Transthoracic Echocardiography in Mice

Abstract

In recent years, murine models have become the primary avenue for studying the molecular mechanisms of cardiac dysfunction resulting from changes in gene expression. Transgenic and gene targeting methods can be used to generate mice with altered cardiac size and function, 1-3 and as a result, in vivo techniques are needed to evaluate their cardiac phenotype. Transthoracic echocardiography, pulse wave Doppler (PWD), and tissue Doppler imaging (TDI) can be used to provide dimensional measurements of the mouse heart and to quantify the degree of cardiac systolic and diastolic performance. Two-dimensional imaging is used to detect abnormal anatomy or movements of the left ventricle, whereas M-mode echo is used for quantification of cardiac dimensions and contractility. 4,5 In addition, PWD is used to quantify localized velocity of turbulent flow, whereas TDI is used to measure the velocity of myocardial motion. 7 Thus, transthoracic echocardiography offers a comprehensive method for the noninvasive evaluation of cardiac function in mice. Video LinkThe video component of this article can be found at http://www.jove.com/video/1738/ Protocol Preparing Mice for Imaging Studies1. Prior to the imaging studies, anesthetize the mouse (2% isoflurane mixed with 0.5 L/min 100% O 2 )in the induction chamber. Be sure to filter waste gas for the safety of the operator. Remove the animal from the induction chamber and use hair clippers to shave the fur from the neckline to mid chest level. Then remove the remaining body hair with hair removal cream. This preparation may be performed a day prior to imaging studies to minimize potential undesired stress responses in the mice. 2. Apply duralube gel to both eyes to prevent drying of the sclera (avoid contacting the cornea with the gel applicator). Place the anesthetized mouse in a supine position atop a heating pad with embedded ECG leads in order to maintain body temperature. 3. Place the snout within a nose cone connected to the anesthesia system to maintain a steady-state sedation level throughout the procedure (1.0% to 1.5% isoflurane mixed with 0.5 L/min 100% O 2 ). Perform a toe or tail pinch to confirm sedation. If necessary, the level of anesthesia can be adjusted to obtain a target heart rate of 450 ± 50 beats per minute (bpm). 4. Gently insert a rectal probe (after lubricating) to continuously monitor and adjust body temperature via the heating pad. It is important to maintain the body temperature within a narrow range (37.0 °C ± 0.5 °C), as even moderate changes in temperature and heart rate affect cardiac function in mice. 5. Apply electrode gel to the four paws and tape them to the ECG electrodes. Evaluating Systolic Function of the Heart1. To begin this procedure, apply a layer of preheated ultrasound gel to the chest, primarily the area overlying the heart. Gel should be warmed to approximate body temperature. A volume of cold gel may rapidly add to the rate of body temperature loss. Avoid air bubbles in the gel, which can interfere with ultrasonic imaging. 2. I...

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