Electrocardiogaram - ECG EKG
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  • ECG GRID  — The ECG is a plot of voltage on the vertical axis against time on the horizontal axis. The electrodes are connected to a galvanometer that records a potential difference. The needle (or pen) of the ECG is deflected a given distance depending upon the voltage measured.
  • The ECG waves are recorded on special graph paper that is divided into 1 mm 2 grid-like boxes. The ECG paper speed is ordinarily 25 mm/sec. As a result, each 1 mm (small) horizontal box corresponds to 0.04 second (40 ms), with heavier lines forming larger boxes that include five small boxes and hence represent 0.20 sec (200 ms) intervals. On occasion, the paper speed is increased to 50 mm/sec to better define waveforms. In this situation there are only six leads per sheet of paper. Each large box is therefore only 0.10 sec and each small box is only 0.02 sec. In addition, the heart rate appears to be one-half of what is recorded at 25 mm/sec paper speed, and all of the ECG intervals are twice as long as normal.Vertically, the ECG graph measures the height (amplitude) of a given wave or deflection, as 10 mm (10 small boxes) equals 1 mV with standard calibration. On occasion, particularly when the waveforms are small, double standard is used (20 mm equals 1 mv). When the wave forms are very large, half standard may be used (5 mm equals 1 mv). Paper speed and voltage are usually printed on the bottom of the ECG.
  • The normal electrocardiogram is composed of several different waveforms that represent electrical events during each cardiac cycle in various parts of the hear. ECG waves are labeled alphabetically starting with the P wave, followed by the QRS complex and the ST-T-U complex (ST segment, T wave, and U wave). The J point is the junction between the end of the QRS and the beginning of the ST segment.


  • 1. Electrocardiogram (ECG) Dr. Fuad Farooq Consultant Cardiologist
  • 2. Conduction System of the Heart
  • 3. Introduction • Electrocardiogram (ECG) retains its central role – even though there continues to be new technologies developed for the diagnostic evaluation of patients with cardiovascular disease • The most important test for interpretation of the cardiac rhythm, conduction system abnormalities and for the detection of myocardial ischemia • Of great value in the evaluation of other types of cardiac abnormalities including valvular heart disease, cardiomyopathy, pericarditis, and hypertensive disease • Finally, the ECG can be used to monitor drug treatment (specifically antiarrhythmic therapy) and to detect metabolic disturbances
  • 4. A systematic approach to interpretation of the ECG is important in order to avoid overlooking important abnormalities
  • 5. Introduction • Graphical record of electric potentials generated by myocytes during each cardiac cycle • Detected on the body surface using electrodes attached to extremities and chest wall • Amplified by the electrocardiograph machine and displayed on special graph paper
  • 6. Electrodes and Leads • Electrodes – Sites at which an electrical potential is measured • ECG leads – Record the difference in potentials between two electrodes
  • 7. Electrodes Standard surface electrodes – Right and left arm – Right and left leg – Six precordial electrodes
  • 8. Leads • Record differences in electrical potentials • Six extremity (limb) leads and six chest (precordial) leads • Two types – Bipolar – between two surface electrodes • Limb Leads I, II and III are bipolar leads – Unipolar – between a surface electrode and the central terminal of Wilson • All leads except the bipolar limb (aVR, aVL, aVF, V1, V2, V3, V4, V5, and V6) leads are unipolar
  • 9. Leads Orientation – Limb Leads • Lead I records potential difference between left arm (the +ve pole) and right arm (-ve pole) • Lead II records between left leg (+ve) and right arm (-ve) • Lead III records between left leg (+ve) and left arm (-ve) • Lead aVR records right arm potentials • Lead aVL records left arm potentials • Lead aVF records left leg (foot) potentials
  • 10. Leads Orientation – Precordial leads • The six chest/precordial leads – represent the voltage difference between the central terminal and electrodes placed in the following positions – – – – – – V1 — 4th intercostal space (ICS), just to the right of the sternum V2 — 4th ICS, just to the left of the sternum V3 — midway between V2 and V4 V4 — 5th ICS in the mid-clavicular line V5 — anterior axillary line, same level as V4 V6 — mid-axillary line, same level as V4 and V5
  • 11. Leads • 12-lead ECG provides spatial information about the heart's electrical activity in 3 approximately orthogonal directions: – Right ⇔ Left – Superior ⇔ Inferior – Anterior ⇔ Posterior
  • 12. I and AVL V3 & v4 V1 & v2 V5 & v6 II, III and AVF Where the positive electrode is positioned, determines what part of the heart is seen!
  • 13. Electrophysiology • If an electrode is placed so that wave of depolarization spreads toward the recording electrode, the ECG records a positive (upward) deflection. • If wave of depolarization spreads away from recording electrode, a negative (downward) deflection occurs.
  • 14. Electrophysiology
  • 15. Electrophysiology
  • 16. Electrophysiology
  • 17. ECG Grid Voltage/amplitude in mvolt Time in msec
  • 18. Standardization Paper speed = 25mm/sec
  • 19. ECG Waves
  • 20. Genesis of Normal ECG
  • 21. Genesis of Normal ECG • P wave – wave preceded by QRS complex • Q wave – first downward deflection after P wave – Signals start of ventricular depolarization • R wave is positive deflection after Q wave • S wave is negative deflection preceded by Q or R waves • T wave follows QRS
  • 22. Intervals and Segments • Segments – ST segment – TP segment • Intervals – PR interval – QRS interval – QT interval – RR interval
  • 23. ECG Interpretation – Stepwise Approach A systematic approach to interpreting an ECG is essential for correct diagnosis Step 1: Rate Is the rate between 60 and 100? Rates less than 60 is bradycardia and greater than 100 is tachycardia Step 2: Rhythm Are P waves present? Is there a P wave before every QRS complex and a QRS complex after every P wave? Are the P waves and QRS complexes regular? Is the PR interval constant? Step 3: Axis Is there left or right axis deviation?
  • 24. ECG Interpretation – Stepwise Approach Step 4: Intervals What is the PR interval? – Short PR interval is suggestive of Wolff-Parkinson-White (WPW) syndrome – Long PR intervals are usually seen in first degree AV block What is the QRS interval? – Long QRS intervals represent a bundle branch block, ventricular preexcitation, ventricular pacing, or ventricular tachycardia What is the QT interval? – Short and long QT intervals may be present
  • 25. ECG Interpretation – Stepwise Approach Step 5: P wave – What is the shape and axis of the P wave? – The P wave morphology should be examined to determine if the rhythm is sinus or from another atrial location – Amplitude and duration should also be analyzed to determine left and right atrial enlargement
  • 26. ECG Interpretation – Stepwise Approach Step 6: QRS complex Is the QRS wide? – If so, examination of the morphology can determine if there is left or right bundle branch block – Increased voltage may indicate left or right ventricular hypertrophy – Are Q waves present? – suggestive of infarction
  • 27. ECG Interpretation – Stepwise Approach Step 7: ST segment-T wave – Is there ST elevation or depression? – Are the T waves inverted? – Abnormalities of the ST segment or T wave may represent myocardial ischemia or infarction
  • 28. ECG Interpretation – Stepwise Approach Step 8: Overall interpretation – Only after the prior steps have been completed should an overall interpretation and possible diagnoses be determined – This ensures assimilation of all information in the ECG and that no detail will be overlooked
  • 29. Step 1 - Heart Rate Heart rate – Both atrial and ventricular rates - if different – Normal heart rate  60-100 beats per minute >100 beats/min = tachycardia <60 beats/min = Bradycardia Methods of measurement – 1500 divided by No. of small boxes in Inter R-R interval – 300 divided by No. of big boxes in Inter R-R interval – What if heart rate irregular?
  • 30. Step 1 – Heart Rate
  • 31. Step 2 – Rhythm Analysis Interpreting the rhythm of the ECG is sometimes difficult Locate the P wave – The most important and first step in rhythm interpretation is the identification of P waves and an analysis of their morphology – Are P waves visible? Each lead needs to be examined for P waves – What is the rate of the P waves (i.e., the PP interval)? If the rate is less than 60, then a bradycardia and if the atrial or P wave rate is over 100, then there is tachycardia – What is the morphology and axis of the P waves? The normal sinus P wave is generally upright in leads I, II, aVF, and V4-V6. It will be negative in lead aVR
  • 32. Step 2 – Rhythm Analysis Establish the relationship between P waves and the QRS complex • To determine the relationship between the P waves and the QRS complexes, addressing the following questions: – Are the P waves associated with QRS complexes in a 1:1 fashion? • If not, are there more or less P waves than QRS complexes and what are the atrial and ventricular rates? – Do the P waves precede each QRS complex? – What is the PR interval, and is this interval fixed?
  • 33. Step 2 – Rhythm Analysis Analyze the QRS morphology • If the QRS complexes are of normal duration (<0.12 sec) and morphology, then the rhythm is supraventricular • It is essential to analyze the QRS in all 12 leads to be sure that it is normal • If the QRS is wide (i.e., >0.12 sec), then the rhythm is either supraventricular with aberrant conduction, pre-excitation, or ventricular pacing, or it is of ventricular origin – take the widest QRS in the 12 lead ECG
  • 34. Step 2 – Rhythm Analysis • State the basic rhythm e.g., "normal sinus rhythm", "atrial fibrillation", etc. • Identify additional rhythm e.g., "PVC's", "PAC's", etc. events if present • Remember that arrhythmias may originate in the atria, AV junction, and ventricles
  • 35. Step 3 – Axis
  • 36. Step 4 - Intervals PR Interval • PR interval includes the P wave as well as the PR segment • Measured from the beginning of the P wave to the first part of the QRS complex (which may be Q wave or R wave) • Includes time for atrial depolarization (the P wave) and conduction through the AV node and the His-Purkinje system (which constitute the PR segment) • The length of the PR interval changes with heart rate, but is normally 0.12 to 0.20 sec (three to five small boxes)
  • 37. Step 4 - Intervals QT interval • Consists of the QRS complex, the ST segment, and T wave • Primarily a measure of ventricular repolarization • Depends upon the heart rate – Shorter at faster heart rates and longer when the rate is slower – Need to be corrected for heart rate (QTc)
  • 38. Step 5 – P wave • The P wave represents atrial depolarization • The normal sinus P wave demonstrates right followed by left atrial depolarization and is an initial low amplitude positive deflection preceding the QRS complex • The duration is generally <0.12 sec (three small boxes) and the amplitude <0.25 mv (2.5 small boxes) • Since right atrial depolarization precedes that of the left atrium (as the sinus node is in the high right atrium), the P wave is often notched in the limb leads and usually biphasic in lead V1 – The initial positive deflection in V1 is due to right atrial depolarization that is directed anteriorly, while the second negative deflection represents left atrial depolarization that is directed posteriorly.
  • 39. Step 6 – QRS complex QRS complex • Represents the time for ventricular depolarization • If the initial deflection is negative, it is termed a Q wave • The first positive deflection of the QRS complex is called the R wave – represents depolarization of the left ventricular myocardium • The negative deflection following the R wave is the S wave – represents terminal depolarization of the high lateral wall • If there is a second positive deflection it is known as an R’
  • 40. • Lower case letters (q, r, or s) are used for relatively small amplitude waves of less than 0.5 mV (less than 5 mm with standard calibration) • An entirely negative QRS complex is called a QS wave • The entire QRS duration normally lasts for 0.06 to 0.10 seconds (1½ to 2½ small boxes) and is not influenced by heart rate • The R wave should progress in size across the precordial leads V1V6. Normally there is a small R wave in lead V1 with a deep S wave. The R wave amplitude should increase in size until V4-V6, due to more left ventricular forces being seen, while the S wave becomes less deep. This is termed R wave progression across the precordium
  • 41. Step 7 – ST Segment ST segment • Occurs after ventricular depolarization has ended and before repolarization has begun • Time of electrocardiographic silence • Initial part of the ST segment is termed the J point • The ST segment is usually isoelectric and has a slight upward concavity • Depressed (below the isoelectric line) in Myocardial ischemia and infarction • Elevated (above the isoelectric line) acute myocardial infarction and pericarditis
  • 42. Step 7 –T wave • T wave represents the period of ventricular repolarization • The rate of repolarization is slower than depolarization, the T wave is broad, has a slow upstroke, and rapidly returns to the isoelectric line following its peak (i.e., slow upstroke, rapid downstroke) – Thus, the T wave is asymmetric and the amplitude is variable – In addition, the T wave is usually smooth up and down – If there is any irregularity on the T wave (bump, notch, rippled, nipple, etc) a superimposed P wave should be considered
  • 43. ECG Interpretation • Conclusion of the above analyses • Interpret the ECG as "Normal" or "Abnormal“ • Occasionally the term "borderline" is used if unsure about the significance of certain findings or for minor changes • List all abnormalities
  • 44. Summary • • • • • • • • A systematic approach to interpretation of the ECG is critically important Rate — Is the rate between 60 and 100? Rhythm — Is it normal sinus or other? Axis — Is there axis deviation? Intervals — Are all intervals normal? P wave — What is its height, width, and axis? QRS complex — Are there pathologic Q waves, bundle branch block, or chamber hypertrophy? ST-T waves — Is it isoelectric, elevated, or depressed relative to the TP segment? Overall interpretation — What is the diagnosis?
  • 45. Myocardial Ischemia and Infarction
  • 46. ECG Changes : Ischemia • • • • T-wave inversion ( flipped T) ST segment depression T wave flattening Biphasic T-waves Baseline
  • 47. ECG Changes : Injury • ST segment elevation of greater than 1mm in at least 2 contiguous leads • Heightened or peaked T waves • Directly related to portions of myocardium rendered electrically inactive Baseline
  • 48. ECG Changes : Infarct Infarct ECG Changes: • Significant Q-wave where none previously existed – Why? • Impulse traveling away from the positive lead • Necrotic tissue is electrically dead • No Q-wave in Subendocardial infarcts – Why? • Not full thickness dead tissue • But will see a ST depression • Often a precursor to full thickness MI • Criteria – Depth of Q wave should be 25% the height of the R wave – Width of Q wave is 0.04 secs – Diminished height of the R wave
  • 49. Evolving MI and Hallmark of AMI Q wave ST Elevation 1 year T wave inversion
  • 50. A Normal 12 Lead ECG A Normal 12 Lead ECG
  • 51. Anterior Myocardial Infarction Myocardial Infarction Anterior – Anterior infarct with ST elevation – Left Anterior Descending Artery (LAD) – V1 and V2 may also indicate septal involvement which extends from front to the back of the heart along the septum
  • 52. Anterior Myocardial Infarction Anterior MI
  • 53. Inferior Myocardial Infarction – Inferior Infarct with ST elevations – Right Coronary Artery (RCA)
  • 54. Inferior Myocardial Infarction Inferior MI
  • 55. Lateral Myocardial Infaction – Lateral Infarct with ST elevations – Left Circumflex Artery – Rarely by itself – Usually in combo
  • 56. Lateral Myocardial Infaction Lateral MI
  • 57. Posterior Myocardial Infarction – Posterior Infarct with ST Depressions and/ tall R wave in V1 and V2 – RCA and/or LCX Artery – Rarely by itself usually in combo
  • 58. Posterior Posterior MI Myocardial Infarction
  • 59. Putting it All Together
  • 60. Non ST Elevation Myocardial Infarction • They are not transmural • Look for diffuse or localized changes and non Q wave abnormalities – T-wave inversions – ST segment depression
  • 61. Non ST Elevation Myocardial Infarction
  • 62. Non ST Elevation Myocardial Infarction
  • 63. Any Questions?