Basics of ECG Flashcards
How does direction of depolarization effect if positive or negative deflection?
What is deflection if repolarization?
What is deflection if perpendicular to axis?
If depolarization (positive) negative going towards positive electrode: positive deflection
If depolarization (positive) positive going towards negative electrode (away from electrode): negative deflection
If repolarization (negative) positive going towards negative electrode (away): will be positive deflection
Positive depolarization going perpendicular between axis of lead you are looking at will create isoelectric line = flat.
Either no net movement of electrical activity or depolarization perpendicular to axis of electrode
What is the PR segment and PR interval?
PR segment: time delay between end of atrial depolarization and start of ventricular depolarization (AVN delay)
PR interval: time between atrial depolarization and ventricular depolarization
What causes activation of the interventricular septum and how does this show in lead II of ECG?
Left septal bundle: produces Q wave = septal depolarization. Gross net charge is going from left to right away from the direction of lead II = negative deflection.
Left bundle branches also has left anterior and left posterior bundle.
What produces R wave in lead II ECG?
Mean R wave vector is negative electrode directed towards positive electrode lead II = positive deflection
As left ventricle is more hypertrophide than right ventricle.
R wave = main mass of ventricles depolarization
What produces S wave in lead II ECG?
S wave = electrical conduction from apex of the heart to the base of the heart
Positive electrical conduction away from positive electrode to negative electrode = negative deflection
S wave= ventricular depolarization of base of heart
What does the T wave in lead II ECG indicate?
What is the vector and deflection?
T wave = ventricular depolarization
As the left ventricle has greatest amplitude –> overall vector leaning more towards left.
Negative charge directed towards negative electrode = positive deflection.
What are the different limb leads and their directional vectors?
Einthovens triangle
left lower limb is another electrode that acts as ground lead
What is the appearance of ECG on leads I, II and III?
They should all appear the same, same general direction and vectors
What does lead I show?
Imagine looking from the positive electrode
What does lead II/III show?
Imagine looking from the positive electrode
What is the appearance of waveform on aVR of ECG?
Imagine looking from positive electrode. Lead aVR is exactly the opposite of lead II (VERY IMPORTANT)
Mean vector is in the middle of both negative electrodes
P wave = negative deflection: going away from positive electrode
Q wave = interventricular depolarization = towards positive elctrode = positive deflection
R wave = main mass of ventricle = away from positive electrode = negative deflection
S wave = towards base of ventricle depolarization = towards positive electrode = positive deflection
T wave = repolarization (negative charge) towards positive electrode = negative deflection
What is the waveform apperance of lead aVL and aVF?
Same waveform as leads I, II and III
Only leads aVR differs as the positive electrode is swapped to the right arm
What information does the aVR tell us about?
What information does the aVL tell us about?
What information does the aVF tell us about?
What is appearance of R and S wave from V1-6
R:S ratio < 1 for V1-3
R:S ratio > 1 for V4-6
What leads give information about RV?
Leads V1-3, aVR
What leads give information about the basal septum?
V2-V3 + aVR
What leads give information about the anterior wall of heart?
V2-4
How to assess in a stepwise fashion of all ECGs?
