Hemodynamic changes in a model of chronic heart failure induced by multiple sequential coronary microembolization in sheep

Coronary microembolization sheep model by adjusting the number of microspheres based on coronary blood flow

BACKGROUND

A heart failure (HF) model using coronary microembolization in large animals is indispensable for medical research. However, the heterogeneity of myocardial response to microembolization is a limitation. We hypothesized that adjusting the number of injected microspheres according to coronary blood flow could stabilize the severity of HF. This study aimed to evaluate the effect of microsphere injection based on the left coronary artery blood flow in an animal model.

METHODS

Microembolization was induced by injecting different numbers of microspheres (polystyrene, diameter: 90 μm) into the left descending coronary artery of the two groups of sheep (400 and 600 times coronary blood flow [ml/min]). Hemodynamic parameters, the pressure-volume loop of the left ventricle, and echocardiography findings were examined at 0.5, 1.5, 3.5, and 6.5 h after microembolization.

RESULTS

End-diastolic pressure and normalized heart rate increased over time, and were significantly higher in 600 × coronary blood flow group than those in 400 × coronary blood flow group (p = 0.04 and p < 0.01, respectively). The maximum rate of left-ventricular pressure rise and normalized stroke volume decreased over time, and were significantly lower in 600 × coronary blood flow group than those in 400 × coronary blood flow group (p < 0.01 and p < 0.01, respectively). The number of microspheres per coronary blood flow was significantly correlated with the decrease in stroke volume and the maximum rate of left ventricular pressure rise in 6.5 h (r = 0.74, p = 0.01 and r = 0.71, p = 0.02, respectively).

CONCLUSIONS

Adjusting the number of injected microspheres based on the coronary blood flow enabled the creation of HF models with different degrees of severity.

First-in-man Implantation of a Cardiac Microcurrent Device for Chronic Systolic Heart Failure

Current therapies significantly improve survival and clinical endpoints in patients suffering from chronic heart failure with reduced ejection fraction (HFrEF), but most are not sufficient to reverse adverse remodeling and improve myocardial contractility. Herein, we report the first-in-man experience with a novel fully implantable device for cardiac electrical microcurrent (C-MIC) application. A 79-year-old man suffering from HFrEF (dilated cardiomyopathy, NYHA class III, left ventricular ejection fraction 30%) successfully underwent implantation of the C-MIC device through left anterolateral thoracotomy. At 30-day follow-up, no device-related complications were observed, demonstrating feasibility of C-MIC implantation in a patient suffering from HFrEF.

Chronic stable heart failure model in ovine species

Establishing a chronic heart failure (HF) model is challenging, particularly in the ovine model. The aim of this study was to establish a reproducible model of HF in an ovine model. Seventeen sheep were operated using the left thoracotomy approach. Chronic HF was induced through ligation of the diagonal and marginal branches only. Perioperative hemodynamic and echocardiographic parameters were compared. A total of (3 ± 1) coronary ligations were used. Thirteen animals survived the procedure and were followed up for (15 ± 5) days. The mean arterial pressure, heart rate (HR), mean pulmonary artery pressure (mPAP), central venous pressure, and cardiac output at baseline and prior to animal sacrifice was (75 ± 14 mmHg) and (68 ± 16 mmHg) P = .261; (72 ± 9 bpm), (100 ± 28 bpm) P = .01; (15 ± 4 mmHg) and (18 ± 5 mmHg) P = .034; (10 ± 6 mmHg) and (8 ± 4 mmHg) P = .326; (3.4 ± 1 L/min) and (3.9 ± 1 L/min) P = .286, respectively. The LVEF at baseline and prior to animal sacrifice was (63 ± 13%) and (43 ± 6%) P = .012. Twelve surviving animals were supported with LVAD in a follow-up procedure. Chronic stable HF in sheep was successively established. Clinical symptoms and drastic increase in the mPAP and HR as well as echo findings were the most sensitive parameters of HF. This reproducible ovine model has proven to be highly promising for research regarding HF.

Impaired Baroreflex Function in an Ovine Model of Chronic Heart Failure Induced by Multiple Coronary Microembolizations

Testing new therapies in heart failure (HF) requires a chronic stable model of HF in large animals. Microembolization of the coronary arteries has been used to model HF previously; however, neural control has not been previously explored in this model. Thus the aim of this study was to further characterize neural control in this model of HF. HF was induced by infusion of microspheres (45 micron; 1.3 ml) into the proximal left coronary artery or left descending coronary arteries, with three sequential embolizations over 3 weeks. Twelve to 14 weeks after the final embolization, and when ejection fraction had decreased below 45%, animals were instrumented to record blood pressure and heart rate. Baroreflex control of heart rate was investigated in conscious animals. Additionally, pressure-volume loops were constructed under anesthesia. Embolization-induced HF was associated with a decrease in mean arterial pressure (67 ± 2 vs. 85 ± 4 mmHg, p < 0.05), an increase in heart rate (108 ± 4 vs. 94 ± 4 bpm, p < 0.05), and a significant increase in left ventricular end-diastolic pressure (11.4 ± 2 vs. 6.2 ± 1 mmHg, p < 0.01). Under conscious conditions, there was a significant decrease in the gain (-8.2 ± 2 vs. -4.1 ± 1 beats/min/mmHg, p < 0.05) as well as the lower plateau of the baroreflex in HF compared to control animals. HF was also associated with significantly increased respiratory rate (107 ± 4 vs. 87 ± 4 breaths/min, p < 0.01) and incidence of apneas (520 ± 24 vs. 191 ± 8 apnea periods >4 s, p < 0.05), compared to control sheep. The microembolization model of heart failure is associated with an increase in left ventricular end-diastolic pressure, impaired cardiac function, and altered baroreflex control of the heart. These findings suggest this chronic model of HF is appropriate to use for investigating interventions aimed at improving neural control in HF.

Novel Porcine Model of Acute Severe Cardiogenic Shock Developed by Upper-Body Hypoxia

Despite the urgent need for experimental research in the field of acute heart failure and, particularly cardiogenic shock, currently there are only limited options in large animal models enabling research using devices applied to human subjects. The majority of available models are either associated with an unacceptably high rate of acute mortality or are incapable of developing sufficient severity of acute heart failure. The objective of our research was to develop a novel large animal model of acute severe cardiogenic shock. Advanced left ventricular dysfunction was induced by global myocardial hypoxia by perfusing the upper body (including coronary arteries) with deoxygenated venous blood. The model was tested in 12 pigs: cardiogenic shock with signs of tissue hypoxia developed in all animals with no acute mortality. Cardiac output decreased from a mean (± SD) of 6.61±1.14 l/min to 2.75±0.63 l/min, stroke volume from 79.7±9.8 ml to 25.3±7.8 ml and left ventricular ejection fraction from 61.2±4.3 % to 17.7±4.8 % (P≤0.001 for all comparisons). In conclusion, the porcine model of acute cardiogenic shock developed in the present study may provide a basis for studying severe left ventricular dysfunction, low cardiac output and hypotension in large animals. The global myocardial hypoxia responsible for the decrease in cardiac contractility was not associated with acute death in this model.

A novel closed-chest porcine model of chronic ischemic heart failure suitable for experimental research in cardiovascular disease

Cardiac pathologies are among the leading causes of mortality and morbidity in industrialized countries, with myocardial infarction (MI) representing one of the major conditions leading to heart failure (HF). Hitherto, the development of consistent, stable, and reproducible models of closed-chest MI in large animals, meeting the clinical realism of a patient with HF subsequent to chronic ischemic necrosis, has not been successful. We hereby report the design and ensuing application of a novel porcine experimental model of closed-chest chronic ischemia suitable for biomedical research, mimicking post-MI HF. We also emphasize the key procedural steps involved in replicating this unprecedented model, from femoral artery and vein catheterization to MI induction by permanent occlusion of the left anterior descending coronary artery through superselective deployment of platinum-nylon coils, as well as endomyocardial biopsy sampling for histologic analysis and cell harvesting. Our model could indeed represent a valuable contribution and tool for translational research, providing precious insights to understand and overcome the many hurdles concerning, and currently quenching, the preclinical steps mandatory for the clinical translation of new cardiovascular technologies for personalized HF treatments.

Two axial-flow Synergy Micro-Pumps as a biventricular assist device in an ovine animal model

OBJECTIVE

This study investigated the use of 2 Synergy Micro-Pumps for full biventricular assist device (BiVAD) support. We examined right-sided and left-sided hemodynamic parameters over a range of right-sided and left-sided pump speeds in an acute, fibrillating, non-beating-heart model in sheep.

METHODS

Five juvenile sheep (43 ± 2 kg) were implanted with two Synergy Micro-Pumps (CircuLite Inc, Saddle Brook, NJ), 1 in the right (RV) and 1 in the left ventricle (LV), through a median sternotomy. The RVAD outflow graft was anastomosed end-to-side to the pulmonary artery and the LVAD outflow to the ascending aorta. After surgical implantation of both pumps, ventricular fibrillation was induced and hemodynamic parameters were measured at 9 different levels of RVAD pump speed (from 20,000 to 28,000 rpm at 1,000-rpm increments), while the speed of the LVAD was set constant at 24,000, then at 26,000, and finally, at 28,000 rpm.

RESULTS

At a fixed LVAD speed, RVAD and LVAD flow both increased identically as RVAD speed was increased. This was due to redistribution of blood volumes that resulted in resetting of pressure gradients across each pump and each vascular bed in a manner dictated by the pump pressure-flow characteristics. Results were similar with LVAD set at 24,000, 26,000, or 28,000 rpm. At the highest LVAD and RVAD speeds, flow averaged 3.1 ± 0.7 liters/min, and pressures in the right atrium, pulmonary artery, left atrium, and aorta averaged 2.2 ± 3.7, 24.4 ± 6.5, 22.4 ± 5.5, and 56.6 ± 8.5 mm Hg, respectively.

CONCLUSION

BiVAD support with the 2 Synergy Micro-Pumps is feasible and able to provide full hemodynamic support in sheep. This approach holds promise for providing biventricular partial support in humans and, in particular, for full support in small adults and children.

Influence of mild metabolic acidosis on cardiac contractility and isoprenaline response in isolated ovine myocardium

The postoperative course after major surgical procedures such as cardiothoracic operations is often accompanied by acute metabolic abnormalities due to large volume and temperature shifts. In general, those intervention-induced trauma might cause the use of catecholamines to stabilize hemodynamics. Within the cardiac community, there are still controversial discussions about standardized medical therapy to treat postoperative acidosis, for example, buffering versus nonbuffering for improving catecholaminergic response of myocardial contractility. The aim of this study was to investigate the influence of mild (and thus clinically relevant) acidosis on myocardial contractility and catecholamine response in explanted trabeculae of ovine hearts. Intact trabeculae (n = 24) were isolated from the right ventricle of healthy sheep hearts. Two different groups (group 1: pH = 7.40, n = 9 and group 2: pH = 7.20, n = 13) were investigated, and force amplitudes were measured at frequencies between 30 and 180 beats per minute and increasing catecholamine concentrations (isoprenaline 0-3 × 10(-6) mM). Force-frequency relation experiments in the presence of a physiological and/or mild acidotic pH solution showed no significant differences. Mean force amplitudes normalized to the lowest frequency showing no significant differences in force development between 0.5 and 3 Hz (n = 9 vs. 13, P = n.s.) (0.5 Hz absolute values 3.1 ± 2.6 for pH = 7.40 vs. 3.8 ± 2.6 mN/mm(2) for pH = 7.20, P = n.s.). Moreover, there was no significant difference in relaxation kinetics between the two groups. Furthermore, the experiments showed similar catecholamine responses in both groups. Force amplitudes normalized to baseline and maximum force showed no significant differences in force development between baseline and maximum isoprenaline concentrations (n = 6 vs. 9, P = n.s.) (baseline absolute values 4.3 ± 4.0 for pH = 7.40 vs. 3.9 ± 1.2 mN/mm(2) for pH = 7.20, P = n.s.). Additionally, relaxation kinetics did not show differences after catecholamine stimulation. The presented experiments revealed no significant negative inotropic effects on isometrically contracting ovine trabeculae with mild metabolic acidosis (pH = 7.2) compared with physiological pH (7.4). Additionally, similar catecholamine responses were seen in both groups. Further investigations (e.g., in vivo and/or in failing hearts with reduced compensatory reserves) will be necessary to examine optimal medical treatment for metabolic abnormalities after cardiac surgery.

Beneficial effect of Cyclovirobuxine D on heart failure rats following myocardial infarction

The effect of Cyclovirobuxine D, an active ingredient from Buxus microphylla, was investigated in the potential prevention of cardiac dysfunction in rats with congestive heart failure. Heart failure was induced by left coronary artery occlusion and verified using echocardiography. Cyclovirobuxine D was administered for 30 days (0.5, 1.0 and 2.0mg/kg, ig) and mortality, cardiac function, hemodynamics, microcirculation, histology and ultrastructure assessments were observed. Results from the present study suggest that Cyclovirobuxine D is beneficial for heart failure induced by myocardial infarction and supports the potential for Cyclovirobuxine D as a new therapy for heart failure.

AMPK - Activated Protein Kinase and its Role in Energy Metabolism of the Heart

Adenosine monophosphate - activated kinase (AMPK) plays a key role in the coordination of the heart's anabolic and catabolic pathways. It induces a cellular cascade at the center of maintaining energy homeostasis in the cardiomyocytes.. The activated AMPK is a heterotrimeric protein, separated into a catalytic α - subunit (63kDa), a regulating β - subunit (38kDa) and a γ - subunit (38kDa), which is allosterically adjusted by adenosine triphosphate (ATP) and adenosine monophosphate (AMP). The actual binding of AMP to the γ - subunit is the step which activates AMPK. AMPK serves also as a protein kinase in several metabolic pathways of the heart, including cellular energy sensoring or cardiovascular protection. The AMPK cascade represents a sensitive system, activated by cellular stresses that deplete ATP and acts as an indicator of intracellular ATP/AMP. In the context of cellular stressors (i.e. hypoxia, pressure overload, hypertrophy or ATP deficiency) the increasing levels of AMP promote allosteric activation and phosphorylation of AMPK. As the concentration of AMP begins to increase, ATP competitively inhibits further phosphorylation of AMPK. The increase of AMP may also be induced either from an iatrogenic emboli, percutaneous coronary intervention, or from atherosclerotic plaque rupture leading to an ischemia in the microcirculation. To modulate energy metabolism by phosphorylation and dephosphorylation is vital in terms of ATP usage, maintaining transmembrane transporters and preserving membrane potential. In this article, we review AMPK and its role as an important regulatory enzyme during periods of myocardial stress, regulating energy metabolism, protein synthesis and cardiovascular protection.

A novel, innovative ovine model of chronic ischemic cardiomyopathy induced by multiple coronary ligations

Heart failure is one of the fastest-growing epidemics worldwide in health care today. Although a wide variety of animal models exist to create chronic heart failure, there are few truly successful, reproducible models with ischemic dilation and mitral regurgitation. Six healthy sheep (36 ± 5 kg) underwent multiple, strategic coronary artery ligations on the left ventricle (LV). Six to eight ligations were performed transmurally on three of four segments of the LV: anterior, lateral, and posterior. Side branches of the left anterior descending and circumflex arteries were ligated to create multiple, patchy areas of myocardial infarction. Cardiac global and regional systolic function was assessed by echocardiography and cardiac magnetic resonance imaging (MRI). The extent, the characteristics, and the location of the myocardial infarction were qualitatively and quantitatively assessed by late gadolinium enhancement imaging. The overall mortality rate was 16.7% (1/6 animals). Animals who survived showed a significantly reduced ejection fraction (mean 60 ± 5% to 28 ± 7%; P < 0.05); additionally, two out of the remaining five (40%) animals developed mild to moderate mitral regurgitation quantified by cardiac MRI. Furthermore, each animal developed clinical signs of heart failure (tachycardia, dyspnea, and tachypnea) consistent with global, dilated cardiomyopathy noted on MRI. Creating and reproducing a model of global, ischemic cardiomyopathy with functional mitral regurgitation is an arduous task. We have developed a promising model of ischemic heart failure using multiple ligations, which mimics the sequelae of human cardiomyopathy. Our proposed model is highly effective, reproducible, and may be used for experimental research on heart failure (cardiac assist devices, heart transplant, etc.).

Adjustment and characterization of an original model of chronic ischemic heart failure in pig

We present and characterize an original experimental model to create a chronic ischemic heart failure in pig. Two ameroid constrictors were placed around the LAD and the circumflex artery. Two months after surgery, pigs presented a poor LV function associated with a severe mitral valve insufficiency. Echocardiography analysis showed substantial anomalies in radial and circumferential deformations, both on the anterior and lateral surface of the heart. These anomalies in function were coupled with anomalies of perfusion observed in echocardiography after injection of contrast medium. No demonstration of myocardial infarction was observed with histological analysis. Our findings suggest that we were able to create and to stabilize a chronic ischemic heart failure model in the pig. This model represents a useful tool for the development of new medical or surgical treatment in this field.