Lecture 9: Cardiac Hypertrophy & Arrhythmia

Question 1

What is arrhythmia?

Answer 1

Abnormalities of electrical rhythm, either benign or malignant

Question 2

What are the symptoms of arrhythmia?

Answer 2

Palpitations, reduced CO

Question 3

What causes arrhythmia?

Answer 3

Altered AP generation or conductance

Question 4

What happens if normal nodal automaticity is altered?

Answer 4

Unstable rhythm, emergence of alternative pacemaker

Question 5

How does sympathetic activity influence pacemakers?

Answer 5

Increase HR by increase If and Ca channels and decreasing K channels

Question 6

How does parasympathetic activity influence pacemaker cells?

Answer 6

Decrease HR by decreasing If and Ca channels and increasing K channels

Question 7

How can a nodal abnormality happen?

Answer 7

Sympathetic effect on a latent pacemaker causing it to take over.

Parasympathetic effect on SA node causing latent pacemaker to take over.

Question 8

What causes trigger of activity in the ventricle?

Answer 8

Altered calcium homeostasis, unstable RMP, oscillation

Question 9

What is early after depolarisation (EAD) and why does it occur?

Answer 9

Depolarisation occurring during AP depolarisation due to long AP duration (QT syndrome).

Question 10

What are the mutations that lead to QT syndrome?

Answer 10

Na channel mutation (SCN5A)

K channel mutation (HERG, KCNQ1)

Question 11

What happens when there is a mutation in the Na channel?

Answer 11

Channel fails to stay inactivated - inward current occurs late in plateau to extend duration

Question 12

What happens when there is a mutation in the K channel?

Answer 12

Decreased depolarising K efflux and plateau termination delayed

Question 13

What is delayed after depolarisation (DAD) and why does it occur?

Answer 13

Depolarisation just after repolarisation due to increased reliance on Na/Ca exchanger for relaxation

Question 14

What are the effects of hypertrophy on the cell exchanging?

Answer 14

More active Na/Ca exchanger, less Ca coming in and out of SR each cycle, more extracellular calcium cycling

Question 15

What is a conduction block?

Answer 15

Inexcusable area in conduction system which may be temporary or permanent and permits latent pacemakers to escape

Question 16

What is a re-entry circuit?

Answer 16

Unidirectional conduction block that produces tachyarrhythmia

Question 17

What are the features of normal conduction block and re-entry?

Answer 17

Branch point alone is not a problem, signals from X through alpha and beta extinguish each other

Question 18

What are the features of forward block at branch point conduction block and re-entry?

Answer 18

A total branch block alone is not a problem, signals from X through alpha can’t traverse beta route from distal position at y

Question 19

What are the features of normal retrograde conduction velocity conduction block and re-entry?

Answer 19

If beta route forward (orthograde) is block but beta reverse route (retrograde) is not, it is only okay if the beta signal is fast and reaches alpha signal when it is in refractory

Question 20

What are the features of slowed retrograde conduction velocity conduction block and re-entry?

Answer 20

If beta route reverse (retrograde) is slowed and reaches alpha route after refractory period finishes then a re-entry circuit is set up

Question 21

What dod you need to produce a conduction re-entry arrhythmia?

Answer 21

Need a branch point and a partial blockage in one of the branches involving slowed conduction in one direction

Question 22

From the re-entry circuit where does the arrhythmic activity spread?

Answer 22

Throughout the electrical syncytium of the myocardial tissue

Question 23

How do hypertrophy and arrhythmia relate?

Answer 23

• Growth means fibrosis
• Cardiac pump function impairment due to sympathetic activation
• Bigger muscle mass means more oxygen demand, ischemic regions and emerging pacemakers
• More external cell calcium cycling, Na/Ca exchanger, DADs