Normal
Figure 17 Rules for NSR
Normal Sinus Rhythm
Regularity: The R–R intervals are constant; the rhythm is regular.
Rate: The atrial and ventricular rates are equal; heart rate is between 60 and 100 bpm.
P Wave: The P waves are upright and uniform. There is one P wave in front of every QRS complex.
PRI: The PR interval measures between 0.12 and 0.20 second; the PRI measurement is constant across the strip.
QRS: The QRS complex measures less than 0.12 second.
Sinus Rhythms 71
For a rhythm to be called NSR, it must have P waves,
one in front of every QRS complex; the rate must be to
bpm, with a R–R interval across the
entire strip. It must have a PRI that measures between and
second, and the PRI must be across
the entire strip. Finally, the QRS measurement must be less than
second, or if it is not, the interpretation must be qualified by calling it a Sinus Rhythm
with a wide QRS complex.
10. Now go back to the Practice Strips for Chapter 3. Look at all the data available from
each strip. Each of these strips has been identified as Sinus Rhythm. Compare your
findings with the rules for NSR to see which patterns comply with the rules for NSR.
Sinus Bradycardia
11. If a rhythm originates in the sinus node, but doesn’t follow one or more of the rules
for NSR, it might fall into one of the other categories of sinus rhythms. If the rate is
lower than 60 bpm, it is called a bradycardia, meaning slow heart. When a rhythm originating in the sinus node has a normal, upright P wave in front of every QRS complex,
a normal PRI and QRS, and it is regular, it is called Sinus Bradycardia since the only
reason it doesn’t fit into NSR is because the rate is too slow (Figure 18). A rhythm can
be identified as Sinus Bradycardia when it fits all of the rules for NSR except that the
rate is less than bpm.
12. Here are the rules for the EKG findings in Sinus Bradycardia (Figure 19):
Regularity: regular
Rate: less than 60 bpm
P Wave: upright, uniform shape; one P wave in front of every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
Sinus Tachycardia
13. The same thing is true for a rhythm that fits all of the rules for NSR except that the
rate is too fast. When the heart beats too fast, it is called tachycardia, meaning fast heart.
uniform
60
100; regular
0.12
0.20; constant
0.12
Practice Strips; (Chapter 3, Parts I
and II)
All are NSR except 3.4, 3.6, 3.10,
3.12, 3.14
60
Figure 18 Mechanism of Sinus Bradycardia
Conduction: normal;
each impulse is conducted
through to the ventricles
Pacemaker: Sinus Node
Rate: <60 bpm
Regularity: regular
The sinus node is the pacemaker, firing regularly at a rate of less than 60 times per minute. Each
impulse is conducted normally through to the ventricles.
72 Chapter 4
So a rhythm that originates in the sinus node and fits all rules for NSR except that
the rate is too would be called a Sinus Tachycardia
(Figure 20). When a rhythm is regular, has a uniform P wave in front of every QRS
complex, has a normal and constant PRI and QRS, but the rate is greater than 100 bpm,
it is called .
14. The rules for Sinus Tachycardia (Figure 21) are:
Regularity: regular
Rate: greater than 100 bpm (usually does not exceed 160 bpm)
P Wave: uniform shape; one P wave in front of every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
fast
Sinus Tachycardia
Figure 19 Rules for Sinus Bradycardia
Regularity: The R–R intervals are constant; the rhythm is regular.
Rate: The atrial and ventricular rates are equal; heart rate is less than 60 bpm.
P Wave: There is an upright, uniform P wave in front of every QRS complex.
PRI: The PR interval measures between 0.12 and 0.20 second; the PRI measurement is constant across the strip.
QRS: The QRS complex measures less than 0.12 second.
Figure 20 Mechanism of Sinus Tachycardia
Conduction: normal;
each impulse is conducted
through to the ventricles
Pacemaker: Sinus Node
Rate: >100 bpm
Regularity: regular
The sinus node is the pacemaker, firing regularly at a rate of greater than 100 bpm. Each impulse is
conducted normally through to the ventricles.
Sinus Rhythms 73
Sinus Arrhythmia
15. The last of the sinus rhythms we will learn is Sinus Arrhythmia (Figure 22). This
rhythm is characterized by a pattern that would normally be considered NSR, except
that the rate is irregular, usually changing with the patient’s respirations. When the
patient breathes in, the rate increases, and when he or she breathes out, the rate slows.
This causes the to be irregular across the strip. The result is a
pattern with an upright P wave in front of every QRS complex, a normal and constant
PRI, a normal QRS complex, but an R–R interval. The difference between NSR and Sinus Arrhythmia is that NSR is regular and Sinus Arrhythmia
is . A true Sinus Arrhythmia will have an obvious pattern of
irregularity across the entire strip. If the rhythm is only very slightly irregular (off by
only 1 or 2 small squares), that can be noted, but the rhythm would be considered only
slightly , and thus not a Sinus Arrhythmia.
R–R interval
irregular
irregular
irregular
Figure 21 Rules for Sinus Tachycardia
Sinus Tachycardia
Regularity: The R–R intervals are constant; the rhythm is regular.
Rate: The atrial and ventricular rates are equal; heart rate is greater than 100 bpm (usually between 100 and 160 bpm).
P Wave: There is an upright, uniform P wave in front of every QRS complex.
PRI: The PR interval measures between 0.12 and 0.20 second; the PRI measurement is constant across the strip.
QRS: The QRS complex measures less than 0.12 second.
Figure 22 Mechanism of Sinus Arrhythmia
Conduction: normal;
each beat is conducted
through to the ventricles
Pacemaker: Sinus Node
Rate: 60–100 bpm
Regularity: irregular
The sinus node is the pacemaker, but impulses are initiated in an irregular pattern. The rate increases
as the patient breathes in and decreases as the patient breathes out. Each impulse is conducted
normally through to the ventricles.
74 Chapter 4
16. Here are the rules for the EKG findings in Sinus Arrhythmia (Figure 23):
Regularity: irregular
Rate: 60–100 bpm (usually)
P Wave: upright and uniform shape; one P wave in front of every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
Review
17. You now know the rules for the first four arrhythmias. Normal Sinus Rhythm originates in the node and has normal conduction within normal
time frames. This means that the wave will be upright and
uniform in front of every QRS complex, the PRI and QRS measurements will be within
limits, and the will be constant. For
NSR, the rate must fall between and
bpm. If the rate drops below 60 bpm but all the other rules to NSR apply, the rhythm
is called ; if the rate is faster than 100 bpm, the rhythm is
called . If the rhythm fits all the rules of NSR except that it is
irregular, the rhythm is called .
18. If a rhythm originates in the sinus node, it will have uniform, upright
waves because the electrical impulses are traveling
from the atria downward through the ventricles, and thus are heading toward
the electrode in Lead II.
19. With NSR, Sinus Tachycardia, Sinus Bradycardia, and Sinus Arrhythmia, the PRI
will always be between and second
and constant.
sinus
P
normal; PRI
60; 100
Sinus Bradycardia
Sinus Tachycardia
Sinus Arrhythmia
P
positive
0.12; 0.20
Figure 23 Rules for Sinus Arrhythmia
Sinus Arrhythmia
Regularity: The R–R intervals vary; the rate changes with the patient’s respirations.
Rate: The atrial and ventricular rates are equal; heart rate is usually in a normal range (60–100 bpm) but can be slower.
P Wave: There is an upright, uniform P wave in front of every QRS complex.
PRI: The PR interval measures between 0.12 and 0.20 second; the PRI measurement is constant across the strip.
QRS: The QRS complex measures less than 0.12 second.
Sinus Rhythms 75
20. Of the four sinus rhythms you have learned, the only one that does not have a
regular R–R interval is .
21. With all rhythms that originate in the sinus node, the QRS measurement should
be . If it is greater than 0.12 second, it cannot be considered , and this should be noted along with your interpretation
of the underlying pattern. For the time being, you can qualify your interpretation by
naming the rhythm and including “ .” If you continue to study
EKGs, you will learn the proper terminology for this phenomenon.
22. Now you must memorize all of the rules for each of the sinus arrhythmias. Then you
can begin gathering data from the strips shown in the Practice Strips at the end of this
chapter and compare them to the rules for each pattern. You should be able to identify
each of the strips. If you have any trouble, or are unsure about the process, you should
seek help before going on to the next section.
If you would like more practice after you finish, go back to the Practice Strips at the
end of Chapter 3. With the information you now know, you should be able to identify
each of those rhythm strips. Check your results with the answer key (on page 93). If you
missed any of these arrhythmias, spend the time now to review this section. Do not go
on until you are very comfortable with the information in this chapter.
Sinus Arrhythmia
less than 0.12 second
normal
with a wide QRS
Practice Strips
76
KEY POINTS
■ Rhythms that originate in the sinus node include:
• Normal Sinus Rhythm
• Sinus Bradycardia
• Sinus Tachycardia
• Sinus Arrhythmia
■ All rhythms that originate in the sinus node will have
upright P waves. This is because the electrical current
flows from the atria toward the ventricles, which is
toward the positive electrode in Lead II.
■ Here are the rules for NSR:
Regularity: regular
Rate: 60–100 bpm
P Wave: upright and uniform; one P wave in front of
every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
■ Here are the rules for Sinus Bradycardia:
Regularity: regular
Rate: less than 60 bpm
P Wave: upright and uniform; one P wave in front of
every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
■ Here are the rules for Sinus Tachycardia:
Regularity: regular
Rate: greater than 100 bpm (usually 100–160 bpm)
P Wave: upright and uniform; one P wave in front
of every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
■ Here are the rules for Sinus Arrhythmia:
Regularity: irregular
Rate: 60–100 bpm (usually)
P Wave: upright and uniform; one P wave in front
of every QRS complex
PRI: 0.12–0.20 second and constant
QRS: less than 0.12 second
■ When a rhythm is determined to have originated in
the sinus node but has a QRS measurement greater
than 0.12 second, this should be noted in the interpretation by calling it a Sinus Rhythm with a wide QRS
complex.
SELF-TEST
Directions: Complete this self-evaluation of the information
you have learned from this chapter. If your answers are all
correct and you feel comfortable with your understanding
of the material, proceed to the next chapter. However, if you
miss any of the questions, you should review the referenced
frames before proceeding. If you feel unsure of any of the
underlying principles, invest the time now to go back over
the entire chapter. Do not proceed with the next chapter
until you are very comfortable with the material in this
chapter.
Questions Referenced Frames Answers
1. Why do sinus rhythms have upright P waves? 3, 4, 7, 17, 18 Because an impulse that
originates in the sinus node will
travel downward through the atria
to the ventricles. In Lead II, the
positive electrode is placed below
the apex, thus the major electrical
flow is toward the positive
electrode in Lead II, creating an
upright wave form.
2. In a Normal Sinus Rhythm, what will the rate range
be?
5, 7, 9, 17 60–100 bpm
3. What is the defined PRI for an NSR? 3, 7, 9, 17, 19 0.12–0.20 second and constant
4. Is NSR defined as being regular or irregular? 6, 7, 9, 17, 20 regular
Sinus Rhythms 77
Questions Referenced Frames Answers
5. What should the QRS measurement be to be called a
Normal Sinus Rhythm?
8, 9, 17, 21 less than 0.12 second
6. What would you call a rhythm that originated in the
sinus node and fits all the rules for NSR except that
the QRS was too wide?
8, 9, 21 Sinus Rhythm with a wide QRS
7. What will the P wave be like for Sinus Bradycardia? 3, 11, 17, 18 upright and uniform; one P wave
in front of every QRS complex
8. In Sinus Bradycardia, what is the rate range? 11, 12 less than 60 bpm
9. Is Sinus Bradycardia regular or irregular? 11, 12, 20 regular
10. What will the PRI measurement be in Sinus
Bradycardia?
11, 12, 19 0.12–0.20 second and constant
11. What is the normal QRS measurement in Sinus
Bradycardia?
11, 12, 21 less than 0.12 second
12. How does Sinus Bradycardia differ from Normal
Sinus Rhythm?
11, 12 The rate in Sinus Bradycardia is
slower than NSR.
13. Is Sinus Tachycardia regular or irregular? 13, 14, 20 regular
14. What is the rate range for Sinus Tachycardia? 13, 14 greater than 100 bpm (usually
does not exceed 160 bpm)
15. What is the PRI for Sinus Tachycardia? 13, 14, 19 0.12–0.20 second and constant
16. What is the normal QRS measurement for Sinus
Tachycardia?
13, 14, 21 less than 0.12 second
17. What do the P waves look like in Sinus Tachycardia? 13, 14, 18 upright and uniform; one P wave
in front of every QRS complex
18. How does Sinus Tachycardia differ from NSR? 13, 14 The rate in Sinus Tachycardia is
faster than NSR.
19. Describe the rhythm (regularity) of Sinus Arrhythmia. 15, 16, 20 It is irregular. The rate increases
with each respiratory inspiration
and decreases with each
expiration.
20. What is the rate range for Sinus Arrhythmia? 15, 16 usually 60–100 bpm
21. What is the PRI measurement in Sinus Arrhythmia? 15, 16, 19 0.12–0.20 second and constant
22. What is the normal QRS measurement in Sinus
Arrhythmia?
15, 16, 21 less than 0.12 second
23. How does Sinus Arrhythmia differ from NSR? 15, 16, 20 Sinus Arrhythmia is irregular,
whereas NSR is regular.
78 Chapter 4
PRACTICE STRIPS (answers can be found in the Answer Key on page 553)
4.1
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.2
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 79
4.3
4.4
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
80 Chapter 4
4.5
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.6
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 81
4.7
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.8
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
82 Chapter 4
4.9
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.10
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 83
4.11
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.12
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
84 Chapter 4
4.13
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.14
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 85
4.15
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.16
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
86 Chapter 4
4.17
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.18
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 87
4.19
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.20
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
88 Chapter 4
4.21
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.22
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 89
4.23
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.24
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
90 Chapter 4
4.25
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.26
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 91
4.27
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.28
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
92 Chapter 4
4.29
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
4.30
Regularity: ______________________________________ PRI: ____________________________________________
Rate: ___________________________________________ QRS: ___________________________________________
P Waves: _______________________________________ Interp: _______________________________________
Sinus Rhythms 93
Interpretation of Chapter 3 Rhythm Strips
3.1 Normal Sinus Rhythm
3.2 Normal Sinus Rhythm (only very slightly irregular)
3.3 Normal Sinus Rhythm
3.4 Sinus Tachycardia
3.5 Normal Sinus Rhythm
3.6 Sinus Tachycardia
3.7 Normal Sinus Rhythm
3.8 Normal Sinus Rhythm
3.9 Normal Sinus Rhythm
3.10 Sinus Arrhythmia
3.11 Normal Sinus Rhythm
3.12 Sinus Bradycardia
3.13 Normal Sinus Rhythm
3.14 Sinus Arrhythmia
3.15 Normal Sinus Rhythm
94
Overview
IN THIS CHAPTER, you will learn the characteristics of an atrial pacemaker, and features that
are shared by all rhythms originating in the atria. You will then learn the names and features of
five different arrhythmias that originate within the atria. For each of these arrhythmias, you will
learn about the etiology, conduction, and resulting EKG features (regularity, rate, P waves, PR
intervals, and QRS complexes).
Atrial Rhythms
1. In Chapter 4 you learned that NSR, Sinus Bradycardia, Sinus Tachycardia, and Sinus
Arrhythmia all originate in the node. These are all rhythms that
originate in the normal pacemaker of the heart. Sometimes, for one reason or another,
the node loses its pacemaking role, and this function is taken
over by another site along the conduction system. The site with the fastest inherent
rate usually controls the function. Since the atria have the next
highest inherent rate after the SA node, it is common for the atria to take over from the
SA node. Rhythms that originate in the atria are called atrial arrhythmias.
sinus
sinus
pacemaking
Atrial Rhythms
5
Atrial Rhythms 95
2. Atrial are caused when the atrial rate becomes faster than the
sinus rate, and an impulse from somewhere along the atrial pathways is able to override the SA node and initiate . This can
happen when a lower site becomes irritable and begins to fire faster than the SA node,
a mechanism called irritability. Or, if the higher site slows down or fails, the lower
site becomes the fastest site and takes over pacemaking responsibility; this is called an
escape mechanism. Regardless of the mechanism, whenever an atrial impulse is able
to take over the pacemaking function from the SA node and initiate depolarization, the
resulting pattern is termed an arrhythmia.
3. As with a sinus rhythm, an impulse that originates in the atria will travel through
the atria to the AV junction and then through the conduction
pathways to the Purkinje fibers. The only difference is in the atria, where the conduction will be a little slower and rougher than it is with sinus rhythms. Since atrial
depolarization is seen on the EKG as a P wave, you would expect the unusual atrial
depolarization seen with arrhythmias to show up in unusual
or atypical waves.
4. The normal sinus P wave is described as having a nice, rounded, uniform wave
shape that precedes the . An atrial P wave will have a different morphology than the P wave. It can be flattened, notched,
peaked, sawtoothed, or even diphasic (meaning that it goes first above the isoelectric
line and then dips below it). A P wave that is uniformly rounded would most likely be
coming from the node, but a P wave that is notched, flattened,
or diphasic would be called an P wave.
5. Atrial arrhythmias have several features in common. They originate above the ventricles and would therefore have a QRS complex. The impulse
has a little trouble getting through the atria, since it originated outside the SA node,
and would thus produce an atrial P wave rather than a typical
P wave. We will be discussing five atrial arrhythmias, each of which will have a
QRS complex and a wave that has a
different shape than the P wave.
Wandering Pacemaker
6. The first atrial arrhythmia we’ll learn is called Wandering Pacemaker (Figure 24).
Wandering Pacemaker is caused when the pacemaker role switches from beat to beat
arrhythmias
conduction
depolarization
atrial
ventricular
atrial
P
QRS complex
sinus
sinus
atrial
normal (narrow)
sinus
normal (narrow); P
sinus
Figure 24 Mechanism of Wandering Pacemaker
Pacemaker: wanders
between SA node, atria,
and AV junction Conduction: normal:
each impulse is conducted
through to the ventricles
SA Node
AV Node
Rate: usually 60–100 bpm
Regularity: slightly
irregular
The pacemaker site wanders between the sinus node, the atria, and the AV junction. Although each
impulse can originate from a different focus, the rate usually remains within a normal range, but it
can be slower or faster. Conduction through to the ventricles is normal.
96 Chapter 5
between the SA node and the atria. The result is a rhythm made up of interspersed sinus
and atrial beats. The sinus beats are preceded by nice, rounded P waves, but the P wave
changes as the pacemaker drops to the atria. The P waves of the atrial beats are not
consistent and can be any variety of atrial configuration (e.g., flattened, notched, diphasic). Sometimes the pacemaker site will drop even lower, into the AV junction, resulting in inverted or even absent P waves. This concept is dealt with in greater detail in
Chapter 6. Wandering Pacemaker is categorized as an atrial arrhythmia characterized
by in the waves from one beat to
the next.
7. Because the pacemaker site is changing between beats, each of the impulses will
vary in the time it takes to reach the ventricles. Therefore, the PRI may be slightly different from one beat to the next. This can also cause a slightly irregular R–R interval.
In Wandering Pacemaker, the rhythm is usually slightly , and
the can vary somewhat from one complex to the next, but
it will be less than 0.20 second. Both the R–R interval and the PR interval are usually
slightly .
8. The rules for Wandering Pacemaker (Figure 25) are:
Regularity: slightly irregular
Rate: usually normal, 60–100 bpm
P Wave: morphology changes from one complex to the next
PRI: less than 0.20 second; may vary
QRS: less than 0.12 second
changes; P
irregular
PRI
irregular
Figure 25 Rules for Wandering Pacemaker
Wandering Pacemaker
Regularity: The R–R intervals vary slightly as the pacemaker site changes; the rhythm can be slightly irregular.
Rate: The atrial and ventricular rates are equal; heart rate is usually within a normal range (60–100 bpm) but can
be slower.
P Wave: The morphology of the P wave changes as the pacemaker site changes. There is one P wave in front of
every QRS complex, although some may be difficult to see, depending on the pacemaker site.
PRI: The PRI measurement will vary slightly as the pacemaker site changes. All PRI measurements should be
less than 0.20 second; some may be less than 0.12 second.
QRS: The QRS complex measures less than 0.12 second.
Atrial Rhythms 97
Ectopics
9. Sometimes pacemaker impulses can arise somewhere along the conduction system,
but is outside of the SA node. This creates a beat that is called ectopic, because it didn’t
come from the normal pacemaker. An beat is a single beat that
arises from a focus outside of the .
10. When an ectopic beat originates in the atria, it is called an atrial ectopic. An ectopic
beat arises when a site somewhere along the system becomes
irritable and overrides the SA node for a single beat. By definition, an ectopic can also be
caused when an ectopic focus initiates an impulse as an escape mechanism, but the most
common use of the term suggests that the site became and
overrode the node.
11. When you see a single ectopic beat interrupting a rhythm, you can easily tell
whether it is caused by irritability or escape. An irritable beat will come earlier than expected, while an escape beat will be delayed because it fires only after
the expected beat is skipped. An early, or premature, beat would be an indication
of , while an beat would be preceded
by a prolonged R–R cycle.
Premature Atrial Complex
12. The next atrial arrhythmia is not really a rhythm at all, but is actually a single
ectopic beat. An atrial ectopic that is caused by irritability is called a Premature Atrial
Complex (PAC) (Figure 26). A PAC is an ectopic beat that comes in
the cardiac cycle and originates in the .
13. When you look for a PAC on an EKG tracing, keep in mind that it is a single beat,
