Lecture 10/21 & 10/23: Cardiac Flashcards
Test 4
T/F: you cannot generate an AP in the absolute refractory period.
T
What happens if you generate an AP in the relative refractory period?
You might not get an AP or get an odd AP
Pumping in heart will take a hit
What is the main pacemaker of the heart? Why?
The SA node
Higher Vrm so depolarizes and reaches threshold potential faster than any other tissue in the heart -> able to generate AP fastest
The _____ vagus nerve stimulates the SA node
The ______ vagus nerve stimulates the AV node
Right
Left
T/F: some branches of vagus nerve extend past SA/AV node
T
Which nervous system is the main innervation of the pacemakers of the heart?
PNS - vagus
Which nervous system is strongest in the atria and ventricles?
SNS
What is the function of the Vagus nerve at the SA node?
suppression of activity of pacemaker cells
The SA node generates an AP every ______ seconds in a healthy person
0.83 seconds
The SA node generates AP at ______ b/m in a healthy person
72
use this exact number
Without vagal and SNS input, how often would the SA node generate an AP?
110 b/m
Without vagal but with SNS input, how often would the SA node generate an AP?
120 b/m
SNS raises by 10 b/m
If we only had Vagal input, how often would the SA node generate an AP?
60-62 b/m
What are our main catecholamines that effect that SNS in the heart?
NE -> Beta-R
Ach -> mAch-R (dominates)
T/F: SNS effects in the heart are local
F
More widespread in atria/ventricles
SA node AP: Describe phase 4
“Diastolic depolarization”
The steeper the slope = faster HR
Slope d/t increase in membrane potential d/t leaky Ca++ & Na+ channels and HCN channels
Describe L-type Ca++ channels
Open slow and stay open longer (close slow)
SA node AP: Describe phase 0
Upstroke of AP
Less upstroke than ventricles d/t no fast Na+ channels
Slow L-type Ca++ channels open
Important for determining how fast AP gets to each cell around the heart via gap junction
SA node AP: Describe phase 1
HAHA there is no phase 1
SA node AP: Describe phase 2/3
Slow L-type Ca++ channels closing
V-G K+ channels open
Repolarization/Reseting of the cell
Phase 2&3 are combined
SOMETIMES THIS IS ONLY REFERRED TO AS PHASE 3
What is the Vrm in the SA node?
-55 mV
What is the threshold potential in the SA node?
-40 mV
Describe where the HCN channels are?
highest density = SA node
alot in the AV node
Sparcely in ventricles
When can the heart generate an AP?
When you go from Vrm to threshold potential
When do HCN channels open?
At Vrm:
after repolarization or during hyperpolarization
What does HCN channels mean?
Hyperpolarization & cyclic nucleotide mediated channel
What cations pass through HCN channels?
- Na+ (primary)
- Ca+
- K+ (not as much)
Describe pathway of beta agonists on Beta-R with HCN channels
Beta agonists increases cAMP
cAMP = cyclic nucleotide –> opens HCN channels –> increase phase 4 slope = decreased time to get to threshold potential –> more AP = increased HR
Ex) Epi, NE
Describe pathway of Muscarinics on the mAch-R with HCN channels
Increase Ach = increase in K+ permeability & decrease in cAMP –> decreases Vrm & decreases HCN channels –> increases time to get to threshold potential –> less AP = decreased HR
Decrease Ach = decrease K+ permeability –> increase Vrm –> decrease time to get to threshold –> increases HR
Small amount of hyperkalemia has what effect on the heart?
Small increase in HR
not applicable to high level increases
You increase Vrm by _____ concentration gradient of K+
This will increase HR
Decreasing
(Less K+ movement)
How does Ca++ effect threshold potential?
MOA is unknown but it does in heart tissue only
Increase in Ca++ = increase threshold potential –> increase phase 4 = decrease HR
Decrease in Ca++ = decreases threshold potential –> decreases phase 4 = increase HR
How fast can the AV node generate an AP?
40-60 b/m
How fast can the purkinje fibers generate AP?
15-40 b/m
T/F: You dont need the atria to fill the ventricle
Why?
T
Purkinje fibers are able to fire an AP but the ventricles wont fill properly. BP will be decreased
The ______ is the conduction system of the ventricles and the _______ is the conduction system of the right atria
Purkinje fibers
Internodal pathways
How does electricity travel in a healthy heart?
SA node –> internodal pathways –> L atria, R atria, & AV node –> Bundle of His –> L BB –> R BB –> Purkinje fibers –> Ventricles –> Last piece of lateral L ventricle
What is the last part of the heart to be depolarized?
Lateral piece of left ventricle
What are the three internodal pathways from right to left?
Posterior
Middle
Anterior
PMA
How long does it take to go through the internodal pathways?
0.03 seconds
How is the L atria depolarized?
Interatrial bundle
A bundle of connective tissue from the internodal pathways that help get electrical signal to the L atria
Where is the internodal pathways?
R atria
How long does it take to depolarize the R atria?
0.07 seconds
How long does it take for electricity to get from the SA node to the end of the interatrial bundle?
0.07 seconds
How long does it take for the L atria to be depolarized?
0.09 seconds
What is the time difference between the end of the interatrial bundle and depolarization of the L atria? Why?
0.02 secs
There no specialized conduction tissue there. Only muscle cells with myofibrils and myofibriles dont conduct electricity very fast
How long does it take to completely depolarize the heart in a healthy person?
0.22 secs
What is another name for the Interatrial bundle?
Bachman’s bundle
L atria depolarization is ___ seconds and means all atrias are ________. This represents a ____ wave on the EKG
0.09
depolarized
P
What is the purpose of the delay at the AV node?
- Gives atria time to contract to help fill ventricles before they start contracting
- Filters crazy electrical activity in the atria from causing an AP during refractory period
What happens if there’s an AP during a refractory period?
- You may not generate another AP
- You may generate an odd AP
How long does it take to get to the AV node from SA node?
0.03 sec
What causes the delay at the AV node?
- AV node is fat, fat, doesn’t conduct, electricity well
- Low amount of gap junctions present
How long of a delay does the AV node cause?
0.12 sec
How long of a delay does the Bundle of His cause?
0.01 sec
How long of a delay does the bundle of His and the AV node cause?
0.13 secs
How long does it take for electricity to get to the bundle branches? What does this indicate?
0.16 sec
PR interval
How long is the PR interval?
0.16 secs
What branches off the Bundle of His?
L & R BB –> Ventricular septum –> Purkinjie fibers
T/F: when a cell is at rest, there is no charge.
T
T/F: You will see the largest deflection when most the tissue is depolarized and a small amount of tissue is at rest
F
largest when half is depolarized and half at rest
T/F: electrons moving towards the positive electrode in depolarization, shows as a positive deflection in a healthy heart
T
Repolarization of the atria happens in the ______ direction of depolarization. Repolarization of the ventricles happens in the _____ direction of depolarization.
Same
Opposite
If electrons are moving towards the positive lead = ________ deflection. If electrons moving towards negative lead = ________ deflection.
positive
negative
Depolarizing is adding _____ signs
Repolaring is adding ______ signs
Resting tissue is ______ signs
negative (-)
positive (+)
positive (+)
Describe ventricle repolarization
What effect does this have on EKG lead II readings
Repolarizing in the opposite direction of depolarization.
From Epicardium to Endocardium (Superficial to deep)
This presents as a positive deflection T-wave
How do the ventricles depolarize? How does this show up in EKG lead II
L&R ventricles
Then endocardium to epicardium
QRS positive deflection
Atria & ventricle depolarization happens from _________. Atria repolarization happens from ________. Ventricle repolarization happens from ________.
R - L
R - L
L - R
What is the average mean electrical axis of a healthy heart? Where is it pointed?
59 degrees
L foot
During early stages of depolarization the _________ is depolarized
L side of the ventricular septum
Where do electrons want to move?
Towards + charges
resting/repolarized tissues
What does the magnitude of deflection depend on?
How much tissue is depolarized vs how much tissue is remaining at rest
What does an EKG measure?
The sum of all current that’s found between electrodes on the body
What is considered a fast AP? Why?
Ventricular conduction systems:AP by the ventricles or the purkinje fibers
phase 0 is very steep d/t fast Na+ channels
What is the normal magnitude of depolarization in the ventricles in an AP?
100 mV
How much of a deflection from the ventricles are you supposed to see in an EKG? How many big & small boxes is this?
about 1.5 mV
3/4 big boxes or
15-20 small boxes
Ventricular depolarization starts in the ______ layer
endocardium
What is the muscle cell in the ventricles called?
Ventricular myocyte
After phase _____ all tissue should be repolarized
3
What causes chronic depolarization?
injury/infarct/ischemia
T/F: An injured area can repolarize
F
An injured area is chronically depolarized.
It gives off NEGATIVE VIBES
It cannot be repolarized
It generates a current of injury
COI =
Current of injury
What is the QT interval?
Depolarization and repolarization of the ventricles
Why is there a huge loss of voltage displayed in 3-lead EKG from AP?
Resistance in heart tissue & where electrodes are places. Farther away from heart, fat and air reduce voltage picked up.
V-leads are closer to heart so you see a larger deflection in them
How is an injury represented?
negative (-) signs
Where will you see abnormal current from an injury in an EKG?
Where we should not have any current.
End of T-wave –> Beginning of P-wave
EKG interpretations lead II: Why would you see an inverted P-wave?
P wave originated in the AV nodes and electrical current traveled from AV node to SA node
EKG interpretations lead II: Describe the P wave
Atria depolarization
0.09 sec long
2.5 boxes long & tall
T/F: Air & fat helps increase electricity conduction
F
Decreases conduction
What condition of the lungs can decrease conduction of electricity in EKGs?
COPD
Losing conduction of electricity in EKG d/t fat & air will result in _____
smaller QRS complexes
EKG interpretations lead II: If the P-wave is taller than normal, what does this indicate?
R atria problem –> R atria hypertropy (enlargement)
EKG interpretations lead II: If the P-wave is longer than normal, what does this indicate?
L atria problem –> L atria too stretched out
EKG interpretations lead II: If the P-wave has a double hump, what does this indicate?
Block preventing spread of electrical activity to L atria
(block at the interatrial branch or bachman’s branch)
EKG interpretations lead II: Describe a Q-wave
Negative deflection before R-wave
All readings wont always have Q-waves
Beginning of Ventricles depolarization
EKG interpretations lead II: Describe R-wave
positive deflection above baseline
Corresponds with half the ventricles being depolarized
EKG interpretations lead II: Describe QRS complex
positive deflection
About 1.5 mV or 3/4 big boxes
Lasts about 0.06 secs
EKG interpretations lead II: Describe S-wave
Negative deflection after R-wave
Why is the Q- wave and S-wave negative deflections?
Q-wave: the venticular septum depolarizing from L to R at the beginning of depolarization of the ventricles
S-wave: The last part of the ventricles to depolarize is a small part of the L lateral part of the ventricle.
EKG interpretations lead II: Where is the atria repolarized?
Hidden within QRS
What condition of the heart can cause large QRS complexes?
Extra ventricular tissue –> Dilated cardiomyopathy
What does the end of the QRS indicates?
All ventricular tissue is depolarized
What is the J-Point?
“Isoelectric point”
end of QRS after S wave where all ventricular tissue is depolarized.
EKG interpretations lead II: Describe T-wave
Ventricular repolarization
Positive deflection d/t repolarization of epicardium to endocardium
Where does odd electrical activity show up from chronically injured tissue in EKG?
After T wave and Before P wave
In healthy hearts, there will be no current here
EKG interpretations lead II: Describe QT interval
Ventricular septum depolarization –> venticular repolarization
0.25 - 0.35 seconds
(Endocardium fastest AP)
What is the ST interval useful for?
Identifying areas of Ischemia/Infarct
What is the physiological reasoning behind increased HR in running a marathon?
ST interval decreases –> decreases QT interval –> Able to fire an AP quicker –> increases HR
Lusitropy
Define lusitropy
Resetting of the ventricles faster than it normally does to increase HR
Define inotropy
Dealing with the strength of contraction
Define dromotropy
Speed of conduction of electrical current
Depends on NA+
Increased Na+ = Increased transmission
Define chronotropy
HR
What is the formula for HR?
(60 secs) / (RR interval) = HR
What is normal RR interval?
0.83 seconds
What was the rate at which they would feed EKG paper through the machine?
25 mm/sec
In an EKG strip, how many mV is a large box?
0.5 mV
In an EKG strip, how many mV is a small box?
0.1 mV
What axis is the mV on in an EKG?
Vertical (Tall)
In an EKG strip, how many seconds is a large box?
0.2 seconds
In an EKG strip, , how many seconds is a small box?
0.04 seconds
What axis is the seconds on in an EKG?
Horizontal (Long)
