ECG Flashcards
What is an electrocardiogram
- a graph of voltage against time
- visual representation of electrical potentials in the heart
- electrical signals stimulate and coordinate contraction of heart
What causes dipoles in the heart
The depolarising and repolarising of cardiac cells (myocytes)
Einthoven triangle
Electrical potential generated from heart form an equilateral triangle when measured from 3 positions in body (wrists and left ankle)
6 limb leads
3 bipolar leads (I, II, III)
3 unipolar leads (aVR, aVL, aVF)
V1 chest lead
4th IC
right sternal edge
V2 chest lead
4th IC
Left sternal edge
V4 chest lead
5th IC
Midclavical line
(Bottom right of left sternum)
V5 chest lead
Left anterior axillary
Edge of left ribcage, in line with v4
V6
Mid axillary line
Under armpit, in line with v4 and v5
Draw P wave
Atrial contraction
Both atria are depolarising
Road bump before QRS
PR interval
Time taken for signal to travel from AVN to Ventricle
AVN conduction time
Draw QRS interval
Ventricular contraction
Ventricles depolarising
Traverse Bundle of His and Purkinje fibres
Negative deflection vs Positive deflection
Negative deflection = become positive electrode
E.g. Q and S
Positive deflection = become negative again
E.g. R
Draw ST segment
Repolarisation of ventricles (T wave)
Isoelectric flat segment
P wave QRS complex T wave are collectively known as…
Sinus rhythm
Buckmans bundle
Transfers electrical impulses from SAN in the right atrium to the left atrium
Normal resting heart rate for adult
50 to 90 bpm
Bradycardia= below range
Tachycardia= above range
Abnormal cardiac rhythm is called…
Arrhythmia
2 types of arrhythmia
1) Conduction abnormalities in SAN and AVN, unable to initiate impulses so no P wave and QRS. Valve fibrosis.
2) Abnormal impulse initiation where ventricles beat abnormally, impairs cardiac output, hypotension and collapse
3 causes of tachyarrhythmia
1) altered automaticity
2) Another depolarisation occurs abnormally
E.g. atria fibrillation and atrial flutter
3) re-entry
Ischaemia
Shortage of oxygen supply to muscle
Ischaemic myocytes have reduced membrane potentials compared to healthy myocytes which displace the ST segment
Injury current
Angina
Chest pain on exercising
Due to chronic arterial narrowing
Myocardial infarction
Heart attack
