7. EKG interpretation is a true “gray” area; there is no black and white to any of the

information you will learn here. When it comes right down to naming a rhythm, you’ll

find that this isn’t always possible, particularly in the more complex tracings. However,

the clues you get from the strip should collectively eliminate most of the possibilities

and point to one or two specific patterns. From there, it is a matter of which possibility has the most clues in its favor. Even though you can’t always identify the rhythm

exactly, the you get from the strip should fit the rules of one or

two arrhythmias, thus suggesting the category of arrhythmia you are trying to identify.

pattern recognition

pacemaker

sinus (SA)

SA

format

clues

clues

50 Chapter 3

8. Let’s repeat the point we just made in the preceding frame, because it will be important as we go over the analysis process. As you approach an arrhythmia, look at the

 and compare them to the rules for arrhythmias. If there are two

possibilities, or two people who disagree on the interpretation, it will be decided by

whoever has the most clues in his or her favor. Therefore, it is critical to pick up the clues

from the strip and compare them to the for each arrhythmia.

Now you can see why it will be essential to memorize the rules for each arrhythmia

and have them comfortably available for recall as you begin arrhythmia interpretation.

9. Although EKG interpretation is acknowledged to be a very negotiable field, and

everyone is entitled to a personal opinion of each arrhythmia’s true identity, we have

been able to agree on a fairly standard format for approaching arrhythmias. This format is outlined in Figure 13 and will be discussed point by point in the next several

frames. Look at Figure 13 and determine which item we will look at first when starting

to analyze an EKG.

Regularity

10. The regularity, also called , of an EKG pattern is determined

by looking at the R-to-R interval (R–R, or RRI). This interval is measured by placing one

point of the calipers on one R wave (or any other fixed, prominent point on the QRS

complex) and placing the other point on the same spot of the next QRS complex. The

R wave is indicative of ventricular and thus should correspond

to the patient’s .

clues

rules

regularity

rhythm

depolarization

pulse

Figure 13 Systematic Approach to Arrhythmia Interpretation

REGULARITY

(also called Rhythm)

• Is it regular?

• Is it irregular?

• Are there any patterns to the irregularity?

• Are there any ectopic beats? If so, are they

early or late?

RATE

• What is the exact rate?

• Is the atrial rate the same as the ventricular

rate?

P WAVES

• Are the P waves regular?

• Is there one P wave for every QRS?

• Is the P wave in front of the QRS or behind it?

• Is the P wave normal and upright in Lead II?

• Are there more P waves than QRS

complexes?

• Do all the P waves look alike?

• Are the irregular P waves associated with

ectopic beats?

PR INTERVAL

• Are all the PRIs constant?

• Is the PRI measurement within normal

range?

• If the PRI varies, is there a pattern to the

changing measurements?

QRS COMPLEX

• Are all the QRS complexes of equal duration?

• What is the measurement of the QRS

complex?

• Is the QRS measurement within normal

limits?

• Do all the QRS complexes look alike?

• Are the unusual QRS complexes associated

with ectopic beats?

Analyzing EKG Rhythm Strips 51

11. When looking to see if the rhythm is regular or irregular, measure the

 across the entire strip. If the pattern is regular, the RRI

should remain constant throughout. A constant RRI would mean that the rhythm

is .

12. A key point in determining regularity is to measure all the RRIs across the rhythm

strip. If you skip around and don’t measure the RRIs, you will

frequently miss a pattern of irregularity.

13. If the pattern is not regular, you must determine whether it is:

• Regularly irregular

(it has a pattern of irregularity)

• Basically regular

(it is a regular rhythm with a beat or two that interrupts it)

• Totally irregular

(it has no patterns at all)

If the rhythm has a pattern to the irregularity, it is said to be

irregular; if it has a beat or two that interrupts the regular pattern, it would be basically ; if it is totally irregular, it would be irregular with

 patterns to the irregularity.

14. If the rhythm is regular across the entire strip, you can consider it a

 rhythm. Sometimes a rhythm will be very nearly regular but

will be “off” by one or even two small squares. This can be especially disconcerting to

the student, who is usually still looking for everything to fit exactly. However, as you

now know, EKG interpretation isn’t always exact, and regularity determination is no

exception. It is not uncommon for a rhythm, especially a slow one, to be “off” by a small

square and still be considered regular. A general guideline is that faster rates should be

more exactly , while slower rates can sometimes have a little

more leeway. The key issue is to make sure that there are no other areas of irregularity.

If there are other areas of irregularity, or if there are patterns of irregularity, you really

can’t consider the rhythm to be .

15. If the rhythm is not regular, measure all combinations of RRIs to see if there is

a pattern to the irregularity. A beat that disrupts the underlying rhythm is called an

ectopic, because it falls in an abnormal place or position. Possible patterns of irregularity include:

• A regular rhythm with one or more ectopic beats

• A combination of normal beats and ectopic beats that produces a pattern of

“grouped” beats

If these possibilities are eliminated, you should consider the rhythm totally

irregular. An irregular EKG strip will be considered totally irregular if it has

no of irregularity.

Rate

16. The next major step in the analysis process (as shown in Figure 13) is rate. There

are several common ways to calculate heart rate, and the method you choose depends

primarily on the regularity of the rhythm. To select the method of calculating rates, you

must first determine whether or not the rhythm is .

R–R intervals

regular

all

regularly

regular

no

regular

regular

regular

patterns

regular

52 Chapter 3

17. If the rhythm is regular, the most accurate way to calculate heart rate is to count

the number of small squares between two R waves and divide the total into 1,500.

A faster way is to count the number of large squares between two R waves and

divide the total into 300. If you count small squares, you would divide the total

into , but if you count large squares, you divide the total

into , since there are five small squares in each large square.

18. There is an even simpler (but less accurate) way to calculate the rate of a regular

rhythm. There is a small rate calculator on the inside back cover of your book. It is

based on the system of dividing the number of large squares into 300, but it requires

that you memorize the simple rate scale shown in Figure 14. This rate scale is well

worth memorizing, since it will probably be the method you use most often. It is a

quick and fairly accurate way to calculate rate, but to use this method, the rhythm must

be .

19. If the rhythm is irregular, it’s very easy to estimate the rate. Look at the sample

rhythm strip in Figure 15. On each strip you will notice small vertical notches in the

upper margin of the paper. Each of these notches is 3 seconds away from the next. So

if you count the number of QRS complexes in a 6-second span, you can multiply that

by 10 to get the heart rate for 1 minute. This method of estimating rate for irregular

rhythms requires that you count the number of QRS complexes in a 6-second span and

multiply by to get the heart rate in beats per minute (bpm).

20. The method described in the preceding frame is the quickest and easiest way to

estimate rate, but it is not very accurate and shouldn’t be used unless the rhythm

is irregular and can’t be calculated any other way. For regular rhythms, you should

count the number of small squares between two R waves and divide the total

into , or count the number of large squares between two

R waves and divide the total into . Again, the most convenient

way to estimate rate for a regular rhythm is to memorize the chart shown in Figure 14.

1,500

300

regular

10

1,500

300

Figure 14 Calculating Heart Rates

METHOD DIRECTIONS FEATURES

1 Count the number of

R waves in a 6-second

strip and multiply by 10.

• Not very accurate

• Used only for very quick estimate

2 2A Count the number of

large squares between

two consecutive R waves

and divide into 300.

or

2B Memorize this scale:

1 large square = 300 bpm

2 large squares = 150 bpm

3 large squares = 100 bpm

4 large squares = 75 bpm

5 large squares = 60 bpm

6 large squares = 50 bpm

• Very quick

• Not very accurate with fast rates

• Used only with regular rhythms

3 Count the number of small

squares between two consecutive

R waves and divide into 1,500.

• Most accurate

• Used only with regular rhythms

• Time-consuming

Analyzing EKG Rhythm Strips 53

21. By now, you would have looked at the rhythm strip and decided whether or not

it was regular and then would have determined the rate. Turn to the Practice Strips at

the end of this chapter and make both of those determinations for each strip in Part I

(strips 3.1–3.6).

22. Now that you have determined regularity and rate for the strip you are analyzing,

the next step is to begin figuring out the wave patterns. This is a very basic step that

you should always follow when approaching arrhythmias. Before you can interpret the

arrhythmia, you must first locate and identify each so that you

can understand what’s happening in the heart.

P Waves

23. To begin marking waves, first identify the P wave. The QRS complex is tempting

because it is usually the largest and most conspicuous, but you will soon learn that the

P wave can be your best friend because it’s more reliable than the other waves. To begin

identifying the waves, look first for the waves.

24. The P wave has a characteristic shape that will often stick out even among a lot

of unidentifiable waves. The morphology (shape) of the P wave is usually rounded

and uniform. Sometimes P wave morphology can change if the pacemaker begins

moving out of the sinus node. But if the sinus node is the pacemaker, and it isn’t

diseased or hypertrophied (enlarged), the P wave will have a smooth, rounded,

uniform .

25. Another characteristic of the P wave is that it is upright

and uniform. If you look back at Figure 5 in Chapter 2, you will see that the electrical

flow is toward the positive electrode in Lead II, which explains why the P wave will

be upright as long as the impulse begins in the sinus node and travels toward the ventricles. As you get more sophisticated in your understanding of arrhythmias, you will

learn that a P wave can sometimes be negative. But for now, you need to remember

that a normal sinus P wave will always be upright. If the P wave originates in the

 node, it will be a smooth, rounded, wave.

Practice Strips (Part I)

wave

P

morphology (shape)

sinus (SA)

SA; upright

Figure 15 Figuring Rates Based on the Number of QRS Complexes in a 6-Second Strip

This sample strip has five R waves within the 6-second period defined by the notches in the margin. To figure the rate,

multiply the R waves by 10 for a rate of 50 cardiac cycles in 60 seconds.

54 Chapter 3

26. Now you know that P waves usually come before complexes, so look at Part 1 of the Practice Strips (strips 3.1–3.6) at the end of this chapter

and label each P wave. It might help you keep things straight if you mark the P above

the wave directly on the strip. (Note: This is a helpful way to learn arrhythmias, but be

careful not to mark up an EKG if it’s the patient’s only original.)

27. Were you able to locate each P wave all across each strip? If you ever have trouble

finding a P wave, or if you can’t decide whether or not a wave is a P wave, there are several tips to remember. First, you know that the normal PRI is

second. So set your calipers at 20 seconds and measure that distance in front of the

QRS complex. If there is a wave there, it’s likely to be a wave.

To determine whether or not a P wave precedes the QRS, look for the P wave

between and second in front of the

QRS complex, since that is the normal PRI measurement.

28. P waves are the most reliable of the waves, so map out the Ps across the strip. If

most of them are regular but a space is missing near the T wave, it is probable that a P is

hidden in another wave. Because P waves are reliably , you can

often assume that a P wave is present just by noting the patterns of the visible P waves.

29. Let’s take a minute to talk about “losing” waves. This is a phenomenon that occurs

when two electrical activities take place at the same time. For instance, if the atria depolarize at the same time the ventricles repolarize, the P wave will be in the same spot

on the EKG as the . When this happens, the largest wave will

usually obscure all or most of the smaller wave. In this situation, the P wave would be

said to be “lost” or “hidden” in the T wave. If the P wave is in

the T wave, you may be able to tell it’s there by mapping out the other P waves or by

looking for a suspicious notch on the T wave where you expect the P wave to be.

30. Once all the P waves are marked, it is usually not as difficult to identify the other

waves. Go to the Practice Strips in this chapter and mark the Q, R, S, and T waves for

the strips in Part I (strips 3.1–3.6). As you’re doing this, make a mental note of the relationships between the waves. That is, does a P wave precede every QRS complex? Is

there only one P wave for every QRS, or are there more P waves than QRS complexes?

PR Intervals and QRS Complexes

31. Now that all the waves are identified, go back through the rhythm strips Part I

(strips 3.1–3.6) and measure the PRIs and QRS complexes to determine whether or

not they are within the normal ranges. If you’ve forgotten the normal measurements,

review the Key Points for Chapter 2 (page 28).

32. You now have all the data you need from these arrhythmias in order to identify

them. The reason you can’t name them now is that you have not yet learned the necessary rules and thus do not know into which category each tracing falls. To identify an

arrhythmia, you must first collect the data from the strip and then compare that data to

the for each arrhythmia.

33. In the next chapter, you will begin learning the rules for each of the arrhythmias.

Before you go on to that, there are one or two more points that must be covered for

you to be able to interpret arrhythmias, rather than just recognize them. For example,

the measurements you have just learned are actually measurements of time. As we

go on to the next chapters, it will become increasingly important for you to think of

QRS

Practice Strips (Part I)

0.12–0.20

P

0.12; 0.20

regular

T wave

lost (hidden)

Practice Strips (Part I)

Practice Strips (Part I)

rules

Analyzing EKG Rhythm Strips 55

measurements such as PRI and QRS as actual activity within the heart and not just

normal or abnormal figures. That is, a PRI is considered abnormal if an impulse

took too long to get from the sinus node through the and

the ; similarly, a QRS is considered abnormal if the impulse

took too long to travel through the . The actual figure is

not as critical as being able to understand what occurred within the heart to produce

that figure.

34. Let’s carry this point a bit further. We know from information gathered during research that it takes 0.12–0.20 second for an impulse to get from the sinus node

through the atria and AV node of a normal heart. On the EKG, this time frame is

depicted as the interval. If this time is extended and the PRI

is elongated, we can deduce that there was some delay somewhere in the atria or

the node.

35. The includes the P wave and the PR segment. The

P wave itself indicates the amount of time it took the impulse to travel through

the and depolarize them. The isoelectric component of

the PRI, or the PR segment, shows the delay in the AV node. Together, these two

parts of the cardiac cycle show us what happened to the impulse before it reached

the . Therefore, the PRI represents the cardiac activity that

takes place above the ventricles in the atria and AV node; this category of activity

is referred to as supraventricular activity. Supraventricular refers to the part of the

heart the ventricles.

Role of the AV Node

36. In Chapter 2, you learned that the is the area of the heart

with the slowest conduction speed. That is, the conductive tissues of the sinus node,

the atria, and the ventricles all conduct impulses than the AV

node. There is one more thing you should know about the AV node. Because it is the

doorway between the atria and ventricles, the node has the responsibility of “holding” impulses until the ventricles are able to receive them. This is why there is a slight

delay at the node before each impulse passes through to the ventricles. In the normal

heart, this is not a particularly critical feature, but occasionally the atria will become

irritable and begin firing impulses very rapidly. The ventricles cannot respond effectively to all these impulses, so the AV node “screens” some of them, allowing only a few

to get through. This vital function of the node is called the heart’s “fail-safe” mechanism, and you will learn much more about it later as you learn about the more complex arrhythmias. The AV node is a vital structure within the heart because it protects

the from having to respond to too many impulses.

Ventricular vs. Supraventricular

37. When a rhythm originates in the sinus node, the atria, or the AV junction, it is

considered to be in the general category of supraventricular arrhythmias because it

originated above the ventricles. rhythms include all those that

originate above the ventricles; in fact, the only rhythms not included in the supraventricular category are those that originate in the ventricles, which are categorized

as ventricular . This basic categorization separates rhythms

that originate in the ventricles from those that originate the

ventricles.

atria

AV node

ventricles

PR

PRI

atria

ventricles

above

AV node

faster

ventricles

Supraventricular

rhythms

above

56 Chapter 3

38. The major EKG finding that can help you distinguish between supraventricular

and ventricular rhythms is the width of the QRS complex. This is because research

data show us that the only way an impulse can get all the way through the ventricles

in less than 0.12 second is if it follows normal conduction pathways; all other means of

depolarizing the ventricles will take a longer time. Therefore, if a rhythm has a normal

QRS measurement of less than 0.12 second, it must have been conducted normally and

thus would have to be in origin. This tells us that a rhythm

is known to be supraventricular, meaning it originated above the ventricles, if it has a

QRS measurement of less than second.

39. Unfortunately, this rule does not apply in the reverse. That is, just because the

QRS is wide does not mean that the rhythm is ventricular. A wide QRS complex can

be caused by:

• A supraventricular impulse that reaches an obstruction in the bundle branches

• A supraventricular impulse that cannot be conducted normally through the ventricles because they are still refractory from the preceding beat

• An irritable focus in the ventricles that assumes pacemaking responsibility

Of these possibilities, the third is by far the most common, telling us that a wide

QRS very frequently is caused by a impulse. However, it can

get you into trouble if you assume that all wide QRSs are ventricular in origin. So,

a normal QRS complex must be supraventricular, whereas a wide QRS complex can

be ventricular, or it can be supraventricular with a conduction defect. A wide QRS

can be either ventricular or supraventricular, but a QRS of less than 0.12 second must

be in origin.

40. By definition, supraventricular arrhythmias must have a normal QRS measurement of less than second. However, as was shown in the

preceding frame, they can frequently have prolonged ventricular conduction, causing a QRS complex. When this happens, you must note it

along with your interpretation of the rhythm. For example, a Normal Sinus Rhythm

should have a QRS of than 0.12 second, but if it had

a disturbance in the ventricles, it would fit all the rules of NSR

except that the QRS would be too . It should then be called

Sinus Rhythm with a wide QRS complex. It is not necessary for you to be more specific in

identifying which type of disturbance is present; if you choose to learn more about EKGs

at a later time, you will most likely also learn to distinguish between these conduction

irregularities. For now, you will simply call attention to an abnormal QRS complex by

calling it a . Regardless of whether or not ventricular conduction is normal, you must give primary attention to identifying the basic arrhythmia.

41. You now have the necessary knowledge to begin learning specific arrhythmias.

The secret to arrhythmia interpretation is practice. So if you have time now, turn to the

Practice Strips at the end of this chapter and practice gathering data from the tracings

in Part II (strips 3.7–3.15).

supraventricular

0.12