Usually visualization of the apical four chamber view is possible only in 65 to 70%of investigated mice. The main advantage of this technique is that the combined usage of both tilting positions enables that requisition in almost all investigated mice. After the mouse has reached the appropriate level of light sedation, fix the mouse on a heated platform and apply electrode gel to the extremities for continuous monitoring of the heart rate and temperature.
Remove the chest hair with depilatory cream and apply a layer of ultrasound coupling gel to the tip of the transducer. For an apical four chamber view with the left and caudal platform tilt, angle the platform 10 to 15 degrees to the left and 10 to 15 degrees caudally. Position the transducer above the apex within the imaging plane, 45 degrees to the coronal plane with the central axis of the ultrasound beam directed cranially posteriorly and to the left.
Press the B-mode button to activate the B-mode to de-imaging and locate the left ventricul, left atrium, right ventricle, right atrium, mitral valve and tricuspid valve on the acoustic window. To ensure that you are in the right position slide the transducer up and down along the coronal plane. Manipulate the imagine plane in the coronal plane and rotate clock and counter clockwise around the central axis until both ventricles are visualized at their longest dimension, and both atria are visible to obtain the four chamber view.
Press cine store to save the recording. Then press scan freeze to pause the system. To measure the transtricuspid blood flow velocity press scan freeze to activate the system and press overlay several times to activate the sample volume for the post wave mode.
With the four chamber imaging view use the track ball to position the sample volume at the opening of the tricuspid valves and click pulse wave mode to measure the inflow velocities. Click cine store to save the optimized recording followed by scan freeze to pause the system. For measurement of the tricuspid annular plane systolic excursion, click scan freeze to activate the system and switch to B-mode.
Some manipulations of the image might be necessary to regain the correct four chamber view. Click overlay several times to activate the sample volume of the M-mode and use the trackball to align the sample volume with the lateral part of the tricuspid annulus. Use the trackball to pull the edges of the sample volume until the entire amplitude of the cardiac movement during the cardiac cycle is covered.
And activate the M-mode. The tricuspid annulus movements should appear as a wave, then click cine store to save the recording and scan freeze to pause the system. For measurement of the tissue doppler parameters activate the system and the B-mode.
Click overlay several times to activate the sample volume for tissue doppler imaging and use the trackball to align the sample volume with the lateral part of the tricuspid annulus, such that the right ventricle free wall creates an angle with the tricuspid valve. Pull the edges of the sample to adjust the sample volume to include the systolic and diastolic extreme positions of the annulus, and click tissue to activate the tissue doppler imaging mode. Then click cine store to save the recording and scan freeze to pause the system.
Tilting the platform to the left and to the right improves the acoustic window and provides images of comparable quality in healthy and diseased mouse hearts in the B-mode. After obtaining the correct positions, measurements in the M-mode, tissue doppler imaging mode and pulsed wave mode provide images of comparable quality with similar diastolic parameter results obtained in either the right cranial or left caudal platform positions in both healthy and diseased hearts. Further, correlation analysis reveals a good agreement between the values obtained from these two facilitated positions.
While attempting this procedure it's important to remember that echocardiography is a non-invasive technique for the evaluation of the cardiac function. Following this procedure, tissue samples can be collected after the physiological measurements to answer additional questions about the morphologic substrate or molecular mechanisms of cardiac dysfunction. This technique has paved the way for the researchers in the field of pulmonary hypertension to explore the mechanisms of the right ventricle adaptation to pressure overload using mouse models of pulmonary hypertension.
To obtain the producible results between experiments, tightly control the physiological parameters of the animal such as heart rate and body temperature and maintain the level of anesthesia as superficial as possible to minimize influencing cardiac function.
