1. health and fitness
2. disease
3. heart disease

12 Lead EKG and
Acute Myocardial Infarction:
A Guide for Nurses
Amy Bertram RN, BSN, PCCN
Fairview Southdale Hospital
Heart Center
Objectives
1) Correlate the coronary artery
anatomy to specific EKG leads
used in diagnosing myocardial
ischemia and infarction
2) Recognize the 12-Lead EKG
patterns
tt
off myocardial
di l iischemia,
h i
injury, and infarction
The 12 Lead EKG
is a display of the electrical
activity of the heart
recorded on the body’s
body s
surface…
It is an Art not a Science!
The 1212-Lead EKG mostly reflects the
electrical activity of the larger
LEFT ventricle
Phalen, T. & Aehlert, B. (2006) The 12-Lead ECG in Acute Coronary Syndromes. (2nd Ed); page 2
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction. slide 8.
The Chambers of the Heart
ƒ Right Heart
ƒ Thin walled – low
pressure
ƒ SA and AV Nodes
ƒ Tricuspid Valve
ƒ Pulmonic Valve
The Chambers of the Heart
ƒ Left Heart
ƒ Thick walled
ƒ Mitral and Aortic
Valves
ƒ Septum
The majority of
Myocardial
Infarctions happen in
the LEFT
VENTRICLE
The Walls of the Heart
• Anterior Wall – Left
front
• Inferior
I f i Wall
W ll – Left
L ft
bottom
• Lateral Wall – Left
side
• Posterior Wall –
Back
The Coronary
y Arteries
Coronary = Crown
The coronary arteries
are formed off of the
aorta (around the top of
the heart) and forming a
“crown” which encircle
the outside of the heart
Right Coronary Artery (RCA)
• Supplies the SA node (55% of population)
• Supplies
S
li th
the AV node
d (90% off population)
l ti )
• Inferior and Posterior (90%) walls of LV
• also supplies:
pp
– Right ventricle: Put patients at risk for
bradycardia, AV block
Left Main Coronary Artery (LM)
• Often referred to as the “widow maker”
• If the left main coronary artery becomes
occluded, the entire left side of the heart
will die
• Left Main branches off into the following:
g
– Left Anterior Descending (LAD)
– Left Circumflex (Circ)
Left Anterior Descending (LAD)
• Comes off of Left Main Coronaryy Artery
y
• Supplies the Anterior Wall of the LV
• Travels in the inter-ventricular groove
• Blockages in LAD put patients at risk for
bundle branch blocks
blocks, heart failure
failure, and
ventricular tachycardias/dysrhythmias
Circumflex Artery (Circ)
• Comes off of Left Main Coronaryy
Artery
• Supplies SA node in 45% of
population
• Supplies Lateral Wall of the LV
• Also supplies the posterior wall of
the LV in 10% of the population
Branches of Coronary Arteries
• LAD b
branch
h
• Diagonal
• Circumflex branch
• Obtuse marginal
• Posterolateral
oste o ate a
• In some patients, there is a branch in-between
the LAD & Circ called the Ramus Intermedius
• “Dominance” refers to which artery feeds the
Posterior Descending Artery and Inferior Wall
– “Right
Right Dominant”
Dominant = RCA feeds inferior wall
• 85% of population
– “Left Dominant” = Circ feeds inferior wall
• 15% of population
The Layers of the Heart
Hea
Myocardium
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction.
Now let’s take a
brief look at the
electrical activation
of the heart…
An EKG complex is a recording of the cardiac cycle of
the heart—
heart—it is depicted by waveforms (deflections)
labeled with alphabetical letters
• In 1906 William Einthoven discovered the
first electrocardiogram (EKG) machine
Einthoven’s Principles
• Heart
H t is
i electrical
l t i l motive
ti fforce within
ithi
the center of the body
• Electrical potentials are produced by
cardiac muscle
• EKG senses and displays these
electrical forces
Method of the EKG
• Electrode: Conductor of electrical activity
applied to the skin
•Lead: Gives continuous recording
between any two electrodes or
between one electrode and
combination of the others
• made up of positive and negative
electrode
• the term “lead” is two-fold:
–The position of the electrode
–The
Th actual
t l ttracing
i obtained
bt i d
• Overall, the heart’s electrical activity always goes
i one di
in
direction
directionÆ
ti Æ from
f
the
th base
b
to
t the
th apex
• Focus on the summation of left
ventricular electrical activity seen from
the positive electrode (positive electrode
= camera)
• Where the camera is located will help us
“see”
see the walls of the left ventricle
A Standard EKG consists of recordings
from 12 Leads, therefore….
12 different leads = 12 different camera
angles
l = 12 diff
differentt views!
i
!
Today we will focus on the views
that reflect myocardial
»Ischemia
»Injury
»Infarction
I f
ti
But first we need to identify and describe
all 12 Leads…
Normal 12 Lead EKG
Limb Leads I, II, III (Einthoven’s Triangle)
Augmented Leads (aVR, aVL, aVF)
– Use
U same electrode
l
d llocations
i
as standard
d d EKG
– Lead aVR + electrode on right arm
– Lead aVL + electrode on left arm
– Lead aVF + electrode on left leg
Precordial Leads (Chest Leads V1V1-V6)
EKG Recording of Electrical Activity
y Lead
on Any
Arrow depicts direction of electrical force
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction.
Normal R
R--wave Progression
Recap
p
• 12 Lead EKG = 12 different
views of the heart
• Today we are focusing on
the views that reflect
myocardial ischemia
ischemia, injury
injury,
and infarction
For our purposes today, the 12 Lead EKG is
going to become a “3 Area EKG”
Heart
Lateral
Inferior
Lateral
Inferior
Inferior
Anterior
Anterior
Anterior
Lateral
Anterior
Petersen, DA. (2003) Myocardial Infarction Window. www.ekgtools.com
Lateral
Myocardial IschemiaÆ
IschemiaÆInjury
InjuryÆ
ÆInfarction
• 20+ years ago, medical staff focused on
patient after a big
g
treatment of a p
infarction….patients came to the ER with dead
heart muscle
• Now…the goal is to PREVENT myocardial
infarction byy EARLY TREATMENT OF
MYOCARDIAL ISCHEMIA
• MYOCARDIAL ISCHEMIA is a
DYNAMIC PROCESS!
Myocardial IschemiaÆ
IschemiaÆInfarction
• Happens
H
iin th
the LEFT ventricle
ti l
• Starts at the innermost layer and
moves outward
• Coronary arteries lie on outside of the
h t so th
heart
the endocardium
d
di
iis th
the llastt
layer to be nourished and the first to
be ischemic
Myocardial
y
Ischemia
Ischemia = a decreased supply of
oxygenated blood to a body part or organ
Represents HYPOXIC tissue
Is reversible (salvageable) if treated promptly
and aggressively by decreasing O2
demand and reperfusing
p
g the area
Ischemia
12 Lead
L d shows
h
inverted
i
t d (fli
(flipped)
d) T waves or ST
depression
T wave inversion is usually the very first change and
most common
ST depression may also be a reflection of infarction
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction.
Myocardial Injury
Represents SEVERE HYPOXEMIA (“Dying Muscle”)
–
–
–
–
Develops
p over time without intervention
Cell membranes become unstable
Spreads from endocardium to epicardium
Surrounded by ischemic tissue
Requires very aggressive treatment
–
–
–
–
Potentially salvageable
Emergency PTCA/Thrombectomy/Stent
Pain management
Hemodynamic manipulation
Injury
• 12 Lead shows ST Elevation
• Significant if > 1 mm in 2 or more
anatomically connected (contiguous) leads
• May also be seen
with an inverted T
wave
•“Tombstone”
Tombstone
configuration
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction.
How to measure the ST segment (“J” Point)
1
2
•Find the jjuncture of the ST segment
g
–1st arrow
•Move right one small box—2nd arrow ( “J” Point)
•Find the baseline (isoelectric line) of the rhythm
•Measure the height of the ST segment at the “J” point
from the baseline
Miller, J. (2007) Coronary Circulation – 12 Lead Link Understanding the 12 Lead ECG.
Myocardial
y
Infarction
Death of myocardial cells due to prolonged ischemia
Represents Necrotic Tissue (“Dead Muscle”)
Irreversible damage
• Cell membranes rupture/cell death
• Spreads from endocardium to epicardium
• Dead tissue cannot initiate or transmit an
i
impulse
l
Infarction
• Necrosis results in “Pathological” Q wave on EKG
– > 0.04 seconds in width
– depth must be at least 25% of the height of the
R wave
– Caused by an absence of depolarization
current in dead tissue
• The positive electrode over dead area sees
only electrical forces “going away” causing
negative deflection on EKG
• Indication of transmural MI—now called “Q
wave infarction”
Reciprocal Changes
• The same currents that produce ST segment
p
elevations over the infarcted area of the LV produce
mirror images (ST depression) in leads opposite
from the site of the acute MI
•
•
•
•
Anterior MI Æ Inferior reciprocal changes
Lateral MI Æ Inferior reciprocal changes
Inferior MI Æ Anterior and/or lateral reciprocal changes
Posterior MI Æ Anterior reciprocal changes
g
depression
p
is an indicator of reciprocal
p
ST segment
change when acute MI is seen elsewhere on the 12
Lead EKG
Full thickness damage =
Q-wave Myocardial
M
di l IInfarction
f ti (MI)
Q-wave (Transmural) infarction
– Also known as “transmural” MI
• endocardium
• myocardium
y
• epicardium
– Necrosis (dead muscle)
• Forms scar tissue
• results in electrical conduction
delay
• Manifests as p
pathological
g
Qwaves on the 12-Lead EKG
– Correlates with cardiac
enzyme
y
elevation
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction. Slide 13.
Partial thickness damage =
Non Q
Q--wave MI
Non-Q wave (Subendocardial) Infarction
– Also known as
“Subendocardial” MI
– Involves inner
(endocardial)
area of myocardium
– No abnormal Qwaves
on 12-Lead EKG
• Correlated with minimal
cardiac enzyme
elevation
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction. Slide 14.
Let’s Review…
•
•
•
•
Anatomyy and Physiology
y
gy of the Heart
Coronary Circulation
Walls of the Heart
Leads on the EKG are “camera” angles of
the different areas of the heart
• Patterns of Ischemia
Ischemia, Injury
Injury, Infarction and
types of MI
So how the heck do I actually
analyze a 12 Lead EKG for
MI???
Systematic Analysis of the 12 Lead EKG
• Always
y look at a 12 Lead EKG in the same
manner
• It is difficult to assess a 12 Lead in
isolation…therefore, always compare the 12
Lead EKG you are analyzing to the last 12
Lead EKG that was done
• Remember you are looking for
CHANGES
Determination of Infarction Æ What
changes should I see?
1 Look for ACUTE CHANGES of
1.
ST elevation and pathological Qwaves
2 Look for RECIPROCAL
2.
CHANGES of ST depression in
leads opposite the surfaces
undergoing injury
Anterior Wall MI
• Involves Left Coronary Artery
• Types of Anterior MIs
– Anterior or Anteroseptal = LAD
blockage = acute changes V1-V4
– Anterolateral = Circumflex blockage =
acute changes I, aVL, V5-V6
– Extensive Anterior = Left Main
bl k
blockage
= acute changes
h
V1
V1-V6,
V6 II,
aVL
Anterolateral / Extensive Anterior MI
#1
Inferior Wall MI
• Involves Right Coronary Artery
• Acute changes seen in leads II, III, aVF
• Reciprocal changes of ST depression in
anterior leads (I, aVL, V1-V6)
– Seen in about 75% of Inferior MIs
• Inferior Lateral MI usually involves occlusion
of Circumflex artery Æ acute changes see in
V5-V6 besides II, III, aVF
Inferior MI
#2
Lateral Wall MI
• Involves Circumflex Artery
• Acute changes seen in I, aVL, V5-V6
Posterior Wall MI
• Usually involves Right Coronary Artery
• Most often occurs with Inferior MI
• Normal 12 Lead doesn’t have leads reflecting
the back side of the LV Æ diagnosis must be
made with reciprocal changes in anterior leads
• ST elevation II, III, aVF, V6 with ST
depression in V1-V3 or V4
• Tall R waves in V1
V1-V2
V2
Inferior/Posterior MI
#3
Right Ventricular MI
• Usually occurs with inferior wall MI (incidence
25-40%)
• Consider possibility of RV infarction in any
patient with inferior wall MI
• Diagnosis
g
often made from clinical findings
g
–
–
–
–
Increased CVP or RA pressure
Neck vein distention
Decreased C
C.O.
O (low BP
BP, oliguria)
Minimal or absence of pulmonary congestion
63 y.o. female, cardiac arrest at Fairview Ridges ER, transported
to Fairview Southdale, cardiac arrest on arrival to cath lab
#4
63 y.o. female 12 Lead EKG post PCI
#5
32 y.o. male developed CP going out of the gym
10 minutes later…still at the gym with
Paramedics…
3rd EKG to confirm 2 minutes later…
37 y.o. female presents to Fairview Ridges ER with
chest burning/pressure
#6
after
ft drinking
d i ki h
her morning
i coffee
ff
After Coronary
y Intervention
#7
4 ½ hours after PCI, patient complained of 5/10
midsternal chest burning, tingling down both arms
#8
After 2nd time to Cath Lab and 3 more stents…
#9
Thank you
Shirley!
Questions….Stories to share?
Thank you for your
attention!
References
American
A
i
C
College
ll
off C
Cardiology
di l
&A
American
i
H
Heartt A
Association.
i ti
(2004)
(2004). M
Managementt off P
Patients
ti t with
ith A
Acute
t
Myocardial Infarction-Practice Guidelines. http://www.acc.org/clinical/guidelines
Conover, MB. (2003). Understanding Electrocardiography (8th ed). Mosby: St. Louis.
Hagen, S. (1994) 12 Lead ECG Interpretation: Patterns of Infarction.
Miller, J. (2007) Coronary Circulation – 12 Lead Link Understanding the 12
Lead ECG.
Petersen, DA. (2003) Myocardial Infarction Window. www.ekgtools.com
Phalen, T & Aehlert, B. (2006) The 12-Lead ECG in Acute Coronary
Syndromes (2nd ed). Mosby: St. Louis.