CVS 7.2 - ECG Abnormalities

Question 1

What causes ventricular ectopic beats?

Answer 1

Ventricular cells gain pacemaker activity

Question 2

What happens as a result of ventricular ectopic beats?

Answer 2

• Causes premature ventricular contraction

- Happens every other beat etc or in couplets, triplets etc

Question 3

How does a ventricular ectopic beat change the ECG wave?

Answer 3

Gives a wide QRS complex due to a slower depolarisation of the ventricle as the purkinje fibres aren’t being used

Question 4

What is atrial fibrillation?

Answer 4

A quivering and irregular heartbeat due to the muscles contracting in an uncoordinated way

Question 5

How does the ECG wave differ during atrial fibrillation?

Answer 5

• P waves are absent as there is no coordinated spread of depolarisation
• Has irregularly irregular fibrillation waves instead

Question 6

What causes atrial fibrillation?

Answer 6

• Many points in the atria behaving like pacemakers
• Overwhelms AVN (has a refractory period)
• No coordinated spread of depolarisation due to multiple depolarisation points

Question 7

Why is the QRS complex unchanged during atrial fibrillation?

Answer 7

QRS = in ventricles where activity is normal so still contracts

Question 8

What is ventricular fibrillation?

Answer 8

Uncoordinated contraction of the ventricular myocardium causing the muscle to quiver

Question 9

How does the ECG wave differ during ventricular fibrillation?

Answer 9

• Abnormal waves due to chaotic and fast ventricular depolarisation
• Looks like shit

Question 10

What happens as a result of ventricular fibrillation?

Answer 10

• No contraction
• No cardiac output, no pulse
• MI

Question 11

What is heart block?

Answer 11

A communication problem between the atria and ventricles

Question 12

How does the ECG wave differ during 1st degree heart block?

Answer 12

• Prolonged P wave (longer than 0.2s)
• Indicates that the AVN is holding the impulse for too long
• Still has ventricular contraction because electrical signals still reach the ventricles

Question 13

How does the ECG wave differ during mobitz 1 second degree heart block?

Answer 13

• Erratic P-R interval
• P-R elongates until QRS complex is dropped
• Indicates AVN is taking longer in the refractory period

Question 14

How does the ECG wave differ during mobitz 2 second degree heart block?

Answer 14

• Regular P-R interval
• Leads to dropped QRS complexes
• Indicates that excitation isn’t passing through the AV node/bundle of His = not all atrial contractions result in ventricular contractions

Question 15

What does mobitz 2 second degree heart block lead to?

Answer 15

• Third degree heart block

- Sudden death

Question 16

How does the ECG wave differ during third degree heart block?

Answer 16

• Inverted QRS complex
• Indicates no AVN conduction = no excitation to the ventricles
• No ventricular contraction but atria are fine

Question 17

Can the ventricles contract during third degree heart block? Why?

Answer 17

• Yes due to ectopic pacemaker cells

- Beats are usually slow

Question 18

What is a bundle branch block?

Answer 18

A delay/obstruction of the electrical excitation in the bundle branches/fascicles

Question 19

What change in the ECG wave is an early indicator of MI?

Answer 19

S-T elevation (indicates injured tissue)