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22nd April 2009
ECG Recording and
Basic Interpretation
Introduction to the E.C.G.
E.C.G is Electrocardiograph or electrocardiogram
It can provide evidence to support a diagnosis, but
Is essential in the diagnosis of chest pain and
abnormal heart rhythms
Is helpful in diagnosing breathlessness
The Electricity of the Heart
Any muscle contraction causes an electrical change
– depolarisation
These changes can be detected by electrodes on
the surface of the body
To ensure recording of only cardiac electrical activity,
the patient must be relaxed
Although a four chamber organ, for E.C.G purposes,
the heart can be thought of as two, as the atria and
ventricles contract together
The Electrical Pathway of the Heart
Each electrical discharge starts in the sino-atrial
node, located in the right atrium
Then spreads through the atrial muscle fibres
There is a delay while depolarisation spreads
through the atrio-ventricular node
Then along single carriageway Bundle of His along
to parallel carriageways of the Right and Left Bundle
Left Bundle Branch carriageway divides into two and
conduction spreads through specialised Purkinje
Normal heart rate is called sinus rhythm and implies
that the electrical activity has commenced in the SA
The Shape of the ECG
Atrial muscle mass is smaller compared with the
ventricles – so the is the electrical charge
Atrial contraction is the P wave
Ventricular muscle mass is larger and creates a
bigger deflection on the ECG
This is represented by the QRS complex
T wave represents repolarisation – the ventricular
muscle mass returning to a resting state
P,Q,R & S are waves, Q,R & S make up a complex,
interval between S and T is called the ST segment
ECG Recording
ECG machines record electrical activity on moving
paper – the speed and the squared paper is
Each large (5mm) square represents 0.2 sec, so 5
large squares per second
1 QRS per 5 squares means a pulse of 60 beats per
PR interval should be 3 – 5 small squares
QRS is usually 3 small squares – any abnormally
long conduction shows as a widened QRS complex
Recording an ECG
12 lead means 12 different “electrical pictures”; does
not refer to wires that connect patient to machine
Good skin contact is essential (chest shaving may
be required)
One electrode on each limb, and one that is
positioned in 6 different places on the chest (or has 6
Electrodes labelled Left Arm, Right Arm, Left Leg
and Right Leg, plus chest 1 to 6
Electrode Placement
Lead V1 is placed over the 4th intercostal space, to the
right of the sternum
Lead V2 is placed over the 4th intercostal space, to the left
of the sternum
Lead V4 is placed over the 5th intercostal space in the midclavicular line
Lead V3 is placed midway between V2 and V4
Lead V5 is placed on the same horizontal level as V4 but
at the anterior axilliary line
Lead V6 is placed on the same horizontal level as V4 and
V5 but on the mid axilliary line
The Shape of the QRS Complex
Normal hearts have more muscle in left ventricle
compared to right
QRS complex represents ventricular activity and is
normally the largest deflection
Information can be gathered from looking at rhythm
Layout of the ECG
12 views are represented and the segments are
labelled I,II, III, aVR, aVL, and aVF.
Most machines display each view horizontally, and
vertically across the page
A rhythm strip is included at the end to enable the
reader to determine rate and regularity of heart
Normal ECG
A normal ECG will contain regular complexes
Each complex will be made up of a P wave, swiftly
followed by a QRS
The QRS should be pointed
The complexes should be of uniform appearance
Normal ECG
Abnormal ECG
Abnormal ECG
Left Bundle Branch Block
Acute ST Depression
Acute ST Elevation Inferior MI
Acute ST Elevation Posterior MI
Atrial Flutter
Atrial Fibrillation
Ventricular Fibrillation
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