ECG - Normal ECG Flashcards
What does the P-wave correspond to?
Atrial depolarisation
What does the QRS complex correspond to?
Ventricular depolarisation
What does the T-wave correspond to?
Ventricular repolarisation
What does positive deflection indicate on an ECG wave?
Depolarisation moving towards the positive electrode causes a positive, or upwards, deflection on the ECG.
What does a negative deflection on an ECG wave indicate in terms of direction of electrical flow?
- Depolarisation moving away from the positive electrode
- Repolarisation towards a positive electrode
Draw the vectors of leads I, II and III, aVR, aVF and aVL
I = L Arm to R Arm
II = R Arm to L leg
III = L Arm to L Leg
What are the positions of V1 to V6 chest leads?
- V1 - 4th intercostal space, right parasternal edge
- V2 - 4th intercostal space, left parasternal edge
- V3 - between V2 and V4
- V4 - 5th intercostal space, midclavicular line
- V5 - 5th intercostal space, anterior axillary line
- V6 - 5th intercostal space, midaxillary line
Which leads look at the left lateral surface?
I and aVL, V5 and V6
Which leads look at the inferior surface?
II, III and aVF
Which leads look at the right atrium?
aVR
Which leads look at the IV septum?
V1 + V2
Which leads look at the anterior walls of the left ventricle?
V3 and V4
What should the ECG running speed be set to?
25 mm/s
How many seconds are in a large square?
0.2 seconds
How many seconds are in a small square?
0.04 seconds
How long should the PR interval be?
0.12 - 0.2 s (3-5 small squares)
How long should a QRS complex be?
<0.12 s (<3 small boxes)
How long should the QT interval last in men at 60 BPM?
< 0.45 s
What determines the magnitude of deflection (either up or down) on an ECG recording?
The magnitude of the deflection is determined by how parallel the electrical force is to the axis of the lead being examined. The more parallel, the greater the magnitude of deflection
If the electrical force was directed perpendicular to an ECG lead, what would be recorded?
The lead would not register any activity
What is the sequence of normal cardiac activation?
https://www.youtube.com/watch?v=zBj6btjdYHU
- Atrial depolarisation (right and left)
- Delay at AV node
- Impulse travels to bundle of His
- Impulse moves into the right and left bundle branches
- Impulse carried along purkinje fibres
What does the R wave of the QRS complex represent?
https://www.youtube.com/watch?v=zBj6btjdYHU
Depolarisation of the bulk of the ventricle from the endocardial to the epicardial surface
What are the criteria for normal sinus rhythm?
- HR - 60–100 BPM
- Regular Rhythm
- “P” wave present - ratio of 1:1, represents SA node is pacing
- Normal PR interval - between 0.12 and 0.20 second.
- Normal QRS complex - <0.12 second.
How can you calculate HR from an ECG?
Rhythm strip at the bottom
Method 1
- Count the number of R-waves in 30 large squares (6 seconds)
- Multiply by 10 to get number of beats over 60 seconds
Method 2
- Rate = 300 / number of large squares in between each consecutive R wave.
Method 3
- Rate = 1500/number of small squares between R waves
What is the maximum duration of QT interval before it is considered abnormal?
0.42 seconds
How would you go about interpreting in ECG?
A = Any electrical activity
R = Rate
I = Irregular or regular
B = Broad or narrow QRS complexes
A = Atrial activity (P-waves)
R = Relationship of P waves to QRS complexes
What is the opposite lead to lead II?
aVR
If looking at leads V1 - V6, how would you determine where the IV septum was?
Transition point
Where the R and S waves are equal - usually betwen V3 and V4
When reading an ECG, what is the order that you would interpret it in?
- Rate
- Rhythm
- Axis
- P-waves
- P-R Interval
- QRS
- ST segment
- T-waves
Which lead is the T wave almost always inverted in?
aVR, V1
What direction does ventricular repolarisation flow; epicardium to sub-endocardium or sub-endocardium to epicardium?
Epicardium to sub-endocardium
Why, during a normal ventricular contraction, is there an initial positive deflection in the QRS complex in V1 and an initial negative deflection inthe QRS complex in V6?
Due to the initial septal depolarisation of ventircular contraction from LBB to RBB
What is the magnitude of signal detected by ECG directly proportional to?
Muscle mass
Depolarisation of which ventricle predominates the signal seen in the QRS complex?
Left ventricle
What is meant by T-wave concordance?
Where T-waves are of the same positive or negativ deflection as the QRS complexes
What is the term for a negative deflection following a positive r-wave called?
S-wave
What is an r-wave?
Any positive deflection above the isoelectric line
If the first deflection of a QRS complex is negative, what is this termed as?
Q-wave
What is the junction between the end of the QRS complex and the ST segment known as?
J-point
Which chest leads are referred to as the septal leads?
V1-V2
Which leads face the inferior surface of the heart?
II, III and aVF
Which leads face the anterior surface of the left ventricle?
V3-V4
Which leads look at the left lateral aspect of the heart?
aVL, I, V5, V6
How does the angle of the vector of depolarisation relative to a lead affect the ECG read out?
The more directly towards the lead the vector of current is, the bigger the deflection on ECG read out. If it is closer to 90 degrees relative to the lead, the smaller the read out becomes
What is meant by the term normal R-wave progression?
The development of dominant R-waves from lead V4-V6
What are the compnents of the LBB?
- Anterior fascicle
- Septal fascicle
- Posterior fascicle
Why is it not uncommon to have q-waves in the inferior leads in a normal ECG?
Due to upwards depolarisation of the IV septum prior to rest of ventricles depolarising
Why are P-waves negative in aVR in a normal ECG?
Due to the depolarisation current moving from SA node away from the lead
How do you calculate corrected QT interval?
QT/SQR(R-R interval)
What is a persistent juvenile pattern on ECG?
Almost perfect concordence of QRS and Twaves in adults
What are the criteria for determining a q-wave as a physicological q-wave?
