Session 6-ECG Flashcards
True or false: ventricular depolarisation from epicardium to endocardium enables coordinated contraction of atria and ventricles
FALSE - depolarisation from endocardium to epicardium
What is the name of the rhythm that the SA node sets?
Sinus rhythm
Where is the AV node located?
In the inter-atrial septum, above the tricuspid valve
What is the AV node continuous with?
Bundle of His
True or false: the bundle of His is the only conducting path from atria to ventricles
TRUE
What separates the atria and ventricles?
Fibrous ring
What do the Purkinje fibres do?
Rapid spread of depolarisation throughout ventricular myocardium
Which area of the heart is the last to be depolarised?
Base of the ventricles
What does ECG record and how does it do this?
Changes on extracellular surface of cardiac myocytes during wave of depolarisation and repolarisation from surface of the body using electrodes pasted on the skin
What does a depolarisation wave going towards a positive electrode look like on an ECG?
Positive (upright)
What does a depolarisation wave going towards the negative electrode look like on an ECG?
Negative (upside down)
What does a repolarisation wave going towards the positive electrode look like on an ECG?
Negative (upside down)
What does a repolarisation wave going towards the negative electrode look like on an ECG?
Positive (upright)
What is the first electrical event, forming the horizontal line at the start of the P wave?
SA node depolarisation
Where does atrial depolarisation spread?
Along muscle fibres and internodal pathways and spreads through right and left atria
What is the direction of atrial depolarisation?
Downwards and to the left towards AV node
Which event results in the p wave?
Atrial depolarisation
Why is there a delay at the AV node?
Allows time for atrial contraction to fill ventricle
How is the delay at the AV node shown on the ECG?
Flat line after p wave
In which direction does the septum depolarise?
From left to right
What is the q wave?
Depolarisation of interventricular septum, producing small downward deflection
What is the R wave?
Depolarisation of apex and free ventricular wall, producing large upward deflection
Why is the R wave large?
Large muscle mass-more electrical activity
What happens to the R wave of the left ventricle hypertrophies?
Will be correspondingly taller
What is the S wave?
Depolarisation spreading upwards to base of ventricles, producing small downward deflection
Why is the S wave small and downward?
Downward because moving away from electrode
Small because not moving directly away
Where does ventricular repolarisation begin?
On epicardial surface
What is the T wave?
Medium upward deflection caused by ventricular repolarisation
What is the P wave?
Atrial depolarisation
What is QRS wave?
Ventricular depolarisation
How many electrodes are used in an ECG?
10 electrodes - 4 on the limbs and 6 on the chest
How many leads does an ECG produce?
12
How many leads are there in the vertical plane?
6 (limb leads)
Which limb leads are looking at the inferior surface of the heart?
Leads II, III and aVF
Which leads are looking at the left side of the heart?
Leads I and aVL
Where do chest leads V1 and V2 face?
Right ventricle and septum
Where do chest leads V3 and V4 face?
Apex and anterior wall of ventricles
Where do chest leads V5 and V6 face?
Left ventricle
What is the normal speed of ECG paper?
25mm/second
How many small squares and how many large squares does the ECG get through per second?
25 small squares
5 large squares
How many large squares in 1 minute?
300 large squares
What counts as 1 heart beat on an ECG?
Each PQRST complex (start of P wave to start of next P) = 1 cardiac cycle
Which interval is used to calculate heart rate on an ECG?
R-R interval
How is heart rate calculated if the rhythm is irregular?
Count the number of QRS complexes in 6 seconds then multiply by 10
What is the normal PR internal?
3-5 small boxes
When is PR interval prolonged?
If >1 large box
Where is PR interval measured from and to?
From start of P wave to end of horizontal line
What is the normal QRS interval?
<3 small boxes
Why is there sometimes slight variation in sinus rhythm?
Respiration
Which parts of an ECG are checked to make sure a patient has normal sinus rhythm? (5)
1) heart rate (60-100bpm)
2) presence of p waves, followed by QRS
3) normal PR interval
4) normal QRS width
5) QRS preceded by p wave
What is a sinus rhythm with rate <60bpm called?
Sinus bradycardia
What is a sinus rhythm with rate >100bpm called?
Sinus tachycardia
