Zabrina Bellina
University of Central Florida
Teaching With Technology Project
At the conclusion of this presentation,
students will able to:
1. Describe coronary circulation and gain
working knowledge of blood supply to
heart structures.
2. Define the term electrocardiography and
describe the electrical conduction system
of the heart.
3. Correlate electrical events in the heart with
the waveform represented in a normal EKG.
3. Gain understanding of EKG interpretation
through waveform measurement, analysis,
and correct rate computation of rhythm
strips.
4. Understand and identify lethal cardiac
arrhythmia waveforms.
Figure 1
Superior & Inferior Vena Cava
Right Atrium
Tricuspid Valve
Right Ventricle
Pulmonary Semi-lunar Valve
Pulmonary Trunk
Right & Left Pulmonary Arteries
Lungs
Pulmonary Veins
Left Atrium
Mitral Valve
Left Ventricle
Aortic Semi-lunar Valve
Aorta
Body
supplies blood to:
Right Atrium
Right Ventricle
the SA Node in 55% of population the LV
inferior wall
the LV posterior wall and ⅓ of the
posterior interventricular septum in 90%
of the population
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
supplies blood to:
the LV anterior and lateral walls
the Left and Right Bundle Branches
the anterior ⅔ of the interventricular
septum
Remember:
The Right Coronary Artery supplies both
the Right and Left heart.
The Left Coronary Artery and its
branches only supply the Left heart.
An electrocardiogram (ECG) , also known as
an EKG, is a graphic recording of the electrical
activity of the heart. It is used as a diagnostic
tool to assess cardiac function.
An EKG is a painless procedure that can be
performed by placing disposable electrodes on
the skin of a person’s chest wall, upper and lower
extremities.
Figure 2
Figure 3
An EKG can be recorded with 12, 15, and
sometimes even 18 leads. However, the
12 lead EKG is the most commonly used
tool to diagnose cardiac conduction
abnormalities, arrhythmias, myocardial
infarction and ischemia.
Remember,
an EKG represents the electrical
impulses that the heart transmits
and are recorded as tracings on
specialized graph paper.
The Conduction System of the Heart
Figure 4
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
Let’s look at a normal conduction pathway:
SA Node
Myocardial
Contraction
AV Node
Purkinje Fibers
Bundle of His
Right and Left
Bundle
Branches
Myocardial Cells = the mechanical cells of the
heart. They contract when they receive an
electrical impulse from the pacemaker cells.
Myocardial = Muscle (Brawn)
Pacemaker Cells are very small cells
within the conduction system which
spontaneously generate electrical
impulses.
Pacemaker = Power Source (Brain)
Electrical Conducting Cells rapidly carry
current to all areas of the heart.
Conducting Cells = Hard Wiring of Heart
(Fuel)
Now, let’s correlate the mechanical activity with the
electrical activity….
Ventricular Systole
Atrial
Systole
Ventricles
repolarize
Atria
depolarize
Figure 5
Ventricles
depolarize
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 EKG,
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).
The PR interval on an EKG reflects conduction
of an electrical impulse from the SA node
through the AV node.
PR = 0.12 – 0.20 seconds
Figure 6
The QRS complex of an EKG 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
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 EKG reflects
ventricular muscle repolarization
(when the cells regain a negative
charge - the “resting state”) and
mechanical relaxation, which is also
known as diastole.
Keep in mind how electricity flows…
When an electrical current moves toward a
positive electrode, the deflection on the EKG
strip will be positive (up).
When an electrical current moves toward a
negative electrode, the deflection on the
EKG strip will be negative(down).
ST Segment Changes
Any elevation in the ST segment that
is greater than two small boxes is
indicative of myocardial injury.
Any ST segment depression greater
than two small boxes indicates
myocardial ischemia.
EKG paper comes in a roll of graph paper
consisting of horizontal and vertical light and
dark lines.
The horizontal axis measures time
Figure 7
The vertical axis measures voltage
One small square = 0.04 seconds
One large square = 0.2 seconds
or
One small square(0.04) x 5
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
Rhythm
Rate
P - waves
PR Interval
QRS Complex
Rate
What’s the normal heart rate for an
adult human being?
60 – 100 beats/ minute
Is the rate in your strip too fast or too
slow?
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.
.
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).
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.
Rules
1. Count the number of QRS’s in a 6 - second
strip, then multiply that number by 10.
2. 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
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
Figure 8
Let’s Practice with an Example:
Figure 9
What is the rate based on Rule #1?
If you said 50 bpm….
You are Correct!!!
 Are the P waves regular or irregular?

Are the R-to-R intervals regular or
irregular?
Are
there P-waves in your rhythm strip?
Is there a P-wave for each QRS
complex?
Do all of the P-waves look the same?
Is
the PR Interval measurement normal?
PR = 0.12 – 0.20 seconds
Is the PR Interval measurement constant?
Is the QRS wide? > 0.10
Is it normal?
QRS = 0.08 – 0.10 seconds
Or is it narrow? < 0.08
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?
Let’s try an example…..
Figure 10
1. Is the rhythm regular or irregular? Regular
2. Are the P-waves identical? Is there a P-wave for
each QRS complex? Yes for both!
3. Is the PR Interval 0.12 – 0.20? Yes, PR = 0.16
4. Is the QRS wide, normal or narrow?
Normal QRS = 0.08
5. Is the T-wave peaked, inverted or flat? No, it’s
normal
6. Is the ST segment elevated or depressed? No
7. Is the QT Interval < 0.43? Yes, QT Interval= 0.36
And last but not least, is there any
ectopy present in this rhythm?
NO!
And the rhythm is….
Normal Sinus Rhythm
Listed below are the cardiac arrhythmias that
are almost always associated with death:
Atrial Fibrillation
Atrial Flutter
Ventricular Fibrillation
Ventricular Tachycardia
3rd degree AV Block
Asystole
Atrial Fibrillation
Figure 11
Rhythm: Atrial fibrillation is irregular and chaotic;
Ventricular rhythm is very irregular
Rate: Atrial is > 350 bpm; Ventricular is 120-200 bpm
P-waves: not consistent (they are fine and fibrillating)
PR Interval: not measurable
Atrial Flutter
Figure 12
Rhythm: Atrial flutter is usually regular
Rate: Atrial is 250-350 bpm
Ventricular rate depends on AV
conduction
P-waves: characterized by “saw tooth” pattern
PR Interval: can not be determined; more flutter
waves than QRS complexes
Ventricular Fibrillation
Figure 13
Rhythm: Totally erratic
VF Rate: 350-450 bpm
P-waves: none
QRS: none
Ventricular Tachycardia
Figure 14
aka “The Widow-Maker”
Rhythm: Typically regular, but can be irregular
Rate: 100 – 220 bpm
P-waves: can be present but have no correlation to QRS
complex
QRS: > 0.12 seconds with an odd, “tomb –stone” shape
3rd Degree AV Block = Complete Heart Block
Figure 15
Rate: 40-60 bpm (narrow QRS and junctional);
20-40 bpm (wide QRS and ventricular)
P-waves: normal, but usually more P-waves than
QRS’s
Asystole
Figure 16
In Asystole, there is no rate because the
person that belongs to this rhythm is
DEAD!
Figure 1. (2009). Image retrieved on February 17, 2009 from
http://images.google.com/imgres?imgurl=http://www.micardia.c
om/images/anatomy-of-the-humanheart.jpg&imgrefurl=http://www.micardia.com/CHF-CongestiveHeart-Failure/Structural-heart-disease-and-mitralprolapses.php&usg=__vAFkAZBOMi2yoKCxSP0R39jzRQE=&h=324
&w=250&sz=48&hl=en&start=288&um=1&tbnid=zVIu6UfvBIh2M:&tbnh=118&tbnw=91&prev=/images%3Fq%3Dblood%2Bflo
w%2Bthrough%2Bheart%26ndsp%3D18%26hl%3Den%26sa%3DN
%26start%3D270%26um%3D1
Figure 2. (2008). Image retrieved on February 15, 2009 from
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AAJA/7KNEAG5TcIY/s1600-h/limb+leads.jpg
Figure 3. (2008). Image retrieved on February 15, 2009 from
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=A39
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Figure 14. (n.d.). Image retrieved on March 1, 2009 from
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Figure 15. (2005). Image retrieved on March 1, 2009 from
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Figure 16. (2006). Image retrieved on march 1, 2009 from
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The End !!!
Kathy