Download Cardiac Anatomy

Cardiac Anatomy, Physiology, and Assessment
Objectives - 2
• Review cardiac structures and function which include:
• Chambers, Valves, Vessels, Coronary arteries, Blood flow and the Conduction system
• Basics of Electrocardiography (ECG)
• Patient Cases
• Discuss Cardiovascular assessment and testing which include:
• History and physical exam, Chest x-ray, Biomarkers, Echocardiography, Cardiac catheterization,
and Cardiac stress testing
The Heart and the Circulatory System – 3
• The heart is a hollow muscular organ which plays a vital part of the circulatory system and consist of:
• Pulmonary circulation – represents blood flow through the lungs
• Systemic circulation – represents blood flow to the body
• Coronary circulation –represents blood flow through the heart
• Circulatory system is a giant circuit with main job of transport:
• Deliver oxygen and nutrients to tissues
• Carry away waste products
• Circulate electrolytes and hormones
• Transport white blood cells (WBC) to fight off an infection
Location and Size of the Heart - 4
The heart is located within the thoracic cavity between the 2 lungs and is slightly tilted to the left. Generally
the size of the heart is the same as a clinched fist, and weighs approximately 300 g (similar to the weight of
grapefruit)
Layers of the Heart - 5
• The heart is protected by a loose double walled membranous sac known as the pericardium which
surrounds the pericardial fluid that baths the heart.
• The epicardium is the outer surface of the heart, and is also in contact with the pericardial fluid.
• Underneath the epicardium lies the thick layer known as the myocardium which is the working muscle
of the heart.
• The endocardium is a smooth thin membrane that lines the inside cavities of the heart which include the
chambers and the valves of the heart.
• Pericardium
- Protective sac
• Epicardium
- Outer surface of the heart
• Myocardium
- Thick layer of muscle
- Thickest in the left ventricle, thinnest in the atria
• Endocardium
- Include the chambers and the valves of the heart
Chambers of the Heart - 6
• The heart is comprised of 4 chambers
• The 2 upper chambers are known as the atrium
• The 2 lower chambers are known as the ventricles
• The atrium act primarily as holding chambers whereas the
ventricles do the work of pumping the blood.
• Collectively the right atrium and ventricle make up what is
known as the right heart, and the left atrium and ventricle make
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up what is known as the left heart.
Valves & Blood Vessels of the Heart - 7
• Separating the atrium from the ventricles are the valves
which keep blood flowing in the correct direction and
prevent the backward flow of blood.
• These are known as the Atrioventricular valves
(between atria and ventricle)
• The tricuspid valve is located on the right side of the
heart and separates the right atrium from the right
ventricle
• The mitral valve is on the left side of the heart and
separates the left atrium from the left ventricle
• Two other important valves include the pulmonic valve
which separates the right ventricle from the pulmonary
artery, and the aortic valve that separates the left
ventricle from the aorta
• The pulmonary artery and the aorta are great vessels
which carry blood away from the heart.
• Arteries carry blood away from the heart
• Veins carry blood back to the heart
• The superior and inferior vena cava are veins that bring
blood back to the heart and empty into the right atrium.
• The Inferior vena cava returns the blood from the lower
extremities while the Superior vena cava returns blood
from the upper extremities.
• The right heart and the left heart are divided by the
septum which is a thick tissue that prevents any blood
from passing through.
• Blood moves from the right heart to left heart by way of
the lungs.
Blood Flow through the Heart - 8
• Deoxygenated blood returns to the heart via the inferior and superior vena cava into the right atrium.
• The blood then passes into the right ventricle where it is pumped through the pulmonary artery into the
lungs.
• In the lungs gas exchange takes place and blood becomes oxygenated.
• This oxygenated blood then returns to the heart via the pulmonary veins into left atrium from there the
blood passes to the left ventricle where it is pumped out through the aorta and to the rest of the body.
• Once the organs & tissues take up the oxygen and nutrients from blood this cycle repeats itself again
→deoxygenated blood goes back to the right atrium
Cardiac Cycle - 9
• The cardiac cycle is a mechanism by which the blood is pushed through the heart.
• This cycle is divided into 2 parts the diastole (relaxation) and systole (contraction)
• During diastole the heart is at rest and the myocardium is relaxed around the atria and ventricles which
allows them to passively fill.
• At the end of diastole almost all blood is in the ventricles.
• When systole begins the atria contract first and inject the final amount of blood into the ventricles.
• Then the atria relaxes causing the atrial pressure to be lower than the ventricular pressure.
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•
•
This is important because it causes the Atrioventricular
valves to shut preventing back-flow of blood when the
ventricles contract.
Next the ventricles begin to contract and as they contract
they inject blood into the pulmonary artery which goes to
the lungs and the aorta which goes to the rest the body.
Coronary Arteries - 10
The heart also needs to be perfused and this is accomplished
through its own network of coronary arteries.
The major ones often discussed in corner artery disease (CAD)
begins with the 2 main arteries that originate off the aorta.
These are the right coronary artery and the left main coronary
artery.
• Right coronary artery (RCA) – supplies blood to the right side of the heart such as the right atrium, right
ventricle, SA node, & AV node. The RCA branches off into the posterior descending artery.
• Posterior descending artery (PDA) – Wraps around the back side of the heart supplying blood
mainly to the posterior septum
Left
main coronary artery (LMCA) – supplies blood to left side of heart; serves left atrium; then
•
branches off into the left circumflex artery and the left anterior descending.
• Left circumflex artery (LCX) – wraps around the back-side of the heart on the left side supplying
blood mainly to the left atrium/ventricle. Similar to posterior descending artery since it wraps around
left side of heart.
• Left anterior descending (LAD) – supplying blood to the anterior (front) part of the heart delivering
blood to the left ventricle and septum
Deoxygenated
blood returns to the right atrium via coronary veins
•
Cardiac Conduction System - 11
The cardiac conduction system is an important concept to understand. An electrical impulse is initiated from
the sinoatrial (SA) node which is located in the upper right-hand corner of the right atrium. This impulse
then spreads to the left atrium via the intranodal tract causing depolarization which creates an atrial
contraction. The impulse then travels down to the AV node were there is
a slight delay before the signal is transmitted towards the ventricles. This
impulse continues to spread downward first hitting the Bundle of His
(AV bundle) and then diverges into the right and left bundle branches
which branches off into the Purkinje fibers which are responsible for
causing the depolarization (contraction) of the ventricles.
• Sinoatrial (SA) node
• Pacemaker
• Located in the right atrium
• Intranodal tract
• Transmits electrical impulse across atria
• Atrioventricular (AV) node
• Located between atria and ventricles
• Sends electrical activity to ventricles
• Bundle of His (AV bundle)
• Sends impulse between the ventricles (AV bundle)
• Bundle branches
• Right and left bundle branch
• Distributes electrical activity toward the ventricles
• Purkinje fibers
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•
Spreads electrical impulse to all areas of ventricles
Electrocardiography - 13
With this basic understanding of the cardiac conduction system we can now understand the
electrocardiogram (ECG) which measures the electrical activity of the heart. It is simple to perform,
noninvasive and inexpensive. The ECG is a fundamental part of cardiac assessment and is a graphical
representation of the electrical activity occurring in the heart. This is an essential tool when investigating
dysrhythmias, cardiac ischemia, or infarction.
Electrocardiography may be presented in 2 ways which include a 12 lead ECG or a rhythm strip. This
rhythm strip gives us a longer time frame to evaluate one particularly lead which is usually lead II, which
helps assess rhythm. It is common for the 12 lead ECG to
also include the rhythm strip.
ECG Paper - 14
The ECG paper consist of small boxes that are 1 mm in
size and has a paper speed of 25 mm/sec
• Horizontal tracings measure time/duration
• Small box (1 mm) = 0.04 seconds
• Large box = 5 small boxes (5 mm) = 0.2 seconds
• Vertical tracings measure size/amplitude of the voltage
• Small box (1 mm) = 0.1 mv
• Large box (5 mm) = 0.5 mv
• Calipers are used to evaluate the ECG by measuring
the small boxes to assess rhythm.
The 12-lead ECG - 15
• Each lead is looking at a different location in the heart.
The information from these leads are combined to form the standard electrocardiogram.
• The 6 Limb leads view the heart in a vertical plane
• I, II, III, aVR, aVL, aVF
• The 6 Precordial leads view the heart in a horizontal plane
• V1, V2, V3, V4, V5, V6
Electrocardiography – 16-19
P wave represents atrial depolarization (contraction of atria)
• PR interval represents AV conduction
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• Reflects atrial depolarization AND conduction through the AV node
• This is measured from the beginning of the P wave to the beginning of the Q wave.
• Normal: 0.12 – 0.20 seconds
• QRS complex = represents depolarization (contraction) of both left and right ventricles
• Normal: < 0.12 seconds. This is measured from the beginning of Q wave to the end of the S wave.
• T wave represents ventricular repolarization and is normally upright, smooth, and rounded in lead II.If
there is a negative deflection it may indicate ischemia also changes in T wave morphology may reflect
electrolyte imbalance
• ST segment is another important part of the ECG and represents early phase of ventricular
repolarization, and extends from the end of the QRS interval to the beginning of the T wave
• Elevation or depression may indicate heart damage such as myocardial infarction (MI)
• QT interval represents the total time required for depolarization and repolarization of the ventricles, and
extends from the beginning of the Q wave to the end of the T wave
• The QT interval varies with heart rate therefore the QTc is calculated = QT/ (√R-R in seconds)
• QT prolongation: increases the risk of life threatening dysrhythmia such as torsades de pointes
• A patient with preexistent QT prolongation would need to being monitored or avoid drugs that cause
QT prolongation. If a drug is started and is known to prolong the QT it is commonly accepted that a
QTc> 500 msec OR a > 60 msec change over baseline is cause to discontinue the drug.
U
wave
represents purkinje fiber repolarization, and is not normally present
•
• If both U wave and T wave are inverted suspect ischemia.
• May represent ischemia if combined with other abnormalities of the ECG or electrolyte disturbance.
Interpreting the ECG Rhythm – 20
Use systemic method to evaluate the ECG.
Determine heart rate (in beats / min → BPM)
• Tachycardia = > 100 beats per minute
• Bradycardia = < 60 beats per minute
• To determine the heart rate divide 1500 by the number of small boxes in one R-R interval
• E.g. 1500/20 = 75 beats per minute
• This method only works when the rate is regular which means the distance of the R-R interval is the
same throughout the ECG
• For irregular rhythms the best way to determine the heart rate is by counting the number of R waves
in a 6 second rhythm strip and multiplying by 10
Determine the rhythm - 21
• Regular or irregular
• The top ECG rhythm shows a regular R-R interval
• The bottom strip shows the R-R interval as irregular which is characteristic of atrial fibrillation
Identify P-waves - 22
• Is there a P-wave for each QRS complex?
• In normal sinus rhythm there is a P wave before every QRS complex
• In the 2nd strip not every QRS complex has a P wave
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•
In the 3rd strip none of the QRS complex are proceeded by a P
wave which means there is no conduction signal coming
through from the atria causing a junctional rhythm where the
AV node is acting as the pacemaker of the heart instead of SA
node
Determine if the PR interval is within normal range AND does I it remain the same throughout the ECG - 23
• This will help identify the presence of a Heart block
• 1st degree – prolonged PR interval
• 2nd degree (type I and type II) – type I is also known as Wenckebach
• 3rd degree – is known as complete heart block where there is no communication of the electrical
signal between the AV node and the conduction pathway of the ventricles
Determine if the QRS duration is within normal limits AND do the
complexes look alike - 24
• This can provide useful information regarding delays in
ventricular depolarization (e.g. A bundle branch block will give a
wide QRS strip when compared to a narrow (normal) QRS
Systematically summarizing the interpretation of the ECG - 25
1. Calculate the rate
2. Determine the rhythm
3. Identify P-waves
4. Determine if the PR interval is within normal range and does it
remain the same throughout the ECG
5. Determine if the QRS duration is within normal limits and do the
complexes look alike
• With all this information together we can then INTERPRET
THE RHYTHM
• Helpful website http://library.med.utah.edu/kw/ecg/
Patient Case #1 – 26; physical exam; chest x-ray; NT-proBNP
• 60 year old male presents to the Emergency Department with
shortness of breath
• Medical history
• Coronary artery disease (CAD), HTN, DM-2, COPD,
Atrial fibrillation
ECG
– Atrial fibrillation
•
• Physical exam – +JVD, +crackles, +S3
• Tests and Labs ordered:
• Chest x-ray: bilateral effusions, cardiomegaly
• CBC, BMP, magnesium, NT-proBNP, troponin, INR, Ddimer
Physical Exam - 28
Jugular venous pressure (JVP)
• Measured on the right side assessing the internal jugular vein relative to the sternal angle
• Indirect assessment of right atrial pressure, and used to assess the severity of peripheral venous
congestion and right heart failure
• Useful in heart failure
• To measure have patient lie supine at an angle of 45° with the head turned to the left
• Normally the JVP is 1-2 cm above the sternal angle, and elevations above this range is evidence of high
right atrial pressure
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•
This is a noninvasive test that is relatively subjective to the clinician performing the test
Physical Exam - Auscultation – 29; listening to sounds arising from organs
• Lung examination – crackles (rales)
• Abnormal breath sound usually caused by excessive fluid in the lungs (pulmonary edema)
• Heard best during inspiration
• Abnormal heart sounds (pt. had abnormal S3 heart sound)
• May help identify heart failure, arrhythmias, hypertrophic cardiomyopathy, aortic stenosis, valvular
defects, and arteriovenous connections
• Auscultation of heart sounds are usually heard clearest in these areas:
• Aortic area (base), Pulmonic area, Third left interspace, tricuspid area, or mitral area (apex)
Heart Sounds - 31
Normal heart sounds – which are usually associated with the “lub dub” sound
• S1 – Closure of the atrioventricular valves, and precedes ventricular contraction
• S2 – Closure of the aortic and pulmonary valves, and follows ventricular contraction
Abnormal heart sounds
• S3 – low pitched sound occurring at the beginning of diastole
• Associated with heart failure
• S4 – dull, low pitched sound occurring just after atrial contraction at the end of diastole and immediately
before ventricular contraction
• Associated with aortic stenosis, hypertrophic cardiomyopathy, HTN, CAD
Heart Murmurs - 32
Murmurs – auditory vibrations caused by turbulent blood flow; abnormal heart sound produced by abnormal
circulation and friction of blood against malfunctioning structures i.e. valves.
• Associated with stenosis, valve regurgitation, cardiomyopathy
• Assessed on their volume and duration
• They are graded based on the intensity of the murmur
• Grade 1: softest - Grade 6: loudest
• Heart sounds website
http://depts.washington.edu/physdx/heart/demo/html
Chest Radiography - 34
• The chest x-ray is a painless noninvasive test that evaluates the
lungs, heart, and chest wall
• It views the position and size of the heart
• It can be performed using 2 views – both show lungs
• Posterioranterior – superior vena cava, R. atrium, pulmonary
artery, Left ventricle
• Lateral – R. ventricle, inferior vena cava, L. Ventricle
• Good to always compare a current chest x-ray to a previous one to
note any changes
• Cardiothoracic ratio (CTR) will determine if the heart is enlarged (cardiomegaly)
• Normal: ≤ 0.45
• This is done by measuring the horizontal distance of the heart and dividing it by the maximal
transverse diameter of the thorax in the posterioranterior view
• HF, HTN, pericardial effusion may cause cardiac enlargement
• Ratio > 50% = abnormal
Impression of X-ray: 35 Bilateral pleural effusion consistent with congestive heart failure also cardiomegaly
is observed (bottom picture).
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Biomarkers of Hemodynamic Stress - 37
• B-type natriuretic peptide (BNP) & N-terminal pro BNP (NT-proBNP)
• NT-proBNP is the precursor to BNP
• Released from ventricular myocytes in response to increased wall stress
• Inter-individual variability
• Higher values in women and elderly
• Lower values in obese patients
★ Normal values (BNP < 100 pg/mL or NT-proBNP < 300 pg/mL) strongly rules out HF
• Elevated values may indicate HF
• May be elevated in other conditions such as PE, COPD, sepsis, renal failure and cirrhosis
Echocardiography - 40
Non-invasive test that uses ultrasound waves to examine cardiac function and structure
• Usefulness→ It can assess – Chamber sizes, function, and wall thickness
• Other critical information include: Ejection fraction, regurgitation of valves, and wall motion
abnormalities
Two
types
•
• Transthoracic echo (TTE) – Less invasive, because the transducer is placed on the outside of the
chest wall
• Transesophageal echo (TEE) – More invasive, because the transducer is placed into the esophagus
which gives better images, and is useful to delineate vegetation (endocarditis) and thrombi
• There are also different Modes to the echo – Slide 41
• M-mode, 2-D, 3-D, and Doppler imaging which gives color to the image and is used to evaluate
regurgitation, and ejection fraction of the heart.
Patient Case #2 – 42; ECG; Troponin; Heart Catherization
• 65 year old male presents to the Emergency Department with
shortness of breath/chest pain
• Medical history or CAD, HTN, DM-2, and COPD
• ECG: ST-elevations→ Medical Emergency! →Active MI
• Tests and Labs ordered
• Chest x-ray (pending), CBC, BMP, magnesium, NTproBNP, troponin, INR
• Cardiology consulted, patient sent emergently to the cardiac cath
lab for left heart catheterization
ST- elevations on an ECG - 44
• Within this 12 lead ECG there is observed abnormal ST elevation in V1, V2, V3, and V4
• Beneath is a rhythm strip showing a normal ST segment as opposed to ST elevation
• It is a medical emergency whenever ST elevation is seen on an ECG. This means the patient is having a
myocardial infarction
• Cardiology is consulted and patient is sent him urgently to the Cardiac Cath Lab for left heart
catheterization
Cardiac Catheterization and Angiography – 47 – viewing of heart
• A diagnostic invasive procedure to view the heart as it pumps
• Angiogram typically lasts 30-60 minutes
• Catheter is introduced into the heart via femoral, brachial, or radial artery
• The purpose of the left heart catheterization is to observe where the infarction is occurring, and to
determine if a stent is needed to allow for reperfusion of the area.
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Left Heart Catheterization – 48
Locates blockage; looks @ coronary arteries; can intervene i.e. stint off embolism; goal →reperfuse heart
Hemodynamic Measurements can be obtained such as:
• Cardiac Output
• Chamber Pressures
• Resistances
Angiography
• Left ventriculography – assesses ejection fraction
• Coronary Angiography – determines blockage of arteries
• Aortography – evaluate for aortic stenosis
• Regurgitation – malfunctioning valves
• Valvular stenosis
Cardiac Catheterization and Intervention – 49
Percutaneous coronary intervention (PCI)
• Percutaneous Coronary Transluminal Angioplasty
• Ballooning →squeezes plaque against artery wall to reperfuse heart
• Stents
• Bare metal stent
• Drug-eluting stents
Biomarkers of Myonecrosis - 51
Cardiac troponins →2 of 3 types are cardiac specific
• Troponin T and I – are cardiac specific
• Preferred biomarker for the diagnosis of myonecrosis
• Detectable 2-4 hours after symptoms and may remain elevated for 5-10 days
• May be elevated in the presence of renal dysfunction
Creatine kinase-MB (CK-MB) →NOT AS SPECIFIC AS CARDIAC TROPONINS
• Not cardiac specific
• Detectable 2-4 hours after symptoms and may remain elevated for 72 hours
• May also be elevated in massive muscle injury
• Useful for detecting recurrent myocardial infarction
Patient Case #3 – 52; Stress test; Risk Factors
• 55 year old male presents to the Emergency Department with shortness of breath/chest pain
• Medical history – DM-2
• Family history – Father had MI at 50 years
• Vital signs are stable
• ECG: normal sinus rhythm
• Physical exam – normal
• Tests and Labs ordered
• Chest x-ray: normal
• BMP, magnesium, CBC, NT-proBNP, troponin, INR
• All labs within normal limits; troponins (-) x 3
• Stress test ordered
• Patient risk factors:
Diabetes
•
Family history
•
Active chest pain
•
Exercise Stress Testing - 54
• Inexpensive and safe procedure used to assess CAD and conduction abnormalities
• Normally performed on a treadmill or exercise bike
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Testing procedure
• Resting BP, HR and ECG is performed
• Exercise is initiated and gradually intensified (speed; elevation) with monitoring of BP, HR and ECG
• Exercise is continued until the patient achieves 85% of maximal predicted HR or is unable to continue
Positive stress test
• Creates 1 mm or more ST-depression/elevation for at least 60-80 msec after the end of the QRS complex
on ECG.
• Shortness of breath or active chest pains are also indications to stop the test.
Pharmacologic Stress Testing - 56
Used in patients where physical exercise is not possible.
Adenosine (Vasodilator → dilates coronary arteries)
• Binds to adenosine receptors on smooth muscle cells in the coronary arterial media coronary dilation
• Methylxanthines block adenosine binding and should be avoided 24 hours prior to testing i.e. coffee,
soda
• 0.140 mcg/kg/min IV over 6 minutes
Dipyridamole (Vasodilator → dilates coronary arteries)
• Blocks cellular uptake of adenosine, increasing extracellular adenosine coronary dilation
• 0.142 mg/kg/min IV over 4 minutes
• May induce severe bronchospasm in patients with a history of asthma
Dobutamine (Inotrope →↑Contractility →↑ 02 demand; ↑HR
• Useful in patients who cannot undergo exercise or vasodilator stress testing
• Dobutamine is administered IV to stress the heart
• Initiated at 10 mcg/kg/min
• Increased by 10 mcg/kg/min every 3 minutes
• Maximum dose of 40 mcg/kg/min
• Discontinue beta-blockers and calcium-channel blockers before the test, because they interfere with the
actions of dobutamine.
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