KEY POINTS

■ Electrodes are devices that are applied to the skin to

detect electrical activity and convey it to a machine for

display.

■ Electrode contact can be improved by:

• Abrading the skin

• Cleaning or drying the skin

• Using a contact medium

■ If electricity flows toward the positive electrode, the patterns produced on the graph paper will be upright; if

the electrical flow is toward the negative electrode, the

patterns will be inverted.

■ Electrode placement is standardized to avoid confusion

in EKG interpretation (Figure 5).

■ A lead is a single view of the heart, often produced by a

combination of information from several electrodes.

■ A monitoring lead is one that clearly shows individual

waves and their relationship to other waves. All the

examples in this book are Lead II (although this is only

one of many monitoring leads).

■ Graph paper is standardized to allow comparative analysis of EKG wave patterns.

■ The isoelectric line is the straight line made on the EKG

when no electrical current is flowing.

■ Vertical lines on the graph paper measure time; horizontal lines measure voltage (Figure 7).

■ A small square on the graph paper (the distance between

two light vertical lines) is 0.04 second.

■ A large square on the graph paper (the distance between

two heavy vertical lines) is 0.20 second.

■ The atria normally contract before the ventricles do.

■ A single cardiac cycle on the EKG includes everything

from depolarization of the atria up to and including

repolarization of the ventricles.

■ A single cardiac cycle is expected to produce a single

heart beat (a pulse).

■ The P wave represents atrial depolarization.

■ The PR segment represents delay in the AV node.

■ The PR interval includes the P wave and the PR segment

and represents both atrial depolarization and delay in

the AV node.

■ The PRI is measured from the beginning of the P wave

to the beginning of the QRS complex.

■ The PRI is normally between 0.12 and 0.20 second.

■ The QRS complex represents ventricular depolarization.

■ The QRS interval is measured from the beginning of the

Q wave to the end of the S wave.

■ The Q wave is the first negative deflection following the

P wave but before the R wave.

■ The R wave is the first positive wave following the P

wave, or the first positive wave of the QRS complex.

■ The S wave is the second negative deflection following

the P wave, or the first negative deflection following the

R wave.

■ The QRS interval is normally less than 0.12 second.

■ External factors capable of producing artifact on the EKG

tracing include muscle tremors, shivering, patient movement, loose electrodes, and 60-cycle electrical current.

■ A cell is electrically refractory when it has not yet repolarized and thus cannot accept and respond to another

stimulus.

■ The absolute refractory period occurs when the cells cannot respond to any stimulus at all.

■ The relative refractory period occurs when some of the

cells are capable of responding if the stimulus is strong

enough.

■ If an impulse falls during the relative refractory period,

the heart might be depolarized, but in an abnormal way.

■ The absolute refractory period encompasses the QRS and

the first part of the T wave.

■ The relative refractory period is the downslope of the T

wave.

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 missed 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.

Waves and Measurements 29

Questions Referenced Frames Answers

1. What is an electrode used for? 1, 2, 4 to pick up electrical activity from

the skin surface

2. List three ways to improve contact between the electrode and the skin.

2, 3, 4, 5 abrade skin; clean skin; use

contact medium

3. If the electrical current flows toward the positive

electrode, will the deflection on the graph paper be

upright or downward?

6, 7, 8, 9, 10, 17 upright

4. Why is it important to standardize electrode

placement?

11, 12 to avoid confusion when interpreting EKG patterns

5. What is a lead, and how does it differ from an

electrode?

12, 13 A lead is a single view of the

heart, often produced by a combination of information from several

electrodes.

6. How many leads do you need to know to interpret

arrhythmias?

12, 13 one; only a monitoring lead

7. Which lead will be discussed throughout this book? 13 Lead II

8. What are the electrode positions for the lead identified in the preceding question?

14 negative electrode below right

clavicle; positive electrode at the

apex; ground electrode below the

left clavicle.

9. What features are important for a good monitoring

lead?

12, 13 clear visualization of the basic

waves

10. In Lead II, will the primary deflections be upright or

downward on the EKG?

14 Upright, because the current

is flowing toward the positive

electrode.

11. Why is it important to use standardized EKG graph

paper?

15, 16 Standardized markings enable

you to measure the EKG and

compare it to “normal.”

12. What is an isoelectric line? 17 It is the straight line on the EKG

made when no electrical current

is flowing.

13. What do the vertical lines on the graph paper tell

you?

16, 17, 20, 21, 22, 23 time

14. What do the horizontal lines on the graph paper tell

you?

16, 17, 18, 19, 23 voltage

15. How much time is involved between two heavy lines

on the graph paper?

16, 21, 22 0.20 second

16. How much time is involved in one small square on

the graph paper?

16, 21, 22 0.04 second

17. Which chambers contract first in a single cardiac

cycle?

24, 25, 26 the atria

18. What must occur for the heart to contract? 27 The muscle cells must receive an

electrical stimulus.

19. What cardiac activity is included in a single cardiac

cycle on the EKG?

28 everything from depolarization of

the atria up to and including repolarization of the ventricles

30 Chapter 2

Questions Referenced Frames Answers

20. How many heart beats would you expect a single

cardiac cycle to produce?

28, 29 one

21. What are the five waves found in a single cardiac

cycle on the EKG?

30, 40 P, Q, R, S, and T

22. Differentiate between waves, segments, and intervals. 30 Waves are deflections, segments are straight lines, and

intervals include both waves and

segments.

23. What does the P wave represent, and how is it found

on the EKG?

31 atrial depolarization; it is measured from the first deflection on

the cardiac cycle until the deflection returns to the isoelectric line

24. What does the PR segment represent? 33, 34 delay in the AV node

25. What is the PR interval, how is it measured, and what

is its normal duration?

35, 36, 41, 42, 43, 48 The PRI includes the P wave and

the PR segment. It is measured

from the beginning of the P wave

to the very beginning of the QRS

complex. It is normally 0.12–0.20

second.

26. What does the QRS represent, how is it measured,

and what is its normal duration?

37, 38, 44, 45, 46,

47, 48

ventricular depolarization; measure from the beginning of the Q

wave to the end of the S wave;

normally less than 0.12 second

27. What does the T wave represent? 39 ventricular repolarization

28. List four external factors capable of producing artifact

on the EKG tracing.

49, 50 muscle tremors, shivering; patient

movement; loose electrodes;

60-cycle electrical current

29. What is meant by electrical refractoriness? 51, 52, 53 The cells are not yet repolarized and thus cannot accept and

respond to another stimulus.

30. Differentiate between absolute refractory period and

relative refractory period.

54, 55, 56 Absolute refractory period means

that the heart cannot accept any

stimulus at all. Relative refractory

period means that some of the

cells are capable of responding to

a strong stimulus.

31. What is so important about the relative refractory

period?

54, 55, 56 If an impulse hits on the relative

refractory period, the heart can be

discharged in an abnormal way.

32. What part of the EKG complex signifies the relative

refractory period?

56 the downslope of the T wave

Waves and Measurements 31

PRACTICE STRIPS (answers can be found in the Answer Key on page 551)

PART I: LABELING WAVES

Directions: For each of the following rhythm strips, label the P, Q, R, S, and T waves of a single cardiac cycle. (Some

of the tracings may not have all of these waves.) As you finish each strip, check your answers. They start on page 551.

2.1 2.2

2.3 2.4

2.5 2.6

32 Chapter 2

2.7 2.8

2.9 2.10

2.11 2.12

When you have completed this exercise, check your answers. They start on page 552. Then return to Frame 41 in this chapter

(page 23).

Waves and Measurements 33

PART II: MEASURING INTERVALS

Directions: For each of the following rhythm strips, measure the PR interval and the QRS complex. As you do each strip,

check your answers. They start on page 39.

2.13

PRI: second

QRS: second

2.14

PRI: second

QRS: second

PRI: second

QRS: second

2.15

34 Chapter 2

2.16

PRI: second

QRS: second

PRI: second

QRS: second

PRI: second

QRS: second

2.17

2.18

Waves and Measurements 35

2.19

PRI: second

QRS: second

PRI: second

QRS: second

PRI: second

QRS: second

2.20

2.21

36 Chapter 2

2.22

PRI: second

QRS: second

PRI: second

QRS: second

PRI: second

QRS: second

2.23

2.24

Waves and Measurements 37

2.25

PRI: second

QRS: second

PRI: second

QRS: second

PRI: second

QRS: second

2.26

2.27

38 Chapter 2

2.28

PRI: second

QRS: second

PRI: second

QRS: second

PRI: second

QRS: second

2.29

2.30

When you complete this exercise, return to Frame 49 in this chapter (page 25).

Waves and Measurements 39

PART II: MEASURING INTERVALS

2.13

PRI QRS

PRI: 0.20 second

QRS: 0.12 second

2.14

PRI QRS

PRI: 0.20 second

QRS: 0.10 second

40 Chapter 2

2.15

PRI QRS

PRI: 0.16 second

QRS: 0.12 second

2.16

PRI QRS

PRI: 0.12 second

QRS: 0.10 second

Waves and Measurements 41

2.17

PRI QRS

PRI: 0.14 second

QRS: 0.08 second

2.18

PRI QRS

PRI: 0.14 second

QRS: 0.10 second

42 Chapter 2

2.19

PRI QRS

PRI: 0.14 second

QRS: 0.10 second

2.20

PRI QRS

PRI: 0.16 second

QRS: 0.14 second

Waves and Measurements 43

2.21

PRI QRS

PRI: 0.20 second

QRS: 0.08 second

2.22

PRI QRS

PRI: 0.12 second

QRS: 0.10 second

44 Chapter 2

2.23

PRI QRS

PRI: 0.16 second

QRS: 0.11 second

2.24

PRI QRS

PRI: 0.16 second

QRS: 0.14 second

Waves and Measurements 45

2.25

PRI QRS

PRI: 0.10 second

QRS: 0.10 second

2.26

PRI QRS

PRI: 0.12 second

QRS: 0.08 second

46 Chapter 2

2.27

PRI QRS

PRI: 0.18 second

QRS: 0.06 second

2.28

PRI QRS

PRI: 0.16 second

QRS: 0.08 second

Waves and Measurements 47

2.29

PRI QRS

PRI: 0.12 second

QRS: 0.08 second

2.30

PRI QRS

PRI: 0.16 second

QRS: 0.12 second

48

Analyzing EKG Rhythm

Strips

3

Overview

IN THIS CHAPTER, you will learn to use an organized analysis format to gather data from a

rhythm strip. You will learn that a systematic format, consistently applied, will provide the data

you need to identify the presenting arrhythmia. You will then learn such a systematic format and

begin to use it consistently to gather data from EKG strips.

Analysis Format

1. In Chapter 2, you learned that there are five distinct wave patterns that make up a

single on the EKG. You also learned that a beating heart will

produce a series of these , which together become an EKG

rhythm strip.

2. EKGs are even more complex than fingerprints. Not only does every person on earth

have his or her own individual EKG, distinct from all others, but one person’s EKG can

look very different from one moment to the next. This is why it is inadequate simply to

cardiac cycle

cardiac cycles

Analyzing EKG Rhythm Strips 49

memorize eight or ten of the most common EKG patterns and hope you can recognize

one the next time you see it. This type of EKG analysis is called pattern recognition and is

a common but haphazard way to approach arrhythmias. A much more reliable way to

approach an EKG tracing is to take it apart, wave by wave, and interpret exactly what’s

happening within the heart to create that tracing. This method of EKG interpretation is

more sophisticated than and will be far more valuable to you

because it’s more reliable.

3. Arrhythmias can be categorized into groups according to which pacemaker site

initiates the rhythm. The most common sites, and thus the major categories of arrhythmias, are:

• Sinus

• Atrial

• Junctional

• Ventricular

Arrhythmias are categorized this way because the impulse for

that rhythm came from one of these sites.

4. The most common cardiac rhythm is sinus in origin, because the

 node is the usual pacemaker of the heart. Therefore, a normal,

healthy heart would be in Normal Sinus Rhythm (NSR) because the rhythm originated

in the node.

5. To get an idea of the variety of EKG patterns possible, look at the Practice Strips at

the end of this chapter. All of the EKG tracings shown are sinus rhythm. You can see

why it is necessary to have an organized format for approaching arrhythmia interpretation. Without a format for deciphering EKGs, you could easily be intimidated

even by a group of “normal” tracings. To develop competency and confidence in interpreting EKGs, you must have an organized for approaching

arrhythmias.

6. Each EKG tracing provides a multitude of clues as to what is happening in that heart.

These clues include wave configurations, rates, measurements, and wave relationships.

Experts have compiled this data and found that each cardiac arrhythmia has its own set

of information. That is, each specific arrhythmia will repeatedly give off the same set

of clues. By looking at the clues available from the strip, you can tell what the rhythm

is, but only if you know in advance the kinds of clues that any specific arrhythmia is

known to produce. We call these clues the “rules” for a specific arrhythmia. For example, NSR has a set of rules, including a specific relationship between P waves and QRS

complexes, and a range for both rate and wave measurements. If you memorize these

rules in advance and then come across a rhythm that meets these rules, you have reason

to believe that this rhythm is NSR. Therefore, it is necessary to memorize the rules for

each rhythm strip and then look for the available from each

strip you approach.