Exam 4 - Lecture 3 Flashcards
Anything that sends electrons towards a positive electrode will
Give a positive reading/positive deflection
If we have depolarization in one direction causing a negative deflection, repolarization in the same direction would cause
Positive deflection
If we have depolarization in one direction causing a negative deflection, repolarization in the same direction would cause
Positive deflection
Phase 4 of ventricle muscle is very ____
Slightly sloped.
Phase 4 of SA node is also called
Diastolic depolarization or phase 4 depolarization
Phase 0 of SA node
Upward stroke up action potential, not as sloped as most AP.
In the nodal areas, phase 0 is ______ channels.
Slow L-type Ca++ channels.
Slower to open, slower to close.
Duration/slope of phase 0 is very important because
Determines how fast the action potentials travel throughout the heart.
If it’s super fast, everything else is super fast from sodium traveling through gap junctions
Phase 3 of nodal areas
L-type closing, VG-K re-opening to set the cell
Definite phases of nodal areas
4, 0 and 3.
Some textbooks will say there is a 2nd phase.
There is not a 1st phase at all.
AV node VRm and slope and threshold compared to SA node , and why?
Not as leaky to sodium and calcium in phase 4.
VRm is more negative than SA node, and less slope.
Thats why it’s slower if it’s the pacemaker.
HCN channels in the heart are found where?
Most in the SA
A lot but less in AV
Ventricles there’s hardly any, but they are there.
Real deep interior ventricular APs are
Pretty long, longer plateau phase
Repolarization is set quicker for epicardium than
Subendocardium
Are atrials pumping against high or low resistance?
Low
Atria APs are compared as
In between a fast and slow AP
SA node HR and how often does it generate an AP?
72 bpm; every 0.83 seconds
If we took all of the nervous influences away from SA node, it would generate a heart rate of ____.
If we add SNS activity ONLY:
110 bpm; 120bpm (up by 10bpm)
What has a greater affect on HR, SNS or PNS (vagal)
PNS is much stronger effect
Secondary pacemaker is ___ and it generates spontaneous APs at __________ per minute.
AV node; 40-60bpm
Other pacemaker system of heart not SA or AV node, and it will spontaneously generate APs at ____ per minute.
purkinje fibers which is conduction system of ventricles, and it will beat at 15-30bpm.
What is the conduction system of the heart specifically for other than the obvious generating APs for heart beat?
Coordinated timing of all of the muscle mass. Needs to be an orderly process for the signals that each take a defined amount of time.
Conduction system in right atria are called
3 internodal pathways (in between SA and AV node)
Anterior
middle
posterior
Anterior internodal pathway is and its also called?
a bundle or collection of tissue that will conduct signals to left atrial pathway
Interatria bundle or bachman’s bundle
Time for AP to go from SA to AV node via internodal pathway
.03 seconds
3/100ths of a second
Time for AP to go from node to right atrial muscle to depolarize
0.07
Time for AP to go from node to left atrial muscle to depolarize
0.09
How long is the duration of the P-wave and what is it
0.09
time for all of the atria to depolarize
Why does it take longer for AP to reach outside of left atria?
no specialized conduction tissue, has to go through myofibrils
Time for a perfectly healthy heart for an AP to go from SA to the entire heart including ventricles?
0.22 seconds
Delay at AV node that causes holdup is due to
Delays so the atrials can contract and fill ventricles before AP goes to ventricles and contracts them to eject blood
If there are extra action potentials, what can fix that?
The delay of the AV node can help reset.
AV node acts as a filter
Why is there a delay in AV node? (physically)
fatty and cells don’t have many gap junctions, causing AP to take longer to travel.
Delay time of AV node
0.12 seconds
Delay in bundle of HIS is how long
.01
Total time for AP to get from SA node to each of main bundle branches is
0.16 seconds
.03 internodal
.12 delay in AV node
.01 delay in bundle of HIS
After an AP from SA node (P-wave), how long will it take QRS to start?
0.16 seconds
Where does QRS start?
Main (left and right) bundle branches in the interventricular septum
If APs hit AV node while its in complete refractory period, will it generate AP?
no.
Direction of electron movement during depolarization of ventricles
toward left foot at 59 degrees on average
0 degrees is considered to be
horizontal
If the put the electrodes closer to heart, the deflections will appear
much larger.
QT interval is measuring
length of time that depolarization happens in ventricular tissue.
T-wave is
Ventricles repolarizing
P-wave is the
SA node generating AP
SA node length and height
positive deflection that is 2 and a half small boxes long and tall
If you have an inverted P-wave, that means
the APs are starting outside the SA node
If you have a peaked P-wave
Hypertrophy or stretched out right atria
more tissue we have, higher magnitude of deflection
If you have a long P-wave
Likely an issue with the left atria to be depolarized
Left atria stretched out
A way to remember peaked and long p-wave issues
Height - Right
Long - Left
If there is a really big problem with left atria, it can have a
double hump, its an electrical block
Q-wave
negative deflection before an R-wave
Not all leads will have a Q-wave, depending on orientation.
R-wave
Positive deflection that is the depolarization of the ventricles
PR interval
Period of time between P-wave and start of R-wave
Dont call it PQ cause not everyone has a Q wave
PR interval length
0.16 seconds
S-wave
neg deflection after R wave
How long does it take depolarize last tip of lateral wall of left ventricle?
.06 seconds between bundle branch and lateral wall of left ventricle, ideallyHo
How long is QRS?
0.06 seconds.
Its the .22 seconds total of heart, minus the .16 (time of nodal tissue and total delays)
If the Lateral wall of left ventricle shows .39 seconds to depolarize, and the SA/AV node takes .21 seconds to depolarize + the delay, how long did it take the ventricles to depolarize? What would this be on the EKG?
.18 seconds
.39 - .21 = .18
QRS complex
Height of QRS
Net deflection of 1.5 mV
+1 to upside, bottom side of 0.3
roughly 1.5 mV and 3 large boxes
Magnitude of deflection of QRS complex is measured how
how far it goes up above baseline + how far it goes below baseline = total magnitude of deflection
If we have a really large QRS complex, it is due to
electrodes really close to heart, or heart tissue is massive (hypertrophy)
Hypertrophy would also make it longer
What would prolong length but not height of QRS?
dilated cardiomyopathy.
Tissue isnt thicker, but it is stretched out and makes it take longer.
Where does atria repolarize?
its hidden by large size of QRS, but it looks like it would be right around S-wave
At the very end of QRS complex, or end of S-wave, all of the ventricular tissue is
depolarized
Reference point for figuring out injury or infarct
J-point or isoelectric point
Reference point at end of QRS complex (end of S-wave)
After the T-wave, all of the ventricular muscle should be
reset/repolarized. Except the unhealthy tissue.
What would area after T-wave look like if there is unhealthy tissue?
Tissue that didnt repolarize and it would show some funky current and generating electrical activity
compare it to J-point
QT interval what is it and how long is it
time between start of depolarization and time that all the tissue is repolarized
.25 - .35 seconds
.25 - .35 seconds (QT interval) is the duration of
endocardial fast action potentials
ST interval area can show
areas of injury or infarcts
not the specific time, but if there is funky currents
Why is the T-wave upward deflection
Repolarization in opposite direction of depolarization.
Its the repolarization from superficial to deep
depolarization is deep to superficial
If we needed a faster heart rate, heart will shorten up
ST segment, QT interval, and of course time in between beats
Ventricles adjust too by speeding up process of pumping and resetting
Lusitropy
Resetting/repolarizing of the ventricle
Positive lusitropy
Repolarizes ventricle faster than it normally does
negative lusitropy
Repolarizes ventricle slower than it normally does
Inotropy
stronger heart beat from more calcium coming into heart/release from SR
Chronotropy
Heart rate
Dromotropy
Speed of conduction of action potentials
What is dromotropy dependent on?
Sodium currents and how much/how fast we have them coming into heart cells
RR interval
time in between R waves
Typical RR interval is
0.83 seconds
60 divided by 0.83 = what is it?
Heart rate.
72bpm
What if there RR interval is .91 seconds?
.43?
66bpm
140bpm
A higher RR interval will result in ________.
A lower RR interval will result in _______.
Lower heart rate
Higher heart rate
Each big box is __ mV
0.5
Each small box is ___ mV and ___ seconds
0.1 mV and .04 seconds
old school eKG machines fed the paper at how fast?
25mm per second
How many big boxes in one second? How many seconds per box?
5 big boxes.
0.2
Cardiac refractory period
time after an AP for the heart to reset itself
Early premature contraction during refractory period
will result in smaller force of contraction, when it contracts before refractory period is over
Where is the relative refractory period?
Very bottom of relative refractory period
If AP starts here, it will still generate contraction, just weaker (early premature contraction)
A later premature contraction will
still contract the same strength
Absolute refractory period
halfway down refractory period, will not elicit much of a contraction, if any at all.
