ECG Interpretation Guide PDF

ELECTROCARDIOGRAPHY Electrocardiography is the aspect of physiology that deals with the recording and analysis of the electrical activities of the heart The heart generates its electrical impulses which are propagated as waves of depolarization and repolarization. The cardi...

ELECTROCARDIOGRAPHY Electrocardiography is the aspect of physiology that deals with the recording and analysis of the electrical activities of the heart The heart generates its electrical impulses which are propagated as waves of depolarization and repolarization. The cardiac electrical impulses are recordable on a graph for visual analysis and interpretation and clinical evaluation. July 01, 2024 1 July 01, 2024 2 PQRST Complex: Building Block of ECG July 01, 2024 3  ECG Paper The graph paper consists of horizontal and vertical lines at 1mm apart that intersect to form small (1mm) and large (5mm) squares July 01, 2024 4  ECG Graph:Time and Voltage Assessment Time Measurement : time is assessment is done horizontally; 1mm represents 0.04s (40ms) Voltage Measurement: voltage assessment is done vertically. 1mm represents 0.1mV Standardization Paper speed: 25mm/s Calibration signal or amplitude indicator: 10mm/mV July 01, 2024 5  ECG Denotations Denotations Descriptions P wave atrial depolarization QRS complex ventricular depolarization Q wave first negative deflection in ventricular depolarization R wave first positive deflection in ventricular depolarization S wave second negative deflection in ventricular depolarization or the first negative deflection after R wave T wave July 01, 2024 ventricular repolarization 6  Intervals in ECG PR interval: period from the onset of atrial depolarization to the beginning of ventricular depolarization QT interval: period from the onset of the ventricular depolarization to the end of ventricular repolarization RR interval: period from the peak of R wave to the other July 01, 2024 7  Other Denotations PR segment: isoelectric line from the end of atrial depolarization to the beginning of ventricular depolarization ST segment: isoelectric line from the end of ventricular depolarization to the beginning of ventricular repolarization J-Junction: the junction between the end of ventricular depolarization and the beginning of S-T segment U wave: any wave between T and P waves July 01, 2024 8  U wave An inconstant wave Exact mechanism of its genesis is still controversial however suggested mechanisms;  repolarization of papillary muscle and neighbouring structures(old concept)  repolarization of mid-myocardial cells (M-cells)  an afterpotentials July 01, 2024 9  ECG Denotations July 01, 2024 10  STANDARD 12-LEAD ECG Standard 12-lead ECG is recorded by the aids of 10 electrodes arranged on specific locations on the body surface One electrode is attached to each limb to produce 6 limb leads 6 electrodes are attached to the chest to produce 6 chest or precordial leads July 01, 2024 11  Classifications of Standard 12 Leads Types of Lead Leads Bipolar limb I, II, III leads Augmented limb aVF, aVL, aVR leads Chest or V1,V2,V3,V4,V5, Precordial leads V6 July 01, 2024 12 
Chest Electrode Placement

V1-4th intercostal space, right sternal edge V2-4th intercostal space, left sternal edge V3-midway between V2 & V4 V4-5th intercostal space,left midclavicular line V5-5th intercostal space, left anterior axillary line V6-5th intercostals space,left mid-axillary line July 01, 2024 13  Placement of Chest Electrodes July 01, 2024 14  Standard 12-Lead ECG July 01, 2024 15  Classification Based on Planes of Location Frontal Plane Leads  These leads are located in the frontal plane  They include all the limb leads; I,II,III, aVL , aVF & aVR Horizontal/Transverse Plane Leads:  These leads are located in the horizontal/transverse plane  They include all the chest leads; V1-V6 July 01, 2024 16  Frontal and Horizontal Planes Frontal plane Horizontal plane July 01, 2024 17 
Lead Classification based on heart regions
Classification Leads Left lateral leads I, aVL,V5 & V6 Inferior leads II,III & aVF Septal leads V3,V4 Anterior leads V1-V6 Right ventricular aVR,V1 & V2 cavity leads July 01, 2024 18  Bipolar limb leads-Augmented Leads Relationship Lead I is perpendicular to aVF Lead II is perpendicular to aVL Lead III is perpendicular to aVR July 01, 2024 19  Einthoven Triangle July 01, 2024 20  Angles of Orientation of Leads Lead Angles of Orientation I 00, 1800 II +600, -1200 III +1200, -600 aVF +900, - 900 aVL -300, +1500 aVR +300, -1500 July 01, 2024 21  Hexaxial Reference System July 01, 2024 22  QRS AXIS QRS axis is the average direction of the ventricular depolarization(QRS) current. The normal axis points mostly downward and to the left because the more muscular left ventricle generates a stronger depolarizing current than the less muscular right ventricle. July 01, 2024 23 
Classification of QRS Axis

Class Range of Angle Normal axis 00 to + 900 Left axis 00 to -900 deviation Right axis +900 to +1800 deviation Extreme axis -900 to 1800 July 01, 2024 24  QRS Axis July 01, 2024 25  Causes of Left Axis Deviation Left anterior fascicular block Left ventricular hypertrophy Inferior myocardial infarction Wolff-Parkinson-White syndrome Artificial cardiac pacing Mechanical shift e.g pregnancy Congenital heart disease e.g atria septal defect(septum primum defect) July 01, 2024 26  Causes of Right Axis Deviation Normal variation in children and thin adult Left posterior fascicular block Left lateral wall infarction Right ventricular hypertrophy Dextrocardia Pulmonary embolism Congenital heart diseases e.g atrial septal defect(septum secundum type),tetralogy of Fallot Wolff-Parkinson-White syndrome July 01, 2024 27  Causes of Extreme Axis Emphysema Artificial cardiac pacing Lead misplacement July 01, 2024 28  QRS Axis Estimation Step I: To locate the class of the QRS axis Step II: To estimate the QRS axis to the nearest 300 July 01, 2024 29  Step I Inspect leads I and aVF Determine the direction of the dominant QRS deflection Identify the QRS axis class; normal,LAD, RAD or indeterminate using the quide below;  Positive in I & aVF: Normal axis  Negative in I & positive in aVF: RAD  Positive in I & negative in aVF: LAD July 01, 2024 30  Negative in I & negative in aVF: extreme  Step I Dominant QRS Dominant QRS QRS Axis Range of deflection in deflection in lead Angles of QRS lead I aVF Axis Positive Positive Normal 00 to +900 Negative Positive +900 to 1800 Right axis deviation Positive Negative Left axis 00 to -900 deviation Negative Negative Extreme axis -900 to July 01, 2024 1800 31  Step II Inspect the limb leads Get lead X with equiphasic QRS complex Identify lead Y ; a lead perpendicular to X Get the angles of orientation of Y Appropriate your answer with step I to get approximate QRS axis July 01, 2024 32  Equiphasic QRS complex An equiphasic QRS complex has an equal positive and negative deflection e.g RS or qr complexes shown below. RS complexes qr complex July 01, 2024 33  Step I: Normal Axis ( 0 to +900) Step II: X= aVL , Y = II ( + 600, -1200) Approximate QRS Axis ≈ + 600 July 01, 2024 34  Estimate the QRS axis July 01, 2024 35  Estimate the QRS axis July 01, 2024 36  Estimate the QRS axis July 01, 2024 37  Estimate the QRS axis July 01, 2024 38  Estimate the QRS axis July 01, 2024 39  Estimation of Heart Rate Heart Rate is estimated using the following formulae; 1.HR = 300/x , where x = no of large(5mm) squares within RR interval 2. HR = 1500/y, where y = no of small(1mm) squares within RR interval 3. HR = 60/RR interval Normal Heart Rate : 60 – 100beats per minute July 01, 2024 40  Estimation of QTc QT interval : period from the onset of ventricular depolarisation to the end of ventricular repolarization QT interval varies with the heart rate When QT is measured , it should be adjusted for heart rate using Bazzet’s Formula; QTc = QTm /RRint ½ , QTc = QT corrected, QTm = measured QT & RRint. = RR interval Normal QTc : 0.36 – 0.44s for male, July 01, 2024 41  ST Segment ST segment : isoelectric line between the end of ventricular depolarisation and the beginning of ventricular repolarization It is the isoelectric line between QRS complex and T wave ST segment begins at the J junction and ends at the K junction ST segment can be elevated or depressed in some cardiac disorders July 01, 2024 42  ST Segment Changes ST segment can be elevated or depressed in some cardiac disorders Causes of ST segment elevation include; early repolarization, acute myocardial infarction and acute pericarditis Causes of ST segment depression include ; myocardia ischaemia(angina pectoris) and hypokalaemia July 01, 2024 43 Fourteen Steps in ECG interpretation

STEP PARAMETERS 1 Standardization 2 Rhythm 3 Rate 4 P wave 5 P-R interval 6 Q wave 7 QRS Complex 8 J-junction 9 ST segment 10 T wave 11 QT interval 12 Miscellaneous 13 Summary 14 Conclusion PARAMETERS Value Standardization 10mm/mV Rhythm Sinus Rate 60-100beats/min P wave Duration: