Establishing a Myocardial Ischemia-Reperfusion Injury Model in Mice and Rats using Left Anterior Descending Artery Ligation and Isolated Heart Experiments

Myocardial infarction (MI) is a leading cause of death globally, with over 730,000 cases each year in the United States alone. Factors involved in the prognosis of an MI include identification of the artery occluded, the time to reperfusion, the size of the infarct, and the degree of cardiomyocyte death. Thus, the treatment of MI typically involves targeting one or more of these factors. Timely opening of an occluded artery to reperfuse the ischemic tissue remains the mainstay treatment through either thrombolytic therapy, arterial stenting, or percutaneous coronary intervention. However, reperfusion itself may cause further damage through the generation of reactive oxygen species (ROS) in a process known as myocardial ischemiareperfusion injury. There are no clinically accepted treatments that directly target cardiomyocyte reperfusion injuries, and the pathophysiology of the process remains complex. Due to the high mortality, lack of positive clinical evidence, and complex pathophysiology, it is difficult to safely measure and study MIR injuries in humans. However, parallel animal models that mimic infarctions in an experimental setting will be essential in furthering the understanding and treatment for MIR injuries. In order to progress research in the field of MIR injury, a reliable and reproducible study model must first be established. The goal of the study is to establish two different models of MIR injury and provide positive evidence that they are reproducible, effective, and reliable. The first model will establish an in vivo Left Anterior Descending (LAD) artery ligation model in mice, which will result in an MIR injury observable through ECG changes and through obtaining a percentage of infarction. The second model will establish a Langendorff model that will show similar cardiomyocyte death, measurable through changes to LVESP, LVEDP, dPTd max, dP/dT min, heart rate and coronary flow, and by obtaining a percentage of infarction. We found that, iIn summary, both models showed evidence of MIR injury confirmable through ECG changes, tissue staining, and cardiac function and coronary flow reduction

Mechano-electric heterogeneity of the myocardium as a paradigm of its function

Myocardial heterogeneity is well appreciated and widely documented, from sub-cellular to organ levels. This paper reviews significant achievements of the group, led by Professor Vladimir S. Markhasin, Russia, who was one of the pioneers in studying and interpreting the relevance of cardiac functional heterogeneity

Isolated heart models for studying cardiac electrophysiology: a historical perspective and recent advances

Experimental models used in cardiovascular research range from cellular to whole heart preparations. Isolated whole hearts show higher levels of structural and functional integration than lower level models such as tissues or cellular fragments. Cardiovascular diseases are multi-factorial problems that are dependent on highly organized structures rather than on molecular or cellular components alone. This article first provides a general introduction on the animal models of cardiovascular diseases. It is followed by a detailed overview and a historical perspective of the different isolated heart systems with a particular focus on the Langendorff perfusion method for the study of cardiac arrhythmias. The choice of species, perfusion method, and perfusate composition are discussed in further detail with particular considerations of the theoretical and practical aspects of experimental settings

CARDIAC RHYTHM DURING MECHANICAL VENTILATION AND WEANING FROM VENTILATION

The transition from mechanical ventilation (MV) to spontaneous ventilation during weaning is associated with hemodynamic alterations and autonomic nervous system (ANS) alterations (reflected by heart rate variability [HRV]). Although cardiac dysrhythmias are an important manifestation of hemodynamic alterations, development of dysrhythmias during MV and weaning and subsequent impact on length of MV has received little attention. The purposes of this dissertation were to 1) evaluate the relationship of heart rate variability (HRV) during weaning to the development of cardiac dysrhythmias and 2) determine the relationship of cardiac dysrhythmias to length of MV. A convenience sample of 35 patients (66.7% men; mean age 53.3 years) who required MV was enrolled in this study. Continuous 3-lead electrocardiographic data were collected for 24 hours at baseline during MV and for the first 2 hours during the initial weaning trial. HRV was evaluated using spectral power analysis. Twenty- seven patients out of 30 were exposed to a combination of pressure support (8-15 cm H2O) and continuous positive airway pressure 5 cm H2O during weaning trial. Three patients self- extubated and received supplemental oxygen through either a partial rebreathing or non-rebreathing mask. Low frequency (LF) power HRV decreased, while high frequency (HF) and very low frequency (VLF) power HRV did not change during weaning. Multiple regression analyses showed that LF and HF HRV were significant predictors of occurrence of ventricular and supraventricular ectopic beats during weaning, while VLF power predicted occurrence of ventricular ectopic beats only. The mean of occurrence of supraventricular ectopic beats per hour during weaning was double the mean at baseline, while the mean of ventricular ectopic beats per hour did not change. Mean number of supraventricular ectopic beats per hour during weaning was a significant predictor of length of MV. This dissertation has fulfilled an important gap in the evidence base for cardiac dysrhythmias during weaning from MV. Cardiac dysrhythmias and HRV alterations should be systemically evaluated during MV and weaning trials in order to decrease length of MV

Mechano-calcium and mechano-electric feedbacks in the human cardiomyocyte analyzed in a mathematical model

Experiments on animal hearts (rat, rabbit, guinea pig, etc.) have demonstrated that mechano-calcium feedback (MCF) and mechano-electric feedback (MEF) are very important for myocardial self-regulation because they adjust the cardiomyocyte contractile function to various mechanical loads and to mechanical interactions between heterogeneous myocardial segments in the ventricle walls. In in vitro experiments on these animals, MCF and MEF manifested themselves in several basic classical phenomena (e.g., load dependence, length dependence of isometric twitches, etc.), and in the respective responses of calcium transients and action potentials. However, it is extremely difficult to study simultaneously the electrical, calcium, and mechanical activities of the human heart muscle in vitro. Mathematical modeling is a useful tool for exploring these phenomena. We have developed a novel model to describe electromechanical coupling and mechano-electric feedbacks in the human cardiomyocyte. It combines the 'ten Tusscher-Panfilov' electrophysiological model of the human cardiomyocyte with our module of myocardium mechanical activity taken from the 'Ekaterinburg-Oxford' model and adjusted to human data. Using it, we simulated isometric and afterloaded twitches and effects of MCF and MEF on excitation-contraction coupling. MCF and MEF were found to affect significantly the duration of the calcium transient and action potential in the human cardiomyocyte model in response to both smaller afterloads as compared to bigger ones and various mechanical interventions applied during isometric and afterloaded twitches. © 2020 The Author(s).Russian Foundation for Basic Research, RFBR: 18‑01‑00059The work was carried out within the framework of the IIP UrB RAS themes (Nos. AAAA‑A18‑118020590031‑8, AAAA‑A18‑118020590134‑6) and was supported by RFBR (18‑01‑00059) and by Act 211 Government of the Russian Federation, contract No. 02.A03.21.0006

Modulation of Output from an Isolated Gastropod Heart: Effects of Acetylcholine and FMRFamide

In this study, two cardioactive drugs, acetylcholine (ACh) and the tetrapeptide FMRFamide, are perfused through the isolated systemic heart of the gastropod, Busycon canaliculatum. Their effect is examined in terms of the regulation of output, and is then related to the in vivo regulation of stroke volume. ACh decreases cardiac output by reducing both stroke volume and heart rate. End-diastolic volume and cardiac reserve increase with drug concentration. These effects are accompanied by a slowing in the rise time of the electromyogram prepotential and an increase in the duration of the plateau phase. Low concentrations of FMRFamide increase output by accelerating the heart rate. Stroke volume is only affected at higher concentrations (5×10−7 moll−1), and then negatively. Enddiastolic volume is reduced. Between 10−9 and 10−8 moll−1, FMRFamide increases the rise time of the prepotential and the amplitude of the plateau; the duration of the plateau is markedly shortened. At 5×10−7 moll−1 and above, the plateau is extended and the cardiac reserve is reduced to zero. The two drugs have opposite effects on the characteristics of the aortic pressure pulse: ACh reduces the amplitude of the pulse, but increases its duration

Arrhythmogenic Hearts in PKD2 Mutant Mice Are Characterized by Cardiac Fibrosis, Systolic, and Diastolic Dysfunctions

Autosomal dominant polycystic kidney disease (PKD) is a hereditary disorder affecting multiple organs, including the heart. PKD has been associated with many cardiac abnormalities including the arrhythmogenic remodeling in clinical evaluations. In our current study, we hypothesized that Pkd2 gene mutation results in structural and functional defects in the myocardium. The structural and functional changes of Pkd2 mutant hearts were analyzed in the myocardial-specific Pkd2 knockout (KO) mouse. We further assessed a potential role of TGF-b1 signaling in the pathology of Pkd2-KO hearts. Hearts from age-matched 6-month-old MyH6•Pkd2wt/wt (control or wild-type) and MyH6•Pkd2flox/flox (mutant or Pkd2-KO) mice were used to study differential heart structure and function. Cardiac histology was used to study structure, and the “isolated working heart” system was adapted to mount and perfuse mouse heart to measure different cardiac parameters. We found that macrophage1 (M1) and macrophage 2 (M2) infiltration, transforming growth factor (TGF-b1) and TGF-b1 receptor expressions were significantly higher in Pkd2-KO, compared to wild-type hearts. The increase in the extracellular matrix in Pkd2-KO myocardium led to cardiac hypertrophy, interstitial and conduction system fibrosis, causing cardiac dysfunction with a predisposition to arrhythmia. Left ventricular (LV) expansion or compliance and LV filling were impaired in fibrotic Pkd2-KO hearts, resulted in diastolic dysfunction. LV systolic contractility and elastance decreased in fibrotic Pkd2-KO hearts, resulted in systolic dysfunction. Compared to wild-type hearts, Pkd2-KO hearts were less responsive to the pharmacological stress-test and changes in preload. In conclusion, Pkd2-KO mice had systolic and diastolic dysfunction with arrhythmogenic hearts

Isolated heart models for studying cardiac electrophysiology: a historical perspective and recent advances

Experimental models used in cardiovascular research range from cellular to whole heart preparations. Isolated whole hearts show higher levels of structural and functional integration than lower level models such as tissues or cellular fragments. Cardiovascular diseases are multi-factorial problems that are dependent on highly organized structures rather than on molecular or cellular components alone. This article first provides a general introduction on the animal models of cardiovascular diseases. It is followed by a detailed overview and a historical perspective of the different isolated heart systems with a particular focus on the Langendorff perfusion method for the study of cardiac arrhythmias. The choice of species, perfusion method, and perfusate composition are discussed in further detail with particular considerations of the theoretical and practical aspects of experimental settings.published_or_final_versio

Pathophysiology in Heart Failure

Heart failure syndrome is defined as the inability of the heart to deliver adequate blood to the body to meet end-organ metabolic needs and oxygenation at rest or during mild exercise. Myocardial dysfunction can be defined as systolic and/or diastolic, acute or chronic, compensated or uncompensated, or uni- or biventricular. Several counterregulatory mechanisms are activated depending on the duration of the heart failure. Neurohormonal reflexes such as sympathetic adrenergic system, renin-angiotensin cascade, and renal and peripheral alterations attempt to restore both cardiac output and end-tissue perfusion. An adequate stroke volume cannot be ejected from the left ventricle, which shifts the whole pressure-volume relationship to the right (systolic failure). Adequate filling cannot be realized due to diastolic stiffness, which shifts the diastolic pressure-volume curve upward without affecting the systolic pressure-volume curve (diastolic failure). Left ventricular heart failure is the dominant picture of heart failure syndrome, but the right heart can develop isolated failure as well. Biventricular failure is mostly an end-stage clinical situation of the heart failure syndrome. More recently, the rise in the incidence of right ventricular failure can be seen after the implantation of a left ventricular assist device. This chapter clarifies and presents pathophysiologic alterations in heart failure syndrome

Evaluation of QTc before and after exercise testing in a population of patients with severe obesity: possible association with obstructive sleep apnoea

openObesity is associated with QT interval prolongation. Obesity is also associated with OSA (obstructive sleep apnoea). OSA as well is associated with prolongation of the QT interval. The purpose of this study is to evaluate the QTc before and after exercise testing in a population of patients with severe obesity, and a possible association between QTc prolongation and OSA