ECG Flashcards
How do surface potentials manifest?
Currents flow when the membrane potential of myocardial tissue changes, which is measured by electrodes
What is a dipole?
Seperated charges or potential differences between cardiac regions constitute an electrical dipole which constitutes a vector
What is a vector?
Made up of:
Magnitude - determined by mass of cardiac muscle that is involved
Direction - determined by the overall activity of the heart at any instant in time
How does repolarisation spread?
Epicardium (outer) -> endocardium (inner)
What is an ECG ‘lead’?
an imaginary line between two electrodes
-one is a recording electrode and one is a reference
What happens when depolarisation moves away from the recording electrode?
reflected downwards on the ECG
What happens when depolarisation moves towards the recording electrode?
reflected upwards on the ECG
What is a 12 lead ECG made up of?
3 standard limb leads (I, II, III)
3 augmented voltage leads (aVR, aVL, aVF)
6 chest leads (V1-V6)
What does the P wave show?
atrial depolarisation 0.12s
What does the Q wave show?
ventricular depolarisation
What does the R wave show?
depolarisation of the ventricular free walls
What does the S wave show?
depolarisation of the ventricles at the base of the heart
What does the T wave show?
ventricular repolarisation
What does the QRS complex show?
ventricular activation 0.1 s
What does the PR interval show?
time for the SA node impulses to reach ventricles
