This unique protocol allows the assessment of neonatal mouse cardiovascular function using electrocardiography technology immediately after birth in a noninvasive manner without the use of anesthetics. Assessing murine cardiovascular function in the early postnatal period will expand our understanding of the neonatal heart in a manner that could directly correlate with human clinical data. To prepare the measuring device for the analysis, plug the device into the USB port of a computer.
The measuring device will automatically begin heating up to 37 degrees Celsius. After about 15 minutes, remove a mouse pup from its home cage and wipe the thorax with 70%ethanol. Place the pup on the heated surface of the plastic and allow the animal to acclimate to the surface for approximately two to five minutes in the dark.
While the mouse is acclimating, collect a small droplet of adhesive electrical conducting gel and gently press the droplet down onto the top of each of the four flattened electrode surfaces, carefully pulling the conducting gel away at an oblique angle from the center of the electrode construct after contact. When each electrode is completely covered with gel, place the neonatal mouse pup onto the platform in the prone position with the head of the pup facing the outgoing USB edge of the platform with each electrode covering a portion of the pup's upper thorax. Gently restrain the forearms while simultaneously applying gentle pressure to the electrodes for approximately one minute.
When the conducting gel is set, secure the pup on the right and left sides with rubber silicone bumpers. Monitor the mouse for a moment adjusting the bumper placement as needed. When the pup is secure, apply any remaining conducting gel to the grounding tail electrode and use gentle pressure to place the electrode on the rump of the pup to allow the gel to set before releasing the pup.
Carefully place the final silicone bumper on top of the rump to hold the grounding electrode in place and gently place the entire platform into the Faraday cage, then check that the pup is not moving excessively and that the body and head of the mouse appear secure. An ideal ECG will have a clear prominent signal that allows all of the waves to be analyzed in several different timeframes. A poor quality reading has no discernible beats, shows clear interference, and exhibits waves or inconsistencies across the reading.
The program provides analysis of the key aspects of the ECG reading, including the heart rate, RR intervals, QRS complex interval, QT interval, and PR interval. Using these data to establish a set of normative values, in this representative analysis, it was determined that pups analyzed in the first postnatal day had an average heart rate of 357.2 beats per minute. For a pup in the first postnatal day, the average RR, PR, QRS, and QT intervals were 169.1, 36.3, 16.9, and 45.4 milliseconds respectively.
Importantly, the setup can be used to analyze ECG patterns from neonatal mice suffering from congenital heart defects. The device is effective and reliable, but also highly sensitive to surrounding electrical interference. Make sure to always remove any unnecessary equipment including laptop chargers and smart devices prior to recording.
Additional possible measurements include respiration and lead III, which is calculated from leads I through II.Additional variables could allow for further overlap with other physiological symptoms and/or specific cardiac arrhythmias.
