ECG

Rate

  • 300/number of large squares between two complexes
    • If irregular rhythm
      • count the number of complexes on the rhythm strip (each strip is 10 seconds long) then multiply the number of complexes by 6 (giving you the average number of complexes in one minute)
      • calculate ventricular and atrial rate separately

Rhythm

  • Look for irregularly irregular rhythms

Axis

  • Normal axis
    • II most positive lead
  • Left axis deviation
    • I positive
    • II negative
    • III negative
  • Right axis deviation
    • I negative
    • III positive

P-waves

  • Are P-waves present?
  • Is each P-wave followed by a QRS complex
  • Check P-wave duration, shape

P-R interval

  • First degree heart block – fixed prolonged PR interval
  • Second degree heart block
    • Mobitz type 1 – progressively prolonged PR interval followed by dropped QRS beat
    • Mobitz type 2 – fixed prolonged PR interval with dropped beats e.g. 2:1, 3:1
  • Third degree heart block (complete heart block) – P waves and QRS are unrelated
  • Wolff Parkinson White – if shortened PR interval (which is usually physiological) associated with delta wave and tachyarrhythmia

QRS complex

  • Duration/width
  • Narrow
  • Broad – consider ventricular ectopics, bundle branch block, VT/VF
  • Tall – consider LVH

Q waves

  • Only of relevance if in an entire territory for evidence of previous MI

QT interval

  • QT interval = 9-11 small squares (0.36 – 0.44 seconds)

J point segment

  • The point where the S wave joins the ST segment
  • Can be elevated in young patients (i.e. high take off / benign early repolarisation) – typically young patients, in multiple ECG territories

ST segment

  • Significant elevation
    • >1 small square in two or more limb leads
    • >2 small squares in two or more chest leads
  • Significant depression
    • > half small square in two or more contiguous leads

T waves

  • Tall – hyperkalaemia, hyperacute STEMI
    • > 5 small squares in the limb leads
      • and
    • > 10 small squares in the chest laeds
  • Inverted
    • Physiological
      • lead III and V1
    • Pathology – ischaemia, bundle branch block, PE, LVH, hypertrophic cardiomyopathy, general illness
      • Other leads – comment on the distribution
  • Biphasic or flattened – ischaemia, hypokalaemia

U waves

  • > half a square deflection after the T wave – best seen in V2 or V3
  • Uncommon finding
  • Electrolyte imbalanes, hypothermia, antiarrhythmics (digoxin, amiodarone)

 

Notes:

  • Avoid using the computer generated diagnosis – simple things like AF can be missed
  • One small square (1mm square) = 0.04 seconds
  • Normal durations
    • P wave = 2-3 small squares (0.8 – 0.11 seconds)
    • PR interval = 3-5 small squares (0.12 – 0.20 seconds)
    • QRS complex = 1.5 – 2.5 small squares (0.06 – 0.11 seconds)
    • QT interval = 9-11 small squares (0.36 – 0.44 seconds)
  • ECG territories
    • II, III, aVF – inferior
    • V1, V2 – septal
    • V3, V4 – anterior
    • I, aVL, V5, V6, – lateral