Question

impulse transmission through the conduction system of the heart generates electrical changes that may be detected on the surface of the body. what is a recording of these charges called.what is a defection wave? what is the significance of each of the following: p wave, P-R interval QRS waves S-T segment and T wave?

Answer 1

The recording of these charges is called an Electrocardiogram (ECG). ECG is a graphical representation of the electrical activity of the heart during a cardiac cycle.

A diagrammatic representation of a standard ECG is shown below:-

Arterial and ventricular depolarisation and repolarisation are represented on the ECG as a series of waves. These are the deflection waves.

Deflection waves are of two types- positive deflection waves and negative deflection waves.

• The first positive deflection wave is the P wave.
• The second wave is the QRS complex. Typically this complex has a series of 3 deflections. By convention, the first deflection in the complex if it is negative, is called a Q wave. The first positive deflection in the complex is called an R wave. A negative deflection after an R wave is called an S wave.
• Thereafter comes another positive deflection wave, the T wave.

Significance of the ECG waves:-

• P-wave -- The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to the contraction of both the atria.
• P-R interval-- It denotes the interval between the onset of atrial depolarisation to the onset of ventricular depolarisation.
• QRS complex- The QRS complex represents the depolarisation of the ventricles , which initiates the ventricular contraction. The contraction starts shortly after Q and marks the beginning of the systole.
• S-T segment-- The S-T segment represents the interval between ventricular depolarisation and repolarisation.
• T-wave-- The T-wave represents the return of the ventricles from excited to normal state (repolarisation). The end of the T-wave marks the end of systole.