ECG Flashcards
Week 3
What is the isoelectric line?
Baseline of the ECG denoting RMP of cardiac cells
positive deflection
electrical activity of the heart is moving towards the positive electrode
negative deflection
electrical impulse is moving away from the positive electrod
how does the electrical activity of individual myocytes produce ECG?
Depolarisation –> positive deflection
Repolarisation –> negative deflection
Perpendicular –> biphasic deflection
describe the type of deflection on ECG for wave of excitation moving TOWARDS + node
Positive deflection
Negative deflection
describe the type of deflection on ECG for a wave of repolarisation moving AWAY from + node
Negative deflection
Positive deflection
What does the P wave represent?
atrial depolarisation
SAN depolarises and spreads to LA via interatrial band
What does the PR interval repesent?
atrioventricular conduction
Isocelectric line as exciation delayed in AV node
What does the QRS complex represent?
ventricular depolarisation
what does the Q wave represent?
Septal Depolarisation
L –> R
Base –> apex
What does the R wave represent?
Depolarisation of most of ventricular free wall
Apex –> base
what does the S wave represent?
Depolarisation of remaining ventricular free wall
what occurs in the ST segment?
Return to isoelectrical line
Phase 2 of AP
what occurs in the T wave?
Ventricular repolarisation
Apex –> base
Epi –> endo cardium
Describe the production of P wave. (Atrial Depolarisation)
SA node impulse initaites atrial Dep –>
impulse spreads through internodal pathway in atria –>
RA depolarises, then LA
= electrical activity of atria depolarisation is P wave
What does the QT interval represent?
ventricular dep and repolarisation
Describe the production of the QRS complex (ventricular Dep)
AV node delay –>
atria finishes contracting –>
impulse moves along BoH –> runs down the bundle branches –>
purkinje fibres spread through ventricular myocardium –>
septam depolarises (Q) –>
free wall dep (R) –>
apex and base depolarise
= rapid dep of ventricles
Why is atrial repolarisation not seen on ECG?
occurs during ventricular depolarisation but hidden due having a smaller amplitude
Sequence of repolarisation that produces T wave
- epicardial repolarisation
- mid-myocardial and endocardial cells repolarise
- difference in repolarisation timing creates a vector = T wave
electrode vs lead
electrode = disc on patient’s skin
lead = view of electrical activity on positive electrode
What are the two divisions of electrodes and what leads make them up?
Bipolar
- I, II, III
Unipolar
- aVL, aVR, aVF and V1-V6
placement of leads:
I
II
III
I- LA –> RA
II (LL –> RA)
Lead III (LL –> LA)
What is R wave progression?
Increased R wave size in precordial leads
what is the electrical axis of the heart?
mean QRS vector (average direction of electrical movement in the heart)
What is the path followed and parts of the heart are affected in the P wave?
SA node –> Atrial muscle –> AV node
What is the path followed parts of the heart are affected in the between the P and Q waves?
Common bundle –> bundle branches –> PF
What is the path followed parts of the heart are affected in the Q wave?
PF fibres –> ventrical muscle
What is the path followed parts of the heart are affected in the R, S and T wave of ECG?
Ventricle muscle
