Basic CV functions - Cardiac AP's and ECG's

Question 1

The role of the SA node is to:

Answer 1

Initiate contraction

Governs heartrate since this is the node that depolarizes the fastest

Question 2

How often does the SA node depolarize?

Answer 2

About every second, OR about 70 times per minute

Question 3

The role of the AV node is to:

Answer 3

Provide a gateway for electrical impulse into ventricles

Delays ventricular contraction, to allow for ventricle filling

This is the ONLY way for an impulse to trigger ventricular contraction in a healthy heart

Question 4

Prior to conduction, heart muscle cells are _____

Answer 4

Polarized

80-90 mV compared to outside the cell

Question 5

How do heart muscle cells maintain their polarized resting membrane potential?

Answer 5

Ion pumps

Sodium, potassium, and calcium

Question 6

Depolarization of a muscle cell causes:

Answer 6

Muscle contraction

Question 7

Depolarization of heart muscle cells is caused by:

Answer 7

Calcium entry into muscle cells

…Which causes muscle contractions

Question 8

Why do heart muscle cells become depolarized if ion pumps should maintain resting membrane potentials?

Answer 8

Leakage through maintenance channels

Question 9

Describe phase 4 of the cardiac action potential.

Answer 9

K+ loss diminishes negative charge - eventually reaching abrupt increase in Na+ permeability

Question 10

Describe phase 0 of the cardiac action potential.

Answer 10

Increased permeability to sodium influx, calcium channels open ~ -60 mV

Depolarization

Question 11

Describe Phase 3 of the cardiac action potential.

Answer 11

Membrane remains permeable, Na+ and K+ are ejected, repolarzing the cell

Question 12

Describe phase 1 of the cardiac action potential

Answer 12

Brief re-polarization from K+ escaping the cell

Question 13

More calcium entry results in…

Answer 13

Stronger contraction (inotropy/contractility)

Question 14

Faster calcium entry results in…

Answer 14

Faster contraction (chronotropy/heart rate)

Question 15

Muscles cannot contract again until…

Answer 15

Repolarization occurs (Phase 3 and 4)

Question 16

Basic knowledge of Cardiac AP’s is important for:

Answer 16

Pharmacology of Non-DHP CCB’s and BB’s, antiarrythmic drugs
Cardiac disorders

QT prolongation, arrythmias, etc.

Question 17

What is an ECG?

Answer 17

Graph of electrical activity in the heart

Detected by electrodes attatched to the patient

Question 18

Describe the P-wave of an ECG.

Answer 18

Depolarization of the atria (contraction)

Question 19

Describe the QRS-complex of an ECG

Answer 19

Depolarization of the ventricles (contraction)

Question 20

Describe the T-wave of an ECG

Answer 20

Repolarization of the ventricles

Question 21

What is the QT interval?

Answer 21

Time of contraction to repolarization of ventricles

Question 22

Basic ECG knowledge is important for

Answer 22

Ischemic condition assessment
Evaluation of arrythmia, as well as risk for arrythmia and CI of drugs