Objectives review the ECG waveform and intervals Define myocardial ischemia injury and infarction Identify the 5 major infarct areas on the 12 lead Name occluded arteries common to the area Differentiate ECG changes reflecting ischemia injury and infarction ID: 778763
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Slide1
2015
BASIC ECG INTERPRETATION
Slide2Objectives
review the ECG waveform and intervals
Define myocardial ischemia, injury and infarction
Identify the 5 major infarct areas on the 12 lead
Name occluded arteries common to the area
Differentiate ECG changes reflecting ischemia, injury and infarction
Slide3Conduction System Review
Slide4CARDIAC CELLS
Action Potential
Five Phase cycle reflecting the difference in concentration of electrolytes (Na+, K+, Ca++, Cl-) which are charged particles across a cell membrane
The imbalance of these charged particles make the cells excitable
Slide5Cardiac Cell Action Potential
Phase 0
Depolarization
Rapid Na+ entry into cell
Phase 1
Early depolarization
Ca++ slowly enters cell
Phase 2
Plateau-continuation of repolarization
Slow entry of Sodium and Calcium into cell
Slide6Cardiac Cell Action Potential
Phase 3
Potassium is moved out of the cell
Phase 4
Return to resting membrane potential
Slide7Slide8CONDUCTION SYSTEM
Sinoatrial Node (SA)
Primary pacemaker
Intrinsic rate 60-100/min
Located in Rt. Atrium
Supplied by sympathetic and para-sympathetic nerve fibers
Blood from RCA-60% of people
Slide9CONDUCTION SYSTEM
AV Node
Supplied by RCA – 85%-90% of people
Left circumflex artery in rest of people
Delay in conduction due to smaller fibers
Slide10CONDUCTION SYSTEM
Bundle of His
Located in upper portion of interventricular septum
Intrinsic rate 40-60/min
Blood from LAD and Posterior Descending
Less vulnerable to ischemia
Slide11CONDUCTION
SYSTEM
Purkinje Fibers
Intrinsic pacemaker rate 20-40/min
Impulse spreads from endocardium to epicardium
Slide12Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
Slide13Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
Slide14The “PQRST”
P wave - Atrial depolarization
T wave - Ventricular repolarization
QRS - Ventricular depolarization
Slide15The PR Interval
Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)
(delay allows time for the atria to contract before the ventricles contract)
Slide16The ECG
Slide17ECG
Records electrical voltage of heart cells
Orientation of heart
Conduction disturbances
Electrical effects of medications and electrolytes
Cardiac muscle mass
Ischemia / Infarction
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Unipolar and Bipolar
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
between
the lead and the heart
Chest leads are unipolar
The heart also is the negative pole
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Views from Augmented and Limb Leads- Frontal
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Precordial lead snapshots
Think of each precordial lead as a horizontal view of the heart at the AV node
With the limb leads and the precordial leads you have a snapshot of heart portions
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Precordial Leads
Slide22ECG
Lead I
Negative electrode
Right arm
Positive electrode
Left arm
Slide23ECG
Lead II
Negative Electrode
Right Arm
Positive Electrode
Left Leg
Slide24ECG
Lead III
Negative Lead
Left Arm
Positive Lead
Left Leg
Slide25ECG
Slide26The ECG Paper
Horizontally
One small box - 0.04 s
One large box - 0.20 s
Vertically
One large box - 0.5 mV
Slide27The ECG Paper (cont)
Every 3 seconds (15 large boxes) is marked by a vertical line.
This helps when calculating the heart rate
.
3 sec
3 sec
Slide28ECG PAPER
Waveforms
Movement from baseline
Positive (upward)
Negative (downward)
Isoelectric –along baseline
Biphasic - Both upward and downward
Slide29ECG
P Wave
First waveform
Impulse begins in SA Node in Right Atrium
Downslope of P wave –is stimulation of left atrium
2.5 mm in height (max)
O.11 sec. duration (max)
Positive in Lead II
Slide30ECG
QRS Complex
Electrical impulse through ventricules
Larger than P wave due to larger muscle mass of ventricles
Follows P wave
Made up of a
Q wave
R wave
S wave
Slide31ECG
Q wave
First negative deflection following P wave
Represents depolarization of the interventricular septum activated from left to right
Slide32ECG
S wave
Negative waveform following the R wave
Normal duration of QRS
0.06 mm – 0.10 mm
Not all QRS Complexes have a Q, R and S
Slide33ECG
T wave
Represents ventricular repolarization
Absolute refractory period present during beginning of T wave
Relative refractory period at peak
Usually 0.5 mm or more in height
Slightly rounded
Slide34ECG
U wave
Small waveform
Follows T wave
Less than 1.5 mm in amplitude
Slide35A normal ECG waveform
Slide36ECG
J Point
Point where the QRS complex and ST-segment meet
Slide37ECG
PR Interval
Measurement where P wave leaves baseline to beginning of QRS complex
0.12 - .20 sec.
QRS Interval
Measurement from beginning of the Q wave until the end of the S wave.
0.06 - .12 sec.
Slide38ECG
QT interval
0.44 sec.
Represents total ventricular activity
Measured from beginning of QRS complex to end of T wave.
Should not exceed ½ the length of the R-R
Slide39Rhythm Analysis
Step 1: Calculate rate.
Step 2: Determine regularity.
Step 3: Assess the P waves.
Step 4: Determine PR interval.
Step 5: Determine QRS duration
.
Step 6:Determine
QRS AXIS
Slide40Step 1: Calculate Rate
Option 1
Count the # of R waves in a 6 second rhythm strip, then multiply by 10
.
9 x 10 = 90
bpm
3 sec
3 sec
Slide41Step 1: Calculate Rate
Option 2
Find a R wave that lands on a bold line.
Count the # of large boxes to the next R wave. If the second R wave is 1 large box away the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc. (
cont
)
R wave
Slide42For regular rhythms
: Rate = 300 / number of large
squares in
between
each consecutive R wave
.
For very fast rhythms
: Rate = 1500 / number of
small
squares
in between each consecutive R wave.
Slide43Step 2: Determine regularity
Look at the R-R distances (using a caliper or markings on a pen or paper).
Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular?
Interpretation?
Regular
R
R
Slide44Step 3: Assess the P waves
Are there P waves?
Do the P waves all look alike?
Do the P waves occur at a regular rate?
Is there one P wave before each QRS?
Interpretation?
Normal P waves with 1 P wave for every QRS
Slide45Step 4: Determine PR interval
Normal: 0.12 - 0.20 seconds.
(
3 - 5 boxes)
Interpretation?
0.12 seconds
Slide46Step 5: QRS duration
Normal:
0.0
6
- 0.12 seconds.
(1 - 3 boxes)
Interpretation?
0.08 seconds
Slide47Axis refers to the mean QRS axis (or vector) during ventricular depolarization. As you recall when the ventricles depolarize (in a normal heart) the direction of current flows leftward and downward because most of the ventricular mass is in the left ventricle. We like to know the QRS axis because an abnormal axis can suggest disease such as pulmonary hypertension from a pulmonary embolism.
Step 6:Determine QRS AXIS
Slide48Step
6:Determine QRS AXIS
The
normal QRS axis
lies
between
-30
o
and
+90
o
.
0
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
A QRS axis that between
-30
o
and
-90
o
is
abnormal and called
left axis deviation
.
A QRS axis that falls between
+90
o
and
+150
o
is abnormal and called
right axis deviation.
A QRS axis that falls between
+150
o
and
-90
o
is
abnormal and called
superior right axis deviation.
Slide490
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
I
II
avF
avL
avR
Limb leads
I = +0
o
II = +60
o
III = +120
o
Augmented leads
avL
= -30
o
avF
= +90
o
avR
= -150
o
I
II
III
Slide500
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
0
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
Now using what you just learned fill in the following table. For example, if the QRS is positive in lead I and negative in lead
avf
what is the QRS axis? (normal, left, right or right superior axis deviation)
QRS Complexes
I
Axis
I
avf
+ +
+ -
normal
left axis deviation
avf
Slide510
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
0
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
… if the QRS is negative in lead I and positive in lead II what is the QRS axis? (normal, left, right or right superior axis deviation)
QRS Complexes
I
Axis
I
avf
+ +
+ -
- +
normal
left axis deviation
right axis deviation
avf
Slide520
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
… if the QRS is negative in lead I and negative in lead II what is the QRS axis? (normal, left, right or right superior axis deviation)
QRS Complexes
I
Axis
I
avf
+ +
+ -
- +
- -
normal
left axis deviation
right axis deviation
right superior axis deviation
0
o
30
o
-30
o
60
o
-60
o
-90
o
-120
o
90
o
120
o
150
o
180
o
-150
o
Avf
Slide53NSR Parameters
Rate 60 - 100
bpm
Regularity regular
P waves
normal
PR interval 0.12 - 0.20 s
QRS duration
0.06
- 0.12 s
Any deviation from above is sinus tachycardia, sinus
bradycardia
or an arrhythmia
Slide54The 12-Lead ECG
The 12-Lead ECG sees the heart from 12 different views.
Therefore, the 12-Lead ECG helps you see what is happening in different portions of the heart.
The rhythm strip is only 1 of these 12 views.
Slide55The 12-Leads
The 12-leads include:
3 Limb leads (I, II, III)
3 Augmented leads (
aVR
,
aVL
,
aVF
)
6 Precordial leads (V
1
- V
6
)
Slide56Views of the Heart
Some leads get a good view of the:
Anterior portion of the heart
Lateral portion of the heart
Inferior portion of the heart
Slide57ECG Changes & the Evolving MI
There are two distinct patterns of ECG change depending if the infarction is:
ST Elevation
(Transmural or
Q-wave),
or
Non-ST Elevation
(Subendocardial
or non-Q-wave)
Non-ST Elevation
ST Elevation
Slide58ST Elevation and non-ST Elevation
MI
When myocardial blood supply is abruptly reduced or cut off to a region of the heart, a sequence of injurious events occur beginning with
ischemia
(inadequate tissue perfusion), followed by
necrosis
(infarction), and eventual
fibrosis
(scarring) if the blood supply isn't restored in an appropriate period of time.
The ECG changes over time with each of these events…
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ECG Changes : Ischemia
T-wave inversion
ST
segment depression
T wave flattening
Baseline
Slide60ST Elevation
One way to diagnose an acute MI is to
look
for elevation of the ST segment.
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ECG Changes: Injury
ST segment elevation of greater than 1mm in at least 2 contiguous leads
Heightened or peaked T waves
Baseline
Slide62ST Elevation Infarction
ST depression, peaked
T-waves, then
T-wave inversion
The ECG changes seen with a ST elevation infarction are:
Before
injury
Normal ECG
ST
elevation
& appearance of Q-waves
ST segments and T-waves return to normal, but Q-waves persist
Ischemia
Infarction
Fibrosis
Slide63Non-ST Elevation Infarction
ST depression & T-wave inversion
The ECG changes seen
witah
a non-ST elevation infarction are:
Before injury
Normal ECG
ST depression & T-wave inversion
ST returns to baseline, but T-wave inversion persists
Ischemia
Infarction
Fibrosis
Slide64ECG Changes
Ways the ECG can change include:
Appearance of pathologic Q-waves
ST elevation & depression
T-waves
peaked flattened inverted
Slide65ECG 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
Slide6666
A Normal 12 Lead ECG
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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
2
nd
Degree Type2
Complete Heart Block
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Anterior MI
Slide69ECG- Inferior
Blue indicates leads
II, III, AVF
Inferior Infarct with ST elevations
Right Coronary Artery (RCA)
1
st
degree Heart Block
2
nd
degree Type 1, 2
3
rd
degree Block
Brady
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Inferior MI
Slide71Right Sided EKG????
RVI occurs around 40% in inferior MI’s
Significance
Larger area of infarct
Both ventricles
Different treatment
Right leads “look” directly at Right Ventricle and can show ST elevations in leads II. III. AVF, V4R , V5R and V6R
Occlusion in RCA and proximal enough to involve the RV
The single most accurate tool used in measuring RVI.
90% sensitive and specific
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Lateral
Red indicates leads
I, AVL, V5, V6
Lateral Infarct with ST elevations
Left Circumflex Artery
Rarely by itself
Usually in combo
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Lateral MI
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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
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Posterior MI
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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
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SubEndo MI
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More than one color shows abnormality
A combination of infarcts such as:
Anterolateral yellow and red
Inferoposterior blue and green
Anteroseptal yellow and green
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Putting it ALL together
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Slide81Slide82Patients
with the following symptoms and signs require immediate assessment for the initiation of the ACS protocol:
• Chest pain or severe
epigastric
pain, non-traumatic in origin, with components typical of myocardial ischemia or AMI:
• Central/
substernal
compression or crushing chest pain;
• Pressure, tightness, heaviness, cramping, burning, aching sensation;
• Unexplained indigestion, belching,
epigastric
pain;• Pain in neck, jaw, shoulders, back, or 1 or both arms;• Associated dyspnea;• Associated nausea and/or vomiting;
• Associated diaphoresis;
If these symptoms are present, obtain vital signs and a stat ECG and transmit immediately to physician on-call.
Slide83The triage nurse should take a brief, targeted, initial history with an assessment of current or past history of:
• Coronary artery bypass graft (CABG), PCI, Coronary Artery Disease (CAD), angina on effort, or MI;
• Nitroglycerin use to relieve chest discomfort;
• Risk factors, including smoking, hyperlipidemia, hypertension, diabetes mellitus, family history of CAD, and cocaine or methamphetamine use;
• Arrhythmia history should include utilization of permanent pacemaker or implantable
cardioverter
-defibrillator;
• Regular and recent medication use.
Slide84Immediate General Treatments and Interventions
The treatment of a patient with chest pain should focus on a rapid assessment, stabilization, diagnosis and if needed reperfusion therapy. Upon arrival to the nursing station, the patient should be connected to continuous cardiac monitoring. Initial physical assessment and a 12-lead ECG should be done within 10 minutes of patient’s arrival to the nursing station. Upon acquisition, all ECGs must be transmitted to the physician on-call for immediate interpretation.
Slide85Special Considerations
•
Patients with diabetes may have atypical presentations due to autonomic dysfunction.
• Elderly patients may have atypical symptoms such as generalized weakness, stroke, syncope, or a change in mental status.
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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
Drawings
by Jill Gregory, Medical Illustrator, CGEY