Cardio Electrophysiology 2

Question 1

Where is the SA node located?

Answer 1

The Endocardial surface of the RA, in the junction of the Superior Vena Cava and RA appendage.

Question 2

What are the dimensions of the SA node?

Answer 2

15 mm x 5 mm x 2 mm thick

Question 3

What are the terms for UNSTABLE resting membrane potential?

Answer 3

Prepotential
Pacemaker potential
Diastolic depolarization

Question 4

What is the resting membrane potential of a SA node?

Answer 4

-70 mV

Question 5

What is the maximum membrane potential of a Ventricular Muscle cell?

Answer 5

+20 mV, (at which point where Fast Na+ channels close)

Question 6

What is the maximum membrane potential of the SA node?

Answer 6

0 mV

Question 7

Sinoatrial (SA node) -

Answer 7

The pacemaker cell; it gives the greatest rhythmicity.

Has UNSTABLE resting membrane potentials, which makes it the “pacemaker”

IT DOES NOT HAVE Fast Na+ Channels

Question 8

What are the 3 factors that act together to produce SA nodal Prepotential (pacemaker potential)?

Answer 8

1) Increased Na+ conductance/permeability at REST
2) Decreasing K+ conductance/permeability
3) Slow Ca2+ influx

Question 9

Verapamil -

Answer 9

It inhibits Prepotential of the SA node by blocking Ca2+ channels, and inhibiting spontaneous pacemaker activity

Question 10

Do AV nodes have Fast Na+ channels?

Answer 10

No, neither does the SA node

Question 11

What are the 3 natural pacemakers of the human heart?

Answer 11

SA node
AV node
Purkinje Fiber (idioventricular pacemaker)

Question 12

What are the firing rates of:
SA node
AV node
Purkinje Fiber

Answer 12

SA node: 60-100 times/ min
AV node: 40-55 times/min
Purkinje Fiber: 25-40 times/min

Question 13

What are the major difference btw the 3 pacemakers of the human heart?

Answer 13

The rate of decay of K+ conductance during PHASE 4

Question 14

What are the 3 ways you can change the firing rate of pacemaker cells?

Answer 14

1) change rate of Diastolic depolarization
2) change resting membrane potential
3) change threshold potential

Question 15

What are the 3 ways to SLOW down the rate of firing of a Pacemaker cell?

Answer 15

1) lower the rate of depolarization
2) Hyperpolarize the cell
3) Change the threshold potential

Question 16

How does the Sympathetic Nervous system change the slope of Pacemaker cells action potential?

Answer 16

It INCREASES the slope of the Prepotential, increasing HR

Question 17

How does the Parasympathetic Nervous system change the slope of Pacemaker cell action potential?

Answer 17

It DECREASES the slope, decreasing the HR

Question 18

Which system is used more, the Sympathetic nervous system or the Parasympathetic nervous system?

Answer 18

The Parasympathetic System.

The SA node is usually 100 beats/min, but the Parasympathetic system is always active, decreasing the SA node to 60-100 beats/min.

Question 19

List the order of the Conduction System of the Heart.

Answer 19

1. Start at SA node
2. Atrial Internodal Pathways
3. AV node
4. Bundle of His or AV bundle
5. Bundle Branches
6. Purkinje System
7. Ventricular (heart) muscle

Question 20

What is the Conduction Velocity of the Atrial Internodal Pathway?

Answer 20

1 meter/sec

Question 21

What is the Conduction Velocity of the AV node?

Answer 21

0.02 meter/sec

Question 22

What is the Conduction Velocity of the Bundle of His/ AV bundle?

Answer 22

1-2 meter/sec

Question 23

What is the Conduction Velocity of the R/L Bundle Branches?

Answer 23

2-4 meter/sec

Question 24

What is the Conduction Velocity of the Purkinje System?

Answer 24

2-4 meter/sec

Question 25

What is the Conduction Velocity of the Ventricular (heart) Muscle?

Answer 25

0.3 meter/sec

Question 26

What controls the Conduction Velocity?

Answer 26

Fast Na+ Channels

Question 27

AN zone -

Answer 27

It is the transitional zone; cell types in this region are a mixture of Atrial and Nodal fibers interspersed w/ connective tissue

Question 28

N zone -

Answer 28

It is the Middle Portion of the AV node

Question 29

N-H zone -

Answer 29

It is the transitional zone; nodal fibers gradually merge w/ fibers from the Bundle of His.

Question 30

What controls the opening and closing of the Connexion gap channels?

Answer 30

pH and Ca2+ Concentration

Question 31

In order for Re-entry to occur, what 2 things must happen?

Answer 31

1) There must be a unidirectional block | 2) The Refractory Period must be slower than propagation time around the loop

Question 32

An ECG/EKG is based off of what 3 suppositions?

Answer 32

1) The body is a conduction medium w/ the heart at the center 2) Heart depolarization generates a flow of ions throughout the extra cellular space of the body 3) Electrodes put on the body can detect ion flow

Question 33

What is the QRS complex?

Answer 33

It is when the Ventricular muscle depolarized, causing systolic contraction

Question 34

What is the T wave?

Answer 34

When the ventricle repolarizes and relaxes

Question 35

What is the P wave?

Answer 35

Atrial Depolarization, when the Atria undergoes systolic contraction