Topic 11: Cardiovascular System - Cardiac Cycle - Electrical Activity

Question 1

What are the 3 components to the cardiac cycle?

Answer 1

1. Electrical activity (ECG)
2. Mechanical Activity
3. Blood flow through heart

Question 2

What is electrical activity? (2)

Answer 2

small currents due to depol/hyperpol of heart move through salty fluids

Question 3

How is the potential difference of electrical activity measured on body surface of ECG? (2)

Answer 3

• using electrode pairs
• one pair = a lead

Question 4

How is electrical activity of the heart recorded? (2)

Answer 4

• recording is seen as waves
• waves are the sum of electrical activity of ALL myocardial cells (NOT AP)

Question 5

What occurs in the P wave of an ECG? (2)

Answer 5

• atrial depolarization
• followed by contraction

Question 6

What occurs in the QRS wave? (2)

Answer 6

• ventricular depolarization and contraction
• atrial repolarization (relaxation) masked by larger ventricular electrical event (larger muscle mass)

Question 7

What occurs in the T wave?

Answer 7

• ventricular repolarization followed by relaxation

Question 8

What are the three ECG intervals and what occurs in them?

Answer 8

1) P-Q = atria contracted, signals pass through AV node
2) S-T = ventricles contracted and atria relaxed
3) T-P = heart at rest

Question 9

What is tachycardia?

Answer 9

• resting HR more than 100bpm

Question 10

What is bradycardia?

Answer 10

• resting HR less than 60 bpm

Question 11

What is a heart block? (3)

Answer 11

• when conduction through AV node slowed
• get an increased P->Q interval
• therefore ventricles may not contract after each atrial contraction

Question 12

What occurs in a 3rd degree heart block? (3)

Answer 12

• no conduction through AV node
• atria fire at SA node rate (75 AP/min)
• ventricles at Bundle/Purkinje rate (30 AP/min)