Cardiology 1

Question 1

Explain the order of action potential propagation through the heart

Answer 1

SA node, AV node, AV bundle, purkinje fibres, ventricular node

Question 2

The Sa node is located ?

Answer 2

at right atrium @ junction of superior and inferior vena cava and is where the AP starts

Question 3

Can action potentials vary across the heart?

Answer 3

yes

Question 4

What drives the pace maker potential?

Answer 4

Influx of sodium through HCN/funny channels

Question 5

Explain the pace maker potential

Answer 5

RMP ~60mV and it gradually increases over time giving it the ability to randomly depolarize without influence of brain

• The funny channel found in the SA node creates a current called the funny current and allows Na to leak into the cell (and K highly regulated so doesn’t leak out)
• When gets to -40mV L-type Ca channel and K channels rush open to allow for larger influx
• deploarization

Question 6

What is the purpose of the AV node//bundle?

Answer 6

limits fibrillation entry to ventricles
latent/back-up pace maker
Delay AP potential to increase ventricular filling

Question 7

How is depolarization in AV nodes/bundles slower?

Answer 7

Have slow inward conduction cation channels, not as high conducting therefore Ca doesn’t flow through as easily and
-also fewer gap junctions- ions have to “lune up” to get out of cell (not only does AP go slowly through cell it takes a while to go to the next)

Question 8

Purkinje fibres

Answer 8

• fast conduction fibres
• rapidly conducts action potential throughout ventricles
• ventricles served by bundle branches
• allows ventricles to contract as a syncitium

Question 9

Is the Na channel expressed in Purkinje fibres slow or fast?

Answer 9

very quick

Question 10

What is unique to the AP in cardiac muscle cells

Answer 10

plateau phase -caused by the removal of Na which is accomplished by getting Ca in and removing Na (Na/Ca exchanger)

Question 11

How are ventricular muscles activated?

Answer 11

Ca that comes in binds to Ryr receptor

Question 12

Electrical activity of the heart can be measured at the skin with?

Answer 12

Electrocardiograms

Question 13

What drug is used to treat ventricular tachycardias? Side effects include?

Answer 13

Lidocaine

-neurological tremors or seizures

Question 14

Arrhythmias arise from

Answer 14

abnormal conducting system or ectopic beats (channels fire inappropriately)

Question 15

Electrocardiogram of an arrhythmia shows

Answer 15

HR >160 in dogs
uncoupling with P waves
wide QRS complex

Question 16

Tachycardia decreases

Answer 16

myocardial perfusion

Question 17

What is the function of ivabradine?

Answer 17

specifically blocks funny channel/HCN in SA node to prevent Na influx
-only binds to open channels

Question 18

A dog is diagnosed with sick sinus syndrome. What is the standard treatment?

Answer 18

Pacemaker