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How to Find Your Way Around

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 remember…..LOOK AT THE PATIENT NOT JUST THE PAPER  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 Branches Left Bundle Branch carriageway divides into two and conduction spreads through specialised Purkinje fibres Normal heart rate is called sinus rhythm and implies that the electrical activity has commenced in the SA node

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 standardised 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 minute 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 “terminals”) Electrodes labelled Left Arm, Right Arm, Left Leg and Right Leg, plus chest 1 to 6

Electrode Placement       Lead V1 is placed over the 4 th right of the sternum Lead V2 is placed over the 4 th of the sternum Lead V4 is placed over the 5 th clavicular line intercostal space, to the intercostal space, to the left intercostal space in the mid 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 strips

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 rhythm

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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