Lecture 4 - ECG Flashcards
At RMP, which sides of theh heart is -ve and +ve?
It’s negatively charged inside, and positively charged outside.
When we depolarise the heart the inside becomes positive and the outside becomes negative.
Is which direction dose the wave of contraction move in the heart?
From 11 to 5 o’clock, from the SA node down to the apex.
When repolarisation occurs, which direction does the wave move?
What kind of wave does a depolarisation towards a positive electrode give?
Gives a positive potential (upwards)
What does a depolarisation away from the positive electrode give on an ECG?
Gives a negative potential (downwards)
What does repolarisation away from the positive electrode give on an ECG?
Positive potential (upwards)
What is the config. for limb lead II
What does each wave of the ECG correspond to
(limb lead II)
- P wave = right left atria depolarising (towards +ve electrode so +ve deflection)
- Q wave = depolarisation of the ventricular septum (moving away from +ve electrode, gives small negative deflection
- R wave = ventricular depolarisation - towards +ve electrode so large +ve deflection
- S wave = Depolarisation of the last portion of the ventricle occurs - this is away from the +ve electrode, so small negative deflection
- T wave = Repolarisation of the ventricle from outside to outside - away from +ve electrode so +ve deflection
What are segments on the ECG?
They are the distances between waves.
The ST segment is the distance between the S wave and beginning of the T wave.
ST segment changes during a heart attack.
What are intervals?
PR (PQ) interval: time taken for the excitation to spread through the atria, AV node and bundle of His.
PR interval is normally 0.12-0.20s.
QS interval: Time taken for the excitation to spread through the ventricles . This is typically 0.12s or less.
What does each lead record the potential between?
What are augmented limb leads?
They are pretty muh the same as standard limb leads, but one electrode is +ve whilst the other two electrodes are negative.
Three new leads are generated (unipolar) which called augmented limb leads (aVR, aVL, aVF)
The term aV refers to the augmented voltage measured with these electrodes.
In which lead setup is the main deflection negative? (whereas it’s positive for the rest of them)
aVR
In chest leads you pretty much move the +ve electrode along the 6 places to get many different views of the heart depolarisation wave.
Chest leads examine the heart in the horizontal plane.
For chest leads, what is the main deflection in the QRS complex for each position?
What is the mean QRS axis?
The average direction in which the dipole causing the QRS complex is oriented is called the mean QRS axis.
The mean QRS axis usually lies within the 0 to 90 degrees quadrant. This is down and left, which corresponds to the anatomical pathway the wave of depolarisation takes.
