Date Published: April 1, 2018
Publisher: American Physiological Society
Author(s): Merry L. Lindsey, Zamaneh Kassiri, Jitka A. I. Virag, Lisandra E. de Castro Brás, Marielle Scherrer-Crosbie.
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.
The measurement of cardiac physiology is the foundation for assessing changes in anatomic and physiological features that occur within the myocardium during aging, in response to genetic alterations, and after a variety of experimentally induced pathologies. Cardiac physiology measurements also provide a means to examine the effects of therapeutic interventions.
Echocardiographic imaging is a widely used, noninvasive means to assess cardiac physiology and architecture in rodent models of heart disease and aging and allows for repeated assessment of heart function over the course of disease progression (8, 15–18, 35, 41, 50, 61, 74, 79, 84, 86, 88, 91, 112, 113, 123, 125, 126, 136, 142, 143, 150–153, 163, 164, 168, 171, 175, 177, 191, 202, 205, 212–214). One reason for its appeal is that echocardiographic ultrasound imaging provides a comprehensive array of information on cardiac anatomy, physiology, and mechanical properties. While ultrasound can also be used to obtain information from the vasculature (arteries and veins), we will focus on the application of echocardiography in analyzing cardiac structure and function. To obtain reliable and reproducible information from echocardiography that can be compared across laboratories, a number of factors need to be considered. These criteria are outlined in terms of the type and depth of anesthesia, the mode of recording, and the (space-time) variables most informative for accurate and precise assessment of various models of heart disease and related interventions.
MRI is a noninvasive, high-resolution imaging technique that can be used to assess myocardial anatomy, perfusion, wall motion and contractility, and physiology in mice (58, 192). Myocardial molecular imaging/tagging is not discussed here to maintain the focus of this discussion on cardiac physiological measurements; please refer to several excellent articles regarding its use (140, 161, 185, 189, 198). The use of MRI in mice has two major challenges: the small size of the heart (spatial resolution) and elevated heart rates (typically 400–650 beats/min depending on the strain) that can introduce motion artifacts. These challenges, in addition to respiration and signal-to-noise ratio limitations, can severely deteriorate image quality. While MRI is the gold standard in the clinic, its use in mice is still in development. Unlike human imaging, which can use single slice acquisitions, imaging of the mouse heart requires stacking images obtained at a particular time in the cardiac cycle to generate the slice image (26). Therefore, in thinned tissue, the imaging quality may not be as robust. Tailored imaging protocols and dedicated cardiac hardware and software are essential to achieve appropriate temporal and spatial resolution for cardiac MRI in rodents. Below, we provide guidelines for cardiac MRI in mice.
Invasive hemodynamic measurements can refine the information on cardiac physiology provided by echocardiography. This approach is not routinely used in mice as a firstline method, however, because this approach is technically challenging and is a nonsurvival procedure precluding this from being a serial assessment, and the results can be difficult to interpret. A micromanometer-tip catheter is inserted into the LV chamber (through the carotid artery, retrogradely or through the apex), where it can directly measure the changes in pressure (and volume when a conductance catheter is used) of the LV over time. Illustrations of pressure-volume loops and how they are altered in cardiac disease are shown in Fig. 2.
As highlighted throughout these guidelines, the measurement of cardiac physiology is a critical component of cardiovascular research. Methods for the accomplishment of this include echocardiography, MRI, and hemodynamic evaluation using pressure-volume catheters. A summary of overall recommendations, including strengths and limitations of each technique, is shown in Table 6. The approach used will vary depending on the questions being addressed; as such, all of the approaches described above may be considered an appropriate approach if they answer the target hypothesis. While echocardiography is the most frequently used technique, due to its availability, technical ease of use, capacity for serial imaging, and cost−all methods discussed in this guidelines article−provide excellent means to evaluate cardiac physiology and can be complementary to each other. A combination of methods is frequently used to overlap limitations of one approach with strengths of the other (10).
Support from the following funding agencies is acknowledged by the authors: National Heart, Lung, and Blood Institute Grants HL-075360, HL-129823, HL-051971, and HL-131613; National Institute of General Medical Science Grants GM-104357 and GM-114833; American Heart Association Grant 14SDG18860050; Biomedical Laboratory Research and Development Service of the Veterans Affairs Office of Research and Development Grant 5I01BX000505; Heart and Stroke Foundation (Canada); and Canadian Institute of Health Research.
The content is solely the responsibility of the authors and does not necessarily represent the official views of any of the funding agencies listed. No conflicts of interest, financial or otherwise, are declared by the authors.
M.L.L. conceived and designed research; M.L.L. prepared figures; M.L.L., Z.K., J.A.I.V., L.E.d.C.B., and M.S-C. drafted manuscript; M.L.L., Z.K., J.A.I.V., L.E.d.C.B., and M.S-C. edited and revised manuscript; M.L.L., Z.K., J.A.I.V., L.E.d.C.B., and M.S-C. approved final version of manuscript.