Session 7 - ECG abnormalities

Question 1

what are the supraventricular rhythms

Answer 1

rhythms arising above the ventricle so either from the sinus node, the atrium or the AV node

Question 2

true or false: supraventricular nodes give a wider QRS complex

Answer 2

false - they have a normal, narrow complex as there is still normal ventricular depolarisation

Question 3

what happens to the QRS complex in ventricular rhythms

Answer 3

it widens as the depolarisation doesn’t conduct through the usual His-Purkinje system and so takes longer

Question 4

what is atrial fibrillation

Answer 4

where there are multiple atrial impulses and so chaotic atrial depolarisation

Question 5

what does an ECG look like in atrial fibrillation

Answer 5

no p waves, wavy baseline, normal QRS complexes

Question 6

true or false - during atrial fibrillation all of the impulses arriving at the AVN are conducted to the ventricles

Answer 6

false - due to the refractory period of the AVN not all impulses will be conducted

Question 7

how often are impulses conducted to the ventricles in atrial fibrillation

Answer 7

at irregular intervals

Question 8

what happens to the pulse and heart rate in atrial fibrillation

Answer 8

they are irregular

Question 9

what is heart block/AV conduction block

Answer 9

where they is a delay or failure to conduct impulses from the atria to the ventricles via the AVN and bundle of His

Question 10

what causes heart block

Answer 10

• myocardial infarction (e.g. lack of blood supplying the AVN node prevents it from working)
• degenerative changes

Question 11

how many types of heart block are there

Answer 11

3

Question 12

what is first degree heart block

Answer 12

where there are prolonged PR intervals which last longer than 5 small squares (0.20 seconds) due to slow conduction

Question 13

what does an ECG look like in primary heart block

Answer 13

normal p wave
normal QRS
increased PR interval

Question 14

what is Mobitz type 1 second degree heart block

Answer 14

where the length of the PR interval progressively increases until a QRS complex cant be conducted

Question 15

what is Mobitz type 2 secondary heart block

Answer 15

where the PR interval is normal and there is a sudden non-conduction of an impulse to the ventricles

Question 16

what is 3rd degree heart block

Answer 16

where atrial depolarisation is normal but no impulses are conducted to the ventricles
the ventricular pacemaker must then takeover

Question 17

what rhythm does the ventricular pacemaker give

Answer 17

the ventricular escape rhythm which is very slow and gives a wide QRS complex

Question 18

why is a pacemaker urgently required in 3rd degree heart block

Answer 18

because the heart rate set up by the ventricular escape rhythm is too slow (30-40bpm) to maintain BP and perfusion

Question 19

what is an ECG of 3rd degree heart block like

Answer 19

no relationship between p waves and QRS
RR intervals much slower
PP intervals constant

Question 20

what are ventricular ectopic beats

Answer 20

when there is an opportunistic beat coming from the ventricles

Question 21

how are ventricular ectopic beats different from the escape rhythm

Answer 21

the ectopic beat is a one off beat that does not occur due to impulse delays

Question 22

what does the QRS complex look like in a ventricular ectopic beat

Answer 22

wider

Question 23

what is it called if there are more than 3 consecutive ventricular ectopic beats

Answer 23

ventricular tachycardia which gives a high risk of ventricular fibrillation

Question 24

what needs to be given during ventricular tachycardia

Answer 24

electrical shock

Question 25

what is ventricular fibrillation

Answer 25

where there is abnormal, chaotic ventricular depolarisation with impulses originating from numerous ectopic sites in the ventricles

Question 26

what happens to the cardiac output in ventricular fibrillation

Answer 26

there is no cardiac output as theres no coordinated contraction leading to cardiac arrest

Question 27

where in the heart is the most vulnerable to reduced perfusion

Answer 27

the sub endocardial muscle as it is the furthest away to the coronary arteries

Question 28

when are ischaemic ECG changes seen

Answer 28

during exercise

or at rest when theres severe narrowing of the artery lumen

Question 29

what changes are seen on an ECG during exercise and why

Answer 29

• ST depression
• T wave inversion
  due to abnormal repolarisation

Question 30

what changes does a myocardial infarction have on an ECG during a complete occlusion of an artery lumen

Answer 30

elevated ST segment

Question 31

what happens to the ECG weeks after an STEMI

Answer 31

the ST and T are normal

persistent Q wave

Question 32

what does the persistent Q wave indicate

Answer 32

muscle necrosis

Question 33

describe the pathological Q waves seen in a MI

Answer 33

1 small square wide
2 small squares deep
more than 1/4 of the height of the R wave

Question 34

what happens to the resting membrane potential in hyperkalaemia and hypokalaemia

Answer 34

• hyper = less negative (more depolarised)

- hypo = more negative (hyper polarised)

Question 35

what happens to the excitability of the heart as the hyperkalamia worsens

Answer 35

It becomes less excitable so theres a prolonged PR interval

Question 36

what happens to the T wave in hyper and hypokalaemia

Answer 36

hyper = tall and pointed 
hypo = low