Normal adult 12-lead
ECG

The diagnosis of the normal
electrocardiogram is made by
excluding any recognised
abnormality. It's description is
therefore quite lengthy.

Normal sinus rhythm
*each P wave is followed by a QRS
*P waves normal for the subject
*P wave rate 60 - 100 bpm with
<10% variation
*rate <60 = sinus bradycardia
*rate >100 = sinus tachycardia
*variation >10% = sinus arrhythmia

Normal QRS axis
*normal P waves
height < 2.5 mm in lead II
width < 0.11 s in lead II
for abnormal P waves see right
atrial hypertrophy , left atrial
hypertrophy , atrial premature
beat , hyperkalaemia

Normal PR interval
0.12 to 0.20 s (3 - 5 small squares)
for short PR segment consider
Wolff-Parkinson-White syndrome
or Lown-Ganong-Levine syndrome
(other causes - Duchenne
muscular dystrophy, type II
glycogen storage disease
(Pompe's), HOCM)
for long PR interval see first
degree heart block and
'trifasicular' block

Normal QRS complex
< 0.12 s duration (3 small squares)
for abnormally wide QRS consider
right or left bundle branch block,
ventricular rhythm,
hyperkalaemia, etc.
no pathological Q waves
no evidence of left or right
ventricular hypertrophy

Normal QT interval
Calculate the corrected QT
interval (QTc) by dividing the QT
interval by the square root of the
preceeding R - R interval. Normal
= 0.42 s.

*Causes of long QT interval
myocardial infarction,
myocarditis, diffuse myocardial
disease
hypocalcaemia, hypothyrodism
subarachnoid haemorrhage,
intracerebral haemorrhage
drugs (e.g. sotalol, amiodarone)
hereditary
Romano Ward syndrome
(autosomal dominant)
Jervill + Lange Nielson syndrome
(autosomal recessive) associated
with sensorineural deafness

Normal ST segment
no elevation or depression
causes of elevation include acute
MI (e.g. anterior, inferior ), left
bundle branch block , normal
variants (e.g. athletic heart,
Edeiken pattern, high-take off),
acute pericarditis
causes of depression include
myocardial ischaemia, digoxin
effect , ventricular hypertrophy,
acute posterior MI , pulmonary
embolus , left bundle branch block

Normal T wave
causes of tall T waves include
hyperkalaemia, hyperacute
myocardial infarction and left
bundle branch block
causes of small, flattened or
inverted T waves are numerous
and include ischaemia, age, race,
hyperventilation, anxiety,
drinking iced water, LVH, drugs
(e.g. digoxin), pericarditis, PE,
intraventricular conduction delay
(e.g. RBBB)and electrolyte
disturbance.
*Normal U wave