3. • QRS complex: ventricular depolarization
• QT interval: mechanical contraction of the ventricles
• T wave: ventricular repolarization- can indicate a recent
MI
• ST segment: isoelectric
4. The U wave
• The U wave is a small (0.5 mm) deflection immediately
following the T wave, usually in the same direction as the
T wave. It is best seen in leads V2 and V3.
Caused by:
• Delayed repolarisation of
Purkinje fibres
• Prolonged repolarisation of
mid-myocardial “M-cells”
• After-potentials resulting from
mechanical forces in the
ventricular wall
U waves are prominent if > 1-
2mm or 25% of the height of
the T wave.
Causes:
• Bradycardia
• Severe hypokalemia
5. • Depolarization from the endocardium > epicardium
• Repolarization from the epicardium > endocardium
• Q wave: 1st negitive after the p wave
• R : 1st positive after p wave
• S : 1st negative after r wave
