Biventricular cardiac dysfunction after acute massive pulmonary embolism in the rat

Rodent models of pulmonary embolism and chronic thromboembolic pulmonary hypertension

Pulmonary embolism (PE) is the third most prevalent cardiovascular disease. It is associated with high in-hospital mortality and the development of acute and chronic complications. New approaches aimed at improving the prognosis of patients with PE are largely dependent on reliable animal models. Mice, rats, hamsters, and rabbits, are currently most commonly used for PE modeling because of their ethical acceptability and economic feasibility. This article provides an overview of the main approaches to PE modeling, and the advantages and disadvantages of each method. Special attention is paid to experimental endpoints, including morphological, functional, and molecular endpoints. All approaches to PE modeling can be broadly divided into three main groups: 1) induction of thromboembolism, either by thrombus formation in vivo or by injection of in vitro prepared blood clots; 2) introduction of particles of non-thrombotic origin; and 3) surgical procedures. The choice of a specific model and animal species is determined based on the objectives of the study. Rodent models of chronic thromboembolic pulmonary hypertension (CTEPH), which is the most devastating complication of PE, are also described. CTEPH models are especially challenging because of insufficient knowledge about the pathogenesis and high fibrinolytic activity of rodent plasma. The CTEPH model should demonstrate a persistent increase in pulmonary artery pressure and stable reduction of the vascular bed due to recurrent embolism. Based on the analysis of available evidence, one might conclude that currently, there is no single optimal method for modeling PE and CTEPH.

Assessment of Right Ventricular Function in the Research Setting: Knowledge Gaps and Pathways Forward. An Official American Thoracic Society Research Statement

BACKGROUND

Right ventricular (RV) adaptation to acute and chronic pulmonary hypertensive syndromes is a significant determinant of short- and long-term outcomes. Although remarkable progress has been made in the understanding of RV function and failure since the meeting of the NIH Working Group on Cellular and Molecular Mechanisms of Right Heart Failure in 2005, significant gaps remain at many levels in the understanding of cellular and molecular mechanisms of RV responses to pressure and volume overload, in the validation of diagnostic modalities, and in the development of evidence-based therapies.

METHODS

A multidisciplinary working group of 20 international experts from the American Thoracic Society Assemblies on Pulmonary Circulation and Critical Care, as well as external content experts, reviewed the literature, identified important knowledge gaps, and provided recommendations.

RESULTS

This document reviews the knowledge in the field of RV failure, identifies and prioritizes the most pertinent research gaps, and provides a prioritized pathway for addressing these preclinical and clinical questions. The group identified knowledge gaps and research opportunities in three major topic areas: 1) optimizing the methodology to assess RV function in acute and chronic conditions in preclinical models, human studies, and clinical trials; 2) analyzing advanced RV hemodynamic parameters at rest and in response to exercise; and 3) deciphering the underlying molecular and pathogenic mechanisms of RV function and failure in diverse pulmonary hypertension syndromes.

CONCLUSIONS

This statement provides a roadmap to further advance the state of knowledge, with the ultimate goal of developing RV-targeted therapies for patients with RV failure of any etiology.

The effect of nitric oxide inhalation on heart and pulmonary circulation in rabbits with acute massive pulmonary embolism

The aim of the present study was to investigate the effect of nitric oxide inhalation (NOI) on cardiac troponin I (CTnI) levels and mean pulmonary arterial pressure (mPAP) in rabbits with acute massive pulmonary embolism (AMPE). Thirty rabbits were used as animal models for AMPE and received different treatments. A total of 4 h after successful modeling, the control group (CON, n=10) received conventional thrombolysis, whereas the treatment group (TRE, n=10) received conventional thrombolysis plus NOI. The experimental group (EXP, n=10) did not receive any treatments. Myocardial necrosis was pathologically confirmed in all 30 rabbits. In group EXP, the post-AMPE CTnI peak level was 0.42±0.12 µg/l, was achieved in 18.8±4.5 h and remained positive for 38.6±5.2 h (≥0.1 µg/l). These values were lower in group TRE when compared with those in groups CON and EXP (P<0.05). Group TRE exhibited significantly reduced mPAP at 24, 28, 32, and 34 h (P<0.05) when compared with group CON. AMPE-induced cardiac impairment was more severe in group EXP when compared with groups CON and TRE. The present findings indicated that the CTnI peak was significantly correlated with the corresponding mPAP. Furthermore, the results suggested NOI may reduce mPAP and CTnI peak levels, with protective effects against AMPE-induced myocardial damage in rabbits.

The effects of low-molecular-weight heparin on lung and pulmonary artery injuries in acute pulmonary embolism rat model via platelet-derived growth factor-β

Objective

To evaluate the effects of anticoagulant agent (low-molecular-weight heparin, LMWH) on the pulmonary artery intima hyperplasia of rats with acute pulmonary embolism (APE) by assaying platelet-derived growth factor-β (PDGF-β).

Methods

A total of 90 Sprague-Dawley rats were randomly assigned into the sham, APE, and LMWH groups with 30 rats in each group. The APE rat models were established by injecting autologous blood clots via external jugular veins. In each group, six mice were sacrificed at the 1st day (D1), 4th day (D4), 7th day (D7), 14th day (D14), and 28th (D28) subsequent to the induction of APE to collect the lungs. Right ventricle pressure (RVP) and mean pulmonary arterial pressure (mPAP) were measured. Western blot and RT-PCR analyses were used to assess PDGF-β expression at various time points. In addition, changes in lung pathology were evaluated using hematoxylin and eosin (H&E) staining and electron microscope.

Results

The overall success rate of establishing APE rat models was 85.7% (60/70). There was no difference in mPAP between the sham group and the APE group at the D1, D4, D7, and D14. However, at the D28, mPAP in the APE group was significantly higher than that in the sham group. There was no difference among the three groups regarding RVP. PDGF-β expression were decreased in the LMWH group at all time points compared with the sham and APE groups (P < 0.01). Furthermore, pulmonary embolism, alveolar wall necrosis and hemorrhage, and inflammation were significantly attenuated in the LMWH group compared with the sham and APE groups subsequent to the induction of APE.

Conclusion

LMWH attenuates lung and pulmonary artery injuries and improves prognosis. Decreased PDGF-β in the lungs may be the important factor in the effects observed.

Captopril improves postresuscitation hemodynamics protective against pulmonary embolism by activating the ACE2/Ang-(1-7)/Mas axis

Acute pulmonary embolism (APE) has a very high mortality rate, especially at cardiac arrest and even after the return of spontaneous circulation (ROSC). This study investigated the protective effect of the angiotensin-converting enzyme (ACE) inhibitor captopril on postresuscitation hemodynamics, in a porcine model of cardiac arrest established by APE. Twenty-nine Beijing Landrace pigs were infused with an autologous thrombus leading to cardiac arrest and subjected to standard cardiopulmonary resuscitation and thrombolysis. Ten resuscitated pigs were randomly and equally apportioned to receive either captopril (22.22 mg/kg) infusion or the same volume saline, 30 min after ROSC. Hemodynamic changes and ACE-Ang II-angiotensin II type 1 receptor (AT1R) and ACE2/Ang-(1-7)/Mas receptor axis levels were determined. APE was associated with a decline in mean arterial pressure and a dramatic increase in pulmonary artery pressure and mean right ventricular pressure. After ROSC, captopril infusion was associated with significantly lower mean right ventricular pressure and systemic and pulmonary vascular resistance, faster heart rate, and higher Ang-(1-7) levels, ACE2/ACE, and Ang-(1-7)/Ang II, compared with the saline infusion. The ACE2/Ang-(1-7)/Mas pathway correlated negatively with external vascular lung water and pulmonary vascular permeability and positively with the right cardiac index. In conclusion, in a pig model of APE leading to cardiac arrest, captopril infusion was associated with less mean right ventricular pressure overload after resuscitation, compared with saline infusion. The reduction in systemic and pulmonary vascular resistance associated with captopril may be by inhibiting the ACE-Ang II-AT1R axis and activating the ACE2/Ang-(1-7)/Mas axis.

Evaluation of autologous blood clot subsegmental pulmonary thromboembolism in minimally invasive experimental canine model

The incidence and significance of subsegmental pulmonary (SSP) thromboembolism is currently under investigation. We aimed to evaluate the clinical and diagnostic features of SSP thromboembolism in an experimental canine model. Obstruction of pulmonary arterial branches was induced in three beagle dogs by intravenous injection of a barium-coated autologous blood clot (size, approximately 1.7 × 5 mm). The clinical signs, haemodynamic changes (blood pressure, electrocardiogram, echocardiography), coagulation (aPTT, PT, FDPs and D-dimer test) and cytokine variations (TNF-a, IL-4, IL-6, and IL-10) were evaluated over a 24-hour period. Multidetector computed tomography (MDCT) with contrast was conducted to evaluate the pulmonary obstruction, and histopathological confirmation was performed. Pulmonary artery pressure gradient (PAPG) was increased 12 h after the autologous blood clot injection (14.2 ± 2.8 mmHg to 23.6 ± 1.7 mmHg, P = 0.003) and normalized 24 h later (P < 0.01). Infused radiopaque clots were confirmed with MDCT and histopathological examination. Pulmonary parenchymal changes such as arterial dilation and inflammatory reactions were also confirmed in histopathological examinations and were barely observable in MDCT. Usually small emboli are not easily detected through CT imaging, and the clinical relevance of these emboli is controversial. In this experimental study, we made radiopaque small emboli and induced SSP thromboembolism. Thus, we infer that obstruction of the small segmental and subsegmental pulmonary arteries does result in a pulmonary thromboembolism (PTE) and PTE-related pulmonary parenchymal changes which could be clinically significant.

Right ventricular responses to massive and submassive pulmonary embolism

It is critically important to quickly recognize and treat acute pulmonary embolism (PE). Submassive and massive PEs are associated with right ventricular (RV) dysfunction and may culminate in RV failure, cardiac arrest, and death. A rapid and coordinated diagnostic and management approach can maximize success and save lives.

Development and comparison of a minimally-invasive model of autologous clot pulmonary embolism in Sprague-Dawley and Copenhagen rats

Background

Experimental models of pulmonary embolism (PE) that produce pulmonary hypertension (PH) employ many different methods of inducing acute pulmonary occlusion. Many of these models induce PE with intravenous injection of exogenous impervious objects that may not completely reproduce the physiological properties of autologous thromboembolism. Current literature lacks a simple, well-described rat model of autlogous PE. Objective: Test if moderate-severity autologous PE in Sprague-Dawley (SD) and Copenhagen (Cop) rats can produce persistent PH.

Methods

blood was withdrawn from the jugular vein, treated with thrombin-Ca⁺⁺ and re-injected following pretreatment with tranexamic acid. Hemodynamic values, clot weights and biochemical measurements were performed at 1 and 5 days.

Results

Infusion of clot significantly increased the right ventricular peak systolic pressure to 45-55 mm Hg, followed by normalization within 24 hours in SD rats, and within 5 days in COP rats. Clot lysis was 95% (24 hours) and 97% (5 days) in SD rats and was significantly lower in COP rats (70%, 24 hours; 87% 5 days). Plasma D-dimer was elevated in surgical sham animals and was further increased 8 hours after pulmonary embolism. Neither strain showed a significant increase in bronchoalveolar chemotactic activity, myeloperoxidase activity, leukocyte infiltration, or chemokine accumulation, indicating that there was no significant pulmonary inflammation.

Conclusions

Both SD and COP rats exhibited near complete fibrinolysis of autologous clot PE within 5 days. Neither strain developed persistent PH. Experimental models of PE designed to induce sustained PH and a robust inflammatory response appear to require significant, persistent pulmonary vascular occlusion.

Right ventricular heart failure from pulmonary embolism: key distinctions from chronic pulmonary hypertension

BACKGROUND

The right ventricle normally operates as a low pressure, high-flow pump connected to a high-capacitance pulmonary vascular circuit. Morbidity and mortality in humans with pulmonary hypertension (PH) from any cause is increased in the presence of right ventricular (RV) dysfunction, but the differences in pathology of RV dysfunction in chronic versus acute occlusive PH are not widely recognized.

METHODS AND RESULTS

Chronic PH that develops over weeks to months leads to RV concentric hypertrophy without inflammation that may progress slowly to RV failure. In contrast, pulmonary embolism (PE) results in an abrupt vascular occlusion leading to increased pulmonary artery pressure within minutes to hours that causes immediate deformation of the RV. RV injury is secondary to mechanical stretch, shear force, and ischemia that together provoke a cytokine and chemokine-mediated inflammatory phenotype that amplifies injury.

CONCLUSIONS

This review will briefly describe causes of pulmonary embolism and chronic PH, models of experimental study, and pulmonary vascular changes, and will focus on mechanisms of right ventricular dysfunction, contrasting mechanisms of RV adaptation and injury in these 2 settings.

Cardiac inflammation contributes to right ventricular dysfunction following experimental pulmonary embolism in rats

Acute right ventricular (RV) failure following pulmonary embolism (PE) is a strong predictor of poor clinical outcome. Present studies test for an association between RV failure from experimental PE, inflammation, and upregulated chemokine expression. Additional experiments test if neutrophil influx contributes to RV dysfunction. PE was induced in male rats by infusing 24 microm microspheres (right jugular vein) producing mild hypertension (1.3 million beads/100 g, PE1.3), or moderately severe hypertension (2.0 million beads/100 g, PE2.0). Additional rats served as vehicle sham (0.01% Tween 20, Veh). In vivo RV peak systolic pressures (RVPSP) increased significantly, and then declined following PE2.0 (51 +/- 1 mm Hg 2 h; 49 +/- 1, 6 h; 44 +/- 1, 18 h). RV generated pressure of isolated, perfused hearts was significantly reduced in PE2.0 compared with PE1.3 or Veh. MCP-1 protein (ELISA) was elevated 21-fold and myeloperoxidase activity 95-fold in RV of PE2.0 compared with Veh or PE1.3. CINC-1, CINC-2, MIP-2, MCP-1, and MIP-1alpha mRNA also increased in RV of PE2.0. Histological analysis revealed massive accumulation of neutrophils (selective esterase stain) and monocyte/macrophages (CD68, ED-1) in RV of PE2.0 hearts in regions of myocyte damage. Electron microscopy showed myocyte necrosis and phagocytosis by inflammatory cells. LV function was normal and did not show increased inflammation after PE2.0. Treatment with anti-PMN antibody reduced RV MPO activity and prevented RV dysfunction. Conclusions-PE with moderately severe pulmonary hypertension (PE2.0) resulted in selective RV dysfunction, which was associated with increased chemokine expression, and infiltration of both neutrophils and monocyte/macrophages, indicating that a robust immune response occurred with RV damage following experimental PE. Experimental agranulocytosis reduced RV, suggesting that neutrophil influx contributed to RV damage.

Is there a place for inhaled nitric oxide in the therapy of acute pulmonary embolism?

Acute pulmonary embolism (PE) is a serious complication resulting from the migration of emboli to the lungs. Although deep venous thrombi are the most common source of emboli to the lungs, other important sources include air, amniotic fluid, fat and bone marrow. Regardless of the specific source of the emboli, very little progress has been made in the pharmacological management of this high mortality condition. Because the prognosis is linked to the degree of elevation of pulmonary vascular resistance, any therapeutic intervention to improve the hemodynamics would probably increase the low survival rate of this critical condition. Inhaled nitric oxide (iNO) has been widely tested and used in cases of pulmonary hypertension of different causes. In the last few years some authors have described beneficial effects of iNO in animal models of acute PE and in anecdotal cases of massive PE. The primary cause of death in massive PE that is caused by deep venous thrombi, gas or amniotic fluid, is acute right heart failure and circulatory shock. Increased pulmonary vascular resistance following acute PE is the cumulative result of mechanical obstruction of pulmonary vessels and pulmonary arteriolar constriction (attributable to a neurogenic reflex and to the release of vasoconstrictors). As such, the vasodilator effects of iNO could actively oppose the pulmonary hypertension following PE. This hypothesis is consistently supported by experimental studies in different animal models of PE, which demonstrated that iNO decreased (by 10 to 20%) the pulmonary artery pressure without improving pulmonary gas exchange. Although maximal vasodilatory effects are probably achieved by less than 5 parts per million iNO, which is a relatively low concentration, no dose-response study has been published so far. In addition to the animal studies, a few anecdotal reports in the literature suggest that iNO may improve the hemodynamics during acute PE. However, no prospective, controlled, randomized clinical trial addressing this issue has been conducted to date. Future investigations addressing the effects of iNO combined with other drugs such as vasoconstrictors and inhibitors of phosphodiesterase III or V, may increase the responsiveness to iNO in acute PE.

Inhibition of prostaglandin synthesis during polystyrene microsphere-induced pulmonary embolism in the rat

Our objective was to test the effect of inhibition of thromboxane synthase versus inhibition of cyclooxygenase (COX)-1/2 on pulmonary gas exchange and heart function during simulated pulmonary embolism (PE) in the rat. PE was induced in rats via intrajugular injection of polystyrene microspheres (25 micro m). Rats were randomized to one of three posttreatments: 1) placebo (saline), 2) thromboxane synthase inhibition (furegrelate sodium), or 3) COX-1/2 inhibition (ketorolac tromethamine). Control rats received no PE. Compared with controls, placebo rats had increased thromboxane B(2) (TxB(2)) in bronchoalveolar lavage fluid and increased urinary dinor TxB(2). Furegrelate and ketorolac treatments reduced TxB(2) and dinor TxB(2) to control levels or lower. Both treatments significantly decreased the alveolar dead space fraction, but neither treatment altered arterial oxygenation compared with placebo. Ketorolac increased in vivo mean arterial pressure and ex vivo left ventricular pressure (LVP) and right ventricular pressure (RVP). Furegrelate improved RVP but not LVP. Experimental PE increased lung and systemic production of TxB(2). Inhibition at the COX-1/2 enzyme was equally as effective as inhibition of thromboxane synthase at reducing alveolar dead space and improving heart function after PE.