Cardiovasular System

Right

Side of the heart that carries blood from body to lungs

Deoxygenated

Venae cavae carry _____ blood from the body

Left

Side of the heart that carries oxygenated blood from lungs to body

Oxygenated

Pulmonary veins carry _____ blood from the lungs

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

Arteries → arterioles → capillaries → venules → veins

Order of blood flow

Arteries

Carry oxygenated blood that has left the heart via the aorta

Pulmonary Artery

Carry oxygenated blood that has left the heart via the aorta

Arterioles

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

Capillaries

Allows for diffusion of nutrients, O2, CO2 across them

1

Endothelial walls are ____ cell layer thick

Venules

Begin the trip back to the heart, carry oxygen poor blood

Veins

Easily distensible, carry deoxygenated bood, thin walled

Pulmonary Veins

Dump oxygenated blood from the lungs into the L atrium

Pulse

Indicates mechanical activity

Sound

Reflects turbulence of the blood

Electrical impulses

What stimulates contractions of myocardial muscles

ECG/EKG

Shows cardiac rates, rhythm, and conduction of time of impulses

P

Waves that depolarize and tell atria to contract

QRS

Waves that tell ventricles to contract while atria relax

T

Waves that tell ventricle to relax

Stroke volume

Volume of blood ejected from each cardiac ventricle with each contraction

Cardiac Output

HR x stroke volume

Dehydration

Decreases stroke volume and cardiac output, so horse has ncreased HR to maintain CO

Cardiac output, arterial resistance, venous blood flow, chainges in air pressure in thorax

Blood pressure depends on

Systole

Contraction of the heart

Diastole

Relaxation of the heart

Resting HR

25-40 bpm

Trotting HR

70-120 bpm

Cantering HR

120-150 bpm

Max, velocity HR

220-240 bpm

Recovery heart rate

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

Congenital cardiac abnormalities and diseases

< 3 years old are more likely to have

Valvular or conduction disturbance

>3 years old are more likely to have

½ to a ¾ of the way up

How far in the jugular furrow can the jugular be seen when a horse is grazing?

Abnormal jugular distension

Occurs during ventricular contraction

Arterial Pulse

Simultaneous ascultation to pick up ventricular arrhythmias

2 seconds

Capillary refill time should be <

30-48/min

Resting heart rate of an adult horse

S4

Atrial contraction sound

S1

Ventricle contraction/ AV valves closing sound

S2

Ending of ventricular contraction/ closing of semilunar valves sound

S3

Rapid ventricular filling phase during systole

Murmurs

Prolonged sounds caused by disrupted laminar flow causing turbulence

Functional

Murmurs that occur in the absence of heart disease, found in young normal horses

Pathologic

Murmurs that are caused by organic heart dieases

Systolic

Murmur due to abnormal blood flow throughout systole from a hamber with higher pressure to a chamber with lower pressure

Diastolic

Murmur caused by aortic valve insufficiency (often musical)

Normal Sinus Rhythm

Rhythm remains regular during both inspiration and expiration

Sinus Arrhythmia

Rate increases during inspiration

1st degree AV block

Progressive lengthening of PR interval

2nd degree Av block

Most common normal rhythm variation in resting horse, associated with high vagal tone, a single P wave or 2 consecutive P waves blocked from entering the AV node

Sinoatrial block

No P waves on ECG, sinus node impulse is formed but is blocked at the SA node junction

Sinus Tachycardia

Heart rate of >50/min, ECg should be done to rule out atrial fibrillation, normally seen in foal/excited horse/after exercise

Echocardiography

Non-invasive ultrasound imaging of heart in real time

M-Mode

One-dimensional image of the heart

B-Mode

Two-dimensional image of the heart

Radiography

Lateral chest x rays

Cardiac Catheterization

Monitors BP and used to obtain blood samples from different parts of the heart

Exercise Testing

Use ofhigh-speed treadmill where heart can be evaluated during exercise

Normal Sinus Rhythm

What does this picture show?

2nd degree AV block

What does this picture show?

Sinus Arrhythmia

What does this picture show?

Sinus Block

What does this picture show?

Sinoatrial Node (SAN)

Originates impulse, produces the fast “inherent” heart rate

Atrioventricular Node (AVN)

Takes over as pacemaker if SAN fails, slow than SAN

Changes in blood pressure

What causes valves to open and close

Sympathetic

Nervous system responsible for fight, flight, or fright response

Parasympathetic

Nervous system reponsible for “calm”

Atrial Fibrillation

The most common clinically significant arrythmia in horses, often occurs with no underlying heart disease, most commonin young male standardbreds and draft horses, often accompanies congestive heart failure

Irregularly irregular

What kind of rhythm and pulse happens with atrial fibrillation

Quinidine

Drug of choice for atrial fibrillation

Digoxin

Drug that complements quinidine for atrial fibrillation

Good, most horses respond to therapy

Prognosis with atrial fibrillation and NO heart disease

Endocarditis

Lesions found on heart valves, most commonly aortic, usually on older horses

NSAIDs, furosemide, hydralazine, digoxin

Treatment for bacterial endocarditis

Furosemide, hydralazine, digoxin, avoid salt supplements, stall rest

Treatment for degenerative endocarditis

Myocarditis

Inflammation of myocardium, treatment is rest, antibiotics, and drugs, prevented by vaccinating for respiratory viruses, prognosis is good if no heart failure

Pericarditis

Inflammation of pericardium that causes excessive amount of fluid, treatment is usually not effective but depends on type

Pericardiocentesis

Type of treatment for effusive pericarditis

Pericardiectomy

Treatment for constrictive pericarditis

Dilated Cardiomyopathy (DCM)

Clinical signs look like heart failure, prognosis is poor, treat same as heart failure, associated with vitamin E/selenium deficienct or cardiac tumors

R Sided heart failure

Right ventricular hypertrophy that causes excessive amount of blood to enter pulmonary circulation, prognosis is poorfor return to normal function, treat with digoxin, treat underlying disease, and diuretics

Congestive Heart Failure

Heart has undergone change, no longer maintains adequate cardiac output to supply oxygen requirements. Treatment is to increase inotropes, use vasodilators, and diuretics

L Heart failure

L side of heart pumps inadequately (usually due to faulty valve)

Sudden Death

Due to electrical abnormalities in myocardium, aortic aneurysm, or great stress combined with rhythm abnormality (such as atrial fibrillation)

Ventricular Septal Defect

Most common cengenital cardiac defect in horse, found in upper portion of ventricular septum, L-R shunting of blood due to aortic pressure. Small defects may need nothing, large will need pasture use only

Ductus arteriosus

Communication between aorta and pulmonary artery durying embryonic development, close after first few breaths

Ligamentum arteriosum

Formed after first few oxygenated breaths cause arterial duct to close

Flunixin meglumine, surgery of neonate

Treatment for Ventricular Septal Defect