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VTT 235/245 Anatomy & Pathology Lab for Veterinary
TechniciansCardiovascular
SystemI. Cardiac System
II. Circulatory System
Cardiac System
The major function of the CVS is transportation, with blood being the transport vehicle.
Circulatory Paths- Systemic Circulation- is blood flow
to and from most parts of the body. Pulmonary Circulation- is blood
flow to and from the lungs, during which it picks up oxygen and returns it to the heart.
Cardiac System
Circulatory Paths- Coronary Circulation- blood flow to the
heart muscle itself. Portal Circulation- a venous system in
which blood returns from the intestines and proceeds to the liver before returning to the heart.
**Venous System- returns blood to the heart.
Arterial System- carries blood away from the heart.
Heart
A muscular, four chambered organ that drives the circulatory system.
Lies in the mediastinum. Base- top of the heart. Apex- bottom of the heart.
Heart…
The outer layer of the heart is called the pericardium.
The pericardium consists of 2 layers: An outer fibrous pericardium- made of
tough, fibrous CT that protects the heart and loosely attaches it to the diaphragm.
An inner serous pericardium- which is also made of 2 layers: Inner Visceral layer(epicardium) Outer parietal layer
Heart…
Inside the sac formed by the pericardium is the thickest layer of heart tissue, the myocardium.
Between the chambers and the myocardium is a thin membranous lining called the endocardium.
Heart…
Compartments- the heart has 4 chambers. The 2 atria receive blood and pump it down
into the respective ventricles, which pump it away from the heart.
Right Atrium- compartment receiving deoxygenated blood. Interatrial septum- the wall separating
the atria. Fossa Ovale- a remnant of the fetal
foramen ovale.
Heart…
Right Ventricle- compartment receiving blood from the right atrium. The right ventricular wall is thinner
because less pressure is required to move blood through the lungs than through the body.
Ventricular septum- separates the ventricles.
Heart…
Left Atrium- the compartment receiving oxygenated blood from the lungs via the pulmonary veins.
Left Ventricle- compartment receiving oxygenated blood from the left atrium and sending it out the aorta to the body (systemic circulation). The left ventricular wall is thicker
because of the higher pressure required for systemic circulation.
Heart…
Ventricular Structures- Papillary Muscles- muscular
projections serving as attachments for the chordae tendineae of the AV valves.
Chordae Tendineae- tough strands anchoring the free edges of the AV valves to the papillary muscles.
Heart…
Valves- AV Valves- prevent backflow into the
atria during ventricular (systole) contractions. Right AV (tricuspid) valve Left AV (bicuspid/mitral) valve “Tri” before you “bi” !!!
Semi-lunar valves- Aortic Pulmonary
Major Vessels
Cranial Vena Cava- the large vein returning blood from the head, neck, and thoracic limbs to the right atrium.
Caudal Vena Cava- large vein returning blood from part of the thorax, viscera, and the caudal part of the body to the right atrium.
Major Vessels…
Pulmonary Trunk- the large vessel carrying blood from the right ventricle to the pulmonary arteries, and thus, to the lungs.
Pulmonary Arteries- the two branches of the pulmonary trunk carrying blood to the right and left lung lobes.
Major Vessels…
Pulmonary Veins- the numerous vessels emptying oxygenated blood into the left atrium.
Aorta- major outflow from the left ventricle into the systemic circulation.
Cardiac Cycle
Both atria contract at virtually the same time.
Blood enters the atria while they are relaxed.
The atrioventricular (AV) valves are open so blood flows rapidly through the ventricles.
Approximately 70% of ventricle filling occurs during this phase.
Cardiac Cycle…
The atria then contract, which is called atrial systole, and the ventricles fill completely.
Next, both ventricles contract and the AV valves are forced to close, producing the first audible heart sound.
Pressure on the ventricles cause the semi-lunar valves to open and blood is ejected into the pulmonary artery and aorta.
Cardiac Cycle…
This contraction is called ventricular systole.
The semi-lunar valves close producing the second heart sound.
The cycle is repeated with the period of relaxation called diastole.
How Blood Pumps Through the Heart
The Right Atrium, receives “deoxygenated blood" from the body. Blood will be pushed through the tricuspid valve to the
Right Ventricle, the chamber which will pump to the lungs through the pulmonic valve to the
Pulmonary Arteries, providing blood to both lungs. Blood is circulated through the lungs where carbon dioxide is removed and oxygen added. It returns through the
Pulmonary Veins, which empty into the Left Atrium, (oxygenated blood) a chamber which will push
the Mitral Valve open. Blood then passes into the Left Ventricle. Although it doesn't always look like it in
drawings done from this angle, this is the largest and most important chamber in the heart. It pumps to the rest of the body. As it pumps, the pressure will close the mitral valve and open the aortic valve, with blood passing through to the
Aorta, where it will be delivered to the rest of the body.
Heart Rate & Cardiac Output
Cardiac output- the amount of blood that leaves the heart.
Determined by: Stroke Volume- the amount of
blood ejected with each cardiac contraction.
Heart Rate- how often the heart contracts.
Conduction System
Each complete contraction and relaxation is called a cardiac cycle.
Two main parts- Systole- when the heart muscle
contracts and blood is ejected from the atria to the ventricles and out the aorta.
Diastole- the heart relaxes and refills with blood.
Conduction System…
The impulse comes from the SA node. A specialized area
of cardiac muscle cells that posses the ability of automatically generating the electrical impulses that trigger the repeated beating of the heart.
Conduction System…
The SA node generates an electrical current by the movement of cations across the outer membranes of it’s cells.
Conduction System…
This process called depolarization, generates an electrical current which causes the heart muscle to contract.
Cardiac muscle can transmit an impulse from one cell to another, so electrical impulses and contractions spread across the heart like a wave.
After the impulse is generated in the SA node, it spreads in a wave across both atria, causing the to contract and push blood through the AV valves into the ventricles, which are still relaxed.
Conduction System…
The impulse travels to the AV node where it encounters a slight delay. This is the only conduction route from the
atria to the ventricles. The delay permits the atria to complete
their systolic contraction before ventricular systole begins.
After the AV node, it travels to the specialized fibers in the ventricles called the bundle of His & the Purkinje fibers.
Pathology
Heart Failure
When blood returning to the heart cannot be pumped out at a rate matching the body’s needs.
Many causes exist. Must determine if the failure is a result
of myocardial dysfunction (pump failure) or circulatory failure (lack of circulating fluid volume.
Congestive Heart Failure- when the failing heart allows fluid congestion and edema to accumulate in the body.
Congestive Heart Failure
A degenerative disease where the valve leaflets become knobby and thickened. Regurgitating blood causes enlargement of the left atrium and left ventricle
Mitral regurgitation most common cause; 30% of small breed dogs > 10 years old are affected
Predisposed breeds include Cavalier King Charles Spaniels, Poodles, Mini Schnauzers, Chihuahuas, Cocker Spaniels, Dachshunds, Boston Terriers, & Fox Terriers
Progression of the disease can take years
CHF (cont)
Present with tachypnea, harsh lung sounds, inspiratory crackles that progress to crackles/wheezes throughout respiration with a distinguishable heart murmur
CHF animals are literally drowning in their own fluids.
Patent Ductus Arteriosis (PDA)-
Most common congenital heart defect of dogs
The duct between the left pulmonary artery and the descending aorta in the fetus does not close at birth
Results in left sided CHF
The resulting murmur is often referred to as a “machinery murmur”.
Valvular Stenosis
A narrowing of one of the heart valves
May be aortic or pulmonic
Causes various types of murmers
Persistent Right Aortic Arch
PRAA The most common
vascular ring anomaly
Causes an obstruction of the esophagus
Regurgitation, and aspiration pneumonia are some signs in young weaning animals
Patent Ovale Foramen
A.K.A. Interatrial Septal Defect
Failure of the opening between the two fetal atria to close.
Chronic Mitral Valve Insufficiency CMVI is the most commonly
encountered acquired cardiac disorders in the dog.
One of the most common causes is chronic periodontal disease. Bacteria living in tartar are showered
into the bloodstream, colonizing on the valve leaflets of the heart.
The stiff, malformed leaflets fail to close sufficiently during systole, resulting in regurgitation back up into the atrium.
Canine Dilated Cardiomyopathy
One of the most common acquired cardiovascular diseases of dogs.
Primarily a disease of older, male large & giant breed dogs.
The disease involves the dilation of all four chambers of the heart.
This dilation (caused by weak, thin, & flabby cardiac muscle) results in: A decrease in cardiac output. An increase in cardiac afterload (blood left
in the heart in diastole).
DCM…
The exact cause is unknown, although viral, nutritional, immune-mediated, and genetic causes have been proposed.
DCM results in impaired systolic function of the ventricles and, therefore, decreased stroke volume. The volume of blood ejected from
the heart with each contraction.
DCM…
The effect on the animal is one of low-output circulatory failure, exhibited by: Weakness Exercise intolerance Syncope Shock
DCM…
Dogs with DCM frequently experience the development of atrial fibrillation, which further contributes to a decrease in cardiac output. Signs of atrial fibrillation include
rapid, irregular heart rhythms or sudden death.
Canine Hypertrophic Cardiomyopathy
An uncommon canine disease. The left ventricular muscle
atrophies decreasing the filling capacity of the ventricle and often blocking the outflow of blood during systole.
Feline Dilated Cardiomyopathy
After the association of the disease with taurine deficiency, additional taurine was added to commercial diets and the incidence of the disease significantly decreased.
The pathologic condition is similar to DCM in dogs.
Evidence has been found of a genetic predisposition to DCM in cats fed taurine-deficient diets.
Feline Hypertrophic Cardiomyopathy The most common feline heart disease. Characterized by hypertrophy of the
left ventricle. Compromise of the left ventricular
chamber results in impaired diastolic relaxation, reduction of ventricular filling, and ultimately an impairment in cardiac output.
Cats with HCM may experience heart failure, arterial embolism, and sudden death.
Canine Heartworm Disease
The female mosquito serves as an intermediate host for Dirofilaria immitis.
These microfilaria develop in the mosquito for 2-3 weeks and are then injected into the skin of a dog through a bite.
The infective larvae migrate within the skin of the new host for about 100 days.
Canine Heartworm Disease…
Young adults enter the vasculature and migrate to the heart where they mature into adults.
Six months after the initial bite, the microfilaria can be detected in the blood.
The presence of the parasites results in right-sided heart enlargement and pulmonary hypertension.
Feline Heartworm Disease
Cats are somewhat resistant to D. immitis infection, having few adult worms, which are eliminated from the host within 2 years.
Most symptoms in the cat relate to the respiratory system (cough, dyspnea) or GI system (vomiting, anorexia).
Sudden death of an asymptomatic cat is fairly frequent.
Ataxia, blindness, and seizures can also occur.
Murmurs
Heart murmurs are abnormal sounds caused by bloodflow turbulence. Due to valvular or non-valvular
problems. Systolic murmur- occurs between
the 1st & 2nd heart sounds. Diastolic murmur- occurs between
the 2nd & 1st heart sounds.
Murmurs…
Valvular murmurs- a sound due to a leaky or narrowed valve. Leaky (insufficiency) murmur Narrowing (stenosis) murmur
Non-valvular murmurs- usually occur due to some type of acquired defect. Patent Ductus Arteriosus Interatrial or Interventricular septal
defect
Diagnostics
The Electrocardiogram
ECG, EKG
Applications
Exact diagnoses of arrhythmias heard on ascultation.
Acute onset of dyspnea Shock Fainting or seizures Monitoring during and after surgery All cardiac murmurs Cardiomegaly found on radiographs Cyanosis
Remember…
DEPOLARIZATION: a heart muscle contraction in response to electrical stimuli. Occurs when electrolytes move across
the cell membrane. Sodium-potassium pump
REPOLARIZATION: heart muscle relaxation occurs when the electrolytes move back across the cell membrane rendering the cell ready for the next electrical impulse.
Electrocardiogram
A graphic recording of electrical potentials produced by the heart muscle during different phases of the cardiac cycle. Each portion of the EKG is like a
visual “picture” of a specific area of the heart.
The Complex
P wave- corresponds to atrial depolarization. May be a positive or negative deflection.
QRS Complex- correspond to ventricular depolarization.
T wave- represents ventricular repolarization. May be positive or negative deflections. Every QRS complex MUST be followed by
a T wave.
Lead Systems
A lead system allows you to look at the heart from different angles.
Lead I- best for determining atrial function
Lead II- determines the function of the whole heart
Lead III- best for testing the left side of the heart
***Lead II is the most often used***
Lead Systems…
***Attachment of the Leads***
BLACK left forearm WHITE right forearm RED left rear leg GREEN right rear leg BROWN chest/grounding
Measuring the EKG (The Old Way)
EKG ABNORMALITIES
Quick & Dirty Guide to EKG Abnormalities
P wave: increased in amplitude or duration- atrial enlargement.
R wave: increased in amplitude- left ventricular enlargement.
S wave: increased in amplitude- right ventricular enlargement.
Arrhythmias
An arrhythmia is an abnormality in the rate, regularity, or site of origin of the cardiac impulse.
A disturbance in conduction of the impulse such that the normal sequence of activation of the atria and ventricles is altered.
Arrhythmia Interpretation
Step 1: Determine the heart rate. Is it rapid? Slow? Normal?
Step 2: Assess the rhythm. Scan the EKG print out for abnormalities.
Step 3: Identify the P waves. A normal P wave indicates the impulse
originated in the SA node. Absence of P waves signifies atrial
fibrillation or atrial standstill. P waves may be superimposed on the QRS
complex in various supraventricular tachycardias.
Arrhythmia Interpretation…
Step 4: Assess the QRS shape & duration. Abnormalities in the shape can
suggest a disturbance of ventricular impulses.
Arrhythmia Interpretation…
Step 5: Look at the relationship between the P waves and the QRS complexes. Normally, there should be one P wave for
every QRS complex with a constant P-R interval.
Long P-R intervals indicate an AV conduction delay (1° AV block).
A P wave not followed by a QRS complex indicates 2˚ AV block.
P-R intervals that vary indicate 3˚ AV block.
Normal Sinus Rhythm
P waves are positive. QRS complexes are normal with a constant P-
R interval. This is NORMAL.
SINUS IMPULSE DISTURBANCES
Sinus Arrhythmia
An irregular rhythm originating in the SA node.
Represented by alternating periods of slower & more rapid heart rates.
Usually related to respiration: Heart rate increases with inspiration
and decreases with expiration. A frequent normal finding in the
dog.
Sinus Arrhythmia…
Often seen in brachycephalic breeds or in chronic respiratory diseases, in which vagal tone is increased by upper airway obstruction.
Atropine eliminates respiratory induced SA.
Sinus Arrhythmia…
Sinus Bradycardia
A regular rhythm, with a slow heart rate. In cats, it is often associated with a serious
underlying disorder, which requires immediate attention.
Causes- intubation, hypothermia, & respiratory disease.
Sinus Tachycardia
A regular sinus rhythm, with a fast heart rate.
The most common arrhythmia in dogs and cats.
Physiologic causes include: exercise, pain, or procedures involving restraint.
Pathologic causes include: fever, hyperthyroidism, shock, anemia, infection, CHF, & hypoxia.
Drugs include: atropine and epinepherine.
Sinus Tachycardia…
SUPRAVENTRICULAR IMPULSE DISTURBANCES
Atrial Premature Contractions
Caused by impulses originating from a site other than the SA node.
The heart rate is usually normal. The P-R interval may be long. A pause usually follows an APC. Seen in both dogs and cats,
usually a result of atrial enlargement (e.g., mitral insufficiency, cardiomyopathy).
Atrial Premature Contractions…
Atrial Tachycardia
A rapid regular rhythm originating from a site other than the SA node.
Three or more APC’s.
Atrial Fibrillation
Caused by numerous disorganized atrial impulses bombarding the AV node.
Has a rapid and totally irregular atrial and ventricular rate.
No P waves. Commonly seen in conditions
associated with atrial enlargement, or dialted cardiomyopathy.
Atrial Fibrillation…
VENTRICULAR IMPULSE DISTURBANCES
Ventricular Premature Contractions Cardiac impulses initiated in the
ventricles instead of the SA node. Associated with weakness,
exercise intolerance, & sudden death.
QRS complexes are typically wide and bizarre.
P waves are dissociated from the QRS complex.
Ventricular Premature Contractions…
A VPC is usually followed by a pause.
Commonly seen in large breed dogs with cardiomyopathy, especially boxers and Dobies.
Common in cats with cardiomyopathy; occasionally seen in cats with hyperthyroidism.
Ventricular Premature Contractions…
Ventricular Premature Contractions…
Ventricular Tachycardia
Three or more VPC’s in a row. The ventricular rate is >150 bpm. QRS complexes are wide and
bizarre. There is no relationship between
the P waves and the QRS complexes. The P waves may precede, be hidden
within, or follow the QRS complexes.
Ventricular Tachycardia…
Ventricular Fibrillation
Occurs when the cells of the ventricular myocardium depolarize in a chaotic and uncoordinated manner.
No pulse can be felt and cardiac output approaches zero.
No QRS complexes or P waves.
Ventricular Fibrillation…
Associated conditions include: Shock, Myocardial
infarction, Electrolyte & acid-
base imbalances, Aortic stenosis Hypothermia
Ventricular Asystole
Indicates the absence of any pacemaker impulses.
Subsequently, there is no depolarization or contraction of the ventricles.
No pulse can be felt and cardiac output approaches zero.
P waves may be present if the animal has complete AV block.
Ventricular Asystole…
No QRS complexes.
IMPULSE CONDUCTION DISTURBANCES
Atrial Standstill
Characterized by an absence of P waves. Patients have SA node function, but impulses do
not cause myocyte activation. Causes include hyperkalemia and atrial disease.
First-Degree AV Block
A delay in the conduction of an impulse through the AV node and bundle of His.
Usually characterized by a prolonged P-R interval.
Generally seen in older patients secondary to degenerative changes in the conduction system.
First-Degree AV Block…
Second-Degree AV Block
Characterized by an intermittent failure or disturbance of AV conduction.
One or more P waves are not followed by QRS complexes.
P-R interval is often variable.
Third-Degree AV Block
The cardiac impulse is completely blocked in the region of the AV junction.
The P wave is normal. The QRS complex is wide and
bizarre. There is no conduction between
the atria and ventricles.
Third-Degree AV Block…
II. Circulatory System
Circulatory System
Consists of the heart, blood vessels, and lymphatics. Blood acquires oxygen in the lungs,
nutrients from the digestive tract, and hormones from endocrine glands.
Blood Vascular System- consists of blood, heart, arteries, capillaries, & veins.
Circulatory System…
Artery- a vessel carrying blood away from the heart. Generally thicker and stronger than
veins. Capillary- a microscopic vessel
that joins others to form an extensive network. Positioned between arteries and
veins. They allow exchange of gasses and
nutrients between the blood and interstitial fluid.
Circulatory System…
Veins- vessels carrying blood towards the heart. Thinner-walled, they carry a greater
volume than arteries.
Circulatory System…
Arteries arterioles capillaries venules veins
Circulatory System…
Valves in veins ensure that blood travels only in the direction of the heart.
Constriction and relaxation allow the vascular system to direct blood to different parts of the body, and to maintain blood pressure when blood volume or cardiac output is decreased.
Notable Vessels
Remember… for every artery taking fresh blood to the body, there is a vein to carry deoxygenated blood back to the heart– just like on and off ramps to the “major highway!
Feline Thromboembolism
a.k.a. a saddle thrombus Classic presentation is
posterior paresis with weak or absent pulses in the rear limbs; foot pads are pale, and the toenails won’t bleed when quicked; the gastrocnemius and tibial muscles are rock hard by 10-12 hrs post-clot
Aggressive thrombolytic therapy may be instituted if the clinician feels the thrombus is recent (2-4 hrs) and the heart disease is manageable but the prognosis is still guarded
Feline Thromboembolism (cont)
Most common site is at the aortic trifurcation
Clinical signs depend on the degree of heart disease and the site of thromboembolism
It may be the first sign of heart disease or sometimes cats will show severe signs of CHF
THE END!
