Noninvasive Electrocardiography in the Perinatal Mouse
Summary
Here, we present a noninvasive electrocardiography (ECG) protocol, optimized for early postnatal mice, that does not require the use of anesthetics.
Abstract
Electrocardiography (ECG) has long been relied upon as an effective and reliable method of assessing cardiovascular (and cardiopulmonary) function in both human and animal models of disease. Individual heart rate, rhythm, and regularity, combined with quantitative parameters collected from ECG, serve to assess the integrity of the cardiac conduction system as well as the integrated physiology of the cardiac cycle. This article provides a comprehensive description of the methods and techniques used to perform a noninvasive ECG on perinatal and neonatal mouse pups as early as the first postnatal day, without requiring the use of anesthetics. This protocol was designed to directly address a need for a standardized and repeatable method for obtaining ECG in newborn mice. From a translational perspective, this protocol proves to be entirely effective for characterization of congenital cardiopulmonary defects generated using transgenic mouse lines, and particularly for analysis of defects causing lethality at or during the first postnatal days. This protocol also aims to directly address a gap in the scientific literature to characterize and provide normative data associated with maturation of the early postnatal cardiac conduction system. This method is not limited to a specific postnatal timepoint, but rather allows for ECG data collection in neonatal mouse pups from birth to postnatal day 10 (P10), a window that is of critical importance for modeling human diseases in vivo, with particular emphasis on congenital heart disease (CHD).
Introduction
Cardiac function can be measured in different ways, the most common of which includes the use of electrocardiography (ECG) to analyze the conduction of electric current through the heart as well as its overall cardiac cycle and function1. Electrocardiography continues to be a useful diagnostic tool for identifying and characterizing cardiac anomalies in both human and animal models of disease1,2. Irregularities in an electrocardiogram reading can be found in abnormal cardiac development (i.e., congenital heart disease (CHD)), and can include arrhythmias manifesting as changes in heart rate (e.g., bradycardia), and rhythm (e.g., “heart blocks”), suggestive of defects in the integrity and/or function of the underlying myocardium. Changes such as these may predispose patients to life-threatening cardiac dysfunction (e.g., congestive heart failure and/or cardiac arrest) and increased mortality3,4. Given the high rates of mortality with severe and untreated CHD, developing a standardized and repeatable method for collecting ECG during this early postnatal period is critical.
Although we are not the first to address this problem, previous methods of collecting ECG on a mouse pups have traditionally included invasive procedures (subcutaneous needle or wire electrodes) and/or the use of anesthetics5,6,7. Advantages of performing noninvasive ECG analysis include minimizing pain and undo stress on the animal. While the experimenter must still be cautious about causing the pup stress, the device is designed to avoid common stressors in order to produce accurate data. In the context of evaluating cardiac function, introducing anesthesia to animals that may have cardiopulmonary abnormalities could potentially mask or even exacerbate underlying conditions. Anesthetics may affect the electrical conduction by altering depolarization and/or repolarization of the cells. Finally, the use of anesthesia can put the newborn pup at an increased risk for hypothermia, which could further confound any inherent pathology. The following protocol does not introduce any anesthetics, invasive procedures, or pronounced discomfort to the pup. Once equipment setup is finalized, device setup and data collection involving the animal can be completed efficiently, after which the pups can be returned to their mother. Additionally, this system allows for repeat and/or serial analyses to be performed, which is ideal for experiments requiring analysis over time, introduction of pharmacological therapies, etc.
Protocol
Representative Results
Discussion
The data points collected in perinatal day 1 mouse pups are slightly below the average expected values for adult mice (500-700 beats per minute).8 There is an increase in heart rate as the mouse ages, which falls more in line for the expected values (Table 1). However, it is important to emphasize that neonatal values were on the lower end of this range, supporting the idea that normative values should be documented in an age-specific manner. This method is different than other el…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
The authors acknowledge generous support from the Saving tiny Hearts Society (KLT), the UNE COBRE Program (NIGMS grant number P20GM103643; LAF), and the SURE Fellowship Program at the University of New England (VLB), as well as patient technical support from Ashish More (iWorx, Dover, NH). Figure 3, Figure 4, and Figure S1 were created with Biorender software.
Materials
| LabScribe4 | iWorx | LabScribe4 | Software used to record ECG | https://www.iworx.com/users/teaching.php |
| Neonatal Mouse ECG & Respiration System | iWorx | RS-NMECG : Neonatal Mouse ECG | ECG device | https://www.iworx.com/research/cardiac-function/rs-nmecg/ |
| Tensive Conductive Adhesive Gel | Parker Laboratories, Inc | 22-60 | Tac-gel used as conductive gel for ECG | https://www.parkerlabs.com/tensive.asp |
Riferimenti
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