Download Blood Flow Through the Heart

(Relates to Chapter 32, “Nursing Assessment: Cardiovascular
System,” in the textbook)
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Heart
 Four chambers
 Composed of three layers
 Endocardium
 Myocardium
 Epicardium
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Blood Flow Through the Heart
Fig. 32-1. Schematic representation of blood flow through the heart. Arrows indicate direction of flow. 1, The right
atrium receives venous blood from the inferior and superior venae cavae and the coronary sinus. The blood then
passes through the tricuspid valve into the right ventricle. 2, With each contraction, the right ventricle pumps
blood through the pulmonic valve into the pulmonary artery and to the lungs. 3, Oxygenated blood flows from the
lungs to the left atrium by way of the pulmonary veins. 4, It then passes through the mitral valve and into the left
ventricle. 5, As the heart contracts, blood is ejected through the aortic valve into the aorta and thus enters the
systemic circulation.
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Fig. 32-2. Anatomic structures of the heart and heart valves.
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Fig. 32-3. Coronary arteries and veins.
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Fig. 34-4. Location of pain during angina or myocardial infarction.
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Conduction system
• Conduction system is a specialized nerve tissue responsible for
creating and transporting the electrical impulse or action potential
• This impulse initiates depolarization and subsequently cardiac
contraction
• Electrical impulse is initiated by the sinoatrial ( SA) node, the
pacemaker of the heart.
• Impulses generated by SA nodes travels through the intraatrial
pathways to depolarize the atria resulting in a contraction
• Pathway of the conduction system : SA nodes – AV nodes – bundle of
his – left and right bundle branches – purkinje fibers
• Climax of the cardiac cycle is the ejection of blood to the pulmonary
and systemic circulation
• It end with repolarization : resting polarized state
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electrocardiogram
• Electrical activity of the heart can be detected on the body surface
through the electrodes placed strategically and is recorded on an
electrocardiogram.
• The letters : P, QRS, T, AND U are used to identify the separate
waveforms
• P wave : first positive deflection, begins with the firing of the SA node
and represents the depolarization of the fibers of atria.
• QRS complex : represents the depolarization from the AV node
through the ventricles
• T wave : represents the repolarization of the ventricles
• U wave : not always seen, is the repolarization of the purkinje fibers or
hypokalemia
• Intervals between these waves ( PR, QRS, QT ) reflect the length of
time it takes for impulse to travel from one area of the heart to
another.
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Fig. 32-8. Relationship of electrocardiogram, cardiac cycle, and heart sounds.
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EKG
• P wave : 0.06 – 0.12 sec
• PR interval : 0.12 – 0.20
• QRS interval : 0.08 – 0.12
• QT interval : 0.34 – 0.43
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Fig. 34-4. Location of pain during angina or myocardial infarction.
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Mechanical System
• Systole: Contraction of myocardium
• Diastole: Relaxation of myocardium
• Cardiac output: Amount of blood
pumped by each ventricle in 1 minute
 CO = SV × HR
• Cardiac index: CO divided by body
surface area ( more accurate )
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Factors Affecting Cardiac Output
• Preload
 Volume of blood in ventricles at the end of
diastole
• Contractility
• Afterload
 Peripheral resistance against which the
left ventricle must pump
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Audience Response Question
A patient is receiving a drug that decreases afterload. To
evaluate the effect of the drug, the nurse monitors the
patient’s:
1. Heart rate.
2. Lung sounds.
3. Blood pressure.
4. Jugular vein distention.
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• Vascular system
 Blood vessels
• Arteries, arterioles
• Veins, venules
• Capillaries
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Fig. 32-5. Comparative thickness of layers of the artery, vein, and capillary.
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• Regulation of the cardiovascular
system
 Autonomic nervous system
 Baroreceptors
 Chemoreceptors
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Autonomic Nervous System
• Consists of sympathetic and parasympathetic nervous system
• Sympathetic system : stimulation of sympathetic system will
increases the HR, this effect is mediated by specific sites in the heart
called the beta adrenergic receptors that are receptors for
norepinephrine and epinephrine.
• Parasympathetic system : mediated by vagus system. Causes the a
decrease in HR .
• Effect of blood vessels :
• sympathetic nervous system : the alpha 1 adrenergic receptors –
increased stimulation causes vasoconstriction and decreased
stimulation causes vasodilation
• Parasympathetic nerves have selective distribution in the blood
vessels
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Baroreceptors
• Baroreceptors are found in the aortic arch and the carotid sinus
• Sensitive to stretch and pressure within the arterial system ex high
blood pressure , fluid overload
• If increased fluid is sensed , massages are related to the brain to
inhibit the sympathetic nervous system and enhancement of the
parasympathetic system, causing a decrease in HR, and peripheral
vasodilation. Decrease in arterial causes an opposite effect.
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Chemoreceptors
• Located in the aortic and carotid bodies
• Chemoreceptors initiate changes in HR and arterial pressure in
response to increased arterial co2, decreased o2, and decreased
plasma PH ( acidosis)
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Blood pressure ( BP = CO X SVR
• Measurement of arterial blood pressure
• Pulse pressure : difference between SBP
and DBP
• Mean arterial pressure :
MAP = ( SBP + 2DBP) /3, MAP > 60
indicates organ perfusion
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• Age alters the cardiovascular response
to physical and emotional stress.
• Heart valves become thick and stiff.
• Frequent need for pacemakers
• Less sensitive to β-adrenergic agonist
drugs
• Increase in SBP; decrease or no change
in DBP
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• Noninvasive studies
 Blood studies
 Chest x-ray
 Electrocardiogram
 Resting ECG
 Ambulatory ECG monitoring
 Event monitor or loop recorder
 Exercise or stress testing
 6-minute walk test
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Chest X-ray
Fig. 32-9. Chest radiograph: Standard posterior-anterior view.
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Audience Response Question
A patient arrives at an urgent care center after experiencing
unrelenting substernal and epigastric pain and pressure for
about 12 hours. The nurse reviews laboratory results with
the understanding that at this point in time, a myocardial
infarction would by indicated by peak levels of:
1. Troponin T.
2. Homocysteine.
3. Creatine kinase-MB.
4. Type b natriuretic peptide.
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• Noninvasive studies
 Echocardiogram
 Nuclear cardiology
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Fig. 32-10. Apical four-chamber two-dimensional echocardiographic view in a normal patient.
LA, Left atrium; LV, left ventricle; MV, mitral valve; RA, right atrium; RV, right ventricle; TV,
tricuspid valve.
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• Noninvasive studies (cont’d)
 Magnetic resonance imaging
 Computed tomography
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Computed Tomography
Fig. 32-11. Examples of coronary calcification of the left anterior descending coronary artery (large
arrow) and left circumflex artery (small arrow) as seen on electron beam computed tomography.
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• Invasive studies
 Cardiac catheterization and coronary
angiography
 Intracoronary ultrasound
 Fractional flow reserve
 Electrophysiology study
 Blood flow and pressure measurements
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Fig. 32-12. Normal left coronary artery angiogram.
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Audience Response Question
A patient returns to the cardiac observation area following a
cardiac catheterization with coronary angiography. Which of
the following assessments would require immediate action
by the nurse?
1. Pedal pulses are 2+ bilaterally.
2. Apical pulse is 54 beats/minute.
3. Mean arterial pressure is 72 mm Hg.
4. ST-segment elevation develops on the ECG.
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