 μseconds), frequency (1, 2, 4 Hz), and number (10 vs. 20 pulses), as well as voltage intensity (50, 250 and 500 Volts). All animals underwent baseline echocardiographic evaluation. Degree of myocardial ablation was determined using repeated echocardiography measurements (days 7 and 28) as well as histologic and morphometric analysis at 28 days.</p><p>Results</p><p>All animals survived 28 days of follow-up. Compared with 50V and 250V, electroporation with 500V was associated with significantly increased myocardial scar and reduction in ejection fraction (67.4%±4% at baseline vs. 34.6%±20% at 28 days; p <0.01). Also, compared with pulse duration of 70 μsec, pulses of 100 μsec were associated with markedly reduced left ventricular function and markedly increased relative scar area ratio (28%±9% vs. 16%±3%, p = 0.02). Decreasing electroporation pulse frequency (1Hz vs. 2Hz, 2Hz vs. 4Hz) was associated with a significant increase in myocardial damage. Electroporation protocols with a greater number of pulses (20 vs. 10) correlated with more profound tissue damage (p<0.05). When compared with myocardial infarction damage, electroporation demonstrated a considerable likeness regarding the extent of the inflammatory process, but with relatively higher levels of extra-cellular preservation.</p><p>Conclusions</p><p>IRE has a graded effect on the myocardium. The extent of ablation can be controlled by changing pulse length, frequency and number, as well as by changing electric field intensity.</p></div

Comparison of myocardial axial section of different protocols.

<p>Every row in the figure compares the axial section of the left ventricle of rats that were treated with two different IRE protocols. Moreover, all the pairs of protocols selected for this figure are different in only one setting of the IRE protocols (i.e. voltage, frequency, etc.) and demonstrate significant differences between their morphometric measurements. Protocol numbers are in the right upper corner of each slide. The pairs of protocols are (from top to bottom): 5 and 3(70μsec and 100μsec), 8 and 3 (MI vs. IRE), 6 and 4 (10 pulses vs. 20 pulses), 5 and 4 (2Hz vs. 1HZ).</p

Summary of echocardiographic measurements.

<p>Summary of echocardiographic measurements.</p

The transient receptor potential vanilloid 2 cation channel is abundant in macrophages accumulating at the peri-infarct zone and may enhance their migration capacity towards injured cardiomyocytes following myocardial infarction.

PURPOSE: A novel family of transient receptor potential (TRP) channels, that may hold a role in calcium homeostasis, has recently been described. By employing a GeneChip array analysis we have demonstrated a clear and specific upregulation of the TRP vanilloid 2 (TRPV2) mRNA in the left ventricles (LV) 3-5 days post-acute myocardial infarction (MI) compared to sham-operated controls, both in rats and in mice. We sought to characterize the cardiac cellular subpopulations in which TRPV2 is overexpressed upon acute MI. METHODS: Lewis rats underwent an acute MI by ligation of the left anterior descending artery or chest opening only (sham). The animals were terminated at various time points and an immunohistochemical (IHC) and immunofluorescent (IFC) staining of the LV sections as well as a flow cytometry analysis of LV-derived cells were carried out, using anti-TRPV2 and anti-monocyte/macrophage antibodies. Rat alveolar macrophage cells, NR8383, transiently transfected with TRPV2 siRNA were allowed to migrate towards hypoxic conditioned media of the rat cardiac myoblast line H9C2 using a trans-well migration assay. The macrophage cells migrating to the bottom side of the inserts were counted. RESULTS: The IHC and IFC staining as well as the flow cytometry data demonstrated a substantial expression of TRPV2 in infiltrating macrophages in the peri-infarct region 3-5 days post-acute MI. The in vitro migration assay data demonstrated that following inhibition of the TRPV2 channel, the number of migrating macrophages towards conditioned medium of hypoxic cardiomyocytes was significantly reduced. CONCLUSIONS: TRPV2 is highly expressed on the peri-infarct infiltrating macrophages and may play an important role in post-MI phagocytosis. Better characterization of this channel may pave the way for identifying a new target for modulating the dramatic post-MI immune reactions

Animal model and electric field distribution After sterile thoracotomy, IRE was applied to the anterior myocardium located to the left of the lower part of the left anterior descending artery (Fig 1.1 and Fig 1.2).

<p>Electric field distribution induced by two-needle electrodes and a 500 volt pulse are illustrated in Fig 1.3. Note that electric field intensity is concentrated in the plane between the two electrodes.</p

Microscopic view of treated myocardium.

<p>In each row the images from right to left represent: low potency IRE protocol (protocol 2), high potency electroporation protocol (protocol 6), MI group (protocol 8). ED1 staining is presented in the upper row, while H&E staining is presented in the lower row. Note: 1) the similar extent of damage between high potency IRE protocol and MI–images 1B and 1C, 2B and 2C. 2). The greater degree of extracellular damage caused by MI compared with low and high potency IRE protocols–images 2C, 2A, 2B respectively. Arrows point to the areas of extensive inflammation.</p

Electroporation protocols used in the study.

<p>Electroporation protocols used in the study.</p

Comparison of morphometric measurements between pairs of protocols.

<p>Morphometric measurements of pairs of protocols with only one changed parameter were compared (using unpaired Student t-test), in order to learn about the effect of different parameters on the potency of each protocol. Only pairs with a statistically significant difference in morphometric measurements are shown. From top to bottom: (3a) presents comparisons of scar areas with significant differences. (3b) presents comparisons of scar thicknesses with significant differences. (3c) presents comparisons of scar perimeters with significant differences.</p