A&P Test 4 Flashcards
what is the serous layer that is connected to the bottom side of the fibrous layer?
serous parietal layer
what is the name of the thin, very elastic, completely clear membrane that sits between the actual heart tissue and the parietal pericardium
serous, visceral pericardial layer
Is there a bunch of fast sodium channels in the purkinje fiber?
Yes
if the fast sodium channels can’t reset for some reason in a fast action potential, what happens?
It turns fast action potentials into slow AP which effects the contraction of the heart
How are AP propagated through cells in the heart?
entirely through gap junctions
What primarily goes through gap junctions?
Na+ and a little Ca++
If it was only Ca++ then the AP would probably be pretty slow
what is one of the down sides to using gap junctions?
What is the upside?
because it isn’t a chemical synapse, it is bidirectional.
Ectopic AP can travel through Gap junctions and move in both directions which can cause problems.
Upside is that it is fast
what protects our heart from having a ton of retrograde action potentials when we’re sick?
refractory periods. Specifically during that time that does not allow another AP to be fired
Which plane is used for a 3 lead EKG?
frontal plane/coronal plane
what are the augmented leads?
leads that are oriented in a different way from the frontal plane 3 leads.
aVR
aVL
aVF
What do the augmented leads look at?
the amount of electrical movement and the direction of the movement in the frontal plane
what is the old school way of placing the 3 leads on the body?
placing leads on both wrists and the left ankle
what is the new school way of placing the 3 leads on the body?
placing leads on both shoulders/upper lateral chests and the left lower side of the torso
For Dr. Smidt’s class, what is the best way to think about the positive lead?
as an eye ball or sensor that is looking at depolarization moving towards it or away from it
depolarization moving towards the “eyeball” will show up as a ______ deflection in both the EKG as well as the individual meter.
depolarization moving away from the “eyeball” will show up as a ______ deflection in both the EKG as well as the individual meter.
positive
negative
Lead 2 is going to have the best picture of
the depolarization wave going towards the positive lead in the right ankle
where is the metaphorical eyeball?
where the positive electrode is.
If things are normal in the heart, you would expect to see what kind of deflection in lead 2?
a big positive deflection
On a 3 lead EKG, which extremity has 2 positive electrodes?
left ankle
On a 3 lead EKG, which extremity has 2 negative electrodes?
right arm
On a 3 lead EKG, which extremity has a positive and negative electrode?
left arm
How is Einthoven’s triangle helpful?
It allows us to look at the angles and better describe what we’re seeing in the 3 leads.
what are the parts of the machine recording a 3 lead EKG?
display or recorder
amplifier- turns the information into something the recorder and sort out.
leads
What is the name of the Dutch (somewhere in Europe) scientist that developed a triangle regarding the 3 lead EKG?
Einthoven
what is the value of the normal mean electrical axis?
59 degrees
what is the normal angle of lead 2?
60 degrees
What is the definition of a Left axis deviation?
mean electrical axis less than 0 degrees
for Smidt’s class it is anything less than 59 degrees
If the entire heart is depolarized, what kind of deflection would you expect to see in leads 1, 2, & 3?
They should all read 0 at this point because there is no electrical current moving when the entire heart is depolarized.
If you tilt the heart to the left what kind of axis deviation would you have?
Left axis deviation
If you tilt the heart to the right what kind of axis deviation would you have?
right axis deviation
what is the definition of a right axis deviation?
a mean electrical axis >90 degrees
for Smidt’s class it is anything more than 59 degrees
what is the net electrical axis?
which way does it normally go?
the overall direction of electrical activity generated by the heart during depolarization
59 degrees towards the left foot
what can cause electrical axis deviations?
- Bundle branch block
- changes in the position of the heart in the chest(breathing)
- COPD (really big lungs)
- one side of the heart being enormous
as lung volume decreases what way does the heart tilt?
Left
If you take in a really deep breath, which way does the heart tilt?
right
If you have a starting horizontal (0 degrees) electrical axis, and you rotate it pointing down perfectly perpendicular, what degree would you call this?
90 degrees
If you have a starting horizontal (0 degrees) electrical axis, and you rotate it pointing down halfway to perfectly perpendicular, what degree would you call this?
60 degrees
If you have a starting horizontal (0 degrees) electrical axis, and you rotate it pointing horizontally in the other direction, what degree would you call this?
180 degrees
If you have a starting horizontal (0 degrees) electrical axis, and you rotate it pointing up perfectly perpendicular, what degree would you call this?
270
If you have a starting horizontal (0 degrees) electrical axis, and you rotate it in a complete circle so that it is pointing in the same direction, what degree would you call this?
360 degrees synonymous with 0 degrees
If the textbook tells you that the mean electrical axis is -60, what do they mean by that?
the electrical axis would rotate counterclockwise from horizontal.
This would also be 300 degrees
If the mean electrical axis is a positive number it is moving in what direction?
Negative?
clockwise
counterclockwise
Where are the negative and positive electrodes in lead 2?
Negative=right arm
Positive=left leg
Where are the negative and positive electrodes in lead 3?
Negative=left arm
Positive=left leg
what is Einthoven’s law?
The net positive deflection we see in lead 2 must be equal to the sum of the deflections in leads 1 and 3
How do you find the net height in lead 1,2 and 3?
in regards to Einthoven’s law
On an EKG:
Subtract the portion of the AP below baseline from the portion of the AP above baseline
At the beginning of the QRS complex when most of the septum is depolarized you would have most of the endocardium and lateral walls still resting. What type of deflections would you expect to see in Leads 1, 2, and 3 at this point?
lead 1- small positive deflection
lead 2- small (but larger than lead 1 &2) positive deflection
Lead 3-small (but larger than lead 1) positive deflection
When half of the ventricular tissue is depolarized and half is resting, What type of deflections would you expect to see in Leads 1, 2, and 3 at this point?
lead 1- large positive deflection
lead 2- large (still larger than lead 1 &2) positive deflection
Lead 3-large (still larger than lead 1) positive deflection
There’s more current so the leads recognize this as the max amount of current
When more than 50% of the ventricular tissue is depolarized, what type of deflections would you expect to see in Leads 1, 2, and 3 at this point?
lead 1- a less positive deflection(NOT NEGATIVE) than shown when half of the tissue is depolarized.
lead 2- a less positive deflection(NOT NEGATIVE) (but larger than lead 1 &2) positive deflection
Lead 3-a less positive deflection(NOT NEGATIVE) (but larger than lead 1) positive deflection
There’s only a small piece of resting tissue left for current to go to so the leads see this as less current
At the end of the QRS complex when almost the entire ventricular tissue is depolarized, what type of deflections would you expect to see in Leads 1, 2, and 3 at this point?
lead 1- a less positive deflection(NOT NEGATIVE) than shown when >50% of the tissue is depolarized.
lead 2- a small negative deflection
Lead 3-a large negative deflection
The mean electrical current changes directions at this time to point towards the left upper arm. This changes the view that the leads have.
which ventricle is thinner in the heart?
why?
right
it only has to pump against the resistance in the pulmonary circulation
what is the last place on the ventricles to depolarize?
Why is it the last?
a little sliver on the superior portion of the left ventricle.
because it is farthest away from the start of depolarization so the AP has a lot of tissue to go through.
If the mean electrical axis was oriented at 90 degrees straight down, what would you expect to see in lead 2?
a fairly large positive deflection bc that is still pretty close to the orientation of lead 2.
What are the 2 questions to ask when something doesn’t look right on the EKG?
what is happening?- can use a 3 lead EKG to solve this
where is it happening?- can use more chest leads to solve this for a better view of the heart
Where are the negative and positive electrodes in lead 1?
negative= right arm
positive = left arm
which direction does the depolarization of the atria take?
at an angle towards the left foot. This is why you’d see a positive deflection
repolarization happens in the same ______ and same _________ as depolarization in the atria
sequence
direction
atrial repolarization -opposite of depolarization headed towards the left foot would give us what kind of deflection?
This is called the atrial t wave. It would be negative but we normally don’t see it because the ventricular depolarization is hiding it
what can you use to diagnose pretty much any conduction problem in the heart?
a 3 lead EKG
why doesn’t the repolarization of the atria obscure the depolarization of the ventricles?
The walls of the atria are very thin compared to the ventricular muscle mass so they don’t create a strong enough AP to overcome the ventricular AP
When can you see atrial depolarization waves making a big difference in the EKG?
If there is something wrong with the SA node and AP are being sent bidirectional from the AV node.
Why is the atrial T wave more spread out than the P wave?
When the conduction system is working retrograde (repolarization happening from right to left) it doesn’t have the same properties as when it is working in the normal direction.
what is the mean axis degree of lead 1?
0 degrees
what is the mean axis degree of lead 2?
60 degrees
what type of deflection would you expect to see in the 3 main events(P, QRS, and T) when viewing lead 2?
large and positive deflection
Which lead would you normal see the largest P, QRS or T wave?
Why?
lead 2
because all of those AP are shooting almost directly towards the left foot where the positive electrode is and lead 2 is oriented to see this.
Which lead cannot view the entire depolarization wave heading towards the Left foot?
Lead 1
what is the mean axis degree of lead 3?
120 degrees
How does the positive deflection seen in lead 1 compare to a positive deflection in lead 2?
It will be smaller in lead 1 d/t Lead 1 pointing horizontally and not being able to see the entire depolarization wave
How can you determine how much smaller the deflection should be in Lead 1 compared to lead 2?
You would have to draw a line from lead 1 until it meets with the net electrical axis and determine the length of the base of that triangle.
It is the amount of right to left movement of depolarization
If our mean electrical axis is 90 degrees, what would you see in lead 1?
nothing.
Lead 1 can’t see this movement.
If our mean electrical axis is >90 degrees, what would you see in lead 1?
a negative deflection
If our mean electrical axis is parallel to lead 1 and moving from left to right, what would you see in lead 1?
a large negative deflection
what is a zero degree electrical axis?
when the net depolarization is moving from the right arm towards the left arm like in lead 1 which is oriented in a horizontal position.
If our mean electrical axis that is parallel to lead 1, moving from right to left, what would you see in lead 1?
a large positive deflection
Which lead is less likely to have an S wave?
Lead 1
(it never sees the deflection going negative)
How do the leads interpret the “arrow” of depolarization pointing towards the right arm when looking at the interventricular septum having depolarization start on the left side?
Lead 1,2,3
What does this relate to?
Lead 1- largely (compared to lead 2) negative deflection
Lead 2- slightly negative deflection
Lead 3- Largely positive deflection
the q wave
what is the deconstructed triangle called on a 3 lead EKG?
Einthoven’s triangle
What are the angles of the triangle formed with a 3 lead EKG?
60 degrees.
it is an equilateral triangle.
Where is the positive electrode (metaphorical eyeball) placed for
lead 1?
lead 2?
lead 3?
Left shoulder
left ankle
left ankle
