topics

10/20/25

measurable

upright and uniform

above

Practice Strips

Figure 33 Rules for Atrial Fibrillation

Atrial Fibrillation

Regularity: The atrial rhythm is unmeasurable; all atrial activity is chaotic. The ventricular rhythm is grossly irregular,

having no pattern to its irregularity.

Rate: The atrial rate cannot be measured because it is so chaotic; research indicates that it exceeds 350 bpm.

The ventricular rate is significantly slower because the AV node blocks most of the impulses. If the ventricular rate is 100 bpm or less, the rhythm is said to be “controlled.” If it is over 100 bpm, it is considered to have a “rapid ventricular response” and is called “uncontrolled.”

P Wave: In this arrhythmia, the atria are not depolarizing in an effective way; instead, they are fibrillating. Thus, no

P wave is produced. All atrial activity is depicted as “fibrillatory” waves, or grossly chaotic undulations

of the baseline.

PRI: Since there are no P waves, the PRI cannot be measured.

QRS: The QRS complex measurement should be less than 0.12 second.

105

KEY POINTS

■ All supraventricular arrhythmias should have a normal

QRS measurement; if they don’t, the anomaly should be

noted by naming the rhythm but saying that it has “a

wide QRS complex.”

■ Atrial arrhythmias occur when an ectopic focus in the

atria assumes responsibility for pacing the heart, either

by irritability or escape.

■ An ectopic focus is one that originates outside of the SA

node.

■ Because an atrial focus is outside of the SA node, any

impulse coming from it would cause an unusual atrial

depolarization wave, thus causing the P wave to have

an unusual configuration; this atrial P wave can be either

flattened, notched, peaked, or diphasic.

■ In Wandering Pacemaker the pacemaker shifts between

the SA node and the atria, causing each P wave to differ

slightly from those around it.

■ Here are the rules for Wandering Pacemaker:

Rhythm: slightly irregular

Rate: usually normal, 60–100 bpm

P Wave: morphology changes from beat to beat

PRI: less than 0.20 second; may vary

QRS: less than 0.12 second

■ Premature Atrial Complexes (PACs) are single beats that

originate in the atria and come early in the cardiac cycle.

■ Ectopic beats that come early in the cardiac cycle are

caused by irritability; ectopic beats that come later

than expected in the cardiac cycle are caused by escape

mechanism.

■ When confronted with ectopics, you must identify both

the ectopic and the underlying rhythm.

■ A rhythm with ectopics in it will be irregular, even if

the underlying rhythm is characteristically regular; this

is because the ectopic(s) interrupt the regularity of the

underlying pattern.

■ Here are the rules for Premature Atrial Complexes:

Rhythm: depends on the underlying rhythm; will

usually be regular except for the PAC

Rate: usually normal; depends on underlying

rhythm

P Wave: P wave of early beat differs from sinus

P waves; can be flattened or notched; may

be lost in preceding T wave

PRI: 0.12–0.20 second; can be greater than

0.20 second

QRS: less than 0.12 second

■ Atrial Tachycardia is caused when a single focus in the

atria fires very rapidly and overrides the SA node.

■ Here are the rules for Atrial Tachycardia:

Rhythm: regular

Rate: 150–250 bpm

P Wave: atrial P wave; differs from sinus P wave; can

be lost in preceding T wave

PRI: 0.12–0.20 second

QRS: less than 0.12 second

■ In Atrial Flutter and Atrial Fibrillation the atria are beating too rapidly for the ventricles to respond, so the AV

node blocks some of the impulses.

■ Here are the rules for Atrial Flutter:

Rhythm: atrial rhythm is regular; ventricular rhythm

is usually regular but can be irregular if there

is variable block

Rate: atrial rate 250–350 bpm; ventricular rate varies

P Wave: characteristic sawtooth pattern (F waves)

PRI: unable to determine

QRS: less than 0.12 second

■ Here are the rules for Atrial Fibrillation:

Rhythm: grossly irregular

Rate: atrial rate greater than 350 bpm; ventricular

rate varies greatly; 100 bpm or less is considered “controlled,” while more than

100 bpm is called “uncontrolled”

P Wave: no discernible P waves; atrial activity is

referred to as fibrillatory waves (f waves)

PRI: unable to measure

QRS: less than 0.12 second

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

106 Chapter 5

Questions Referenced Frames Answers

1. How does an atrial P wave differ from a sinus P

wave?

3, 4, 5, 42 Sinus P waves are upright and

uniform. Atrial P waves can be

flattened, notched, irregular, or

even inverted.

2. What two basic mechanisms can cause an atrial focus

to take over pacemaking responsibilities?

1, 2, 11 irritability or escape

3. What is an ectopic focus? 9, 10 It is a site of electrical activity

other than the SA node.

4. Which atrial arrhythmia is characterized by a pacemaker that shifts between the SA node and various

foci in the atria, sometimes even dropping down to

the AV junction?

6, 7, 8 Wandering Pacemaker

5. What is a PAC (Premature Atrial Complex)? 9, 10, 11, 12, 13, 14,

20, 21, 22

It is a single beat that originates in

the atrium and comes early in the

cardiac cycle.

6. Is a PAC an ectopic? 9, 10, 11, 12, 13, 22 Yes, because it originates outside

of the SA node.

7. If an ectopic is caused by irritability, will it come

earlier than expected or later than expected?

11, 14, 18, 22 Earlier; if the ectopic comes later

than expected, it was caused by

escape mechanism.

8. Is Wandering Pacemaker a single ectopic beat? 6, 9 No, it is an entire arrhythmia.

9. What is the most characteristic feature of Wandering

Pacemaker?

6 It is the changing shapes of the

P waves as the pacemaker site

shifts locations.

10. What should the QRS measurement be for a PAC? 5, 17, 19, 21, 42 less than 0.12 second

11. What will the P wave look like on a PAC? 5, 16, 19, 20, 21, 42 It would have the characteristic

look of atrial P waves. It could be

flattened, notched, diphasic, or

peaked.

12. If the P wave of a PAC was not clearly visible, where

might you consider looking for it?

18 in the T wave of the preceding

complex

13. Is Atrial Tachycardia caused by one irritable focus or

by many?

22 Only one, which is why it is

usually so regular.

14. What is the usual rate range for Atrial Tachycardia? 24, 25, 26 150–250 bpm

15. Does Atrial Tachycardia have a P wave in front of

every QRS complex?

26 Yes, although you may have some

trouble seeing them if they are

superimposed on the T waves of

the preceding complexes.

16. What does the P wave look like in an Atrial

Tachycardia?

5, 23, 26, 43 It looks just like the P wave of a

PAC. In fact, AT looks very much

like a lot of PACs connected

together.

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.

Atrial Rhythms 107

Questions Referenced Frames Answers

17. What happens if the atria begin beating too rapidly

for the ventricles to respond to them?

28, 29, 30 The AV node may block some of

the impulses so that they aren’t

conducted to the ventricles. This

results in more P waves than QRS

complexes.

18. Which two atrial arrhythmias do you know that

involve the phenomenon described in the preceding

question?

29, 36 Atrial Flutter and Atrial Fibrillation

19. What’s the atrial rate in Atrial Flutter? 27, 29, 33, 34 250–350 bpm

20. Is the ventricular rhythm regular or irregular in Atrial

Flutter?

30, 34 This depends on how the AV

node is blocking impulses. If atrial

impulses are being conducted in

a regular pattern (e.g., 2:1 or 4:1),

the ventricular rhythm would be

regular. But if the conduction ratio

varied (e.g., 2:1, 3:1, 2:1, etc.),

the ventricular rhythm would be

irregular.

21. In Atrial Flutter, would the ventricular rate be faster

or slower than the atrial rate?

29, 30, 33, 34 The ventricular rate would always

be slower, unless the conduction

ratio was 1:1. This is because

not all of the P waves are able to

produce QRS complexes.

22. What does the atrial activity look like in an Atrial

Flutter?

29, 30, 33, 34 The Flutter waves usually take

on a characteristic sawtooth

appearance, although not always.

23. How would you describe the atrial activity in Atrial

Fibrillation?

35, 36, 41 The atria are not contracting;

instead, they are quivering

chaotically. This causes the

isoelectric line to undulate in a

very irregular fashion. There are

no visible P waves, only fibrillatory

waves (f waves).

24. What is the atrial rate in Atrial Fibrillation? 36, 41 over 350 bpm (typically not

measurable)

25. Is there a relationship between atrial activity and ventricular activity in Atrial Fibrillation?

36, 38, 41 Yes, there is. Some of the

impulses are conducted through

to the ventricles, but it is not

possible to determine a PRI

because there is no clear P wave.

26. What is the ventricular rate for Atrial Fibrillation? 36, 39, 41 That depends on how many of the

impulses are conducted through

to the ventricles. If the ventricular

rate is 100 bpm or less, the

rhythm is called Atrial Fibrillation

with “controlled ventricular

response,” or “Atrial Fibrillation,

controlled.” If the rate is over

100 bpm, it is called a “rapid

ventricular response,” or “Atrial

Fibrillation, uncontrolled.”

27. What are the two most characteristic features of Atrial

Fibrillation?

36, 37, 41 It has no discernible P waves,

and the R–R interval is grossly

irregular.

108 Chapter 5

PRACTICE STRIPS (answers can be found in the Answer Key on page 555)

5.1

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________