10. Interactive Session

Question 1

What is the most likely cause of a stress test making your heart rate increase?

Answer 1

Increased slope of phase 4 of the SA nodal cells (phase 4 is RMP, so if that increases=quicker firing= faster HR)

Question 2

When are fast Na+ channels opened in the atria?

Answer 2

during middle of P wave

Question 3

When does the ventricle repolarize?

Answer 3

during T wave

Question 4

Decreased parasympathetic nervous system activation increases heart rate, so if we wanted to decrease the activation of PSNS, what receptor would we block?

Answer 4

Muscarinic and NT acetylcholine

Question 5

What is the difference between a positive chronotropic effect and inotropic effect?

Answer 5

Chronotropic will increase the speed of the HR

Ionotropic will increase the strength of contraction

Question 6

What are the 5 steps for cardiac glycosides and how they work?

Answer 6

1. Digoxin blocks Na/K ATPase pump
2. Intracellular Na+ concentration increase causing the concentration gradient to decrease
   3/4. Na/Ca2+ exchanger is less effective causing intracellular Ca2+ concentration to increase
3. More Ca2+ availble during contraction having a positive ionotropic effect without increasing energy demand

Question 7

What is preload?

Answer 7

Tension in the aortic walls of the chamber before contraction, before volume increases

Question 8

What is afterload?

Answer 8

Aortic pressure after contraction, which has greatly increased. (pressure in ventricule neccessary to eject blood in pulmonary artery)

Question 9

Is a QRS complex of 0.2ms normal?

Answer 9

No, abnormal = bundle branch block/ ventricular beat

Question 10

When is the voltage difference greater?

Answer 10

In the T wave!