lecture 3: guyton chapter 11 Flashcards
what 2 types of nervous systems act on the pacemaker activity
sympathetic and parasymphathetic
explain 3 ways which the parasympathetic nervous system can affect pacemaker activity
1) slower depolarization (less sodium entering cells, slower HR)
2) lower resting membrane potential (more energy needed to reach threshold)
=longer=slower HR
3) more positive threshold
longer to reacher=slower HR
true or false: ventricular cells have leaky sodium which allows them to have inherent excitatory abilities
false, no leaky
need exact energy for thresholf
explain phase 0 of ventricular AP
depolarizing impulse activates fast NA+ channels and inactivates K+ channels.
explain phase 1 of ventricular Ap
Transient opening of K+ channels and Na+ channels begin to close
(k+ starts to excite the cell)
explain phase 2 of ventricular AP
Ca2+ channels are open, the key difference between nerve AP.
balance between the influx of calcium and the efflux of K
what is the key difference between ventricular AP and muscle AP
calcium channels are open for a period of time while K+ channel are also open
explain phase 3 of AP ventricular
repolarization, Ca2+ inactivate and K+ channels open.
explain phase 4 of the ventricular AP
resting membrane potential near the K+ equilibrium potential.
(few leaky channels)
the resting potential of the heart is near the K+ equi, the Ca2+ or the NA+ equilibrium
k+
where is AP generated
SA node
why is AP generated in SA node
leaky cells
explain the steps or conduction in the heart
1) AP initiated in SA node
2) AP travels through atrial cells (they get depolarized easily through syncytium)
3) Signal gets collected at AV node and gets slowed down because of less gap junctions
4) signal passes through a bundle of His to the ventricles
5) moves through Purkinje fibers to the apex of the heart
6) signal moves inside to outside and upwards to facilitate the emptying during contraction
why and how the signal slowed down at the AV node
to allow the atrium to contract before the ventricles (max filling)
they have fewer gap junctions
why is the signal collected at the bundle of His
only place where the signal can travel through the fibrous membrane between atrium to ventricle
what device is used to record the depolar and repolar wave
voltmeter
if the depolarization wave moves towards the positive node, what type of reading on the volt meter
positive
if the repolarization wave moves towards the positive node, what type of reading on the volt meter
negative
the depolar and repolar waves move from the BLANK electrode to the BLANK electrode
negative to positive
true or false: when the cardiomyocyte is either completely depolarized or repolarized there is no potential recorded
true
the mean vector through a partially depolarised heart goes towards where
down towards the apex of the heart
what records the signal (negative or positive)
positive node
what does bipolar lead mean
ECG is recorded from 2 electrodes on the body
explain where lead 1 is placed
The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left arm.
explain where lead 2 is placed
The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left leg.
explain where lead 3 is placed
The negative terminal of the electrocardiogram is connected to the left arm, and the positive terminal is connected to the left leg
what does einthoven’s law state
that the electrical potential of any limb equals the sum of the other two (+ and - signs of leads must be observed).
lead 1+ lead BLANK= lead BLANK
led 1 + lead 3 = lead 2
the amplitude of the R wave is recorded highest at what lead
the lead that is facing closest to the apex of the heart
what augments unipolar limb leads are used
aVR aVL and AVF
where is the electrode for AVR
For aVR the + electrode is the right arm, and the – electrode is the left arm + left leg;
where is electrode for aVL
aVL + electrode is left arm
where is electrode for aVF
positive electrode on left foot
how many chest leads are there
6
v1-v6
are chest leads unipolar or bipolar
unipolar
true or false: chest leads are placed around the heart
true
chest leads give readings in the plane BLANK to the limb leads
perpendicular plane
what is another name for chest leads
precordial leads
what are chest leads very sensitive to
very sensitive to electrical potential changes
underneath the electrode.
for a 12 lead ECG how many beats are needed to make an interpretation
1 beat
true or false: each lead for an 12 lead ECG has 2 positive electrodes
false, only 1
which electrode acts like the camera
positive
where is the view from in an ECG
View is from the positive electrode towards the negative electrode.
what is the portion of the left ventricle that each lead “sees” determined by
by the location of the positive electrode
true or false: no matter where you place the electrodes, you will get the same viewpoint
false. Different placements of the electrodes will yield different viewpoints.
what leads look at an inferior view of the heart wall and how do they look
leads II, III and aVF
from the left leg up
which leads get a view of the posterior heart wall
leads V1 and V2
which leads give a view of the lateral heart wall (for high lateral)and how do they look
leads I and AVL
looks from the left arm towards the heart
which leads give a view of the lateral heart wall (low lateral or apical view) and how do they look
leads V5 and V6
looks from left lateral chest towards heart
which leads give view of entire lateral heart wall and how do they look
leads I, aVL, V5 and V6
look at liateral wall from two diff perceptions
which leads give a view of anterior heart wall and how do they look
leads v3 and v4
from left anterior chestt
which leads give a view of septal heart wall and how do they look
leads v1 and v2
look along sternal borders
true or false: you should get different HR when using different leads
false, always same HR
what does the p wave represent
Represents positive and negative deflections of atrial contraction and relaxation
=atrial depolarization
what is the PR intervant
Distance between the P wave and the R wave. Should be consistent
=delay of the contraction from atrium to ventricles
what does an inconsistent PR interval mean
problem with AV node (not slowing the signal down properly)
what does the QRS complex represent
the ventricle depolarization
what is the Q R and S waves
Q wave: First negative deflection
Normal in I, aVL, V1, V6
Significant or pathologic if one box wide and/or 1/3 the height of the R wave
R Wave: First positive deflection
S Wave: Next negative deflection
what is the ST segment
essentially isoelectric (slopes gently upwards)
what is the J point and what does it give info on
the point at which the ST Segment takes off from the QRS complex
gives info on heart function
what type of wave is the t wave (de or repol)
repolarization
explain the t wave (in terms of sings)
Upright always in leads I, II, V2-V6. aVR is always negative. Leads III, aVL, aVF, and V1 can be positive or negative
what is the Uwave
Seen best in V3, the same polarity as T wave, represents the last part of ventricular repolarization, and can be a sign of hypokalemia
what is hypokalemia
lack of k+ in the body
what is the QT interval
one complete ventricular cycle
what 4 structures can ECG not show the activity of
SA node
AV node
Bundle of his (and branches)
purkinje network
what is the P wave a small bump in comparison to the QRS wave
The P wave or atrial depolarization is a small bump because the walls of the atria are thinner than the walls of the ventricle, therefore, the total amount of electrical activity is smaller than the QRS wave.
what do the individual squares of the ECG represent
measure time and amplitude.
3 squares ventricle is what amplitude
0.3 mv
each square of ECG is how many seconds
0.04 sec
what do ECGS diagnose
Cardiac arrhythmias
Heart rate
Axis deviations
Chamber enlargement
Conduction abnormalities
What determines the amplitude of the waves in an ECG
the mass of the cells (ex: atrial thinner than ventricles so faster)
what is the 1st step when interpreting ECG
evaluate the P wave
what does the P wave indicate on ECG
if atrial rhythm is normal
what are the 3 questions to ask about P waves
Are all the P waves occurring at regular intervals?
Do all the P waves have the same appearance on the ECG?
Are the P waves visible at all?
true or false: P wav es occur at reg intervals during normal sinus rhythm
true
what is the 2nd step when interpreting ECG
determine whether the ventricles are activated from inside or from another location.
This can be done by looking at the duration (time) of the QRS complex.
what is the duration of a normal QRS complex
0.04-0.06
what does a QRS compelx of longer than 0.06 seconds indicate
waves have left normal pathways (conduction tissues) and occur within ventricular myocardium.
what is a longer QRS called and what does it cause
Ventricular Complex and causes the QRS complex to have a wide and bizarre appearance on the ECG
what is the 3rd step when analyzing ECG
define the relationship between the P wave and the QRS complex.
what does the relationship between the P wave and the QRS complex determine
This determines whether the atria and ventricles are working in sync!
what are you looking for in terms of the relationship between P wave and QRS
You must control whether the P wave is always, never or sometimes associated with the QRS complex.
Does the P wave always come before the QRS complex?
what is the 4th step when analyzing the ECG
look for anything abnormal.
Arrhythmias
Escaped beats
Or anything else that does not resemble the classical PQRST complex.
what are different waves of calculated HR
Count the R waves registering within 6 seconds and
multiply by 10. (quick, but inaccurate method)
R-R interval = 0.83 sec
Heart rate = (60 sec)/(0.83 sec) = 72 beats/min min beat
what is respitory sinus arrythmia
Looks the same as the normal heart sinus rhythm, except that the heart rate is variable because it corresponds with respiration.
as a patient inhales, the heart rate BLANKS
increases
as a patient exhales, the HR blank
decreases
why does a wandering pacemaker (P wave) happen
This happens when the P waves have varied conformation, spacing and size within the same lead.
The pacemaker site may shift locations within the sinoatrial node, causing the vectors to shift slightly.
what is a wandering pacemaker a sign of
arrythmias
what are the 3 common artifact types
Sixty-cycle interference
Muscle tremors
Wandering Baseline
what is sixty cycle interference
This is an electrical interference pattern that occurs when the electrical equipment is not properly grounded
Looks like continuous electrical stimulations on readout.
how can you fix sixty cycle interference
Make sure the power cord is grounded, clips are contacting skin, clips are clean and securely attached to the cable, pull plugs on nearby equipment, turn off fluorescent lights, make sure cables are not touching one another, and that no one else is touching cables.
what are muscle tremors
These look like rapid and random movements of the baseline.
how to fix muscle tremors
calm them
place hand on them for calm
stop talking
true or false: muscle tremors on ECG can be caused by talking
true
use of muscles
what is a wandering baseline caused by
caused by the moving chest when the patient breathe.
how to fix wandering baseline
make sure the patient holds his/her breath for 20-30 seconds to get a quick reading
true or false: Avr , AVl and AVF are new leads
false, by using the limb leads and computers you can manipulate for different angles
why is it called augmented unipolar limb leads
because 1 lead is ground while the other is the electrode
signal comes from BLANK TO BLANK
but view is from opposite
signal is from negative to positive
view is from psotive to neg
