Heart

Question 1

What happens when the heart is stimulated by an electrical signal?

Answer 1

It contracts and then relaxes, enabling the heart to pump blood around the body

Question 2

Where do the signals first spread?

Answer 2

Through all the nerve cells of the atria, causing the atria to contract, forcing blood into ventricles.

Question 3

Where do the signals go after the atria?

Answer 3

They pass to the atrioventricular node, which delays the pulse for about 0.1 second before passing it on to the nerve cells of ventricles

Question 4

What do the nerve cells of the ventricles cause the ventricles to do when the signal is passed on to them?

Answer 4

They cause the ventricles to contract and blood is pumped through two valves to the longs and body. As this happens, the nerve cells of the atria relax, which is followed by the relaxation of the ventricles.
This is one beat of the heart

Question 5

What does the ECG show?

Answer 5

It is a plot of the potential difference between electrodes against time.

Question 6

What are ECGs used for?

Answer 6

To find out the condition of the heart being examined

Question 7

What does the P wave correspond to?

Answer 7

The contraction of the atria

Question 8

What does the QRS wave correspond to?

Answer 8

This comes about 0.2 seconds after the P wave and corresponds to the contraction of the ventricles. This signal is much greater than the P wave and completely swamps the trace produced by the relaxation of the atria

Question 9

What does the T wave correspond to?

Answer 9

This comes about 0.2 seconds after the QRS wave and corresponds to the relaxation of the ventricles

Question 10

How do you obtain an ECG trace?

Answer 10

• Electrodes are placed on the chest and the limbs

- The signal is heavily attenuated by the body and needs to be amplified using a high impedance amplifier

Question 11

How is electrical resistance reduced when obtaining an ECG trace?

Answer 11

• Hairs and dead skin cells at the point of contact are removed
• A conductive gel is used
• The electrodes are securely attached

Question 12

How can unwanted signals be reduced when obtaining an ECG trace?

Answer 12

• The patient should remain relaxed and still during the procedure
• The leads should be shielded from any possible interference from a.c. sources in the area