ECG

Question 1

What is the P wave and how long is it meant to last?

Answer 1

It is a deflection of the outside of the cardio myocytes becoming depolarised.
Meant to last for 120-200ms.

Question 2

What are the best leads for looking at problems in the lateral wall of the left ventricle?

Answer 2

Leads I and aVL look at the left side of the heart.

Question 3

What are the leads best used for looking at the inferior surface of the heart?

Answer 3

Leads II, III, AVF are looking at the inferior surface of the heart, this best leads to detect problems in the inferior surface of the heart.

Question 4

What do the other leads face?

Answer 4

V1 and V2 face the right ventricle and septum ‘SEPTAL LEADS’

V3 and V4 face the apex and anterior wall of the ventricles
‘ANTERIOR LEADS’

V5 and V6 face the left ventricle
‘LATERAL LEADS’

Question 5

What does 5 large squares (25 small squares) mean on a ECG?

Answer 5

1 second

Question 6

How do you calculate the heart rate when the rythm is regular?

Answer 6

1 minute is 300 large boxes so you divide the 300 by how many complexes there are in 300. Easier to count R-R interval than P-P.

Question 7

If the heart rate is irregular then how do you calculate heart rate?

Answer 7

Count the number of QRS complexes in 6 seconds (30 large squares) then multiply by 10.

Question 8

How do you know when the PR interval is delayed and what is this due to?

Answer 8

The PR interval should be 0.12-0.20 seconds (3-5 small boxes)
Prolonged if > 1 large boxes
Prolonged PR interval: delayed conduction through AV node and bundle of His.

Question 9

What is the QRS interval?

Answer 9

The width of QRS complex.
Time taken for ventricular depolarisation
<0.12 seconds
<3 small boxes

Widened QRS: usually a depolarisation arising in ventricle, not spreading via the His- Purkinje system, hence takes more time.

Question 10

How long should a QT interval be and what does a prolonged QT mean?

Answer 10

The QT is the time taken for depolarisation and repolarisation of the ventricle, it actually varies with the heart rate/
There is an upper limit of CORRECTED QTc interval which is than 0.44-0.54 seconds (11 small boxes).

Question 11

What is the cause for a prolonged PR?

Answer 11

COULD BE HEART BLOCK- ATRIOVENTRICULAR CONDUCTION BLOCK, DELAYED conduction of the inter-ventricular septum.

Question 12

What are the causes of ‘heart block’ (Delay/failure of conduction of impulses from atrium to ventricles via AV node).

Answer 12

Acute myocardial infarction

Degenerative changes

Question 13

What are the types of heart block?

Answer 13

There is first degree heart block
Second degree heart block which is separated in type 1 and type 2
Third degree heart block (Complete heart block).

Question 14

What would you expect to see on an ECG of someone with 1st degree heart block?

Answer 14

The PR interval would be prolonged, would be greater than 0.2 seconds (5 small boxes)

Question 15

What do you expect to see in an ECG in second degree heart block?

Answer 15

Successively longer PR intervals until one QRS has dropped. Before the cycle starts again.

Question 16

What is second degree (mobitz type 2) heart block?

Answer 16

You have mobitz type 2 where the PR intervals DO NOT LENGTHEN but dropped QRS, in this there is a high risk of progression to complete heart block.

Question 17

What is 3rd degree heart block?

Answer 17

This is the complete failure of atrioventricular conduction, the atria and ventricles are depolarising independently. Ventricular pacemaker takes over and there is usually wide QRS complexes, ventricular rate is very slow and often too slow to maintain BP an urgent pacemaker insertion is usually required

Question 18

What are the abnormal rhythms may arise from?

Answer 18

You can get abnormal supraventricular rhythms arising from the SA node, the atrium and the AV node.
Then you can get abnormal ventricular rhythms.

Question 19

What is the difference of an ECG in a supra ventricular rythm and a ventricular rythm.

Answer 19

In a supra ventricular rhythm you get normal (narrows) QRS complexes.

In a ventricular rythm you get wide and bizarre QRS complexes.

Question 20

So what is atrial fibrillation?

Answer 20

Atrial fibrillation is a supra ventricular rhythm, it arises from multiple atrial foci and produces rapid, chaotic impulses. There are no p waves, just a wavy baseline.

Impulses reach AV node at a rapid irregular rate and not all are conducted due to the AV node refractory period.

Question 21

What happens when conducted to the ventricles?

Answer 21

There are narrow QRS complexes with irregular R-R intervals.

Question 22

What is the consequence of atrial fibrillation on haemodynamics?

Answer 22

The atrial contraction is lost, the ventricles contract normally (but at an irregular rate due to atrial contraction),the heart rate and pulse is irregular.

Question 23

What is the rate like for an irregular heart beat due to atrial fibrillation?

Answer 23

Irregularly irregular rhythm (the rhythm is irregular and it happens irregular) the drop in the QRS complex is irregular and it happens at irregular intervals.

Question 24

What are ventricular ectopic beats?

Answer 24

Ectopic focus in ventricle muscle, the impulse does not spread via the fast His purkinje system and there is much slower depolarisation of the ventricular muscle. There is a wide QRS complex.

Question 25

What is ventricular fibrillation?

Answer 25

Abnormal, chaotic, fast, ventricular depolarisation. The impulses are from numerous ectopic sites in ventricular muscle, no co-ordinated contraction.

Question 26

Why is ventricular fibrillation so dangerous?

Answer 26

There is no cardiac output and therefore cardiac arrest occurs.

Question 27

What are the ECG changes of ischaemia and MI?

Answer 27

Coronary artery occlusion leads to ischaemia or infarction (necrosis) in area supplied by an artery. Changes seen in leads facing affected area of ventricle. Need to look at PQRST in all 12 leads, needs to know which groups of leads look at different parts of the heart.

Question 28

What happens in myocardial ischaemia and infarction?

Answer 28

You get reduced perfusion due to a narrowed coronary arteries.
Partial narrowing of lumen causes:
Sub endocardial ischaemia/ injury

Question 29

What does Partial narrowing of lumen causes?

Answer 29

Sub endocardial ischaemia/ injury
This area is furthest away from coronary arteries which lie on the surface of heart
Hence most vulnerable region involved first.
What is the complete occlusion of lumen causes?
Full thickness (trans mural) injury
Including sub pericardial region.

Question 30

What is a STEMI?

Answer 30

ST segment elevation myocardial infarction, due to complete occlusion of coronary artery by thrombus, the full thickness of myocardium involved and there is sub epicardial injury causes ST segment elevation in leads facing affected area.