THE NORMAL ELECTROCARDIOGRAM

Shahd AlAli

• QRS complex: ventricular depolarization• QT interval: mechanical contraction of the ventricles • T wave: ventricular repolarization- can indicate a recent

MI• ST segment: isoelectric

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

• 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

ECG leads

•3 bipolar leads ( I,II,III)•3 augmented leads (aVR, aVF, aVL)•6 precordial leads

ECG bipolar leads

Lead II shows the best picture of the heart

Augmented Limb leads Opposite

Precordial leads • V1-V6

• V1 : 4th intercostal space, right parasternal• V2 : 4th intercostal space, left parasternal• V3 : between V2, V4• V4 : 5th intercostal space, midclavicular line • V5 : anterior axillary • V6 : mid-axillary

Cardiac abnormalities • Lead I• Lead III, aVF

• We don’t diagnose it with Lead II

Normal ECG

Left Ventricular hypertrophy

Right Ventricular Hypertrophy