Transcript Waves and Measurements

Waves and
Measurements
We have learned that arrhythmias are
manifestations of the electrical activity of
the heart.
You have learned that electrocardiography
is the study of the heart’s electrical activity.
We must transform the electrical activity into
a form that can be seen in order to study
it.
Electrodes
• Can be attached to the skin
• Then connected to a machine that will
display the electrical activity on graph
paper.
• Electrical activity is displayed best if you
assure good contact between the
electrode and the skin by:
Abrading the skin slightly.
Removing any obstacles like dirt or hair
Using a contact medium, like saline or
commercial gel.
When the EKG machine is turned
off:
• The writing point (stylus) will produce a
straight line.
• This line is called the isoelectric line.
• No current is flowing, and the electrical
forces are equal.
Once the EKG machine is
connected to the patient and turned
on:
• The current is flowing, and the needle will
move above or below the isoelectric line.
Rule of Electrical Flow
• States that “if the electricity flows toward
the positive electrode, the patterns
produced on the graph paper will be
upright. If the electricity flows away from
the positive electrode (or toward the
negative electrode), the pattern will be a
downward deflection”.
Review
• The electrical current is flowing toward the
positive electrode. This will produce a
positive deflection.
True or False?
TRUE
Monitoring Leads
• We must be sure that the electrodes are
always in same place on patients.
• They are always positioned the same, or
standardized.
• The positioning of electrodes for
monitoring will allow you to see the
electrical pattern of the heart for a single
view.
• By rearranging the electrodes, you can get
several views.
Lead
• Each view of the heart is called a lead.
• Leads can be changed by a knob on the
EKG monitor.
True or False?
• Leads can be changed by simply using a
knob on the EKG machine.
• One lead shows only one view of the
heart.
Leads…
• A combination of electrodes that reflects
the flow of electricity between two points
on opposing sides of the heart.
• Bipolar- one positive and one negative
• Unipolar-single positive, and a neutral
opposing location situated to reference the
center of the heart.
• Single leads that give good pictures of the
basic waves are called monitoring leads,
because they are used to monitor patterns
such as arrhythmias.
• The most common one is Lead II.
• MCL1 is also common.
Positioning of Lead II
Negative
(Below right clavicle)
Positive (Apex)
Ground
Positioning of MCL1
Negative
(below left clavicle)
Positive
(4th intercostal, r. sternal border)
Ground
• The primary deflection in Lead II is positive
or upright.
• Why?
Because…
• The electrical current is flowing from the
SA node in the right atrium to toward the
ventricles. The current is going in the
direction toward the positive electrode.
Graph Paper
• It is standardized and uniform.
• The size of the graph and the speed at
which the paper moves through the EKG
machine are always constant.
• This allows us to have a “norm” and a
comparison.
Graph Paper
• The lines on the graph paper can help
determine the direction and the magnitude
of the deflections.
• Voltage-compare to horizontal lines
• Time-compare to vertical lines
What is “voltage”?
• It is the strength of the current.
• The height of the deflection will indicate
the voltage(amplitude).
• Measured by the horizontal lines of the
graph paper.
Cardiac Cycle
•
•
•
•
Heart has 4 chambers.
2 atria at the top work together
2 ventricles at the bottom work together
In the normal heart, blood will enter both
atria simultaneously and it is then forced
into both ventricles simultaneously while
the atria contract.
How do we measure “time” on the
graph paper?
• The vertical lines tell you how much time it
took for the electrical current within the
heart to travel from one area to another.
• Standard rate is 25 millimeters per
second.
• It takes .20 seconds to get from one heavy
vertical line to the next.
• The distance (in time) between two light
vertical lines is .04 seconds.
Chambers of the Heart
Remember…
• Before the atria can contract, an electrical
current must first stimulate the muscle cell.
• For a myocardial cell to contract it must
first receive an electrical stimulus.
• During each phase of the cardiac cycle, a
distinct pattern is produced on the EKG
graph paper.
What makes up a cardiac cycle?
• It begins with the initiating impulse from
the pacemaker and includes all phases
until the ventricles are repolarized.
• You will see on the graph paper all of the
wave patterns that this causes.
Waves…
• The deflections above or below the
isoelectric line.
• In one cardiac cycle, there are 5 prominent
waves.
• P, Q, R, S, T
• The area between waves is called an
interval.
• A straight line (inactivity) between waves
is called a segment.
P Wave
• The first wave.
• It starts with the first deflection from the
isoelectric line. This wave is indicative of
atrial depolarization(current is discharging
or flowing).
True or False?
• If you see a P wave, this means that the
atria contracted.
FALSE
• It does mean that an electrical current
stimulated it, but the muscle cell might not
have contracted in response to it.
• You cannot tell by simply looking at the
EKG. You have to use also the
mechanical function assessments. How
do you do that?
• When the impulse leaves the atria and
goes to the AV node, there is a slight
delay.
• This is because the tissues of the node
conduct impulses slower than other
myocardial tissue.
• This is the PR segment (inactivity).
• The SA node, the atria, and the ventricles
all conduct impulses faster than the AV
node.
• This allows time for the atrial contraction
and complete filling of the ventricles.
PR Interval
• All of the electrical activity before it goes to
the ventricles.
QRS Complex
• Remember…the PR interval begins at the
first sign of the P wave and ends at the
first deflection of the next wave.
• This wave is called the QRS complex.
True or False?
• The PR interval includes all atrial activity
and all nodal activity, but does not include
ventricular activity.
TRUE
What does QRS wave indicate?
• Ventricular depolarization
• Larger than the P wave because
ventricular depolarization involves greater
muscle mass than atrial depolarization.
Components of QRS
• Q wave is negative deflection, follows the
P wave, but before R wave
• R wave is first positive deflection following
the P wave
• S wave is the second negative deflection
after the R wave.
Review
• What does the QRS complex indicate?
It indicates…
Ventricular depolarization.
Another wave? Yes…
• T wave, ventricular repolarization.
• NOTE: The atria repolarize as well, but it
is usually hidden in the QRS complex.
• Why? Because their repolarization usually
occurs at the same time as ventricular
depolarization.
Normal Measurements
• PRI, between .12 and .20 seconds,
otherwise it is “short” or “prolonged”
• A long PRI would suggest a delay in the
AV node, not a P wave or atrial problem
What about the ST segment
and T wave?
• The section between the S wave and the T
wave.
• Most segments are straight lines, but the
ST is usually not because of the transition
between the QRS complex and the T
wave.
How long is a QRS complex?
• Anything less than .12 seconds.
• This would mean that the ventricles took a
normal amount of time to depolarize if they
did it in less than .12 seconds.
Now that you know the waves…
•PRACTICE,
PRACTICE,
PRACTICE!!!