not an entire rhythm. So you really have two jobs: to identify the underlying rhythm

and to locate any ectopics. When interpreting an arrhythmia that has ectopics in it, you

must identify both the and the .

14. The first thing you will notice about a PAC is that it comes prematurely; that

is, it comes you would expect the next beat. This causes

a normally regular rhythm to be , since the ectopic(s)

ectopic

SA node

conduction

irritable

sinus

irritability; escape

early

atria

underlying rhythm; ectopics

before

irregular

Figure 26 Mechanism of Premature Atrial Complex

Pacemaker: an irritable

focus within the atrium

Rate: depends on

underlying rhythm

Regularity: the ectopic

interrupts the regularity

of the underlying rhythm

Conduction: normal:

each impulse is conducted

through to the ventricles

The pacemaker is an irritable focus within the atrium that fires prematurely and produces a single

ectopic beat. Conduction through to the ventricles is normal. This is a single beat, not an entire

rhythm; the underlying rhythm also must be identified.

98 Chapter 5

will interrupt the regularity of the underlying rhythm. A rhythm with PACs will

be because the ectopics come prematurely and interrupt

the rhythm.

15. However, in identifying the regularity of the rhythm, you

should determine whether or not it is regular in places where there are no ectopics

to interrupt it. It would be inaccurate to label a normally regular rhythm as irregular

simply because it is interrupted by PACs. To determine whether or not the underlying

rhythm is regular, you should measure the R–R intervals on a section of the strip where

there are no .

16. Because PACs originate in the atria, they will have a characteristic atrial P wave that

differs in morphology from the P waves. An atrial P wave will

usually be .

17. As with Wandering Pacemaker, conduction through the AV node and the ventricles is usually with a PAC; therefore, the PRI will usually

be – second, and the QRS will be less

than second. It is possible, though, for the PRI to be prolonged

if the AV node is refractory.

18. Since a PAC comes in the cardiac cycle, it will usually fall

very close to the end of the preceding QRS complex. This often means the atrial P wave

that initiated the PAC will fall very near the T wave and may be “lost” in it entirely. If

visible, the PAC will have a typical atrial P wave, but it might not be visible, since it can

be in the preceding .

19. As with all other supraventricular rhythms, a PAC should have normal

 through the AV node and ventricles and therefore have a QRS

complex of normal duration. It is possible, though, for any of these arrhythmias to have

a conduction problem, thus causing a prolonged QRS complex. For all of our purposes,

it is sufficient simply to call attention to this abnormality by calling it a PAC with a

wide QRS complex. However, for an ectopic with a wide QRS complex to fit the rule of

a PAC, it must have an atrial P wave in front of it. A PAC with a QRS complex greater

than 0.12 second in duration should be called a PAC with a .

20. When an atrial focus becomes irritable and fires a pacemaker impulse to override the sinus node, the premature ectopic beat is called a .

This beat will be characterized by P waves with a morphology that is different

from P waves. However, the PRI and QRS measurements

will be . PACs cause an rhythm

because they come earlier than expected and interrupt the regularity of the underlying

rhythm.

21. The rules for PACs (Figure 27) are:

Regularity: depends on the underlying rhythm; regularity will be interrupted by

the PAC

Rate: depends on the underlying rhythm

P Wave: P wave of early beat differs from the sinus P waves; can be flattened or

notched; may be lost in the preceding T wave

PRI: 0.12–0.20 second; can exceed 0.20 second

QRS: less than 0.12 second

irregular

underlying

underlying

ectopics (PACs)

sinus

flattened, notched, peaked, or

diphasic

normal

0.12; 0.20

0.12

early

lost; T wave

conduction

wide QRS complex

PAC

sinus

normal; irregular

Atrial Rhythms 99

Atrial Tachycardia

22. A PAC is caused when an irritable focus in the takes over

the pacemaking function for a single beat. It is also possible for a single site in the atria

to become so irritable that it begins to fire very regularly and thus overrides the SA node

for the entire rhythm. This arrhythmia is called Atrial Tachycardia (AT) (Figure 28). AT

is caused by a single site in the that fires repetitively to override the SA node and thus assumes pacemaking responsibility for the entire rhythm.

23. Atrial Tachycardia will have all of the characteristics of a PAC, except that it is an

entire instead of a single beat. All of the P waves in AT will

atria

atria

rhythm

Regularity: Since this is a single premature ectopic beat, it will interrupt the regularity of the underlying rhythm.

Rate: The overall heart rate will depend on the rate of the underlying rhythm.

P Wave: The P wave of the premature beat will have a different morphology than the P waves of the rest of the strip.

The ectopic beat will have a P wave, but it can be flattened, notched, or otherwise unusual. It may be hidden

within the T wave of the preceding complex.

PRI: The PRI should measure between 0.12 and 0.20 second but can be prolonged; the PRI of the ectopic will

probably be different from the PRI measurements of the other complexes.

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

Figure 27 Rules for Premature Atrial Complex

Premature Atrial Complex

Figure 28 Mechanism of Atrial Tachycardia

Pacemaker: a single

irritable focus within

the atrium

Rate: 150–250 bpm

Conduction: normal:

each impulse is conducted

through to the ventricles

Regularity: regular

The pacemaker is a single irritable site within the atrium that fires repetitively at a very rapid rate.

Conduction through to the ventricles is normal.

100 Chapter 5

have an atrial configuration; they will be peaked, flattened, notched, or diphasic. The PRI is

usually normal, and the QRS should be normal. As with PACs, Atrial Tachycardia will

have a normal interval and a normal

duration. The P waves will be typically in configuration and

hence different from sinus P waves.

24. Atrial tachycardia is characteristically a very regular arrhythmia. It is usually

very rapid, with a rate range between 150 and 250 bpm. At this rate it is very common for the P waves to be hidden on the preceding T waves. The usual rate for AT

is bpm, and the rhythm is characteristically very

 .

25. When you see a very regular supraventricular rhythm that has atrial P waves and

a rate between 150 and 250 bpm, you should suspect that it is .

26. The rules for Atrial Tachycardia (Figure 29) are:

Regularity: regular

Rate: 150–250 bpm

P Wave: atrial P wave; differs from sinus P wave; can be lost in T wave

PRI: 0.12–0.20 second

QRS: less than 0.12 second

Atrial Flutter

27. When the atria become so irritable that they fire faster than 250 bpm, they are said

to be fluttering. It is theorized that an area in the atrium initiates an impulse that is

PR; QRS

atrial

150–250

regular

Atrial Tachycardia

Figure 29 Rules for Atrial Tachycardia

Atrial Tachycardia

Regularity: The R–R intervals are constant; the rhythm is regular.

Rate: The atrial and ventricular rates are equal; the heart rate is usually 150–250 bpm.

P Wave: There is one P wave in front of every QRS complex. The configuration of the P waves will be different from

that of sinus P waves; they may be flattened or notched. Because of the rapid rate, the P waves can be

hidden in the T waves of the preceding beats.

PRI: The PRI is between 0.12 and 0.20 second and constant across the strip. The PRI may be difficult to measure

if the P wave is obscured by the T wave.

QRS: The QRS complex measures less than 0.12 second.

Atrial Rhythms 101

conducted in a repetitive, cyclic pattern, creating a series of atrial waves with a sawtooth

appearance (called Flutter or F waves). This rhythm is called Atrial Flutter (Figure 30).

Atrial Flutter is an atrial arrhythmia that occurs when ectopic foci in the atria exceed a rate

of bpm; the atrial rate is usually in the range of 250–350 bpm.

28. In Atrial Flutter, the atrial rate is between 250 and 350 bpm. The problem with a

heart rate this rapid is that the ventricles don’t have enough time to fill with blood

between each beat. The result is that the ventricles will continue to pump but they won’t

be ejecting adequate volume to meet body needs. The heart

has a built-in protective mechanism to prevent this from happening: the AV node. The

AV is responsible for preventing excess impulses from reaching the ventricles. So when the heart beats too fast, the will

prevent some of the impulses from reaching the . This blocking

action allows the ventricles time to fill with blood before they have to contract.

29. On the EKG, the blocking of impulses will be seen as a very rapid series of P waves

(called Flutter, or F, waves) with an atrial rate of 250–350, but not every one is followed

by a QRS complex. The ventricular rate will thus be quite a bit slower than the atrial

rate. In Atrial Flutter the atrial rate range will be bpm, but the

ventricular rate will be much .

30. The AV node usually allows only every second, third, or fourth impulse to be conducted through to the ventricles. On the EKG this will look like two, three, or four

sawtooth F waves between each QRS complex. If the node is consistent in how it lets

the impulses through, the ventricular rhythm will be regular. However, the node can

be erratic about conducting impulses. When this happens, the ratio between F waves

and QRS complexes can vary between 2:1, 3:1, and 4:1, thus creating an irregular

R–R interval. This is called variable block, and it causes the R–R interval in Atrial Flutter

to be .

31. When the atria are fluttering, it is virtually impossible to determine the PRI accurately. So when you gather data from the strip, the PRI is not measured. In an Atrial

Flutter, the is not measured.

32. The QRS complex is normal in Atrial Flutter. As with other supraventricular

arrhythmias, if the rhythm is normal, the QRS complex will be less than 0.12 second.

If the QRS is greater than 0.12 second, the arrhythmia should be considered abnormal

and should be labeled Atrial Flutter with a .

250

blood

node

AV node

ventricles

250; 350

slower

irregular

PRI

wide QRS complex

Figure 30 Mechanism of Atrial Flutter

Intermittent

Block

Pacemaker: a single

irritable focus within

the atrium

Rate: atrial rate 250–350

bpm; ventricular rate varies

depending on conduction

ratio, will be less than atrial

rate

Conduction: AV node

blocks some impulses

but allows others through

to the ventricles; those that

do get through are

conducted normally.

Regularity: atria are

beating regularly; ventricles

can be regular or irregular,

depending on conduction

ratio

A single irritable focus within the atria initiates impulse in a rapid, repetitive fashion. To protect the

ventricles from receiving too many impulses, the AV node blocks some of the impulses from being

conducted through to the ventricles. Those that do get through are conducted normally.

102 Chapter 5

33. When you see an EKG tracing that has more than one P wave for every QRS complex, with an atrial rate of 250–350 bpm, particularly if the P waves have a sawtooth

configuration, you would know that there is a lot of irritability in the atria and that they

are fluttering. This rhythm is called .

34. The rules for Atrial Flutter (Figure 31) are:

Regularity: 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

PRI: unable to determine

QRS: less than 0.12 second

Atrial Fibrillation

35. The last atrial arrhythmia you will learn about is called Atrial Fibrillation

(Figure 32). This rhythm results when the atria become so irritable that they are no longer beating, but instead are merely quivering ineffectively. This ineffective quivering

is called fibrillation. On the EKG tracing it is seen as a series of indiscernible waves

along the isoelectric line. In most arrhythmias the P wave is reliably present, and nearly

always regular, thus providing a helpful clue for interpreting the rhythm. But in Atrial

Fibrillation, there are no discernible P waves, and when you do see one or two here or

Atrial Flutter

Figure 31 Rules for Atrial Flutter

Atrial Flutter

Regularity: The atrial rhythm is regular. The ventricular rhythm will be regular if the AV node conducts impulses

through in a consistent pattern. If the pattern varies, the ventricular rate will be irregular.

Rate: Atrial rate is between 250 and 350 bpm. Ventricular rate will depend on the ratio of impulses conducted

through to the ventricles.

P Wave: When the atria flutter, they produce a series of well-defined P waves, known as Flutter, or F, waves. When

seen together, Flutter waves have a sawtooth appearance.

PRI: Because of the unusual configuration of the Flutter waves, and their proximity to the QRS complexes, it is

often impossible to determine a PRI in this arrhythmia. Therefore, the PRI is not measured in Atrial Flutter.

QRS: The QRS complex measures less than 0.12 second; measurement can be difficult if one or more Flutter

wave is concealed within the QRS complex.

Atrial Rhythms 103

there, they cannot be mapped out across the strip. Atrial Fibrillation characteristically

has no discernible waves. The fibrillatory waves characteristic

of Atrial Fibrillation are called f waves.

36. In Atrial Fibrillation, the atria are quivering at a rate in excess of 350 times

per minute. But this is an academic point, since there are no waves

with which we can measure the atrial rate. We do know, though, that the atria are

fibrillating so rapidly that the AV must block some of the

impulses in order to keep the ventricular rate reasonable. Unlike Atrial Flutter, where

the sawtooth P waves are conducted through in a semiregular fashion, the fibrillatory

waves of Atrial Fibrillation are conducted in an extremely chaotic pattern, producing a

grossly irregular interval. The rhythm of Atrial Fibrillation is

grossly because the fibrillatory waves are conducted in a very

chaotic way.

37. The two most characteristic features of Atrial Fibrillation, and the reasons why this

arrhythmia is so easily recognized, are that there are no discernible P waves and the

rhythm is grossly irregular. As the ventricular rate becomes faster, the R waves get closer

together on the EKG paper, which makes the rhythm appear more regular. But even

with rapid rates, Atrial Fibrillation is grossly and has no discernible waves. Whenever you encounter an irregular rhythm

with no obvious P waves, you should consider the possibility of Atrial Fibrillation.

38. Because Atrial Fibrillation originates above the ventricles, conduction through to

the ventricles will proceed within normal time frames (for those impulses that are conducted), thus resulting in a QRS measurement. The QRS measurement in Atrial Fibrillation will normally be less than 0.12 second.

39. One other thing is important to note about Atrial Fibrillation. There is a big difference between an Atrial Fibrillation where the ventricles are responding at normal rate

(100 bpm or less), and an Atrial Fibrillation with an excessively rapid ventricular

response. This is because the rapid rate will create symptoms in the patient, whereas

the slower rate is less likely to cause problems. A controlled ventricular response

indicates that the ventricular rate is 100 bpm , while a

rapid ventricular response (uncontrolled) means that the ventricles are beating

at than 100 bpm.

P

P

node

R–R

irregular

irregular

P

normal (narrow)

or less

faster

Figure 32 Mechanism of Atrial Fibrillation

Intermittent

Block

Conduction: AV node

blocks some impulses

but allows others to

proceed normally

through to the

ventricles

Pacemaker: multiple

irritable foci within the

atria

Rate: atrial rate >350

bpm; ventricular rate

slower, can be in

normal range

Regularity: grossly

irregular

The atria are so irritable that a multitude of foci initiate impulses, causing the atria to depolarize

repeatedly in a fibrillatory manner. The AV node blocks most of the impulses, allowing only a limited

number through to the ventricles.

104 Chapter 5

40. Since you can’t identify legitimate P waves in an Atrial Fibrillation, it is impossible

to determine a interval. You would note this on your data

sheet as “not able to measure,” or “unable,” or “none.” In an Atrial Fibrillation, the PRI

is not .

41. The rules for Atrial Fibrillation (Figure 33) are:

Regularity: grossly irregular

Rate: atrial rate greater than 350 bpm; ventricular rate varies greatly

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

42. You now know five atrial arrhythmias and four sinus rhythms. You know that

rhythms originating in the sinus node have a characteristic,

P wave. The P wave associated with atrial arrhythmias can be flattened, peaked,

notched, diphasic, or even inverted. But all of these patterns should have a normal

QRS measurement since they originate the ventricles.

43. As with the sinus rhythms, you must now memorize all of the rules for each of the

atrial 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 with relative ease. If you have any trouble,

or are unsure about the process, you must seek help before going on to the next chapter.