Experimental parameters and infarct size in closed chest pig LAD ischemia reperfusion models; lessons learned

Abstract

Background Preclinical models that resemble the clinical setting as closely as possible are essential in translating promising therapies for the treatment of acute myocardial infarction. Closed chest pig left anterior descending coronary artery (LAD) ischemia reperfusion (I/R) models are valuable and clinically relevant. Knowledge on the influence of experimental design on infarct size (IS) in these models is a prerequisite for suitable models. To this end, we investigated the impact of several experimental features (occlusion and follow-up time and influence of area at risk (AAR)) on IS. Methods A total of fifty-one female Landrace pigs were subjected to closed chest LAD balloon occlusion and evaluated in three substudies with varying protocols. To assess the relationship between time of occlusion and the IS, 18 pigs were subjected to 60-, 75- and 90 min of occlusion and terminated after 24 h of follow-up. Influence of prolonged follow-up on IS was studied in 18 pigs after 75 min of occlusion that were terminated at 1, 3 and 7 days. The relation between AAR and IS was studied in 28 pigs after 60 min of occlusion and 24 h of follow-up. The relation between VF, number of shocks and IS was studied in the same 28 pigs after 60 min of occlusion. Results Increasing occlusion time resulted in an increased IS as a ratio of the AAR (IS/AAR). This ranged from 53 ± 23% after 60 min of occlusion to 88 ± 2.2% after 90 min (P = 0.01). Increasing follow-up, from 1 to 3 or 7 days after 75 min of occlusion did not effect IS/AAR. Increasing AAR led to a larger IS/AAR (r2 = 0.34, P = 0.002), earlier VF (r2 = 0.32, P = 0.027) and a higher number of shocks (r2 = 0.29, P = 0.004) in pigs subjected to 60 min of occlusion. Conclusions These experiments describe the association of occlusion time, follow-up duration, AAR and VF with IS in closed chest pig LAD I/R models. These results have important implications for future I/R studies in pigs and can serve as a guideline for the selection of appropriate parameters and the optimal experimental design.

A comprehensive and longitudinal cardiac magnetic resonance imaging study of the impact of coronary ischemia duration on myocardial damage in a highly translatable animal model

“…We report on the longitudinal structural changes that affect the infarcted myocardium and show that at 42 days post‐STEMI, scar size is comparable among pigs subjected to 60 min or longer and smaller than that observed on day 3. Previous studies in closed‐chest pig LAD ischemia/reperfusion have also shown that increasing occlusion times result in an increased infarct size (expressed per AAR) reaching a plateau, and ischemia times longer than 2 h have not shown to lead to larger infarcts as compared to persistent coronary occlusion 18,20 . Notably, CMR was not available in these studies.…”

“…They reported no significant differences in infarct size expressed as the risk area between animals banded for 60 min or above, supporting the need to reperfuse within 1 h after occlusion. In a study in a closed‐chest model of balloon‐induced MI, Silvis et al 20 evaluated the impact of 60, 75 and 90 min of ischemia followed by 24 h reperfusion in thiopental anaesthetised pigs. No differences were observed in the AAR as % LV between the different occlusion groups.…”

“…39 Because of their human cardiovascular resemblance (comparable hemodynamics, anatomy and metabolic requirements and lack of collateral circulation), closed-chest pig models of LAD ischemia/ reperfusion have become mandatory for final proof-ofconcept studies before moving into clinical trials aimed to test cardioprotective/regenerative strategies. Yet, although the time course of infarct evolution in the setting of ischemia/reperfusion has been studied in several animal models of STEMI, including pigs [17][18][19][20][40][41][42] and in a few clinical studies, 43,44 it is still unclear which is the impact of the duration of ischemia on modern and clinically available CMR imaging techniques in translational studies. 45 As such, no preclinical study has determined the influence of ischemia time on critical structural parameters, including cardiac necrosis, oedema and MVO, and on global and regional parameters of LV performance and remodelling.…”

“…An in-depth characterization of the impact of coronary ischemia time on myocardial tissue and function has yet to be performed to determine the time window of opportunity to salvage the ischemic heart with accurate techniques. So far, studies in pigs have implemented postmortem fluoroscopy and histology staining approaches to determine the impact of ischemia time on the area at risk and infarct size acutely post-MI (24 h postreperfusion) [17][18][19][20] Yet, none has assessed the impact of coronary ischemia time by implementing cardiac magnetic resonance (CMR), the gold standard noninvasive imaging technique for evaluating cardiac anatomy, volumes and function as well as myocardial tissue characterization in the setting of MI. This is of paramount importance since multiple dynamic tissue changes occur in MI (oedema, microvascular obstruction, haemorrhage, cardiomyocyte necrosis and ultimately replacement by fibrosis) that contribute to long-term prognosis.…”

Neutral Effects of Combined Treatment With GLP-1R Agonist Exenatide and MR Antagonist Potassium Canrenoate on Cardiac Function in Porcine and Murine Chronic Heart Failure Models

“…Therefore, pigs were exposed to prolonged ischemia times and the mice were subjected to permanent ligation. By comparing 60, 75 and 90 min occlusion in the closed chest LAD ligation model in pigs it was recently shown that increasing occlusion times lead to significantly larger infarct sizes, with almost complete transmural infarcts upon 90 min occlusion time (Silvis et al, 2021) In the current study, we used a porcine model of severe IR injury with 150 min occlusion time and a mice model of permanent myocardial infarction. Consequential to the prolonged ischemia time the damage is presumably in an irreversible state, thereby limiting the therapeutic benefit on salvaging myocardial ischemiareperfusion-related injury.…”