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 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

Looking at the ECG you'll see that  Rhythm - Regular  Rate - less than 60 beats per minute  QRS Duration - Normal  P Wave - Visible before each QRS complex  P-R Interval - Normal  Usually benign and often caused by patients on beta blockers

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 intercostal space, to the right of the sternum  Lead V2 is placed over the 4 th intercostal space, to the left of the sternum  Lead V4 is placed over the 5 th intercostal space in the mid- clavicular 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 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

Sinus Tachycardia  Rhythm - Regular  Rate – Greater than normal for child’s age  P Wave - Visible before each QRS complex  P-R Interval - Normal  The impulse generating the heart beats are normal, but they are occurring at a faster pace than normal.

Sinus Bradycardia Rhythm - Regular Rate - less than 60 beats per minute QRS Duration - Normal P Wave - Visible before each QRS complex P-R Interval - Normal Usually benign and often caused by patients on beta blockers

Ventricular Tachycardia (VT)  Rhythm - Regular  Rate Beats per minute  QRS Duration - Prolonged  P Wave - Not seen  Results from abnormal tissues in the ventricles generating a rapid and irregular heart rhythm. Poor cardiac output is usually associated with this rhythm thus causing the pt to go into cardiac arrest. Shock this rhythm if the patient is unconscious and without a pulse

Ventricular Fibrillation (VF)  Looking at the ECG you'll see that:  Rhythm - Irregular  Rate , disorganized  QRS Duration - Not recognizable  P Wave - Not seen  This patient needs to be defibrillated!! QUICKLY

Asystole Rhythm - Flat Rate - 0 Beats per minute QRS Duration - None P Wave - None Carry out CPR!!!

Atrial Flutter  As with SVT the abnormal tissue generating the rapid heart rate is also in the atria, however, the atrioventricular node is not involved in this case.  Rhythm - Regular  Rate – Atrial rate ranges 240 – 300 per min.  QRS Duration - Usually normal  P Wave - Replaced with multiple F (flutter) waves, usually at a ratio of 2:1 (2F - 1QRS) but sometimes 3:1  P Wave rate beats per minute  P-R Interval - Not measurable

Atrial Flutter

Atrial Fibrillation  Many sites within the atria are generating their own electrical impulses, leading to irregular conduction of impulses to the ventricles that generate the heartbeat. This irregular rhythm can be felt when palpating a pulse. Rhythm - Irregularly irregular  Rate – Atrial rate ranges from per min. The ventricular response is irregularly irregular and may be fast or slow.

Atrial Fibrillation  QRS Duration - Usually normal  P Wave - Not distinguishable as the atria are firing off all over  P-R Interval - Not measurable  The atria fire electrical impulses in an irregular fashion causing irregular heart rhythm

Ventricular Fibrillation