LEARN ECG IN 5 MINUTES - A SIMPLE GUIDE TO ECG

Normal P waves 

Height less than 2.5 mm in lead II 

Width less than 0.11 s in lead II 

Abnormal P waves see in right atrial hypertrophy, left atrial hypertrophy, atrial premature beat, hyperkalaemia

Normal PR interval 

0.12 to 0.20 s (3 - 5 small squares) 

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) 

Long PR interval see first degree heart block and 'trifasicular' block 

Normal QRS complex 

Less than 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 

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 

cCauses 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.

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by

Akshaya Srikanth, Dr.Chandra Babu*

Pharm.D Internee, *Asso.Professor of Medicine

RIMS Medical college, Kadapa.