< ECG

Calibration

  • paper speed is normally 25mm/second
    • therefore each 1mm box in the x axis = 0.04sec
  • a 1mV test pulse is normally over 10 mm
    • therefore each 1mm box in the y axis = 0.1 mV

Rhythm

  • P wave upright in I, II, AVF
  • PR interval > 0.12
  • P wave for every QRS
  • QRS for every P wave

Rate

  • 300,150,100,75, 60, 50 rule
  • If rhythm is not normal count the number of QRS complexes in 25 big boxes (5 seconds) and multiply by 12
  • (an alternative method is to count the number of QRS complexes in a 10 second duration and multiply by 6)
  • tachycardia >100bpm
  • bradycardia <60bpm

Axis

  • QRS upright in I and aVF
  • If not upright in aVF look @ II
    • If upright then axis is normal
    • If not then there is left axis deviation

Intervals

  • PR 0.12-0.20 (3-5 squares)
  • QRS < 0.10 (2.5 square)
  • QT <0.44 (11 squares)

Atrial enlargement

  • Right atrium - lead II - p wave wave's initial component is enlarged, taller 2.5mm
  • Left atrium - Lead V1 - p wave downward deflection of terminal component

Ventricular hypertrophy

  • Right ventrical - tall R waves in V1 and V2, deep S in V6
  • Left ventrical - tall R wave in V6, deep S in V1, plus one of
    • R in V5/6 > 26mm
    • S in V1 or 2 + R in V5 or V6 > 35 mm
    • R+S in any chest lead > 45mm
    • R in aVL > 11mm
    • R in I > 15mm

Bundle Branch Blocks

note: normally depolarization of the ventricular septum is stimulated by a branch of the left bundle

incomplete block: QRS 0.10-0.12 (2.5-3 squares) complete block: QRS > 0.12 (3)

RBBB

  • R' in V1
  • S in V6

LBBB

  • absent normal R in V1 and Q in V6 (initial depolarization directed to LV)
  • terminal R' in V6 and downward deflection in V1

LAFB

  • Q wave in I, aVL
  • initial R wave in II, III, aVF

LPFB

  • Q in II, III, aVF
  • initial R wave in I, aVL

Q waves

  • may be normal in V6 and aVL
  • pathologic > 0.04, depth >25% QRS height

Inferior: II, III, aVF RCA Anteroseptal: V1-V2 LAD Anteroapical: V3-V4 LAD (distal) Aterolateral: V5-V6, I, aVL CFx Posterior: V1-V2 (tall R, no Q) RCA


MI

  • ST elevation - returns to baseline in days
  • T wave inversion - weeks to months
  • Q wave - persists
  • if ST remains elevated - fibrotic scar (ventricular anurysm) developed

Pericarditis

  • diffuse ST elevation
  • PR depression

Hyperkalemia

  • tall "peaked" T waves
  • flat p
  • wide QRS

Hypokalemia

  • U wave
  • ST depression
  • flat T

Hypercalcemia

  • decreased QT interval

Hypocalcemia

  • increased QT interval

Other OSCE modules

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