Basic Principles of the
Cardiovascular System
Patient Care Techncian
Objectives
– Describe the structures of the heart.
– Explain the pumping mechanism of the heart
and the path of blood flow through the heart.
– Distinguish between pulmonary circulation
and systemic circulation.
– List the components of the conduction system
and the sequence of impulse origination.
– State four properties of cardiac cells.
Anatomy of the Heart
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4 chambered pump
Weighs less than 1 pound
Size of closed fist
Located in mediastinum – between lungs,
sternum, spine
Chambers
Valves
Question
• The right side of the heart pumps just as
much blood as the left side – why are the
walls of the right side thinner than those of
the left?
Where are these valves?
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Tricuspid valve
Mitral valve
Pulmonary semilunar valve
Aortic valve
Chordae tendoneae
Heart Layers
Heart Layers
• Endocardium – layer of smooth cells that
line heart
• Myocardium – layer of muscle that cause
contraction (myocardial infarction)
• Epicardium – fatty layer that protects heart
• Pericardial sac – holds heart in place,
reduces friction of beat
Circulation
• Pulmonary
• Systemic
• Coronary
Pulmonary Circulation
Pulmonary Circulation
Systemic Circulation
Coronary Circulation
Coronary Circulation
Coronary Circulation
• Anterior (A) and posterior
(B) views of epicardial
coronary circulation. LAD
indicates left anterior
descending coronary
artery; AIV, anterior
interventricular vein; CFX,
circumflex coronary artery;
RCA, right coronary artery;
GCV, great cardiac vein;
PDA, posterior descending
artery; CS, coronary
sinus; MCV, middle
coronary vein; and SCV,
small coronary vein.
Question
• Where and when do coronary arteries fill?
Coronary Sinus
Blood Vessels
• Define the following:
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Artery
Arteriole
Vein
Venule
Capillary
Aorta
Vena Cava
Pulmonary artery
Pulmonary vein
Question
• What vessels, structures and/or organs
are included in each type of circulation?
Question
• Show the path of a drop of blood from the
right atrium back to the right atrium.
– Be sure to include major vessels, organs, and
valves.
Cardiac cycle
• Series of events that constitute complete
heartbeat
– Atrial systole - Contraction of atria to pump blood to
ventricles
– Ventricle systole – contraction of ventricles to pump
blood to body
– Atrial diastole – the atria begin refilling during
ventricular systole
– Ventricular diastole – blood from the atria begins
refilling the ventricles during atrial systole.
Conduction Pathways
• Network of conducting tissue
• Specialized cells – do not contract
• Initiates each heartbeat and controls
rhythm
Sinoatrial Node
• Located in right atrium
• Main cardiac pacemaker
• Normally generates impulses at rate of 60
to 100 beats per minute
Atrioventricular Node
• Receives impulse via internodal pathways
• Located in floor of atrium near septum
• Delay the impulse to allow ventricular
filling
• Intrinsic rate 40 to 60
• Two basic functions
– Protect ventricles from fast heart rate that may
originate in atrium
– Serves as pacemakers if SA node fails
AV Bundle or Bundle of His
• Conducts impulse from AV Node
• Divides into right and left bundle branches
at intraventicular septum
– Right bundle branch supplies right ventricle
– Left bundle branch splits
• Anterior supplies upper portion of left ventricle
• Posterior supplies lower portion of left ventricle
Purkinje Fibers
• Enlarged fibers
• Spread along septum toward apex and
over lateral walls of ventricles
• Work with Bundle of His and bundle
branches to contract ventricles
• Intrinsic rate 20 to 40
• May act as backup pacemaker
Cardiac Electrical System
Cool Website!
• http://science.howstuffworks.com/environ
mental/life/human-biology/heart4.htm
Special Properties of Cardiac Cells
• Automaticity – ability to generate own
impulse and maintain rhythmic activity
• Excitability – ability of all heart cells to
respond to impulse
• Conductivity – cardiac cell able to relay
impulse to neighboring cells and create
wave of excitation
• Contractility – ability to respond to
electrical impulse with pumping action
Two Types of Cardiac Cells
• Capable of contraction
• Capable of conduction
Contraction of the Heart
• Cell membrane must be electrically
activated
• Depolarization - Positive ions move into
cell and negative ions move out of cell
• Repolarization – negative ions return to
inside of cell and positive ions move out of
cell
• This movement of ions is recorded by
EKG
Cardiac Terminology
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Systole
Electrical Cycle Depolarization
Mechanical
Cycle
Diastole
Repolarization
Activation
Recovery
Excitation
Recovery
Contraction
Relaxation
Emptying
Filling
Shortening
Lengthening
EKG Representation of Heartbeat
The Normal
Electrocardiogram
Objectives
• Explain how electrical current in the heart is
generated
• Differentiate between EKG waves, segments,
intervals, and complexes
• Describe how the movement of electricity
through the heart produces predictable wave
patterns
• Describe the method of detection and recording
of these wave patterns by the EKG machine
Detection and Recording
• Transmembrane potential – electrical difference
between the inside and outside of the cell
• Action potential – changes that occur during the
process of depolarization and repolarization
within a cell as activated by electrical impulse
• Refractory period – time during which the cell is
unable to respond to a stimulus
• Vector – path of impulse displaying the direction
and magnitude of the electrical current
Normal Heart
• Vector proceeds in same sequence
• Vector is predictable
EKG machine
• Writing arm
• Recording device (galvanometer)
– Stylus needle responds by heat or pressure
• Lead wires
– Attaches electrodes to machine
• Electrodes
– Provides direct contact with skin
EKG
• Tracing of electrical voltage produced by
continual depolarization and repolarization
of heart
• Shows direction and magnitude of
electrical current produced by the heart
Waves
Deflections from the baseline
Designated as: P, QRS, T
Waves
• P wave – depolarization of atria
• Q wave – (may be absent) activation in
intraventicular septum, first negative deflection
of QRS
• R wave – impulse progression through right and
left ventricles, first upward deflection of QRS
• S wave – completion of left ventricular activation
• T wave – repolarization of ventricles
Waves
Segments
• Straight lines or spaces between waves
• ST segment
– Measured from end of S wave to beginning of T wave
– 0.35 to 0.45 seconds
– Isoelectric (flat)
Segments
Intervals
• Consists of wave and a connecting straight line
• P-R Interval - measured from onset of P wave to
beginning of QRS
– Normal 0.12 to 0.20 seconds
• QT Interval - measured from start of Q to end of T wave
Intervals
Complexes
• Groups of related recorded waves
• QRS complex
– Represents depolarization or contraction of
the ventricles
– Normal length 0.04 to 0.10
Complexes
Explanation of EKG paper
Measuring Time
Normal cycle 0.8 seconds
Heart Rate Calculation #1
• Count the number of large squares between R
waves and divide into 300
Heart Rate Calculation #2
• Count number of large blocks between R
waves
Heart Rate Calculation #3
• Count number of small squares between r
waves and divide that number into 1500
• Most accurate method but can only be
used for regular rhythms.
Heart Rate Calculation #4
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Get 6 second strip
Count number of complete complexes
Multiply by 10 (6 x 10 = 60 seconds or 1 minute)
Special Note: Only method that can be used for
irregular rhythm
Normal Rhythm Identification
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All P waves appear like all other P waves
QRS complexes resemble each other
P-R intervals are constant
P-P intervals are constant
R-R intervals are constant
P before every QRS
Rate is between 60 to 100 beats per
minute
Normal Sinus Rhythm
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Regular
P before every QRS, every complex looks the same
P-R int. = 0.20
QRS = 0.10
Rate = approx. 75
Five Step Method
• Step 1 evaluates the speed of the rhythm to determine if it is normal,
too slow or too fast. A speed between 60-100 maintains the best
hemodynamic stability. Rates less than 60 or greater than 100, can
lead to hemodynamic instability and become symptomatic.
• Step 2 asks if the rhythm is regular. Rhythms originating from the
normal pacemakers in the heart will be regular. Irregular rhythms
indicate extra beats or abnormal rhythms.
• Step 3 assesses the shape of the complex. A narrow complex is
normal. A wide complex indicates conduction abnormalities.
• Step 4 asks if a P-wave precedes the QRS complex. This
represents normal conduction from the atria to the ventricles. If the
P-wave is absent, the impulse is being generated from elsewhere in
the heart.
• Step 5 assesses whether all the complexes look the same. Normal
conduction follows the same pathway with each beat. Different
looking complexes indicate the some impulses are following
alternative or aberrant pathways.
Abnormal rhythms – Sinus
Bradycardia
• Less than 60 beats per minutes
• May be normal in athletes
• Other aspects of EKG normal
Abnormal Rhythms - Tachycardia
• Over 100 beats per minute
• May be caused by exercise or fever
• Other aspects of EKG are normal
Neat Websites
• http://highered.mcgrawhill.com/sites/0073520713/student_view0/
chapter29/ecg_rhythm_exercises1/basic_
ecg_anatomy/rhythm_strip_quiz_1.html
• http://www.mauvila.com/ECG/ecg.htm
• http://www.ems1.com/columnists/EKG/arti
cles/311340-Case-4-The-Pseudo-Normal/
Lead Systems
Objectives
• Describe the purpose of an EKG lead
• Differentiate between unipolar and bipolar
leads
• Describe the orientation of all 12 leads
• Explain chest and limb lead placement
Leads
• Each lead views the heart at a unique
angle
• Each lead has a positive and a negative
pole – measures the electrical difference
between the poles
Limb Leads
• Placed on arms and legs
• Reflect impulses moving in vertical or
frontal plane
• Six leads: I, II, III, AVR, AVL, AVF
Remember
• Right and left refers to the patient’s right
and left
Limb Lead Placement
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RA right arm between elbow and shoulder
LA left arm between elbow and shoulder
RL right leg a few inches above ankle
LL left leg a few inches above ankle
– Alternate placement for leg leads
upper legs as close to torso as possible
Chest Leads
• Demonstrate forces moving anteriorly and
posterior in a tranverse plane
Precordial Lead Placement
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V1 – right sternal border at 4th intercostal space
V2 – left sternal border at 4th intercostal space
V3 – Midway between 2nd and 4th V leads
V4 – 5th intercostal space straight down from
midclavicular notch
• V5 – at anterior axillary line at same horizontal
level as V4
• V6 – at midaxillary line on the same horizontal
level as V4 and V5
Overview by Lead
Identifying Rhythms
Objectives
• Identify normal sinus rhythm.
• Differentiate between various sinus
rhythms
• Identify and distinguish each atrial
dysrhythmia
• Compare and contrast atrial and
ventricular dysrhythmias
Clinical Significance of EKG’s
• PCT must recognize abnormal patterns
and alert MD
Sinus Rhythms
• Rhythms beginning in the SA node
• Characteristics
– 1:1 relationship between P and QRS
– P, QRS, T are in order and consistent in
configuration
– P-R interval is within 0.12 to 0.20 seconds
– QRS interval is within 0.04 to 0.10
– Heart rate is 60 to 100
– P-R, P-P, R-R intervals are regular
Terminology Question
• What’s the difference?
– Arrhythmia
– Dysrhythmia
Dysrhythmias Occur When
• Disturbance in automaticity – rate to slow
or too fast
• Disturbance in conductivity – site of
impulse formation is not in SA node
• Combination of altered automaticity and
conductivity – impulse conduction is
abnormal
Sinus Tachycardia
• Impulse formation faster than normal
• Rate is 100-160 beats per minute
• Faster than normal but not fast enough to decrease
cardiac output
• Causes: exercise, fever, anxiety, hypovolemia
(decreased fluid volume)
• Same characteristics as Normal Sinus Rhythm except
rate
Sinus Bradycardia
• Rate is 30 to 60 beats per minute
• Slow rate can decrease cardiac output
• Can be caused by vomiting, tracheal suctioning,
valsalva maneuver, drug side effects
Sinus Arrhythmia
• Impulses originate in SA node but speed up with
inspiration and slow with expiration
• P-P and R-R intervals vary
Sinus Arrest or Pause
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Potentially lethal
SA Node fails
Beats dropped but bets that do occur appear normal
Sudden decrease in cardiac output can cause dizziness,
syncope or angina
• Patient may need permanent pacemaker
Atrial Arrhythmias
• Abnormal electrical activity occurring in the
atria before the sinus impulse can occur
Premature Atrial Contractions
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Early firing from ectopic focus in the atria
Appear earlier than normal in cycle
Have abnormal P wave and abnormal P-R
QRS usually normal
May be caused by alcohol, caffeine, nicotine, low
potassium, heart or lung disease
Arial Tachycardia
• Heart rate is 150 to 200
• P wave may be abnormal or hidden in preceding
T wave
• Decreased cardiac output due to rate and
increased oxygen demand
Atrial Fibrillation
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Possibly lethal
No P waves, P-R can’t be measured
QRS normal but R-R irregular
Causes: underlying heart disease
May be chronic
Danger of clots (pulmonary or cerebral) – patient may be on blood
thinner to prevent
Atrial Flutter
• Ectopic atrial focus takes over - generates impulse faster than SA
node
• Multiple P waves in sawtooth pattern
• QRS normal
• Atrial rate 250 to 350, regular
• Ventricular rate varies but is regular
• AV node blocks some impulses
Junctional Rhythms
• Impulses originating from ectopic focus in
AV node region – fire earlier than SA node
• P wave is negative and may occur before,
during, or after the QRS
• P-R may be shortened or not measurable
• QRS usually normal
• May predispose heart to more serious
dysrhythmias
Junctional Rhythm
Ventricular Rhythms
• Impulse originates from an ectopic in the bundle
branches, Purkinje fibers, or ventricular muscle
before SA node
• Beat caused by this impulse does not produce
adequate cardiac output
• P wave is absent – no P-R interval
• ORS is premature, wide, bizarre
• May be caused by hypoxemia, stress, electrolyte
imbalance, caffeine, nicotine, alcohol,
medication toxicity, myocardial infarction
• MAY BE NORMAL FOR PATIENT
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Unifocal
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Multifocal
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Couplet
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Salvo or triplet
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Bigemeny
Premature Ventricular Contractions
• Wide, bizarre complex which occurs early
• Example: Trigeminy
R-on-T
• Occurs when R of PVC falls on T of preceeding
beat
• Heart vulnerable to electrical stimulation
• Usually does not produce a sustained ventricular
dysrhythmia
Ventricular Tachycardia
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Three ectopic ventricular beats
Rate 100 to 250 per minute, regular
Possible lethal arrhythmia
No P waves, no P-R
QRS consecutive, wide, bizarre
Decreased or NO cardiac output
Will deteriorate into V Fib if not treated
Ventricular Fibrillation
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CHECK LEADS!!!!!
Ventricular rhythm is chaotic
Results from multiple ectopic foci in ventricles
Ventricles quiver instead of contracting – NO CARDIAC
OUTPUT
• Will deteriorate into asystole
Agonal
• Wide bizarre complexes from multiple ventricular
pacemakers
Asystole
• CHECK LEADS
• No electrical activity
S-T elevation
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Rhythm - Regular
Rate - varies
QRS Duration - Normal
P Wave - Normal
S-T Element does not go isoelectric which indicates
infarction
A-V Block – First Degree
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Caused by a conduction delay through the AV node but all electrical signals
reach the ventricles
Rarely causes any problems by itself – may be seen in athletes
Rhythm - Regular
Rate - Normal
QRS Duration - Normal
P Wave - Ratio 1:1
P Wave rate - Normal
P-R Interval - Prolonged (>5 small squares)
A-V Block – Second Degree Type I
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Also called Wenckebach
Conduction block of some, but not all atrial beats getting through to the ventricles
Progressive lengthening of the PR interval and then failure of conduction of an atrial
beat, this is seen by a dropped QRS complex.
Rhythm - Regularly irregular
Rate - Normal or Slow
QRS Duration - Normal
P Wave - Ratio 1:1 for 2,3 or 4 cycles then 1:0.
P Wave rate - Normal but faster than QRS rate
P-R Interval - Progressive lengthening of P-R interval until a QRS complex is dropped
A-V Block – Second Degree Type II
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Electrical excitation sometimes fails to pass through the A-V node or bundle of His
Constant P-R interval but not regularly followed by ventricular contraction
Rhythm - Regular
Rate - Normal or Slow
QRS Duration - Prolonged
P Wave - Ratio 2:1, 3:1
P Wave rate - Normal but faster than QRS rate
P-R Interval - Normal or prolonged but constant
A-V Block – Third Degree
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Atrial contractions are 'normal' but no electrical conduction is conveyed to the ventricles.
Ventricles then generate their own signal through an 'escape mechanism' from a focus
somewhere within the ventricle.
Ventricular escape beats are usually 'slow'
Rhythm – Regular P and Regular QRS but they are not related!
Rate - Slow
QRS Duration - Prolonged
P Wave - Unrelated
P Wave rate - Normal but faster than QRS rate
P-R Interval - Variation
Paced Rhythms
Acquiring the EKG
Objectives
• Demonstrate correct use of EKG equipment
• Perform simple maintenance and
troubleshooting
• Perform accurate, diagnostic EKGs
• Explain effects of patient position
• Understand concept of electrical conduction
through the skin
• Demonstrate proper skin prep and lead
placement
• Recognize artifact and practice artifact
prevention
Equipment
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Modern machines are multichannel
Can transmit EKG via telephone lines
Machine may store EKGs
Has 10 lead wires
Always follow manufacturers directions for
use, cleaning, storage
Other considerations
• Drape lead wires over machine – do not
fold or tie
• Inspect lead wires for breaks/frays
• Do not put food or liquids on cart
• Do not put anything on screen
• Be sure machine stays plugged in when
not in use
• Store electrodes properly – gel can dry out
Question
• What are beginning actions for any
procedure?
Patient Preparation
• Check physician order or be familiar with
protocol
• Check patient ID with two identifiers
• Wash hands
• Explain procedure
• Provide privacy
Patient Position
• Place patient in supine position
• Patient may be at 45 degree angle if short
of breath
• Have patient uncross legs
Skin Preparation
• Electrode contact with skin important
• May have to wash dirty/scaly skin –
– Epidermis is poor conductor
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Chest hair should be shaved
Use alcohol to remove skin oils
Wipe excess perspiration with 4 x 4
Apply pressure to edges of electrode – not
center
Recognizing Artifact
• Extraneous electrical activity
• Can be reduced by having patient touch
only the mattress – not bed rails
• Keep patient quiet and calm
• Keep patient warm
• Position electrodes high on extremities if
patient has tremor
• Be sure all leads are attached
Wandering Baseline
60 cycle interference
Patient Movement
BE SURE THAT YOU ARE
TREATING THE RHYTHM NOT THE ARTIFACT!
Special Situations
• Dextrocardia – reverse precordial leads
• Large breasts – do NOT place electrodes on top
of breast
• Bilateral breast implants you should apply V4,
V5, and V6 close to the midaxillary line.
• Note patient abnormalities on EKG
• Do not place electrodes on open wounds,
burns, or clear dressings
• Do not allow electrodes to touch one another