ECG Arrhythmias

Question 1

ECG provides info on

Answer 1

about rate, rhythm and the timing of events in the cardiac cycle
– arrhythmias, conduction blocks
heart muscle

Question 2

what do increased voltage in ECG suggest

Answer 2

increased muscle mass - hypertrophy

Question 3

what do wider waves suggest

Answer 3

slowed conduction

Question 4

what does left axis deviation mean

Answer 4

left ventricle hypertrophy
more muscle mass pulls depolarisation to the left
deflections in lead I get bigger but aVF get smaller

Question 5

what does right axis deviation mean

Answer 5

– right axis deviation
– right ventricle hypertrophy
– more muscle mass, pulls depolarisation to the right
– deflections in AvF get bigger, while lead I gets smaller

Question 6

how is delayed conduction conveyed

Answer 6

elongated PR interval, QRS or QT

Question 7

when is ST depression seen

Answer 7

– only seen in leads pointing towards damage ischaemia

Question 8

when is ST elevation seen

Answer 8

(infarction)
– only seen in leads pointing towards damage
– acute infarction, full thickness of the myocardium

Question 9

tachycardia

Answer 9

> 100 bpm

Question 10

bradycardia

Answer 10

<60 bpm

Question 11

name 2 types of irregular rhythms

Answer 11

regularly irregular - irregular pattern

irregularly irregular - does not repeat an irregular pattern

Question 12

arrhythmia

Answer 12

It collectively describes a change in the normal sequence of electrical impulses

Question 13

causes if arrhythmia

Answer 13

altered rate - too fast or too slow
irregular patterns
conduction problems

Question 14

how does ischaemia affect the heart

Answer 14

disrupt individual membrane potential in individual myocytes

Question 15

• Sinus tachycardia and cause

Answer 15

: increased rate but normal rhythm
– mainly sympathetic as in exercise or secondary to low blood pressure
– also increased high temperatures or cardiac toxicity

Question 16

Sinus bradycardia

Answer 16

decreased rate but normal rhythm
– seen in athletes, low rate but larger stroke volume
– increased vagus (PNS) activity (e.g. carotid sinus syndrome)

Question 17

Sinus arrhythmia:

Answer 17

a regularly irregular rhythm from the SA node
– Cross talk between cardiorespiratory signals
– heart rate increases on inspiration

Question 18

Arrhythmias may arise due to a number of reasons

Answer 18

1. Changes in automaticity
2. Triggered activity (after depolarisation)
3. Conduction delay and appearance of re-entry circuits

Question 19

is the SA alone in its automaticity

Answer 19

The SA node is not alone in its automaticity

– but it is the fastest

Question 20

SA node depolarisation rate what does the its rate depend on?

Answer 20

depolarisation rate 60-100/min

– depends on the autonomic nervous system

Question 21

AV node depolarisation rate

Answer 21

depolarisation rate 40-50/min

Question 22

Purkinje fibres depolarisation rate

Answer 22

depolarisation rate ~35/min

Question 23

Afterdepolarisations

Answer 23

abnormal stimuli outwith the normal activity

Question 24

types of afterdepolarisations

Answer 24

early (EAD) or delayed afterdepolarisations (DAD

Question 25

when do EADs occur

Answer 25

EADs occur when stimulation occurs during the plateau (Phase 2) or repolarisation phase (Phase 3)

Question 26

when do DADs occurs

Answer 26

DADs occur during Phase 4 (resting) and trigger depolarisation, but before the time normally expected – due to elevated Ca2+ levels

Question 27

what parts of the heart DONT depolarise

Answer 27

blood vessels, damaged fibrotic tissue

Question 28

what happens when depolarisation in regions of heart that dont typically depolarise

Answer 28

When depolarisation hits these areas it cannot go through, but must go around can be a problem if there new route is longer than typical path of conduction

Question 29

issues that can arise when typical path of conduction is deviated to longer path of conduction

Answer 29

– fibrous plaques or dilated heart increases path length – ischaemia slows conduction, due to high K+ and depolarisation – this goes back to the refractory period

Question 30

paroxysmal tachycardia

Answer 30

• Bursts of tachycardia due to re-entry pathways | – classified by origin: either ventricular or supraventricular

Question 31

types of paroxysmal tachycardia

Answer 31

ventricular and supraventricular

Question 32

what can ventricular paroxysmal tachycardia lead to? what is ventricular paroxysmal tachycardia? what are its causes?

Answer 32

may lead to fibrillation and death – fibrillation is the uncoordinated depolarisation – usually due to ischaemic damage or some drugs

Question 33

supraventricular paroxysmal tachycardia

Answer 33

it originates above the ventricles so is either atrial or AV node – atrial (inverted P wave) or AV node (hidden P wave) – more common in young, seldom has morbidity

Question 34

fibrillation

Answer 34

• Rather than the coordinated spread of depolaristion through the heart this is uncoordinated and sporadic

Question 35

Atrial fibrillation

Answer 35

no coordinated depolarisation of the atria, so no P wave | – irregular transmission to ventricles, irregularly irregular tachycardia

Question 36

Ventricular fibrillation

Answer 36

individual myocytes depolarising so no discernible waveform | – no coordinated contraction, no cardiac output

Question 37

ectopic beats of the atria

Answer 37

These are premature contractions due to abnormal impluses from ectopic (abnormal) foc

Question 38

causes of ectopic beats of atria

Answer 38

– areas of ischaemia (altered membrane potential) – excessive stretch of muscle fibres – drug actions

Question 39

what does ectopic beats of atria look like on ECG

Answer 39

– show up as extra P wave and weak pulse on the ectopic beat Looks similar to premature AV node contraction weak pulse no P wave

Question 40

ectopic beats of ventricle

Answer 40

premature ventricular contractions (PVCs)

Question 41

what does ectopic beats of ventricles look like on ECG

Answer 41

• Present as a widened and QRS and inverted T wave – conduction through muscle is slower than conducting system – the slow conduction means fibres that depolarised first also repolarise first

Question 42

causes of Ectopic beats

Answer 42

Minor PVCs caused by drugs (nicotine/coffee) but others are major and may lead to fibrillation

Question 43

heart block

Answer 43

• Decreased or total block of AV conduction | – due to ischaemia/compression/inflammation of AV-node

Question 44

how is 1st degree heart block characterised

Answer 44

the delay in conduction | – characterised by an increased PR interval (>0.2 sec or one large box)

Question 45

how is 2nd degree heart block characterised

Answer 45

the increased delay | – so that now some QRS complexes are dropped (PQRS > P > PQRS > P…)

Question 46

how is 3rd degree heart block characterised

Answer 46

3rd Degree is the complete block – ventricles contract (automaticity /”ventricular escape”) but slower (~40 bpm) – SA node still firing but no relationship between P and QRS