Monitoring reperfused myocardial infarction with delayed left ventricular systolic dysfunction in rabbits by longitudinal imaging

A novel method for the percutaneous induction of myocardial infarction by occlusion of small coronary arteries in the rabbit

Arrhythmic sudden cardiac death (SCD) is an important cause of mortality following myocardial infarction (MI). The rabbit has similar cardiac electrophysiology to humans and is therefore an important small animal model to study post-MI arrhythmias. The established approach of surgical coronary ligation results in thoracic adhesions that impede epicardial electrophysiological studies. Adhesions are absent following a percutaneously induced MI, which is also associated with reduced surgical morbidity and so represents a clear refinement of the approach. Percutaneous procedures have previously been described in large rabbits (3.5-5.5 kg). Here, we describe a novel method of percutaneous MI induction in smaller rabbits (2.5-3.5 kg) that are readily available commercially. New Zealand White rabbits (n = 51 males, 3.1 ± 0.3 kg) were anesthetized using isoflurane (1.5-3%) and underwent either a percutaneous MI procedure involving microcatheter tip deployment (≤1.5 Fr, 5 mm), coronary ligation surgery, or a sham procedure. Electrocardiography (ECG) recordings were used to confirm ST-segment elevation indicating coronary occlusion. Blood samples (1 and 24 h) were taken for cardiac troponin I (cTnI) levels. Ejection fraction (EF) was measured at 6-8 wk. Rabbits were then euthanized (Euthatal) and hearts were processed for magnetic resonance imaging and histology. Mortality rates were similar in both groups. Scar volume, cTnI, and EF were similar between both MI groups and significantly different from their respective sham controls. Thus, percutaneous coronary occlusion by microcatheter tip deployment is feasible in rabbits (2.5-3.5 kg) and produces an MI with similar characteristics to surgical ligation with lower procedural trauma and without epicardial adhesions.NEW & NOTEWORTHY Surgical coronary ligation is the standard technique to induce myocardial infarction (MI) in rabbits but is associated with procedural trauma and the generation of thoracic adhesions. Percutaneous coronary occlusion avoids these shortcomings and is established in pigs but has only been applicable to large rabbits because of a mismatch between the equipment used and target vessel size. Here, we describe a new scalable approach to percutaneous MI induction that is safe and effective in 2.5-3.5-kg rabbits.

Single-Dose Treatment with Rapamycin Preserves Post-Ischemic Cardiac Function through Attenuation of Fibrosis and Inflammation in Diabetic Rabbit

Robust activation of mTOR (mammalian target of rapamycin) signaling in diabetes exacerbates myocardial injury following lethal ischemia due to accelerated cardiomyocyte death with cardiac remodeling and inflammatory responses. We examined the effect of rapamycin (RAPA, mTOR inhibitor) on cardiac remodeling and inflammation following myocardial ischemia/reperfusion (I/R) injury in diabetic rabbits. Diabetic rabbits (DM) were subjected to 45 min of ischemia and 10 days of reperfusion by inflating/deflating a previously implanted hydraulic balloon occluder. RAPA (0.25 mg/kg, i.v.) or DMSO (vehicle) was infused 5 min before the onset of reperfusion. Post-I/R left ventricular (LV) function was assessed by echocardiography and fibrosis was evaluated by picrosirius red staining. Treatment with RAPA preserved LV ejection fraction and reduced fibrosis. Immunoblot and real-time PCR revealed that RAPA treatment inhibited several fibrosis markers (TGF-β, Galectin-3, MYH, p-SMAD). Furthermore, immunofluorescence staining revealed the attenuation of post-I/R NLRP3-inflammasome formation with RAPA treatment as shown by reduced aggregation of apoptosis speck-like protein with a caspase recruitment domain and active-form of caspase-1 in cardiomyocytes. In conclusion, our study suggests that acute reperfusion therapy with RAPA may be a viable strategy to preserve cardiac function with the alleviation of adverse post-infarct myocardial remodeling and inflammation in diabetic patients.

Isoproterenol-Induced Cardiomyopathy Recovery Intervention: Amlexanox and Forskolin Enhances the Resolution of Catecholamine Stress-Induced Maladaptive Myocardial Remodeling

The increasing incidence of stress-induced cardiomyopathy is due to the complexities of our modern-day lives, which constantly elicit stress responses. Herein, we aimed to explore the therapeutic potential of Amlexanox and Forskolin in promoting the recovery from stress-induced cardiomyopathy. Isoproterenol-induced cardiomyopathy (ICM) models were made, and the following treatment interventions were administered: 5% v/v DMSO as a placebo, Amlexanox (2.5 mg/100 g/day) treatment, Forskolin (0.5 mg/100 g/day), and Amlexanox and Forskolin combination, at their respective aforementioned dosages. The effects of Amlexanox and Forskolin treatment on ICM models were assessed by eletrocardiography and echocardiography. Also, using histological analysis and ELISA, their impact on myocardial architecture and inflammation were ascertained. ICM mice had excessive myocardial fibrosis, hypertrophy, and aggravated LVSDs which were accompanied by massive CD86+ inflammatory cells infiltration. Amlexanox treatment attenuated the myocardial hypertrophy, fibrosis, and inflammation and also slightly improved systolic functions. Meanwhile, forskolin treatment resulted in arrhythmias but significantly enhanced the resolution of myocardial fibrosis and inflammation. Intriguingly, Amlexanox and Forskolin combination demonstrated the most potency at promoting the recovery of the ICM from LVSD by attenuating maladaptive myocardial hypertrophy, fibrosis, and inflammatory responses. Our findings highlight the Amlexanox and Forskolin combination as a potential therapeutic intervention for enhancing cardiac function recovery from stress-induced cardiomyopathy by promoting the resolution of maladaptive cardiac remodeling.

Development and Long-Term Follow-Up of an Experimental Model of Myocardial Infarction in Rabbits

Simple Summary

Ischemic heart disease is one of the leading causes of death. A series of processes occur during acute myocardial infarction that contribute to the development of ventricular dysfunction, with subsequent heart failure and ventricular arrhythmias, which account for most episodes of sudden cardiac death in these patients. These complications are associated with the adverse cardiac remodeling that occurs during the healing process following an acute episode. The remodeling causes the appearance of a substrate that can trigger life-threatening arrhythmias, such as tachycardia and/or ventricular fibrillation. The development of experimental models for analyzing the basic mechanisms involved in the pathophysiology of myocardial infarction enables the study of different therapeutic approaches aimed at improving the patient´s prognosis. The present study describes the methodology and the results obtained in a 5-week chronic infarction (one hour followed by reperfusion) in a rabbit model. The viability of the model, the care provided, the characteristics and extent of the lesions, the inducibility of arrhythmias, and the reproducibility of the methods and results have been analyzed.

Abstract

A chronic model of acute myocardial infarction was developed to study the mechanisms involved in adverse postinfarction ventricular remodeling. In an acute myocardial infarction (AMI), the left circumflex coronary artery of New Zealand White rabbits (n = 9) was occluded by ligature for 1 h, followed by reperfusion. A specific care protocol was applied before, during, and after the intervention, and the results were compared with those of a sham operated group (n = 7). After 5 weeks, programmed stimulation and high-resolution mapping were performed on isolated and perfused hearts using the Langendorff technique. The infarct size determined by 2,3,5-triphenyltetrazolium chloride inside of the area at risk (thioflavin-S) was then determined. The area at risk was similar in both groups (54.33% (experimental infarct group) vs. 58.59% (sham group), ns). The infarct size was 73.16% as a percentage of the risk area. The experimental infarct group had a higher inducibility of ventricular arrhythmias (100% vs. 43% in the sham group, p = 0.009). A reproducible chronic experimental model of myocardial infarction is presented in which the extent and characteristics of the lesions enable the study of the vulnerability to develop ventricular arrhythmias because of the remodeling process that occurs during cardiac tissue repair.

Evaluation of cardiac arrhythmic risks using a rabbit model of left ventricular systolic dysfunction

Patients with heart disease have a higher risk to develop cardiac arrhythmias, either spontaneously or drug-induced. In this study, we have used a rabbit model of myocardial infarction (MI) with severe left ventricular systolic dysfunction (LVSD) to study potential drug-induced cardiac risks with N-(piperidin-2-ylmethyl)-2,5-bis(2,2,2-trifluoroethoxy)benzamide (flecainide). Upon ligation of the left circumflex arteries, male New Zealand White rabbits developed a large MI and moderate or severe LVSD 7 weeks after surgery, in comparison to SHAM-operated animals. Subsequently, animals were exposed to escalating doses of flecainide (0.25-4 mg/kg) or solvent. Electrocardiograms (ECG) were recorded before surgery, 1 and 7 weeks after surgery and continuously during the drug protocol. The ECG biomarker iCEB (index of Cardio-Electrophysiological Balance = QT/QRS ratio) was calculated. During the ECG recording at week 1 and week 7 post MI, rabbits had no spontaneous cardiac arrhythmias. When rabbits were exposed to escalating doses of flecainide, 2 out of 5 rabbits with MI and moderate LVSD versus 0 out of 5 solvent-treated rabbits developed arrhythmias, such as ventricular tachycardia/ventricular fibrillation. These were preceded by a marked decrease of iCEB just before the onset (from 4.09 to 2.42 and from 5.56 to 2.25, respectively). Furthermore, 1 out of 5 MI rabbits with moderate LVSD and 1 out of 7 MI rabbits with severe LVSD developed total atrioventricular block after flecainide infusion and died. This rabbit model of MI and severe LVSD may be useful for preclinical evaluation of drug (similar mechanism as flecainide)-induced arrhythmic risks, which might be predicted by iCEB.