Cardiac arrhythmicity

Question 1

List the cardiac pacemakers in order of fastest to slowest

Answer 1

Sinoatrial node
Atrioventricular node
Bundle of His
Purkinje fibres

Question 2

What is the pace of the SA node?

Answer 2

60-100 beats/min

Question 3

What is the pace of the AV node?

Answer 3

40-60 beats/min

Question 4

What is the pace of the bundle of His?

Answer 4

40-60 beats/min

Question 5

What is the pace of the Purkinje fibres?

Answer 5

20-40 beats/min

Question 6

What three tracts come off the SA node?

Answer 6

Anterior: Bachman’s bundle
Middle: Weckenbach’s
Posterior: Thorel’s

Question 7

Describe an SA node action potential

Answer 7

4
0
3
4
Smooth

Question 8

Describe a ventricular action potential

Answer 8

4
0
1
2
3
4
Pointy

Question 9

How is a signal propagated in the heart?

Answer 9

From cell to cell

Question 10

What does the heart form?

Answer 10

A functional syncytium

Question 11

What allows the passage of ions between cells?

Answer 11

Gap junctions

Question 12

What is the effect of the sympathetic nervous system on SA node action potential?

Answer 12

Sympathetic nervous system speeds up action potential

Question 13

What is the effect of the parasympathetic innervation of the SA node?

Answer 13

Slows down action potentials

Question 14

What is happening at phase 4 in the SA node?

Answer 14

Spontaneous depolarisation
Slow influx leakage of Na+
Slow leakage of Ca2+

Question 15

What is happening at phase 0 in the SA node?

Answer 15

Depolarisation
Influx of Ca2+
Through L-type channels

Question 16

What is happening at phase 3 in the SA node?

Answer 16

Repolarisation
Efflux of K+
No Ca2+ comes in

Question 17

What is happening at phase 0 in the AV node?

Answer 17

Rapid depolarisation

Influx of Na+

Question 18

What is happening at phase 1 in the AV node?

Answer 18

Partial repolarisation
Na+ stops coming in
K+ efflux

Question 19

What is happening at phase 2 in the AV node?

Answer 19

Plateau phase
K+ efflux
Ca2+ influx

Question 20

What is happening at phase 3 in the AV node?

Answer 20

Repolarisation
K+ efflux
No movement of Ca2+

Question 21

What is happening at phase 4 in the AV node?

Answer 21

Ventricle diastole
Pacemaker depolarisation
Ions return to original location
Via Na+/K+ATPase
Na+/Ca2+ transporter
Ca2+ ATP pump

Question 22

What is the absolute refractory period?

Answer 22

A second action potential cannot be generated

Question 23

What is the PQRST complex?

Answer 23

A heart beat seen on the ECG

Question 24

What is P to R?

Answer 24

Atrial systole

Ventricle diastole

Question 25

What is R to S?

Answer 25

Isovalemic contraction AV valves close Valves out of the heart are not open

Question 26

What is S to T?

Answer 26

Ventricle systole | Ejecting blood

Question 27

What is the T wave?

Answer 27

Isovalemic relaxation | Ventricles are relaxing but not filling with blood

Question 28

What is T to P?

Answer 28

Ventricles filling with blood

Question 29

What is R to T?

Answer 29

Ventricle contraction

Question 30

Define arrhythmia

Answer 30

A disturbance in the rate, rhythm, or pattern with which the heart contracts

Question 31

How many people in the UK have arrhythmias?

Answer 31

2 million

Question 32

What causes arrhythmia?

Answer 32

Coronary artery disease leading to myocardial ischemia or infarction Structural changes that accompany heart failure Drugs Electrolyte imbalance Congenital defects

Question 33

What are consequences of arrhythmias?

Answer 33

Produce vascular stasis (e.g. atrial fibrillation) | Reduce cardiac output

Question 34

What is the primary classification of arrhythmias?

Answer 34

Anatomical origin

Question 35

What are supraventricular arrhythmias?

Answer 35

``` Originate higher up the conduction route than the ventricle e.g. Sinus bradycardia Sinus tachycardia Atrial tachycardia Atrial fibrillation AV block Wolff-Parkinson-White syndrome ```

Question 36

What are ventricular arrhythmias?

Answer 36

``` Originate in the ventricle e.g. Ventricular premature beats Salvos Bigemini Ventricular tachycardia Ventricular fibrillation Torsades de Points ```

Question 37

What is an ECG

Answer 37

Electrocardiogram | Measures the change in electrical field during propagation of a cardiac action potential

Question 38

What does the PR interval tell us?

Answer 38

Time of conduction through the AV node

Question 39

What does the QT interval tell us?

Answer 39

Duration of ventricular action potential

Question 40

What are the two classifications of arrhythmia based on mechanisms?

Answer 40

Disturbances in conduction | Disturbances in impulse formation

Question 41

What is the most common conduction block?

Answer 41

Complete block of the forward movement of the action potential between the SA node and the ventricular myocardium

Question 42

What would be the result of a block in the Weckenbach's bundle?

Answer 42

Reduced ventricular rate

Question 43

What would be the result of a block in the bundle of His?

Answer 43

Asystole (no ventricular contraction) | Bradycardia

Question 44

What would be the result of a block in either branch of the purkinje system?

Answer 44

No change in heart rate but reduced cardiac output

Question 45

What makes the heart more susceptible to re entry?

Answer 45

When conduction velocity is slow and the cardiac cells spend less time in a refractory state

Question 46

What makes re entry less likely?

Answer 46

Long wavelength

Question 47

What must happen for re entry to occur?

Answer 47

Presence of a unidirectional block within a conduction pathway Critical timing Refractory state of normal tissue that the wavefront encounters

Question 48

What might be the cause of slow conduction velocity?

Answer 48

Ischemia

Question 49

Are re entrant arrhythmias confined to one heart chamber?

Answer 49

No

Question 50

What shape do reentrant arrhythmias form?

Answer 50

Spiral

Question 51

What is ventricular tachycardia?

Answer 51

Ventricular rates generally around 100 to 200 beats per minute

Question 52

What is ventricular fibrillation?

Answer 52

Life threatening | Many small waves propagate throughout the ventricles

Question 53

What is atrial flutter?

Answer 53

Atrial rates of 250-350 beats per minute | Ventricular rate substantially slower

Question 54

What is atrial fibrillation?

Answer 54

Rapid atrial rate (350-600 beats per minute) not immediately life threatening

Question 55

What are the two kinds of disturbance in impulse formation?

Answer 55

Early delayed after depolarisations | Delayed after depolarisations

Question 56

What does triggered activity mean?

Answer 56

Refers to a situation where heart tissue is stimulated once but results in the production of more than one conducted beats

Question 57

What are early delayed after depolarisations?

Answer 57

Prolonged action potential duration is necessary for generation Can contribute to initiation of arrhythmia syndrome, Torsades de pointes

Question 58

What is Torsades de Pointes?

Answer 58

Drug induced blockade of K+ channel leads to prolonged action potential depolarisation If net inward currents are larger than outward currents during phase 3 this causes an EAD Causes multifocal ventricular tachycardia

Question 59

What are delayed after depolarisations?

Answer 59

Cellular Ca2+ overload in the SR Phasic release of Ca2+ Depolarising inward current