ECG

Question 1

What are the natural pacemakers of the heart

Answer 1

Sinus node (60-100bpm) - reliable pacemaker
Junctional pacemaker (in the distal conduction system) - 40-60 bpm, located in the atrioventricular junction. Quite reliable. Risk of it stopping completely is low.

Ventricular Pacemaker - 15-40 bpm. unreliable. might not fire off, leading to asystole

Question 2

QRS - narrow or broad

Answer 2

Narrow QRS: when junctional pacemakers are operating. as they can depolarise and fire off charge quickly. Utilises the hisperjinke system

Ventricular pacemaker - QRS is wider. as the his-purkinje system cannot be used to distribute charge, and it takes longer to spread cell-to-cell

Bundle branch block -> charge spreads down one side vis his-perkinje but has to move cell to cell on the other side

Question 3

Junctional rhythm

Answer 3

doesnt have a chance to kick in in normal circumstances

Question 4

What is second and third degree heart block

Answer 4

Mobitz type 2 and third degree heart block are typically due to disease below the AV node

Question 5

How can heart block be localised?

Question 6

Types of 2nd degree heart block

Answer 6

single non-conducted p waves (2:1 block)

Every 2nd p wave is not conducted to ventricle (high grade AV block)

Two or more p waves in a row are not conducted to ventricle

3 or more p waves in a row (high grade AV block 3:1 block)

Question 7

Mobitz BLock

Answer 7

due to disease at AV node - behaves in predictable manner
Single non-conducted p wave
Progressive PR prolongation before a blocked beat followed by a shorter PR interval for the next conducted beat
Av node tires out between pulses -> takes longer -> progressive PR elongation before a blocked beat followed by a shorter PR interval

Considered less dangerous due to -> complete heart block at the AV node -. there will be a junctional escape rhythm (unreliable)

Question 8

Mobitz II Block

Answer 8

Single non-conducted p wave
Disease is in the HIS-purkinje system - works in all or nothing fashion

Fixed PR interval before and after blocked beats
QRS can be wide

More dangerous -> complete heart block below atrioventricular junctional -> relying on ventricular escape rhythm which is unreliable

Question 9

2:1 block