1
Florida Heart CPR*
Telemetry
8 hours
Because of the length of this course it is recommended that the student print the course
out. Then log back on to MEDCEU and take the accompanying test when finished
studying the text.
Due to the large number of graphics and illustration this course may take longer to
download than many others. Please be patient.
Have you ever had trouble identifying a rhythm or just wished you could recognize an
EKG quickly and easily? After completing this course you will be able to rapidly identify
most rhythms.
When we were initially trained in school to identify rhythms, we had to memorize what
the rhythm
looked like to identify it. But the trick is to understand what is happening to the heart,
more specifically the Electrophysiology of the heart. It is important to understand
what's going on with the heart to interpret any rhythm. Understanding is the key to
knowledge. Today we are going to learn how to understand and read EKG's. It's
simple and easy. You just have to follow the 5 basic steps of rhythm recognition. If you
apply these steps you will be able to identify most rhythms with no tools or calipers, just
your eyes and head.
The electrocardiogram (EKG) will be our main area of study today. We will
cover several topics in this course including cardiac anatomy and physiology,
electrodes, lead placement, measuring heart rates, and identifying EKG wave forms.
Note: Although we freely use the term EKG as an abbreviation for electrocardiogram,
the abbreviation ECG is the proper term but is easily confused with
electroencephalograph (EEC).
Anatomy and Physiology
Heart Chambers
The heart is a four chambered structure made up of two receiving chambers called atria
and two pumping chambers called ventricles. The right atrium receives oxygen poor
blood returning from the body through the superior and inferior vena cava. The right
ventricle pushes the oxygen poor blood to the lungs through the pulmonary arteries.
The left atrium receives oxygen rich blood returning from the lungs through pulmonary
veins.
The left ventricle pushes the oxygen rich blood out through the aorta, which directs the
Florida Heart CPR*
Telemetry
2
blood to all parts of the body. The right and left atria are separated by the
interatrial septum while the right and left ventricles are separated by the interventricular
septum.
Heart Valves
When blood flows through the heart it follows a unidirectional pattern. It first enters both
atria
and then fills both ventricles before leaving the heart. In order to prevent backflow
against this pattern there are four valves in the heart that serve this function.
Found between the atria and ventricles are two atrioventricular (A-V) valves
that prevent blood from reentering the atria. The valve that guards the right
atrium is called the tricuspid valve while the valve guarding the left atrium
is called the bicuspid or mitral valve.
The two remaining valves are called semilunar valves. The valve located where the
pulmonary trunk meets the right ventricle is called the pulmonary semilunar valve.
The valve found where the aorta and left ventricle meet is called the aortic semilunar
valve. Both semilunar valves prevent backflow of blood into the ventricles.
Heart Muscle (Myocardium)
The heart is a specialized structure, which is made of muscle that has unique
characteristics.
The cell membranes of myocardial cells form very close connections to each other.
These connections are called intercalated disks and allow groups of muscle
cells to function as one. This unique contractile ability of myocardium is known
as a syncytium. The muscle cells that make up the atria and ventricles act as two
separate
syncytia, therefore contracting as two single units.
Florida Heart CPR*
Telemetry
3
Cardiac muscle has the ability to adapt to the amount of blood being delivered to it.
There is
a direct proportion between the amount of blood returning to the heart and the force of
cardiac muscle contraction. The more blood returning through the veins, the stronger
the muscular contraction ejecting blood out of the heart into the arteries. This occurs
due to the heart muscle responding to a stretch in the chamber walls as a result of an
increased amount of blood volume entering the heart. The ability of the heart to be able
to equalize the amount of blood entering and exiting it is called Frank-Starling’s law of
the heart.
Compared to skeletal muscle, heart muscle cells have a longer rest or refractory
period.
This allows the myocardium to relax after each contraction preventing a tetanic
contraction
of the heart. It also gives the heart chambers time to fill with blood before the next
contraction.
Unlike skeletal muscle, which needs nerve innervation for stimulation, cardiac muscle
needs no outside stimulus. This is what is known as automaticity. Heart muscle also
possesses inherent rhythm, which means it will contract at a regular rate.
Conduction System
The conduction system of the heart explains how heart muscle has automaticity
and is able to contract without the help of outside nervous or hormonal innervation.
It is made up of specialized cardiac cells that initiate and guide myocardial
contraction. The conduction system consists of the sinoatrial node (S-A node),
atrioventricular node (A-V node), atrioventricular bundle (A-V bundle or A-V bundle of
His),
Purkinje fibers and bundle branches.
The S-A node is located in the posterior wall of the right atrium. It sets off impulses
that trigger atrial contraction. It discharges impulses quicker than any other part of
Florida Heart CPR*
Telemetry
4
the heart and establishes the rate and rhythm for the entire
heart. Because of this it is more commonly known as the pacemaker.
Note: A node is the same thing as a pacer or pacemaker.
The contracted atrial cells then send the impulse to the A-V node, which is located in
the
atrial wall near the interatrial septum. Once the A-V node picks up the signal, the speed
of impulse transmission is slowed down to allow the atria
time to complete contraction before ventricular contraction occurs.
From the A-V node the impulse then travels to the A-V bundle (bundle of His)
which is made up of special fibers called Purkinje fibers. The A-V bundle begins
at the right side of the interatrial septum and runs down to the beginning of the
interventricular septum. It then branches into right and left bundle branches
that run down the length of the interventricular septum. The bundle branches further
divide into Purkinje fibers that cover the inner surface of the ventricles. The impulses
relayed from the Purkinje fibers initiates ventricular contraction.
The Electrocardiogram
The EKG is a recording of the electrical impulses produced by the heart.
The body acts as a giant conductor of electrical currents. Any two points on the body
may be
connected by electrical leads (electrodes) to register an EKG or to monitor the rhythm of
the heart.
The tracing recorded from the electrical activity of the heart forms a series of waves and
complexes that have been arbitrarily labeled (in alphabetical order) the P, Q, R, S, T
waves,
and sometimes the U wave. The waves or deflections are separated in most patients by
regularly occurring intervals.
Florida Heart CPR*
Telemetry
5
Depolarization (electrical firing) of the atria produces the P wave. Depolarization of the
ventricles produces the QRS complex .
Repolarization (electrical recharging) of the ventricles causes the T wave. The
significance of the U wave is uncertain, but it may be
due to repolarization of the Purkinje system.
The key to rhythm interpretation is the analysis of the form and interrelations of the P
wave, the PR interval,
and the QRS complex. The EKG should be analyzed with respect to its rate, its rhythm,
the site of the
dominant pacemaker, and the configuration of the P and QRS waves.
P Wave:.
The P wave is generated by the Sinoatrial(SA) Node or sinus node. Once the SA node
fires the electricity goes though both atria and a P wave is then
present on the monitor. That's why we call it a sinus rhythm. OK let me put it like this; if
the rhythm has one P wave for every QRS complex
and is under 150 BPM, then we call it a sinus rhythm because it is generated by the
Sinus node (SA node).
If the rhythm has more than one P wave for each QRS we call it an Atrial rhythm. If for
some reason the sinus (SA) node fails to act as the normal cardiac pacemaker, other
atrial foci may take over, and the P wave may have a different configuration.
Alternatively, a secondary pacemaker (eg, the AV junction)
may provide an "escape rhythm."
PR Interval: When conduction through the atria, the AV node, or bundle of His is
slowed, the PR interval
becomes longer. Changes in conduction through the AV node are the most common
cause of changes in the PR interval.
The P to R interval is important in identification of heart blocks. We'll cover some of that later on.
The PR interval extends from the beginning of the P wave (the beginning of atrial
depolarization) to the onset of the
QRS complex (the beginning of ventricular depolarization). It should not exceed 0.20
seconds as measured on
EKG graph paper, where each small square represents 0.04 seconds.
QRS Complex. The QRS complex represents the electrical
depolarization of the ventricles. The upper limit of normal duration of the QRS complex
is less than 0.12 seconds. A QRS
complex duration of less than 0.12 seconds means that the impulse was initiated from
the AV node or above (supraventricular).
A wide QRS complex (more than 0.12 seconds) may signify conduction that either
arises from the ventricle or comes from
supraventricular tissue. Prolonged conduction through the ventricles produces a
widened QRS complex.
If there is a delay or interruption in conduction in either bundle branch, the QRS will
widen in a
Florida Heart CPR*
Telemetry
6
manner typical for either right or left bundle branch block. An ectopic focus that initiates
an impulse from the
ventricle also can alter the shape of the QRS. When an ectopic beat arises above the
bundle branches, the
ventricles are activated in a normal fashion and the QRS complex will remain the same,
assuming that there is no
conduction delay in either bundle branch. If the depolarization occurs below the bundle
branches, the QRS complex
will be widened and notched or slurred because a different sequence of conduction will
ensue.
A wide QRS complex with no P waves is usually a ventricular rhythm.
Lead Placement
There are many types of cardiac monitoring systems, but they generally consist of a
monitor screen
(cathode ray oscilloscope) on which the EKG is displayed and a write-out system that
directly transcribes the rhythm strip onto paper. The write-out may be automatic or
controlled by a switch, and a ratemeter may be set to write out a rhythm strip if the rate
goes below a preset figure (eg, 50 beats per minute) or above a certain rate (eg, 120
beats per minute) for at least 6 seconds, and sometimes for as long as 30 seconds.
A ratemeter triggered by the QRS complex of the EKG is usually part of the system.
Lights and beepers may provide visual and audible signals of the heart rate.
Monitor leads or electrodes may be attached to the patient's chest or extremities. The
chest leads must be placed to show clearly the waves and complexes of the EKG strip.
Conventional locations for the chest electrodes are illustrated below. The arrow
indicates the direction of polarity from negative to positive. In lead I the positive
Florida Heart CPR*
Telemetry
7
electrode is below the left clavicle and the negative below the right.
Lead I
In lead II the positive
electrode is below the left pectoral muscle and the negative below the right clavicle .
Lead II
Lead III is displayed by attaching the positive electrode beneath
the left pectoral muscle and the negative below the left clavicle. Although these simulate
or approximate the I, II, and III leads
of the standard EKG, they are not identical.
Lead III
Another popular monitoring lead is the MCL1 lead. To connect this lead, the negative
electrode is placed near the left shoulder,
usually under the outer third of the left clavicle, and the positive is placed to the right of
Florida Heart CPR*
Telemetry
8
the sternum in the fourth intercostal space.
Lead MCL1
The ground electrode in all four leads can usually be placed almost anywhere but is
commonly located below the right pectoral muscle or under the left clavicle. The
electrodes are often color-coded for ease of application, lessening confusion in
location.
The negative lead is usually white, the positive lead is red, and the ground lead is black,
green, or brown. The popular phrase "white-to-right, red-to-ribs, and black left over"
helps to recall where the leads for lead II should be placed.
Remember the following points when monitoring patients:
1. A prominent P wave should be displayed if organized atrial activity is present. Leads
that show the P wave clearly should be chosen.
2. The QRS amplitude should be sufficient to properly trigger the ratemeter.
3. The patient's pericardium must be kept exposed so that defibrillation paddles can be
readily used if necessary.
4. Monitoring is for rhythm interpretation only. One should not try to read ST
abnormalities or attempt more elaborate EKG interpretation.
5. Artifacts should be noted: a straight line will show if the electrode is loose, or a
bizarre, wavy baseline resembling ventricular fibrillation (VF) may appear if an electrode
is loose or the patient moves. Sixty-cycle interference also may be present.
Always remember that any EKG findings should be correlated with clinical observations
of the patient.
Different electrode placements may be used for telemetry or other special purposes.
The positive electrode should be to the left or below the negative electrode. Otherwise
the deflections will all be reversed and the rhythm strips can be confusing.
How To Identify an EKG
Alright, lets get down to it. In order to identify rhythms, we need to follow the 5 basic
steps
Florida Heart CPR*
Telemetry
9
of rhythm recognition.
1. Rate (Calculate the heart rate)
2. Rhythm (Measure the regularity or rhythm of the R waves)
3. P-wave (Examine the P-wave)
4. P to R interval ( Measure the P to R interval)
5. QRS (Measure the duration of the QRS complex)
Step 1 - Rate
Ok, first thing is rate. In order to identify a rhythm we need to know the heart rate. The
patient's heart rate reveals a great deal of information. If the rate is slow (under 60
beats per minute), we call it bradycardia.
If the heart rate is fast (over 100 beats per minute) then it is called tachy or tachycardia.
There are several ways to determine a heart rate.
You can actually take a radial pulse.
The second way to obtain a rate is to look at a strip from the monitor. We call this strip
of paper graph paper.
EKG paper is a grid where time is measured along the horizontal axis.
Each small square is 1 mm in length and represents 0.04 seconds.
Each larger square is 5 mm in length and represents 0.2 seconds.
Voltage is measured along the vertical axis.10 mm is equal to 1mV in voltage.
The diagram below illustrates the configuration of EKG graph paper and where to
measure the components of the EKG wave form.
Heart rate can be easily calculated from the EKG strip:
The graph paper that the EKG records on is standardized to run at 25mm/second, and
is marked at 1 second intervals on the top and bottom. The horizontal axis correlates
the length of each electrical event with its duration in time. Each small block (defined by
lighter lines) on the horizontal axis represents 0.04 seconds. Five small blocks (shown
by heavy lines) is a large block, and represents 0.20 seconds. Duration of a waveform,
segment, or interval is determined by counting the blocks from the beginning to the end
of the wave, segment, or interval.
When the rhythm is regular, the heart rate is 300 divided by the number of large
squares between the QRS complexes. For example, if there are 4 large squares
between regular QRS complexes, the heart rate is 75 (300/4=75).
Florida Heart CPR*
Telemetry
10
Another sequence method gives an approximate heart rate through simple waveform
observation.
To calculate the atrial rate, find a P wave that peaks on a heavy black line. Count off the
following heavy black lines as 300, 150, 100, 75, 60, and 50, respectively until you
reach the next heavy black line on which the next P wave peaks. The number assigned
to this line is the estimated atrial rate. Calculate the ventricular rate by repeating the
above calculation, using the R wave instead of the P wave.
The second and easier method can be used with a regular or irregular rhythm to
estimate the rate.
Count the number of R waves in a 6 second strip and multiply by 10.
For example, if there are 7 R waves in a 6 second strip, the heart rate is 70 (7x10=70).
Lets give it a try. Look at the rhythm above and count all the R waves.
There are 8 R waves, so our patient's rate is 8 X 10 or 80.
Then there's the1500 Method. You can only use this method if the cardiac rhythm is
regular. To calculate the atrial rate, identify two consecutive P waves. Select identical
points in each wave. Count the number of small blocks between these two points.
Divide 1500 by the number of small blocks counted. The resulting number is the atrial
rate. Calculate the ventricular rate by repeating the above calculation, but count the
number of small blocks between the R waves. Another way to calculate your patient's
heart rate is to look in the upper right hand corner of the monitor, if they're on a monitor.
The heart rate should be displayed there. So remember step 1 is the heart rate.
Step 2 - Rhythm
Step 2 is rhythm. Is the rhythm regular or is it irregular? Very few rhythms are irregular.
For example, atrial fibrillation is always irregular. So if your rhythm is regular it's not afib.
This is a regular rhythm.
This is an irregular rhythm.
Step 3 - P Wave
Florida Heart CPR*
Telemetry
11
Step 3 is the P wave. Does the rhythm have a P wave? If it does, and you know that the
P wave is generated by the SA node, then we would usually call it a sinus rhythm since
it comes from the Sinus node or SA node. However, it's a sinus rhythm only if there's
one P wave for every QRS, and the rate is under 150 bpm. This will be come clearer in
the next chapter when we do some examples.
The P wave represents atrial depolarization - the time necessary for an electrical
impulse from the sinoatrial (SA) node to spread throughout the atrial musculature.
Look at the rhythm and ask yourself?
Are P waves present?
Do P waves have a normal shape - usually upright and rounded on the rhythm strip?
Are all the P waves similar in size and shape?
Do all the P waves point in the same direction?
Do you see a 1:1 relationship between P waves and QRS complexes?
Is each P wave the same distance from it's QRS complex?
Step 4 - P to R Interval
The P to R interval represents the time it takes an impulse to travel from the atria
through the AV node, bundle of His, and bundle branches to the Purkinje's fibers.
Location: The P to R interval extends from the beginning of the P wave to the
beginning of the QRS complex.
Duration: 0.12 to 0.20 seconds.
The P to R interval is important in order to determine if there's a heart block or
conduction system disease.
Now the P to R interval should take about .20 seconds or one box on the graph paper.
I'll give you examples of the P to R interval in a few chapters from now.
Florida Heart CPR*
Telemetry
12
Look at the P to R interval and ask yourself?
What is the duration of the P to R interval? (Normal 0.12 to 0.20 seconds)
Is the P to R interval constant?
Step 5 - QRS Complex
The QRS complex represents ventricular depolarization. The QRS complex consists of
3 waves: the Q wave, the R wave, and the S wave. The Q wave is always located at the
beginning of the QRS complex. It may or may not always be present. The R wave is
always the first positive deflection.
The S wave, the negative deflection, follows the R wave.
Location: Follows the P-R interval.
Duration: No longer than 0.10 seconds.
Look at the QRS and ask yourself?
Are all the complexes the same size and shape?
What is the duration of the QRS complex? (Normal duration is no more than 0.10
seconds; if greater, it indicates a Bundle Branch Block (BBB))
Are all the QRS complexes the same distance from the T waves that follow them?
Do all the QRS complexes point in the same direction?
Are any QRS complexes present that appear different from the other QRS complexes
on the strip? If so, measure and describe each one individually.
Note: The S-T segment represents the end of the ventricular depolarization and the
beginning of ventricular repolarization. The Q-T interval represents the time necessary
for ventricular depolarization and repolarization. The T wave represents the
repolarization of the ventricles. On rare occasions, a U wave can be seen following the
T wave. The U wave reflects the repolarization of the His-Purkinje's fibers.
In the next chapter we'll put these 5 steps together and see how it works.
Florida Heart CPR*
Telemetry
13
This is a 6 second strip.
The first step is calculating the heart rate. Count the R's and multiply by 10.
There are 8 R waves, so the rate is 80. Is 80 beats per minute fast (tachy), slow (brady),
or
or normal. ( 60 to 99bpm is normal for most people)
Step 1 rate is normal.
Step 2, is this a regular or irregular rhythm? Look at the rhythm. Are the R to R intervals
regular?
Does this rhythm seem to have a regular beat? It does. If a rhythm is regular it's not afib. Step 2 rhythm is regular.
Step 3, are P waves present? Yes, look up there! You should easily be able to see that
P waves
precede each QRS complex. If there's a P wave present and only one P wave for each
QRS complex, and the rate is under 150 then it's a sinus rhythm. We call it a sinus
rhythm because the Sinus node or SA node generates to P wave.
Note: In a Sinus rhythm the P wave is upright.
Step 3 it's a sinus rhythm.
Step 4 is the P to R interval. A normal P to R interval is quick, less than .20 seconds, or
about one big box on the graph paper.
If the P to R interval is delayed or longer than .20 seconds (one big box on the graph
paper) then there may be conductive system disease or what we call a heart block.
We'll do the blocks later.
Florida Heart CPR*
Telemetry
14
Step 4 is the P to R interval normal (within .20 seconds) or is there a delay or a heart
block? It looks normal to me.
Step 5 is the QRS complex. Is it there and if so, is it wide or narrow? The QRS complex
indicates ventricular depolarization, or contraction of the ventricles. Analyze the QRS
complex. Are all the complexes the same size and shape? What is the duration of the
QRS complex?
(Normal duration is no more than 0.10 seconds or about half a box on the graph paper;
if greater, it indicates a Bundle Branch Block (BBB).)
Are all the QRS complexes the same distance from the T waves that follow them?
Do all the QRS complexes point in the same direction?
Are any QRS complexes present that appear different from the other QRS complexes
on the strip? If so, measure and describe each one individually.
Step 5 the QRS looks ok to me.
Now lets put it all together and see what we get!
Step1 rate 80 bpm, Normal.
Step 2 rhythm, regular.
Step 3 P wave, the P wave is there so its a sinus rhythm.
Step 4 P to R interval is normal, no blocks.
Step 5 The QRS complex is within normal limits (WNL).
So, from the steps above we get a Normal (rate), Sinus (there's a P wave), Rhythm.
Very good, the above rhythm is Normal Sinus Rhythm or NSR.
Normal Sinus Rhythm
NSR is the normal rhythm produced when the cardiac electrical impulse is initiated by
the SA node.
Rate: 60 - 99.
Rhythm: Regular.
P waves: Upright and normal.
P to R Interval: WNL .12 - .20 seconds, less than one big box on the graph paper.
QRS Complexes: WNL .10 seconds, about half a box on the graph paper.
Significance: We should all be this lucky.
Florida Heart CPR*
Telemetry
15
OK, let's try another one.
1.What's the rate? Count the R waves. The rate is 120. There are 12 R waves and we
multiply 12
times 10 and the answer is 120bpm. Is that fast, slow, or normal. It's fast so we call it a
tachy rhythm
or tachycardia.
2. Is it regular?
Yes
3. Are there P waves?
Yes, there is one P wave for every QRS and they are upright. P waves are from the SA
node, so it's a sinus rhythm.
4. If there are P waves present, then what is the P to R interval?
The P to R is WNL less then .20 seconds or one box on the graph paper. It's not a
block.
5. Examine the QRS complex, Is it wide or narrow or normal?
It looks normal.
What is this rhythm?
It is Sinus( P wave) Tachycardia( rate over 100 tachy).
Sinus Tachycardia
Sinus tachycardia is characterized by an increase in the rate of discharge of the sinus
node. Perhaps secondary to multiple factors
(eg, exercise, fever, anxiety, hypovolemia), it is a physiological response to a demand
for a higher cardiac output.
Never "treat" sinus tachycardia; treat the cause of sinus tachycardia.
Rate: Greater than 100 bpm.
Rhythm: Regular.
P wave: Upright and normal (Sinus Rhythm).
P to R interval: WNL .12 - .20 seconds, one box on the graph paper.
QRS Complex: WNL <.10 seconds, half a box on the graph paper.
Florida Heart CPR*
Telemetry
16
Ok this looks easy!
1. Rate is 50 bpm which is slow so we'll call it brady or bradycardia.
2. Rhythm is regular, that's good.
3. P waves are upright and normal (sinus rhythm).
4. P to R interval is WNL.
5. QRS is WNL.
So we have Sinus (P wave) Bradycardia (under 60 bpm).
Sinus Bradycardia is characterized by a decrease in the rate of atrial depolarization
due to slowing
of the sinus node. It may be secondary to sinus node disease, increased
parasympathetic tone, or
drug effects (eg, digitalis, propranolol, or verapamil).
Rate: Sinus bradycardia is a sinus rhythm of less than 60 bpm.
Rhythm: Regular.
P wave: Normal in size and configuration. The P wave precedes each QRS complex.
P to R interval: WNL.
QRS: WNL
This looks different.
Start with the 5 basic steps.
What is the rate? 190bpm (Count the R waves). This is tachy or tachycardia
The rhythm is regular. Are there P waves present? Don't see any. Just looks like a lot of
QRS complexes. If there is no P wave, then it can't be a sinus rhythm. And if there are
no P waves, then forget about the P to R interval. But there are a lot of QRS complexes.
Where do they come from? The QRS complex comes from the AV Node.
Florida Heart CPR*
Telemetry
17
So since the QRS complex comes from the Atrio Ventricular node then we'll call it a
Ventricular rhythm. We call it a ventricular rhythm because it's generated by the atrio
VENTRICULAR node (AV Node). The QRS complex is wider than normal, that also tells
you that its a ventricular rhythm.
Rate: Greater than 100 beats per minute and usually not faster than 220 beats per
minute
Rhythm: Usually regular but may be irregular.
P waves: In rapid VT the P waves are usually not recognizable. At slower ventricular
rates, P waves may be recognized and may represent normal atrial depolarization from
the sinus node at a rate slower than VT, but the electrical activities do not affect one
another.
QRS, ST segment, T wave: The PVC is premature; ie, it must occur before the next
expected sinus beat unless atrial fibrillation is present since preactivity cannot be
assessed. The width of the QRS is 0.12 second or greater. The QRS morphology is
often bizarre, with notching. The ST segment and T wave are usually opposite in
polarity to the QRS. When multiformed (or multifocal),
the coupling interval and morphology of the QRS vary.
Ventricular Tachycardia (VT) is defined as three or more beats of ventricular origin in
succession at a rate greater than 100 beats per minute. There are no normal-looking
QRS complexes. The rhythm is usually regular, but on occasion it may be modestly
irregular. This arrhythmia may be either well tolerated or associated with grave, lifethreatening hemodynamic compromise. The hemodynamic consequences of VT
depend largely on the presence or absence of myocardial dysfunction (such as might
result from ischemia or infarction) and on the rate of VT. Atrioventricular dissociation
usually is present. This means that the sinus node is depolarizing the atria in a normal
manner at a rate either equal to or slower than the ventricular rate. Thus sinus P waves
sometimes can be recognized between QRS complexes. They bear no fixed relation to
the QRS complexes unless the atrial and ventricular rates happen to be equal.
Conduction from atria to ventricles is usually prevented because the AV node or
ventricular conduction system is refractory due to ventricular depolarizations.
Sometimes retrograde conduction from ventricles to atria occurs. In this instance there
will be a relation between the QRS complex and the retrograde P wave.
Occasionally an atrial impulse arrives when the AV node and His-Purkinje system are
not refractory and AV conduction can occur. This results in a capture beat, in which
ventricular conduction occurs over the normal pathways, resulting in a normalappearing (narrow) QRS complex. A capture beat occurs at a shorter RR interval than
the RR interval of the VT. AV conduction also may occur simultaneously with
depolarization of the ventricular focus. In this instance the ventricle will be depolarized
in part over the normal pathway and in part from the ventricular focus. The resulting
QRS complex will be intermediate in morphology between a normal QRS and a QRS of
ventricular origin. In this instance the RR interval will not change. This is called a fusion
Florida Heart CPR*
Telemetry
18
beat. Ventricular tachycardia may be monomorphic (all QRSs with the same shape) or
polymorphic (varying QRS shapes during the tachycardia).
Treatment: Ventricular tachycardia when sustained but hemodynamically stable is
initially treated with lidocaine, procainamide, or bretylium. The tachycardia algorithm
presents the recommended pharmacologic agents and sequence of interventions.
Ventricular tachycardia that is hemodynamically unstable should be treated the same as
VF.
Occasionally a narrow QRS complex may occur with a slightly shorter RR interval
(capture beat), or a QRS complex may be seen with morphological features
intermediate between a beat of ventricular origin and one of supraventricular origin but
with a constant RR interval (fusion beat).
Rate: Rate is very rapid and usually too disorganized to count.
Rhythm: The rhythm is irregular. The electrical waveforms vary in size and shape.
There is no QRS complex. ST segments, P waves, and T waves are absent as well.
P wave: None.
P to R interval: None.
QRS Complex: There are no normal-looking QRS complexes.
Ventricular Fibrillation (VF)
Description
Ventricular fibrillation is the single most important rhythm for the health care provider to
recognize. It is a rhythm in which multiple areas within the ventricles display marked
variation in depolarization and repolarization. Since there is no organized ventricular
depolarization, the ventricles do not contract as a unit. When observed directly, the
ventricular myocardium appears to be quivering.
There is no cardiac output. This is the most common mechanism of cardiac arrest
resulting from myocardial ischemia or infarction. The terms coarse and fine have been
used to describe the amplitude of the waveforms in VF. Coarse VF usually indicates the
recent onset of VF, which can be readily corrected by prompt defibrillation. The
presence of fine VF that approaches asystole often means there has been a
considerable delay since collapse, and successful resuscitation is more difficult.
Florida Heart CPR*
Telemetry
19
Treatment: Initial treatment is always defibrillation. Only defibrillation provides definitive
therapy. The exact benefit of antifibrillatory agents administered to persistent VF
independent of defibrillation is unknown. Because their contribution (if any) remains
doubtful, never delay defibrillation while waiting for pharmacologic agents to have an
effect.
Asystole (Cardiac Standstill)
Rate: None
Rhythm: None
P wave: None
P to R interval: None
QRS complex: None
Asystole represents the total absence of electrical activity. Since depolarization does
not occur, there is no ventricular contraction. This may occur as a primary event in
cardiac arrest, or it may follow VF or pulseless electrical activity.
Asystole can occur also in patients with complete heart block in whom there is no
escape pacemaker. VF may masquerade as asystole; it is best always to check two
leads perpendicular to each other to make sure that asystole is not VF. In addition, the
distinction between very fine VF and asystole without any escape beats (agonal QRS
complexes) may be very difficult. If it might be VF, it should be treated, like VF, with
defibrillation. However, shocks to asystole are potentially harmful. Sometimes, however,
P waves may occur, or rare, erratically occurring ventricular escape beats (agonal
beats) may be seen. Patients with these beats will not have a pulse and must be treated
immediately if they are to be saved. If no organized QRS complex is seen and the
patient has a pulse, then the EKG is improperly connected, turned off, or improperly
calibrated.
Florida Heart CPR*
Telemetry
20
Treatment: Use CPR, external pacer, epinephrine, atropine and actively search for
reversible causes.
Rate: The atrial rate as a rule cannot be counted. In the untreated patient, the
ventricular rate is usually 160 to 180 beats per minute.
Rhythm: The ventricular rhythm is irregularly irregular. Where there are clearly
fibrillatory waves indicating the presence of atrial fibrillation but the QRSs are regular,
there must be some additional factor present, such as third-degree AV block or
accelerated junctional rhythm or both. Both of these are often the result of digitalis
intoxication.
Note: A-Fib is always irregular.
P waves: Organized atrial electrical activity is absent, so there are no P waves. Chaotic
electrical activity, or fibrillatory waves, may be seen.
P to R interval: None.
QRS interval: Ventricular depolarization is normal unless aberrant ventricular
conduction occurs.
Atrial Fibrillation (A-Fib)
Atrial fibrillation may result from multiple areas of reentry within the atria or from
multiple ectopic foci. Atrial fibrillation may be associated with sick sinus syndrome,
hypoxia, increased atrial pressure, pericarditis, and many other conditions. In the setting
of acute ischemic heart disease, increased left atrial pressure secondary to congestive
heart failure is the most common cause. The atrial electrical activity is very rapid
(approximately 400 to 700 per minute), but each electrical impulse results in the
depolarization of only a small islet of atrial myocardium rather than the whole atrium.
As a result, there is no contraction of the atria as a whole. Since there is no uniform
atrial depolarization, there is no P wave. The chaotic electrical activity does produce a
deflection on the ECG, referred to as a fibrillatory wave. Fibrillatory waves vary in size
and shape and are irregular in rhythm. Transmission of these multiple atrial impulses
into the AV node is thought to occur at random, resulting in an irregular rhythm. Some
impulses are conducted into but not through the AV node; ie, they are blocked within the
AV node. This is a form of "concealed conduction" and is important since such
nonconducted impulses contribute to the overall refractoriness of the AV node. For this
reason the ventricular rate of atrial fibrillation is often slower (averaging 160 to 180 per
minute) than that seen in atrial tachycardia or atrial flutter. Atrial fibrillation is usually the
result of some underlying form of heart disease (usually with congestive heart failure)
Florida Heart CPR*
Telemetry
21
and may occur intermittently or as a chronic rhythm. It may, however, be seen in a
paroxysmal form in which there is no other evidence of heart disease.
Treatment: Rate control is the initial treatment goal, using agents such as diltiazem,
verapamil, ß blockers, or digoxin. Chemical cardioversion, usually after a period of
anticoagulation, can then be attempted with procain-amide or quinidine. Electrical
cardioversion is the third therapeutic option, after rate control and chemical
cardioversion. Place a higher priority on electrical cardioversion in symptomatic patients
if the atrial fibrillation is of new onset and is known to be of short duration, eg, 1 to 3
days.
If the patient with atrial fibrillation and a rapid ventricular response is in clinical distress,
synchronized cardioversion is the treatment of choice. Hypotension induced by atrial
fibrillation is usually seen only in patients with acute myocardial infarction or
abnormalities of ventricular filling, eg, idiopathic hypertrophic subaortic stenosis or mitral
stenosis. These patients should be immediately cardioverted. The vast majority of
patients with atrial fibrillation will have ventricular rates of 120 to 200 beats per minute. If
acute ischemic heart disease is present, cardioversion is recommended. Other
asymptomatic patients, even those with a modest response (less than 120 beats per
minute), can be treated conservatively by controlling their rate initially with digitalis,
verapamil, or ß-adrenergic blocking agents. In the undigitalized patient, ß-adrenergic
blocking agents and verapamil may not cause sufficient slowing and may lead to
congestive heart failure.
Once the heart rate is controlled or if symptoms occur, a decision about cardioversion
should be made. Success in cardioverting and preventing recurrence of atrial fibrillation
depends on atrial size and the length of time the patient has been in atrial fibrillation.
The larger the atrial size and the longer the patient has been in atrial fibrillation, the
lower the likelihood of successful maintenance of sinus rhythm. Before cardioversion is
attempted either electrically or pharmacologically with an agent such as quinidine or
procainamide, anticoagulation should be considered. Patients with mitral stenosis,
cardiomyopathy, and large atria are more likely to have thrombus in the atrium and are
thus at higher risk for emboli and stroke. Anticoagulation must be considered.
Rate: Atrial usually 300 beats per minute, ranging between 220 and 350 beats per
minute
Rhythm: The atrial rhythm is regular. The ventricular rhythm may be regular if a
constant degree of AV block is present (such as 2:1 or, less commonly, 1:1) but can be
grossly irregular if variable block is present.
P waves: Flutter waves resemble a sawtooth or picket fence and are best seen in leads
Florida Heart CPR*
Telemetry
22
II, III, or aVF. In the presence of 2:1 or 1:1 conduction ratios, it may be difficult to identify
the flutter waves. In this instance carotid sinus massage (or IV adenosine used
diagnostically) may produce a transient delay in AV nodal conduction, resulting in a
higher degree of AV block. This will "uncover" the flutter waves, permitting their
identification.
P to R interval: Usually the PR interval is regular, but it may vary.
QRS complex: This pattern is usually normal, but aberrant ventricular conduction,
usually with right bundle-branch block, can occur.
Atrial Flutter
If there are P waves but they occur rapidly with a characteristic "sawtooth" appearance,
then the rhythm is atrial flutter.
This arrhythmia is the result of a reentry circuit within the atria . Atrial depolarization
occurs in a caudad-to-cephalad direction and hence is best observed in leads II, III. It is
often described as resembling a sawtooth or picket fence. Such a wave is called a
flutter wave.
While it is possible to have 1:1 AV conduction, more commonly there is a physiological
block at AV nodal level because the refractory period of the AV node results in 2:1 AV
conduction or even higher grades of block.
Since the atrial rate is most commonly about 300 per minute, 2:1 AV block usually is
present, and the ventricular rate is usually 150 per minute. The AV conduction ratio may
be altered by AV nodal disease, increased vagal tone, and certain drugs (eg, digitalis,
propranolol, verapamil) that will induce a higher degree of AV block (eg, 3:1, 4:1) or at
times a variable block. Atrial flutter seldom occurs in the absence of organic heart
disease. It is seen in association with mitral or tricuspid valvular heart disease, acute or
chronic cor pulmonale, and coronary heart disease. It is rarely a manifestation of
digitalis intoxication.
Treatment: If the patient is hypotensive, having ischemic pain, or in severe congestive
heart failure, synchronized cardioversion is the treatment of choice. If the patient is only
mildly symptomatic, pharmacologic therapy can be tried first. However, many experts
recommend that cardioversion should always be the initial therapy. The ventricular rate
can be slowed with diltiazem, verapamil, digitalis, or ß-blocking agents. Verapamil and ß
blockers may exacerbate bradycardia and congestive heart failure. If digitalis is used to
control the rate, care must be taken to avoid digitalis intoxication. Once the rate is
controlled, the patient can be placed on a type I antiarrhythmic agent, such as quinidine
or procainamide, to convert flutter. After a reasonable trial of pharmacologic conversion,
the patient should be electrically cardioverted.
Florida Heart CPR*
Telemetry
23
Rate: Slowed
Rhythm: Regular.
P waves: Each P wave is followed by a QRS complex.
P to R interval: This interval is prolonged beyond 0.20 second. It usually remains
constant but may vary.
QRS complex: There is a normal-looking QRS.
First-degree AV Block
First-degree AV block is simply a delay in passage of the impulse from atria to
ventricles. This delay usually occurs at the level of the AV node but may be infranodal.
Remember that in the normal ECG every QRS complex is preceded by a P wave, and
the time between the two forms is less than 0.20 second. Heart blocks are rhythms that
are caused by altered conduction through the AV node. As conduction in the AV node
slows, the interval between the P wave and the QRS complex lengthens. If slowing in
the node becomes pronounced, some P waves will be blocked in the AV node. In the
worst case no P waves will pass through the AV node to excite the ventricles.
The heart blocks are divided into three degrees. First-degree heart blocks are
characterized by P to R intervals longer than 0.20 second and all of the P waves are
followed by QRS complexes. Second-degree heart blocks are characterized by some P
waves being blocked at the AV node. This results in some P waves occurring without
following QRS complexes. Third-degree heart block is characterized by a complete
dissociation between P waves and QRS complexes. A hint for separating the heart
blocks into degrees is that first- and third-degree blocks usually have regular QRS rates.
Atrioventricular Block
Atrioventricular block is defined as a delay or interruption in conduction between atria
and ventricles. It may be due to (1) lesions along the conduction pathway (eg, calcium,
fibrosis, necrosis), (2) increases in the refractory period of a portion of the conduction
pathway (such as may occur in the AV node when digitalis is administered), or (3)
shortening of the supraventricular cycle length, ie, rapid atrial rates, with encroachment
on the normal refractory period (as with atrial flutter, in which 2:1 AV block at the level of
Florida Heart CPR*
Telemetry
24
the AV node occurs because the normal AV node refractory period will not allow
conduction at a rate of 300 beats per minute but will allow it at 150 beats per minute).
AV block may be classified in two ways:
1. According to the degree of block:


Partial blocks
o First-degree AV block
o Second-degree AV block (type I and type II), 2:1, and advanced (3:1 or
greater)
Third-degree or complete AV block
2. According to the site of block:


AV node
Infranodal
o Bundle of His
o Bundle branches
Each degree of block (first, second, third) may occur either at the level of the AV node
or below it. This distinction is not academic since pathogenesis, treatment, and
prognosis differ.
Treatment: Treatment for first-degree heart block is usually unnecessary when it occurs
without symptoms.
Rate: The atrial rate is unaffected, but the ventricular rate will be less than the atrial rate
because of the nonconducted beats.
Rhythm: The atrial rhythm is usually regular. The ventricular rhythm is usually irregular
with progressive shortening of the RR interval before the blocked impulse. The RR
interval that brackets the nonconducted P wave is less than twice the normal cycle
length.
P waves: The P waves will appear normal, and each P wave will be followed by a QRS
complex except for the blocked P wave.
P to R interval: There is a progressive increase in PR interval until one P wave is
blocked.
QRS complex: WNL.
Florida Heart CPR*
Telemetry
25
Second-Degree AV Block
In second-degree AV block, some impulses are conducted and others are blocked. This
type of block is subdivided into two additional types.
Type I Second-Degree AV Block (Wenckebach)
This form of block almost always occurs at the level of the AV node (rarely at His bundle
or bundle branch level) and is often due to increased parasympathetic tone or to drug
effect (eg, digitalis, propranolol, or verapamil). It is usually transient and prognosis is
good. Second-degree type I AV block is characterized by a progressive
prolongation of the PR interval. Decreasing conduction velocity through the AV node
occurs until an impulse is completely blocked. Usually only a single impulse is blocked,
and the pattern is repeated.
The repetition of this pattern results in "group beating," eg, three conducted sinus beats
with progressively lengthening PR intervals and a fourth sinus beat that is not followed
by a QRS. Such a "group" is referred to as 4:3 conduction. Although the conduction
ratio may remain constant, it is usual for it to change, eg, 4:3, 3:2, 2:1. The ventricular
rhythm is irregular except in the presence of 2:1 block.
Treatment: Specific treatment is rarely needed unless severe signs and symptoms are
present. Clinicians should place a high priority on identifying underlying causes.
Rate: The atrial rate is unaffected, but the ventricular rate will be less than the atrial
rate.
Rhythm: The atrial rhythm is usually regular, whereas the ventricular rhythm is most
often irregular, with pauses corresponding to the nonconducted beats.
P waves: The P waves will appear normal, and each will be followed by a QRS except
for the blocked P wave.
P to R interval: This interval may be normal or prolonged, but it will remain constant.
There may be shortening of the PR interval after a pause.
QRS complex: The QRS will be normal when the block is at the bundle of His.
However, the QRS will be widened with the features of bundle-branch block if the block
is at the bundle branches.
Type II Second-Degree AV Block
Florida Heart CPR*
Telemetry
26
This form of second-degree AV block occurs below the level of the AV node either at
the bundle of His (uncommon) or the bundle branches (common). It is usually
associated with an organic lesion in the conduction pathway, and unlike type I seconddegree AV block, it is rarely the result of increased parasympathetic tone or drug effect.
It is thus associated with a poorer prognosis, and complete heart block may develop. A
hallmark of this type of second-degree AV block is that the PR interval does not
lengthen before a dropped beat. More than one nonconducted beat may occur in
succession. This type of block most often occurs at the level of the bundle branches.
For a dropped beat to occur, there must be complete block in one bundle branch (ie,
right or left bundle-branch block) with intermittent interruption in conduction in the
contralateral bundle as well. Thus, type II second-degree AV block is often associated
with a wide QRS complex.
When block occurs at the His bundle, the QRS may be narrow since ventricular
conduction is not disturbed in beats that are not blocked. The rhythm may be irregular
when block is intermittent or when the conduction ratio is variable. With a constant
conduction ratio (eg, 2:1) the ventricular rhythm is regular
Rate: The atrial rate will be unaffected by third-degree AV block. The ventricular rate
will be slower than the atrial rate. With intranodal third-degree AV block, the ventricular
rate is usually 40 to 60 beats per minute; with infranodal third-degree AV block, the
ventricular rate is usually less than 40 beats per minute.
Rhythm: The atrial rhythm is usually regular, although sinus arrhythmia may be
present. The ventricular rhythm will be regular.
P waves: Normal.
P to R interval: Since the atria and ventricles are depolarized from different
pacemakers, they are independent of each other, and the PR interval will vary.
QRS complex: Generally normal looking. When block occurs at the AV node or bundle
of His, the QRS complex will appear normal. When block occurs at bundle branch level,
the QRS complex will be widened.
Third-Degree AV Block
Third-degree AV block indicates complete absence of conduction between atria and
ventricles. The atrial rate is always equal to or faster than the ventricular rate in
Florida Heart CPR*
Telemetry
27
complete heart block. It may occur at the level of the AV node, the bundle of His, or the
bundle branches. As in second-degree AV block, this distinction is not merely academic
since pathogenesis, treatment, and prognosis may vary considerably, depending on the
anatomic level of block. When third-degree AV block occurs at the AV node, a junctional
escape pacemaker frequently will initiate ventricular depolarization. This is usually a
stable pacemaker with a rate of 40 to 60 beats per minute. Since it is located above the
bifurcation of the bundle of His, the sequence of ventricular depolarization usually is
normal, resulting in a normal QRS. This type of third-degree AV block can result from
increased parasympathetic tone associated with inferior infarction, from toxic drug
effects (eg, digitalis, propranolol), or from damage to the AV node.
When third-degree AV block occurs at the infranodal level, it is most often due to block
involving both bundle branches. This indicates the presence of extensive infranodal
conduction system disease. When it results from coronary atherosclerosis, it is usually
associated with extensive anterior myocardial infarction. It usually does not result from
increases in parasympathetic tone or from drug effects. The only escape mechanism
available is in the ventricle distal to the site of block. Such a ventricular escape
pacemaker has an intrinsic rate that is slow, less than 40 beats per minute. Like any
depolarization originating in a ventricle, the QRS complex will be wide. It is not a stable
pacemaker, and episodes of ventricular asystole are common.
Treatment: The major interventions are atropine, transcutaneous pacing,
catecholamine infusions (dopamine or epinephrine), and transvenous pacemaker.
Isoproterenol is rarely indicated.
Rate: WNL
Rhythm: Irregular.
P waves: The sinus P wave is usually obscured by the QRS, ST segment, or T wave of
the PVC. It may, however, sometimes be recognized as a notching during the ST
segment or T wave. Retrograde P waves may occur. The presence of a sinus P wave
(when it cannot be seen) may be inferred by the presence of a fully compensatory
pause.
P to R interval: WNL
QRS: Not normal looking. Usually broadened to more than 0.12 second.
Premature Ventricular Complex
Some patients will have regular QRS complexes interspersed with occasional unusuallooking complexes. These unusual conformations are called PVCs. This aberrant
Florida Heart CPR*
Telemetry
28
activity can cause more serious ventricular arrhythmias. Clinical deterioration depends
on the frequency of the PVCs.
A PVC is a depolarization that arises in either ventricle before the next expected sinus
beat, ie, prematurely. It may result from the firing of an automatic focus or reentry.
Since PVCs originate in the ventricle, the normal sequence of ventricular depolarization
is altered; ie, instead of the two ventricles depolarizing simultaneously, they depolarize
sequentially. In addition, conduction occurs more slowly through the myocardium than
through specialized conduction pathways. This results in a wide (0.12 second or
greater) and bizarre-appearing QRS. The sequence of repolarization is also altered,
usually resulting in an ST segment and T wave in a direction opposite to the QRS
complex.
The interval between the previous normal beat and the PVC (the coupling interval)
usually remains constant when PVCs are due to reentry from the same focus (uniform
PVCs). When the coupling interval and the QRS morphology vary, the PVCs may be
arising from different areas within the ventricles, or if the PVCs are arising from a single
focus, ventricular conduction may vary. Such PVCs are referred to as multifocal or,
more appropriately, multiformed.
A PVC may occur nearly simultaneously with the firing of the sinus node. The antegrade
impulse originating in the sinus node (resulting in normal atrial depolarization) and the
retrograde impulse traveling toward the atria from the ventricles may meet in the AV
node. Then neither can spread further because of the other's refractory period. Since
the rhythm of the sinus node is undisturbed, a fully compensatory pause usually results
(ie, the next P wave should occur at the proper time). However, on occasion retrograde
conduction can spread to the atria and reset the SA node.
PVCs may occur as isolated complexes, or they may occur repetitively in pairs (two
PVCs in a row). When three or more PVCs occur in a row, VT is present. When VT lasts
for more than 30 seconds, it is arbitrarily defined as sustained ventricular
tachycardia.
If every other beat is a PVC, ventricular bigeminy is present. If every third beat is a
PVC, the term ventricular trigeminy is used; if every fourth beat is a PVC, ventricular
quadrigeminy is present; and so forth.
A PVC that falls on the T wave (during the so-called vulnerable period of ventricular
repolarization) may precipitate VT or VF. However, PVCs occurring after the T wave
may also initiate such VT.
Treatment: Isolated or non–VT PVCs are rarely treated except for needed symptomatic
relief. In the setting of an acute myocardial infarction, PVCs indicate the need to
aggressively treat the ischemia/infarction with oxygen, nitroglycerin, morphine, and
thrombolytic therapy. Simply making the PVCs diminish with lidocaine does little to the
Florida Heart CPR*
Telemetry
29
underlying pathology and can lure physicians into an invalid clinical security that the
problem has been resolved.
Rate: Varies.
Rhythm: Irregular.
P waves: Because atrial depolarization is usually retrograde, P waves are generally
negative in leads II and III.
P waves can precede, coincide with, or follow the QRS. Either a noncompensatory or a
fully compensatory pause may occur.
P to R interval: If the P wave precedes the QRS, the PR interval is usually less than
0.12 second. However, the PR interval may be
prolonged. Complete AV block may occur.
QRS: Usually normal. The interval may sometimes be widened (aberrant ventricular
conduction), usually indicating right bundle-branch block.
In some patients conducting tissue near the AV node has taken over the pacemaker
function of the heart. These patients will have slow heart rates (40 to 60 beats per
minute) and inverted but narrow QRS complexes, and often one can see retrograde P
waves in leads II and III.
Premature Junctional Complexes
Description
A premature junctional complex is an electrical impulse that originates in the AV junction
and occurs before the next expected sinus impulse. This often results in retrograde
atrial depolarization (hence the P wave in leads II, III, and aVF will be negative). The
retrograde P wave may precede, coincide with, or follow the QRS. The relation of a
retrograde P wave to QRS complex depends on the relative conduction times from the
site of origin within the junction to the atria and ventricles. It is therefore likely that an
impulse arising in the higher portion of the junction, above the AV node, would result in
a P wave occurring before or during the QRS complex, whereas one arising at a lower
level would result in a P wave that occurs after the QRS complex. Conduction from the
junction to the ventricles usually occurs along normal pathways. Thus the QRS complex
is usually normal, although it can be wide owing to either a bundle-branch block or
aberrant conduction. The pause following a premature junctional complex may be
noncompensatory (if the sinus node is depolarized by the premature beat) or fully
compensatory if the sinus node has discharged before it is reached by the premature
beat.
Florida Heart CPR*
Telemetry
30
Treatment: Specific suppressive treatment is rarely needed.
Junctional Escape Rhythm
Rate: A junctional escape rhythm has a rate of 40 to 60 beats per minute.
Rhythm: The presence of some junctional escape complexes may lead to an irregular
rhythm. Junctional escape complexes occur approximately 1.0 second or more following
the last depolarization. A junctional escape rhythm is usually regular.
P waves: Retrograde P waves (negative) may be seen in leads II, III, and aVF. P waves
may precede, coincide with, or follow the QRS. Sinus P waves, at a rate equal to or
slower than the junctional rhythm, may occur. This may result in AV dissociation
(discussed in more detail in "Ventricular Tachycardia").
P to R interval: This interval is variable but is usually less than the PR interval of the
normally conducted beat from the sinus node.
QRS interval: Ventricular conduction is usually normal unless a ventricular conduction
problem is present or aberrant conduction occurs.
Description
The AV junction can function as a pacemaker. It initiates impulses at a rate of 40 to 60
beats per minute, equivalent to an RR interval between 1.0 and 1.5 seconds. Under
normal circumstances, the sinus node pacemaker, which is faster, predominates. If the
AV node is not depolarized by the arrival of a sinus impulse within approximately 1.0 to
1.5 seconds, it will initiate an impulse. This is called a junctional escape complex. It
occurs because of failure of the sinus node to initiate an appropriately timed impulse or
because of a conduction problem between the sinus node and the AV junction. A
repeated series of such impulses is referred to as a junctional escape rhythm.
Treatment: Most commonly, junctional escape complexes and rhythms are events of
automaticity. They may also be due to digitalis intoxication. In nonparoxysmal junctional
tachycardia due to digitalis intoxication, digitalis should be withheld. The serum
potassium level should be checked, and if low, potassium should be given to raise the
serum potassium to the normal range. If the patient is severely compromised,
antibodies to digitalis may be used.
Glossary Of Terms
Aberrant: Abnormal
Arrhythmia: Irregularity or absence of a heartbeat. See dysrhythmia.
Asystole: (Cardiac Arrest, Ventricular Standstill): The absence of a heartbeat.
Atrioventricular Block: A cardiac impulse conduction disturbance in the
Florida Heart CPR*
Telemetry
31
atrioventricular (AV) node, bundle of His, or it's branches.
Automatic Beat: An impulse arising in an automatic focus, independent of the
dominant rhythm.
AV Dissociation: The independent beating of the atria and ventricles.
Bigeminy: A normal beat alternating with a premature beat.
Block: A pathologic delay or interruption in impulse conduction.
Bradycardia: A heart rate slower than the normal for that pacemaker site; e.g., less
than 60 beats/minute for the sinoatrial (SA) node.
Bradydysrhythmia: Any rhythm disturbance causing a slow heart rate (less than 60
beats/minute).
Bundle Branch Block: An abnormality in cardiac impulse conduction through the fibers
of the bundle of His.
Compensatory Pause: The period following a premature contraction during which the
heart regulates itself, allowing the SA node to resume normal conduction.
Conduction Time: The interval between the origination of an impulse at the SA node
and the stimulation of ventricular contraction.
Coupling: The relationship of a premature beat and the preceding beat.
Dysrhythmia: Any disturbance in the normal rhythm of the heartbeat; irregularities may
occur in discharge of impulses from the SA node, or in conduction of impulses through
the cardiac tissue.
Ectopic Beat: A beat originating from a source of cardiac stimulus other than the SA
node, usually caused by some irritation of the myocardium.
EKG (or ECG): Electrocardiogram; a graphic tracing of the electrical activity of the
heart.
Electromechanical Dissociation: Electrical activity without evidence of myocardial
contraction.
Escape Beat: An automatic beat that occurs after an interval longer than the dominant
cycle.
Extrasystole: An ectopic beat, occurring before the next dominant beat, that depends
on and couples with the preceding beat; contraction of
the heart that occurs prematurely and interrupts the normal cardiac cycle.
Fibrillation: Quivering or uncoordinated muscular contraction.
Fusion Beat: Simultaneous activation of one chamber of the heart by two foci.
Group Beating: A pattern of repetitive QRS complexes.
Heart Block: Impairment of cardiac conduction so that electrical impulses from the atria
fail to pass through the AV node to the ventricles.
Idiojunctional Rhythm: A relatively slow, independent rhythm that arises in the AV
junction and controls the ventricles.
Idioventricular Rhythm: A relatively slow rhythm that originates from and controls the
ventricles.
Junctional Dysrhythmia: The irregular heartbeat that results when the AV node
assumes the SA node's role as the heart's primary pacemaker.
Mobitz Type I (Wenckebach) Block: A second-degree or partial AV block in which the
P-R interval increases progressively until the atrial impulse arrives during the absolute
refractory period and the corresponding ventricular beat is not conducted.
Mobitz Type II Block: A second-degree or partial AV block characterized by the
Florida Heart CPR*
Telemetry
32
sudden nonconduction of an atrial impulse and a periodic nonconducted beat that
occurs without warning - without previous lengthening of the P-R interval.
Pacemaker: The SA node, so called because it initiates the electrical impulse that sets
the rhythm of cardiac contractions. An artificial pacemaker is an electrical device
implanted to pace a cardiac rhythm, used particularly when a patient has symptomatic
heart block.
Parasystole: An ectopic, independent rhythm that operates concurrently with the
dominant rhythm, whose foci can't be discharged by the dominant pacemaker impulses.
Paroxysmal: Recurring suddenly and abruptly.
Sinus Arrhythmia: A slight variation or irregularity in sinus rhythm or normal
heartbeats.
Systole: Contraction of the heart, which causes ejection of blood from the heart
chambers into the circulatory system.
Tachycardia: A heart rate faster than the normal for that pacemaker site; e.g., greater
than 100 beats/minute for the SA node.
Tachydysrhythmia: Any rhythm disturbance causing a fast heart rate (over 100
beats/minute).
Florida Heart CPR*
Telemetry
33
Florida Heart CPR*
Telemetry Assessment
1. The heart is a four chambered structure made up of two receiving chambers
called ___
and two pumping chambers called ____.
a. Ventricles / nodes
b. Atria / nodes
c. Ventricles / atria
d. Atria / ventricles
2. ______ prevent backflow of blood into the ventricles.
a. A-V valves
b. Tricuspid valves
c. Mitral valves
d. Semilunar valves
3. Unlike skeletal muscle, which needs nerve innervation for stimulation, cardiac
muscle
needs no outside stimulus. This is what is known as
a. Myocardial independence
b. Autonomic rhythm
c. Automaticity
d. Inherent innervation
4. The _____is located in the posterior wall of the right atrium. It sets off impulses
that trigger atrial contraction. It discharges impulses quicker than any other part
of
the heart and establishes the rate and rhythm for the entire heart. Because of this
it is more commonly known as the pacemaker.
a. S-A node
b. A-V node
c. Semilunar node
d. Bundle node
5. The Bundle of His is also known as the
a. S-A bundle
b. A-V bundle
c. Purkinje bundle
d. Pacemaker bundle
6. The EKG is a recording of the _____ produced by the heart.
a. Muscle contractions
b. Blood
c. Electrical impulses
Florida Heart CPR*
Telemetry
34
d. A and B
7. ______is generated by the Sinoatrial (SA) Node or sinus node. Once the SA
node fires the electricity goes though both atria and ______ is then present on
the monitor.
a. The P wave
b. The QRS complex
c. The T wave
d. The U wave
8. When conduction through the atria, the AV node, or bundle of His is slowed, the
_____ becomes longer. Changes in conduction through the AV node are the
most common cause of changes in the ______.
a. QRS complex
b. T wave
c. P Wave
d. PR interval
9. The _____ represents the electrical depolarization (or contraction) of the
ventricles.
a. U wave
b. QRS complex
c. T wave
d. PR interval
10. _______ is characterized by a decrease in the rate of atrial depolarization due to
slowing
of the sinus node. It may be secondary to sinus node disease, increased
parasympathetic tone, or drug effects (eg, digitalis, propranolol, or verapamil).
a. Sinus Tachycardia
b. Sinus Bradycardia
c. Ventricular Tachycardia
d. Fusion beat
Florida Heart CPR*
Telemetry