CVS 7.1 - ECG Flashcards
What does the P wave on an ECG show?
Atrial depolarisation
What does the Q wave on an ECG show?
Septal depolarisation (not always seen)
What does the R wave on an ECG show?
Main ventricular depolarisation (spreads along the axis to the left of the septum)
What does the S wave on an ECG show?
End ventricular depolarisation (up to the base of the ventricles)
What does the T wave on an ECG show?
Ventricular repolarisation
What is the purpose of an ECG?
- Measure the electrical activity of the heart
- Shows if it’s working correctly
How is the ECG measured?
- Signals are recorded during systole
- Measured extracellularly with electrodes
How does the ECG change when there is a depolarisation towards the electrodes?
There is a positive deflection from the baseline
How does the ECG change when there is a depolarisation away from the electrodes?
There is a negative deflection from the baseline
How does the ECG change when there is a repolarisation towards the electrodes?
There is a negative deflection from the baseline
How does the ECG change when there is a repolarisation away from the electrodes?
There is a positive deflection away from the baseline
What is temporal dispersion?
Repolarisation that doesn’t happen in a uniform manner
Describe the pattern of spread of excitation over the heart
1) SAN
2) Internodal tracts
3) Spreads to AVN and is delayed for ~120ms
4) Bundle of His
5) Right/left bundle branch
6) Purkinje fibres
7) Over myocardium from inside to outside
When do the cardiac myocytes begin to repolarise?
After about 280ms
In what direction does repolarisation spread?
- Opposite direction to depolarisation
- Outside to inside/ epicardial to endocardial surface
