Lecture 10 Theme B

Question 1

What are the types of cardiac arrhythmia?

Answer 1

some arrhythmias are benign. Others are malignant.

Question 2

What are symptoms of arrhythmias?

Answer 2

palpitations to critical reduction.

Question 3

Why does the SA node control the heart’s contraction?

Answer 3

SA node pacemaker overdrives the other pacemakers. (fastest creeper to threshold is the one that controls the heartbeat)

Question 4

How is SA node activity regulated?

Answer 4

SA node activity is modulated by the action of sympathetic and parasympathetic hormones.

Question 5

How do hormones influence heart beat?

Answer 5

increase in I-funny, Land T type calcium channels and a decrease in I-K occurs in response to adrenaline and sympathetic hormones.

Opposite happens in response to muscarinic receptor activation by Ach.

Question 6

How can increased neurotransmitter activity cause arrhythmia?

Answer 6

Increase in sympathetic activity causes other muscle cells to suddenly become pacemakers.

Increase in parasympathetic activity causes latent pacemakers to emerge.

Question 7

How does injury affect pacemaker cells?

Answer 7

injured node area cells develop pacemaker function which causes loss of RMP.

Question 8

What are the 2 types of arrhythmicity?

Answer 8

Normal nodal altered automaticity.

Triggered activity in the ventricle (ectopic pacemaker)

Question 9

What causes the formation of an ectopic pacemaker?

Answer 9

Altered calcium ion homeostasis.

Oscillation of RMP

Question 10

What are the types of oscillation of the RMP?

Answer 10

Early afterdepolarisation

Delayed afterdepolarisation

Question 11

What happens during early afterdepolarization (EAD)?

Answer 11

during early afterdepolarization there is a spike in electric potential right before repolarization (opening of potassium channels) occurs. This can continue and could cause long AP duration which causes long QT syndromes.

Question 12

What goes wrong during EAD?

Answer 12

Repolarization typically goes wrong due to faulty potassium channels causing tacchyarryhthmias.

Question 13

What happens if a sodium channel is mutated?

Answer 13

Channel fails to stay inactivated meaning inward current occurs late in the plateau leakage of more positive into the cell causing an extended AP duration.

Question 14

What does the P wave represent on an ECG?

Answer 14

P wave is when action potential is spreading across most of the surfaces into the tissues of the atria to move blood into the ventricle from the atria.

Question 15

What happens at the QRS complex of the ECG?

Answer 15

At the QRS complex the ventricular action potential is spreading through the muscles of the ventricle via the purkinje fibers.

Question 16

What does the T wave represent?

Answer 16

T waves mark repolarization.

Question 17

What is the main fast sodium channel called?

Answer 17

SCN5A

Question 18

What potassium channels are typically mutated to cause EAD?

Answer 18

KCNQ1

HERG

Question 19

How do mutated potassium channels cause EAD?

Answer 19

decrease in repolarization K efflux and plateau termination is delayed. As a result there is a long QT interval.

Question 20

What occurs during delayed afterdepolarization (DAD)?

Answer 20

after completed action potential another depolarization occurs soon after.

Question 21

Why are hypertrophied cells more likely to experience arrhythmias (DAD)?

Answer 21

hypertrophied cells rely on external calcium due to the weakness in the SERCA2 protein. Extracellular calcium cycling results in higher chance of forming an action potential within the cell

Question 22

How does digitalis increase the RMP?

Answer 22

Digitalis increases the amount of sodium in the cell which is exchanged with calcium as the built up sodium flows out. After contraction the built up calcium exits the cell and sodium enters the cell the amount of sodium is higher due to blocked Na/K exchanger and so the RMP is higher.

Question 23

Why is it dangerous to have a higher RMP (as is the case with digitalis)?

Answer 23

Delayed afterdepolarization can occur while the fast sodium channels remain dormant, as a result the L-type channels can activate due to hitting the threshold. This causes ectopic beats to form.

Question 24

What are the causes of a conduction block in the heart?

Answer 24

A conduction block could occur due to ischemia or fibrosis (hypertrophy could cause fibrosis). These blocks could be temporary or permanent and could cause latent pacemakers to activate.

Question 25

What is a re-entry circuit?

Answer 25

A re-entry circuit is a unidirectional conduction block that produces tachyarrhythmia.