Contrast-enhanced MRI of right ventricular abnormalities in Cx43 mutant mouse embryos

Mouse Cardiovascular Imaging

The mouse is the mammalian model of choice for investigating cardiovascular biology, given our ability to manipulate it by genetic, pharmacologic, mechanical, and environmental means. Imaging is an important approach to phenotyping both function and structure of cardiac and vascular components. This review details commonly used imaging approaches, with a focus on echocardiography and magnetic resonance imaging, with brief overviews of other imaging modalities. In this update, we also emphasize the importance of rigor and reproducibility in imaging approaches, experimental design, and documentation. Finally, we briefly outline emerging imaging approaches but caution that reliability and validity data may be lacking. © 2024 Wiley Periodicals LLC.

Clinical impact of the right ventricular impairment in patients following transcatheter aortic valve replacement

The right ventricular (RV) impairment can predict clinical adverse events in patients following transcatheter aortic valve replacement (TAVR) for severe aortic stenosis (AS). Limited reports have compared impact of the left ventricular (LV) and RV disorders. This retrospective study evaluated two-year major adverse cardiac and cerebrovascular events (MACCE) in patients following TAVR for severe AS. RV sphericity index was calculated as the ratio between RV mid-ventricular and longitudinal diameters during the end-diastolic phase. Of 239 patients, 2-year MACCE were observed in 34 (14%). LV ejection fraction was 58 ± 11%. Tricuspid annular plane systolic excursion (TAPSE) and RV sphericity index were 20 ± 3 mm and 0.36 (0.31-0.39). Although the univariate Cox regression analysis demonstrated that both LV and RV parameters predicted the outcomes, LV parameters no longer predicted them after adjustment. Lower TAPSE (adjusted hazard ratio per 1 mm, 0.84; 95% confidence interval, 0.75-0.93) and higher RV sphericity index (adjusted hazard ratio per 0.1, 1.94; 95% confidence interval, 1.17-3.22) were adverse clinical predictors. In conclusion, the RV structural and functional disorders predict two-year MACCE, whereas the LV parameters do not. Impact of LV impairment can be attenuated after development of RV disorders.

Importance of Cx43 for Right Ventricular Function

In the heart, connexins form gap junctions, hemichannels, and are also present within mitochondria, with connexin 43 (Cx43) being the most prominent connexin in the ventricles. Whereas the role of Cx43 is well established for the healthy and diseased left ventricle, less is known about the importance of Cx43 for the development of right ventricular (RV) dysfunction. The present article focusses on the importance of Cx43 for the developing heart. Furthermore, we discuss the expression and localization of Cx43 in the diseased RV, i.e., in the tetralogy of Fallot and in pulmonary hypertension, in which the RV is affected, and RV hypertrophy and failure occur. We will also introduce other Cx molecules that are expressed in RV and surrounding tissues and have been reported to be involved in RV pathophysiology. Finally, we highlight therapeutic strategies aiming to improve RV function in pulmonary hypertension that are associated with alterations of Cx43 expression and function.

Cardiovascular Imaging in Mice

The mouse is the mammalian model of choice for investigating cardiovascular biology, given our ability to manipulate it by genetic, pharmacologic, mechanical, and environmental means. Imaging is an important approach to phenotyping both function and structure of cardiac and vascular components. This review details commonly used imaging approaches, with a focus on echocardiography and magnetic resonance imaging and brief overviews of other imaging modalities. We also briefly outline emerging imaging approaches but caution that reliability and validity data may be lacking.

Translational paradigms in scientific and clinical imaging of cardiac development

Congenital heart defects (CHD) are the most prevalent congenital disease, with 45% of deaths resulting from a congenital defect due to a cardiac malformation. Clinically significant CHD permit survival upon birth, but may become immediately life threatening. Advances in surgical intervention have significantly reduced perinatal mortality, but the outcome for many malformations is bleak. Furthermore, patients living while tolerating a CHD often acquire additional complications due to the long-term systemic blood flow changes caused by even subtle anatomical abnormalities. Accurate diagnosis of defects during fetal development is critical for interventional planning and improving patient outcomes. Advances in quantitative, multidimensional imaging are necessary to uncover the basic scientific and clinically relevant morphogenetic changes and associated hemodynamic consequences influencing normal and abnormal heart development. Ultrasound is the most widely used clinical imaging technology for assessing fetal cardiac development. Ultrasound-based fetal assessment modalities include motion mode (M-mode), two dimensional (2D), and 3D/4D imaging. These datasets can be combined with computational fluid dynamics analysis to yield quantitative, volumetric, and physiological data. Additional imaging modalities, however, are available to study basic mechanisms of cardiogenesis, including optical coherence tomography, microcomputed tomography, and magnetic resonance imaging. Each imaging technology has its advantages and disadvantages regarding resolution, depth of penetration, soft tissue contrast considerations, and cost. In this review, we analyze the current clinical and scientific imaging technologies, research studies utilizing them, and appropriate animal models reflecting clinically relevant cardiogenesis and cardiac malformations. We conclude with discussing the translational impact and future opportunities for cardiovascular development imaging research.

High-resolution MRI of early-stage mouse embryos

Both the availability of methods to manipulate genes and the completion of the mouse genome sequence have led to the generation of thousands of genetically modified mouse lines that provide a new platform for the study of mammalian development and developmental diseases. Phenotyping of mouse embryos has traditionally been performed on fixed embryos by the use of ex vivo histological, optical and high-resolution MRI techniques. Although potentially powerful, longitudinal imaging of individual animals is difficult or impossible with conventional optical methods because of the inaccessibility of mouse embryos inside the maternal uterus. To address this problem, we present a method of imaging the mouse embryo from stages as early as embryonic day (E)10.5, close to the onset of organogenesis in most physiological systems. This method uses a self-gated MRI protocol, combined with image registration, to obtain whole-embryo high-resolution (100 µm isotropic) three-dimensional images. Using this approach, we demonstrate high contrast in the cerebral vasculature, limbs, spine and central nervous system without the use of contrast agents. These results indicate the potential of MRI for the longitudinal imaging of developing mouse embryos in utero and for future applications in analyzing mutant mouse phenotypes.

Xenograft and transgenic mouse models of epithelial ovarian cancer and non-invasive imaging modalities to monitor ovarian tumor growth in situ: applications in evaluating novel therapeutic agents

Epithelial ovarian cancer (EOC) is the most commonly fatal gynecologic malignancy in developed countries. Most EOC patients are diagnosed at an advanced stage when disease has spread beyond the ovary. While many patients initially respond to surgery and chemotherapy, the long-term prognosis is generally unfavorable, with recurrence and development of drug-resistant disease. There is a critical need to identify new therapeutic agents that prolong disease-free intervals and effectively manage recurrent disease. Murine models of ovarian carcinoma are excellent models to study tumor biology in the search for new treatments for EOC. Described in this unit are methods for establishing xenograft or allograft models of EOC using ovarian carcinoma cell lines, in vivo imaging strategies for detection and quantification of EOC in transgenic and in xenograft/allograft models, and procedures for necropsy and pathological evaluation of experimental animals.

In utero phenotyping of mouse embryonic vasculature with MRI

The vasculature is the earliest developing organ in mammals and its proper formation is critical for embryonic survival. MRI approaches have been used previously to analyze complex three-dimensional vascular patterns and defects in fixed mouse embryos. Extending vascular imaging to an in utero setting with potential for longitudinal studies would enable dynamic analysis of the vasculature in normal and genetically engineered mouse embryos, in vivo. In this study, we employed an in utero MRI approach that corrects for motion, using a combination of interleaved gated acquisition and serial coregistration of rapidly acquired three-dimensional images. We tested the potential of this method by acquiring and analyzing images from wildtype and Gli2 mutant embryos, demonstrating a number of Gli2 phenotypes in the brain and cerebral vasculature. These results show that in utero MRI can be used for in vivo phenotype analysis of a variety of mutant mouse embryos.

Assessment of a single monomorphic ventricular ectopy from the right ventricular outflow tract in standard and high resolution electrocardiogram

INTRODUCTION

High-resolution electrocardiography (ECG-CREM) is a method based on digital electrocardiography. In order to facilitate the interpretation of the Crem records the technique of vectorcardiography was used. In comparison the origin of the ventricular premature complexes (VPCs) could be estimated based on a standard 12-lead electrocardiogram. The aim of the study was to assess the point of origin of the VPCs in ECG-CREM and correlate it with standard electrocardiography (ECG-Stand).

MATERIAL AND METHODS

Our study included 26 patients (16 females, 10 males), aged 51-83 years (avg. 58.1 ±12.3), who presented with recurrent, during at least 6 months' observation, VPCs. The point of origin of VPCs was compared in both methods.

RESULTS

The performed analysis of collected ECG-Stand records revealed the presence of arrhythmogenic focal points in six different locations (1, 3, 5, 7, 8, 9). However, we did not affirm their presence in points 2,4,6. They were most commonly located in RVOT zones 8 (30.7%), 9 (23.0%), 5 (23.0%), and most seldom in zones 1, 3, 7 (7.6% each). In the simultaneous record of ECG-CREM with a single VPC it was confirmed that the FPb zone was activated the most frequently (40.0%); the next in relation to frequency were SD and ST (20.0%). Less frequent VPCs have their origin in Crem zones SP, FPa and SB (6.6%).

CONCLUSIONS

Electrocardiogram of high signal resolution (ECG-CREM) might be useful in recognition of the origin of ventricular premature complexes from RVOT.

Three-dimensional micro-MRI analysis of cerebral artery development in mouse embryos

Vascular system development involves a complex, three-dimensional branching process that is critical for normal embryogenesis. In the brain, the arterial systems appear to develop in a stereotyped fashion, but no detailed quantitative analyses of the mouse embryonic cerebral arteries have been described. In this study, a gadolinium-based contrast perfusion method was developed to selectively enhance the cerebral arteries in fixed mouse embryos. Three-dimensional magnetic resonance micro-imaging (micro-MRI) data were acquired simultaneously from multiple embryos staged between 10 and 17 days of gestation, and a variety of image analysis methods was used to extract and analyze the cerebral arterial patterns. The results show that the primary arterial branches in the mouse brain are very similar between individuals, with the patterns established early and growth occurring by extension of the segments, while maintaining the underlying vascular geometry. To investigate the utility of this method for mutant mouse phenotype analysis, contrast-enhanced micro-MRI data were acquired from Gli2(-/-) mutant embryos and their wild-type littermates, showing several previously unreported vascular phenotypes in Gli2(-/-) embryos, including the complete absence of the basilar artery. These results demonstrate that contrast-enhanced micro-MRI provides a powerful tool for analyzing vascular phenotypes in a variety of genetically engineered mice.

Ultrasound and magnetic resonance microimaging of mouse development

Ultrasound biomicroscopy (UBM) and magnetic resonance microimaging (micro-MRI) provide noninvasive, high-resolution images in mouse embryos and neonates, enabling volumetric and functional analyses of phenotypes, including longitudinal imaging of individual mice over critical stages of in utero and early-postnatal development. In this chapter, we describe the underlying principles of UBM and micro-MRI, including the advantages and limitations of these approaches for studies of mouse development, and providing a number of examples to illustrate their use. To date, most imaging studies have focused on the developing nervous and cardiovascular systems, which are also reflected in the examples shown in this chapter, but we also discuss the future application of these methods to other organ systems.