ECG Flashcards
What does P wave represent
Atrial depolarisation (contraction)
Normal parameters of P wave
3 small squares duration
2.5 small squares high
Upright in leads I, AvF, V3-V6
What does PR segment represent and how high should it be
Delay at AV node
Should be 0. Should be on baseline
PR interval represent?
what Duration normal?
Atrial depolarisation and delay at AV node
3-5 small squares
What does qrs complex represent
Ventricular depolarisation
What is the R wave
always the first positive deflection
what is the q wave
Any negative wave before the R wave
What is the S wave
Any negative wave that follows the R wave
What is the R’ wave
Any subsequent positive wave that follows the R wave
What does the QT interval represent
Whole ventricular action potential
Normal duration of QT interval
males 2 big squares
Females 11 small or 2 big 1 small
ST segment represent?
What elevation is normal
plateau phase of ventricular action potential
up to 2mm normal on chest leads
T wave represent?
Ventricular repolatisation
How to assess rate
Count the number of large squares between two peaks of R waves.
Divide 300 by this number
How to assess rate when there are irregular rhythms
Count the number of QRS complexes on the entire rhythm strip and multiply this number by 6
How to assess rhythm
Mark the R waves with a piece of paper and move this along the ECG to see if all the waves match up
What would cause a regular irregular rhythm
2nd degree heart block
What would cause an irregularly irregular rhythm
AF
What is cardiac axis
The overall direction of electrical spread in the heart when the ventricles contract
What is the normal direction of the cardiac axis
When can this axis be deviated
-30° ￫ 90°
Axis is deviated if electrical activity is stronger on one side - e.g. in Left Ventricular Hypertrophy
what condition could P waves be absent
AF
IN a normal axis, what will the QRS complexes look like in lead 1 and aVF
Both point up
In a left axis deviation, what will the QRS complexes look like in lead 1 and aVF
LEad 1 the QRS will point up
aVF QRS will point down
In a r axis deviation, what will the QRS complexes look like in lead 1 and aVF
Lead 1 the QRS will point down
aVF the QrS will point up
In extreme axis, what will the QRS look like
Both point down
What to assess in P waves
is each P wave followed by a QrS complex
Is each QRS complex preceded by a P wave
Do P wave look normal
What conditions cause prolongation of PR interval
certain heart blocks (1st degree, 2nd degree Mobitz type 1)
What does a shorted PR interval indicate
Pre-excitation syndromes
What can cause a broad QRS
(i) Abnormal depolarisation (e.g. bundle branch blocks, ventricular ectopic beats)
(ii) Pre-excitation (accessory pathways)
Where is the ST segment supposed to be
On isoelectric line
How elevated must ST segment be to be considered abnormal
by at ;east 1mm in limb leads
2mm in chest leads
AND
they must occur in 2+ adjacent leads e.g. leads v1,v2,v3
or leads 2, aVF and III
What does elevated ST segment indicate
ST Elevation of >1mm (limb leads)/>2mm (chest leads) in adjacent leads indicates ST Elevation Myocardial Infarction (STEMI)
What does depressed ST segment indicate
Ischaemia
What does abrnoma T wave look like
What would this indicate
Tall and tented
Tall:
At least ½ the amplitude of the preceding QRS complex)
Tented:
Look as if they’ve been pinched from above - i.e. a pointed peak, narrow base
Hyperkalaemia
When is T wave inversion normal
Lead aVR
normal variant in leads V1 and III
What could t wave inversion indicate
non-specific sign for Ischaemia, Bundle Branch Blocks, Pulmonary Embolism (PE), Hypertrophic Cardiomyopathy (HCM) etc.
What does a flattened T wave indicate
Non specific sign of ischaemia or electrolyte imbalance e.g. hypokalaemia
What is there a risk of if the QT interval is prolonged
Life threatening arrhythmias
