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10/20/25

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

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

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

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

normal; PRI

60; 100

Sinus Bradycardia

Sinus Tachycardia

Sinus Arrhythmia

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

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: ___________________________________________