Download 1.5. Electrocardiogr..

MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Learning Activity 1.5. Electrocardiography
An electrocardiogram (ECG, or EKG, from the German kardio) is a recording of the electrical activity of the heart. As
the recording electrodes are placed on the body surface, it forms a composite of the electrical activity of numerous
cells and therefore appears quite different from the action potential tracings of individual cardiac cells. The basic
principles of ECG interpretation are quite logical, think in terms of the basic underlying electrical events than simply
memorising criteria for the various abnormalities. This will assist your understanding, and improve your ability to
successfully interpret an ECG.
Hill, J., & Timmis, A. (2002). ABC of clinical electrocardiography: Exercise tolerance testing. British Medical Journal,
324(7345), 1084-1087. [Free Full Text]
Outline prognostic indications for exercise testing.
1.
2.
3.
4.
5.
6.
Briefly describe the Bruce test protocol.
How is workload measured and what is this a reflection of?
1 MET
=
2.5 ml/kg/min
3.5 ml/kg/min
4.5 ml/kg/min
What is the intensity of activities of daily living (ADL) equivalent to?
Describe a ‘normal’ ECG trace during exercise.
What are the main limitations?
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 1 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
What are ‘abnormal’ ECG changes during exercise?
Identify the obvious ‘abnormal’ events in the tracing below and outline the significance.
Outline ECG criteria for stopping a test.
1.
2.
3.
4.
5.
6.
7.
8.
Identify signs and symptoms that may indicate stopping a test.
1.
2.
3.
4.
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 2 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
What findings suggest high probability of coronary artery disease?
1.
2.
3.
4.
5.
6.
Why is exercise testing of asymptomatic patients deemed controversial?
Kligfield, P., & Lauer, M.S. (2006). Exercise electrocardiogram testing: Beyond the ST segment. Circulation, 114(19),
2070-2082. [Free Full Text]
Outline manifestation of ST segment depression.
What is the suggested relationship between ST segment depression and heart rate?
Outline two three (3) key points for each of the following.
QRS Duration
1.
2.
3.
QRS Amplitudes
1.
2.
3.
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 3 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
QRS Amplitudes
1.
2.
3.
QT Interval
1.
2.
3.
Define the rate-recovery loop.
What is the agreement for determining functional capacity.
Describe the chronotropic response to exercise.
Tavel, M. E. (2001). Stress testing in cardiac evaluation. Chest, 119(3), 907-925. [Free Full Text]
The authors suggest that modern exercise testing with ECG monitoring remains a cornerstone of cardiovascular
evaluation, providing a valuable source for several types of information, including;
1.
2.
3.
4.
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 4 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Dunbar, C. (2010). ECG Interpretation for the clinical exercise physiologist. New York: Lippincott, Williams & Wilkins.
Chapter 1 Basic terminology and measurements
Describe the QRS complex morphology B-4b
Measure the PR interval and the QRS duration B-12b
Measure the PR interval and the QRS duration B-15b
Measure the rate (RR interval). B-28c
Is anything present on the resting ECG that would cause concern and/or require consultation before proceeding with
the stress portion of the test? S-1a
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 5 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Peak Exercise - What is shown on this ECG? Is it “positive” for myocardial ischemia? S-2b
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 6 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Rest - Is anything present on the resting ECG that would cause concern and/or require consultation before
proceeding with the stress portion of the test? S-5a
Key Points: Outline three (3) key learning points from this topic.
1.
2.
3.
Professional Vocabulary: Define the following terms as part of your professional vocabulary.
P wave
PR segment
QRS complex
T wave
ST segment
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 7 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Overview
 Electrocardiography (ECG) is a non-invasive diagnostic tool for assessing cardiac function, which is based on
the heart’s generation of electrical changes occurring in the myocardium (heart muscle) during the cardiac
cycle.
 ECG records the cardiac electrical currents, which is then transferred to the skin by means of metal electrodes
placed on the surface of the body.
 The ECG tracing is simply a graphic illustration of the heart’s electrical activity
Review - Theoretical Background
1. Graphical representation of electrical activity of the heart.
2. 12 lead ECG- 12 views of the heart- 3D view (Einthoren’s Triangle).
3. Accurate determination of heart rate.
4. Measure of cardiac function.
5. Detect disease/dysfunction
Characteristics of a normal ECG trace
• P wave: represents the wave of depolarisation that spreads from the SA node throughout the atria, and is
usually 0.08 to 0.1 seconds in duration.
• PR Interval: time taken for depolarisation to spread from SA node to the AV node and normally ranges from
0.12 to 0.20 seconds in duration.
• QRS complex: ventricular depolarisation. The duration of the QRS complex is normally 0.06 to 0.1 seconds.
This relatively short duration indicates that ventricular depolarisation normally occurs very rapidly. If the QRS
complex is prolonged (> 0.1 sec), conduction is impaired within the ventricles.
 Ventricles begin to contract at the end of the R wave.
• ST segment: beginning of ventricular repolarisation.
• T wave: represents repolarisation of the ventricles, lasting no longer than depolarisation in duration
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 8 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
12-Lead ECG Procedures
Electrodes and Leads
• On a standard twelve-lead ECG, ten electrodes are used; six placed on the chest, and four placed on or near
the limbs (one each). Of the leads placed on the limbs, only three are used to measure the electric potential,
while the fourth lead (right leg) is used as a non-recording ground.
• From the remaining nine electrodes, twelve “pictures” of the electrical impulses as they travel through the
heart muscle (myocardium) are recorded. By examining these tracings, it is possible to identify abnormalities
in the functioning and/or position of the heart.
• Conduction patterns are analysed to determine: the heart rate (beats per minute), the heart rhythm (origin of
electrical impulse); the heart’s axis (orientation in the chest); the presents of myocardial hypertrophy
(enlargement of the heart muscle); the presents of myocardial ischaemia (decreased blood flow of a coronary
artery); and the presents of myocardial infarction (complete blockage of a coronary artery).
• The 12 leads can be divided into two groups:
6 extremity (limb) leads,
6 chest (precordial) leads.
The six limb leads e further divided into two subgroups: bipolar and unipolar leads.
The six limb leads can be represented schematically in terms of a triangle, called Einthoven’s Triangle.
• Three bipolar leads, designated as leads I, II, and III, form the sides of the triangle, while the three unipolar
leads, designated as leads aVR, aVL, and aVF, form the apexes of the triangle.
• Lead I records the electrical potential between the right arm (-) and left arm (+) electrodes.
• Lead II records the electrical potential between the right arm (-) and the left leg (+).
• Lead III records the potential between the left arm (-) and the left leg (+).
• For the unipolar leads, the electrical potential is measured between one of the leads, designated as positive,
and the other two, designated as negative.
• aVR records the electrical potential between left arm and left leg (-), and the right arm (+)
• aVL records the electrical potential between right arm and left leg (-), and the left arm (+);
• aVF records the electrical potential between right arm and left arm (-), and the left leg (+).
• The precordial leads (V1 – V6) show the electrical currents of the heart detected by electrodes placed on
different portions of the chest wall, starting from the upper right portion of the heart, and moving to the
lower left portion.
Electrocardiographic Recording
• Skin preparation: The most critical point of the electrode-amplifier recording system is the interface between
electrode and skin.
• Electrode placement: Electrode placement affects ST segment slope/ amplitude.
V1= 4th intercostal space right of sternum
V2= 4th intercostal space left of sternum
V3= Positioned between V2 and V4
V4= 5th intercostal space on the mid clavicular line
V5= 5th intercostal space on anterior axillary line
V6= 5th intercostal space on mid axillary line
• 6V leads enable electrical views of the heart in the transverse plane
V1 and V2 view the right ventricle
V3 and V4 view the ventricular septum
V5 and V6 view the anterior and lateral walls of the left ventricle
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 9 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Analysis of ECG Tracing
1. Heart Rate: The heart rate can be estimated by dividing 300 by the number of large squares (5 mm)
(example: 5 and ½ large squares - 300/5.5 = 55), or calculated exactly by dividing 1500 by the number of small
squares (1 mm) between successive R waves (example: 27 small squares - 1500/27 = 55). Normal rate is
between 60 and 100 beats/min.
o If the heart rate is < 60 beats/min, then bradycardia is detected.
o If the heart rate is > 100 beats/min, then tachycardia is detected.
2. Heart Rhythm: The heart rhythm refers to two aspects of the heart beats: 1) the site from which the impulse
has originated, and 2) the tempo of the contractions (regularity of the heart beats). The first aspect of heart
rhythm is determined by looking at any lead for the presence of a P wave. The second aspect of heart rhythm
is determined by observing the R-R intervals (spacing between the QRS complexes). Proper heart rhythm is
known as normal sinus rhythm.
o QRS complex is preceded by a P wave, sinus rhythm is detected.
o QRS complex is not preceded by a P wave, junctional rhythm is detected.
o R-R interval is equal (or nearly so), normal rhythm is detected.
o R-R interval is unequal, then arrhythmia is detected.
3. Heart Axis: The presence of axis deviation (abnormal orientation) of the heart can be determined by looking
at all of the limb leads (I - aVF). Normal axis is between 0-90 degrees.
o Using the lead axis and their perpendiculars method, determine the approximate axis (30o range).
o Using the vector analysis method, determine the exact axis.
4. Hypertrophy: An increase in muscle mass will lead to an increase in electrical activity in the ECG tracing.
Hypertrophy (enlargement) of the heart muscle can be determined by the magnitude of the electrical
impulses. This hypertrophy may be indicative of a cardiovascular disorder
o Tall P wave (greater than 0.3 mV [3 mm]) is recorded, right atrial hypertrophy is detected.
o Wide P wave (greater than 0.12 sec [3 mm]) is recorded, left atrial hypertrophy is detected.
o Llead V1, if the hight of the R wave exceeds the depth of the S wave, right ventricular hypertrophy is
detected.
o Depth of the S wave in lead V1 added to the height of the R wave in either lead V5 or V6 exceeds 35
mm, left ventricular hypertrophy is detected.
o None of the above amplified electrical impulses are observed, no hypertrophy is detected
5. Anomalies: Myocardial ischaemia, premature ventricular contractions (PVC’s), and myocardial infarction are
conditions that may affect cardiac functioning. These conditions can be detected by the appearance of
abnormal deflections in the PQRST complex
o ST segment is depressed, or the T wave is inverted, then myocardial ischaemia is detected. The lead
in which the ST segment depression or inverted T wave appears will give some indication of where
the ischaemia is located.
o Wide (greater than 3 small squares) and distorted complex is observed, PVC’s may be occurring.
o Leads V1-V6, if the Q wave is greater than 0.04 seconds (1 mm) in duration and/or greater than 0.2
mV (2 mm) in depth, then myocardial infarction has occurred. The lead in which the abnormal Q
wave appears will give some indication as to the location of the damage.
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 10 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Five-Step Method
Step 1. Heart Rate: Is it fast, slow, or normal?

Count the number of R waves in 6 seconds (or 30 boxes) and multiply by 10 to find the rate per minute.
This method works with regular and irregular rhythms.
 normal heart rate is 60 - 100 bpm
 < 60 bpm bradycardia
 > 100 tachycardia
Step 2. Heart Rhythm. Is it regular or irregular?

To compare the intervals, measure them either with calipers or with a strip of paper marked at the
beginning and end of one interval. Then place the strip of paper over subsequent intervals to compare.

When the width varies, then the rhythm is said to be irregular.
Step 3. Atrial activity. Are there P waves present and are they of the same size and shape?

Determine whether or not the P wave is present. Then, look at its shape compared with other P waves.
Finally, see if its deflection is positive or negative.

Normal atrial activity:
 P waves present;
 shape of P waves consistent;
 P waves must form a positive deflection in lead 2
Step 4. QRS duration. Is it normal or wide?

QRS complex measured from the beginning of the QRS, where it leaves the baseline, to the end of the
QRS, where it returns to the baseline.

QRS complex represents ventricular depolarization.
 If it takes a long time for depolarization, then the QRS complex will be wide.
 Wide QRS complex portrays lengthy depolarization, which could represent a problem is
electrical conduction

Normal duration of QRS complex
 < .12 seconds, or fewer than three small blocks
Step 5. P to QRS relationship. Is there a P wave for every QRS complex, what is the P to R interval?

PR interval is measured from the beginning of the P wave to the beginning of the QRS complex where it
leaves the baseline.

PR interval represents the spread of the electrical impulse from the SA node, through the A V junction, to
the ventricles

Normal PR interval
 0.12 to .20 seconds, or three to five small blocks
Evaluation of ECG rhythm strips is based on the identification of five sinus rhythms
1.
Normal sinus rhythm. All parameters are within normal range
2.
Sinus bradycardia. HR is abnormally slow, but all other items are normal.
3.
Sinus tachycardia. HR is abnormally fast, but all other parameters are normal.
4.
Sinus arrhythmia. Only abnormality is irregular rhythm, (R-R distance varies).
5.
Sinus arrest. Occasional prolonged failure of the SA node to initiate an electrical impulse. The P-QRS-T
complex is missing.
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 11 of 12
MODULE 1. INTRODUCTION TO CLINICAL EXERCISE ASSESSMENT AND PRESCRIPTION
Unit 1 Concepts in clinical exercise assessment
Discussion Questions
1.
What does an ECG measure and what do its component waveforms represent?
2.
Describe the normal changes in an ECG trace with exercise.
3.
Outline the purpose of analysing the heart’s conduction patterns.
4.
What is the difference between bipolar and unipolar leads?
5.
How is Einthoven’s triangle formed? What does it demonstrate?
6.
What is the normal mean electrical axis for the heart? What is a left and right axis deviation?
7.
Why is the shape of the QRS complex different for each of the limb leads?
8.
Describe, in terms of vectors, how the QRS complex is generated and why the QRS appears differently
when viewed by different leads
EHR509 Clinical Assessment and Exercise Prescription in Chronic Conditions | Charles Sturt University
Page 12 of 12