Mouse Echocardiography: A Non-invasive Technique to Assess Cardiac Morphology

First, apply echocardiography gel to the ultrasound transducer and to the shaved chest of an anesthetized mouse secured to a warming plate. Place the transducer to the left of the sternum, facing the right side of the neck, to obtain a view through the heart called the parasternal long-axis view.

Turn the transducer 90 degrees clockwise for the parasternal short-axis view. Using this view, record M-mode images to capture movement of the heart over time as it beats. To measure the dimensions of the left ventricle, identify four landmark tissue-fluid interfaces on the recorded images.

These are the interface between the right ventricular cavity and the anterior wall of the left ventricle; between this wall and the left ventricular cavity; between this cavity and the posterior wall of the left ventricle; and between this wall and the pericardium.

Then, calculate the distances between these four interfaces. Repeat the same measurements when the heart is in diastole, or is relaxed, and when it is in systole, or is contracted.

To begin, while lightly holding a mouse by its tail, use a standard laboratory balance to determine the body weight of the animal. After anesthetizing the mouse according to the text protocol, lightly squeeze a rear foot and observe if the leg retracts. Use a commercial rodent shaver to shave the left side of the thorax and the left armpit.

Position the animal on a warm pad set at 40 to 42 degrees Celsius in a shallow left-sided position, with the head at 12 o'clock and the tail at 6 o'clock. Then, use tape to fix the left arm, left leg, and tail. Apply pre-warmed echocardiography gel onto the shaved chest and the head of the transducer.

Next, place the echocardiograph transducer parasternal left, directing it to the right side of the neck to obtain a two-dimensional parasternal long-axis view on the level of the papillary muscle. Then, turn the transducer 90 degrees clockwise to obtain a short-axis view. Establish a minimal depth setting and a zoom to maximize image quality and frame rate. Set the sweep speed to the maximum. Record 2D-guided M-mode images in short-axis view. Record at least 3 series of 3 heartbeat cine loops for each animal.

After obtaining successful recordings, remove the tape from the limbs and tail. Wipe off the echocardiography gel from the mouse thorax, heating pad, and transducer. Leave the mouse under observation on the heating pad, covered with tissue to avoid unnecessary light exposure and heat loss until it wakes up. Then, put the animal back in the cage.

Analyze recorded M-mode images from short-axis view to determine left ventricular or LV dimensions and function. Using the identification of the tissue-blood interface on the stored images, measure the thickness of the LV anterior wall in systole and diastole, the LV internal end-systolic and end-diastolic diameters, and the LV posterior wall thickness in systole and diastole. Measure the diastolic dimensions at the time of the apparent maximal LV diastolic dimensions and the LV end-systolic dimensions at the end of the most anterior systolic excursion of the LV posterior wall. Tap the touchscreen on the "Analyze" icon, and then on the "LVAWd" icon. Position the electronic caliper on the interface between the right ventricular cavity and the LV anterior wall in diastole.

Next, position the electronic caliper on the interface between the LV anterior wall and the LV cavity to obtain LV diastolic anterior wall thickness. Position the caliper on the interface between the LV cavity and the LV posterior wall to obtain the LV internal and diastolic diameter. Position the caliper on the interface between the LV posterior wall and the pericardium to obtain the LV diastolic posterior wall thickness.

For LV systolic dimensions, tap the touchscreen on the "LVAWs" icon and position the electronic caliper on the interface between the right ventricular cavity and the LV anterior wall in systole. Position the electronic caliper on the interface between the LV anterior wall and the LV cavity to obtain the LV systolic anterior wall thickness. Position the caliper on the interface between the LV cavity and the LV posterior wall to obtain the LV internal and systolic diameter. Position the caliper on the interface between the LV posterior wall and the pericardium to obtain the LV systolic posterior wall thickness.