Arrhythmias

Question 1

Three type of heart arrhythmias

Answer 1

Atrial fibrillation
Superventricular tachycardia
Bradycardia

Question 2

Atrial fibrillation

Answer 2

HB irregular and fast (350 to 600 beats per minute), not immediately life-threatening. Most common.

Question 3

Superventricular tachycardia

Answer 3

Episodes of abnormally fast heart rate at rest. Ventricular rate generally around 100 to 200 beats per minute.

Question 4

Bradycardia

Answer 4

Slow heart beat

Question 5

Hierarchy of cardiac pacemakers

Answer 5

SA node - 60-100 beats/min
AV node - 40-60
Bundle of His - 40-60
Purkinje Fibres - 20-40

Question 6

Cardiac conduction pathway

Answer 6

SA node is the natural pacemaker it releases electrical stimulant at a regular rate, rate is dictated to the bodies needs. Electrical stimulus from the SA node reaches the AV node and is delayed briefly so all contraction atrial have enough time to pump all the blood into ventricles. AV valve closes and the atria begins to refill. Conductance passes through the AV node and bundle of His into the bundle branches and purkinje Fibres.

Question 7

How does electrical propagation in the heart happen?

Answer 7

Propagation is from cell to cell. Depolarisation in cell decays electronically to neighbour, and depolarises it to its threshold. Gap junctions allow cell to cell passage of ions allowing the threshold of neighbouring cells to be met.

Question 8

What ion channels are activated during spontaneous depolarisation of SA node (threshold -40 & amp; -30mV)

Answer 8

if (voltage-dependent)
iT,Ca (voltage-dependent)
iL,Ca (coltage-dependent)

Question 9

What ion channels are activated during depolarisation?

Answer 9

iKr,Ks activate

Question 10

What ion channels are activated during repolarisation?

Answer 10

iKAch (activated by Acetylcholine)

Question 11

Ventricular action potential ion channel activation

Answer 11

Depolarisation 
iNa voltage-dependent
iL,Ca voltage-dependent
iNa time-dependent
iL,Ca time-dependent

Repolarisation
iL,Ca and iNa/Ca
iKr,Ks activates
iK1 activates

Question 12

A functional change in ion transporters can lead to?

Answer 12

Arrhythmias
Na Ca exchanger
Na-K pump

Question 13

What is an arrhythmia?

Answer 13

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

Question 14

Causes of arrhythmias

Answer 14

Coronary artery disease leaving to myocardial ischemia or infarction.
Structural changes that accompany heart failure
Many drugs
Electrolyte imbalance (K+, Na+, Ca2+)
Congenital defects

Question 15

What is fibrillation?

Answer 15

Quivering movement due to uncoordinated contraction of individual fibrils.

Question 16

What can arrhythmias produce

Answer 16

Vascular stasis or reduce cardiac output to the point that adequate blood flow cannot be maintained to vital organs.

Question 17

Arrhythmia classification based on anatomical origin

Answer 17

Superventricular - originates higher up the conduction route than the ventricle.
Ventricular - originates in the ventricle.

Question 18

How can ECG measure arrhythmias?

Answer 18

Measurement of change in the electrical field during propagation of cardiac action potential.

Question 19

Arrhythmia classification based on mechanisms

Answer 19

Disturbance in conduction:
Conduction block, re-entry

Disturbance in impulse formation (Automaticity):
Early delayed after depolarisation (EADs), delayed after depolarisation (DADs)

Question 20

AV node block causes

Answer 20

Reduced ventricular rate = reduced CO

Question 21

Bundle of His block causes

Answer 21

Asystole (no ventricular contraction) or Bradycardia (reduced heart rate.)

Question 22

Purkinje fibre block causes

Answer 22

No change in heart rate but reduces cardiac output.

Question 23

Why is the refractory period important?

Answer 23

Prevents tetany and prevents against re-entrant arrhythmias.

Question 24

Wavelength equation

Answer 24

Wavelength = Conduction velocity x ERP

Question 25

What is the relationship between wavelength and re-entrant circuit formation?

Answer 25

Increase in wavelength, re-entrant circuit formation is less likely to occur.

Question 26

The heart is more susceptible to re-entry and arrhythmia when?

Answer 26

The conduction velocity is slow and when cardiac cells spend less time in the refractory state.

Question 27

What is the mechanism of re-entry

Answer 27

Presence of a unidirectional block within a conducting pathway, critical timing and refractory state of normal tissue that the wave-front encounter.
When conduction velocity is slowed by local damage (ischemia). The slow wave-front may find adjacent tissue no longer in the refractory period which may then propagate the signal further, becoming an arrhythmia.

Question 28

What dimension does the re-entrant arrhythmia form?

Answer 28

Three-dimensional scroll wave. Can be confined to both single or several chambers.

Question 29

Ventricular fibrillation

Answer 29

Life threatening, many small waves propagate throughout the ventricles.

Question 30

Atrial flutter

Answer 30

Atrial rate 250 to 350 beats per minute, ventricular rate substantially slower

Question 31

EADs and DADs triggered activity

Answer 31

The heart tissue is stimulated once, but results in the production of more than one conducted beats.

Question 32

What is necessary for a EAD to generate?

Answer 32

A prolonged action potential duration (APD). If net inward currents during repolarisation (phase 3) are larger than outward currents, this can form and EAD. Can create a substrate for producing triggered beats in multiple locations, resulting in multifocal ventricular tachycardia.

Question 33

Dispersion of repolaristaion and Torsades de Pointes

Answer 33

Heterogeneity in action potential duration (dispersion of repolarisation) results in a myocardium that is more vulnerable to multiple sites of re-entrant excitation.

Question 34

Delayed afterdepolarisations

Answer 34

Cellular Ca2+ overload swamps SR with Ca2+. Phasic (oscilaroty) release of Ca2+ from SR via RyR2. Oscilatory depolarising inward current (NCX).