Lecure 6 - Cardiac ElectroPhysiology

Question 1

What are specialized regions of intercellular connections between cardiac cells called?

Answer 1

Intercalated disks

Question 2

What are the 3 types of junctions within an intercalated disk?

Answer 2

1. Fascia Adherens
2. Macula Adherens
3. Gap Junctions

Question 3

What are the anchoring sites for actin that connect to the closest sarcomere?

Answer 3

Fascia Adherens

Question 4

What adhering junctions have low resistance connections that allow current (Action potentials) to conduct between cardiac cells?

Answer 4

GAP JUNCTIONS

Question 5

What holds cells together during contraction by binding intermediate filaments, joining cells together like a SPOT WELD?

Answer 5

Macula Adherens

• DESMOSOMES

Question 6

What is HEALING OVER?

Answer 6

an increase in INTERNAL RESISTANCE that results from a decrease in the # of open gap junctions

Question 7

What are 2 causes of healing over?

Answer 7

1. Increase in intracellular (cytosolic) Ca2+
2. increase in intracellular H+ ions (decrease ph)
   - Ca is usually LOW in the cell

Question 8

What is a clinical application of HEALING OVER?

Answer 8

Electrical isolation of damaged tissue that results from Myocardial Infarction

Question 9

Describe the following for SA & AV Nodes:

1. Function
2. Conduction ( slow/fast)
3. Contraction (weak/strong)
4. DIAMETER
5. # of Gap Junction connections
6. Myofibrils

Answer 9

1. Pacemaker activity
2. SLOW CONDUCTION
3. WEAK CONTRACTION
4. small diameter (large internal resistance, small space constant)
5. few gap junctions
6. few Myofibrils

Question 10

Describe the following for Atrium and Ventricles:

1. Function
2. Conduction ( slow/fast)
3. Contraction (weak/strong)
4. DIAMETER
5. # of Gap Junction connections
6. Myofibrils

Answer 10

1. Conduction/ Contraction
2. Fast conduction
3. STRONG contraction
4. medium diameter
5. Abundant gap junctions
6. Abundant MYOFIBRILS

Question 11

Describe the following for His Bundle, Bundle Branches, and Purkinje Fibers:

1. Function
2. Conduction ( slow/fast)
3. Contraction (weak/strong)
4. DIAMETER
5. # of Gap Junction connections
6. Myofibrils

Answer 11

1. VERY RAPID CONDUCTION!!!!!!!!!!!!
2. VERY RAPID conduction
3. weak contraction!
4. LARGE DIAMETER
5. abundant gap junctions
6. FEW MYOFIBRILS

Question 12

What factors determine cardiac conduction?

Answer 12

1. Space Constant

2. Rate of Rise AND Amplitude of Action Potential

Question 13

How is Rm (membrane resistance) related to K+ permeability?

Answer 13

INVERSLEY related

-as membrane resistance decreases, K+ permeability increases

Question 14

How is Ri (internal resistance) related to gap junctions and cell diameter?

Answer 14

• Inversely related to both

- internal resistance decreases with GREATER number of GAP JUNCTIONS and a GREATER CELL DIAMETER

Question 15

How is the space constant defined by Rm and Ri?

Answer 15

space constant = (Rm/Ri) 1/2

square root

Question 16

What 3 factors determine the rate of rise AND amplitude of AP?

Answer 16

1. Level of Resting Membrane Potential (fast -response only)
2. Slow vs. fast response AP’s
3. Premature Responses initiated during RELATIVE REFRACTORY period

Question 17

At what mV is the number of NA+ channels maximum? When is it ZERO?

Answer 17

1. Max at about -80, -90
2. Zero at -50

(at -60 = 50% of Na channels open OR conductance)

Question 18

What defines conductance?

Answer 18

The number of channels open or closed

Question 19

What are 3 conditions that influence the AP upstroke (depolarization phase- Na influx) as a result of changes in the RMP?

Answer 19

1. Hyperkalemia (more positive RMP)
2. Premature Excitation during relative refractory period
3. Ischemia or Myocardial Injury

Question 20

An abnormal increase in EXTRACELLULAR K+ will cause a more positive or negative RMP?

• What CHannels are inactivated as a result?

Answer 20

More POSITIVE

• fast Na channels are inactivated

Question 21

If Na channels are inactivated due to increase in extracellular K+, what happens to the rate of rise & amplitude size?
What is the MAJOR result of this?

Answer 21

1. SLOWER rate of rise,
2. Decrease Amplitude AP
3. SLOWER CONDUCTANCE!!!! of the AP

Question 22

During ischemia/infarct, what can leak out of damaged cells?

Answer 22

K+ ions

• accumulate in interstitial (extracellular) fluid bathing the cells
• LOCAL concentration of K+ can increase to 20 mEq/L ( normal is 4)

Question 23

An increase in interstitial (extracellular) K+, causes what change to the voltage?

Answer 23

MORE POSITIVE VOLTAGE (positive RMP)

• since K+ moving from high to low, thus moving IN to the cell instead of out
• inactivates Na channels

Question 24

What is a major cause of arrhythmia? How is this defendant on K+ concentration and Na+ channel?

Answer 24

1. SLOWER CONDUCTANCE
2. If K+ higher outside cell, RMP is positive, thus cell depolarizes and Na channels inactivated
3. If fast Na channels inactivated in a damaged region = SLOWER CONDUCTION

(reliant on slow Ca2+ channels)

Question 25

What interval on an EG is responsible for the conduction time of Atria to Ventricular Muscle? For Intra- Ventricular Conduction time?

Answer 25

1. P-R interval | 2. QRS interval

Question 26

Does Atrio-Ventricular delay or increase conduction?

Answer 26

DELAY to increase optimal ventricular filling

Question 27

The AP of Atrio-Ventricular conduction is slow or fast?

Answer 27

SLOW conduction= slow response AP due to slow inward Calcium current

Question 28

Atrio-Ventricular conduction (AV Node) has a long or short refractory period? What is the function of this?

Answer 28

LONG refractory period - long because if protects the ventricles from abnormally HIGH ATRIAL rates = Atrial Flutter/Fibrillation - AV conduction time determined by P-R interval

Question 29

Describe the following blocks in AV Nodal Abnormalities: 1st Degree Heart Block 2nd Degree Heart Block 3rd Degree

Answer 29

1. abnormally prolonged P-R interval (more than 200 milliseconds or 0.2 seconds) 2. Atrial Impulses fail to activate ventricles, not all P waves followed by QRS complex 3. complete AV nodal bloc, no consistent P-R interval

Question 30

The following describes 1st, 2nd, or 2rd degree block: complete AV nodal bloc, no consistent P-R interval

Answer 30

3rd

Question 31

The following describes 1st, 2nd, or 2rd degree block: abnormally prolonged P-R interval (more than 200 milliseconds or 0.2 seconds)

Answer 31

1st

Question 32

The following describes 1st, 2nd, or 2rd degree block: Atrial Impulses fail to activate ventricles, not all P waves followed by QRS complex

Answer 32

2nd

Question 33

Is Ventricular conduction rapid or slow?

Answer 33

RAPID - conduction through His-Purkinje System

Question 34

Where does Ventricular Conduction bring the electrical impulse?

Answer 34

- to the endocardial surface - from there it goes from ENDO to EPICARDIUM Result = end to epicardial activation of the ventricles

Question 35

Because the Ventricular Conduction is so rapid, how does the QRS interval look as a result?

Answer 35

very NARROW - less than 100 msec

Question 36

What determines intra-ventricular conduction time? What is the function of Ventricular Conduction?

Answer 36

Duration of the QRS complex (interval) - to synchronize ventricular activation (contraction)

Question 37

Hyperkalemia, Ischemia, and Ventricular tachycardia show what kind of EKG recording?

Answer 37

SLURRED QRS complex - slowed intra-ventricular conduction = abnormal wall motion

Question 38

Asynchronous electrical activation of left and right ventricles is often caused by what? How does this look on EKG?

Answer 38

1. Left and/or right bundle branch BLOCKS | 2. Notched QRS complex

Question 39

What occurs during Supraventricular Tachycardia?

Answer 39

1. conduction is normal in ventricles - impulse comes from Atria and travels thru AV node into His-Purkinje system 2. QRS is normal 3. Ventricular wall motion is normal = stroke volume not significantly affected

Question 40

What occurs during Ventricular Tachycardia?

Answer 40

1. Conduction in Ventricles is not normal = SLOW 2. impulse originates in ventricular muscle & does not travel through His -Purkinje 3. QRS is abnormally prolonged (SLURRED)

Question 41

What happens to the ventricular wall motion & stroke volume in Supraventricular & Ventricular Tachycardia?

Answer 41

1. Normal 2. Ventricular wall motion is abnormal - Stroke volume compromised

Question 42

The shape of the P wave of EKG determined what conduction?

Answer 42

ATRIAL

Question 43

During Atrial & Ventricular Fibrillation, what occurs? Which is life threatening?

Answer 43

- atria & ventricles NOT IN SYNCHRONY = pumping action ceases - Ventricular Fibrillation is FATAL, but Atrial is not

Question 44

Where is acetylcholine released from? (Parasympathetic or sympathetic?)

Answer 44

Vagus nerve --> PARASYMPATHETIC

Question 45

Which receptors does acetylcholine use? Norepinephrine?

Answer 45

1. MUSCARINIC | 2. beta-1 adrenergic receptors

Question 46

What does ACh do to the permeability of the membrane?

Answer 46

- increases K+ permeability via G-protein | - HYPERPOLARIZES away from threshold

Question 47

What inhibits adenylyl cyclase acitvity & cAMP synthesis? What is the result of this inhibition?

Answer 47

- ACETYLCHOLINE! | - decreases slow inward Ca current indirectly via inhibition of cAMP synthesis

Question 48

``` What NT (ACh or Norepinephrine) : 1. Inhibits ATRIAL muscle contraction (negative ionotropic effect) ``` 2. Inhibits SA node pacemaker activity = SLOWER HEART RATE 3. INHIBITS AV NODE CONDUCTION What does inhibiting AV node conduction result in?

Answer 48

1. ACh!! | - inhibiting AV node conduction results in LONGER P-R interval

Question 49

Does ACh have an effect onbasal ventricular muscle function?

Answer 49

NO EFFECT on basal ventricular muscle function

Question 50

Where is NE released?

Answer 50

SYMPATHETIC NERVES

Question 51

NE acts via what receptors? What areas of the heart does it act on?

Answer 51

1. ALL AREAS OF HEART | 2. Beta-1 adrenergic receptors to INCREASE cAMP

Question 52

How does NE affect the Calcium current? What does this do to atrial and ventricular contraction? Is this a positive or negative inotropic effect?

Answer 52

- INCREASES slow inward Calcium current (calcium low inside) - INCREASES contraction - positive inotropic effect

Question 53

Which NT (NE or ACh) inhibits and which increases SA node and AV node conduction?

Answer 53

1. Ach inhibits both SA node = sow heart rate, lengthen R-R AV Node = lengthens P-R interval 2. NE: INCREASES both - increases atrial & VENTRICULAR contraction - increases SA NODE RATE = increase heart rate = decrease R-R interval -icrease AV NODE CONDUCTION = decrease P-R interval

Question 54

What is the effect of increases AV node conduction on the EKG? What about increasing SA node conduction?

Answer 54

1. increase AV node = DECREASE P-R interval | 2. increase SA node = DECREASE R-R interval (from one QRS to next)