Tutorial in Basic ECG for Medical Students

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This is the lecture notes that I have been giving to the medical students (2nd, 3rd, final year) for the last two years (updated 2008).

Transcript of Tutorial in Basic ECG for Medical Students

  • Tutorial in ECG Dr. Chew Keng Sheng Emergency Medicine Universiti Sains Malaysia http://emergencymedic.blogspot.com
  • The Basics
    • Standard calibration
      • 25 mm/s
      • 0.1 mV/mm
    • Electrical impulse that travels towards the electrode produces an upright (positive) deflection relative to the isoelectric baseline
  • Vertical and horizontal perspective of the ECG Leads Leads Anatomical II, III, aVF Inferior surface of heart V1 to V4 Anterior surface of heart I, aVL, V5, and V6 Lateral surface of heart V1 and aVR Right atrium
  • Location of MI and Affected Coronary Arteries Location of MI Affected Artery Lateral Left circumflex Anterior LAD Septum LAD Inferior RCA Posterior RCA Right Ventricle RCA
  • Right Sided & Posterior Chest Leads
  • Sinus Rhythm
    • The P wave is upright in leads I and II
    • Each P wave is usually followed by a Q
    • The heart rate is 6099 beats/min
  • Normal Sinus Rhythm
  • Instant Recognition of Axis Deviation
  • Cardiac Axis Normal Axis Right Axis deviation Left Axis Deviation Lead I Positive Negative Positive Lead II Positive Positive Negative Lead III Positive Positive Negative
  • Calculating Cardiac Axis
  • P wave
    • Always positive in lead I and II in NSR
    • Always negative in lead aVR in NSR
    • < 3 small squares in duration
    • < 2.5 small squares in amplitude
    • Commonly biphasic in lead V1
    • Best seen in leads II
  • Right Atrial Enlargement
    • Tall (> 2.5 mm), pointed P waves (P pulmonale
  • Left Atrial Enlargement
    • Prominent terminal P negativity (biphasic) in lead V1 (i.e., "P-terminal force") duration >0.04s, depth >1 mm
    • Notched/bifid (M shaped) P wave (P mitrale) in limb leads with the inter-peak duration > 0.04s (1 mm)
    Left Atrial Enlargement
  • P Pulmonale and P Mitrale
  • RAH and LAH Right Atrial Hypertrophy Left Atrial Hypertrophy
  • Short PR Interval
    • WPW (Wolff-Parkinson-White) Syndrome
    • Accessory pathway (Bundle of Kent) allows early activation of the ventricle (delta wave and short PR interval)
  • QRS Complexes
    • Nonpathological Q waves are often present in leads I, III, aVL, V5, and V6
    • The R wave in lead V6 is smaller than the R wave in V5
    • The depth of the S wave, generally, should not exceed 30 mm
    • Pathological Q wave > 2mm deep and > 1mm wide or > 25% amplitude of the subsequent R wave
  • QRS In Hypertrophy
  • RVH Changes
    • A tall positive (R) wave
      • instead of the rS complex normally seen in lead V1
      • an R wave exceeding the S wave in lead V1
      • in adults the normal R wave in lead V1 is generally smaller than the S wave in that lead
    • Right axis deviation (RAD)
    • Right ventricular "strain" T wave inversions
  • Conditions with Tall R in V1
  • Right Atrial and Ventricular Hypertrophy
  • COPD
  • Left Ventricular Hypertrophy
    • Sokolow & Lyon Criteria (Am Heart J, 1949;37:161)
      • S in V1+ R in V5 or V6 > 35 mm
    • An R wave of 11 to 13 mm (1.1 to 1.3 mV) or more in lead aVL is another sign of LVH
    • Others: Cornell criteria (Circulation, 1987;3: 565-72)
      • SV3 + R avl > 28 mm in men
      • SV3 + R avl > 20 mm in women
  • Hypertrophy Strain Pattern vs ACS
  • ST Segment
    • Normal ST Segment is flat (isoelectric)
      • Same level with subsequent PR segment
    • Elevation or depression of ST segment by 1 mm or more, measured at J point IS ABNORMAL
    • J (Junction) point is the point between QRS and ST segment
  • Variable Shapes Of ST Segment Elevations in AMI Goldberger AL. Goldberger: Clinical Electrocardiography: A Simplified Approach. 7th ed: Mosby Elsevier; 2006.
  • T wave
    • The normal T wave is asymmetrical, the first half having a more gradual slope than the second half
    • The T wave should generally be at least 1/8 but less than 2/3 of the amplitude of the corresponding R wave
    • T wave amplitude rarely exceeds 10 mm
    • Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted.
  • T wave
    • As a rule, the T wave follows the direction of the main QRS deflection. Thus when the main QRS deflection is positive (upright), the T wave is normally positive.
    • Other rules
      • The normal T wave is always negative in lead aVr but positive in lead II.
      • Left-sided chest leads such as V4 to V6 normally always show a positive T wave.
  • QT interval
    • QT interval decreases when heart rate increases
    • A general guide to the upper limit of QT interval. For HR = 70 bpm, QT