How to read a 12-lead ECG:
examination sequence
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To determine heart rate and rhythm
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Normal if QRS complexes +ve in
leads I and II
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Tall P waves denote right atrial
enlargement (P pulmonale) and notched P waves denote left atrial enlargement
(P mitrale)
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Normal = 0.12-0.20 secs.
Prolongation denotes impaired AV nodal conduction. A short PR interval occurs
in Wolff-Parkinson-White syndrome (p. 565)
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If > 0.12 secs then ventricular
conduction is abnormal (left or right bundle branch block)
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Large QRS complexes occur in slim
young patients and in patients with left ventricular hypertrophy
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May signify previous myocardial
infarction (MI)
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ST elevation may signify MI,
pericarditis or left ventricular aneurysm; ST depression may signify
myocardial ischaemia or infarction)
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T-wave inversion has many causes,
including myocardial ischaemia or infarction, and electrolyte disturbances
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Normal < 0.42 secs. QT
prolongation may occur with congenital long QT syndrome, low K+,
Mg2+ or Ca2+, and some drugs (see Box 18.35, p. 568)
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Depolarisation towards electrode:
positive deflection
Depolarisation away from electrode: negative deflection
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Sensitivity: 10 mm = 1 mV
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Paper speed: 25 mm per second
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Each large (5 mm) square = 0.2 s
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Each small (1 mm) square = 0.04 s
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Heart rate = 1500/RR interval (mm)
(i.e. 300 ÷ number of large
squares between beats)
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How to report an ECG(Shortly) : 1.Rhythm,
2.Conduction Intervals. 3.Cardiac axis.
4. A description of QRS complex, 5.
A description of the ST segments and
T-wave.
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