CVS - ECG Abnormalities

Question 1

Why do abnormal heart rhythms arise?

Answer 1

• abnormal impulse formation

- abnormal conduction

Question 2

Where can rhythms arise from within the heart?

Answer 2

• sinus node (supraventricular)
• atrium (supraventricular)
• AV node (supraventricular)
• ventricle

Question 3

What do the QRS complexes look like when the heart is in a supraventricular rhythym?

Answer 3

The ventricular depolarisation is normal, so the QRS complexes are also normal and narrow

Question 4

What do the QRS complexes look like in ventricular rhythms?

Answer 4

They are wide (due to depolarisation taking longer) and vary in shape depending on where the rhythm originates from

Question 5

What is the difference between sinus tachycardia and sinus bradycardia?

Answer 5

Sinus bradycardia is a sinus rhythm with a rate of less than 60 bpm. Sinus tachycardia is a sinus rhythm with a rate of over 100 bpm.

Question 6

What is atrial fibrillation?

Answer 6

When impulses originate from multiple atrial foci, resulting in chaotic depolarisation. There are no P waves, just a ‘wavy’ unsteady baseline and a narrow irregular QRS complex.

Question 7

True or false - the pulse and heart rate remain regular in atrial fibrillation?

Answer 7

False - they are irregularly irregular

Question 8

What is a ‘heart block’?

Answer 8

Delay/failure of impulses from atria to ventricles via the AV node and Bundle of His

Question 9

Give two causes of AV conduction blocks

Answer 9

• acute myocardial infarction

- degenerative changes

Question 10

What is first degree heart block?

Answer 10

Slow conduction in AV node and Bundle of His means that PR interval is prolonged (over 5 small squares). The QRS is normal, and P wave is normal.

Question 11

What is the difference between the two types of 2nd degree heart block?

Answer 11

Mobitz type 1 involves progressive lengthening of PR interval until one P is not conducted and the QRS complex doesn’t occur. The cycle then begins again.

Mobitz type 2 has a normal PR interval, but a sudden non-conduction of a beat occurs. This has a high risk of progression to complete heart block.

Question 12

What is 3rd degree heart block?

Answer 12

Atrial depolarisation is normal but impulses not conducted to the ventricle, so the ventricular pacemaker must take over (ventricular escape rhythm). The HR is very slow and has wide QRS complexes, requires urgent pacemaker insertion.

Question 13

What is the relationship between P waves and QRS complexes in third degree heart block?

Answer 13

There isn’t one - PR interval is completely variable from beat to beat

Question 14

Why do ventricular ectopic beats appear larger than a normal QRS complex on ECG traces?

Answer 14

The impulse is not spread via the fast His-Purkinje system, so there is a much slower depolarisation of the ventricle and a wide QRS complex

Question 15

What must occur for a rhythm to be described as “ventricular tachycardia”?

Answer 15

Must be run of three consecutive ectopics

Question 16

Why is persistent ventricular tachycardia dangerous?

Answer 16

There is a high risk of it becoming ventricular fibrillation

Question 17

What is ventricular fibrillation?

Answer 17

Abnormal/chaotic/fast ventricular depolarisation which occurs due to impulses originating from numerous ectopic sites in ventricular muscle. There is no co-ordinated contraction and the ventricles appear to quiver. No cardiac output.

Question 18

Why is ventricular fibrillation more dangerous than atrial fibrillation?

Answer 18

Ventricular fibrillation has no cardiac output as the ventricles are unable to contract, while atrial fibrillation still has cardiac output

Question 19

Which leads should be checked if the lateral area of the heart is suspected to be damaged?

Answer 19

I, aVL, V5 and V6

Question 20

Which leads should be checked if the inferior area of the heart is suspected to be damaged?

Answer 20

II, III and aVF

Question 21

Which leads should be checked if the septal area of the heart is suspected to be damaged?

Answer 21

V1 and V2

Question 22

Which leads should be checked if the anterior area of the heart is suspected to be damaged?

Answer 22

V3 and V4

Question 23

Which muscle region in the heart is at most risk of reduced perfusion?

Answer 23

The sub endocardium muscle is furthest from the coronary arteries and therefore most vulnerable

Question 24

How would sub-endocardial muscle damage be seen in an ECG?

Answer 24

ST segment depression and T wave inversion due to abnormal current during repolarisation.

Question 25

What is “ST segment elevation myocardial infarction (STEMI)”?

Answer 25

Muscle injury which extends full thickness from endocardium to epicardium due to complete occlusion of lumen by thrombus. Can lead to muscle necrosis.

Question 26

What do pathological Q waves indicate?

Answer 26

Muscle necrosis has occurred following a myocardial infarction

Question 27

How does hyperkalaemia affect the resting membrane potential?

Answer 27

It becomes less negative (more depolarised)

Question 28

How does hypokalaemia affect the resting membrane potential?

Answer 28

It becomes more negative (hyperpolarised)

Question 29

How does hyperkalaemia affect an ECG?

Answer 29

At first, the T wave is elevated. As hyperkalaemia worsens, PR interval becomes prolonged, ST segment is depressed and there is a high T wave. Eventually, there is an atrial standstill and intraventricular block, progressing to ventricular fibrillation

Question 30

How does hypokalaemia affect an ECG?

Answer 30

Low T wave, then low T wave and high U wave, then also has a low ST segment

Question 31

What is the cardiac axis?

Answer 31

The average direction of spread of the ventricular depolarisation (usually downward and to the left)

Question 32

What is left axis deviation?

Answer 32

This occurs when overall direction of ventricular depolarisation is upwards and to the left (less than 30 degrees). May occur as a result of conduction block of the anterior branch of the left bundle, inferior MI or left ventricular hypertrophy

Question 33

What is right axis deviation?

Answer 33

When overall direction of ventricular depolarisation is downwards and to the right (more than 90 degrees). Associated with right ventricular hypertrophy