Test 4 - 10/23 Flashcards
Sending electrons towards a positive electrode will give us a ______ deflection.
Positive
If depolarization is happening L to R, towards a positive electrode that will give us a ____ deflection
positive
If we have repolarization happening from L to R towards a negative electrode that would give us a _______ deflection
negative
The height of a positive deflection will be determined by what?
How much current we have
Depolarization that is happening L to R heading towards a positive electrode will give us a ______ deflection
positive
If this repolarization is happening from left to right, would this be considered a positive or negative deflection?
Negative
Why is the T wave a positive deflection in the EKG?
Because the repolarization is taking place in the opposite direction as the depolarization.
Why is the slope on the fast AP not very steep?
Because there are not very many HCN or leaky Na or Ca in the ventricle.
How does the slope of phase 4 differ from the fast AP vs the slow AP
Fast AP it is almost horizontal, slow up it is steeper
What is the first phase in the slow action potential in the heart? include both names
Phase 4 or diastolic depolarization
What is diastolic depolarization?
The initial phase (phase 4) of a slow AP in the heart.
What is the second phase in a slow AP in the heart? What happens?
Phase 0, no fast Na channels. primarily L type Ca channels (slow)
How does phase 0 differ in slow AP vs fast AP in the heart?
Fast is super steep bc of the fast Na channels, slow isn’t.
What differs between the fast Na channels in phase 0 in a fast AP and the L type Ca channels in a slow AP?
Fast Na is fast.
L type are slow to open and slow to close
The duration of a slow AP in the heart is longer than a neuron, why?
Because of the slow L type Ca channels (slow to open and slow to close)
Discuss what determines how fast an AP will move through the heart.
The slope of phase 0. If its super steep like the ventricular fast AP it will move through those gap junctions. the Na will also go through and the Na can depolarize more cells.
If it is like the slow AP (Like in the atria) it is slower to move through those gap junctions
In the atria there are ______ fast Na channels involved in AP
fewer
Why don’t slow AP move around the gap junctions as fast?
Because it primarily involves Ca and Ca is bigger and likely doesnt fit through the gap junctions as well
What takes place in phase 3 of a slow AP?
Repolarization. closing of L type Ca channels and voltage gated K channels open
How many phases are in a slow AP?
Three
4, 0, 3.
However, some texts include phase 2
Phase 2 in a slow AP
some texts would describe this as the plateau phase
There is no phase ______ in slow AP in the heart
one
What kind of action potentials would occur at the SA node?
slow AP
What is Vrm for the heart action potentials?
-55
what is threshold for the heart AP’s
-40
The AV node is a ______ pacemaker
slower
Why is the AV node called a slower pacemaker?
Because its not as leaky to Na and Ca during phase 4.
But also the Vrm is lower so it will take longer for those cells to generate its own AP
The AV node has a slower ________ compared to the SA node
automaticity
Are there HCN channels in the SA node?
yes, a lot
Compare the amount of HCN channels in the AV node to the amount in the SA node
more in the SA node. still a lot in the AV just not as many
Describe the amount of HCN channels in the ventricles
There are some because of the slope of phase 4 but very sparse
Which action potential would represent the SA node?
A
Which action potential would represent the ventricular muscle
F and G
Discuss the length of the AP in the ventricles
they will vary in length. the deep interior ventricular AP will be longer.
Which AP would take place in a deep ventricular area? like the subendocardium
F
Which AP would we most likely see in a more superficial ventricular myocyte?
G
(ventricular AP) Repolarization in the ______ happens faster compared to the _______
-Epicardium
-Subendocardium
Depolarization in the ventricles moves from _____ to ______
inside to outside
What is the T wave showing us?
repolarization of the ventricular tissue
The action potentials get started _____ in the deep parts of the heart and they finish _____
earlier
later
Why are the deep AP longer compared to the superficial AP?
Because we need them both to be contracting at the same time so we can have a good amount of force to eject the blood
Why are the atrial muscle AP not as long?
because they aren’t pumping against a high resistance putting blood into an empty ventricle
The ______ wall is pretty thin (part of the heart)
atrial wall
The vagus attachment tends to be more concentrated at the ______
nodal areas
The sympathetic chain tends to have endings that are _____
distributed throughout the heart. ventricles, atria, small amt at the nodal tissue.
(widespread coverage)
The self depolarization rate at the SA node under healthy conditions will give us an AP every _____.
0.83 seconds
If we have an AP in the SA node every 0.83 seconds, what would our HR be?
72 BPM
The SA node on its own, without input from the vagus nerve or the sympathetic chain, would generate give us a heart rate of _____
110 BPM
If we have the SA node + the SNS activity without the input from the vagus nerve that would give us a HR of _____
120 BPM
SNS bring the heart rate up by _____
10 BMP
What has the bigger effect on governing the HR? vagus or sympathetic chain
vagus
If we have normal SA node activity plus the vagus nerve and remove the SNS activity we would have a heart rate of _____
60-62 BPM
What keeps the breaks of the heart rate?
vagus nerve
The _____ is the origin of pacing in the heart
SA node
The SA node is the origin of pacing in the heart because ___
it self depolarizes and generates AP faster than any of the other pacemakers of the heart
What is the secondary pacemaker
AV node
The AV node will generate spontaneous AP to give us a heart rate of ___
40-60 BPM
What happens if something is wrong with the SA node?
The AV node is our secondary pacemaker and it will give us a HR of 40-60 BPM. not ideal
What is the third pacemaker of the heart?
Purkinje fibers.
What is the conduction tissue within the ventricles?
purkinje fibers
The _____ are buried within the muscle mass in the ventriclur heart tissue
purkinje fibers
If the purkinje takes over as the primary pacemaker of the heart that will give us a heart rate of
15-30 BPM
The conduction system in the heart gives us _____ timing of all the muscle mass
coordinated
If we take the atria out of the equation for the conduction what would happen?
We dont need a ton of help from the atria to but it does help. without the help the ventricle wont be as full therefore decreased output. over a period of time this would give us a low BP
What is in charge of making sure the AP that is generated at the SA node arrives at the AV node?
Conduction tissue
What is the conduction system of the ventricles?
Purkinji fibers
What is the conduction system of the atria?
R atria internodal pathways.
Purple
SA node
Green
Anterior internodal pathway
Orange
AV node
Pink
middle internodal pathway
blue
posterior internodal pathway
What are the different internodal pathways?
- anterior
- middle
- posterior
What is special about the anterior internodal pathway?
There is a branch of conduction tissue off of the anterior internodal pathway that will help us propagate the left atrium.
dark green
interatrial bundle
What is another name for the interatrial bundle
Bachmans bundle
What is the job of the interatrial bundle
make sure the AP from the SA node makes it to the L atrium
How long does it take for the AP to go from the SA node to the AV node via the internodal pathways (if it follows conduction pathways)
0.3 seconds
How long does it take for the entire R atria to depolarize under normal conditions?
0.7 seconds
How long does it take for the AP to reach the posterior lateral side of the R atria
0.5 seconds
How long does it take for the entire L atria to depolarize?
0.9 seconds
What is the duration of the P wave? Why
0.9 seconds, that is how long it takes for the entire atrium to depolarize
When does the P wave start and end?
When the AP starts at the SA node. It ends when the entire atrium have been depolarized
Why would it take 0.3 seconds to depolarize the medial portion of the L atrium and 0.9 seconds to depolarize the inferior lateral portion of the L atria
Bc the AP has to spread through the muscle and there are lots of myofibrils and they are big and clunky and don’t conduct electricity at a fast rate.
The top half of the heart is what? What is included?
R and L atria, AV node, SA node
How long would it take for the AP to reach the last part of the ventricles?
0.22 seconds
Why would it take longer than 0.22 seconds for the last part of the ventricles to be depolarized?
Older heart, more tissue for the AP to get through
Why is there a delay in the time between when the AP reaches the AV node (0.3 seconds) vs the last part of the ventricles (0.22 seconds)?
There is a delay at the AV node to allow atria to contract to fill ventricles
What is the refractory period in an AP
Resetting of the AV node. prevents the ventricles from contracting before the atria are finished
What happens if an AP hits the AV node during the refractory period? what could cause this to happen?
The AV node will filer out some of that extra electrical activity.
Afib could cause this
Why is there slower conduction through the AV node?
Fewer gap junctions between the cells that make up that area as well as the AV node being fatty, fat doesn’t conduct electrical signals very well
How long is the delay going through the AV node?
0.12 seconds
What is the delay through the bundles of His?
0.01 seconds
What is the last part that crosses over from the atria to the ventricles at the septum?
Bundle of His
What is the bundle of His
the portion from the AV node that branches off to make the Right and Left bundle branch
How long does it take for an AP to get from the SA node to the main bundle branchs in the ventricles. Include the delays.
0.16 seconds total.
0.03 seconds between SA and AV node
0.12 seconds through AV node
0.01 seconds through bundle of His
How long would it take before the QRS complex starts?
0.16 seconds
What is the QRS complex?
The initiation of the AP in the main bundle branches in the interventricular septum
the PR interval is ____ seconds
0.16
What helps prevent ventricular tachycardia if there is a conduction issue in the atria
the AV node
A negative charge will move toward tissue that is _____ or in the ______ state
resting; repolarized
If we put a positive electrode on the L foot and a negative electrode on the R arm this would give us a _______ deflection throughout depolarization
big positive
What is the average angle of the electrical movement during a typical heartbeat?
59 degrees
During depolarization of a typical heartbeat, what way should the positive current flow?
towards to L foot/L torso
What we see in an EKG is a result of ______ in the heart
all the AP happening
What is the magnitude of depolarization in the ventricular muscle AP
100mV
If the leads are placed on the upper body, what is the magnitude of deflection of the EKG?
1.5mV
Why is there such a smaller magnitude of deflection between the fast AP and the EKG?
There is a lot of resistance between the heart tissue and where the electrodes are placed.
What could cause us to get a larger magnitude of deflection in an EKG?
if we put the leads closer to the heart (maybe 3 or 4 mV)
What would be the difference in magnitude of deflection in an EKG between a 12 lead and a 3 lead.
In the 12 lead, V1-6 are placed right around the heart so it will be bigger.
in the 3 lead we have a lot of loss of voltage bc they are further away but also (air in lungs, fat)
What part of the EKG corresponds to the length of a fast AP? (specifically endocardial)
Q-T interval
The Q-T interval will tell us
the length of time it takes for depolarization in the ventricular tissue
Lead 2 is the ____ lead
rhythm
The start of the P wave is determined by
the start of an AP by the SA node
How long/tall should the P wave be?
2.5 boxes long, 2.5 boxes tall
P should be a _____ deflection because it is happening in the direction of the ______
positive.
L foot
If the P wave were to originate at the AV node and travel backwards to the SA node that would give us a ____ deflection
negative
The P wave duration should last for ____ seconds.
0.09 seconds
If the P wave is inverted the AP is _____
Starting in the wrong place
What would cause the P wave to be higher. is high there is a problem with the R atria..hypertrophy
Problem with the R atria, hypertrophy or r atria getting stretched out.
The higher the deflection..the more muscle tissue
What would the EKG reflect if there is extra tissue in the R atria?
Taller P wave
If our P wave is 4 boxes high this might indicate what?
Hypertrophy of the R atria
If the P wave is too long this would be a ______ problem in the ______
conduction
L atria
P wave long =
P wave height=
Long = Left atria
Height = Right atria
What can cause the P wave to have a double hump?
Really big problem in the L atria. Probs electrical block that is preventing it from spreading to the L side.
R side should be good
The Q wave is a _____ before the R wave
negative deflection
The R wave is a _____ deflection that represents _____
positive deflection above baseline;
depolarization of the ventricles
Why is the P-R interval not called the PQ interval?
because not all leads have the Q wave
What is the period of time between the start of an AP from the SA node and initiation of electrical activity in the ventricle
P-R interval
what is the duration of the P-R interval
0.16 seconds
S wave is a _____ deflection
negative
What is the ideal duration of the QRS complex? How do we get this?
0.06 seconds.
we subtract 0.22 seconds (time it takes for the last sliver of the ventricle to depolarize) from 0.16 seconds (time the ventricular depolarization starts..right after bundle of His)
What would spread out the duration of the QRS complex
not ideal conditions. hypertension, drinking lots of caffeine
What could cause the QRS complex to have an increased magnitude of deflection?
the electrodes might be placed close to the heart
or enlargement of the ventricles (more muscle= more electrical activity)
What would cause the length of the QRS complex to be more wide without increasing the magnitude of deflection?
Dilated cardiomyopothy.
ventricle walls more stretched out..not thicker just stretched out.
Repolarization of the atria is not shown on the EKG because of ____
the large size QRS complex.
The QRS complex ends when
All of the ventricular tissue has been depolarized
At what point on the EKG should the entire bottom half of the heart be depolarized?
At the very end of the QRS complex
What is the point immediately following the QRS complex?
J-point or isoelectric point
The J-point or isometric point is a point where _____
All of the ventricular tissue should be depolarized
Why is the J-point/isometric point important?
It will give us a good idea of when the entirety of the ventricles are depolarized and if there is an area of infarction in the ventricle those parts will remain continuously depolarized and generate electrical activity…we would be able to see this activity after the T wave.
We compare the crazy activity after the T segment to the J point
The QT interval corresponds to
the start of depolarization in septum up until all the tissue has been repolarized.
How long should the QT interval be?
between 0.25 and 0.35 seconds.
What would be the duration of AP in endocardial heart tissue?
Between 0.25 and 0.35 seconds (duration of the QT interval)
What can we see between the S wave and the T wave?
if there are areas of injury
The T wave is ______ of the ventricles and has a _____ deflection
repolarization;
positive
If we have a physiologic increase in HR (playing bb) the heart will shorten the _____
ST segment (which would by default shorten the Q-T interval)
What would happen if we are playing bball and we have an increase in HR.
ventricle repolarizes earlier causing a shortened ST segment and allowing us to fire another AP earlier
Lusitropy
resetting of the heart after an AP
positive lusitropy agent
repolarizes the ventricle faster than it normally does. shaving time off of the ST segment
inotropy
stronger heartbeat due to more Ca coming into heart being released from the SR
Chronotropy
heart rate
Dromotropy
speed of conduction of the AP. dependent on Na current.. more Na = faster transmission
RR interval
time between the two QRS complex (0.83 seconds). Heart rate = 72 BPM
What can the RR interval be used for?
to calculate the HR
Each big box on an EKG will be ____ mV of amplitude
0.5
one small box on an EKG would be ____ mV
0.1 mV
When they did paper EKG’s what was the rate at which the paper was fed through?
25mm/second
(X axis - time) Each big box on an EKG is _____ seconds
0.2 seconds
(X axis; time) each of the small boxes on the EKG is ____ seconds
0.04 seconds
When they fed the EKG paper through the machine how many big boxes went through per second?
5 boxes
What is the relative refractory period?
period where the heart cell is reset enough to generate an AP but the AP will be weaker.
What is the difference between an early premature contraction vs later premature contraction?
Early will be wearker, happening in the relative refractory period.
Later premature contraction we be just a little earlier but it is completely out of the refractory period
What are the different phases of the refractory period?
Absolute and relative.
Absolute = no AP
Relative= reset enough can have a weak AP
