P Wave

•Positive wave

• Shape is up rounded deflection

• Cause: Depolarisation of atrial musculature.

• Duration: 0.1 sec

• Intensity: 0.1-0.12 mV

• Represents functional activity of atria.

Clinical Aspects:

1 Mitral stenosis: left atrium is hypertrophied and P wave is larger and prolonged.

2 Tricuspid stenosis: Right atrium is hypertrophied and P wave is taller but there is no change (normal) duration.

3 Atrial fibrillation: P wave disappears and is replaced by fine irregular oscillations.

4 Ectopic Pacemaker: (reverse) The impulses are sent from AV node to SA node.

QRS COMPLEX

• Q wave is often absent.

• Cause: Ventricular Depolarisation.

• Duration: 0.08 sec ( less than P wave)

• Intensity: 0.1 mV to 0.2 mV ( amplitude is more)

• R wave is 1 mV

• S wave is 0.4 mV

• Total Intensity is 1.5 mV to 1.6 mV

Clinical Aspects

1 Deep Q wave: more than 0.2 mV. This is seen Myocardial Infarction.

2 Tall R wave: more than 0.1 mV. This is seen in ventricular hypertrophy.

3 Low Voltage QRS Complex:  This is related to hormones and pericardial fluid. Hypothyroidism and Pericardial fluid around the heart.

4 QRS COMPLEX: Prolonged in bundle branch block.

T wave 

• Cause: Ventricular Repolarization.

• It’s positive wave because the direction of Ventricular repolarization is opposite to depolarization.

• Duration: 0.27

• Intensity: 0.3 mV

Clinical Aspects

1 Flattened T wave: old age.

2 Height increases: during exercise.

3 Inverted T wave: this is seen in myocardial infarction.

4 Tall and peaked T wave:  Hyperkalaemia.

U wave

• Positive round wave

• Repolarization of papillary muscled

• Duration: 0.08 sec

• Intensity: 0.2 mV

• Rarely seen

• Prominent in hypokalaemia.

P R interval 

• Onset of P wave to onset of QRS complex (PQ interval)

• Represents AV conduction time.

• Duration: 0.12 to 0.21 sec

Clinical Aspects

1 Prolonged PR interval: AV conduction block.

J Point 

• The meeting point of QRS complex with ST segment.

• It represents the end of Depolarisation and beginning of repolarization.

• At this point, no current flows around heart.

– Written by Anisha Valli