Module 2 - Electrocardiograms

Question 1

Electrocardiography:

Answer 1

• In hospitals a machine called a cardiac monitor is used to detect and record the waves of excitation as they travel through the heart muscle during the cardiac cycle.
• Electrodes are placed on the skin over opposite sides of the heart, and a recording is made of the electrical potentials.
• The result is a graph of voltage against time. It is called an electrocardiogram or ECG.

Question 2

P wave…

Answer 2

• Depolarisation of atria in response to SA node triggering.
• P wave corresponds to the wave of excitation passing through the atrial walls.
• Atrial systole.

Question 3

PR interval…

Answer 3

-Delay of AV node to allow filling of ventricles.

Question 4

QRS complex…

Answer 4

• Depolarisation of ventricles, triggers main pumping contractions.
• QRS complex corresponds to the wave of excitation passing through the ventricular walls.
• Ventricular systole.

Question 5

ST segment…

Answer 5

-Beginning of ventricular repolarisation should be flat.

Question 6

T wave…

Answer 6

• Ventricular repolarisation.
• T wave corresponds to the recovery of ventricular walls.
• Ventricular diastole.

Question 7

Suggest the physiological reason for the period of electrical recovery experienced each cycle? (T wave)

Answer 7

• During a period of electrical recovery, the heart muscle cannot contract.
• This ensures that the heart has an enforced rest and will not fatigue, nor accumulate lactic acid.

Question 8

Heart attack: (myocardial infarction)

Answer 8

• Occurs when blood supply to part of heart muscle is partly or totally blocked.
• Cardiac muscles in that region are deprived of oxygen and stop contracting.
• Elevated S-T portion of the ECG wave confirms heart attack.

Question 9

Atrial fibrillation:

Answer 9

• Wall of atria contract with an abnormal rhythm.
• No distinct P wave.
• This prevents ventricles filling efficiently.
• Inconsistent blood supply.

Question 10

Ventricular fibrillation:

Answer 10

• No regular pattern.
• Ventricles unable to contract.
• No blood circulation.
• Cause of cardiac arrest and sudden cardiac death.

Question 11

Tachycardia:

Answer 11

• High resting heart (above 100 bpm).
• ECG shows little gap between the T wave of one cycle and P wave of the next.
• Less time for atria and ventricle to fill so less blood is forced out in each beat.

Question 12

Bradycardia:

Answer 12

• Very slow resting heart rate (40-60 bpm).
• Gap between each peak in the trace is very long, causing a long gap between the T wave and the next P wave.
• Can be sign of very active/healthy person or an inactive SAN.
• Can cause insufficient blood flow to organs.