Electrophysiology of the Heart

Question 1

3 Muscles of the Heart

Answer 1

1. Atrial Muscles2. Ventricular Muscles3. Conductive Muscle Fibers

Question 2

Intercalated Discs

Answer 2

Connection of heart muscle cells

Question 3

Desmosomes

Answer 3

Structural element that combines them

Question 4

Gap Junctions

Answer 4

Ion channels that allow ions to move freely between cells, allowing electrical impulse

Question 5

Contractile Cells

Answer 5

1. Compose most of the heart2. Contract when stimulated

Question 6

Auto-rhythmic Cells

Answer 6

1. Comprise the conducting system2. Self-stimulating and can contract/depolarize without external stimulus

Question 7

Fast Response Cells

Answer 7

1. Atrial and Ventricular Myocytes2. Purkinje Fibers

Question 8

Examples of Slow Response Cells

Answer 8

1. SA Node2. AV Node

Question 9

Resting Membrane Potential

Answer 9

-80-90mV Interior Negative

Question 10

Phase 0

Answer 10

• Higher K insid ethe cell- Sudden opening of fast and slow Na+ channels- Rise in Na+ permeability- Drop in K+ permeability

Question 11

Tetrodotoxin

Answer 11

Blocks Na+ Channels

Question 12

Phase 1 (Also called?)Blocked by?

Answer 12

Repolarization- K+ channels open- Primarily caused by closing of Na+ ion channels and opening of K+ ion channelsBlocked by 4-aminopyridine

Question 13

Phase 2 Activators and Blockers

Answer 13

A: Catecholamines: Increase ECF-Ca2+ ConcentrationB: Ca2+ Antagonists and Mn2+

Question 14

Phase 2 (Or?)1. What changes to voltage?2. What channels are open?3. What’s happening?

Answer 14

Plateau Phase1. Voltage is constant2. Ca2+ channels are open (Some K+ leaking out, causing balance)3. Prolongs duration of contraction, prevent overstimulation

Question 15

Phase 3 (Or?)What channels are open?

Answer 15

Genesis/Final RepolarizationOnly K

Question 16

Phase 4 (Or?)1. What is working in this stage?2. What happens to Ca2+?

Answer 16

Rest Phase

1. Na-K ATPase pump works to remove Na+ and returns K+
2. Ca2+ exchanged for Na+

Question 17

Major Differences of Skeletal and Cardiac Muscles?

Answer 17

1. Presence of both fast Na+ and slow Ca2+ channels in Cardiac Muscles2. Decreased K+ channel permeability after action potential: Prevents premature return to resting levels

Question 18

Absolute Refractory Period

Answer 18

Cannot be stimulated no matter what

Question 19

Effective Refractory Period

Answer 19

Can only be stimulated by a larger than normal stimulus

Only a local response can be produced

No action potential generated

Question 20

Relative Refractory Period

Answer 20

Action Potential can only be stimulated by a larger than normal stimulus

Question 21

Supernormal Period

Answer 21

More excitable than normal; ala a weaker stimulus can cause depolarization

Question 22

Full Recovery Time in Fast Response and Slow Response cell is dependent on?

Answer 22

Fast-Response: Voltage-DependentSlow-Response: Time-Dependent

Question 23

Effects of VMAX

Answer 23

More VMAX :: More Conduction

Question 24

Diameter

Answer 24

Fatter Cell : Faster

Question 25

Changing Resting Membrane Potential

Answer 25

More Negative :: More Quicker

Question 26

Conducting System Pathway

Answer 26

SA Node -> Atrium -> AV Node -> Bundles of His -> Purkinje Fibers -> Ventricular Muscles

Question 27

SA Node Resting Potential

Answer 27

-55 to -60mV

Question 28

Why is the SA Node Membrane Naturally Leaky to Sodium Ions?

Answer 28

- Enter through slow sodium channels- More permeable to Na due to higher extracellular concentration- Faster heart rate : More Sodium

Question 29

Fast, Slow, or both Na+ channels for SA Nodes?

Answer 29

Only slow, fast channels are blocked due to less negativity

Question 30

Threshold Voltage of SA Node

Answer 30

-40 mV

Question 31

Bachmann's Bundle

Answer 31

Conducts impulse from SA node -> Left Atrium

Question 32

AV Node Function

Answer 32

Delays the impulse from the atria to the ventricle to allow for more contraction time

Question 33

Purkinje System Transmission Rate

Answer 33

1.5-4m/s (Fastest)

Question 34

Hierarchy of Pacemakers

Answer 34

1. SA Node: 70-80 bpm2. AV Node: 40-60 bpm3. Purkinje Fibers: 15-40 bpm

Question 35

Which pacemaker is most dominant and why?

Answer 35

The SA Node, because it has the fastest rate of depolarization preventing others from self-exciting

Question 36

Stokes-Adam Syncope

Answer 36

Occurs when SA node fails and takes time for the AV node to take over; causes you to faint

Question 37

Parasympathetic Nerves:1. Innervates2. Secretes

Answer 37

1. Mainly sinus and AV node, some parts of the two atria and little to the ventricular muscles2. Acetylcholine

Question 38

Acetylcholine Effects

Answer 38

1. Decreases rate of rhythm of sinus node2. Decreases excitability of the AV junctional fibers between atrial musculature and AV node3. Slows down heart rate

Question 39

Mechanism of Parasympathetic Nerves

Answer 39

Increases permeability of K+ ions out of cell, causing hyperpolarization

Question 40

Sympathetic Nerves1. Innervates2. Secretion

Answer 40

1. All parts of the heart2. Norepinephrine

Question 41

Norepinephrine Effects

Answer 41

1. Increases rate of sinus node discharge2. Increases rate of conduction and excitability3. Increases force of contraction

Question 42

P Wave

Answer 42

Atrial Depolarization

Question 43

QRS Complex

Answer 43

Ventricular Depolarization

Question 44

T Wave

Answer 44

Ventricular Repolarization

Question 45

ECG X and Y Axis

Answer 45

X: TimeY: Voltage

Question 46

ECG Small Box, Big Box

Answer 46

Small Box: 0.04sBig Box: 0.2s (equal to 5 small boxes)

Question 47

Normal QRS Axis

Answer 47

Between -30 and +90 degrees

Question 48

Increased Voltage in ECG

Answer 48

- Normal 0.5 to 2.0mV- Commonly caused by ventricular hypertrophy

Question 49

Decreased Voltage in ECG

Answer 49

- Decreased Muscle Mass- Pericardial Effusion: Fluid shorts the currents- Pulmonary Emphysema: Excessive air in lungs act as insulators

Question 50

Prolonged QRS Complex

Answer 50

- Cardiac Hypertrophy or Dilation: Increased distance for current to travel to depolarize- Purkinje System Blocks

Question 51

T Wave Abnormality

Answer 51

Caused by conduction blocks, premature contractions or prolonged depolarizatoin

Question 52

Tachycardia

Answer 52

> 100 BPM- Increased temperature- Sympathetic Stimulation

Question 53

Bradycardia

Answer 53

< 60 BPM