Clin Lab: EKG Flashcards
PowerPoints: EKG Cardiac physiology, EKG basics, EKG fields & vectors
What is responsible for maintain a membrane potential at rest?
Na/K ATP pump
Where is there more Na+?
outside the cell
Where is there more K+?
inside the cell
Explain Na/K movement with the Na/K ATP pump.
3 Na+ in; 2 K+ out
How does the Na/K ATP pump create electrical signals.
pumping the Na+ & K+ sets up a potential difference on each side of the cell membrane
What are the phases of a cardiac action potential?
Depolarization
Repolarization
Refractory period
Contraction
Depolarization
Rapid depolarization b/c Na+ channels open & causes influx (gives us the rapid spike in AP)
Ca+ channel open & causes influx and K+ channels open & causes outflow (gives us the plateau in AP)
Repolarization
Ca+ channels close & additional K+ channels open
Refractory period
resetting of everything occurs.
Na/K pump moves Na+ back out & K+ back in
What is the reversal of membrane potential?
Depolarization
What makes a heart action potential to be longer compared to neurons?
influx of Ca++
Describe the physiology of cardiac muscle cells.
branched, make connections w/ other cells, laid down in layers, & go in different directions
Desmosomes
structural connections that act like Velcro
hold the cell membrane in place so the cell doesn’t pull apart from each other when the heart is contracting.
Gap junctions
function as tunnels that connect cytoplasms. This is how depolarization can spread from one cardiac cell to the next so quickly.
What is responsible for spontaneous depolarization??
pacemaker cells
Primary pacemaker?
SA node
How are pacemaker cells unique?
no nerve control
never really at a resting potential, there is always some Na+ trickling in
(This is why the heart keeps beating even if there is no connection to the brain.)
Why is the SA node the primary pacemaker?
it spontaneously depolarizes the fastest
What & how does the body control the rate of Na+ inflow?
The Nervous System (sympathetic & parasympathetic) influences the rate by changing the number of Na+ channels that open.
SA node location
upper right atrium
What separates the atria & ventricles?
a layer of non-conductive CT which is where the AV valves are embedded.
AV bundle divides to form…
left & right AV bundles
The left AV bundle divides into…
anterior & posterior fascicle
AV node location
floor of the right atrium
Describe an electrical field.
any time there is a separation of charges (dipole). Some cells have depolarized & some haven’t.
No electrical fields & no electrical signal is also known as
resting state
What does no electrical signal show on the EKG?
nothing
Describe visual depiction of a vector.
an arrow that points towards the positive side & a cross on the negative side
In which direction do electrical fields point?
always point towards the positive
Describe the electric vectors of the heart.
During atrial or ventricular depolarization there a lot of small electrical fields in all directions.
Electrical fields in a particular direction are summed together to create one overall vector which is what the EKG machine picks up.
What is another name for the overall electrical vector?
major prime electrical vector
Einthoven’s original electrode
Left arm, right arm, left leg
Why was the additional electrode added?
place on right leg to be a ground lead which detects background signal
What are examples of background pertaining to EKG?
breathing noises & muscle tone
Does the EKG machine pick up activity inside, outside, or in both places?
outside of the cell
EKG showing when the is no depolarization
straight line of the EKG tracing
What is the straight line on the EKG tracing called?
isoelectric baseline
What does the EKG tracing show if the overall vector points towards a positive electrode?
upward deflection
What does the EKG tracing show if the overall vector points away from a positive electrode?
downward deflection
What does the EKG tracing show if the overall vector is perpendicular to the positive electrode?
biphasic deflection
How many electrodes are used in a standard 12 lead EKG?
10
List the 10 electrodes
RA, LA, LL, RL (ground)
V1-V6
Location of leads RA & LA.
outwardly on shoulders (preferable on bone)
Location of V1 & V2
4 intercostal space on either side of the sternum
Location of V3
halfway b/t V2 & V4
Location of V4 - V6
along a horizontal line, wraps around the heart to under axillae
List the limb leads
I, II, III, aVR, aVL, aVF
List the chest leads
V1-V6
Explain bipolar leads.
One electrode is (+) & the other is (-) for any given lead
2 electrodes make up one lead
Describe lead 1
left arm (+) right arm (-)
Describe lead II
left leg (+) right arm (-)
Describe lead 3
left leg (+) left leg (-)
Describe augmented limb leads
they consist of a positive electrode which is then compared to a negative space; they are unipolar
Location of the augmented leads
aVR - right arm (+)
aVL - left arm (+)
aVF - left foot (+)
Which electrode is the most often used & why?
Lead II
the most anatomically aligned to the normal heart
What do the limb leads show us?
the heart’s electrical activity in the frontal plane
Describe Lead I view
horizontally across the top of the heart
Describe Lead II view
upwards at the heart from the left hip
Describe Lead III view
upwards at the heart from the right hip
Describe aVF view.
straight up at the heart from the feet
Describe aVR view
looking down at the heart from the right shoulder
Describe aVL view
looking down at the heart from the left shoulder
Describe the precordial (chest) leads.
six electrodes placed on the chest which correspond w/ 6 unipolar leads on the EKG; horizontal plane.
What do leads V1 & V2 look at?
right ventricle
What do leads V5 & V6 look at?
left ventricle
What do leads V3 & V4 look at?
septum
Dimensions of small boxes on EKG paper.
1mm x 1mm
Dimension of big box on EKG paper.
5x5 small boxes. (5mm x 5mm)
What’s does the horizontal axis on EKG paper represent?
time
Time for 1 small box.
40 ms (0.04 sec)
Time for 1 big box
200 ms (0.20 sec)
Time for 5 big boxes
1000 ms (1sec)
The amount of time on a standard 12 lead paper.
10 seconds
What does the vertical axis on EKG paper represent?
Voltage (mV)
Voltage for 1 small box
0.1 mV
Voltage for 1 big box
0.5 mV
Voltage for 2 big boxes
1 mV
Most times, how do we clinically use the vertical axis on EKG paper.
too assess if a wave is too big or too small, not really actual numbers.
Which lead is opposite of lead II?
aVR
First deflection
P wave
- smaller amplitude than other waves.
- represents atrial depolarization
- first part is right atrium & second part if the left atrium
Large deflection
QRS complex
- represents ventricular depolarization
- first negative wave = Q wave
- first positive wave = R wave
- next negative wave = S wave
Do you see all ways on all leads?
No, it depends on the lead
Last deflection
T wave
- ventricular repolarization
- larger signal than atria (but smaller height)
- spread out and more rounded
Describe a segnment
a relatively flat (isoelectric) area b/t two deflections
Describe an interval
encompasses at least 1 deflection (+) or (-) and 1 flat (isoelectric) segments
How is the P wave created?
an impulse from the SA node
Boundaries of the PR segment
end of the P wave to start of the QRS complex
Describe the atria during the PR segment.
all atrial cells are depolarized
Describe the impulse during the PR segment.
impulse is held by the AV node
How long should be PR segment be?
<200ms (1 big box or 5 small boxes)
Boundaries of the PR interval
start of the P wave to start of QRS complex
PR interval represents
time it takes for the impulse to travel through the atria & the AV node
Describe the impulse & result during the QRS complex
once the impulse is through the AV node, rapid depolarization occurs throughout the ventricles & this produces ventricular contraction.
There are leads that normally don’t have Q waves, but if they do this could mean?
pathological issue like damage to the heart (new or old)
Boundaries of the ST segment
flat area b/t the end of the QRS complex & the beginning of the T wave
What two things should be the same height on the EKG?
PR & ST segments
What is happening with the ventricles during the ST segment?
All ventricular cells have depolarized
What is the J point?
point of inflection where the S wave ends & the ST segment begins
How do we assess if the PR & ST segments are aligned?
the J point
Changes to the ST segment can represent…
ischemia - assessed for heart attacks. (STEMI or NSTEMI)
Describe what is happening w/ ions during the T wave.
K+ ions leaving the cell returning the cell interior to a negative charge
Boundaries of the QT interval
beginning of the QRS complex to the end of the T wave
QT interval is also known as
systole
Which is long systole or diastole?
diastole
Describe an isoelectric line
the flat segments b/t the P, QRS, & T waves
What is happening on the EKG during isoelectric lines?
EKG is electrically silent
Describe depolarization of the septum.
it depolarizes first & does this from left to right
Second (+) wave after S wave
R’ wave
Positive wave after T wave and before P wave
U wave
Normal time for PR interval
120 - 200 ms (< 1 big box)
Normal time for QRS complex
60 - 100 ms (< 3 small boxes)
Gray zone time for QRS complex
100 - 120 ms
Abnormal time for QRS complex
> 120ms (> 3 small boxes)
Normal time for QT interval
360 - 440 ms
Describe the measuring facts when it comes to the QT interval
- varies by HR
- QT corrected (QTc) accounts for this
Normal time for QTc in men & women.
< 440ms in men
< 460ms in women
Describe the two types of EKGs
Rhythm strip - continous from 1 or 2 leads. (mostly in the ED, assessing underlying rhythm)
12 lead - standardized printout from all 12 leads (some will print a rhythm strop at the bottom)
