ECG Flashcards
two types of cardiac cells
myocardial cells
specialized cells
Conductivity
ability to transmit impulses from one area of the heart to another
Excitability
(irritability) capability of the cell
to respond to a stimulus
Automaticity
capacity to initiate an impulse or stimulus
Rhythmicity
property of regularitiy of the intervals at which impulses are formed.
Refractoriness
Property of being unresponsive to an impulse
Sodium and potassium concentration in and around the cell
potassium is high inside the cell and sodium is high outside the cell
The inside of the cell is ____ when at rest or in the polarized state
the inside is negative compared to the outside
how the sodium moves into the cell
when the cells are stimulated the cell membrane changes its permeability and allows sodium to move rapidly into the cell making the inside + and the outside negative. this is called depolarization
depolarized is ____ inside the cell
positive
polarized is ____ inside the cell
negative
Refractory periods
absolute refractory Period (heart cant respond-during depolarization)
Relative refractory period (can only respond to a strong stimulus-repolarization is n progress.) (this is the T-wave)
Subnormal period (will respond to weaker stimulus- just before reoplarization is completed)
Nonrefractory period (heart is completely repolarized and ready to respond to a stimulus)
SA node rate
60-100
AV node rate
40-60
Purkinje Fibers rate
20-40
Bachmans bundle
pathway from RA to LA
what does the p wave represent
atrial depolarization
What does the QRS represent
ventricular depolarization
unipolar electrode records what
the electrical activity between the positive electrode and the center of the heart
a bipolar electrode records what
the electrical activity between the positive and negative terminal
which way is the impulse going in an upward deflection
toward the positive electrode
which way is the impulse going in a downward deflection
toward the negative electrode (from the positive in a bipolar electrode)
list the unipolar chest leads
V1, V2, V3, V4, V5, V6
List the bipolar leads
Lead I, Lead II, Lead III
List the unipolar leads
aVR, aVL, aVF
commonly used monitoring lead
MCL1 (modified chest lead) and Lead II
Where are the electrodes in Lead II
+ over the apex of the heart (4-5ics MCL)
- right side, MCL 2nd ics
Where are the electrodes in Lead I
+ left upper MCL (2ics)
- R upper MCL (2ics)
Were are the electrodes in Lead 3
+ Left lower
- Left upper
Where are the electrodes in V1 MCL1
+ right lower
-left upper
Voltage
measured on vertical axis
Duration
measured on the horizontal axis by a
series of vertical lines; the interval between
vertical lines equals 0.04 second
small box
0.04
large box
0.20
isoelectric
baseline- no electric activity
An upright p wave means what
that it is coming from the SA node
Normal PRI
0.12 - 0.20 seconds
where is the PRI measured
from the start of the P wave to the start of the QRS
What does the PRI represent?
atrial depolarization and delay through the AV node
QRS complex duration
less than 0.12
how to measure the QRS
from the beginning of the QRS (Q or R
wave, whichever is present) to the end of the S
wave
J point
end of QRS and beginning of ST segment.
what does the T wave represent
Ventricular repolarization (revcovery)
it is normally upright in Lead II
What does a U wave indicate
Hypokalemia
QT interval represents what
the time it takes for the ventricle to depolarize
and repolarize.
Normal QT interval
usually 0.34-0.43
for a quick measure if its within 1/2 of the R-R its probably WNL
is based on heart rate. A QTc is corrected by the equation to a heartrate of 60 bpm
A prolonged QT does what?
what is considered prolonged
increases the risk of lethal arrhythmias and sudden cardiac death
QTc >500ms
Interpretation of ECG
is there a p for every QRS
is the PRI regular
QRS wide or narrow
what is the atrial rate, what is the ventricular rate
calculating HR - big box method
300 / the number of big boxes between QRS complexes
Calculating HR - small box method
1500 / # small boxes between QRSs
another way to calculate HR
10 multiplied by the # of QRS in 6 seconds
Most accurate way to check rate on irregular rhythms
count # of R waves for 1 minute.
How do you measure the atrial rhythm?
How about Ventricular rhythm?
measuring P to P
Measuring R to R
How to interpret the P wave
is it present? is it upright (in lead II) is there a p for every qrs do all the p waves look alike are the Ps regular do they occur where they should
How to interpret the P-R interval?
what is the PRI duration
(short or prolonged)
are the durations consistent across the strip (progressively longer)
is there a pattern to the changing PRI
How to interpret the QRS?
duration of the QRS?
do all of them look the same
does it bear a fixed relationship to the P
Nl < 0.12
Premature v. Escape
Premature = early Escape = back up rhythm
(Escape rate is based on origin of the impulse)
NODAL =
Junctional / escape
Characteristics of junctional rhythm
PR interval - regular or absent since the P wave may be absent
P wave - pacemaker site is the junction so in lead II the p wave may be inverted before the QRS, buried in the QRS or inverted behind the QRS.
PRI (if there is a p wave) PRI will be 0.12 or less
Normal junctional rate
40-60
Accelerated junctional rate
61-100
Clinical signs and symptoms of junctional escape rhythm
Slow regular pulse
Often a temporary Dysrhythmia
If rate dramatically decreases CO may drop
Are junctional rhythms regular
Yes
S & S of accelerated junctional rhythm
Usually benign
