Below are simple protocols to follow that will broaden your understanding and skill in ECG monitoring. These easy-to-implement studies will bring about changes in ECG signal in your animals that are intuitive and translatable to human life. As such, as you pursue your own animal models and studies, the insights you glean from these exercises will greatly enhance your assimilation of ECG signals that you may see in your research. Please contact us any time to discuss your observations and data!
|Title||Effects of Caffeine on Heart|
|Number of animals||3|
|Species/strain||Balb/c mice recommended|
|Instrumentation needed||ECGenie instrumentation|
|Reagents required||Mountain Dew Soda|
|Time to perform||15 minutes day 1 & 15 minutes day 2|
Heart rate measurement is routine in clinical establishments. The perception that monitoring the heart is difficult in small animals, however, makes ECG measurements in the laboratory the exception rather than the rule. The ECGenie, though, makes it incredibly simple to record the ECG in mice, rats, hamsters, and guinea pigs, from day 1 of life, through old age or death.
This provides tremendous opportunities for vital sign monitoring, general health monitoring, phenotyping, and discovery in animal models of human diseases. For example, mice with cardiac hypetrophy can be discerned by prolonged QRS interval durations. Mice in heart failure can be discerned by significantly reduced heart rate variability. The cardiotoxic effects of experimental therapeutics can include arrhythmia and prolonged QT interval duration. The ECGenie enables these non-invasive measurements to become routine in conscious lab animals.
As in humans, many factors can affect heart rate, heart rate variability, and the ECG interval durations [PR, QRS, QT, etc.] in small animals such as mice. Moreover, there are strain, gender, and age differences in the cardiovascular properties among mice. Here we present a very simple protocol to perturb the cardiovascular system by orally administered caffeine, and show the effects of ingestion of caffeine on the electrocardiogram.
This easy and fast protocol provides investigators an opportunity to learn 1st hand how even ingestion of a seemingly safe drug can have measurable effects on the cardiovascular system.
- Provide 3 mice housed in one cage free access to regular drinking water.
- Place subjects onto the ECGenie recording platform; allow them to acclimatize for ~10 minutes.
- Capture and store about 5 seconds of signals for each mouse.
- Replace their drinking water with an identical bottle containing Mountain Dew soda [flattened].
- After 24 hours, repeat the ECG measurements.
- Actual data collection should take <15minutes for the 3 mice, at baseline and after the caffeine ingestion.
- Analyze the ECG signals via EzCG. Computation time should take <10 minutes.
- Group/compare ECGs from the animals, n=3 baseline vs. n=3 caffeine-treated.
Mice readily consume the sweet soda. Compare your findings with the data shown here in Figure 1. Heart rate increased significantly, and heart rate variability decreased significantly in Balb/c mice after 24 hours access to caffeine.
Caffeine has many effects, including central nervous system stimulation. Caffeine is believed to act as an adenosine receptor antagonist, increasing release of free fatty acids, and increasing calcium release and uptake. Consistent with what is known [and our own personal experiences no doubt], caffeine causes an increase in heart rate in mice. Since decreased heart rate variability (HRV) is a major risk factor for sudden death and cardiovascular disease, and caffeine consumption is quite popular, it is of interest to explore models and conditions in which subjects are more vulnerable to caffeine’s effects on HRV. In our hands, HRV was significantly reduced after 24 hour access to the caffeinated beverage.
The effects of caffeine our likely strain dependent. Of note, chronic [subcutaneous administration] of caffeine to pregnant dams (C57BL/6) led to activation of the renin-angiotensin system of the offspring, resulting in cardiac remodeling. These findings highlight the urge to encourage pregnant women to avoid caffeine. Via the LifeSpoon™ plug-in module for ECG recording in neonatal mice, it may be interesting to examine the effects of caffeine on the heart rate and heart rate variability of mice nursed by dams that consume caffeine.