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FHB Exam 1 - Cardiovascular Physiology > Lecture 7 - Cardiac Refractory Periods > Flashcards

Lecture 7 - Cardiac Refractory Periods Flashcards

1
Q

Define the Effective Refractory Period.

A
  • Channels responsible for the action potential upstroke are completely inactivated
  • NO action potentials can be elicited
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2
Q

Define the Relative refractory period.

A
  • Channels responsible for the action potential upstroke are partially recovered
  • ABNORMAL action potentials CAN be elicited at this time.
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3
Q

What has a longer RRP (relative refractory period) fast response Na or slow response Ca?

A

SLOW RESPONSE Calcium channels

  • ## activates and inactivates slowly
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4
Q

Systole occurs during ARP(absolute) or RRP(relative)?

A

Absolute refractory period!

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5
Q

During an RRP, is conduction time increased or decreased? Why?

A
  • conduction time is INCREASED
  • less Na channels open for depolarization = less upstroke = slower conduction time, ABNORMAL AP!! (can kill via arrhythmia)
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6
Q

Slow response refractoriness primarily depends on what? Fast response refractoriness?

A
  1. Slow response refractory period depends on TIME

2. Fast response depends on VOLTAGE ( membrane potential)

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7
Q

What Na gate recovers with repolarization? What can occur upon depolarization of the cell?

A

H gate

  • Action Potential can occur
  • allows Na channels to go from inactive to resting state
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8
Q

Premature beats CANNOT be elicited during an RRP. True or False?

A

FALSE

  • Premature beats can be elicited
  • slow upstroke, slow conduction = arrhythmia
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9
Q

What is considered the “Vulnerable” period of the heart?

A

RRP!

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10
Q

What is the R on T phenomenon?

A

premature beat (R wave) that occurs during the relative refractory period (T wave) of the previous beat

R = beat
T = refractory period
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11
Q

What causes a non-sustained ventricular tachycardia? What else is often caused by this phenomenon?

A
  1. premature beat (R) on the RRP (vulnerable period) of the T wave –> previous beat
    - monomorphic
  2. Torsades de pointes (polymorphic ventricular tachycardia)
    - AP twisting around multiple points
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12
Q

What is the term for the lethal disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart (precordial region)? What is it a form of?

A
  1. Commotio Cordis
    (commotio = earthquake, cordis = heart)
  2. Ventricular Fibrillation
  • not mechanical damage to heart or area around it
  • not a result of heart disease
  • -> can SOMETIMES be reversed w/ defibrillation (more common in young boys, especially baseball players)
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13
Q

What is Post-Response Refractoriness? If the cell completely repolarizes, can the cell depolarize?

A

Slow response refractory period outlasts Action Potential duration (longer than the AV Node AP)

  • no cell is STILL IN REFRACTORY
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14
Q

Why can slow response refractoriness NOT cause depolarization again? Specifically in relation to Ca channels.

A
  • cell is still in refractory

- recovery period of Ca channels is more dependent on TIME than voltage (like in fast Na channels)

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15
Q

What does Post-Response Refractoriness prevent?

A

prevents rapid VENTRICULAR activation during ATRIAL Fibrillation

(atrial tachy-dysrhythmias = fibrillation or flutter)

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16
Q

If Ca channels are excited immediately following depolarization, will depolarization occur?

A

NO!!!

  • Ca (time dependent) channels have not recovered from the previous beat
  • increase TIME = increase action potentials since Ca channels are recovering
17
Q

What occurs in atrial fibrillation?

A
  1. Ventricular rate is too rapid
  2. Ventricular Rhythm is irregularly irregular
  • AV node filtering impulses irregularly due to irregular Atrial conduction
18
Q

What is the interval-duration relationship?
As heart rate increases, does the Action Potential duration increase or decrease?
What is the purpose of this mechanism?

A
  1. the rate (interval) at which the heart is beating will determine the DURATION of the action potential
  2. Action potential duration(systole) DECREASES
  3. Restore some of the loss in diastolic (filling) time due to the HIGHER HEART RATE
19
Q

The interval-duration relationship appears on the EKG how?

A
  • increase in heart rate, AP decreases

= decrease in Q-T interval (systole)

20
Q

How can one INCREASE the Relative Refractory Period?

A

give Calcium channel blockers!

  • if calcium does not recover, AP can not be administered = slow down the conduction of the heart
21
Q

In atrial fibrillation, what is determining the rate and rhythm of the ventricular activation? (test)

A

AV NODE REFRACTORY PERIOD determines the conduction of the ventricular rate

22
Q

How do you slow ventricular rate in a patient with atrial fibrillation?

A

give CALCIUM CHANNEL BLOCKERS

23
Q

In atrial fibrillation, what filters the impulses irregularly?

A

AV Node Refractory Period

  • impulse from atria not getting through to ventricles in a regular pattern
24
Q

How can atrial fibrillation cause a stroke? What can we do to prevent the stroke?

A

depending on the length of atrial fibrillation if we use a difribillator

  • can push the clot
  • cause a stroke
  1. GIVE ANTI-COGULATES
    - they come back and then you defibrillate them
25
Q

What autonomics can slow down conduction through the AV NODE?

A
  1. Parasympathetic stimulants (Not acetylcholine –> this is how Sarin gas works, it inhibits the cholinesterase enzymes)
  2. BETA-BLOCKERS = b-adrenergic channels blocked
26
Q

What shortens more during increased Heart Rate: Systole or Diastole? How can one conserve diastole?

A
  1. DIASTOLE
    - decreases filling
  2. by shortening the (AP), you work to conserve the DIASTOLE
27
Q

What is prolonged Q-T syndrome? What are the acquired Q-T syndromes?
Congenital?

A
  1. Longer Q-T interval due to decrease in heart rate

A) Bradycardia
B) Hypokalemia
C) Quinidine

Congenital = genetic lesion in Na and/or K channels

28
Q

What is Torsades De Pointes? What may this be due to?

A

Polymorphic Ventricular Tachycardia

  1. results from conditions in which Q-T internal is ABNORMALLY prolonged
  2. may be due to development of early after depolarizations (EAD)
29
Q

What is bradycardia?

A

pathologically slow heart rate (but not always pathologic bcuz during sleep heart becomes bradycardic but not PATHOLOGIC )

30
Q

How does hypokalemia affect the Q-T interval and thus heart rate? What is its affect on the Action Potential?

A
  1. Increase Q-T interval
  2. Decrease Heart Rate
  3. Prolonged Action Potential
31
Q

Does low potassium in the HEART increase or decrease potassium permeability? This occurs why?

A
  1. DECREASES K+ (Ik1) permeability

- due to inactivation of inward rectifying channels

32
Q

Does hypokalemia lengthen or decrease the AP?

A

lengthens the AP

  • potassium does not leave since membrane permeability decreases (inactivation of inward rectifying channels)

FHB Exam 1 - Cardiovascular Physiology (26 decks)

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