Lecture 7: ECG

Question 1

What is a syncytium?

Answer 1

One large cell having many nuclei that are not separated by cell membrane

Question 2

What is a functional syncytium?

Answer 2

Many cells functioning as one

Question 3

What are the 3 types of cardiac myocyte cell?

Answer 3

Pacemaker cells
Conducting cells
Contractile cells

Question 4

How quickly do contractile cells propagate the signal?

Answer 4

0.3-0.5m/s

Question 5

How quickly do conducting cells (purkinje fibres) propagate the signal?

Answer 5

Up to 5m/s

Question 6

How quickly does the AV node propagate the signal?

Answer 6

0.05m/s

Question 7

How quickly do internal bundles propagate the signal?

Answer 7

1m/s

Question 8

What are the 4 internal bundles?

Answer 8

Anterior (to AVN)
Middle (to AVN)
Posterior (to AVN)
Bachmanns (to LA)

Question 9

How long is the delay of excitation from atria to ventricles by AV node?

Answer 9

0.1-0.2s

Question 10

What is a lead on an ECG?

Answer 10

A configuration of electrodes

Question 11

Describe lead 2.

Answer 11

Positive electrode on left leg, negative electrode on right arm and ground electrode on right leg

Question 12

What are the 12 standard leads?

Answer 12

3 Bipolar
3 Augmented
6 Precordial

Question 13

What is shown by the QRS complex?

Answer 13

Transmission of depolarisation through the ventricular myocardium

Question 14

What is shown by P-wave?

Answer 14

Depolarisation of the atria

Question 15

What is shown by PR segment?

Answer 15

Delay of AV node to allow filling of ventricles

Question 16

What is shown by T wave?

Answer 16

Ventricular repolarisation

Question 17

What is shown by ST segment?

Answer 17

Beginning of ventricle repolarisation - should be flat

Question 18

What is sinus tachycardia?

Answer 18

Tachycardia driven by the SA node beating too quickly - normal PR intervals and each P is matched with a QRS

Question 19

What is the normal duration of PR interval?

Answer 19

3-5 boxes

120-200ms

Question 20

What is the normal duration of QRS complex?

Answer 20

2-3 boxes

80-120ms

Question 21

What is the normal duration of QT interval?

Answer 21

9-11.5 boxes

360-460ms

Question 22

How many ms is one little box?

Answer 22

40ms

Question 23

How many ms is one big box?

Answer 23

200ms

Question 24

How do you calculate beats per minute?

Answer 24

Rate = 300/big boxes

1 big box = 300bpm
2 = 150
3 = 100
4 = 75
5 = 60 
6 = 50
10 = 30

Question 25

What is atropine?

Answer 25

Muscarinic antagonist | reduces parasympathetic activity

Question 26

What are the causes of heart block?

Answer 26

Ischaemia of AVN Compression of AVN Inflammation of AVN

Question 27

What are the symptoms of heart block?

Answer 27

``` Can be asymptomatic Palpitation Dizziness Malaise Syncope Risk of sudden death ```

Question 28

What is first degree heart block?

Answer 28

When PR interval is greater than 5 little boxes (200ms) But all Ps followed by QRS Young people, rarely treated

Question 29

What is Mobitz type 1 second degree heart block?

Answer 29

Wenchebach PR interval gets longer until QRS wave fails to follow P wave Likely cause is AV node damage No treatment given

Question 30

What is Mobitz type 2 second degree heart block?

Answer 30

Hay Some P waves are blocked and are not followed by QRS, PR interval remains the same Likely problem is bundle of his High risk

Question 31

What is third degree heart block?

Answer 31

Atrial signals consistently fail to arrive at ventricles, ventricular rate is consistent (30-40 bpm) Time between atrial beats is variable PR interval varies radically

Question 32

What is an escape beat?

Answer 32

When the atrial signal is very delayed or prevented - triggered by the natural rhythmicity of non-atrial tissue

Question 33

What is a premature beat?

Answer 33

Triggered by irritable tissue

Question 34

What do premature ventricular contractions look like on ECG?

Answer 34

Unusually wide ventricular activity No S wave, instead a wide negative dip where the T wave should be

Question 35

What does AF look like on ECG?

Answer 35

No P wave, instead flat line or wiggly line

Question 36

What is respiratory sinus arrhythmia?

Answer 36

Heart beat slightly faster during inspiration and slightly slower during expiration

Question 37

What is the iso-electric baseline?

Answer 37

From the end of T to the next P