Session 7 ILOs - ECG Flashcards
- Understand and be able to describe the electrical conducting system of the heart
- Understand and be able to describe spread of excitation through myocardium
- label a diagram of the electrical conducting system of the heart and describe how excitation normally spreads through the myocardium
1) Sinoatrial Node
2) Atrioventricular node
3) Bundle of HIS
4) Left Bundle Branch and Right Bundle branch
5) Purkinje Fibres
- Action potentials are initiated in the SAN
- Depolarisation spreads across the atrium, where they are picked up at the AVN and there is a slight delay
- Depolarisation then passes through into the bundle of His which splits into the left and right bundles is carried down through the interventricular septum
- Finally, depolarisation passes back up through towards the base of the heart via the Purkinje fibres
Describe the correct positioning of recording electrodes for performing a 12 lead ECG (including colours)
Show and describe the correct positioning of recording electrodes for performing a 12 lead ECG (including colours) and be able to place electrodes correctly to record from ECG leads I, II, III, aVR, aVL, aVF and the chest leads V1-6
Electrode = Wires you place on body
Lead = Views of heart and recordings of ECG
- 10 Electrodes
- 12 Leads
Limb leads: (placed on wrists and ankles)
- RA limb lead (red) Ride
- LA limb lead (yellow) Your
- LL limb lead (green) Green
- RL limb lead (black / grounding) Bike
+ augmented limb leads (make up other 3 leads)
Chest leads:
To remember colours - Ride your great big brown pony
V1 - Red - 4th intercostal space at right sternum edge
V2 - Yellow - 4th intercostal space at left sternum edge
V3 - Green - Midway between V2 and V4
V4 - Blue - 5th intercostal space at mid-clavical line (line down from clavicle)
V5 - Orange - Left anterior axillary line (horizontal with V4)
V6 - Purple - Left mid-axillary line (horizontal with V4 and V5)
1) Limb lead 1: voltage difference between electrode RA and LA; LA (+)electrode
2) Limb lead II: voltage difference between electrode RA and LL; LL (+)electrode (apex)
3) Limb Lead III: voltage difference between electrode LA and LL; LL (+)electrode
Augmented limb leads:
Augmented Limb Leads aVR, aVL and aVF unipolar- only have a positive electrode
– Other “electrode” actually represents the average of the remaining 2 electrodes and is designated “neutral” or reference
– The positive electrodes for these augmented leads are located on:
• Right arm for aVR (between right arm and left arm and leg)
• Left arm for aVL (between left arm and right arm and left leg)
• Left leg aVF (F for foot) (between left leg and right and left arm)
ECG Lecture part 1, 24.23 for visuals
Explain what signal you would see on a a positive recording electrode when depolarisation and repolarisation spreads towards and away from that electrode
OR
State rules governing the sign of the signal recorded by a positive recording electrode when depolarisation and repolarisation spreads towards and away from that electrode
Depolarisation travelling towards the positive electrode = upwards deflection
Depolarisation travelling away from the positive electrode = downwards deflection
Repolarisation travelling away from the positive electrode = upwards deflection
Repolarisation travelling towards the positive electrode = downwards deflection
Draw the ECG trace recorded by an electrode ‘viewing’ the heart from the apex. Label the waves PQRST and identify the signals associated with atrial depolarisation, ventricular depolarisation, and ventricular repolarisation
Apex = lead 2
describe how the QRS complex will change if the viewing electrode is moved around a circle with the heart at its centre
State the meaning of sinus rhythm
Sinus rhythm: each QRS complex is preceded by a normal P wave
determine if an ECG is in sinus rhythm
Explain how you would calculate the heart rate from a rhythm strip for a regular and irregular heart rhythm
Regular heart rate:
Method 1: One big box is 0.2 seconds, so count the number of QRS complexes there are in the time period so 4 beats in 3.2 seconds (if 16 boxes), then use a ratio to get up to 60 seconds
Method 2 (squares method): count number of big squares between 2 QRS complexes then do 300 / number
Irregular method:
Count the number of QRS complexes in 6 seconds (30 big squares) then X 10
Explain how you would calculate the following interval durations and determine if they are in their normal range:
- PR interval
- QRS interval
- QT interval
PR interval
- Measure from beginning of P wave, to the start of the QRS complex
- Normal range: 0.12 - 0.2 seconds (3-5 small boxes)
QRS interval
- Measure from beginning QRS complex to the end of the QRS complex
- Normal range: <0.12 seconds ( < 3 small boxes)
QT interval
- Measure from beginning of QRS complex to the end of the T wave
- Normal range: 0.42 seconds
Describe each stage of the ECG trace for the Limb Lead II
P wave: atrial depolarisation
Isoelectric line: delay at AVN
Q part: depolarisation of interventricular septum
R part: depolarisation of apex and ventricular walls
S part: depolarisation up to the base of the ventricles
T wave: repolarisation of ventricles
Students should be able to identify and describe common cardiac arrythmias including: 1) Three types of heart block 2) Atrial fibrillation 3) Ventricular ectopic beats 4) Ventricular tachycardia & fibrillation
1) First degree heart block:
- All normal P waves are followed by QRS complexes, but PR interval is longer than normal (> 0.2 second)
- P wave normal
- QRS normal
2) Second degree heart block Mobitz type 1:
- The PR interval gets successively longer
- Until one P is not conducted (this allows time for AVN to recover) and it’s not followed by a QRS complex,
- Cycle begins again
3) Second degree heart block Mobitz type 2:
- PR interval normal (as opposed to lengthening)
- Sudden non-conduction of a beat (p wave not followed by QRS complex)
- Dropped QRS
- High risk of progression to complete heart block
4) Third Degree heart block
- Atria and ventricles are depolarising independently – complete failure of AV conduction
- Ventricular pacemaker takes over (escape rhythm) – slow -20-40 bpm
- Typically too slow to maintain blood pressure and perfusion
- Wide QRS Complexes
5) Atrial fibrillation
CHECK THE REST AGAINST LECTURE AND FILL IN WHEN DONE
identify changes associated with hyperkalaemia and hypokalaemia
• describe in outline the ECG changes associated with
o the acute phase of myocardial infarction
o persistent changes from a previous myocardial
infarction
o myocardial ischaemia
o predict the area of the heart involved in changes due to ischaemia or myocardial infarction from the grouping of leads affected
CHECK WITH LECTURE AND FILL IN
examine 12 lead ECG traces and comment on rhythm, rate and abnormalities of the complexes
