ECGs Flashcards
ECG electrodes are made of…
Silver/silver chloride
Describe the two different lead types.
Unipolar and bipolar.
What is the range (in mV) of electrical signal change in the heart?
0.5mV to 2mV.
List methods to reduce ECG artefact.
Improving signal detection (e.g. removing hair, using conductive paste, ensuring skin is otherwise dry etc).
Minimising external interference (e.g. common earthed environment, use of diathermy, shivering pt etc)
What does the P-wave represent?
Depolarisation of atrial muscle.
What does the PR interval represent?
AV node conduction.
What does the QRS represent?
Depolarisation of ventricular muscle.
What does the peak of the R wave represent?
Beginning of isovolumetric contraction.
What does the T-wave represent?
Ventricular re-polarisation.
What is the sampling rate of the ECG electrode?
10,000 - 15,000 Hz.
This is in order to detect pacing spikes.
What amplification/gain factor is required?
1000x
What is differential amplification?
Only the difference between the pair of electrodes is amplified, rather than the absolute voltages. This eliminates source of noise/interference that effect all electrodes equally (common-mode rejection).
Regarding filtering, what is high-input impedance?
This decreases the conduction of high frequency signals, thus eliminating mains interference and EMG signal.
Regarding filtering, what is low pass filtering?
This eliminates movement artefact.
What is the frequency range of most ECG signals?
1 to 3 Hz
