Ses 7 CVS ECG Flashcards
state rules governing the sign of the signal recorded by a positive
recording electrode
• Depolarisation spreading towards a positive recording electrode yields an upward deflection
• Depolarisation spreading away from a positive recording
electrode yields a downward deflection
• Repolarisation spreading towards a positive recording electrode yields a downward deflection
• Repolarisation spreading away from a positive recording
electrode yields an upward deflection
Framework for ECG viewing
RATE
RHYTHM
regular, sinus arrhythmia, irregular
AXIS
Intervals:
PR
QRS
QTc
ST/T
R wave progression
HR from ECG
Method 1 - 300/no of big boxes between R waves - for regular rhythms
Method 2 - No of QRS complexes per 6s strip multiplied by 10 - irregular rhythms
Electrode placement notion
4 limb electrodes which are placed on bony parts e.g. wrists and ankles:
Right arm – Red electrode
Left arm – Yellow electrode
Left leg – Green electrode
Right leg – Black electrode
Ride Your Green Bike - starting from the right wrist and working clockwise when looking at the front of the patient.
6 chest electrodes. Each of these gives its own lead/view of the heart. V1-V6 which are placed across the chest in specific positions:
V1 – right sternal edge, 4th intercostal space (ICS)
V2 – left sternal edge, 4th ICS
V3 – halfway between V2 and V4
V4 – mid-clavicular line, 5th ICS
V5 – hallway between V4 and V6 - anterior axillary line
V6 – mid-axillary line in line with V4
What leads view what part of the heart notion
How are depolarisation and repolarisation seen
Depolarisation towards the electrode is seen as an upward deflection.
Depolarisation away from the electrode is seen as a downward deflection
Repolarisation towards the electrode is seen as a downward deflection.
Repolarisation away from the electrode is seen as an upward deflection.
Which is the only one that is inverted
aVR
7 things to look for in ECG
- Rate between 60-120bpm
- Reg rhythm - can be irregular, sinus arrhythmia
- Axis - which one is most positive eg if aVL then left axis deviation, if lead 3 then right.
- Intervals:
PT interval - 120-200ms
QRS complex - 3 small boxes - taller or broader
QT - 2 large squares
ST segment - elevation, depression, inversion
P waves = atrial activity
QRS = ventricles
Abnormalities
Arrhythmias
Heart block
Ischaemia and injury
Electrolyte disturbances
Afterdepolarisations
Atrial Tachycardia - arrhythmia notion
Cause - AV nodal re-entry tach - small circuit in AV node which sends off conduction to ventricles.
Due to IHD, RHD
ECG - P and T waves merge
A flutter - arrhythmia - notion
re-entry loop in the atria. AV node cannot keep up so some P waves not conducted (2:1 AV block where 2 atrial beats for 1ventricular beat).
Cause - hypertension, IHD, alcoholism, hyperthyroidism
ECG - 2 flutter waves for every QRS, sawtooth baseline.
Atrial fibrillation - arrhythmia - notion
Cause - multiple ectopic foci in the atrial myocardium
Dilated LA, hypertension, IHD, hyperthyroidism, alcohol.
ECG - impulses that are conducted to the ventricles occur randomly, resulting in irregular R-R intervals. No P waves, wavy baseline.
Irregularly irregular pulse - don’t know when ventricles will beat AND don’t know how strong how strong the pulse will be - length of time between each ventricular contraction is diff so amount of time for ventricles to fill with blood is diff.
Quivering atria - stasis - thrombus - in left auricle - embolism and ischaemic stroke.
VF
Cause - numerous ectopic foci in V myocardium so chaotic depolarisation- no-coordination between atria and ventricles.
Dec CO then cardiac arrest.
MI, IHD
ECG - no normal features,
Heart block
1st
Delayed conduction through AV node
Prolonged PR interval
IHD + hypokalemia
2nd
Mobitz type I – the PR interval becomes progressively longer until one of the QRS complexes is dropped. The PR interval then returns to normal and repeats the cycle.
Mobitz type II – the PR interval is normal and constant, but occasionally the P wave is not conducted so a QRS complex is dropped.
2:1 Block - Another type of second degree AV block where alternate P waves are not conducted
Third degree AV block is when there is no impulse transmission between the atria and ventricles and therefore they work independently. There is no relationship between the P wave and QRS.
3rd degree - The ventricular pacemaker takes over as an escape rhythm. Escape rhythms occur when the conduction system is blocked, and so the ventricle have to manage themselves and become their own pacemaker. The QRS complex becomes wider because the impulse isn’t travelling via the His-Purkinje system.
