interpreting ecg
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Dr…………………………..
Interpreting ECG
Topics:
1. Coronary circulation.2. Electrical conduction system of the heart3. Electrocardiography elements4. Electrical events & the waveform in a normal
ECG.5. ECG interpretation6. Identify lethal cardiac diseases7. The learning
1
Coronary circulation
Coronary Circulation Review
Figure 1
Coronary Circulation Review
Superior & Inferior Vena Cava
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonary Semi-lunar Valve
Coronary Circulation Review
Pulmonary Trunk
Right & Left Pulmonary Arteries
Lungs
Left Atrium
Pulmonary Veins
Coronary Circulation Review
Mitral Valve
Left Ventricle
Aortic Semi-lunar Valve
Aorta
Body
Right Coronary Artery
Supplies blood to: Right Atrium Right Ventricle The SA Node and in 55% of population the LV
inferior wall The LV posterior wall and ⅓ of the posterior
interventricular septum in 90% of the population
Left Circumflex Artery
Supplies blood to: the Left Atrium the LV lateral wall the SA Node in 45% of the population and to the LV
posterior wall ⅓ of the interventricular septum AV Node and Bundle of His in 10% of the population
Left Anterior Descending Artery
Supplies blood to: the LV anterior and lateral walls the Left and Right Bundle Branches the anterior ⅔ of the interventricular septum
Coronary Artery Blood Supply
Recall: The Right Coronary Artery supplies both the Right
and Left heart. The Left Coronary Artery and its branches only
supply the Left heart.
2
Electrical conduction of the heart
Cardiac Conduction
The Conduction System of the Heart
Cardiac Conduction
The SA Node is the primary pacemaker for the heart at 60-100 beats/minute
The AV Node is the “back-up” pacemaker of the heart at 40-60 beats/ minute.
The Ventricles (bundle branches & Purkinje fibers) are the last resort and maintain an intrinsic rate of only 20-40 beats/minute
Cardiac Conduction
The normal conduction pathway:
SA Node AV Node
Bundle of His
Right & Left Bundle
Branches
Purkinje Fibers
Cardiac Conduction
Correlation of the mechanical activity with the electrical activity….
Cardiac Conduction
Depolarization occurs when sodium channels open fast and the inside of the membrane becomes less negative (electrical stimulation). This is manifested as the P wave on an ECG, which
signifies atrial muscle depolarization. The plateau that immediately follows the P
wave represents atrial systole, when calcium channels open slowly and potassium channels close (at this time mechanical contraction of the atria takes place).
Cardiac Conduction
The PR interval on an ECG reflects conduction of an electrical impulse from the SA node through the AV node. PR = 0.12 – 0.20 seconds
Cardiac Conduction
The QRS complex of an ECG reflects ventricular muscle depolarization (the electrical impulse moves through the Bundle of His, the left and right bundle branches and Purkinje fibers). QRS = 0.08 – 0.10 seconds
The QT interval measures the time from the start of ventricular depolarization to the end of ventricular repolarization. QT interval = < 0.43 seconds or ½ of the R-to-R
interval.
Cardiac Conduction
The ST segment reflects the early ventricular repolarization and lasts from the end of the QRS complex to the beginning of the T wave.
The T-wave on an ECG reflects ventricular muscle repolarization (when the cells regain a negative charge - the “resting state”) and mechanical relaxation, which is also known as diastole.
3
ECG elements
Heart Revisited
Myocardial Cells = the mechanical cells of the heart. They contract when they receive an electrical impulse from the pacemaker cells. Myocardial = Muscle
Pacemaker Cells are very small cells within the conduction system which spontaneously generate electrical impulses. Pacemaker = Power Source
Electrical Conducting Cells rapidly carry current to all areas of the heart. Conducting Cells = Hard Wiring of Heart
What is an ECG?
An electrocardiogram (ECG) is a graphic recording of the electrical activity of the heart.
The machine is called Electrocardiograph while the recording is called Electocardiogram & is used as a diagnostic tool to assess cardiac function..
ECG Paper
ECG paper comes in a roll of graph paper consisting of horizontal and vertical light and dark lines.
The horizontal axis measures time
The vertical axis measures voltage.
ECG Paper
One small square = 0.04 seconds
One large square = 0.2 seconds Or [One small square(0.04)] x 5
ECG Paper
The light lines circumscribe small squares of 1 x 1 mm. One small square = 0.1 mV
The dark lines delineate large squares of 5 x 5 mm One large square = 0.5 mV
Electrocardiogram
ECG is a painless procedure that is performed by placing disposable electrodes on the skin of a person’s chest wall, upper & lower extremities.
In the ECG, the 12 lead one is the most commonly used tool to diagnose cardiac conduction abnormalities, arrhythmias, myocardial infarction and ischemia.
Electrocardiogram
The ECG represents the electrical impulses that the heart transmits and are recorded as wave tracings on specialized graph paper.
Electrocardiogram – 12 leads
6 limb leads 6 precordial leads Positioning measures 12 perspectives or views
of the heart The 12 perspectives are arranged in vertical
columns Limb leads are I, II, III, AVR, AVL, AVF Precordial leads are V1, V2, V3, V4, V5, V6 Horizontal marks time Vertical marks amplitude
Electrocardiogram - 12-Leads
Each limb lead I, II, III, AVR, AVL, AVF records from a different angle
All 6 limb leads intersect and visualize a frontal plane
The 6 chest leads (precordial) V1, V2, V3, V4, V5, V6 view the body in the horizontal plane to the AV node
The 12 lead ECG forms a camera view from 12 angles
Electrocardiogram - 12-Leads
I and AVL
II, III and AVF
V3 & v4
V1 & v2
V5 & v6
Where the positive electrode is positioned, determines what part of the heart is seen!
Electrocardiogram Lead Placement
Each positive electrode acts as a camera looking at the heart
10 leads attached for 12 lead diagnostics. The monitor combines 2 leads.
Mnemonic for limb leads White on right Smoke(black) over
fire(red) Snow(white) on
grass(green)
Unipolar and Bipolar leads
Limb leads I, II, III are bipolar and have a negative and positive pole Electrical potential differences are measured between the
poles AVR, AVL and AVF are unipolar
No negative lead The heart is the negative pole Electrical potential difference is measured betweeen the lead
and the heart Chest leads are unipolar
The heart also is the negative pole
Precordial leads
Anteroseptal: V1, V2, V3, V4 Anterior: V1–V4 Anterolateral: V4–V6, I, aVL Lateral: I and aVL Inferior: II, III, and aVF Inferolateral: II, III, aVF, and
V5 and V6
Precordial leads
Anteroseptal: V1, V2, V3, V4 Anterior: V1–V4 Anterolateral: V4–V6, I, aVL Lateral: I and aVL Inferior: II, III, and aVF Inferolateral: II, III, aVF, and
V5 and V6
Precordial leads
The 12-Lead ECG
Color Coding ECG’s Anterior
Yellow indicates V1, V2, V3, V4 Anterior infarct with ST
elevation Left Anterior Descending
Artery (LAD) V1 and V2 may also indicate
septal involvement which extends from front to the back of the heart along the septum
Left bundle branch block Right bundle branch block 2nd Degree Type2 Complete Heart Block
Anterior MI
2004 Anna Story 40
Color Coding ECG- Inferior
Blue indicates leads II, III, AVF Inferior Infarct with ST
elevations Right Coronary Artery
(RCA) 1st degree Heart Block 2nd degree Type 1, 2 3rd degree Block N/V common, Brady
Inferior MI
Color Coding ECG- Lateral
Red indicates leads I, AVL, V5, V6 Lateral Infarct with ST
elevations Left Circumflex Artery Rarely by itself Usually in combo
Lateral MI
Color Coding ECG- Posterior
Green indicates leads V1, V2 Posterior Infarct with ST Depressions and/ tall R
wave RCA and/or LCX Artery
Understand Reciprocal changes The posterior aspect of the
heart is viewed as a mirror image and therefore depressions versus elevations indicate MI
Rarely by itself usually in combo
Posterior MI
Color Coding ECG- SubEndo
No color for SubEndocardial infarcts since they are not transmural
Look for diffuse or localized changes and non – Q wave abnormalities T-wave inversions ST segment
depression
SubEndo MI
More colors show abnormality
A combination of infarcts such as: Anterolateral yellow and red Inferoposterior blue and green Anteroseptal yellow and green
ECG Distribution
Anteroseptal: V1, V2, V3, V4 Anterior: V1–V4 Anterolateral: V4–V6, I, aVL Lateral: I and aVL Inferior: II, III, and aVF Inferolateral: II, III, aVF, and
V5 and V6
The 12-Lead ECG
The 12-Lead ECG
The 12-Lead view
Deflection on leads
When an electrical current moves toward a positive electrode, the deflection on the ECG strip will be positive (up).
When an electrical current moves toward a negative electrode, the deflection on the ECG strip will be negative(down).
4
Electrical events and the waveform in ECG
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
ECG Rate Analysis
Rate What’s the normal heart rate for an adult human
being?▪ 60 – 100 beats/ minute
Remember: In terms of rate computation, heart rate generally
refers to the number of ventricular contractions that occur in 60 seconds or one minute.
When calculating rates, if there is a P-wave in front of every R-wave, the atrial and ventricular rates will be the same.
ECG Rate Analysis
Atrial rate can be calculated by measuring the interval of time between P-waves (the P-to-P intervals).
Ventricular rate can be calculated by measuring the time intervals between QRS complexes (the R-to-R intervals).
Check: Is the rate in the strip too fast or too slow?
ECG Rate Analysis
Why is it necessary to know both the atrial and ventricular rates? There are instances, such as 2nd and 3rd degree
AV block, in which the atrial rate and ventricular rates are different.
This is why it is important to know how to determine both atrial and ventricular rates.
ECG Rate Computation
Rules Count the number of QRS’s in a 6 - second strip,
then multiply that number by 10. Determine the time between R-R intervals, then
divide that number by 60. For example:
▪ 40 ÷ (20 small boxes x 0.04 seconds each)▪ = 50 beats per minute
ECG Rate Computation
Rules Memorize these numbers: 300, 150, 100, 75, 50
Normal Heart rate for an adult = 60 -100 bpm This means that 3 to 5 large blocks should exist
between R – R intervals. Bradycardia = more than 5 large blocks Tachycardia = less than 3 large blocks.
ECG Rate Computation
Rule of 300- Divide 300 by the number of boxes between each QRS = rate
HR of 60-100 = normal HR > 100 = tachycardia HR < 60 = bradycardia
ECG Rate Computation
ECG Rate Analysis
Let’s Practice with an Example:
What is the rate based on Rule #1? If it is 50 bpm…., you are Correct!!!
ECG Rate Analysis
Let’s Practice with an Example:
What is the rate based on Rule #1? 300/6= 50 bpm
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
Rhythm
Sinus Originating from SA
node P wave before every
QRS P wave in same
direction as QRS
Normal Intervals
PR 0.20 sec (less than one
large box) QRS
0.08 – 0.10 sec (1-2 small boxes)
QT 450 ms in men, 460 ms
in women Based on sex / heart rate Half the R-R interval with
normal HR
Prolonged QT
Normal Men 450ms Women 460ms
Corrected QT (QTc) QTm/√(R-R)
Causes Drugs (Na channel
blockers) Hypocalcemia,
hypomagnesemia, hypokalemia
Hypothermia AMI Congenital Increased ICP
Blocks
AV blocks1. First degree block
▪ PR interval fixed and > 0.2 sec
2. Second degree block, Mobitz type 1 ▪ PR gradually lengthened, then drop QRS
3. Second degree block, Mobitz type 2 ▪ PR fixed, but drop QRS randomly
4. Type 3 block ▪ PR and QRS dissociated
ECG Rhythm Analysis
Are the P waves regular or irregular?
Are the R-to-R intervals regular or irregular?
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
ECG P-wave Analysis
Are there P-waves in the rhythm strip?
Is there a P-wave for each QRS complex? Do all of the P-waves look the same?
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
ECG PR Interval Analysis
Is the PR Interval measurement normal?
PR = 0.12 – 0.20 seconds Is the PR Interval measurement constant?
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
ECG QRS Analysis
Is the QRS wide? > 0.10
Is it normal? QRS = 0.08 – 0.10 seconds Or is it narrow? < 0.08
ECG QRST analysis
Is the T-wave peaked, inverted or flat?
Is the ST segment elevated, depressed or normal?
Is the QT Interval < 0.43 seconds? Is there any ectopy present?
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
QRS Axis and deviation
Represents the overall direction of the heart’s activity and Axis of –30 to +90 degrees is normal.
The Quadrant Approach
QRS up in I and up in aVF = Normal
What is the axis?
Normal- QRS up in I and aVF
Hypertrophy
Add the larger S wave of V1 or V2 in mm, to the larger R wave of V5 or V6.
Sum is > 35mm = LVH
ECG Analysis
Rate Rhythm (including intervals and blocks) P - waves PR Interval QRS Complex
Axis Hypertrophy Ischemia
Cardiac ischaemia changes
Ischaemia….. Usually indicated by ST segment changes
1. Elevation = Infarction▪ Any elevation in the ST segment that is greater than 2 small boxes
is indicative of myocardial injury.
2. Depression = Ischemia▪ Any ST segment depression greater than 2 small boxes indicates
myocardial ischemia.
Can manifest as T wave changes Remote ischemia shown by Q waves
ECG Changes : Ischemia
T-wave inversion ( flipped T) ST segment depression T wave flattening Biphasic T-waves
Baseline
ECG Changes: Injury
ST segment elevation of greater than 1mm in at least 2 contiguous leads
Heightened or peaked T waves Directly related to portions of myocardium
rendered electrically inactive
Baseline
ECG Changes: Infarct
Significant Q-wave where none previously existed Why?
▪ Impulse traveling away from the positive lead▪ Necrotic tissue is electrically dead
No Q-wave in Subendocardial infarcts Why?
▪ Not full thickness dead tissue▪ But will see a ST depression▪ Often a precursor to full thickness MI
Criteria Depth of Q wave should be 25% the height of the R wave Width of Q wave is 0.04 secs Diminished height of the R wave
Evolving MI & AMI Hallmarks
1 year
Q wave
ST Elevation
T wave inversion
5
ECG interpretation
ECG Interpretation
Let’s try an example…..
Is the rhythm regular or irregular?
Are the P-waves identical? Is there a P-wave for each QRS complex?
Is the PR Interval 0.12 – 0.20?
Regular
Yes for both!
Yes, PR = 0.16
ECG Interpretation
Let’s try an example…..
Is the Is the QRS wide, normal or narrow??
Is the T-wave peaked, inverted or flat?
Is the ST segment elevated or depressed?
Is the QT Interval < 0.43?
Normal QRS = 0.08
No, it’s normal
No
Yes, QT Interval= 0.36
ECG Interpretation
Is there any ectopy present in this rhythm?
No
ECG Interpretation
So, the rhythm is …..
Normal sinus rhythm
6
Identify lethal cardiac diseases
Cardiac Arrhythmias
The cardiac arrhythmias that are almost always associated with death include:1. Atrial Fibrillation
2. Atrial Flutter
3. Ventricular Fibrillation
4. Ventricular Tachycardia
5. 1st , 2nd and 3rd degree AV Block
6. Asystole
7. Ischaemia
Cardiac arrythmias
Atrial fibrillation…..
Rhythm
Rate
P-waves
PR interval
Atrial fibrillation is irregular + chaotic; Ventricular rhythm is very irregularAtrial is > 350 bpm; Ventricular is 120-200 bpmNot consistent (they are fine and fibrillating)Not measurable
Cardiac arrythmias
Atrial flutter…..
Rhythm
Rate
P-waves
PR interval
Atrial flutter is usually regular;
Atrial is 250- 350 bpm; Ventricular rate depends on AV conductioncharacterized by “saw tooth” pattern
cannot be determined; more flutter waves than QRS complexes
Cardiac arrythmias
Ventricular fibrillation…..
Rhythm
Rate
P-waves
PR interval
Ventricular rhythm is totally erratic
Ventricular rate is 350-450 bpm
None
None
Cardiac arrythmias
Ventricular tachycardia….. Aka widow maker
Rhythm
Rate
P-waves
PR interval
Typically regular, but can be irregular
Ventricular rate is 100-220 bpm
can be present but have no correlation to QRS complex0.12 seconds with odd “tomb –stone” shape
ECG Rhythm Analysis
Type 1st degree AV block
PR is fixed and longer than 0.2 sec
ECG Rhythm Analysis
Type 1 - 2nd degree AV block [Wenckebach]
ECG Rhythm Analysis
Type 2 - 2nd degree AV block
Dropped QRS
Cardiac arrythmias
3rd degree AV block….. Complete heart block
Rhythm
Rate
P-waves
PR interval
40-60 bpm (narrow QRS and junctional); 20-40 bpm (wide QRS and ventricular)Normal, but usually more P-waves than QRS’s
Cardiac arrythmias
Asystole…..
Rhythm
Rate
P-waves
PR interval
No rate as the person that belongs to this rhythm is DEAD
Cardiac ischaemia
What is the diagnosis…..
Acute inferior MI with ST elevation in leads II, III, aVF
Cardiac ischaemia
What is the diagnosis…..
ST depression II, III, aVF, V3-V6 = ischemia
Cardiac ischaemia
What is the diagnosis…..
Anterior MI with lateral involvementST elevations V2, V3, V4 ST elevations II, AVL, V5
Cardiac ischaemia
What is the diagnosis…..
Anteroseptal MIST elevations V1, V2, V3, V4
Cardiac ischaemia
What is the diagnosis…..
Inferior MIST elevation 2,3 AVF
Cardiac ischaemia
What is the diagnosis…..
Inferior lateral MIST elevations 2, 3, AVF
ST elevations V5
Cardiac ischaemia
What is the diagnosis…..
Acute inferior MILateral ischemia
FromSample ECGs
Ventricular tachycardia
Supraventricular tachycardia
Narrow complex, regular; retrograde P waves, rate <220
1st degree heart block
2nd degree heart block – Mobitz type II
(Wenckebach)
PR interval fixed, QRS dropped intermittently
Left Bundle Branch block
Monophasic R wave in I and V6, QRS > 0.12 sec; Loss of R wave in precordial leads; QRS T wave discordance I, V1, V6; Consider ischemia if a new finding
Right Bundle Branch block
V1: RSR prime pattern with inverted T waveV6: Wide deep slurred S wave
Accelerated Idioventricular
Ventricular escape rhythm, 40-110 bpm; Seen in AMI, a marker of reperfusion
Junctional rhythm
Rate 40-60, no p waves, narrow complex QRS
Hyperkalaemia
Tall, narrow and symmetric T waves
Hypokalaemia
U wavesCan also see PVCs, ST depression, small T waves
Wellen’s sign
ST elevation & biphasic T wave in V2 and V3;Sign of large proximal LAD lesion
Wolff-Parkinson-White Syndrome
Short PR interval <0.12 sec; Prolonged QRS >0.10 sec; Delta waveCan simulate ventricular hypertrophy, BBB and previous MI
Brugada syndrome
RBBB or incomplete RBBB in V1-V3 with convex ST elevation
Brugada syndrome
Autosomal dominant genetic mutation of Na+ channels
Causes syncope, v-fib, self terminating VT, and sudden cardiac death
Can be intermittent on ECG Most common in middle-aged males Can be induced in EP lab Need ICD
Premature Atrial Contractions
Trigeminy pattern
Atrial Flutter with Variable Block
Sawtooth waves; Typically at HR of 150
Torsades De Pointes
Notice twisting patternTreatment: Magnesium 2 grams IV
Digitalis
Lateral wall MI
Reciprocal changes
Infero-lateral wall MI
ST elevation II, III, aVFST depression in aVL, V1-V3 are reciprocal changes
Right ventricular MI
Found in 1/3 of patients with inferior MI, Increased morbidity and mortalityST elevation in V4-V6 of Right-sided ECG
Antero-lateral, Inferior wall ischemia
LVH, AV junctional rhythm, bradycardia
Acute Pulmonary Embolism
S1, QIII, TIII in 10-15%; T-wave inversions, especially occurring in inferior and anteroseptal simultaneously; RAD
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1522004 Anna Story
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References
Twelve Lead Electrocardiography for ACLS Providers, D. Bruce Foster, D.O.W.B. Saunders Company
Rapid Interpretation of EKG’s , Dale Dubin, M.D., Cover Publishing Co. 1998
ECG’s Made Easy, Barbara Aehlert, RN, Mosby, 1995 The 12 Lead ECG in Acute Myocardial Infarction, Tim Phalen, Mosby, 1996 Color Coding EKG’s , Tim Carrick, RN, H &H Publishing, 1994 www.ecglibrary.com/ecghome.html www.urbanhealth.udmercy.edu/ekg/read.html www.ecglibrary.com/ecghome.html www.nyerrn.com/h/ekg.htm
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