CARDIAC OVERVIEW

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CARDIAC OVERVIEW
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Assessment of the Cardiovascular System

• On Your Own
• Review the anatomy of the heart and vessels
• Review normal circulation
• Review coronary circulation

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Coronary Circulation
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Conduction System of the Heart
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Conduction

• SA node
• Located at junction of right atrium and the
  superior vena cava
• Main regulator of heart rate
• Initiates impulses at a rate of 60 to 100
• Transmits impulses to surrounding atrial tissue
• Initiates depolarization and activation of all
  myocardial cells

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Conduction

• AV Node
• Located in junctional area
• Briefly delays conduction of the impulse,
  allowing atria to contract completely
• Intrinsic rate is 40 to 60 beats per minute

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Conduction

• Bundle of His
• Continuation of the AV node
• Located in the interventricular septum
• Divides into right and left bundle branch
• Purkinje fibers are the terminal branches and
  carry the wave of depolarization to both
  ventricular walls.
• Purkinje fibers can act as intrinsic pacemaker
  with a discharge rate of only 20 to 40

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Cardiac Cycle

• Diastole
• 2/3 of the cardiac cycle
• Relaxation and filling of the atria and
  ventricles
• Systole
• 1/3 of the cardiac cycle
• Contraction and emptying of the atria and
  ventricles

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Mechanical Properties of the Heart

• Cardiac Output
• The amount of blood pumped from the left
  ventricle each minute
• Cardiac Output Heart Rate X Stroke Volume
• Cardiac Index
• Determined by dividing Cardiac Output (CO) by the
  body surface area (normal range 2.7 3.2
  L/min/meters squared of body surface area)

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Mechanical Properties of the Heart

• Heart Rate
• Number of times ventricles contract each minute
• Normal adult 60-100
• Stroke Volume
• Amount of blood ejected by the ventricles during
  each systole

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Variables that Influence Stroke Volume

• Preload
• Degree of myocardial fiber stretch at the end of
  diastole and just before contraction
• Determined by left ventricular end diastolic
  pressure (LVED)
• Starlings Law the more the heart fills during
  diastole, the more forcefully it contracts

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Variables that Influence Stroke Volume

• Afterload
• Pressure or resistance that the ventricles must
  overcome to eject blood through the semilunar
  valves and into the peripheral blood vessels.
• Impedance (the peripheral component of afterload)
• Pressure heart must overcome to open the aortic
  valve
• Amount of impedance depends upon aortic
  compliance and total systemic vascular
  resistance, a combination of blood viscosity and
  arteriolar constriction

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Preload and Afterload
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Variables that Influence Stroke Volume

• Contractility
• The force of cardiac contraction independent of
  preload
• Increased by
• Sympathetic stimulation
• Calcium release
• Decreased by
• Hypoxia and acidemia

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Vascular System

• On Your Own
• Review Purpose, Structure and Function
• Physiology of blood pressure
• Keep in mind Blood pressure is determined
  primarily by cardiac output (amount of blood
  flow) and arteriole resistance
• Blood Pressure CO X PVR

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Regulators of Blood Pressure

• Autonomic Nervous System
• Baroreceptors
• Chemoreceptors
• Stretch receptors
• Renal System
• Renin-Angiotensin-Aldosterone Mechanism
• External Factors
• Emotional behaviors
• Increased physical activity
• Body temperature

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Assessment History Patients will be queried
regarding

• History of cardiac symptoms
• Dyspnea
• Fatigue
• Paroxysmal nocturnal dyspnea
• Orthopnea
• Chest pain
• palpatations

• Syncope
• Cough
• Past health history
• Medicattions
• Risk factors
• Age
• Diet
• Activity
• Smoking

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Pack-years

• Smoking history should be reported in pack years
• Number of packs per day multiplied by the number
  of years has smoked
• (0.5 pack X 10 years 5 pack years)

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Physical Exam

• Cyanosis
• Petechiae
• Edema
• Pulses
• Heart sounds
• Murmurs
• Bruits
• Blood pressure

• Neck vein distention
• Skin color
• Hair distribution on extremities
• Lesions
• Clubbing
• dysrhythmias

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Assessment of Clubbing

• Schamroth Method
• Place fingernails of the ring fingers together
  and hold up to light
• If a diamond shape can be seen between the nails
  findings are normal
• Absence of the diamond shape indicates clubbing

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Assessing for Clubbing
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Diagnostic Tests

• Chest xray
• ECG
• Cardiac Catheterization
• Arteriography
• Thallium scan
• Exercise stress test
• CK-MB

• LDH
• Cholesterol
• Triglycerides
• Lipoproteins
• Myoglobin
• Troponins
• C-reactive protein

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Important Markers of Myocardial Damage

• Creatine Kinase
• specific to brain, myocardial, and skeletal
  muscle cells
• Presense in blood indicates tissue necrosis or
  injury
• Isoenzymes identify specific source
• CK-MB activity is most specific for MI with
  predictable rise over 3 days (peak at 24 hours
  after onset of chest pain)

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Early Markers

• CK-MB antibody assay can detect myocardial
  necrosis within 3 hours of ED admission
• CK-MB subforms 1 and 2 (early and specific
  indicators)
• Myoglobin (early, sensitive, but non-specific)
• Troponin T and I (early with wide diagnostic time
  frame)

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Additional Labs

• Homocysteine
• Blood coagulation tests
• PT
• PTT
• ABGs
• Serum electrolytes
• CBC

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Radiographic Examinations

• Chest xray
• Cardiac Fluoroscopy
• Angiography

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Cardiac Catheterization

• Provides
• Visualization of coronary blood flow
• Measurement of pressures in heart chambers
• Determination of O2 saturation of the blood
• Visualization of the valves
• Procedure
• One or more catheters inserted (femoral
  brachial)
• Dye injected
• Takes about 1 hour

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Cardiac Catheterization

• Before the test
• ECG
• Chest x-ray
• Urine
• Blood
• BUN
• Fast 8-12 hours
• IV started
• Patient Education
• Length of procedure
• May feel palpitations and flushing
• Basic Pre-op preparation

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Cardiac Catheterization

• Indications
• Chart 33-5, p. 642
• Complications
• Chart 33-6, p. 642

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Cardiac Catheterization

• During the test
• May be asked to cough or deep breathe
• After the test
• Firm pressure over site observe for bleeding,
  hematoma
• Circulatory checks every 15 minutes for 1-2 hours
  then every 1-2 hours after stable
• Observe for dysrhythmias
• Keep leg or arm straight for several hours
• Increase fluids to flush out dye
• Watch for orthostatic hypotension when first up

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Other Diagnostic Tests

• ECG
• Resting ECG
• Ambulatory ECG (Holter Monitor)
• Electrophysiologic Studies
• Exercise ECG (Stress Test)
• Echocariography
• Dobutamine Stress Echo
• Transesophageal Echo
• Phonocardiography
• Myocardial Nuclear Perfusion Imaging
• Technetium
• Thallium
• Cardiac Blood Pooling Imaging
• Positron Emission Tomography
• MRI

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Hemodynamic Monitoring

• Invasive system used in critical care to provide
  quantitative information about vascular capacity,
  blood volume, pump effectiveness, and tissue
  perfusion.
• Directly measures pressures in heart and great
  vessels
• Provides more accurate measurements of blood
  pressure, heart function and volume status

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Hemodynamic Monitoring

• Involves significant risks, informed consent is
  required
• Components
• Catheter with infusion system
• Transducer
• Monitor

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Hemodynamic Monitoring
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Hemodynamic Measurements

• Right Atrial Pressure (direct)
• Normal 1-8 mm Hg
• Left Atrial Pressure (indirect)
• Normal 15-28 mm Hg
• Pulmonary Wedge Pressure
• Indirect measurement of LVEDP
• Normal 4-12 mm Hg
• Cardiac Output
• SV02
• Normal 60-80

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Central Venous Pressure Monitoring

• Similar to right atrial pressures, but measured
  in cm of water
• Chart 33-7, p. 652
• Normal 7-12 cm H20
• Elevated right ventricular failure
• Low hypovolemia