Lecture 3 Test 4 Flashcards
When looking at the electrode meter, if you’re moving away from the + electrode (repolarize), you will see
A negative deflection on the meter
When looking at the electrode meter, if you’re towards the + electrode (depolarization), you will see
A positive deflection on the meter
Compare Action potentials in the ventricles depolarization vs repolarization
-Depolarization (current flow is neg>pos) shows as a positive deflection.
-Repolarization (current flow is pos>neg) shows as a positive deflection.
aka double negative.
Why is T wave a positive deflection?
Because the repolarization current flow is going from pos>neg = positive deflection.
What causes a negative deflection on the t wave?
If the current flow is neg>pos = negative deflection
What phase is resting membrane potential?
Phase 4
Fast action potential to phase 4 looks like……
a little slope because not much HCN, leak Na+, or Ca++ at the moment.
Will there be a spontaneous AP that can occur in your heart?
It could if you give it enough time.
What’s another name for phase 4 (nodal area)?
-Diastolic depolarization
-Phase 4 depolarization
The faster the rate of diastolic depolarization leads to a….
faster AP to increase hr.
Phase 0 in the nodal area
Upstroke of AP. compared to other AP that go straight up (fast Na+ ch), in a heart AP (nodal area), its more of a slope
Uses L type Ca++ ch (slow to open and close) = extended time
What happens if there’s a really fast AP that occurs in the heart leading to a fast and high slope?
The AP get propagated to the next cell and entails Na current in the ventricle. Depolarization occurs in the area where Na channels came in and move through gap junctions to their neighbor.
What determines how fast of the AP moves around the heart?
The slope of phase 0
Phase 0 is affected by which specific ion?
Ca++; big and clunky and slow influx maybe r/t slow AP.
What phase is repolarization in the heart?
Phase 3
L-type channel closing, VG K+ channels open in what phase?
Phase 3
Is there a phase 2 in the nodal area?
Most often not. but if there is, it’s the plateau phase d/t slow L type ca++
SA node Vrm
Threshold mV
-55 mV
-40 mV
Is aV node the same as SA node AP?
No, it is not as leaky to Na+, Ca++ in phase 4
AV node phase 4 and Vrm
more negative, longer to generate an AP
Where in the heart can you find HCN channels?
More in the SA node and some in AV node and the rest of the ventricles.
Why does the inside of the heart AP longer than the outside of the heart?
It causes the endocardium and epicardium to have an AP at the same time > endocardium is depolarizing while epicardium is depolarizing > simultaneous contraction > stronger heartbeat to pump blood
Does the atria have long/extended APs?
No, it doesn’t need it because its muscle walls are thin and works with less pressures.
Where are the PNS attachments in the heart?
Vagus attachments are more concentrated at the nodal areas
Where are the SNS attachments in the heart?
The attachments are widespread throughout the heart (ventricles, atria, nodal tissues)
Resting hr (healthy heart/patient)
72bpm
60 secs / (0.83 secs) RR int = HR
= 72bpm
- If the SA node (PNS) had no inputs anywhere else, it would generate APs at a rate of?
- SNS can add how many more bpm?
110 bpm
SNS ( adds 10 bpm) = 120 bpm
which has more input on the conduction system? PNS or SNS?
PNS
SNS can add how many more bpm?
10 bpm
PNS can generate how many bpm?
110 bpm
If you just have Vagal tone, you have approx. how many bpm?
60-62 bpm
Generates how many bpm?
-SA node
-AV node
-Purkinjie system
72 bpm
40-60 bpm
15-30 bpm
What are the 3 internodal pathways for the right atria? (between the SA and AV nodes)
Anterior
Middle
Posterior
What does the anterior internodal pathway control? What’s another name for this?
Electrical system of the Left atrium
aka Interatrial bundle “Bachman’s bundle”
How long does the AP take to get from SA node to AV node?
0.03 (3 hundredths) of a seconds
How long does it take for the right atria to depolarize?
0.07 (7 hundredths) of a second
How long does it take for the left atria to depolarize?
What does this depict on the cardiac rhythm strip?
0.09 (9 hundredths) of a second
-P wave duration
What does Dr. Schmidt mean by top half?
bilateral atrias and SA/AV nodes
How long does it take for the AP to reach from the SA node all the way to the tip of the purkinjie fibers? Basically the whole heart.
Ideally 0.22 secs (22 hundredths)
Maybe longer for older, sick patients
Why is there a 0.2 secs delay at the AV node?
Gives the atria time to contract and fill the ventricles
Other functions of the AV nodes
Filters extraneous AP from the SA node that may lead to fast ventricular conductions
Does the AV nodes have gap junctions within its cells?
Very little, that’s why APs take longer to pass through; hence, the delay
How long is the delay in the AV node?
Delay in the bundle of his?
Total AP time from SA node down to the Left/right bundle branch?
0.12 secs
0.01 secs
Total 0.13 secs (AV delay)
+ 0.03 secs (SA to AV)
Total 0.16 secs (PR interval)
Other ways the AV node acts as a filter
ex.
Abnormally fast APs from the atria that may hit the AV node while in refractory period. Protects us from causing ventricular tachyarrhythmias
What is the general pattern of the electrical signals
Going towards the left foot
If we put a (+) electrode on the left foot and (-) electrode to the right arm what would we see on a meter?
A big positive deflection during depolarization. The magnitude depends on how much tissue still remaining to depolarize
When do you have the biggest current in the magnitude of deflection?
Its when you have half depolarized and half depolarized.
How many degrees is the angle of electrical signals from right arm to left foot?
59 degrees is the average electrical movement
(59 degrees lower than horizontal)
What do we measure in the EKG
All of the APs in the heart
EKG magnitude of depolarization is approx.
100mV
QRS magnitude of deflection when leads are on the limbs
when its closer to the heart (ex. chest leads) magnitude of deflection are around…
+1.5mV
+ 3 - 4mV
What causes the lower readings of magnitude of deflection through the electrodes?
Things in the way such as air in the lungs since electricity doesn’t travel through air
QT interval is the…
length of time for ventricle depolarization
Normal P wave size on egg strip
2.5 boxes height x 2.5 boxes width (positive deflection - > +)
What does it mean if the P wave is high?
Right Atrial hypertrophy
What does it mean if the P wave is too long?
Long conduction maybe due to a left atrium being stretched out
What does it mean if there’s a double hump on the P wave?
Possible electrical block
What is a Q wave
negative deflection before the R wave
What is the R wave?
Positive deflection
T/F: Not everyone has a Q wave that’s why it’s called PR interval not QR int
True
Normal PR interval
0.16 secs
Total heart depolarization 0.22 minus total depolarization from SA node to the tip of bundle branch 0.16 is
QRS complex of 0.06 secs (ideally)
Normally longer
Normal height deflection of QRS complex (total electrical activity)
Typically +1.5 mV (5 large boxes)
Reasons why a QRS complex can be super large
Electrodes are really close to the heart, Heart tissue is massive, enlarged ventricular tissue.
Cardiomyopathy
Prolonged QRS and longer depolarization
Can you see the atrial repolarization on a EKG?
No, it’s usually hidden behind the QRS wave
When do you know if all of the ventricular process has been depolarized?
at the end of the QRS aka” J-point” or “Isoelectric point”
Area between the end of T wave and beginning of P wave should be?
Flat; meaning the healthy heart tissue should be at rest.
If there’s movement = unhealthy heart tissues
Where in the EKG can you find if there are unhealthy ventricle tissues and why?
Between the end of S wave and T wave (should be flat), low in nutrients unable to repolarize causing abnormal tracings of depolarization. (elevated/depressed ST segments)
What is the QT interval? Normal time for QT interval?
start of ventricle depolarization and end of repolarization.
0.25 - 0.35 secs (duration of endocardium fast APs)
Repolarization of the ventricle is labeled as
T wave (positive deflection)
If we need to make our hr faster d/t activity the heart will
shorten the QT interval to make an AP happen quicker
What is Lusitropy?
Depolarizes/resetting the ventricle faster than it normally does.
What can you give to make the heart repolarize quicker and eventually increase HR?
a positive Lusitropic agent.
Define:
Inotropy
Chronotropy
Dromotropy
Lusitropy
- Stronger heart contraction/beat (more Ca++ influx)
- Increase heart rate
- Speed of conduction (electrical impulse d/t NA+ current)
- Resetting of the heart during an AP
Calculate hr with RR int:
normal hr = 60 secs / 0.83 secs (RR interval)
72 bpm
Each big box is about how many mV?
0.5 mV
Each big box is divided by?
5 small boxes = 0.04secs/small box
Cardiac rhythm strips are fed through the machine at a rate of?
25 mm/sec
How many big boxes in a 1 sec strip?
How many secs per big box?
How many secs per small box?
5 big boxes
0.2 secs
0.04 secs
What is a refractory period?
resetting of the heart after an AP
What is a relative refractory period?
It’s when the cell is not fully reset before another AP or else result with a weaker conduction (early premature contraction)
What happens in the absolute refractory period?
The heart will not be able to fully reset and unable to elicit an AP.
What is the most important for the hearts potential?
Coordination and timing!
