Basic ECG Interpretation

Basic ECG Interpretation Self-directed Learning Package: Module 1 2018

Introduction This package is part three of three self-directed modules designed to provide an introduction to interpreting ECGs: Module One -Basic ECG Interpretation Module Two -Intermediate ECG interpretation Module Three - Advanced ECG interpretation This module is required to be completed and submitted to the Nurse Educator, Professional Nursing and Midwifery Services (ph. 4433 3759) This course complements the Clinical Competency Assessments which you can access on QHEPS. http://qheps.health.qld.gov.au/tville/cdsu/clinical-competency-ax/nmsc-ecg-12-leadrecording.pdf

Module Editor Version 4 CNC Cardiac services, Townsville Hospital Copyright Statement Copyright Creative Commons BY-NC-ND Attribution – Non-Commercial – No Derivatives

© State of Queensland (Queensland Health) 2009. This document is licensed under a Government Information Licensing Framework Attribution Non-Commercial No Derivative License http://www.gilf.gov.au/restrictive-licence-template. Use of this material is limited according to agreed permissions and restrictions. For permissions beyond the scope of this license contact: Intellectual Property Officer, Queensland Health, GPO Box 48, Brisbane Q 4001, email IP_Officer@health.qld.gov.au, phone (07) 3234 1479.

Statement of Indemnity Material in this document cannot be reproduced in part or in whole without the express permission of Queensland Health and remains the intellectual property of Queensland Health. Queensland Health does not accept any responsibility for the use of this material outside the scope for which it has been designed and outlined in the appropriate Curriculum Document.

This program has been reviewed and endorsed by the Acute Cardiac Education Training Support (ACETS) Committee. We acknowledge the contributions to content of the previous Education for Practice in Queensland (EPiQ) Advisory Committee.

Clinical Education and Clinical Simulation Services

Page 2

Table of contents Basic ECG Interpretation ................................................................................................................ 4 Electrocardiogram ........................................................................................................................... 4 Recording a 12 Lead ECG .............................................................................................................. 4 Lead Placement .............................................................................................................................. 4 Activity 1 ......................................................................................................................................... 5 Critical Point 1................................................................................................................................. 5 Artefact ........................................................................................................................................... 5 Critical Point 2................................................................................................................................. 6 Documentation ................................................................................................................................ 6 Critical Point 3................................................................................................................................. 7 Conclusion ...................................................................................................................................... 7 The 12-Lead ECG ........................................................................................................................... 8 Critical Point 4................................................................................................................................. 8 Einthoven’s Triangle ....................................................................................................................... 9 Unipolar Leads .............................................................................................................................. 10 Depolarisation and the Cardiac Cycle ........................................................................................... 12 Assessing Heart Rate ................................................................................................................... 15 The Normal 12 Lead ECGs ........................................................................................................... 17 ECG Paper ................................................................................................................................... 17 Activity 3 ....................................................................................................................................... 20 Activity 4 ....................................................................................................................................... 21 Activity 5 ....................................................................................................................................... 21 Activity 6 ....................................................................................................................................... 24 Rhythm Interpretations .................................................................................................................. 25 Evaluate Overall Appearance of the rhythm .................................................................................. 26 Activity 7 ....................................................................................................................................... 26 Critical Point 5............................................................................................................................... 28 Steps for ECG Interpretation ......................................................................................................... 30 Activity 7 ....................................................................................................................................... 31 Multiple choice questions ................................................................. Error! Bookmark not defined.

Reference: .................................................................................................................................... 34 Clinical Education and Clinical Simulation Services

Page 3

Basic ECG Interpretation Electrocardiogram The aim of this section is to outline best practice for performing an ECG. The ECG is the most frequently used procedure for the diagnosis of heart disease, providing information about the type, location, extent, and in some cases, the coronary artery responsible for myocardial ischemia. 2 The skilled clinician integrates the ECG as part of their cardiovascular assessment. It is a non-invasive, safe, simple to perform, reproducible, and relatively inexpensive procedure. 3

Recording a 12 Lead ECG It is important to realise that the ECG is standardised only if the ECG is performed in a standardised fashion.1 The correct procedure and consistency between clinicians is paramount for valid diagnosis and comparative interpretation.

Common errors: 1 1: Recording speeds. The normal recording speed is 25 mm/s; recording at 50 mm/s will make the ECG appear slower; at 10 mm/s it will make the ECG appear faster than it is.

2: Recording voltage. The normal Voltage for recording ECG is 10 mm/mV. If the voltage is halved (5mm/mV) the machine will automatically reduce the size of the complexes; this can cause inaccuracy with diagnosing various conditions such as Acute Coronary Syndromes (ACS) (i.e. ST/ T wave changes).

Lead Placement The ECG provides a wealth of information, but the accuracy of these interpretations is dependent on the leads being placed in the correct positions. 1

Clinical Education and Clinical Simulation Services

Page 4

Activity 1 In the table below, identify the standardised lead placements: AVR AVL AVF V1 V2 V3 V4 V5 V6

Critical Point 1 Reversal of the right and left arm leads is the most common error in placement of the limb leads and it is usually recognizable by reversal of the appearance of the QRS complex in lead aVR which is usually facing downwards and lead aVL which the QRS is usually facing upwards.

Standard ECG interpretation is based on recording the limb leads, not the trunk.

This can lead to misinterpretation of the ECG and affects comparative analyse with sequential ECGs.

Correct placement of the chest leads can be challenging in women or in obese individuals because of breast tissue. In this situation, the skin electrodes often are placed under the breast tissue, or protuberant adipose tissue, in a location below the accepted location.

Studies show that R wave height can be altered when the electrodes are placed under the breast tissue compared with placing the skin electrode on top of the tissue. This may have implications when diagnosing heart attacks. In this situation, it is recommended that the skin electrodes be placed on top of the breast or adipose tissue as opposed to below the tissue in order to maintain accurate recording of the ECG waveform. 4

Artefact Artefact interrupts cardiac monitoring, makes interpretation difficult and may lead to misdiagnosis.

Artefact is due to a variety of causes: • Patient movement • Poor skin contact of electrodes (i.e. perspiration, oily skin, or dried out electrodes) • Excessive paste or overlapping electrodes (confluence effect) • Placing electrodes over bony prominences • Damage to cabling or corroded connections • Electrical equipment or improper grounded beds • Static electricity • Respiratory patterns.1

Clinical Education and Clinical Simulation Services

Page 5

Minimising the amount of electrical and muscular interference contributes to an accurate interpretation of the ECG. Additionally, obtaining a straight baseline is particularly important in 12-lead ECG interpretations as ST segment evaluation is an essential diagnostic tool in ACS. The filter option is for reducing muscle or electrical artefact on a recording. Using the filter button on the ECG machine reduces the amplitude of the measured waves.

Critical Point 2 The filter should only be selected when all other processes to reduce the artefact have been exhausted, and this should be clearly marked on the ECG as being used.

Documentation Documentation on the ECG should include the following: • The patient’s name, UR number, date and time of recording • Any variations from the standard recording (i.e. filter, speed, voltage or lead placement) • Document the rationale for taking the ECG; if the patient is having serial ECGs then clearly number the ECGs for easy identification • If chest pain is present during the recording, include vital signs, and any therapies that are administered prior to or during the recording of the ECG.

Clinical Education and Clinical Simulation Services

Page 6

Critical Point 3 Checklist for a High-Quality ECG Recording • Position the patient in the supine position with the head raised at a 30degree angle and ask them to lay still •

•

Ensure the recording is standardised at 25mm/s and 10mm/mV. Ensure limb leads are correctly applied: -

Use limbs, not trunk

-

Check for reversed leads

-

Avoid bony prominences

Ensure chest leads are correctly applied: -

V1 and V2 should be in the 4th intercostal space

-

V4 should be in the midclavicular line

-

V6 should be in the mid-axillary line

-

Electrodes should be left insitu or lead positions should be marked for serial ECGs

-

Avoid confluence effect (excessive paste or electrodes overlapping)

•

Check electrode integrity

•

Fix a wandering baseline:

•

•

-

Have adequate skin contact

-

Make sure skin is dry

-

Ask patent to breathe shallow or hold breath if respiratory artefact

Trouble shoot muscle tremor: -

Reassure the patient

-

Make sure skin is warm

-

Have the patient relax his/her arms

Trouble shoot AC interference: -

check electrode application

•

If interference is present in all leads, suspect a significant electrical leak and have the ECG machine and the environment checked for electrical safety. 1,4

•

Document clearly on the ECG

Conclusion To develop a high level of skill in recording and troubleshooting ECGs you will need to practice recording ECGs regularly in your clinical unit and/or healthcare.

Clinical Education and Clinical Simulation Services

Page 7

The 12-Lead ECG The 12-lead ECG records electrical activity as it spreads through the heart from 12 different leads that are recorded through electrodes placed on the arms, legs, and specific spots on the chest.

In a 12 lead ECG, three groups of leads are used.

Bipolar limb leads, consisting of two electrodes with opposite polarity Unipolar limb leads, one electrode and a reference point Unipolar precordial (chest) lead, also one electrode and a reference point The combination of recording electrodes represents different views of the heart.

A bipolar lead has a positive pole and a negative pole. A unipolar lead has one positive pole and a reference pole in the centre of the chest that is algebraically determined by the ECG machine. 3

Critical Point 4 It is important to know the positive and negative pole for each lead on the ECG, as this helps you to understand how we look at different surfaces of the heart; and is vital to understanding what a normal ECG looks like, so you can then identify any abnormalities.

Clinical Education and Clinical Simulation Services

Page 8

Einthoven’s Triangle Einthoven, a Dutch physiologist, was the first person to introduce the standard bipolar limb leads I, II and III. These three (3) bipolar limb leads form Einthoven’s triangle, a combination of the limb leads AVR, AVL, and AVF.

Figure 1 - Bipolar limb lead system

Figure 1: A camera analogy makes the 12-lead ECG /bipolar leads easier to understand.

Each lead of the ECG represents a picture of the electrical activity in the heart taken by the camera. In any lead, the positive electrode is the recording electrode or the camera lens.

The negative electrode tells the camera which way to “shoot” its picture and determines the direction in which the positive electrode records. When the positive electrode detects electrical activity travelling toward it, it records an upright or positive deflection on the ECG. When the positive electrode detects electrical activity travelling away from it, it records a negative deflection. If a positive electrode is positioned where electrical activity travels both toward it and away from it, a biphasic deflection is recorded. If the electrical activity travels perpendicular to a positive electrode, no activity is recorded (Figure 2). 3

Clinical Education and Clinical Simulation Services

Page 9

Figure 2

Figure 2: A strip of cardiac muscle depolarising in the direction of the arrow. A positive electrode at B sees depolarisation coming toward it and records an upright (positive) deflection. A positive electrode at A sees depolarisation going away from it and records a negative deflection. A positive electrode at C records a flat line because depolarisation is travelling perpendicular to the electrode's view. 3

Unipolar Leads Figures 3 and 4B illustrates the three unipolar leads aVR, aVL, and aVF. The camera represents the location of the positive electrode: on the right shoulder for aVR, on the left shoulder for aVL, and at the foot (left leg) for aVF. The “negative end” of the unipolar leads is the reference point in the centre of the chest that is obtained. Figure 4-C shows the six unipolar precordial leads recording from their locations on the chest and “shooting” toward the reference point in the centre of the chest. 3 Figure 3 – Augmented limb leads

Clinical Education and Clinical Simulation Services

Page 10

Figure 4: The 12 leads of the ECG. The camera represents the location of the positive, or recording, electrode in each lead. (A) Bipolar frontal plane leads I, II, and III. (B) Unipolar frontal plane leads aVR, aVL, and aVF. (C) Unipolar precordial leads V1-V6. 1

Clinical Education and Clinical Simulation Services

Page 11

Depolarisation and the Cardiac Cycle

The normal sequence of depolarisation originates in the Sino Atrial (SA) node high in the right atrium and spreads left through the left atrium and downward toward the Atrio Ventricular (AV) node low in the right atrium. Depolarisation is transmitted through the A−V node (Atrio-Ventricular node), the A−V bundle (the Bundle of His), and then through the ventricles by the Purkinje fibers.

The cardiac cycle is initiated in the sinus node in the atrium, which causes contraction of the right and left atrium (P wave). The depolarisation is delayed at the A−V node before passing to the A−V bundle and splitting into a right branch bundle and a left branch bundle, depolarising to the muscle of the right ventricle and the left ventricle (QRS), respectively. The delay at the A−V node prevents the atria and ventricles from contracting at the same time. During ventricular contraction the wave of depolarization in the cardiac muscle moves from the endocardium to the pericardial surface through the myocardium.

Once depolarisation is complete, the resting periods begins, which is the relaxation or repolarisation of ventricle - ST segment and T wave.

Depolarisations and repolarizations corresponding to these waves can be summarised by: •

Atrial depolarization/contraction (P Wave)

•

Depolarisation/contraction (QRS Complex)

•

Ventricular repolarisation/relaxation (T Wave)

R Wave Progression From V1 to V6 the positive electrode gets closer and closer to the mean current flow (or axis) in the thick walled left ventricle, and the R wave (positive component) becomes taller and taller. This normal R wave progression reflects intact anterior forces; if anterior forces are lost, so are the R waves.

Normal R-wave progression means that the R wave gets progressively larger from V1 to V6, or that V6 is predominantly an R wave compared with V1, which is predominantly an S wave. Often the largest precordial R wave is recorded in lead V4 or V5. Many variations of the above patterns exist among individuals and may represent normal variants in the ECG or pathology. Variations in P-wave and T- wave morphology can also be normal variants depending on how the heart physically sits in the chest. 3 As the R wave becomes taller across the precordial leads, the S wave becomes smaller.

Usually between V3 and V4 the R and S waves are equal. These equiphasic complexes define the transitional zone, which represents these leads looking perpendicular to the main electrical axis of the heart. See Figure 5 for examples of R wave progression and Figure 6 for an example of the shape of the QRS complexes in a normal 12 lead ECG.

Figure 5 Clinical Education and Clinical Simulation Services

Page 12

Clinical Education and Clinical Simulation Services

Page 13

Figure 6

Clinical Education and Clinical Simulation Services

Page 14

Assessing Heart Rate Heart rate can be determined from the ECG strip by several methods.

Method 1: 6 Second Rule If every small square is worth 0.04 seconds, then a large square (made up of five small squares) is worth 0.2 seconds. Thirty large squares therefore makes up six seconds (30 x 0.2 = 6 seconds). 3 Mark six seconds. Count the number of R waves in six seconds and multiply by 10 to obtain the number in 60 seconds. This is a better method when the QRS complexes are irregular, as during atrial fibrillation, in which case the RR intervals may vary from beat to beat.

Clinical Education and Clinical Simulation Services

Page 15

Method 2: 300 Rule For regular rhythms, the 300 rule may be used (as there are 300 large squares in 60 seconds). Count the number of large squares between two R waves and divide into 300.

For example, if there are four large squares between the R waves: 300 / 4 = 75.

If two consecutive R waves are separated by only one large box, then the rate is 300 beats per minute. If the R waves are separated by two large blocks, then the ventricular rate is 150 bpm.

Clinical Education and Clinical Simulation Services

Page 16

The Normal 12 Lead ECGs ECG Paper The ECG paper, on the horizontal axis refers to time. When the paper is running through the printer at 25 millimetres per second, each small square = 0.04 seconds. The vertical axis of the paper refers to voltage or electrical energy. Each vertical small block is 0.1 millivolt of electrical energy or one millimetre.

Wave Components The ECG is a graphic representation of the electrical activity of the heart (see Figure 7).

The ECG complex consists of: •

P wave

•

QRS complex T wave

•

U wave

P Wave The P wave is the first deflection in the cardiac cycle and is caused by depolarisation of the atria. Normal P waves are small, rounded and positive in lead II. There should be one P wave preceding each QRS complex. A P wave of normal size, shape and direction indicates that the electrical impulse originated in the SA node and that normal depolarisation of the atria has occurred. If the P wave is abnormal, it indicates that the sinus impulse travelled through altered or damaged atrial tissue, or that the impulse responsible for the P wave originated in a site outside the SA node.

QRS complex The Q, R and S waves represent ventricular depolarisation. These are grouped together and termed the QRS complex. The QRS complex represents ventricular depolarisation.

The QRS complex is normally narrow and should be less than 0.10 seconds. 3

Clinical Education and Clinical Simulation Services

Page 17

The first downward deflection of the QRS complex is termed a Q wave.

The first upward deflection is termed an R wave.

The downward deflection that follows the R wave is termed an S wave if it descends below the baseline.

QRS complex can be predominantly positive (upright), predominantly negative (inverted) or equiphasic (equally positive and equally negative).

The image below depicts the various shapes of QRS waves which can be described by the following points: The large waves that form major deflections are identified by upper case letters (QS, R, S) Smaller waves that are less than half the amplitude of the major deflection are identified by lower case letter (q, r, s) •

Ventricular depolarisation can be depicted more accurately by using upper and lower case letters to the waves (for example, qR, Rs, qRs).

T Wave Clinical Education and Clinical Simulation Services

Page 18

The T wave is reflective of the later stage of ventricular repolarisation. Normal T waves are upright, rounded and slightly asymmetrical. They are positive in Lead II, with amplitude less than five millimetres (five small squares high) and duration of 0.10–0.25 seconds or greater (approximately six small squares wide). 4 Abnormal T waves may be: •

Tall and peaked

•

Biphasic

•

Flattened or inverted

P-R interval The P-R interval is the time required for the electrical impulse to leave the SA node and travel through the atria, AV node, bundle branches, and Purkinje network. It is measured from the beginning of the P wave as it leaves the baseline to the beginning of the QRS complex.

P-R interval = 0.12–0.2 seconds (that is 3-5 small squares).

Q-T Interval The Q-T interval represents the period from the beginning of ventricular depolarisation until the end of ventricular repolarisation. Heart rate, age and sex of the patient affect the Q-T interval. In the absence of a Q wave, the Q-T interval is measured from the beginning of the R wave to the end of the T wave. To quickly determine the Q-T interval, when the heart rate is less than 100 beats per minute, a general rule is: the Q-T interval is half or less that of the R-R interval. 2 Prolonged QT intervals occur as a result of prolonged ventricular repolarisation, thus increasing the refractory period. Prolonged QT intervals can lead to life threatening arrhythmia such as torsades de pointes.

Some causes of prolonged QT are: • Ischaemic heart disease • Electrolyte imbalances • Drugs (including anti-arrhythmic and anti-depressant agents) • Genetic tendency

Clinical Education and Clinical Simulation Services

Page 19

Activity 3 - Answer the following questions to consolidate your learning (Please Highlight) 1.

The normal heart rate is initiated in the: SA node AV node Bundle of his Purkinje fibres.

2.

The structure that briefly delays the impulse (to let the ventricles fill) is the: SA node AV node Bundle of his Purkinje fibres

3.

The QRS represents: Atrial repolarisation Atrial depolarisation Ventricular depolarisation Ventricular repolarisation

4.

The T wave represents: Atrial repolarisation Atrial depolarisation Ventricular depolarisation Ventricular repolarisation

5.

If the QRS complex has an initial negative deflection, it is called a: Q wave R wave S wave

6.

If the QRS complex has an initial positive deflection, it is called a: Q wave R wave S wave

Clinical Education and Clinical Simulation Services

Page 20

Activity 4 For the following rhythm strips and circle if the intervals are short, normal or prolonged.

Activity 5 Rhythm Strip 1

P-R Interval: normal / shortened / prolonged QRS Duration: normal / shortened / prolonged Q-T Interval: normal / shortened / prolonged Rhythm Strip 2

P-R Interval: normal / shortened / prolonged QRS Duration: normal / shortened / prolonged Q-T Interval: normal / shortened / prolonged

Clinical Education and Clinical Simulation Services

Page 21

Rhythm Strip 3

P-R Interval: normal / shortened / prolonged QRS Duration: normal / shortened / prolonged Q-T Interval: normal / shortened / prolonged

ST Segment The ST segment represents the early part of repolarisation of the right and left ventricles. It is this segment that should be isoelectric with no deflections present. Positive and negative deflections represent ventricular muscle injury. The point where the QRS complex and the ST segment meet is called the J-point. The J Point represents the joining point of the last portion of the QRS complex and the very beginning of the ST segment. 4 The J Point: Where is it?

One standard text defines J point elevation as: “the point where the QRS ends and the ST segment begins.” One of the more specific descriptors states that the J point is the “first point of the inflection on the upstroke of the S wave.” See Figure 20.

STE and the J point In theory the ST segment is normally neither elevated nor depressed. When assessing the ST segment deviation, begin by finding the PR segment as your baseline.

Clinical Education and Clinical Simulation Services

Page 22

There is some conflict in the literature, however most clinicians measure ST segment deviation 60 milliseconds after the J point. This reference has been shown to be superior when evaluating fibrinolytic or Primary Coronary Intervention (PCI) criteria. In the example below, there is 1mm of STE 60msec after the J point. 11 Figure 20 - Examples of J point determination

Elevation or depression of the ST segment is considered significant when it is greater than one millimetre (one small square) and it occurs in at least two leads representative of the same area of the heart.

ST segment depression more than 0.5 millimetre is suggestive of myocardial ischemia ST segment elevation of more than one millimetre is suggestive of myocardial injury.

Clinical Education and Clinical Simulation Services

Page 23

Activity 6 Using the following rhythm strips, mark the isoelectric line, circle if the ST segment is elevated or depressed, and note how many millimetres the segment is deviated.

Rhythm Strip 1 S-T Segment: elevated or depressed

Rhythm Strip 2 S-T Segment: elevated or depressed

Clinical Education and Clinical Simulation Services

Page 24

Rhythm Interpretations A cardiac rhythm is the graphic representation of the heart's electrical activity; it does not relate the electrical activity to the clinical situation at hand. That is the role of the interpreter. Therefore, a systematic approach is required, which includes the following: Assess the rate Assess rhythm or regularity Identify and examine P waves Assess intervals Evaluate the overall appearance of the rhythm Interpretation of the rhythm Assess the Rate Is the heart rate normal? (60â&#x20AC;&#x201C;100 per minute) Is there a tachycardia? (rate > 100 per minute) Is there a bradycardia? (rate < 60 per minute) Is the atrial rate the same as the ventricular rate?

Assess Rhythm or Regularity Evaluate the regularity by measuring the distance between the R-R intervals across the entire six second strip. Is the rhythm: Regular Irregular Regular with irregularities Irregularly irregular?

Identify and Examine the P wave Is there a P wave?

Is the P wave normal (upright)? It should be upright in Lead II. Does the P wave occur before, during or after the QRS complex?

If there is no P wave, is there any other atrial wave that may give rise to the conduction of the cardiac impulse? (for example, flutter or fibrillatory waves.)

P waves may be absent, not visible or present.

Assess Intervals (evaluate conduction) PR interval (conduction) is measured from the point where the P wave leaves the isoelectric line to the beginning of the QRS. 4 Is it normal? (that is 0.12-0.20 seconds) Is it constant?

Does it vary?

Clinical Education and Clinical Simulation Services

Page 25

QRS complex (conduction) duration is measured from the beginning of the QRS to the point where the first wave of the complex deviates from the isoelectric line.

Is it normal? (< 0.10 seconds) Is it widened? (> 0.10 seconds) Does it look like a normal shaped QRS for the lead we are examining or does it look bizarre or unusual in its morphology?

QT Interval is measured from the beginning of the QRS complex to the end of the T wave.

If there is no Q wave, measure from the beginning of the R wave to the end of the T wave.

Is it normal? (less than half of the R-R interval)

Evaluate Overall Appearance of the rhythm ST Segment The ST segment is evaluated by identifying the isoelectric line. Determine whether there is elevation or depression from the isoelectric line.

T wave Are the T wave’s upright and normal height?

Interpretation Interpret the rhythm by identifying the site or origin (pacemaker site) of the rhythm (sinus), the mechanism (bradycardia), and the ventricular rate. 3 Sinus Rhythm

Rate

60–100 bpm

Rhythm

Regular, PP interval regular and RR interval regular

P waves

Positive lead II, Present and before every QRS

PR Interval

0.12–0.2 sec and constant

QRS Duration

< 0.10 sec

QT Interval

< ½ the R-R interval (<0.44sec QTc)

Activity 7 Clinical Education and Clinical Simulation Services

Page 26

Using the systematic approach provided, interpret the following rhythms.

Rhythm 1

Assess the Rate: Assess Rhythm or regularity: Identify and Examine P waves: Assess Intervals: PR: Evaluate the overall appearance of the rhythm: Interpretation of the rhythm:

Atrial:

QRS: ST Segment

Ventricular:

QT: T wave

Rhythm 2

Assess the Rate: Assess Rhythm or regularity: Identify and Examine P waves: Assess Intervals: PR: Evaluate the overall appearance of the rhythm: Interpretation of the rhythm:

Atrial:

QRS: ST Segment

Ventricular:

QT: T wave

Rhythm 3 Clinical Education and Clinical Simulation Services

Page 27

Assess the Rate: Assess Rhythm or regularity: Identify and Examine P waves: Assess Intervals: PR: Evaluate the overall appearance of the rhythm: Interpretation of the rhythm:

Atrial:

QRS: ST Segment

Ventricular:

QT: T wave

Critical Point 5 Computerised interpretation should serve as a useful aid to ensure that all aspects of ECG tracing have been analysed. The ECG analysis program is of assistance in identifying an abnormality that may have been overlooked.

However, the inadequacy of some computer analysis systems and discrepancies between different programs means that the final analysis and responsibility for clinical decisions must rest with the clinician.

To ensure that quality standards of ECG interpretation are maintained, staff should train themselves to first interpret the ECG without reference to the automated analysis and check the analysis only to make sure that nothing has been overlooked.

Clinical Education and Clinical Simulation Services

Page 28

ECG changes in Acute Coronary Syndromes (ACS) This section is an overview of the ECG changes that are evident in Acute Coronary Syndrome (ACS). The term ACS is used to refer to the pathophysiologic continuum that begins with plaque rupture in a coronary artery and ultimately results in permanent cell damage (infarction) if the process is not arrested. ACS encompasses three distinct phases of this continuum: (1) unstable angina (UA), (2) non- ST elevation Myocardial Infarction (NSTEMI), and (3) ST elevation MI (STEMI). 1

Myocardial Ischemia Myocardial ischemia can result in several changes on the ECG (Fig. 17). The most familiar pattern of ischemia is T-wave inversion (TWI), although TWI is often a non-specific finding and can be due to a variety of causes other than ischemia. Other indicators of ischemia include horizontal or downsloping ST-segment depression; and tall, wide-based T waves.

Myocardial Injury Myocardial injury is most often indicated by ST-segment elevation of 1 mm or more above the baseline in leads with positive electrodes facing the infarcted area. Other signs of acute injury include tall, peaked T waves; and symmetric T-wave inversion.

ECG Diagnosis of STEMI ST-segment elevation and T-wave inversion are recorded in leads where the positive electrode facing the damaged myocardium and are called the indicative changes of infarction. Other leads not facing the involved tissue are often affected by the loss of electrical forces in damaged tissue and record mirror-image changes called reciprocal changes.5 Reading ECGs is an integral skill, especially given the fact that ST segment elevation (STE) on an ECG may require emergency treatment. STE is generally measured in reference to the J point (the end of the QRS segment and the beginning of the ST segment). This short review will focus on identifying the J point in order to determine an accurate measurement of ST segment. 11

ECG Diagnosis of UA/NSTEMI UA and NSTEMI are subsets of ACS and are diagnosed when the ECG shows ST depression or prominent TWI without the presence of STE in patients with chest pain typical of ACS. 1

Clinical Education and Clinical Simulation Services

Page 29

Steps for ECG Interpretation 1.

Assess the patient – pain and clinical status. Implement management of urgent problems, for example hypotension

2.

Analyse the rhythm – implement management as indicated

3.

Determine the cardiac axis

4.

Initially review the frontal plane limb leads – leads I, II, III, aVR, aVL and aVF. Analyse the leads for: •

STE or depression

•

T wave flattening, inversion or tall T waves

•

QRS complex height

•

Q wave development

5.

Group leads together with same changes

6.

Determine the meaning of changes, for example ischemia, injury, or infarction

7.

Now review the six (6) chest leads V1 – 6 (plus V4R if recorded) using steps 3 – 6;

8.

Determine if the R wave progression is normal or abnormal

9.

Compare this ECG with previous ECGs and identify if changes are new or old

10.

Determine your interpretation of the ECG considering the patient’s clinical presentation.

Clinical Education and Clinical Simulation Services

Page 30

Activity 7 Provide an interpretation for the following ECGs

Clinical Education and Clinical Simulation Services

Page 31

Clinical Education and Clinical Simulation Services

Page 32

Clinical Education and Clinical Simulation Services

Page 33

Reference: 1.

Thompson P.L. Coronary Care Manual. Chatswood, NSW: Elsevier; 2011

2.

Moser DK & Riegel B. Cardiac Nursing a Companion to Braunwald's Heart Disease.

St. Louis, Missouri: Saunders Elsevier; 2008.

3.

Woods S, et al, editors. Cardiac Nursing. 6th ed. Philadelphia: Wolters Kluwer/ Lippincott Williams & Wilkins; 2010

4.

Urden L, Stacy K, Lough M. Thelan's Critical Care Nursing: diagnosis and management. 6th ed. St Louis, Massachusetts: Elsevier; 2010.

5.

Garcia T.B. 12-Lead ECG: The Art of Interpretation. 2nd ed.2013

6.

Hampton J.R., The ECG Made Easy 8th ed., Churchhill Livingstone, Elsevier 2013.

7.

Balady.G. J.,Bufalino. V.J., Gulati.M.,et.al,(2016).COCATS 4 Task Force 3: Training in Electrocardiography, Ambulatory Electrocardiography, and Exercise Testing.,Journal of the American College of Cardiology.,65(17).

8.

Hollander, J.E & Chase M. (2012). Evaluation of chest pain in the emergency department. Up to Date. Literature review current through: Dec 2012. | This topic last updated: Apr 3, 2012.

9.

Miller C & Granger C.B (2012). Evaluation of patients with chest pain at low or intermediate risk for acute coronary syndrome. Up to Date. Literature review current through: Dec 2012. | This topic last updated: Jul 17, 2012.

10.

Reeder G.S. & Kennedy H.L (2012). Criteria for the diagnosis of acute myocardial infarction. Up to Date. Literature review current through: Dec 2012. | This topic last updated: Dec 12, 2012.

Clinical Education and Clinical Simulation Services

Page 34