2/13/2014 Systematic Approach to 12 Lead ECG Interpretation Prepared by: Shadi Kakish Dr. Halia Al Shahri How to Read ECG Understand the Heart’s Electrical Message 1 2/13/2014 How to Read ECG Your Knowledge is Vital for Saving Lives Systematic Approach • • • • Calibration Rate Rhythm Axis • • • • • • • P-wave PR interval QRS complex ST segment QT- Interval T-wave U- Wave 2 2/13/2014 ECG Leads Impulse Conduction & the ECG Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers 3 2/13/2014 The “PQRST” P wave = Atrial depolarization QRS = Ventricular depolarization T wave = Ventricular repolarization The ECG Paper Horizontally One small box - 0.04 s One large box - 0.20 s Vertically One large box - 0.5 mV 4 2/13/2014 Calibration • Check that your ECG is calibrated correctly • Height  10mm = 1mV  Look for a reference; which should be the rectangular looking wave somewhere near the left of the paper. It should be 10mm (10 small squares) tall • Paper speed  25mm/ s 25 mm (25 small squares / 5 large squares) equals one second How to Read ECG • Rate 5 2/13/2014 Rate Regular : HR= 300/Nnumber of large squares between 2 Rs Rate Irregular : Count number of complexes in rhythm strip × 6 14 (R waves) x 6 = 84 b/m 6 2/13/2014 Rhythm Lead II P wave= Sinus Rhythm No P wave= Non sinus How to Read ECG Axis 7 2/13/2014 Axis • The electrical axis of the heart is the mean direction of the cardiac impulse during ventricular depolarization • Leftward and downward Axis • Normal QRS axis between -30o and +90o. • A QRS axis between -30oand -90o is LAD • A QRS axis between +90o and +150o is RAD • A QRS axis between +150o and -90o is superior RAD -150o -90o -60o -120o -30o 180o 0o 30o 150o 120o 90o 60o 8 2/13/2014 Place your thumb over leads I & aVf pointing in the direction of the QRS NORMAL RAD LAD NO MANS LAND P-wave • P wave represents atrial depolarization, which causes atrial contraction. • Normally a dome-like structure • Height a P wave over 2.5mm should arouse suspicion • Length a P wave longer than 0.08s (2 small squares) should arouse suspicion 9 2/13/2014 Abnormalities of P-wave • A tall P wave (over2.5mm) can be called P pulmonale which Occurs due to R atrial hypertrophy, causes can be: pulmonary hypertension Pulmonary stenosis Tricuspid stenosis P-pulmonale 10 2/13/2014 Abnormalities of P-wave • Length A P wave with a length>0.08 seconds (2 small squares) and (M) shape is called P mitrale which caused by left atrial hypertrophy and delayed left atrial depolarization, causes can be: Mitral valve disease LVH P mitrale 11 2/13/2014 The PR interval • The PR interval corresponds to the time period between depolarization of the atria and ventricular depolarization or its represent the delay in transmission in AV node • A normal PR interval is between 0.12 and 0.2 seconds (3-5 small squares) • The PR interval is measured between the start of the P wave to the start of the QRS complex The PR Interval Atrial depolarization + delay in AV junction (AV node/Bundle of His) 12 2/13/2014 1 AV Block • PR Interval > 0.2 seconds (5 small sq) Second Degree AV Block (2º) Mobitz Type I (Wenkebach) Progressive PR prolongation 13 2/13/2014 Second Degree AV Block (2º) Mobitz Type II PR interval is constant Third Degree AV Block (3º) (Complete) P P QRS P P QRS Ps > QRSs 14 2/13/2014 Q Waves Non Pathological Q waves Q waves of less than 2mm are normal Pathological Q waves Q waves of more than 2mm indicate full thickness myocardial damage from an infarct Late sign of MI Pathological Q waves 15 2/13/2014 QRS Height • If the QRS complexes in the chest leads look very tall, consider left ventricular hypertrophy (LVH) • If the depth of the S wave in V1 or V2 added to the height of the R wave in V5 or V6 comes to more than 35mm, LVH is present Left Ventricular Hypertrophy R in V5 (or V6) + S in V1 (or V2) > 35 mm 16 2/13/2014 QRS • Width • The width of the QRS complex should be less than 0.12 seconds (3 small squares) • If the QRS is wider than this, it suggests a ventricular conduction problem - right or left bundle branch block (RBBB or LBBB) LBBB • If left bundle branch block is present, the QRS complex may look like a (W) shape rS- in V1 and/ or an (M) shape – RsR wave- in V 6 • New onset LBBB with chest pain consider Myocardial infarction • Not possible to interpret the ST segment 17 2/13/2014 RBBB • It is also called rSR pattern • Terminal R wave in lead V1 • Slurred S wave in leads I and V6 ST Segment • The ST segment represents period between ventricular depolarization and repolarisation. • The ventricles are unable to receive any further stimulation • The ST segment normally lies on the isoelectric line. 18 2/13/2014 Ischemia/Infarction Ischemia/Infarction II III AVF =Inferior I AVL = Lateral V1 V2 = Septal V3 V4 = Anterior V5 V6 = High Lateral 19 2/13/2014 Inferior MI Anterior MI 20 2/13/2014 Anterolateral MI T wave • T wave generally shouldn’t be taller than half the size of the preceding QRS • Hyperacute T waves occur with ST segment elevation in acute MI or hyperkalemia • If the T wave is flat, it may indicate hypokalemia • If the T wave is inverted it may indicate ischemia 21 2/13/2014 QT interval • The QT interval is measured from the start of the QRS complex to the end of the T wave • The QT interval varies with heart rate • QTc= QT/√RR (Corrected QT interval) • The normal range for QTc is 0.38 – 0.42 QT interval Short QTc interval may indicates hypercalcaemia Long QTC has many causes; 3 Hypos, Antiarrhythmic drugs and congenital Long QTc interval increase the risk of developing arrhythmia?!! 22 2/13/2014 U wave • U waves occur after the T wave and are often difficult to see • U waves are thought to represent repolarization of the papillary muscle or Purkenji fibers • Prominent U waves can be a sign of hypokalaemia hyperthyroidism • could normally be seen in younger, athletic individuals References • The ECG made easy, 6th edition. John R. Hampton • Always at your side… ECG Notes interpretation and management guide. Shirly A.Jones, 2005 • www.thh.nhs.uk/documents/_Departments/U ndergraduates/.../ECG • EKG-boken Ylva Lind, Lars Lind, Liber, 2011 • Cardiology Journal 2008, Vol. 15, No. 5, pp. 408–421 23 2/13/2014 How to read ECG Hopefully you understand my Message Thank You 24