Introduction to Cardiac Rhythm Analysis

Overview

ekg analysis illustration

This page provides an introduction to cardiac rhythm analysis with links to training materials on this website.

The EKG (ECG) Waveform

EKG waveforms are displayed on monitors or paper. These EKG tracings have important features which can be analyzed to reveal a normal or an abnormal rhythm (a dysrhythmia).

EKG can include various waveform components which are can be interpreted to understand if the EKG is a sinus rhythm or abnormal:

  • P Wave
  • PR Interval
  • PR Segment
  • QRS Complex
  • QT Interval
  • ST Segment

The P wave indicates atrial depolarization and it is normally an upward deflection in the EKG tracing. Next the QRS complex indicates ventricle repolarization. It typically starts with a negative deflection, then a large positive movement and then a negative movement, the S wave. A T wave normally follows the QRS complex. It is typically a upwards waveform, indicating repolarization of the ventricles. Intervals such as the PR interval, PR segment, QT interval and ST segment can also be analyzed to understand the heart's condition.

Click To Begin Cardiac Rhythm Analysis Training Module

Overview

Introduction to Cardiac Rhythm Analysis

Thomas E. O'Brien
AS CCT CRAT RMA

Objectives

At the conclusion of this training module the reader will be able to:

  • Recall the following:
    • Time is represented horizontally
    • Voltage/amplitude is represented vertically on the graph paper
    • Each small box has a time value of 0.04 second
    • Each large box has a time value of 0.20 second
    • Standard paper speed is 25mm/sec and can be adjusted
    • Standard calibration is 10mm/mV and can be adjusted
  • Recognize the difference between regular and irregular rhythms
  • Utilize proper method for determining heart rate
  • Properly describe P wave and recall the origin of the electrical activity
  • Accurately measure the PR interval and recall the normal range
  • Properly describe the QRS complex and recall what this electrical event represents
  • Accurately measure QRS complex and recall the normal range

Using This Presentation

how to use this presentation image

Introduction

Part 1

  • Basic principles of rhythm analysis require an understanding of speed and voltage (amplitude).
  • Standard recording speed is 25 mm/sec.
  • It is important to remember this unit of measure because it lends consistency to measurement when analyzing interval, complex and segment durations.
  • Part 2

  • If the print speed is increased or decreased, it will not only affect the distance of one cardiac complex to the next, it will affect the measurement duration of critical aspects of the cardiac complex.
  • Paper speed is often marked on the tracing. It is important to check this setting prior to printing and analyzing any tracing.
  • Part 3

  • Voltage is represented vertically in the cardiac tracing.
  • Standard calibration or gain is set at 10 mm/mV. It is important to remember this unit of measure because it lends consistency to measurement when analyzing the height and depth of cardiac waves.
  • If the gain is increased (20 mm/mV) or decreased (5 mm/mV), it will affect the size of the waves in a cardiac complex. This can be a useful feature when a patient’s cardiac tracing is either too small to analyze effectively or so large that the waveforms are overlapping or tracing off of the paper.
  • Part 4

    • It is important to be aware of the settings on the equipment you are working with daily.
    • Many times a calibration pulse is seen at the beginning, end or both on a cardiac tracing (it looks like a rectangle about 5 mm wide and 10 mm tall in “standard calibration”). Some units will simply print 10 mm/mV on the bottom or top of the tracing, some machines will do both. Make sure you are familiar with your equipment.
    ekg rhythm analysis image

    Graph Paper

    Time 1

    • The value of time and voltage just discussed is very important to understand, but it must be combined with an understanding of the grid or graph paper the tracing is printing upon that you are analyzing.
    • The grid is broken down in small boxes (1 X 1 millimeter) and heavier darkened lined boxes.
    • There are five small boxes going from left to right and bottom to top of each large box (5 X 5 mm).

    Time 2

  • Each small box has a time value of 0.04 second.
  • If there are five small boxes going across each large box, then the value of time for each large box equals 0.20 second
  • (5 small boxes X 0.04 second = 0.20 second)
  • (5 LARGE BOXES X 0.20 SECOND = 1 SECOND)

  • analysis ecg image 102

    Voltage 1

    • Voltage is important when measuring the height or depth of a waveform.
    • The height or depth provides an indication of the amount of electrical activity occurring within the heart.
    • Voltage can be affected by a number of different factors to include the amount of viable muscle mass in the heart.
    • When analyzing cardiac tracings, the question always comes up “where do I measure from”?

    Voltage 2

  • To keep it as clear as possible, it is important to establish the isoelectric line or baseline.
  • There are times when this can prove to be impossible, but in most cases if you can see the PR segment, ST segment and TP segment, you should have a strong sense that this is where the isoelectric line is located.
  • However, all three segments are not always on the isoelectric line
  • Where two out of the three of them are located when analyzing horizontally, this is typically where the isoelectric line is located.

  • analysis ecg image 103

    Step 1 - Rhythm Analysis

    Introduction

    • When analyzing cardiac rhythm strips it is important to recognize what the cardiac complex represents and what is considered normal versus abnormal.
    • The technique and interpretation of cardiac rhythms is a combination of science and art.
    • The more you practice rhythm analysis the more comfortable you will be with the process involved and the intuitive aspects of interpretation.

    Description

    • When a normal heart is beating this is the result of electrical impulses that spread through the atria and then the ventricles in an organized, sequential manner. Atria, then ventricles, atria, then ventricles over and over again.
    • When analyzing the tracing you will first check R wave to R wave across the strip. If the intervals vary by 1 ½ small boxes or less the rhythm is considered regular.
    • If you take your own pulse now and then again in 10 minutes it is unlikely that your heart rate will be exactly the same number. This is because of a number of factors all working together in an effort to maintain our body within a specific range of “normal”, often referred to as homeostasis.
    • R wave to R wave analysis refers to the rhythmicity of the ventricles.
    • Now measure the P wave to P wave intervals. This refers to the rhythmicity of the atria.

    Practice 1

    Analyze this tracing. Its is regular or irregular?

    analysis ecg image 104
    Regular
    Irregular


    Practice 2

    Analyze this tracing. Its is regular or irregular?

    analysis ecg image 105
    Regular
    Irregular



    Step 2 - Heart Rate Regular

    Regular Rhythms

    • If the rhythm varies by less than two small boxes, then the rhythm is considered regular.
    • The heart rate determination technique used will be the 1500 technique.
    • Starting at the beginning of the tracing through the end, measure from one R wave to the next R wave (ventricular assessment), then P wave to P wave (atrial assessment), then count the number of small boxes between each and divide that number into 1500.
    • This technique will give you the most accurate heart rate when analyzing regular heart rhythms. You may include ½ of a small box i.e. 37.5/1500 = 40 bpm (don’t forget to round up or down if a portion of a beat is included in the answer).
    analysis ecg image 106

    Irregular Rhythms

    • If the rhythm varies by two small boxes or more, the rhythm is considered “irregular”.
    • The heart rate determination technique used for irregular rhythms will be the “six-second technique”.
    • Simply count the number of complete cardiac complexes in six seconds and multiply by ten.
    analysis ecg image 107

    Practice 1

    Analyze this tracing. What is the heart rate?

    analysis ecg image 108
    Reveal Answer


    Practice 2

    Analyze this tracing. What is the heart rate?

    analysis ecg image 105
    Reveal Answer



    Step 3 - P wave Morphology (Shape)

    Description

    • The lead most commonly referenced in cardiac monitoring is lead II.
    • For the purposes of this training module, lead two will specifically referenced unless otherwise specified.
    • The P wave in lead II in a normal heart is typically rounded and upright in appearance.
    • Changes in shape must be reported. This can be an indicator that the locus of stimulation is changing or the pathway taken is changing.
    • P waves may come in a variety of morphologies i.e. rounded and upright, peaked, flattened, notched, biphasic (second complex, pictured), inverted and even buried or absent!
    • Remember to describe the shape. This can be very important to the physician when diagnosing the patient.
    analysis ecg image 110

    P Wave Practice 1

    Analyze this tracing. Describe the P waves.

    analysis ecg image 111
    Reveal Answer


    P Wave Practice 2

    Analyze this tracing. Describe the P waves.

    analysis ecg image 111
    Reveal Answer



    Step 4 – PR interval (PRi)

    Description

    • Measurement of the PR interval reflects the amount of time from the beginning of atrial depolarization to the beginning of ventricular depolarization.
    • Plainly stated, this measurement is from the beginning of the P wave to the beginning of the QRS complex.
    • The normal range for PR interval is: 0.12 – 0.20 seconds (3 to 5 small boxes)
    • It is important that you measure each PR interval on the rhythm strip.
    • Some tracings do not have the same PRi measurement from one cardiac complex to the next. Sometimes there is a prolonging pattern, sometimes not.
    • If the PR intervals are variable, report them as variable, but note if a pattern is present or not.
    analysis ecg image 113 analysis ecg image 114

    PR Interval Practice 1

    Analyze this tracing. What is the PR interval Measurement?

    analysis ecg image 115
    Reveal Answer


    PR Interval Practice 2

    Analyze this tracing. What is the PR interval Measurement?

    analysis ecg image 116
    Reveal Answer



    Step 5 – QRS Complex

    Description

    • The QRS represents ventricular depolarization.
    • It is very important to analyze each QRS complex on the tracing and report the duration measurement and describe the shape (including any changes in shape).
    • As discussed earlier in step 3, when referring to P waves, remember changes in the shape of the waveform can indicate the locus of stimulation has changed or a different conduction pathway was followed. It is no different when analyzing the QRS complex.
    • The difference is that in step 3, we were looking at atrial activity. Now we are looking at ventricular activity.
    • Measure from the beginning to the end of ventricular depolarization.
    analysis ecg image 117

    Description 2

    • The normal duration of the QRS complex measures from: 0.06 – 0.10 second
    • When the QRS measurement is 0.12 seconds or greater it indicates a delay in the electrical impulse as it is passing through the ventricular conduction system
    • Abnormal duration QRS
    analysis ecg image 118

    QRS Practice 1

    Analyze this tracing. What is the QRS duration?

    analysis ecg image 119
    Reveal Answer


    QRS Practice 2

    Analyze this tracing. What is the QRS duration?

    analysis ecg image 120
    Reveal Answer



    Closing

    Interpretation

    • The previous slides presented the five-steps of rhythm analysis. These five steps must be followed regardless of how simple of complex the tracing is you are reviewing.
    • The information gathered in these steps are telling a story.
    • The title of that story is the interpretation.

    Irregular Rhythms

    • In our other modules on this website, you can learn about the features of different dysrhythmia categories and specific criteria for each dysrhythmia within a category.
    • Regardless of the category or dysrhythmia, it is important to always follow the discipline of the five-step rhythm analysis technique.

    Test Questions 1-3

    Question #1

    When analyzing a rhythm strip, it qualifies as being regular when

    A. the QT intervals are the same
    B. the PR interval measures the same
    C. the QRS complexes measures the same
    D. the R - R intervals measure the same




    Question #2

    Which of the following steps is not one of the five-steps of rhythm analysis?

    A. PR interval measurement
    B. Rhythm regularity
    C. TP interval measurement
    D. QRS complex measurement




    Question #3

    Which of the following is considered normal range of the QRS complex?

    A. 0.12 - 0.20 minutes
    B. 0.06 - 0.10 minutes
    C. 0.12 - 0.20 seconds
    D. 0.06 - 0.10 seconds




    Question #4

    Which of the following is considered normal range of the PR interval?

    A. 0.12 - 0.20 minutes
    B. 0.06 - 0.10 minutes
    C. 0.12 - 0.20 seconds
    D. 0.06 - 0.10 seconds





    Test Questions 4-6

    Question #4

    Which of the following is considered normal range of the QRS Complex?

    A. 0.12 - 0.20 minutes
    B. 0.06 - 0.10 minutes
    C. 0.12 - 0.20 seconds
    D. 0.06 - 0.10 seconds




    Question #5

    The QRS complex measurement represent the period of time for which of the following?

    A. Ventricular depolarization
    B. Atrial depolarization
    C. Ventricular repolarization
    D. Atrial repolarization




    Question #6

    Which term is utilized to describe the PR interval when the measurement is not the same each time?

    A. Variable
    B. Absent
    C. Unmeasurable
    D. Indeterminable





    Test Questions 7-9

    Question #7

    Which technique is used to determine the most accurate heart rate for regular rhythms?

    A. 300 technique
    B. 1500 technique
    C. Six-second technique




    Question #8

    Which of the following terms best describes the cardiac tracing below?

    A. Irregular
    B. Regular
    C. Unable to determine


    analysis ecg image 121

    Question #9

    What is the heart rate of the tracing below?

    A. 100
    B. 75
    C. 50
    D. Unable to determine


    analysis ecg image 121


    Test Questions 10-12

    Question #10

    Which technique is used to determine the most accurate heart rate for irregular rhythms?

    A. 300 technique
    B. 1500 technique
    C. Six-second technique
    D. Unable to determine




    Question #11

    Which of the following terms best describes the rhythmicity of cardiac tracing below?

    A. Irregular
    B. Regular
    C. Unable to determine


    analysis ecg image 122

    Question #12

    What is the heart rate in this tracing?

    A. 120
    B. 98
    C. 83
    D. 65


    analysis ecg image 122


    Test Questions 13-14

    Question #13

    Select the heart rate most closely associated with this tracing.

    A. 50
    B. 70
    C. 90
    D. 110


    ekg rhythm analysis quiz tracing 12

    Question #14

    What is the most correct description of the P wave in the fifth complex?

    A. Biphasic
    B. Monophasic
    C. Upright and uniform
    D. Inverted


    ekg rhythm analysis quiz tracing 12


    Test Questions 15-17

    Question #15

    What would be the most proper description of the atrial activity in this tracing?

    ekg ventricular quiz tracing 15
    A. Inverted
    B. Absent
    C. Variable
    D. Biphasic




    Question #16

    Which term is most appropriately used to describe the P wave in the fifth cardiac complex in this tracing?

    ekg ventricular quiz tracing 15
    A. Inverted
    B. Notched
    C. Absent
    D. Biphasic




    Question #17

    Which term is most appropriately used to describe the P wave in the fourth cardiac complex in this tracing?

    ekg ventricular quiz tracing 15
    A. Inverted
    B. Notched
    C. Absent
    D. Biphasic





    Test Questions 18-21

    Question #18

    . What is the standard paper speed for cardiac tracings?

    A. 10 mm/mV
    B. 25 mm/mV
    C. 10 mm/sec
    D. 25 mm/sec




    Question #19

    What is the gain set to in standard calibration?

    A. 10 mm/mV
    B. 25 mm/mV
    C. 10 mm/sec
    D. 25 mm/sec




    Question #20

    What is the value of time for one small box?

    A. Six seconds
    B. One second
    C. 0.20 second
    D. 0.04 second




    Question #21

    How many large boxes are in six seconds?

    A. Five
    B. Ten
    C. Fifteen
    D. Thirty





    EKG Self Test

    EKG Rhythms Self Test

    If you would like to tests the knowledge and skills learned in this module, use our EKG Rhythms Self Test. You can choose to focus this self-test on any of all of the following:

    • Sinus Mechanisms
    • Atrial Rhythms
    • Junctional Rhythms
    • Ventricular Rhythms
    • Atrioventricular Blocks
    • Pacemaker Rhythms

    EKG Rhythm Tests »

    `

    Training Resources

    Cardiac Rhythm Analysis Training

    A good starting point for learning cardiac rhythms analysis is our training module. It presents a five step analysis method for quickly learning to interpret EKG tracings.

    Cardiac Rhythm Analysis »

    EKG Rhythm Tests

    Hundreds heart rhythms in this practice test. Test can be tailored for specific learning needs.

    EKG Rhythm Tests

    Cardiac Arrhythmia Information

    For additional information about cardiac arrhythmia and many other EKG topics, visit PracticalClinicalSkills.com.



    External References

    Wikipedia
    Body Mass Index Guide