Download 2195Anatomy and Physiology of the Cardiovascular System

Anatomy and Physiology of
the Cardiovascular System
Prepared by
Miss Fatima Hirzallah
• The heart is a hollow, muscular organ
situated in the space between
lungs(mediastinum) , its about 12 cm in
length & about 9 cm in width
Cardiac Muscle
• Contract as a single unit
• Simultaneous contraction due to
depolarizing at the same time
•
Automaticity
• The heart is about the size of a clenched
fist and comprises.
• The heart composd of four layers:
• Endocardium,
• Myocardium,
• Epicardium,
• and the pericardium..
• endocardium is the inner layer and is consists
of endothelial tissue that lines the inner surface
of the heart and the cardiac valves.
• The myocardium is the middle layer and is
composed of muscle fibers that enable the heart
to pump.
• Epicardium is the outer layer, is tightly
adherent to the heart and the base of the great
vessels.
• A thin, fibrous, double-layered sac known as the
pericardium surrounds the heart.
• The outer layer is known as the parietal
pericardium
• and the inner layer is called the visceral
pericardium
• Between these two layers is a small amount of
pericardial fluid (30 to 50 mL) that serves as a
lubricant between the two layers
• The heart consists of four chambers:
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right and left atrium
right and left ventricles.
Heart valves
• The cardiac valves are composed of fibrous
tissue and allow blood to flow in one direction.
• The valves open and close as a result of blood
flow and pressure differences.
• The tricuspid and mitral valves are known as the
atrioventricular (AV) valves because they are
located between the atria and the ventricles.
• The pulmonic and aortic valves are known as
the semilunar valves because each has three
leaflets shaped like half-moons.
Circulation of the blood
• The blood passes through the tricuspid valve
into the right ventricle, which then pumps the
blood through the pulmonic valve into the
pulmonary circulation.
• After gas exchange in the lungs, oxygenated
blood returns to the left atrium, passes through
the mitral valve, enters the left ventricle, passes
through the aortic valve, and finally enters the
aorta
Coronary Arteries
• The left and right coronary arteries and their branches
supply arterial blood to the heart. These arteries
originate from the aorta just above the aortic valve
leaflets.
• The heart has large metabolic requirements, extracting
approximately 70% to 80% of the oxygen delivered
(other organs consume, on average, 25%).
The left coronary artery has three branches.
1-the artery from the point of origin to the first
major branch is called the left main coronary
artery.
two bifurcations arise off the left main coronary
artery
2- left anterior descending artery (LAD), which
courses down the anterior wall of the heart
3-circumflex artery, which circles around to the
lateral left wall of the heart.
• The right side of the heart is supplied by the
right coronary artery, which progresses around
to the bottom or inferior wall of the heart.
• The posterior wall of the heart receives its blood
supply by an additional branch from the right
coronary artery called the posterior
descending artery.
• The coronary arteries are perfused during
diastole. An increase in heart rate shortens
diastole and can decrease myocardial perfusion.
• Patients, particularly those with coronary artery
disease (CAD), can develop myocardial
ischemia (inadequate oxygen supply) when the
heart rate accelerates.
Cardiac Output
• Cardiac output is the amount of blood pumped
out of the ventricle .
• The cardiac output in a resting adult is about 5 L
per minute but varies greatly depending on the
metabolic needs of the body. Cardiac output is
computed by multiplying the stroke volume by
the heart rate.
• Stroke volume (SV) :The amount of blood
ejected by the left ventricle with each
heartbeat .
• the heart rate is 60 to 80 beats per minute
(bpm)
• The average resting stroke volume is
about 70 mL, and Cardiac output can be
affected by changes in either stroke
volume or heart rate.
Cardiac Output/Index
• Cardiac output
– CO = HR (beats/minute) X SV (liters/beat)
– Normal adult: 4-8 liters/minute
• Cardiac index
– CI = CO(liter/minute)/Body surface area (m2)
– Normal adult: 2.8-4.2 liter/minute/m2
– Normalizes liter flow to body size
Stroke Volume
• Preload
• Afterload
• Contractility
Stroke Volume
• Preload
– The amount of stretch placed on the cardiac muscle just prior
to systole (the amount of the ventricle at end diastole)
– Diastole : filling stage of cardiac cycle.
• Afterload
– The force or pressure at which the blood is ejected from
the left ventricle
– Equated with systemic vascular resistance (SVR)
• Contractility is a term used to denote the force
generated by the contracting myocardium under any
given condition
• . The resistance of the systemic BP to left ventricular
ejection is called systemic vascular resistance.
•
The resistance of the pulmonary BP to right ventricular
ejection is called pulmonary vascular resistance
• The percentage of the end-diastolic
volume that is ejected with each stroke is
called the ejection fraction (EF)
(EF) = 50-70%
Patient Assessment:
Cardiovascular System
• HEALTH HISTORY AND
• CLINICAL MANIFESTATIONS
For the patient experiencing an acute MI, the nurse
obtains the health history using a few specific questions
about the onset and severity of chest discomfort,
associated symptoms, current medications, and
allergies.
At the same time, the nurse observes the patient’s
general appearance and evaluates hemodynamic status
(heart rate and rhythm, BP).
Cardiac Signs and Symptoms
• Chest pain or discomfort (angina pectoris, MI, valvular
heart disease) Shortness of breath or dyspnea (MI, left
ventricular failure, HF)
• Edema and weight gain (right ventricular failure, HF)
• Palpitations (dysrhythmias resulting from myocardial
ischemia, stress, electrolyte imbalance)
•
Fatigue (earliest symptom associated with several
cardiovascularndisorders)
• Dizziness and syncope or loss of consciousness (postural
hypotension, dysrhythmias, vasovagal
effect,cerebrovascular disorders)
Physical Exam
• Inspection
– General appearance
– Jugular venous distension
(JVD)
– Skin
– Extremities
• Palpation
– Pulses
– Point of maximal impulse
(PMI)
• Percussion
• Auscultation
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Good stethoscope
Positioning
Normal tones – S1/S2
Extra tones – S3/S4
Murmurs
Rubs
HEART SOUNDS
HEART SOUNDS
The normal heart sounds, S1 and S2, are produced primarily by
the closing of the heart valves. The time between S1 and S2
corresponds to systole This is normally shorter than the
time between S2 and S1 (diastole). As the heart rate increases diastole
shortens.
S1—First Heart Sound. Closure of the mitral and tricuspid valves
creates the first heart sound (S1),
S2—Second Heart Sound. Closing of
the aortic and pulmonic valves
produces the second heart sound (S2).
• Murmurs are created by the turbulent flow
of blood.
• The causes of the turbulence may be a critically
narrowed valve,
• a malfunctioning valve that allows regurgitant
blood flow,
• a congenital defect of the ventricular wall, a
defect between the aorta and the pulmonary
artery,
Diagnostic Evaluation
• Laboratory test(Cardiac Labs)
• Chest X-ray
• ECG
• CARDIAC STRESS TESTING
• ECHOCARDIOGRAPHY(ECO)
• Echocardiography is a noninvasive ultrasound test that is
used to examine the size, shape, and motion of cardiac
structures.
Important Cardiac Labs
• Enzymes – CK, CK-MB, LDH
• Other important cardiac biomarkers that are
assessed include the myoglobin and troponin T or
I. Myoglobin
•
early marker of MI, is a heme protein with
a small molecular weight. This allows it to
be rapidly released from damaged
myocardial tissue and accounts for its
early increase, within 1 to 3 hours after the
onset of an acute MI. Myoglobin peaks in
4 to 12 hours and returns to normal in 24
hours.
• Lipid studies – Cholesterol, triglycerides
Coagulation studies – PTT and PT/INRI
(nternational
• Normalized Ratio (INR). The INR provides a
standard method for reporting PT level
• Electrolytes – Potassium, magnesium, and
calcium
Invasive Tests
• Cardiac catheterization
• Coronary angiography
Cardiac Conduction
Cardiac Electrophysiology
• The cardiac conduction system generates
and transmits electrical impulses that
stimulate contraction of the myocardium.
• To pump effectively, large portions of
cardiac muscle must receive an action
potential nearly simultaneously.
• Special cells that conduct action potentials
extremely rapidly are arranged in
pathways through the heart.
• Before mechanical contraction, an action
potential travels quickly over each cell
membrane and down into each cell’s.
• Three physiologic characteristics of two
specialized electrical cells, the nodal cells and
the Purkinje cells, provide this synchronization:
• Automaticity: ability to initiate an electrical
impulse
• Excitability: ability to respond to an electrical
impulse
• Conductivity: ability to transmit an electrical
impulse from one cell to another
Cardiac Conduction
• Sinoatrial (SA) node – Fires at 60–100
beats/minute
• Intranodal pathway
• Atrioventricular (AV) node – Fires at 40-60
beats/minute
• Atrioventricular bundle of His
– Ventricular tissue fires at 20-40 beats/minute
and can occur at this point and down
• Right and left bundle branches
• Purkinje fibers
Action Potential
12-Lead ECG
• Limb leads
– Standard leads: I, II, and III
– Augmented leads: aVR, aVL, and aVF
• Precordial leads
– V1,V2,V3,V4,V5, and V6
• Axis
– The direction of the flow of electricity
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P wave : atrial depolarization
up to 0.12 second in duration .
QRS complex : ventricular depolarization
normal measure is 0.08-0.12 second
T wave : ventricular repolarization , rounded
upright, not exceeds 0.2 sec of duration
PR interval : the interval between the beginning
of p wave and the beginning of R wave it
measures between ( 0.12-0.2
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ST segment : the isoelectric line between
the end of QRS and the beginning of T
wave
QT interval : the interval between the
beginning of Q wave and the end of T
wave , it measures ( 0.32 – 0.40 )
second
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Normal Timing
• PR interval – 0.12 to 0.20 seconds
• QRS interval – less then 0.12
• QT interval – varies with rate. It is usually
less then ½ the R-to-R distance on the
preceding waves
Steps to reading ECGs
• What is the rate? Both atrial and ventricular if they are not
the same.
• Is the rhythm regular or irregular?
• Do the P waves all look the same? Is there a P wave for
every QRS and conversely a QRS for every P wave?
• Are all the complexes within normal time limits?
• Name the rhythm and any abnormalities.
Rate
• Look at complexes in a 6-second strip and
count the complexes; that will give you a
rough estimate of rate
• Count the number of large boxes between
two complexes and divide into 300
• Count the number of small boxes between
two complexes and divide into 1500
• Estimate rate by sequence of numbers.
Normal Sinus Rhythm
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Rate is between 60 and 100 beats/minute
The rhythm is regular
All intervals are within normal limits
There is a P for every QRS and a QRS for
every P
• The P waves all look the same
Sinus Tachycardia
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Rate above 100 beats/minute
The rhythm is regular
All intervals are within normal limits
There is a P for every QRS and a QRS for every P
The P waves all look the same
Caused by fever, stress, caffeine, nicotine, exercise, or by
increased sympathetic tone
• Treatment is to take care of the underlying cause
Sinus Bradycardia
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Rate is lower than 60 beats/minute
The rhythm is regular
All intervals are within normal limits
There is a P for every QRS and a QRS for every P
The P waves all look the same
Caused by beta-blocker, digitalis, or calcium channel
blockers. Normal for athletes
• Don’t treat unless there are symptoms. Can use pacing or
atropine
Sinus Arrhythmia
• Rate is between 60 and 100 beats/minute
• The rhythm is irregular. The SA node rate can increase or
decrease with respirations
• All intervals are within normal limits
• There is a P for every QRS and a QRS for every P
• The P waves all look the same
• More common in children and athletes
• Ask the patient to stop breathing and the rate will become
regular
The source of the impulse is some
where above ventricles , but the
impulse then spread to the ventricles
so the heart beats faster than normal .
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Supraventricular Tachycardia
(SVT)
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Rate is between 150 and 250 beats/minute
The rhythm is regular
QRS intervals can be within normal limits
There can be a P wave, but more likely it will be
hidden in the T wave or the preceding QRS wave
• Starts and stops abruptly
• Treat with Valsalva maneuver or adenosine IV
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• CAUSES :
1- hypothyroidism .
2- anxiety .
3- pericarditis .
4- heart failure .
5- structural abnormality .
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• Occurs when multiple irritable focuses
in both atria started to initiate impulses
that resulting in chaotic , irregular
excitation of the atrium .
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Atrial Fibrillation
• Atrial rate is between 350 and 600
beats/minute; ventricular rate can vary
• The rhythm is irregular
• There is no PR interval; QRS may be
normal
• There are many more f waves then QRS
• Unlike flutter where the f wave will appear
the same, in fib the f waves are from
different foci so they are different
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Atrial Fibrillation
• CAUSES
1- anterior myocardial infarction .
2- inferior myocardial infarction .
3- valvular heart disease .
4- heart failure .
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Atrial Flutter
• Atrial rate is between 250 and 350 beats/minute.
Ventricular rate can vary
• The rhythm is regular or regularly irregular
• There is no PR interval. QRS may be normal
• 2:1 to 4:1 f waves to every QRS
• There are no P waves; they are now called flutter waves
• Problem: Loss of atrial kick and ventricular conduction is
too fast or too slow to allow good filling of the ventricles
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• CAUSES :
1- atrial enlargement .
2- hyper thyroidism .
3- inferior myocardial infarction .
4- anterior myocardial infarction .
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Premature Ventricular
Contractions (PVC)
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Early beat that is wide (>0.12)
Originates the ventricles
No P wave
Compensatory pause
Can be defined by couplet or triplet;
anything more would be considered
ventricular tachycardia
• Monomorphic or polymorphic
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• Multi focal means that the ectopic beat has
more than one foci , that discharge many
shapes of QRS & T .
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• That means that 2 consequences impulses
discharged prior to the next anticipated
sinus rhythm impulse .
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Ventricular Tachycardia
• Rate is between 100 and 200 beats/minute
• The rhythm is regular, but can change to
different rhythms
• No PR interval; QRS is wide and aberrant
• There may be a P wave, but it is not related
to the QRS
Ventricular Fibrillation
• Rapid, irregular rhythm made by stimuli
from many different foci in the ventricula
• Produces no pulse, blood pressure, or
cardiac output
• Can be described as fine or coarse
• Most common cause of sudden cardiac
death
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