ventricular`

supraventricular

0.12

conduction

less

conduction

wide

wide QRS complex

Practice Strips (Part II)

57

KEY POINTS

■ The beating heart produces a series of cardiac cycles,

which together become an EKG rhythm strip.

■ Arrhythmias are categorized according to which pacemaker site initiates the rhythm.

■ The normal heart rhythm originates in the sinus node

and thus is called Normal Sinus Rhythm.

■ It is necessary to memorize the rules for each arrhythmia

in order to it.

■ EKG interpretation is based on how closely the clues

gathered from the rhythm strip comply with the rules

for a given arrhythmia.

■ Because EKG interpretation can be so complex, it is

essential to develop a routine format for analyzing

rhythm strips and then use it consistently when identifying arrhythmias. An example of such a format is as

follows:

• Rhythm (also called regularity)

• Rate

• P Wave

• PR Interval (PRI)

• QRS Complex (QRS)

■ Rhythm, or regularity, is determined by measuring the

R–R intervals, or possibly the P–P intervals, across the

entire strip. If the pattern is not regular, note whether it is

regularly irregular, basically regular, or totally irregular.

Look for patterns to the irregularity that could indicate

ectopics or grouped beating.

■ Rate can refer to either the ventricular rate (most common) or the atrial rate, if they differ. Rate can be calculated in one of three ways:

1. Count the number of small squares between two

R waves and divide the total into 1,500.

2. Count the number of large squares between two

R waves and divide the total into 300. A table based

on this formula can be memorized for quick reference.

3. Count the number of R waves in a 6-second strip and

multiply by 10. This last method should only be used

when other methods aren’t possible, since it is the

least accurate.

■ The P wave should be found preceding the QRS complex.

It should be upright and uniform. The P waves should

be regular across the entire strip, and there should be

only one P wave for each QRS complex. It is possible for

the P wave to be hidden in the T wave of the preceding

complex.

■ The PR interval is an indication of the electrical activity

taking place within the atria and the AV node. It encompasses all electrical activity above the ventricles. The PRI

consists of the P wave and the PR segment. The PR segment is caused by the delay of the impulse at the AV

node. The PRI should be constant across the strip and

should measure between 0.12 and 0.20 second.

■ The QRS complex can help you determine whether the

rhythm originated from a supraventricular focus or from

the ventricles. A supraventricular focus normally produces a QRS complex measuring less than 0.12 second.

However, it is possible for a supraventricular rhythm to

have a wider QRS complex if there was a conduction disturbance within the ventricles. If the rhythm originated

in the ventricles, the QRS complex will be 0.12 second

or greater. A narrow QRS complex indicates that the

impulse is supraventricular, while a wide QRS complex

can be either supraventricular with a conduction disturbance, or it can be ventricular.

SELF-TEST

Directions: Complete this self-evaluation of the information

you have learned in 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.

58 Chapter 3

Questions Referenced Frames Answers

1. What is a cardiac cycle on the EKG? 1 the electrical impulses associated

with a single heart beat: the P, Q,

R, S, and T waves

2. What is the name of the normal cardiac rhythm associated with a healthy heart?

4 Normal Sinus Rhythm

3. Why is it necessary to have an organized format for

approaching arrhythmia interpretation?

2, 5, 9 There are so many possible

configurations of EKGs that you

would never be able to memorize

all of them. You must be able to

systematically gather all of the

available information and then

compare it to the rules for the

rhythms. Without a routine format,

you could overlook important

clues.

4. Why do you have to memorize the rules for each of

the arrhythmias?

2, 6, 7, 8, 9 so you can compare them to the

findings on an EKG strip and thus

identify the arrhythmia

5. What are the five parts of the analysis format that you

learned in this chapter?

9 Regularity (rhythm), Rate, P

Waves, PR Intervals, QRS

complexes

6. How can you tell whether or not an arrhythmia is

regular?

10, 11, 12, 14 Measure R–R intervals or P–P

intervals across the entire strip.

7. What does the phrase “regularly irregular” mean? 13, 15 There is a pattern to the

irregularity.

8. What does the phrase “basically regular” mean? 13, 15 The underlying rhythm is regular,

but it is interrupted by ectopics.

9. What does it mean when you call an arrhythmia

“totally irregular”?

13, 15 There is no pattern to the

irregularity.

10. If you wanted to calculate accurately the rate of a

regular rhythm, you could count the number of small

squares between two R waves and divide it into what

number?

16, 17, 18, 20 1,500

11. If you counted the number of large squares between

two R waves, what number would you divide that

total into to determine the heart rate?

16, 17, 18, 20 300

12. When an arrhythmia is irregular, you should determine the heart rate by counting the number of R

waves in 6 seconds and multiplying that total by what

number?

19, 20 10

13. What is the first wave you should try to locate and

map out when analyzing a rhythm strip?

22, 23 the P wave

14. What does a normal sinus P wave look like? 23, 24, 25 It has a smooth, rounded shape; it

is upright and uniform.

15. Where can you normally find the P wave? 26 It is usually located immediately in

front of the QRS complex.

16. Are P–P intervals usually regular or irregular? 23, 28 They are usually very regular.

Analyzing EKG Rhythm Strips 59

Questions Referenced Frames Answers

17. What is meant when a P wave is said to be “lost” in

the T wave?

29 It means that the P wave occurred

on or near the T wave and is

thus obscured beyond clear

identification.

18. In your analysis of a rhythm strip, what waves should

you look for after you have located the P waves?

30, 31 the QRS and the T waves

19. Why is it important for you to know all these waves

and measurements?

32, 33 because they reflect cardiac

activity, and can help you identify

the arrhythmia

20. What is a “supraventricular” arrhythmia? 33, 34, 35, 36, 37, 38,

39, 40

an arrhythmia that originates

above the ventricles

21. If a QRS complex measures less than 0.12 second,

where can you assume that it originated?

38, 39, 40 from a supraventricular focus

22. Rhythms that originate in the ventricles produce QRS

complexes measuring 0.12 second or greater. What

else might explain a wide QRS complex?

38, 39, 40 it might have originated in the

ventricles; a rhythm that originates

in the ventricles will have a QRS

measurement of 0.12 second or

more.

It might be a supraventricular

rhythm that encountered a

conduction disturbance within the

ventricles.

60 Chapter 3

PRACTICE STRIPS (answers can be found in the Answer Key on page 553)

PART I: ANALYZING EKG STRIPS

3.1

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.2

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Analyzing EKG Rhythm Strips 61

3.3

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.4

62 Chapter 3

3.5

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.6

Analyzing EKG Rhythm Strips 63

3.7

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

64 Chapter 3

PART II: GATHERING INFORMATION FROM STRIPS

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.8

3.9

Analyzing EKG Rhythm Strips 65

3.10

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.11

66 Chapter 3

3.12

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.13

Analyzing EKG Rhythm Strips 67

3.14

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

Regularity: ______________________________________ PRI: ____________________________________________

Rate: ___________________________________________ QRS: ___________________________________________

P Waves: _______________________________________

3.15

68

Overview

IN THIS CHAPTER, you will learn the characteristics of rhythms produced by a sinus pacemaker,

and features that are shared by all rhythms originating in the sinus node. You will then learn the

names and features of four different arrhythmias that originate in the sinus node. 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).

Introduction

1. The first category of arrhythmias you will learn is the category of rhythms that originate in the sinus node. This group includes:

• Normal Sinus Rhythm (NSR)

• Sinus Bradycardia

• Sinus Tachycardia

• Sinus Arrhythmia

Sinus Rhythms

4

Sinus Rhythms 69

Each of these arrhythmias will be discussed individually. You will need to memorize the information provided because it will give the rules necessary for you to

be able to identify that arrhythmia again. You will eventually need to memorize

the for all of the arrhythmias, but we will begin just with those

originating in the node.

Normal Sinus Rhythm

2. First, we will discuss Normal Sinus Rhythm (Figure 16). We will look at what a

normal rhythm is and what defines it as normal, and then we will begin looking at

arrhythmias and how they differ from . Technically speaking, NSR is not an arrhythmia because it is a normal, rhythmic pattern. However, you

will often hear phrases like arrhythmia, dysrhythmia, and rhythm being used loosely

to describe both normal and abnormal EKG patterns. Although NSR is not actually

an because it has a normal, rhythmic pattern, we will include

it in general discussions of all arrhythmias.

3. In Normal Sinus Rhythm, the pacemaker impulse originates in the sinus node

and travels through the normal conduction pathways within normal time frames.

Because the pacemaker originates in the node, the P waves

will be uniform, and since conduction is normal, one P wave will be in front of every

QRS complex. In NSR, there will be P waves, one in front of

every complex.

4. In NSR, the atria are stimulated by the sinus impulse, and depolarize before the

ventricles do. Because the major thrust of the electrical current is traveling toward the

positive electrode in Lead II, there will be an upright wave.

5. Since the SA node inherently fires at a rate of 60–100 times per minute,

a Normal Sinus Rhythm must, by definition, fall within this rate range. If an EKG

rhythm is slower than beats per minute (bpm) or faster

than bpm, it is not .

6. NSR is defined as being a regular rhythm. That is, the

interval must be regular across the entire strip. Even if a normal sinus rhythm is interrupted by an ectopic beat, the underlying pattern must have a regular R–R measurement to be called .

rules

sinus

normal

arrhythmia

sinus

uniform

QRS

P

60

100; Normal Sinus Rhythm

R–R

Normal Sinus Rhythm

Figure 16 Mechanism of Normal Sinus Rhythm

Conduction: normal;

each impulse is conducted

through to the ventricles

Pacemaker: Sinus Node

Rate: 60–100 bpm

Regularity: regular

The sinus node is the pacemaker, firing regularly at a rate of 60–100 times per minute. Each impulse

is conducted normally through to the ventricles.

70 Chapter 4

7. You now know that a Normal Sinus Rhythm must be a regular pattern, at a rate

between and , with an upright

P wave in front of every QRS complex. When you measure the PR interval, it must

fall between 0.12 and 0.20 second, and it must be of the same duration across the

entire strip. That is, if it is less than second or greater than

 second, it is outside the normal range and not defined as

. Further, if the PRI is, for instance, 0.16 second, then each PRI

on the strip must be 0.16 second. If the PRI changes from one complex to the next,

even if it stays within the normal range, it would not be considered a Normal

Sinus Rhythm. In NSR, the PRI must be between

and second and must be constant across the

 strip.

8. Finally, the QRS measurement for a true NSR must be within the normal range;

that is, than 0.12 second. This can be a little tricky, because

a sinus rhythm might fit all the other rules but still have a wide QRS complex. When

this happens, the rhythm must be qualified by calling it a “Sinus Rhythm with a

wide .” Notice that the pattern is no longer called “Normal”

Sinus Rhythm, but simply “Sinus Rhythm.” If you go on to study EKGs to greater

depth, you will learn the reasons behind this phenomenon of the wide QRS complex

and will learn the proper terminology for identifying it, but for now, just remember

that unless the QRS is less than second, the rhythm is not

a Sinus Rhythm.

9. To summarize the rules for the EKG findings in NSR (Figure 17):

Regularity: regular

Rate: 60–100 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

60; 100

0.12

0.20

NSR

0.12

0.20

entire

less

QRS complex

0.12