11 ECGs Flashcards
Fill in the missing labels of the structures in the heart that make up the conducting system:
What are the fucntions of the 4 fibrous rings which are found in the heart (dense CT)?
-
Electrical insulator
- Allows atria to contract separately from ventricles
- Passageway for conducting system of heart (can only conduct through bundle of his)
- Anchors myocardium and valves
Which structure has the fastest rate of depolarisation?
SA Node
What does the SA Node set?
Sinus rhythm
What does the AV node do?
Slows conduction
Gives time for atria to contract before ventricles
What do the bundles branches and purkinje fibres do?
Spread depolarisation throughout ventricular myocardium (4m/s)
Fill in the missing labels:
What does the ECG record?
Electrical changes on extracellular surface of cardiac myocytes
Why is a downward deflection recorded in an electrocardiogram as a result of repolarisation?
Define the P wave.
Depolarisation of the atria
What is the QRS complex?
Depolarisation of ventricles
In which direction does depolarisation spread in the interventricular septum?
Left to right
How many electrodes are required to record an ECG?
10
- 4 Limb leads
- 6 Chest leads
How many ‘views’ of the heart do the 10 electrodes give?
12
Fill in the missing limb lead labels:
Where should the chest leads be placed for an ECG?
Which parts of the heart do each of the chest leads face?
Which leads look at the inferior surface of the heart?
yellow
III
aVF
II
Which leads look at the (left) lateral surface of the heart (ventricles)?
green
I
aVL
V5
V6
Which leads look at the anterior surface of the heart?
blue
V3
V4
Which lead look at the right ventricle and the septum?
brown
V1
V2
How does the QRS complex vary in each lead?
How do you calculate heart rate from an ECG?
Each cardiac cycle:
1 PQRST complex= P wave to start of next P wave
- Count how many large squares between adjacent r waves
- 300/number of large squares= hear rate
- (300 large squares= 1 minute)
Fill in the missing labels:
How long should the PR interval be?
3-5 small boxes (0.12-0.20 seconds)
Prolonged is > 1 large box
What does a delayed PR interval show?
Delayed conduction between AV node and bundle of His
How long should the QRS interval be?
<3 small boxes
(<0.12 seconds)
What might a widened QRS interval suggest?
Depolarisation not spreading via rapid conducting His-Purkinje system
What does the QT interval show and what does it vary with?
Time taken for depolarisation and repolarisation of ventricle
Varies with heart rate
What is the upper limit for a corrected QT (QTc) interval?
11 small boxes (0.44-0.45 seconds)
What does a prolonged QTc indicate?
Prolonged ventricular repolarisation
