Cine-MRI versus two-dimensional echocardiography to measure in vivo left ventricular function in rat heart

Functional Cardiovascular Characterization of the Common Marmoset (Callithrix jacchus)

Appropriate cardiovascular animal models are urgently needed to investigate genetic, molecular, and therapeutic approaches, yet the translation of results from the currently used species is difficult due to their genetic distance as well as their anatomical or physiological differences. Animal species that are closer to the human situation might help to bridge this translational gap. The common marmoset (Callithrix jacchus) is an interesting candidate to investigate certain heart diseases and cardiovascular comorbidities, yet a basic functional characterization of its hemodynamic system is still missing. Therefore, cardiac functional analyses were performed by utilizing the invasive intracardiac pressure-volume loops (PV loop) system in seven animals, magnetic resonance imaging (MRI) in six animals, and echocardiography in five young adult male common marmosets. For a direct comparison between the three methods, only data from animals for which all three datasets could be acquired were selected. All three modalities were suitable for characterizing cardiac function, though with some systemic variations. In addition, vena cava occlusions were performed to investigate the load-independent parameters collected with the PV loop system, which allowed for a deeper analysis of the cardiac function and for a more sensitive detection of the alterations in a disease state, such as heart failure or certain cardiovascular comorbidities.

The Role of Cardiac Imaging in the Evaluation of Cardiac Involvement in Systemic Diseases

For systemic diseases like rheumatoid arthritis, systemic lupus erythematosus (SLE), systemic sclerosis, systemic vasculitis, myopathies, and mixed connective tissue diseases, cardiac disease is a major contributing factor for morbidity and mortality. The cardiovascular manifestations are the result of various pathophysiological components, which complicate management. Furthermore, the signs and symptoms can be subtle and missed due to the complex nature of the underlying condition. As a result, various imaging approaches play an imperative role in diagnosis and prognosis. The evolving role of these modalities could lead to risk stratification and improved therapies in the future. In conclusion, our review article will highlight the role of cardiac imaging in the evaluation of cardiac involvement for systemic diseases.

Remodeling after myocardial infarction and effects of heart failure treatment investigated by hyperpolarized [1-13 C]pyruvate magnetic resonance spectroscopy

PURPOSE

Hyperpolarized [1-¹³ C]pyruvate MRS can measure cardiac metabolism in vivo. We investigated whether [1-¹³ C]pyruvate MRS could predict left ventricular remodeling following myocardial infarction (MI), long-term left ventricular effects of heart failure medication, and could identify responders to treatment.

METHODS

Thirty-five rats were scanned with hyperpolarized [1-¹³ C]pyruvate MRS 3 days after MI or sham surgery. The animals were re-examined after 30 days of therapy with β-blockers and ACE-inhibitors (active group, n = 12), placebo treatment (placebo group, n = 13) or no treatment (sham group, n = 10). Furthermore, heart tissue mitochondrial respiratory capacity was assessed by high-resolution respirometry. Metabolic results were compared between groups, over time and correlated to functional MR data at each time point.

RESULTS

At 30 ± 0.5 days post MI, left ventricular ejection fraction (LVEF) differed between groups (sham, 77% ± 1%; placebo, 52% ± 3%; active, 63% ± 2%, P < .001). Cardiac metabolism, measured by both hyperpolarized [1-¹³ C]pyruvate MRS and respirometry, neither differed between groups nor between baseline and follow-up. Three days post MI, low bicarbonate + CO₂ /pyruvate ratio was associated with low LVEF. At follow-up, in the active group, a poor recovery of LVEF was associated with high bicarbonate + CO₂ /pyruvate ratio, as measured by hyperpolarized MRS.

CONCLUSION

In a rat model of moderate heart failure, medical treatment improved function, but did not on average influence [1-¹³ C]pyruvate flux as measured by MRS; however, responders to heart failure medication had reduced capacity for carbohydrate metabolism.

Accuracy of cardiac functional parameters measured from gated radionuclide myocardial perfusion imaging in mice

BACKGROUND

Quantitative cardiac contractile function assessment is the primary indicator of disease progression and therapeutic efficacy in small animals. Operator dependency is a major challenge with commonly used echocardiography. Simultaneous assessment of cardiac perfusion and function in nuclear scans would reduce burden on the animal and facilitate longitudinal studies. We evaluated the accuracy of contractile function measurements obtained from electrocardiogram-gated nuclear perfusion imaging compared with anatomic imaging.

METHODS AND RESULTS

In healthy C57Bl/6N mice (n = 11), 99mTc-sestamibi SPECT and 13N-ammonia PET underestimated left ventricular volumes (23 to 28%, P = 0.02) compared to matched anatomic images, though ejection fraction (LVEF) was comparable (%, SPECT: 73 ± 8 vs CMR: 72 ± 6, P = 0.1). At 1 week after myocardial infarction (n = 13), LV volumes were significantly lower in perfusion images compared to CMR and contrast CT (P = 0.003), and LVEF was modestly overestimated (%, SPECT: 37 ± 8, vs CMR: 27 ± 7, P = 0.003). Nuclear images exhibited good intra- and inter-reader agreement. Perfusion SPECT accurately calculated infarct size compared to histology (r = 0.95, P < 0.001).

CONCLUSIONS

Cardiac function can be calculated by gated nuclear perfusion imaging in healthy mice. After infarction, perfusion imaging overestimates LVEF, which should be considered for comparison to other modalities. Combined functional and infarct size analysis may optimize imaging protocols and reduce anaesthesia duration for longitudinal studies.

The POU4F2/Brn-3b transcription factor is required for the hypertrophic response to angiotensin II in the heart

Adult hearts respond to increased workload such as prolonged stress or injury, by undergoing hypertrophic growth. During this process, the early adaptive responses are important for maintaining cardiac output whereas at later stages, pathological responses such as cardiomyocyte apoptosis and fibrosis cause adverse remodelling, that can progress to heart failure. Yet the factors that control transition from adaptive responses to pathological remodelling in the heart are not well understood. Here we describe the POU4F2/Brn-3b transcription factor (TF) as a novel regulator of adaptive hypertrophic responses in adult hearts since Brn-3b mRNA and protein are increased in angiotensin-II (AngII) treated mouse hearts with concomitant hypertrophic changes [increased heart weight:body weight (HW:BW) ratio]. These effects occur specifically in cardiomyocytes because Brn-3b expression is increased in AngII-treated primary cultures of neonatal rat ventricular myocytes (NRVM) or foetal heart-derived H9c2 cells, which undergo characteristic sarcomeric re-organisation seen in hypertrophic myocytes and express hypertrophic markers, ANP/βMHC. The Brn-3b promoter is activated by known hypertrophic signalling pathways e.g. p42/p44 mitogen-activated protein kinase (MAPK/ERK1/2) or calcineurin (via NFAT). Brn-3b target genes, e.g. cyclin D1, GLUT4 and Bax, are increased at different stages following AngII treatment, supporting distinct roles in cardiac responses to stress. Furthermore, hearts from male Brn-3b KO mutant mice display contractile dysfunction at baseline but also attenuated hypertrophic responses to AngII treatment. Hearts from AngII-treated male Brn-3b KO mice develop further contractile dysfunction linked to extensive fibrosis/remodelling. Moreover, known Brn-3b target genes, e.g. GLUT4, are reduced in AngII-treated Brn-3b KO hearts, suggesting that Brn-3b and its target genes are important in driving adaptive hypertrophic responses in stressed heart.

Cmah-dystrophin deficient mdx mice display an accelerated cardiac phenotype that is improved following peptide-PMO exon skipping treatment

Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin protein, leading to progressive muscle weakness and premature death due to respiratory and/or cardiac complications. Cardiac involvement is characterized by progressive dilated cardiomyopathy, decreased fractional shortening and metabolic dysfunction involving reduced metabolism of fatty acids-the major cardiac metabolic substrate. Several mouse models have been developed to study molecular and pathological consequences of dystrophin deficiency, but do not recapitulate all aspects of human disease pathology and exhibit a mild cardiac phenotype. Here we demonstrate that Cmah (cytidine monophosphate-sialic acid hydroxylase)-deficient mdx mice (Cmah-/-;mdx) have an accelerated cardiac phenotype compared to the established mdx model. Cmah-/-;mdx mice display earlier functional deterioration, specifically a reduction in right ventricle (RV) ejection fraction and stroke volume (SV) at 12 weeks of age and decreased left ventricle diastolic volume with subsequent reduced SV compared to mdx mice by 24 weeks. They further show earlier elevation of cardiac damage markers for fibrosis (Ctgf), oxidative damage (Nox4) and haemodynamic load (Nppa). Cardiac metabolic substrate requirement was assessed using hyperpolarized magnetic resonance spectroscopy indicating increased in vivo glycolytic flux in Cmah-/-;mdx mice. Early upregulation of mitochondrial genes (Ucp3 and Cpt1) and downregulation of key glycolytic genes (Pdk1, Pdk4, Ppara), also denote disturbed cardiac metabolism and shift towards glucose utilization in Cmah-/-;mdx mice. Moreover, we show long-term treatment with peptide-conjugated exon skipping antisense oligonucleotides (20-week regimen), resulted in 20% cardiac dystrophin protein restoration and significantly improved RV cardiac function. Therefore, Cmah-/-;mdx mice represent an appropriate model for evaluating cardiac benefit of novel DMD therapeutics.

Cardioprotective effect of the secretome of Sca-1+ and Sca-1− cells in heart failure: not equal, but equally important?

Aims

Both progenitor and differentiated cells were previously shown to secrete cardioprotective substances, but so far there has been no direct comparison of the paracrine effects of the two cell types on heart failure. The study sought to compare the paracrine effect of selected progenitors and the corresponding non-progenitor mononuclear cardiac cells on the cardiac function of transgenic heart failure mice. In addition, we aimed to further enhance the paracrine effect of the cells via pretreatment with the heart failure mediator aldosterone.

Methods and results

Transgenic heart failure mice were injected with the supernatant of murine cardiac stem cell antigen-1 positive (Sca-1+) and negative (Sca-1−) cells with or without aldosterone pretreatment. Cardiac function was determined using small animal magnetic resonance imaging. In addition, heart failure markers were determined using enzyme-linked immunosorbent assay, RT–PCR, and bead-based multiplexing assay. While only the secretome of aldosterone pretreated Sca-1+ cells led to a significant improvement in cardiac function, N-terminal pro brain natriuretic peptide plasma levels were significantly lower and galectin-1 levels significantly higher in mice that were treated with either kind of secretome compared with untreated controls.

Conclusion

In this first direct comparison of the paracrine effects of progenitor cells and a heterogeneous population of mononuclear cardiac cells the supernatants of both cell types showed cardioprotective properties which might be of great relevance for endogenous repair. During heart failure raised aldosterone levels might further increase the paracrine effect of progenitor cells.

A novel echocardiographic method closely agrees with cardiac magnetic resonance in the assessment of left ventricular function in infarcted mice

Cardiac Magnetic Resonance (CMR) is the gold standard for left ventricular (LV) function assessment in small rodents and, though echocardiography (ECHO) has been proposed as an alternative method, LV volumes may be underestimated when marked eccentric remodeling is present. In the present study we described a novel echocardiographic method and we tested the agreement with CMR for LV volumes and ejection fraction calculation in mice with experimental myocardial infarction. Sham-operated and infarcted mice, subjected to Coronary Artery Ligation, underwent ECHO and CMR. Volumes and ejection fraction were calculated by ECHO using a standard Simpson’s modified method (ECHO pLAX) or a method from sequential parasternal short axis (ECHO pSAX) acquired mechanically by translating the probe every 1 mm along the left ventricle. The mean differences ±1.96 standard deviation near to zero suggested close agreement between ECHO pSAX and CMR; contrarily ECHO pLAX agreement with CMR was lower. In addition, ECHO was three times shorter and cheaper (Relative cost difference: pLAX: −66% and pSAX −57%) than CMR. In conclusion, ECHO pSAX is a new, fast, cheap and accurate method for LV function assessment in mice.

Micro-utrophin Improves Cardiac and Skeletal Muscle Function of Severely Affected D2/mdx Mice

Duchenne muscular dystrophy (DMD) is an X-linked muscle-wasting disease caused by mutations in the dystrophin gene. DMD boys are wheelchair-bound around 12 years and generally survive into their twenties. There is currently no effective treatment except palliative care, although personalized treatments such as exon skipping, stop codon read-through, and viral-based gene therapies are making progress. Patients present with skeletal muscle pathology, but most also show cardiomyopathy by the age of 10. A systemic therapeutic approach is needed that treats the heart and skeletal muscle defects in all patients. The dystrophin-related protein utrophin has been shown to compensate for the lack of dystrophin in the mildly affected BL10/mdx mouse. The purpose of this investigation was to demonstrate that AAV9-mediated micro-utrophin transgene delivery can not only functionally replace dystrophin in the heart, but also attenuate the skeletal muscle phenotype in severely affected D2/mdx mice. The data presented here show that utrophin can indeed alleviate the pathology in skeletal and cardiac muscle in D2/mdx mice. These results endorse the view that utrophin modulation has the potential to increase the quality life of all DMD patients whatever their mutation.

Experimental Spinal Cord Injury Causes Left-Ventricular Atrophy and Is Associated with an Upregulation of Proteolytic Pathways

Spinal cord injury (SCI) causes autonomic dysfunction, altered neurohumoral control, profound hemodynamic changes, and an increased risk of heart disease. In this prospective study, we investigated the cardiac consequences of chronic experimental SCI in rats by combining cutting edge in vivo techniques (magnetic resonance imaging [MRI] and left-ventricular [LV] pressure-volume catheterization) with histological and molecular assessments. Twelve weeks post-SCI, MRI-derived structural indices and in vivo LV catheterization-derived functional indices indicated the presence of LV atrophy (LV mass in Control vs. SCI = 525 ± 38.8 vs. 413 ± 28.6 mg, respectively; p = 0.0009), reduced ventricular volumes (left-ventricular end-diastolic volume in Control vs. SCI = 364 ± 44 vs. 221 ± 35 μL, respectively; p = 0.0004), and contractile dysfunction (end-systolic pressure-volume relationship in Control vs. SCI = 1.31 ± 0.31 vs. 0.76 ± 0.11 mm Hg/μL, respectively; p = 0.0045). Cardiac atrophy and contractile dysfunction in SCI were accompanied by significantly lower blood pressure, reduced circulatory norepinephrine, and increased angiotensin II. At the cellular level, we found the presence of reduced cardiomyocyte size and increased expression of angiotensin II type 1 receptors and transforming growth factor-beta receptors (TGF-β receptor 1 and 2) post-SCI. Importantly, we found more than a two-fold increase in muscle ring finger-1 and Beclin-1 protein level following SCI, indicating the upregulation of the ubiquitin-proteasome system and autophagy-lysosomal machinery. Our data provide novel evidence that SCI-induced cardiomyocyte atrophy and systolic cardiac dysfunction are accompanied by an upregulation of proteolytic pathways, the activation of which is likely due to loss of trophic support from the sympathetic nervous system, neuromechanical unloading, and altered neurohumoral pathways.

4D cardiac magnetic resonance imaging, 4D and 2D transthoracic echocardiography: a comparison of in-vivo assessment of ventricular function in rats

Preclinical cardiovascular research is the foundation of our understanding and broad knowledge of heart function and cardiovascular disease. Reliable cardiac imaging modalities are the basis for applicable results. Four-dimensional cardiac magnetic resonance (4D CMR) has been set as the gold standard for in-vivo assessment of ventricular function in rodents. However, technical improvements in echocardiography now allow us to image the whole heart, which makes four-dimensional echocardiography (4DE) a possible alternative to 4D CMR. To date, no study has systematically assessed 4DE in comparison with 4D CMR in rats. In total we studied 26 juvenile Sprague-Dawley rats (Crl: CD (SD) IGS). Twenty rats underwent echocardiographic imaging (2D and 4D) and 4D CMR. Five of those rats underwent a ligation of the superior and inferior vena cava to reduce the cardiac inflow as a disease model. Six additional rats were used to assess reproducibility of echocardiography and underwent three echocardiographic examinations. 4D CMR was performed on a 7T scanner; 2D and 4D echocardiography was conducted using a 40 MHz transducer. Correlation between 4D CMR, 4DE and 2DE for left-ventricular ejection fraction (LVEF) was assessed. An excellent correlation was observed between 4DE and 4D CMR ( r = 0.95, p < 0.001). Correlation of 2DE and 4D CMR was weak ( r = 0.57, p < 0.01). 4DE provides results that are equally precise as 4D CMR and highly reproducible with less technical effort than 4D CMR.

Evaluation of a commercial multi-dimensional echocardiography technique for ventricular volumetry in small animals

BACKGROUND

The assessment of ventricular volumes using conventional echocardiography methods is limited with regards to the need of geometrical assumptions. In the present study, we aimed to evaluate a novel commercial system for three-dimensional echocardiography (3DE) in preclinical models by direct comparison with conventional 1D- and 2D-echocardiography (1DE; 2DE) and the gold-standard technique magnetic resonance imaging (MRI). Further, we provide a standard operating protocol for image acquisition and analysis with 3DE.

METHODS

3DE was carried out using a 30 MHz center frequency transducer coupled to a Vevo®3100 Imaging System. We evaluated under different experimental conditions: 1) in vitro phantom measurements served as controlled setting in which boundaries were clearly delineated; 2) a validation cohort composed of healthy C57BL/6 J mice and New Zealand Obese (NZO) mice was used in order to validate 3DE against cardiac MRI; 3) a standard mouse model of pressure overload induced-heart failure was investigated to estimate the value of 3DE.

RESULTS

First, in vitro volumetry revealed good agreement between 3DE assessed volumes and the MRI-assessed volumes. Second, cardiac volume determination with 3DE showed smaller mean differences compared to cardiac MRI than conventional 1DE and 2DE. Third, 3DE was suitable to detect reduced ejection fractions in heart failure mice. Fourth, inter- and intra-observer variability of 3DE showed good to excellent agreement regarding absolute volumes in healthy mice, whereas agreement rates for the relative metrics ejection fraction and stroke volume demonstrated good to moderate observer variabilities.

CONCLUSIONS

3DE provides a novel method for accurate volumetry in small animals without the need for spatial assumptions, demonstrating a technique for an improved analysis of ventricular function. Further validation work and highly standardized image analyses are required to increase reproducibility of this approach.

Guidelines for measuring cardiac physiology in mice

Cardiovascular disease is a leading cause of death, and translational research is needed to understand better mechanisms whereby the left ventricle responds to injury. Mouse models of heart disease have provided valuable insights into mechanisms that occur during cardiac aging and in response to a variety of pathologies. The assessment of cardiovascular physiological responses to injury or insult is an important and necessary component of this research. With increasing consideration for rigor and reproducibility, the goal of this guidelines review is to provide best-practice information regarding how to measure accurately cardiac physiology in animal models. In this article, we define guidelines for the measurement of cardiac physiology in mice, as the most commonly used animal model in cardiovascular research.

Listen to this article’s corresponding podcast at http://ajpheart.podbean.com/e/guidelines-for-measuring-cardiac-physiology-in-mice/.

Sustained cardiac programming by short-term juvenile exercise training in male rats

KEY POINTS

Cardiac hypertrophy following endurance-training is thought to be due to hypertrophy of existing cardiomyocytes. The benefits of endurance exercise on cardiac hypertrophy are generally thought to be short-lived and regress to sedentary levels within a few weeks of stopping endurance training. We have now established that cardiomyocyte hyperplasia also plays a considerable role in cardiac growth in response to just 4 weeks of endurance exercise in juvenile (5-9 weeks of age) rats. The effect of endurance exercise on cardiomyocyte hyperplasia diminishes with age and is lost by adulthood. We have also established that the effect of juvenile exercise on heart mass is sustained into adulthood.

ABSTRACT

The aim of this study was to investigate if endurance training during juvenile life 'reprogrammes' the heart and leads to sustained improvements in the structure, function, and morphology of the adult heart. Male Wistar Kyoto rats were exercise trained 5 days week^-1 for 4 weeks in either juvenile (5-9 weeks of age), adolescent (11-15 weeks of age) or adult life (20-24 weeks of age). Juvenile exercise training, when compared to 24-week-old sedentary rats, led to sustained increases in left ventricle (LV) mass (+18%; P < 0.05), wall thickness (+11%; P < 0.05), the longitudinal area of binucleated cardiomyocytes (P < 0.05), cardiomyocyte number (+36%; P < 0.05), and doubled the proportion of mononucleated cardiomyocytes (P < 0.05), with a less pronounced effect of exercise during adolescent life. Adult exercise training also increased LV mass (+11%; P < 0.05), wall thickness (+6%; P < 0.05) and the longitudinal area of binucleated cardiomyocytes (P < 0.05), despite no change in cardiomyocyte number or the proportion of mono- and binucleated cardiomyocytes. Resting cardiac function, LV chamber dimensions and fibrosis levels were not altered by juvenile or adult exercise training. At 9 weeks of age, juvenile exercise significantly reduced the expression of microRNA-208b, which is a known regulator of cardiac growth, but this was not sustained to 24 weeks of age. In conclusion, juvenile exercise leads to physiological cardiac hypertrophy that is sustained into adulthood long after exercise training has ceased. Furthermore, this cardiac reprogramming is largely due to a 36% increase in cardiomyocyte number, which results in an additional 20 million cardiomyocytes in adulthood.

Left ventricular remodeling leads to heart failure in mice with cardiac-specific overexpression of VEGF-B167: echocardiography and magnetic resonance imaging study

Cardiac-specific overexpression of vascular endothelial growth factor (VEGF)-B₁₆₇ is known to induce left ventricular hypertrophy due to altered lipid metabolism, in which ceramides accumulate to the heart and cause mitochondrial damage. The aim of this study was to evaluate and compare different imaging methods to find the most sensitive way to diagnose at early stage the progressive left ventricular remodeling leading to heart failure. Echocardiography and cardiovascular magnetic resonance imaging were compared for imaging the hearts of transgenic mice with cardiac-specific overexpression of VEGF-B₁₆₇ and wild-type mice from 5 to 14 months of age at several time points. Disease progression was verified by molecular biology methods and histology. We showed that left ventricular remodeling is already ongoing at the age of 5 months in transgenic mice leading to heart failure by the age of 14 months. Measurements from echocardiography and cardiovascular magnetic resonance imaging revealed similar changes in cardiac structure and function in the transgenic mice. Changes in histology, gene expressions, and electrocardiography supported the progression of left ventricular hypertrophy. Longitudinal relaxation time in rotating frame (T_1ρ ) in cardiovascular magnetic resonance imaging could be suitable for detecting severe fibrosis in the heart. We conclude that cardiac-specific overexpression of VEGF-B₁₆₇ leads to left ventricular remodeling at early age and is a suitable model to study heart failure development with different imaging methods.

Systemic autoimmunity induced by the TLR7/8 agonist Resiquimod causes myocarditis and dilated cardiomyopathy in a new mouse model of autoimmune heart disease

Systemic autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) show significant heart involvement and cardiovascular morbidity, which can be due to systemically increased levels of inflammation or direct autoreactivity targeting cardiac tissue. Despite high clinical relevance, cardiac damage secondary to systemic autoimmunity lacks inducible rodent models. Here, we characterise immune-mediated cardiac tissue damage in a new model of SLE induced by topical application of the Toll-like receptor 7/8 (TLR7/8) agonist Resiquimod. We observe a cardiac phenotype reminiscent of autoimmune-mediated dilated cardiomyopathy, and identify auto-antibodies as major contributors to cardiac tissue damage. Resiquimod-induced heart disease is a highly relevant mouse model for mechanistic and therapeutic studies aiming to protect the heart during autoimmunity.

Summary: A novel mouse model of autoimmune-mediated heart damage to study the underlying mechanisms and test therapeutic options for systemic autoimmunity.

Chronological Change of Right Ventricle by Chronic Intermittent Hypoxia in Mice

Study Objective

No studies have investigated sequential changes in the heart on magnetic resonance imaging (MRI), along with observation of functional lung phenotypes and genetics, over the duration of chronic intermittent hypoxia (CIH). We investigated chronological changes in heart and lung phenotypes after CIH using a mouse model to provide new insights into the pathophysiology of sleep apnea-induced cardiovascular disease.

Methods

C57BL/6J adult male mice were randomized to 4 or 8 weeks of CIH. Cardiac cine-MRI images were analyzed to assess functional parameters of right ventricle (RV). Histopathological features of myocytes and pulmonary vessels, as well as genes involved in the endothelin (ET) system, were investigated.

Results

Function of the RV reduced significantly at 4 weeks and continuously decreased following another 4 weeks of CIH, although the rate of decrease was attenuated. Notably, persistence of reduced ejection fraction and end-systole RV wall thickness (WT) and increases in the ET system of the lungs and blood strongly implied the development of pulmonary hypertension after 8 weeks of CIH.

Conclusions

RV dysfunction with reduced end-systole RV WT could be a late phenotype in long-standing CIH and possibly also in obstructive sleep apnea.

Feasibility of detecting myocardial infarction in the sheep fetus using late gadolinium enhancement CMR imaging

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging has enabled the accurate assessment of myocardial infarction (MI). However, LGE CMR has not been performed successfully in the fetus, where it could be useful for animal studies of interventions to promote cardiac regeneration. We believe that LGE imaging could allow us to document the presence, extent and effect of MI in utero and would thereby expand our capacity for conducting fetal sheep MI research. We therefore aimed to investigate the feasibility of using LGE to detect MI in sheep fetuses.

METHODS

Six sheep fetuses underwent a thoracotomy and ligation of a left anterior descending (LAD) coronary artery branch; while two fetuses underwent a sham surgery. LGE CMR was performed in a subset of fetuses immediately after the surgery and three days later. Early gadolinium enhancement (EGE) CMR was also performed in a subset of fetuses on both days. Cine imaging of the heart was performed to measure ventricular function.

RESULTS

The imaging performed immediately after LAD ligation revealed no evidence of infarct on LGE (n=3). Two of four infarcted fetuses (50%) showed hypoenhancement at the infarct site on the EGE images. Three days after the ligation, LGE images revealed a clear, hyper-enhanced infarct zone in four of the five infarcted fetuses (80%). No hyper-enhanced infarct zone was seen on the one sham fetus that underwent LGE CMR. No hypoenhancement could be seen in the EGE images in either the sham (n=1) or the infarcted fetus (n=1). No regional wall motion abnormalities were apparent in two of the five infarcted fetuses.

CONCLUSION

LGE CMR detected the MI three days after LAD ligation, but not immediately after. Using available methods, EGE imaging was less useful for detecting deficits in perfusion. Our study provides evidence for the ability of a non-invasive tool to monitor the progression of cardiac repair and damage in fetuses with MI. However, further investigation into the optimal timing of LGE and EGE scans and improvement of the sequences should be pursued with the aim of expanding our capacity to monitor cardiac regeneration after MI in fetal sheep.

Longitudinal observations of progressive cardiac dysfunction in a cardiomyopathic animal model by self-gated cine imaging based on 11.7-T magnetic resonance imaging

The purpose of this study was to longitudinally assess left ventricular function and wall thickness in a hamster model of cardiomyopathy using 11.7-T magnetic resonance imaging (MRI). MRI were performed for six cardiomyopathic J2N-k hamsters and six J2N-n hamsters at 5, 10, 15, and 20 weeks of age. Echocardiography was also performed at 20 weeks. The ejection fraction (EF) at 15 and 20 weeks of age in J2N-k hamsters showed a significant decrease compared with those in controls. Conversely, the end-systolic and end-diastolic volumes in cardiomyopathic hamsters showed a significant increase compared with those in controls. Moreover, the heart walls of J2N-k hamsters at 15 and 20 weeks were thicker than those of controls at end-systole; however, there were no significant differences at end-diastole. Optical microscopy with Masson’s trichrome staining depicted no fibrosis in the control myocardium, although it showed interstitial fibrosis in the 20-week-old J2N-k cardiomyopathic myocardium. There were no differences in EF and the wall thickness observed on MRI and those observed on echocardiography. These results indicate the presence of systolic dysfunction in cardiomyopathic hamsters. Self-gated cine imaging based on 11.7-T MRI can be used for serial measurements of cardiac function and wall thickness in a cardiomyopathic model.

Assessment of Longitudinal Reproducibility of Mice LV Function Parameters at 11.7 T Derived from Self-Gated CINE MRI

The objective of this work was the assessment of the reproducibility of self-gated cardiac MRI in mice at ultra-high-field strength. A group of adult mice (n = 5) was followed over 360 days with a standardized MR protocol including reproducible animal position and standardized planning of the scan planes. From the resulting CINE MRI data, global left ventricular (LV) function parameters including end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), and left ventricular mass (LVM) were quantified. The reproducibility of the self-gated technique as well as the intragroup variability and longitudinal changes of the investigated parameters was assessed. Self-gated cardiac MRI proved excellent reproducibility of the global LV function parameters, which was in the order of the intragroup variability. Longitudinal assessment did not reveal any significant variations for EDV, ESV, SV, and EF but an expected increase of the LVM with increasing age. In summary, self-gated MRI in combination with a standardized protocol for animal positioning and scan plane planning ensures reproducible assessment of global LV function parameters.

Dynamic Tracking of Injected Mesenchymal Stem Cells after Myocardial Infarction in Rats: A Serial 7T MRI Study

Purpose. To track the fate of micron-sized particles of iron oxide (MPIO) labeled mesenchymal stem cells (MSCs) in vivo in a rat myocardial infarction model using 7T magnetic resonance imaging (MRI) scanner. Materials and Methods. Male MSCs (2 × 10⁶/50 μL) dual-labeled with MPIO and CM-DiI were injected into the infarct periphery 7 days after myocardial infarction (MI). The control group received cell-free media injection. The temporal stem cell location, signal intensity, and cardiac function were dynamically assessed using a 7T MRI at 24 h before transplantation (baseline), 3 days, 2 weeks, and 4 weeks after transplantation, respectively. Results. MR hypointensities caused by MPIOs were observed on T2^⁎-weighted images at all time points after MSCs injection. Cine-MRI showed that MSCs moderated progressive left ventricular remodeling. Double staining for iron and CD68 revealed that most of the iron-positive cells were CD68-positive macrophages. Real-time PCR for rat SRY gene showed the number of survival MSCs considerably decreased after transplantation. MSC-treated hearts had significantly increased capillary density in peri-infarct region and lower cardiomyocytes apoptosis and fibrosis formation. Conclusions. Iron particles are not a reliable marker for in vivo tracking the long-term fate of MSCs engraftment. Despite of poor cell retention, MSCs moderate left ventricular remodeling after MI.

High field magnetic resonance imaging of rodents in cardiovascular research

Transgenic and gene knockout rodent models are primordial to study pathophysiological processes in cardiovascular research. Over time, cardiac MRI has become a gold standard for in vivo evaluation of such models. Technical advances have led to the development of magnets with increasingly high field strength, allowing specific investigation of cardiac anatomy, global and regional function, viability, perfusion or vascular parameters. The aim of this report is to provide a review of the various sequences and techniques available to image mice on 7-11.7 T magnets and relevant to the clinical setting in humans. Specific technical aspects due to the rise of the magnetic field are also discussed.

Serum Bicarbonate and Structural and Functional Cardiac Abnormalities in Chronic Kidney Disease - A Report from the Chronic Renal Insufficiency Cohort Study

BACKGROUND

Heart failure (HF) is a frequent occurrence in chronic kidney disease (CKD) patients and predicts poor survival. Serum bicarbonate is associated with increased rates of HF in CKD; however, the mechanisms leading to this association are incompletely understood. This study aims to assess whether serum bicarbonate is independently associated with structural and functional cardiac abnormalities in CKD.

METHODS

The association between serum bicarbonate and left ventricular (LV) hypertrophy (LVH), LV mass indexed to height2.7, LV geometry, ejection fraction (EF) and diastolic dysfunction was assessed in 3,483 participants without NYHA class III/IV HF, enrolled in the Chronic Renal Insufficiency Cohort study.

RESULTS

The mean estimated glomerular filtration rate was 42.5 ± 17 ml/min/1.73 m2. The overall prevalence of LVH was 51.2%, with 57.8, 50.9 and 47.7% for bicarbonate categories <22, 22-26 and >26 mmol/l, respectively. Participants with low bicarbonate were more likely to have LVH and abnormal LV geometry (OR 1.32; 95% CI 1.07-1.64, and OR 1.57; 95% CI 1.14-2.16, respectively). However, the association was not statistically significant after adjustment for demographics, traditional cardiovascular risk factors, medications and kidney function (OR 1.07; 95% CI 0.66-1.72, and OR 1.27; 95% CI 0.64-2.51, respectively). No association was found between bicarbonate and systolic or diastolic dysfunction. During follow-up, no significant changes in LV mass or EF were observed in any bicarbonate strata.

CONCLUSIONS

In a large CKD study, serum bicarbonate was associated with LV mass and concentric LVH; however, this association was attenuated after adjustment for clinical factors suggesting that the observed cardiac effects are mediated through yet unknown mechanisms.

The pulsatility volume index: an indicator of cerebrovascular compliance based on fast magnetic resonance imaging of cardiac and respiratory pulsatility

The influence of cardiac activity on the viscoelastic properties of intracranial tissue is one of the mechanisms through which brain-heart interactions take place, and is implicated in cerebrovascular disease. Cerebrovascular disease risk is not fully explained by current risk factors, including arterial compliance. Cerebrovascular compliance is currently estimated indirectly through Doppler sonography and magnetic resonance imaging (MRI) measures of blood velocity changes. In order to meet the need for novel cerebrovascular disease risk factors, we aimed to design and validate an MRI indicator of cerebrovascular compliance based on direct endogenous measures of blood volume changes. We implemented a fast non-gated two-dimensional MRI pulse sequence based on echo-planar imaging (EPI) with ultra-short repetition time (approx. 30-50 ms), which stepped through slices every approximately 20 s. We constrained the solution of the Bloch equations for spins moving faster than a critical speed to produce an endogenous contrast primarily dependent on spin volume changes, and an approximately sixfold signal gain compared with Ernst angle acquisitions achieved by the use of a 90° flip angle. Using cardiac and respiratory peaks detected on physiological recordings, average cardiac and respiratory MRI pulse waveforms in several brain compartments were obtained at 7 Tesla, and used to derive a compliance indicator, the pulsatility volume index (pVI). The pVI, evaluated in larger cerebral arteries, displayed significant variation within and across vessels. Multi-echo EPI showed the presence of significant pulsatility effects in both S0 and [Formula: see text] signals, compatible with blood volume changes. Lastly, the pVI dynamically varied during breath-holding compared with normal breathing, as expected for a compliance indicator. In summary, we characterized and performed an initial validation of a novel MRI indicator of cerebrovascular compliance, which might prove useful to investigate brain-heart interactions in cerebrovascular disease and other disorders.

[Prognostic value of cardiovascular MRI in diabetics]

CLINICAL/METHODICAL ISSUE

Despite an increased cardiovascular risk in patients with diabetes mellitus they are a heterogeneous population with very different individual manifestation of diseases; therefore, a profound stratification is recommended.

STANDARD METHODS

Clinical examinations and blood biomarkers are typically used in diabetic patients to determine the risk for developing cardio-cerebrovascular events.

METHODICAL INNOVATIONS

Cardiac as well as whole-body magnetic resonance imaging (MRI) including cardiovascular sequences are established methods for clinical diagnostics. Their significance in predicting the outcome and the corresponding risk stratification for patients with diabetes is becoming increasingly more important based on recent study results.

PERFORMANCE

Late gadolinium enhancement (LGE) in cardiac MRI detects silent myocardial ischemia in up to 30% of diabetic patients, which is associated with a hazard ratio of 3-6 for cardiovascular events. Regional left ventricular wall motion abnormalities and decreased ejection fraction also have a prognostic value in diabetics. Based on whole-body MRI, the vessel score as well as carotid artery stenosis have been evaluated as additional predictors for cardio-cerebrovascular events.

ACHIEVEMENTS

The MRI-based predictors have independent and incremental prognostic value beyond traditional risk stratification for cardio-cerebrovascular events; however, only the comprehensive assessment of whole-body MRI including angiography allows the identification of patients who remain free of cardio-cerebrovascular events over a period of 6 years.

PRACTICAL RECOMMENDATIONS

Cardiac MRI, particularly the detection of LGE, can be recommended for risk stratification of patients with diabetes mellitus. The clinical relevance of the added prognostic value of whole-body MRI needs to be clarified in further studies.

Cardiovascular imaging: what have we learned from animal models?

Cardiovascular imaging has become an indispensable tool for patient diagnosis and follow up. Probably the wide clinical applications of imaging are due to the possibility of a detailed and high quality description and quantification of cardiovascular system structure and function. Also phenomena that involve complex physiological mechanisms and biochemical pathways, such as inflammation and ischemia, can be visualized in a non-destructive way. The widespread use and evolution of imaging would not have been possible without animal studies. Animal models have allowed for instance, (i) the technical development of different imaging tools, (ii) to test hypothesis generated from human studies and finally, (iii) to evaluate the translational relevance assessment of in vitro and ex-vivo results. In this review, we will critically describe the contribution of animal models to the use of biomedical imaging in cardiovascular medicine. We will discuss the characteristics of the most frequent models used in/for imaging studies. We will cover the major findings of animal studies focused in the cardiovascular use of the repeatedly used imaging techniques in clinical practice and experimental studies. We will also describe the physiological findings and/or learning processes for imaging applications coming from models of the most common cardiovascular diseases. In these diseases, imaging research using animals has allowed the study of aspects such as: ventricular size, shape, global function, and wall thickening, local myocardial function, myocardial perfusion, metabolism and energetic assessment, infarct quantification, vascular lesion characterization, myocardial fiber structure, and myocardial calcium uptake. Finally we will discuss the limitations and future of imaging research with animal models.

Variability of Mouse Left Ventricular Function Assessment by 11.7 Tesla MRI

We studied intraobserver (n = 24), interobserver (n = 24) and interexperiment (n = 12) reproducibility of left ventricular (LV) mass and volume measurements in mice using an 11.7 T MRI system. The LV systolic function was assessed with a short-axis FLASH-cine sequence in 29 mice, including animals having undergone transverse aortic constriction. Bland-Altman and regression analysis were used to compare the different data sets. Reproducibility was excellent for the LV mass and end-diastolic volume (coefficient of variability (CoV) between 5.4 and 11.8 %), good for end-systolic volume (CoV 15.2-19.4 %) and moderate for stroke volume and ejection fraction (CoV 14.7-20.9 %). We found an excellent correlation between LV mass determined by MRI and ex vivo morphometric data (r = 0.92). In conclusion, LV systolic function can be assessed on an 11.7 T MRI scanner with high reproducibility for most parameters, as needed in longitudinal studies. However, data should be interpreted taking into account the moderate reproducibility of small volumes.

Prevention of exercised induced cardiomyopathy following Pip-PMO treatment in dystrophic mdx mice

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disorder caused by mutations in the Dmd gene. In addition to skeletal muscle wasting, DMD patients develop cardiomyopathy, which significantly contributes to mortality. Antisense oligonucleotides (AOs) are a promising DMD therapy, restoring functional dystrophin protein by exon skipping. However, a major limitation with current AOs is the absence of dystrophin correction in heart. Pip peptide-AOs demonstrate high activity in cardiac muscle. To determine their therapeutic value, dystrophic mdx mice were subject to forced exercise to model the DMD cardiac phenotype. Repeated peptide-AO treatments resulted in high levels of cardiac dystrophin protein, which prevented the exercised induced progression of cardiomyopathy, normalising heart size as well as stabilising other cardiac parameters. Treated mice also exhibited significantly reduced cardiac fibrosis and improved sarcolemmal integrity. This work demonstrates that high levels of cardiac dystrophin restored by Pip peptide-AOs prevents further deterioration of cardiomyopathy and pathology following exercise in dystrophic DMD mice.

Impaired in vivo mitochondrial Krebs cycle activity after myocardial infarction assessed using hyperpolarized magnetic resonance spectroscopy

BACKGROUND

Myocardial infarction (MI) is one of the leading causes of heart failure. An increasing body of evidence links alterations in cardiac metabolism and mitochondrial function with the progression of heart disease. The aim of this work was to, therefore, follow the in vivo mitochondrial metabolic alterations caused by MI, thereby allowing a greater understanding of the interplay between metabolic and functional abnormalities.

METHODS AND RESULTS

Using hyperpolarized carbon-13 ((13)C)-magnetic resonance spectroscopy, in vivo alterations in mitochondrial metabolism were assessed for 22 weeks after surgically induced MI with reperfusion in female Wister rats. One week after MI, there were no detectable alterations in in vivo cardiac mitochondrial metabolism over the range of ejection fractions observed (from 28% to 84%). At 6 weeks after MI, in vivo mitochondrial Krebs cycle activity was impaired, with decreased (13)C-label flux into citrate, glutamate, and acetylcarnitine, which correlated with the degree of cardiac dysfunction. These changes were independent of alterations in pyruvate dehydrogenase flux. By 22 weeks, alterations were also seen in pyruvate dehydrogenase flux, which decreased at lower ejection fractions. These results were confirmed using in vitro analysis of enzyme activities and metabolomic profiles of key intermediates.

CONCLUSIONS

The in vivo decrease in Krebs cycle activity in the 6-week post-MI heart may represent an early maladaptive phase in the metabolic alterations after MI in which reductions in Krebs cycle activity precede a reduction in pyruvate dehydrogenase flux. Changes in mitochondrial metabolism in heart disease are progressive and proportional to the degree of cardiac impairment.

Functional assessment of the mouse heart by MRI with a 1-min acquisition

In vivo assessment of heart function in mice is important for basic and translational research in cardiology. MRI is an accurate tool for the investigation of the anatomy and function in the preclinical setting; however, the long scan duration limits its usage. We aimed to reduce the acquisition time of cine MRI to 1 min. We employed spatiotemporal compressed sensing and parallel imaging to accelerate retrospectively gated cine MRI. We compared the functional parameters derived from full and undersampled data in Cartesian and radial MRI by means of Bland-Altman plots. We found that the scan time for the whole heart could be reduced to 2 min with Cartesian sampling and to 1 min with radial sampling. Despite a reduction in the signal-to-noise ratio, the accuracy in the estimation of left and right ventricular volumes was preserved for all tested subjects. This method can be used to perform accurate functional MRI examinations in mice for high-throughput phenotyping or translational studies.

T₁ mapping detects pharmacological retardation of diffuse cardiac fibrosis in mouse pressure-overload hypertrophy

BACKGROUND

Diffuse interstitial fibrosis is present in diverse cardiomyopathies and associated with poor prognosis. We investigated whether magnetic resonance imaging-based T1 mapping could quantify the induction and pharmacological suppression of diffuse cardiac fibrosis in murine pressure-overload hypertrophy.

METHODS AND RESULTS

Mice were subjected to transverse aortic constriction or sham surgery. The angiotensin receptor blocker losartan was given to half the animals. Cine-magnetic resonance imaging performed at 7 and 28 days showed hypertrophy and remodeling and systolic and diastolic dysfunction in transverse aortic constriction groups as expected. Late gadolinium-enhanced magnetic resonance imaging revealed focal signal enhancement at the inferior right ventricular insertion point of transverse aortic constriction mice concordant with the foci of fibrosis in histology. The extracellular volume fraction, calculated from pre- and postcontrast T1 measurements, was elevated by transverse aortic constriction and showed direct linear correlation with picrosirius red collagen volume fraction, thus confirming the suitability of extracellular volume fraction as an in vivo measure of diffuse fibrosis. Treatment with losartan reduced left ventricular dysfunction and prevented increased extracellular volume fraction, indicating that T1 mapping is sensitive to pharmacological prevention of fibrosis.

CONCLUSIONS

Magnetic resonance imaging can detect diffuse and focal cardiac fibrosis in a clinically relevant animal model of pressure overload and is sensitive to pharmacological reduction of fibrosis by angiotensin receptor blockade. Thus, T1 mapping can be used to assess antifibrotic therapeutic strategies.

PET/MRI assessment of the infarcted mouse heart

Heart failure originating from myocardial infarction (MI) is a leading cause of death worldwide. Mouse models of ischaemia and reperfusion injury (I/R) are used to study the effects of novel treatment strategies targeting MI, however staging disease and treatment efficacy is a challenge. Damage and recovery can be assessed on the cellular, tissue or whole-organ scale but these are rarely measured in concert. Here, for the first time, we present data showing measures of injury in infarcted mice using complementary techniques for multi-modal characterisation of the heart. We use in vivo magnetic resonance imaging (MRI) to assess heart function with cine-MRI, hindered perfusion with late gadolinium enhancement imaging and muscular function with displacement encoded with stimulated echoes (DENSE) MRI. These measures are followed by positron emission tomography (PET) with 18-F-fluorodeoxyglucose to assess cellular metabolism. We demonstrate a protocol combining each of these measures for the same animal in the same imaging session and compare how the different markers can be used to quantify cardiac recovery on different scales following injury.

Evolution of cardiac and renal impairment detected by high-field cardiovascular magnetic resonance in mice with renal artery stenosis

BACKGROUND

Renal artery stenosis (RAS) promotes hypertension and cardiac dysfunction. The 2-kidney, 1-clip mouse model in many ways resembles RAS in humans and is amenable for genetic manipulation, but difficult to evaluate noninvasively. We hypothesized that cardiovascular magnetic resonance (CMR) is capable of detecting progressive cardiac and renal dysfunction in mice with RAS and monitoring the progression of the disease longitudinally.

METHODS

RAS was induced at baseline in eighteen mice by constricting the renal artery. Nine additional animals served as normal controls. CMR scans (16.4 T) were performed in all mice one week before and 2 and 4 weeks after baseline. Renal volumes and hemodynamics were assessed using 3D fast imaging with steady-state precession and arterial spin labelling, and cardiac function using CMR cine. Renal hypoxia was investigated using blood oxygen-level dependent (BOLD) MR.

RESULTS

Two weeks after surgery, mean arterial pressure was elevated in RAS mice. The stenotic kidney (STK) showed atrophy, while the contra-lateral kidney (CLK) showed hypertrophy. Renal blood flow (RBF) and cortical oxygenation level declined in the STK but remained unchanged in CLK. Moreover, cardiac end-diastolic and stroke volumes decreased and myocardial mass increased. At 4 weeks, STK RBF remained declined and the STK cortex and medulla showed development of hypoxia. Additionally, BOLD detected a mild hypoxia in CLK cortex. Cardiac end-diastolic and stroke volumes remained reduced and left ventricular hypertrophy worsened. Left ventricular filling velocities (E/A) indicated progression of cardiac dysfunction towards restrictive filling.

CONCLUSIONS

CMR detected longitudinal progression of cardiac and renal dysfunction in 2K, 1C mice. These observations support the use of high-field CMR to obtain useful information regarding chronic cardiac and renal dysfunction in small animals.

Comparison of echocardiographic measurements of left ventricular volumes to full volume magnetic resonance imaging in normal and diseased rats

BACKGROUND

Clinical two-dimensional (2D) and clinical three-dimensional echocardiography are validated against cardiac magnetic resonance imaging (CMR), the gold standard for left ventricular (LV) volume measurement. In rodents, there is no widely accepted echocardiographic measure of whole LV volumes, and CMR measurements vary among studies. The aim of this study was to compare LV volumes by 2D echocardiography (using a hemisphere-cylinder [HC] model) with HC and full-volume (FV) CMR in normal and diseased rats to measure the impact of geometric models and imaging modalities.

METHODS

Rats (n = 27) underwent ascending aortic banding, myocardial infarction induction by either permanent left anterior descending coronary artery ligation or ischemia-reperfusion, and sham thoracotomy. Subsequently, end-diastolic volume, end-systolic volume, and ejection fraction were measured using an HC 2D echocardiographic model combining parasternal short-axis and long-axis measurements, and these were compared with HC and FV CMR.

RESULTS

Diseased groups showed LV dilatation and dysfunction. HC echocardiographic and FV CMR measures of end-diastolic volume, end-systolic volume, and ejection fraction were correlated. On Bland-Altman plots, end-diastolic volumes were concordant between both methods, while HC echocardiography underestimated end-systolic volumes, resulting in a modest overestimation of ejection fractions compared with FV CMR. Other 2D echocardiographic geometric models offered less concordance with FV CMR than HC. HC CMR overestimated LV volumes compared with FV CMR, while HC echocardiography underestimated HC CMR volumes. Echocardiography underestimated corresponding LV dimensions by CMR, particularly short axis.

CONCLUSIONS

Concordant measures of LV volume and function were obtained using (1) a relatively simple HC model of the left ventricle inclusive of two orthogonal 2D echocardiographic planes and (2) FV CMR in normal and diseased rats. The HC model appeared to compensate for the underestimation of LV dimensions by echocardiography.

Cardiac-respiratory self-gated cine ultra-short echo time (UTE) cardiovascular magnetic resonance for assessment of functional cardiac parameters at high magnetic fields

BACKGROUND

To overcome flow and electrocardiogram-trigger artifacts in cardiovascular magnetic resonance (CMR), we have implemented a cardiac and respiratory self-gated cine ultra-short echo time (UTE) sequence. We have assessed its performance in healthy mice by comparing the results with those obtained with a self-gated cine fast low angle shot (FLASH) sequence and with echocardiography.

METHODS

2D self-gated cine UTE (TE/TR = 314 μs/6.2 ms, resolution: 129 × 129 μm, scan time per slice: 5 min 5 sec) and self-gated cine FLASH (TE/TR = 3 ms/6.2 ms, resolution: 129 × 129 μm, scan time per slice: 4 min 49 sec) images were acquired at 9.4 T. Volume of the left and right ventricular (LV, RV) myocardium as well as the end-diastolic and -systolic volume was segmented manually in MR images and myocardial mass, stroke volume (SV), ejection fraction (EF) and cardiac output (CO) were determined. Statistical differences were analyzed by using Student t test and Bland-Altman analyses.

RESULTS

Self-gated cine UTE provided high quality images with high contrast-to-noise ratio (CNR) also for the RV myocardium (CNRblood-myocardium = 25.5 ± 7.8). Compared to cine FLASH, susceptibility, motion, and flow artifacts were considerably reduced due to the short TE of 314 μs. The aortic valve was clearly discernible over the entire cardiac cycle. Myocardial mass, SV, EF and CO determined by self-gated UTE were identical to the values measured with self-gated FLASH and showed good agreement to the results obtained by echocardiography.

CONCLUSIONS

Self-gated UTE allows for robust measurement of cardiac parameters of diagnostic interest. Image quality is superior to self-gated FLASH, rendering the method a powerful alternative for the assessment of cardiac function at high magnetic fields.

Heart involvement in rheumatoid arthritis: multimodality imaging and the emerging role of cardiac magnetic resonance

OBJECTIVES

Patients with rheumatoid arthritis (RA) exhibit a high risk of cardiovascular disease (CVD). CVD in RA can present in many guises, commonly detected at a subclinical level only.

METHODS

Modern imaging modalities that allow the noninvasive assessment of myocardial performance and are able to identify cardiac abnormalities in early asymptomatic stages may be useful tools in terms of screening, diagnostic evaluation, and risk stratification in RA.

RESULTS

The currently used imaging techniques are echocardiography, single-photon emission computed tomography (SPECT), and cardiac magnetic resonance (CMR). Between them, echocardiography provides information about cardiac function, valves, and perfusion; SPECT provides information about myocardial perfusion and carries a high amount of radiation; and CMR-the most promising imaging modality-evaluates myocardial function, inflammation, microvascular dysfunction, valvular disease, perfusion, and presence of scar. Depending on availability, expertise, and clinical queries, "right technique should be applied for the right patient at the right time."

CONCLUSIONS

In this review, we present a short overview of CVD in RA focusing on the clinical implication of multimodality imaging and mainly on the evolving role of CMR in identifying high-risk patients who could benefit from prevention strategies and early specific treatment targeting the heart. Advantages and disadvantages of each imaging technique in the evaluation of RA are discussed.

Immunohistochemical expression of oncological proliferation markers in the hearts of rats during normal pregnancy

Aim: Pregnancy is characterized by left ventricular hypertrophy that is potentially accounted for by cardiomyocyte proliferation, although no such evidence is currently available. This study investigates if the left ventricular mass (LVM) increase during pregnancy implies cell hyperplasia. Materials & methods: In nonpregnant and late-pregnant rats, cardiac function and LVM were evaluated by MRI, and cardiomyocyte dimensions and proliferations were assessed quantitatively by morphometric analysis and immunohistochemistry using oncological markers (Ki67 and MCM2). Results: In late-pregnant rats, LVM and cardiomyocyte area were greater. No mitotic figures were found nor was there any significant difference between groups in Ki67 expression. MCM2 expression was related to LVM. Conclusion: During pregnancy, rat cardiomyocytes undergo hypertrophy but not hyperplasia; the expression of MCM2, related to LVM, suggests it could be a marker of protein synthesis. The application of oncological markers to physiological contexts may provide insight into their role within the cell cycle.

Long-term left ventricular remodelling in rat model of nonreperfused myocardial infarction: sequential MR imaging using a 3T clinical scanner

Purpose. To evaluate whether 3T clinical MRI with a small-animal coil and gradient-echo (GE) sequence could be used to characterize long-term left ventricular remodelling (LVR) following nonreperfused myocardial infarction (MI) using semi-automatic segmentation software (SASS) in a rat model. Materials and Methods. 5 healthy rats were used to validate left ventricular mass (LVM) measured by MRI with postmortem values. 5 sham and 7 infarcted rats were scanned at 2 and 4 weeks after surgery to allow for functional and structural analysis of the heart. Measurements included ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), and LVM. Changes in different regions of the heart were quantified using wall thickness analyses. Results. LVM validation in healthy rats demonstrated high correlation between MR and postmortem values. Functional assessment at 4 weeks after MI revealed considerable reduction in EF, increases in ESV, EDV, and LVM, and contractile dysfunction in infarcted and noninfarcted regions. Conclusion. Clinical 3T MRI with a small animal coil and GE sequence generated images in a rat heart with adequate signal-to-noise ratio (SNR) for successful semiautomatic segmentation to accurately and rapidly evaluate long-term LVR after MI.

Mice expressing a human K(ATP) channel mutation have altered channel ATP sensitivity but no cardiac abnormalities

AIMS/HYPOTHESIS

Patients with severe gain-of-function mutations in the Kir6.2 subunit of the ATP-sensitive potassium (K(ATP)) channel, have neonatal diabetes, muscle hypotonia and mental and motor developmental delay-a condition known as iDEND syndrome. However, despite the fact that Kir6.2 forms the pore of the cardiac K(ATP) channel, patients show no obvious cardiac symptoms. The aim of this project was to use a mouse model of iDEND syndrome to determine whether iDEND mutations affect cardiac function and cardiac K(ATP) channel ATP sensitivity.

METHODS

We performed patch-clamp and in vivo cine-MRI studies on mice in which the most common iDEND mutation (Kir6.2-V59M) was targeted to cardiac muscle using Cre-lox technology (m-V59M mice).

RESULTS

Patch-clamp studies of isolated cardiac myocytes revealed a markedly reduced K(ATP) channel sensitivity to MgATP inhibition in m-V59M mice (IC(50) 62 μmol/l compared with 13 μmol/l for littermate controls). In vivo cine-MRI revealed there were no gross morphological differences and no differences in heart rate, end diastolic volume, end systolic volume, stroke volume, ejection fraction, cardiac output or wall thickening between m-V59M and control hearts, either under resting conditions or under dobutamine stress.

CONCLUSIONS/INTERPRETATION

The common iDEND mutation Kir6.2-V59M decreases ATP block of cardiac K(ATP) channels but was without obvious effect on heart function, suggesting that metabolic changes fail to open the mutated channel to an extent that affects function (at least in the absence of ischaemia). This may have implications for the choice of sulfonylurea used to treat neonatal diabetes.

Nebivolol improves diastolic dysfunction and myocardial remodeling through reductions in oxidative stress in the transgenic (mRen2) rat

Angiotensin II contributes to myocardial tissue remodeling and interstitial fibrosis through NADPH oxidase-mediated generation of oxidative stress in the progression of heart failure. Recent data have suggested that nebivolol, a third-generation β-blocker, improves diastolic dysfunction by targeting nitric oxide (NO) and metabolic pathways that decrease interstitial fibrosis. We sought to determine if targeting NO would improve diastolic function in a model of tissue renin-angiotensin system overactivation. We used the transgenic (TG) (mRen2)27 rat, which overexpresses the murine renin transgene and manifests insulin resistance and left ventricular dysfunction. We treated 6- to 7-wk-old TG (mRen2)27 rats and age-matched Sprague-Dawley control rats with nebivolol (10 mg·kg(-1)·day(-1)) or placebo via osmotic minipumps for a period of 21 days. Compared with Sprague-Dawley control rats, TG (mRen2)27 rats displayed a prolonged diastolic relaxation time and reduced initial filling rate associated with increased interstitial fibrosis and left ventricular hypertrophy. These findings were temporally related to increased NADPH oxidase activity and subunits p47(phox) and Rac1 and increased total ROS and peroxynitrite formation in parallel with reductions in the antioxidant heme oxygenase as well as the phosphorylation/activation of endothelial NO synthase and PKB/Akt. Treatment with nebivolol restored diastolic function and interstitial fibrosis through increases in the phosphorylation of 5'-AMP-activated protein kinase, Akt, and endothelial NO synthase and reductions in oxidant stress. These results support that targeting NO with nebivolol treatment improves diastolic dysfunction through reducing myocardial oxidative stress by enhancing 5'-AMP-activated protein kinase and Akt activation of NO biosynthesis.

In vivo MRI characterization of progressive cardiac dysfunction in the mdx mouse model of muscular dystrophy

AIMS

The mdx mouse has proven to be useful in understanding the cardiomyopathy that frequently occurs in muscular dystrophy patients. Here we employed a comprehensive array of clinically relevant in vivo MRI techniques to identify early markers of cardiac dysfunction and follow disease progression in the hearts of mdx mice.

METHODS AND RESULTS

Serial measurements of cardiac morphology and function were made in the same group of mdx mice and controls (housed in a non-SPF facility) using MRI at 1, 3, 6, 9 and 12 months after birth. Left ventricular (LV) and right ventricular (RV) systolic and diastolic function, response to dobutamine stress and myocardial fibrosis were assessed. RV dysfunction preceded LV dysfunction, with RV end systolic volumes increased and RV ejection fractions reduced at 3 months of age. LV ejection fractions were reduced at 12 months, compared with controls. An abnormal response to dobutamine stress was identified in the RV of mdx mice as early as 1 month. Late-gadolinium-enhanced MRI identified increased levels of myocardial fibrosis in 6, 9 and 12-month-old mdx mice, the extent of fibrosis correlating with the degree of cardiac remodeling and hypertrophy.

CONCLUSIONS

MRI could identify cardiac abnormalities in the RV of mdx mice as young as 1 month, and detected myocardial fibrosis at 6 months. We believe these to be the earliest MRI measurements of cardiac function reported for any mice, and the first use of late-gadolinium-enhancement in a mouse model of congenital cardiomyopathy. These techniques offer a sensitive and clinically relevant in vivo method for assessment of cardiomyopathy caused by muscular dystrophy and other diseases.

Cardiosphere-derived cells improve function in the infarcted rat heart for at least 16 weeks--an MRI study

Aims

Endogenous cardiac progenitor cells, expanded from explants via cardiosphere formation, present a promising cell source to prevent heart failure following myocardial infarction. Here we used cine-magnetic resonance imaging (MRI) to track administered cardiosphere-derived cells (CDCs) and to measure changes in cardiac function over four months in the infarcted rat heart.

Methods and Results

CDCs, cultured from neonatal rat heart, comprised a heterogeneous population including cells expressing the mesenchymal markers CD90 and CD105, the stem cell marker c-kit and the pluripotency markers Sox2, Oct3/4 and Klf-4. CDCs (2×10⁶) expressing green fluorescent protein (GFP+) were labelled with fluorescent micron-sized particles of iron oxide (MPIO). Labelled cells were administered to the infarcted rat hearts (n = 7) by intramyocardial injection immediately following reperfusion, then by systemic infusion (4×10⁶) 2 days later. A control group (n = 7) was administered cell medium. MR hypointensities caused by the MPIOs were detected at all times and GFP+ cells containing MPIO particles were identified in tissue slices at 16 weeks. At two days after infarction, cardiac function was similar between groups. By 6 weeks, ejection fractions in control hearts had significantly decreased (47±2%), but this was not evident in CDC-treated hearts (56±3%). The significantly higher ejection fractions in the CDC-treated group were maintained for a further 10 weeks. In addition, CDC-treated rat hearts had significantly increased capillary density in the peri-infarct region and lower infarct sizes. MPIO-labelled cells also expressed cardiac troponin I, von Willebrand factor and smooth muscle actin, suggesting their differentiation along the cardiomyocyte lineage and the formation of new blood vessels.

Conclusions

CDCs were retained in the infarcted rat heart for 16 weeks and improved cardiac function.

A comparison of retrospectively self-gated magnetic resonance imaging and high-frequency echocardiography for characterization of left ventricular function in mice

Non-invasive imaging methods like echocardiography and magnetic resonance imaging (MRI) are very valuable in longitudinal follow-up studies of cardiac function in small animals. To be able to compare results from studies using different methods, and explain possible differences, it is important to know the agreement between these methods. As both self-gated high-field MRI and high-frequency echocardiography (hf-echo) M-mode are potential methods for evaluation of left ventricular (LV) function in healthy mice, our aim was to assess the agreement between these two methods. Fifteen healthy female C57BL/6J mice underwent both self-gated MRI and hf-echo during the same session of light isoflurane anaesthesia. LV dimensions were estimated offline, and agreement between the methods and reproducibility for the two methods assessed using Bland-Altman methods. In summary, hf-echo M-mode had better inter-observer repeatability than self-gated MRI for all measured parameters. Compared with hf-echo, systolic posterior wall thicknesses were significantly higher when measured by MRI, while diastolic anterior wall thicknesses were found to be significantly smaller. MRI measurements of diastolic LV diameter were also higher using MRI, resulting in larger fractional shortening values compared with the values obtained by hf-echo. In conclusion, hf-echo M-mode is easy to apply, has high temporal and spatial resolution, and good reproducibility. Self-gated MRI might be advantageous in cases of abnormal LV geometry and heterogeneous regional myocardial function, especially with improvements in spatial resolution. The moderate agreement between the methods must be taken into account when comparing studies using the two modalities.

Feasibility of functional cardiac MR imaging in mice using a clinical 3 Tesla whole body scanner

OBJECTIVES

To test the feasibility of cardiac MR imaging in mice using a clinical 3 Tesla whole body MR system for structural and functional analysis. Standard protocols for bright blood cine imaging were adapted for murine dimensions. To validate measurements of functional parameters the MR data were compared with high-resolution echocardiographic measurements.

MATERIALS AND METHODS

Cardiac imaging was carried out in CD 1 wild-type mice (n = 8). MR imaging studies were performed using a clinical 3 Tesla MR system (Achieva, Philips). All mice received 2 MR scans and 1 echocardiographic evaluation. For optimal MR signal detection a dedicated solenoid receive-only coil was used. Electrocardiogram signal was recorded using a dedicated small animal electrocardiogram monitoring unit. For imaging we used a retrospectively triggered TFE sequence with a repetition time of 12 ms and an echo time of 4 ms. A dedicated software patch allowed for triggering of cardiac frequency of up to 600 BPM. Doppler-echocardiography was performed using a VisualSonics Vevo 770 high-resolution imaging system with a 30 MHz scanhead. Axial/lateral resolution was 40 of 100 microm and temporal resolution was 150 to 300 frames/s (B-mode) and 1000 frames/s (M-mode) depending on the setting.

RESULTS

MR imaging was successfully carried out in all mice with a sufficient temporal resolution and good signal-to-noise ratio and contrast-to-noise ratio levels allowing for identification of all relevant structures. Accordingly, there was a good scan-rescan reproducibility of MR measurements: Interassay coefficients of variance ranged from 4% for ejection fraction to 12% for endsystolic volume (ESV). Magnetic resonance imaging and echocardiography gave comparable results when using the same geometric model (Teichholz method): EDV: 60.2 +/- 6.1 microL/59.1 +/- 12.3 microL, ESV: 20.0 +/- 2.6 microL/20.7 +/- 7.7 microL, EF: 66.7% +/- 4.0%/65.2% +/- 9.9%, CO 19.5 +/- 3.6 mL/17.9 +/- 2.9 mL. Bland-Altman analysis gave acceptable limits of agreement between both methods: EDV (+28.2/-26.1), ESV (+16.3/-17.7), EF (+19.0/-16.1), CO (10.7/-7.5). When applying the Simpson's method MR volume estimates were significantly higher compared with echocardiography resulting in a lower estimate for the ejection fraction (60% +/- 3.9% vs. 66.7% +/- 4.0%).

CONCLUSIONS

Cardiac MR imaging of mice using a clinical 3 Tesla MR system for functional analysis is feasible with sufficient spatial and temporal resolution, good repeatability and reliable results when compared with high-resolution echocardiography.

Magnetic resonance imaging evaluation of remodeling by cardiac elastomeric tissue scaffold biomaterials in a rat model of myocardial infarction

Grafting of elastomeric biomaterial scaffolds may offer a radical strategy for the prevention of heart failure after myocardial infarction by increasing efficacy of stem cell delivery as well as acting as mechanical restraint devices to constrain scar expansion. Biomaterials can be partially optimized in vitro, but their in vivo performance is most critical and should ideally be monitored serially and noninvasively. We used magnetic resonance imaging (MRI) to assess three scaffold materials with a range of structural moduli equal to or greater than myocardial tissue: poly(glycerol sebacate) (PGS), poly(ethyleneterephathalate)/dimer fatty acid (PED), and TiO(2)-reinforced PED (PED-TiO(2)). Patches, 1  cm in diameter, were grafted onto the hearts of infarcted rats, with biomaterial-free infarcted rat hearts used as controls. MRI was able to determine scaffold size and location on the heart and identified unexpectedly rapid in vivo degradation of the PGS compared with previous in vitro testing. PED patches did not withstand in vivo attachment, but the more rigid PED-TiO(2) material was detrimental to heart function, increasing chamber and scar sizes and reducing ejection fractions compared with controls. In contrast, the mechanically compatible PGS scaffold successfully reduced hypertrophy, giving it potential for limiting excessive postinfarct remodeling. PGS was unable to support systolic function, but it would be suitable for strategies to deliver cardiac stem/progenitor cells, to limit remodeling during the period of functional cellular integration, and to degrade after cell assimilation by the heart. This work has also shown for the first time the value of using MRI as a noninvasive tool for evaluating and optimizing therapeutic biomaterials in vivo.

Critical role of complex III in the early metabolic changes following myocardial infarction

AIMS

The chronically infarcted rat heart has multiple defects in metabolism, yet the location of the primary metabolic abnormality arising after myocardial infarction is unknown. Therefore, we investigated cardiac mitochondrial metabolism shortly after infarction.

METHODS AND RESULTS

Myocardial infarctions (n = 11) and sham operations (n = 9) were performed on Wistar rats, at 2 weeks cardiac function was assessed using echocardiography, and rats were grouped into failing (ejection fraction < or =45%), moderately impaired (46-60%), and sham-operated (>60%). Respiration rates were decreased by 28% in both subsarcolemmal and interfibrillar mitochondria isolated from failing hearts, compared with sham-operated controls. However, respiration rates were not impaired in mitochondria from hearts with moderately impaired function. The mitochondrial defect in the failing hearts was located within the electron transport chain (ETC), as respiration rates were suppressed to the same extent when fatty acids, ketone bodies, or glutamate were used as substrates. Complex III protein levels were decreased by 46% and complex III activity was decreased by 26%, in mitochondria from failing hearts, but all other ETC complexes were unchanged. Decreased complex III activity was accompanied by a three-fold increase in complex III-derived H(2)O(2) production, decreased cardiolipin content, and a 60% decrease in mitochondrial cytochrome c levels from failing hearts. Respiration rates, complex III activity, cardiolipin content, and reactive oxygen species generation rates correlated with ejection fraction.

CONCLUSION

In conclusion, a specific defect in complex III occurred acutely after myocardial infarction, which increased oxidative damage and impaired mitochondrial respiration. The extent of mitochondrial dysfunction in the failing heart was proportional to the degree of cardiac dysfunction induced by myocardial infarction.

Comparison of wall thickening and ejection fraction by cardiovascular magnetic resonance and echocardiography in acute myocardial infarction

OBJECTIVES

The purpose of this study was to compare cardiovascular magnetic resonance (CMR) and echocardiography (echo) in patients treated with primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) with emphasis on the analysis of left ventricular function and left ventricular wall motion characteristics.

METHODS

We performed CMR and echo in 52 patients with first AMI shortly after primary angioplasty and four months thereafter. CMR included cine-MR and T1-weighted first-pass and late-gadolinium enhancement (LGE) sequences. Global ejection fraction (EF(CMR), %) and regional left ventricular function (systolic wall thickening %, [SWT]) were determined from cine-MR images. In echo the global left ventricular function (EF(echo), %) and regional wall motion abnormalities were determined. A segment in echo was scored as "infarcted" if it was visually > 50% hypokinetic.

RESULTS

EF(echo) revealed a poor significant agreement with EF(CMR) at baseline (r: 0.326; p < 0.01) but higher correlation at follow-up (r: 0.479; p < 0.001). The number of infarcted segments in echocardiography correlated best with the number of segments which showed systolic wall thickening < 30% (r: 0.498; p < 0.001) at baseline and (r: 0.474; p < 0.001) at follow-up. Improvement of EF was detected in both CMR and echocardiography increasing from 44.2 +/- 11.6% to 49.2 +/- 11% (p < 0.001) by CMR and from 51.2 +/- 8.1% to 54.5 +/- 8.3% (p < 0.001) by echocardiography.

CONCLUSION

Wall motion and EF by CMR and echocardiography correlate poorly in the acute stage of myocardial infarction. Correlation improves after four months. Systolic wall thickening by CMR < 30% indicates an infarcted segment with influence on the left ventricular function.

Bone marrow-derived stromal cells home to and remain in the infarcted rat heart but fail to improve function: an in vivo cine-MRI study

Basic and clinical studies have shown that bone marrow cell therapy can improve cardiac function following infarction. In experimental animals, reported stem cell-mediated changes range from no measurable improvement to the complete restoration of function. In the clinic, however, the average improvement in left ventricular ejection fraction is around 2% to 3%. A possible explanation for the discrepancy between basic and clinical results is that few basic studies have used the magnetic resonance (MR) imaging (MRI) methods that were used in clinical trials for measuring cardiac function. Consequently, we employed cine-MR to determine the effect of bone marrow stromal cells (BMSCs) on cardiac function in rats. Cultured rat BMSCs were characterized using flow cytometry and labeled with iron oxide particles and a fluorescent marker to allow in vivo cell tracking and ex vivo cell identification, respectively. Neither label affected in vitro cell proliferation or differentiation. Rat hearts were infarcted, and BMSCs or control media were injected into the infarct periphery (n = 34) or infused systemically (n = 30). MRI was used to measure cardiac morphology and function and to determine cell distribution for 10 wk after infarction and cell therapy. In vivo MRI, histology, and cell reisolation confirmed successful BMSC delivery and retention within the myocardium throughout the experiment. However, no significant improvement in any measure of cardiac function was observed at any time. We conclude that cultured BMSCs are not the optimal cell population to treat the infarcted heart.