Lecture 7 - Cardiac Refractory Periods Flashcards
Define the Effective Refractory Period.
- Channels responsible for the action potential upstroke are completely inactivated
- NO action potentials can be elicited
Define the Relative refractory period.
- Channels responsible for the action potential upstroke are partially recovered
- ABNORMAL action potentials CAN be elicited at this time.
What has a longer RRP (relative refractory period) fast response Na or slow response Ca?
SLOW RESPONSE Calcium channels
- ## activates and inactivates slowly
Systole occurs during ARP(absolute) or RRP(relative)?
Absolute refractory period!
During an RRP, is conduction time increased or decreased? Why?
- conduction time is INCREASED
- less Na channels open for depolarization = less upstroke = slower conduction time, ABNORMAL AP!! (can kill via arrhythmia)
Slow response refractoriness primarily depends on what? Fast response refractoriness?
- Slow response refractory period depends on TIME
2. Fast response depends on VOLTAGE ( membrane potential)
What Na gate recovers with repolarization? What can occur upon depolarization of the cell?
H gate
- Action Potential can occur
- allows Na channels to go from inactive to resting state
Premature beats CANNOT be elicited during an RRP. True or False?
FALSE
- Premature beats can be elicited
- slow upstroke, slow conduction = arrhythmia
What is considered the “Vulnerable” period of the heart?
RRP!
What is the R on T phenomenon?
premature beat (R wave) that occurs during the relative refractory period (T wave) of the previous beat
R = beat T = refractory period
What causes a non-sustained ventricular tachycardia? What else is often caused by this phenomenon?
- premature beat (R) on the RRP (vulnerable period) of the T wave –> previous beat
- monomorphic - Torsades de pointes (polymorphic ventricular tachycardia)
- AP twisting around multiple points
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?
- Commotio Cordis
(commotio = earthquake, cordis = heart) - 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)
What is Post-Response Refractoriness? If the cell completely repolarizes, can the cell depolarize?
Slow response refractory period outlasts Action Potential duration (longer than the AV Node AP)
- no cell is STILL IN REFRACTORY
Why can slow response refractoriness NOT cause depolarization again? Specifically in relation to Ca channels.
- cell is still in refractory
- recovery period of Ca channels is more dependent on TIME than voltage (like in fast Na channels)
What does Post-Response Refractoriness prevent?
prevents rapid VENTRICULAR activation during ATRIAL Fibrillation
(atrial tachy-dysrhythmias = fibrillation or flutter)
If Ca channels are excited immediately following depolarization, will depolarization occur?
NO!!!
- Ca (time dependent) channels have not recovered from the previous beat
- increase TIME = increase action potentials since Ca channels are recovering
What occurs in atrial fibrillation?
- Ventricular rate is too rapid
- Ventricular Rhythm is irregularly irregular
- AV node filtering impulses irregularly due to irregular Atrial conduction
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?
- the rate (interval) at which the heart is beating will determine the DURATION of the action potential
- Action potential duration(systole) DECREASES
- Restore some of the loss in diastolic (filling) time due to the HIGHER HEART RATE
The interval-duration relationship appears on the EKG how?
- increase in heart rate, AP decreases
= decrease in Q-T interval (systole)
How can one INCREASE the Relative Refractory Period?
give Calcium channel blockers!
- if calcium does not recover, AP can not be administered = slow down the conduction of the heart
In atrial fibrillation, what is determining the rate and rhythm of the ventricular activation? (test)
AV NODE REFRACTORY PERIOD determines the conduction of the ventricular rate
How do you slow ventricular rate in a patient with atrial fibrillation?
give CALCIUM CHANNEL BLOCKERS
In atrial fibrillation, what filters the impulses irregularly?
AV Node Refractory Period
- impulse from atria not getting through to ventricles in a regular pattern
How can atrial fibrillation cause a stroke? What can we do to prevent the stroke?
depending on the length of atrial fibrillation if we use a difribillator
- can push the clot
- cause a stroke
- GIVE ANTI-COGULATES
- they come back and then you defibrillate them
