The ECG Flashcards
Label the ECG
How does excitation normally spread through the heart?
1) SAN depolarises,
2) impulse spreads through atria,
3) held up at AVN,
4) spreads to ventricle via Bundle of His,
5) spreads rapidly down R and L bundles and purkinje system,
6) myocytes of IV septum are depolarised first,
7) apex, RV and LV free walls are polarised next,
8) ventricle bases last to depolarise
9) repolarisation of ventricles in reverse order
Where is the SAN located in the heart?
Top R hand corner of the R atrium
How does SAN depolarisation appear on an ECG
First electrical event: insufficient signal to register on ECG = flat line
What does the P wave correspond to?
Atrial depolarisation = upwards as towards +ve electrode = SAN must be setting HR, can be absent in which case AV will be setting pace
What does 1b on an ECG correspond to?
AVN delay = time for atria to contract and ventricles to fill = stops simultaneous contraction = flat line. Also depolarisation travelling down Bundle of His
How are the atria electrically isolated from the ventricles?
Fibrous ring – 4 heart valves
What does the Q wave correspond to?
Septum depolarising L to R = downward deflection because moving away
What does the R wave correspond to?
Depolarisation of the apex and ventricular wall – large due to muscle mass
What does the S wave correspond to?
Depolarisation of base of ventricles (muscle close to atria)
What does the T wave correspond to?
Ventricular repolarisation – upward wave as repolarisation is moving away from +ve electrode
State the rules about the signal recorded when depolarisation spread towards the recording electrode
Wave of -ve charge travelling to +ve electrode = upward wave = +ve complex
State the rules about the signal recorded when depolarisation spread away from the recording electrode
Wave of –ve charge travelling away from +ve electrode = downward wave = -ve complex
State the rules about the signal recorded when repolarisation spread towards the recording electrode
Wave of +ve charge travelling towards the +ve electrode = downward wave = -ve complex
State the rules about the signal recorded when repolarisation spread away from the recording electrode
Wave of +ve charge travelling away from the +ve electrode = upward wave = +ve complex
Draw the correct positions of the CHEST recording electrodes for performing a 12 lead ECG and the names of the leads
V1 = 4th intercostal space, R sternal border
V2 = 4th intercostal space, L sternal border
V3 = mid-way between V2 and V4
V4 = 5th intercostal space, mid-claviclar line
V5 = 5th intercostal space, beginning of axilla
V6 = 5th intercostal space, mid-axillary line
Draw a normal ECG trace from an electrode viewing the heart from the apex
What are the 12 different view of the heart?
Limbs: I, II, III, aVR, aVL, aVF.
Chest: V1, V2, V3, V4, V5, V6
Describe how the QRS complex will change if the viewing electrode is moved around a circle with the heart at the centre
The transition zone is where the QRS complex changes from predominately negative to predominately positive, this usually occurs at V3 or V4.
It is normal to have the transition zone at V2 (called “early transition”), and at V5 (called “delayed transition”).
What is sinus rhythm?
any cardiac rhythm where depolarisation of the cardiac muscle begins at the sinus node = presence of P wave
What is normal sinus rhythm?
reg rhythm,
HR 60-100,
p wave present and upright in leads I and II,
PR interval 3-5 small boxes,
every p wave followed by QRS,
QRS <3 small boxes
What is the speed of ECG paper?
25mm/sec
1 second on ECG paper is = to?
25 small squares, 5 large squares
How do you calculate a regular heart rate?
300 divided by how many large boxes between R-R interval:
300/4 = 75bpm
How do you calculate an irregular heart rate?
Number of QRS complexes in 6 seconds then x by 10
Draw the different intervals present on an ECG
What does an abnormal R-R interval indicate?
Shorter = faster HR
What does an abnormal QRS complex indicate?
Wider = ventricular depolarisations that are not initiated by the normal conductance mechanism
What does an abnormal P-R interval indicate?
Lower = slow conduction from atria to ventricle = heart block
What does an abnormal ST segment indicate?
Should be isoelectric (flat line) – if raised or depressed = MI or ischaemia
What does an abnormal Q-T interval indicate?
Prolonged = prolonged repolarisation of ventricles = can lead to arrhythmias as occur in long QT syndrome
On a 12 lead ECG where are the LIMB electrodes placed?
Ride your green bike
What view of the heart does each electrode have?
Inferior: II, III, aVF
Lateral: I, aVL, V5, V6
Anterior: V3, V4
Septal: V1, V2
