Cardiac Electrophysiology Lecture Powerpoint

Question 1

How does the wave of electrical current generated in the heart spread to adjoining cells?

Answer 1

gap junctions allow ions to pass freely from cell to cell

Question 2

During depolarziation of the cardiac cells ___ occurs in the cardiac myocytes, during repolarization ___ occurs

Answer 2

Contraction, relaxation

Question 3

In cell, for depolarization of resting membrane potential must become less ____

Answer 3

negative

Question 4

At resting state, what ion is found in higher conc inside the cardiac muscle cell?

Answer 4

K+

Question 5

Where are the 3 normal areas of the heart to have automaticity?

Answer 5

• SA node
• AV nde
• Bundle of His/purkinje fibers

Question 6

The pacemaker cell with the ___ rate will over ride the others

Answer 6

highest

Question 7

At rest, Na+ conc. is higher ___ the cell. K+ conc. is higher ___ cell, Ca2+ is at higher conc. ___ cell

Answer 7

outside, inside, outside

Question 8

Threshold value to initiate an AP in a pacemaker cell

Answer 8

-40 mV

Question 9

Cardiac muscle AP is much ____ than skeletal muscle because of a longer ____

Answer 9

Slower, refractory period

Question 10

Skeletal vs cardiac muscle differences (4)

Answer 10

• intrinsic impulse generation in cardiac
• plateau phase in cardiac
• longer refractory period in cardiac
• summation not possible in cardiac

Question 11

There are NO _____ channels operating in the SA node, but they are present in the cardiac muscle

Answer 11

fast Na+

Question 12

Action potential generation in autorhythmic cell mech of action

Answer 12

• autorhythmic cells begin depolarizing (becomes less negative) due to slow continuous inward movement of Na+ and reduced outward movement of K+ from -60mV approx resting potential
• upon reaching threshold -40mV, Ca2+ channels open and Ca2+ rushes into cell making cell much less negative, depolarization occurs
• K+ channels are triggered at -10mV and opened and Ca2+ channels close resulting in K+ flow out of the cell (repolarization)
• Ion pumps use ATP to move Ca2+ back to extracellular space and Na/K ATPase pumps Na+ out of cell and K+ back into cell

Question 13

Action potential generation in cardiac myocyte mech of action

Answer 13

• -90mv is resting potential for the cardiac myocyte
• Positive ions moving thru gap junctions create small voltage change initiating depolarization
• this stimulates opening of fast Na+ cells at -70mV, begins depolarization
• myocyte contraction begins here
• Depolarization to +20mV triggers opening of slow Ca2+ channels, allowing Ca2+ entry from extracellular space
• At same time, depolarization to +20mV triggers K+ channels to allow K+ to begin leaving the cell
• This generates the plateau phase
• Ca2+ channels close and more K+ channels open causing cell to become less positive (repolarization)
• myocyte relaxation begins here
• simultaneously, ions pump Ca2+ out to extracellular space and Na+/K+ATPase pumps Na+ out and K+ back in

Question 14

Effective/Absolute refractory period

Answer 14

Protective mech by limiting frequency of APs preventing tetany, period where 2nd AP cannot be initiated occurring during the majority of the AP cycle

Question 15

Relative refractory period

Answer 15

Period following the effective/absolute refractory period where a 2nd AP is inhibited but not impossible, requiring supra threshold stimulation to elicit AP, they tend to be slower and wider since not all Na+ channels have had time to recover

Question 16

Primary pacemaker of heart normally and where is it located anatomically?

Answer 16

SA node, posterior wall of right atrium

Question 17

Intrinsic rate of the heart of the SA node

Answer 17

100-110 BPM

Question 18

Vagal tone

Answer 18

Sympathetic nervous influence that slows the heart rate from its intrinsic beat at rest (100-110 bpm) to 60-80bpm in healthy patient

Question 19

Internodal tracks

Answer 19

Speed up conduction thru gap junctions to spread an AP thru the atrium quickly, alongside nonconductive tissue that insulates the atrium from the ventricles

Question 20

AV node function and intrinsic rate

Answer 20

Slows signal from SA node down by 120 msec allowing ventricles to fill allowing for complete atrial depolarization, contraction, and emptying of blood into ventricle prior to ventricular contraction, intrinsic rate is 40-60bpm

Question 21

Bundle of His

Answer 21

High speed conduction network that forms the narrow QRS complex allowing for ventricular contraction, receives signal (delayed by) the AV node and transmits signal to rest of heart

Question 22

Premature ventricular contraction/extra systole

Answer 22

Extra abnormal heartbeats that begin in the ventricle and can give the sensation of a skipped beat in chest, normal in moderation but if continuous could indicate a problem

Question 23

How does a PVC/extra systole appear on the EKG?

Answer 23

As an extra, often widened and inverted QRS complex with an absence of a P wave preceding the contraction

Question 24

4 big classes of drugs that we can use to alter AP in the heart

Answer 24

• Na+ channel blockers
• B blockers
• K+ channel blockers
• Ca2+ channel blockers

Question 25

How does a drug that partially inactivates fast Na+channels impact AP in ventricular myocyte and thus conduction veolcity in the ventricle?

Answer 25

It decreases conduction velocity

Question 26

Example of when there is increased vagal tone and decreased vagal tone

Answer 26

• sleeping causes increased vagal tone

- being startled can decrease vagal tone

Question 27

When heart cells lack O2 they become ___. This makes the resting membrane potential ___, therefore many….

Answer 27

depolarized, less neg (-75mV vs -90mV)
…many Na+ channels are inactivated leading to altered impulse formation and conduction decreasing contractility and increasing arrhythmia

Question 28

AV block

Answer 28

Occurs when an impulse starting in SA node cannot enter the ventricle because of block at AV node causing increased PR interval (ventricular bradycardia)

Question 29

1st degree vs 2nd and 3rd degree AV block

Answer 29

Depends on the ratio of how many p waves occur without ventricular contraction on the EKG

Question 30

Bundle branch block

Answer 30

Occurs when either right or left bundle branch is blocked, impulses are still fired from atria to ventricles and SA node is still origination, it will take longer to depolarize the ventricles tho manifesting as an extended QRS complex that is misshapen

Question 31

Hemiblock

Answer 31

Occurs when the left anterior or posterior fascicle of the left bundle branch becomes blocked (more often anterior than posterior) resulting in left axis deviation on EKG

Question 32

Voltage gated channel definition

Answer 32

Ion specific channels that open in response to a particular potential gradient across the cell membrane (in mV) being achieved, with them closing at a particular voltage as well

Question 33

K+ leakage current and Na+ leakage current

Answer 33

Refers to tendency for K+ ions at resting potential in a pacemaker cell to be driven outside the cell by the slight permeability of the cell membrane to K+ slowly changing the voltage until reaching threshold, and Na+ ions in resting potential in pacemaker cell to be driven inside the cell by slight permeability of the cell membrane to Na+ slowly changing the vooltage until reaching threshold

Question 34

Resting membrane potential is negative because…

Answer 34

…there are more positive ions outside the cell than inside, making the cell relatively more negative inside

Question 35

Ectopic foci

Answer 35

Sites that spontaneously depolarize and produce AP independent of SA node (normally overridden by SA node), occurs anytime the pacemaker of the heart is not the SA node, acts as a protective mechanism to ensure the heart still beats even in the absence of the SA node

Question 36

Purkinje fibers

Answer 36

Network of conducting cells that receive a signal from the bundle of His and spread the AP fastest to the rest of the heart activating the ventricles from the apex upwards

Question 37

A lack of a p wave on an EKG would indiacte…

Answer 37

…no SA node activity

Question 38

Intrinsic ventricular rhythm range

Answer 38

20-40 bpm (too slow to sustain life?)

Question 39

Sometimes nonpacemaker cells after becoming hypoxic will…

Answer 39

…change into pacemaker cells that then depolarize spontanously and demonstrate automaticity resulting in irregular beats and arrhythmia

Question 40

Reentry mechanisms

Answer 40

Refers to how ischemia can cause a block in conduction but partial retrograde conduction occurs setting up a circus rhythm allowing for reentry of the signal

Question 41

Global reentry

Answer 41

Occurs between the atria and ventricles and often involves abnormal accessory pathways such as the bundle of kent

Question 42

Wolff-parkinson-white syndrome mech of action

Answer 42

-Due to presence of bundle of kent episodes of tachycardia occur via AP traveling via bundle of kent to the ventricle then retrograde to the AV node

Question 43

Local reentry

Answer 43

Sites within the atria or ventricles that often involve abnormal accessory pathways resulting in tachyarrhythmias