CPR 7.04 Cardiac Electrophysiology

Question 1

How would sympathetic activation of the heart affect the slope of phase 4 and the action potential threshold.

Answer 1

Increases slope

Reduces threshold

Question 2

What effect would sympathetic activation of the heart have on I-f and L-type Ca++ channels?

Answer 2

• Increases I-f

- Opens Ca++ channels earlier

Question 3

How would vagal activation of the heart affect the slope of phase 4 and the action potential threshold.

Answer 3

Decreases slope

Increases threshold

Question 4

What effect would vagal activation of the heart have on I-f and L-type Ca++ channels?

Answer 4

Decreases I-f

Opens Ca++ channels later

Question 5

What effect would vagal activation of the heart have on K-ACh channels and explain what this would accomplish

Answer 5

• Opens K-ACh channels.

- K interacts with K+ coupled Muscarinic channels

Question 6

An increased K+ concentration will have what effect on HR?

Why?

Answer 6

Decreased HR

small increases in K+ opens K+ efflux channels and hyper polarizes the cell.

Question 7

Hyperthyroidism will have what effect on HR?

Why?

Answer 7

Increased HR due to increased metabolism of nodal cells.

Question 8

What effect will nodal ischemia/hypoxia have on HR and why?

Answer 8

Decreased HR due to decreased ATOP opening K ATP channels and causing hyper polarization

Question 9

What is the pace set by AV node?

Answer 9

40-60bpm

Question 10

What is the pace set by Purkinje fibers?

Answer 10

30-40bpm

Question 11

Name something that pre-disposes a patent for after-depolarizations.

Answer 11

Prolonged QT syndrome: genetics, drugs, etc.

Question 12

How are action potentials passed from cell to cell in the heart? (through what component of these cells?)

Answer 12

Low resistance gap junctions

Question 13

Describe 1st degree AV block

Answer 13

Increased PR interval due to delayed condition through AV node, but still NSR

Question 14

Describe 2.1 AV block

Answer 14

PR gradually lengthened, then drop QRS

Question 15

Describe 2.2 AV block

Answer 15

PR fixed, but drop QRS randomly

Question 16

Describe 3rd degree AV block

Answer 16

PR and QRS dissociated

Question 17

Wht type of arrhythmia is Global reentry likely to cause?

Example?

Answer 17

SVT

WPW

Question 18

Local reentry within atria or ventricles is likely to cause what types of arrythmias?

Answer 18

• Atrial tachycardia

- Vetnricular tachycardia

Question 19

Local reentry within the AV node is likely to cause what type of arrhythmia?

Answer 19

SVT

Question 20

What are the abnormal requirements in order for reentry to occur? (in regards to abnormal conduction in the heart)

Answer 20

• Partial depolarization of a conduction pathway
• Uniderectional block that only conducts AP in 1 direction
• Timing beyond the ERP