Introduction to Arrhythmias

Question 1

Arrhythmia

Answer 1

Disturbance heart rate or rhythm which can be caused by changes in impulse formation/ impulse conduction

Question 2

Causes of changes in impulse formation

Answer 2

Changes in automaticity or triggered activity

Question 3

Causes of changes in impulse conduction

Answer 3

Re-entry, conduction block or accessory tracts

Question 4

Examples of latent pacemakers and their rate

Answer 4

AVN- 50-60bpm

Purkinje fibres- 30-40bpm

Question 5

Overdrive suppression

Answer 5

SAN pacemaking is dominant over latent pacemakers

Question 6

Requirement for SAN to exert its normal rate and rhythm

Answer 6

It must discharge action potentials at a regular frequency greater than any other structure in the heart

Question 7

ectopic rhythm

Answer 7

one not generated by SAN

Question 8

Triggered activity

Answer 8

normal action potential may trigger abnormal oscillations in membrane potential during or after repolarisation (AD), this can cause premature action potentials and beats

Question 9

At which point do EADs occur?

Answer 9

During the inciting AP, ie Phase 2 and Phase 3

Most likely to occur when HR is low

Usually in purkinje fibres

Question 10

What mediates the AD in phase 2?

Answer 10

Ca2+ channels when Na+ are still inactivated

Question 11

What mediates the AD in phase 3?

Answer 11

Na+ channels, when they have partially recovered from inactivation

Question 12

When do DADs occur?

Answer 12

After complete repolarisation

Question 13

What causes DADs?

Answer 13

Large increase in Ca2+ conc, releasing Ca2+ from SR and causing a transient inward current in P4

Question 14

When are DADs most likely to occur?

Answer 14

When HR is fast

Question 15

Requirements of a re-entrant circuit block

Answer 15

Unidiretional block +

Slow retrograde conduction velocity

Question 16

Re-entry

Answer 16

Self sustaining electrical circuit stimulates myocardium repeatedly and rapidly