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E.C.G.
- P wave - represents atrial depolarization -Duration: < 2.5mm (0.10 sec.).
- PR interval: 0.12-0.20 sec (3-5 squ.).
- Q wave: < 0.04 sec. Wide & < 2mm depth.
- QRS complex (represents ventricular depolarization): In limb leads amplitude should be 5mm or more. In chest lead 10mm or more. Duration of QRS Complex 0.10 sec.
- QT interval: In males – 0.42 sec.; In females – 0.43 sec.
- ST segment: Usually isoelectric. Planar elevation (> 1mm) or depression (> 0.5 mm). Usually implies infarction or ischaemia respectively.
- T wave (represents ventricular repolarisation): Abnormal if inverted in I, II & V4-V6. It is peaked in hyperkalaemia & flattened in hypokalaemia. T waves are termed tall when the height exceeds 10mm.
- U wave: Increase in U wave amplitude in hypokalaemia.
Abnormal E.C.G.
- P wave: Enlarged & notched (M-shaped) in Lt atrium enlargement, known as p-mitral. When p wave is tall and peak is called p-pulmonale.
- QRS amplitude: It is decreased also k/a (low voltage ECG) in emphysema, myxoedema, and pericardial effusion.
- Pathological Q wave: Seen in V1-V4 in anteroseptal MI. Seen in lead II, III, and AVF in inferior MI.
- ST segment elevation: Due to MI or acute pericarditis.
- QT interval: increased in hypokalaemia and hypocalcaemia.
- Osborn wave or ‘J’ wave: seen in hypothermia.
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