Cardiovascular Exam

Vena cavae → R atrium → tricuspid valve valve → R ventricle → pulmonic valve → pulmonary artery → Lungs → pulmonary veins → L atrium → mitral valve → L ventricle → aortic valve → aorta → body

Order of blood flow through the heart

Artery → arterioles → capillaries → venules → veins

Orde through vesselsr of blood flow

Artery

Carry oxygenated blood that has left the heart via the aorta

Arterioles

Smaller and more numerous than artieries, mostly smooth muscle in walls and not as elastic

Capillaries

Diffusion of nutrients, O2, and CO2 into tissues

Venules

Carry oxygen poor blood back to heart

Veins

Easily distensible, carry deoxygenated blood

Left side because it has to pump blood throughout the body

Which side of the heart is a high pressure system and why?

Right side because lungs accomodate blood easily

Which side of the heart is a low pressure system and why?

Allows for elastic recoil

Arteries with smooth muscle and elastic tissue in their walls because _____

Veins

Where is up to 70% of the blood volume contained? Why?

Endocardium

Lines the interior of the heart and makes up the valves

Myocardium

Muscle layer that makes up the bulk of the atria and ventricles

Epicardium

External surface of the heart

Pericardium

Sack surrounding the heart

Stroke Volume

Volume of blood ejected from each cardiac ventricle with each contraction

Cardiac Output

Output of blood from the heart, HR x stroke volume

Decrease in stroke volume, decrease in cardiac output

What happens to HR when a horse is dehydrated? Why?

Recovery Rates

Used to assess fitness of horses competing in endurance rides, eventing, etc.

Respiratory, musculoskeletal disorders

Primary causes of poor performance and/or exercise intolerance

Dyspnea

Shortness of breath

¼ way up

Where in the jugular furrow is the jugular pulse seen if NORMAL when the horse is grazing?

Halfway up, bulging

What does an abnormal jugular pulse look like?

Left heart failure, less blood being pumped out into systemic circulation

Reasons for weak arterial pulse

Dropped beats

Reasons for a pulse deficit

Severe aortic regurgitation, laminitis, sole abscess

Reasons for a high intensity pulse

S1 and S2

Which 2 heart sounds are the most prominent?

Atrial Systole (Atrial contraction)

Associated with S4

Ventricular Contraction/AV Valve Closure

Associated with S1

Semilunar Valve closure & end of ventricular contraction

Associated with S2

S1 and S2

Systole is between which 2 heart sounds?

S2 and S1

Diastole is between which 2 heart sounds?

Systole

Contraction

Diastole

Relaxation

Heart Murmur

Prolonged sounds, caused by disrupted laminar flow

Diastolic Murmur

Often musical, associated with aortic valve insufficency

Systolic Murmur

Abnormal blood flow from high to low pressure chamber, associated with tricuspid valve

Anemia, increased diameter of heart, increases in cardiac output, abnormal blood flow, colic

Causes for murmurs

Pathologic

Murmurs caused by organic heart disease

Normal Sinus Rhythm

Rhythm remains regular during both inspiration and expiration, P waves are normal

Sinus Arrhythmia

Rate increases during inspiration, P waves without QRS

1st Degree AV Block

Progressive lengthening of PR interval

2nd Degree AV Block

Disappears with exercise or atropine, 2 non-conducted p waves

Sinoatrial Block

Sinus node is formed but blocked at SA node junction, no P wave

Sinus Tachycardia

Increased heart rate, secondary to colic/shock/septicemia/fever/ pain/heart failure

Parasympathetic

What part of the nervous system is responsible for decreased heart rate and several rhythm variations?

Sympathetic

What part of the nervous system is responsible for increased heart rate?

2nd Degree AV Block

What is the most common rhythm variation in the resting horse?

Evaluate heart size, detect blood flow, abnormal fluid,

Uses for radiography for heart disease

Can’t define disease, poor sensitivity, hard to see right side

Limitations of radiography for heart disease

Cardiac Catheterization

Passing catheter into side of the heart to evaluate function

Exercise Testing

Having the horse work while being tested

Verifies presence, cause, and prognosis

Reasons to use ECG

Rate, rhythm, and conduction time

What do ECG’s evaluate?

SAN

Pacemaker - originates impulse

AVN

Takes over as pacemaker if other fails, slower but still regular

His-Bundles

Cardiac conduction fiber connecting AV node to left and right bundle branches

Purkinje FIbers

Cardiac muscle cells that transmit electrical impulses through the heart’s ventricles

P

Waves for atrial depolarization

PR interval

Slowing of impulse while going through the AV node

QRS complex

Impulse spreading through Bundle of His

R

Waves asociated with ventricular depolarization

T

Waves associated with ventricular repolarization

Biphasic P wave

Two distinct phases - usually an initial positive followed by negative

Atrial Fibrillation

Often occurs with no obviously underlying heart disease, most common in young male standardbreds and draft horses, irregularly irregular rhythm and pulse

Give quinidine and digoxin

Treatment for atrial fibrillation with no heart disease

Treat underlying disease

Treatment for atrial fibrillation with heart disease

Most horses respond to therapy, but with congestive heart failure it’s poor

Prognosis for atrial fibrillation

Brachycardia

Abnormally slow heart rate

Electrical signal’s from atria are interrupted before making it to ventricles

What causes 2nd degree AV Block?

Exercise or atropine

How can you abolish 2nd degree AV Block

Atrial Fibrillation

What is the most common clinically significant arrhythmia in the horse?

Atrial Fibrillation

What does this ECG show?

Atropine

When and why

Quinidine

The main medicine used in atrial fibrillation

Furosemide

Dieuretic used for heart disease (endocarditis)

Digitalis/Digoxin

Used to complement quinidine for heart disease

Endocarditis

Lesions found on aortic heart valve, treatment for bacterial is NSAID’s, treatment for degenrative is furoseminde/digoxin/hydralazine and avoid salt supplements

Pericarditis

Inflammation of pericardium, prognosis is poor, prevent by vaccinating for respiratory viruses,

R Sided Heart Failure

Right ventricle hypertrophy secondary to disorders that cause excessive amount of blood to enter pulmonary circulation, prognosis is poor for returning to normal function

Congestive Heart Failure

Heart undergoes change and no longer has proper output, treatment is increase inotropes/vasodilators/diuretics

PDA, Patent Ductus Arterious

Arterial duct doesn’t close after birth, causes L → R shunting of blood because of aortic pressure, L sided heart failure and sudden death

Machinery-type murmur, coughing, increased respiratory rate and effort

Clinical signs of PDA

Surgery of neonate, flunixin meglumine

Therapy for PDA

VSD, Ventricular Septal Defect

Most congenital cardiac defect, causes L → R shunting of blood, increases amount of blood to lungs and dilates R ventricle

Small → do nothing, large → pasture use only

How to treat VSD

Exercise intolerance, lethargy, heart failure (both sides), murmur

Clinical signs of VSD in large defect

Monensin Toxicity

Selenium Deficiency

White Muscle Disease

Jugular Thrombophlebitis

Caused by injections, prolonged catheterization, repeated IV injections

Affected vein is enlarged and painful, affected side has swelling of cheek and eye tissues, distension of vessels, elevated temp, anorexia, depression

Clinical signs of jugular thrombophlebitis

Remove catheter, topical DMSO, elevate head, NSAID’s, surgical excision and venous grafting

Treatment for jugular thrombophlebitis

Good if non-septic, guarded if septic

Prognosis for jugular thrombophlebitis

Thrombus

Clot formation within and attached to a vessel wall, usually due to catheterization

Embolus

Foreign material or showers of tiny clots carried in blood. These can lodge in small vessels w presence of parasites and cause severe colic.

Blockages from parasites like strongylus vulgaris, hind limb lameness, exercise intolerance, sweating

What are the signs of thrombus?

Aneurysm

Dilation/bulge of the wall of a blood vessel, may rupture and cause sudden death

Aortic Rupture

Can be a result of weak point in vessel wall or spontaneous at level of aortic valve. Can rupture at rest or during exercise

Death, sudden decrease in speed, collapse, ataxia

What are the signs of aortic rupture?