Horse Cardiology

Equipment costs

xray 80K
probes 50K
ultrasound 5-25k

only buy if you have enough money to fund it

Ataxic

In horses, ataxia refers to a lack of voluntary muscle coordination, causing an unsteady or "wobbly" gait.

- Symptoms: Staggering, dragging toes, hindquarter swaying, or crossing limbs when walking.
- Common Causes: Neurological conditions such as Equine Protozoal Myeloencephalitis (EPM), Wobbler Syndrome (Cervical Vertebral Stenotic Myelopathy), or trauma to the spinal cord.

Grades of Ataxia

Definition: Neurological deficits in horses are graded on a scale from 0 to 5:

1. Grade 0: Normal neurological function.

2. Grade 1: Subtle deficits only detected during special maneuvers (e.g., backing up, tight circles).

3. Grade 2: Mild deficits that are visible at a normal walk.

4. Grade 3: Moderate deficits; incoordination is obvious and the horse may weave or stumble.

5. Grade 4: Severe deficits; the horse is highly unstable and prone to falling during normal movement.

6. Grade 5: Recumbent; the horse is unable to stand up

Lameness

horse is unable to walk properly, left foot down gingerly, right foot drag, then hop, limp

Atlas Vertebrae of horse

atlas is the first vertebrae, Its primary function is to protect the spinal cord at the base of the skull and support the head, allowing for a range of motion between the skull and the neck.

Axis Vertebrae of horse

second vertebrae, head side to side, longest vertebra, provides surface for neck muscles and supporting head, protects spinal cord from skull through neck

How blood moves through the heart

1. Deoxygenated blood returns from the body via the vena cava into the Right Atrium.

2.It passes through the tricuspid valve into the Right Ventricle.

3.The right ventricle pumps the blood through the pulmonary valve to the lungs via the pulmonary artery.

4.Oxygenated blood returns from the lungs via pulmonary veins into the Left Atrium.

5.It passes through the mitral valve into the Left Ventricle.

6.The left ventricle pumps the oxygenated blood through the aortic valve into the Aorta to be distributed to the rest of the body.

Pressures in left and right sides

left is high pressure, right is low pressure

What are the chordae tendinae?

anchor the leaflets of the mitral and tricuspid valves to the papillary muscles in the heart ventricles. They prevent the atrioventricular (AV) valves from inverting (prolapsing) into the atria during ventricular contraction (systole), thus preventing blood backflow and ensuring one-way flow

What is a heart murmur?

when the chordae tendinae is loose and causes the heart to make a whooshing noise

What is the one thing that is common for all heart diseases for horses?

exercise intolerance

What is the function of the veins?

The veins are to take away, only one carries oxygenated blood
remove de-oxygenated blood
walls much thinner and less elastic tissue
lower pressure
venous intima folds to form venous valves

venules = veins = vena cava

What do the arteries do?

Arteries deliver oxygenated blood

• High pressure system.

• Aorta and other larger arteries contain a large amount

of elastic tissue.

• Aorta=> Arteries=>Arterioles=>Metarterioles

• Only one artery carries de-oxygenated blood.

Capillaries

• Where the action is!

• In the lungs gas is exchanged.

• In body oxygen and nutrients delivered.

• Junctions between endothelial cells

• Vesicular transport

• Fenestration

• Capillary sphincters

• A-V shunts

A-V shunts

These shunts bypass the capillary network, allowing high-pressure arterial blood to flow directly into low-pressure veins or chambers (right atrium, right ventricle, or coronary sinus)

Vesicular transport

Vesicular transport is a fundamental, ATP-dependent active process in cells where substances move within membrane-bound sacs called vesicles, facilitating cargo delivery between organelles (ER, Golgi, lysosomes) or across the plasma membrane (endocytosis/exocytosis)

endothelial cells

Endothelial cells (ECs) are a thin, specialized layer of cells forming the inner lining of all blood vessels, lymphatic vessels, and the heart, acting as a crucial, dynamic barrier between blood and tissues. They regulate vascular tone, blood flow, nutrient exchange, and immune responses while inhibiting blood clotting. These cells are essential for angiogenesis (forming new vessels) and wound healing.

Fenestration

Fenestrated capillaries are blood vessels with tiny pores (fenestrations or "windows") in their endothelial cells, allowing for rapid filtration and exchange of water, nutrients, hormones, and waste between blood and tissues

Why does the Heart Beat?

• Cardiac Conduction System.

• Sinoatrial node (SA node).

• Internodal atrial pathways.

• Atrioventricular node AV node).

• Bundle of His

• Purkinje system

• All can spontaneously discharge

What is arrhythmia?

An arrhythmia is an irregular, too-fast (tachycardia), or too-slow (bradycardia) heartbeat caused by faulty electrical signals, often described as an "out of sync" or fluttering heart.

Sinoatrial Node

• SA node discharges most rapidly.

• Cardiac pacemaker in right atrium

Internodal atrial pathways

Internodal atrial pathways are specialized routes of conductive heart tissue connecting the SA node (natural pacemaker) to the AV node, ensuring rapid, organized electrical signal spread across the atria for coordinated contraction

Atrioventricular node AV node

The Atrioventricular (AV) Node is a crucial part of the heart's electrical system, acting as a gateway between the atria (upper chambers) and ventricles (lower chambers) to coordinate heartbeats, delaying electrical signals to ensure the atria fully contract and fill the ventricles with blood before the ventricles themselves contract

bundle of HIS

A bundle of specialized heart muscle cells that passes from the AV node into the interventricular septum. It divides into left and right bundle branches to conduct impulses to the apex of the heart.

Purkinje Fibers

A network of specialized fibers that extend from the bundle branches into the subendocardial tissue of the ventricles. They have a very fast conduction rate (approx. 75 milliseconds) to ensure rapid depolarization of the ventricles.

Automatic Nervous System

a component of the peripheral nervous system that regulates involuntary physiological processes, Parasympathetic, enteric (gastrointestinal control), and sympathetic systems

parasympathetic

relaxing system
medulla makes saliva
vagus nerve: slows heartbeat, constricts lungs/bronchii, bile release, bladder contract, stim secretion/peristalsis

sympathetic

fight or flight, active excited, dilates pupil, inhibits saliva, accelerates heart, dilates bronchi, solar plexus: inhibits peristalsis and secretion, liver converts glycogen to glucose, secretion of adrenaline and noradrenaline, inhibits bladder contraction

Sympathetic system in horses digestive system

shuts down the intestines and stomach, feels pain and therefore the horse wants to run or fight

Parasympathetic system in horses

vagus tone makes them drop a beat, cardiovascular function that facilitates adaptive responses to environmental challenge, makes them relax, skip a beat

How to count heart rate in horses?

15 sec x 4
or 30 secs x 2
count how many beats in those seconds and multiply by the additional number

What happens when the horse is scared?

Horses heartbeat can be 80 plus if animal is fearful.

• Horses know who the Vet is.

• Frequently have to take heartbeat last to let animal relax.

What are heart sounds?

Heart sounds are the closing of the cardiac valves.

• Lub is the closing of the mitral and tricuspid valves

(S1).

• Dub is the closing of the aortic and pulmonary valves

(S2).

• S3 is caused by rapid ventricular filling.

• S4 is from atrial contracting to fill ventricle

• In the horse , S4-S1-S2-S3

Electrocardiogram

Electrical activity of cardiac muscle.
Qrs ventricular depolarization (contraction) and is primarily used to diagnose cardiac arrhythmias, conduction abnormalities (like bundle branch blocks), ventricular hypertrophy, myocardial infarction (heart attack), and electrolyte imbalances
electrical system of the heart is the SA
ventricular contract is the qrs, T is where everything depolarizes, relaxes to normal

SA node does what?

makes atrium contract

If you see changes in QRS

likely afib, in humans clogged artery means a part can die and you will see changes in qrs

horse heart attack

not a real attack, but rupture of aortic, blood fills the abdominal cavity, brain shuts down and then death

Myocardial (muscular tissue) not an issue

• Aortic rupture

– Peak athletic exertion.

– Sudden death post race

– No external signs, white mm

Membrane Potential

• Normal resting membrane potential is -70mv

– Cardiac muscle is -90mv

• Na+ actively transported out of cell

• K+ actively transported into cell

• Once threshold is met. Na+ channels open

Muscle Contraction

• Muscle fibers are the building blocks.

• Cell membrane = Sarcolemma with T-tubule system

• Muscle Fiber=>Myofibrils=>Filaments

• Filaments made up of contractile proteins

• Myosin

• Actin

• Tropomysin

• Troponin I, T, C

Myosin

A molecular motor protein that converts chemical energy (ATP) into mechanical energy (force).

Forms thick filaments with heads that bind to actin.

Powers movement by "walking" along actin filaments.

thick filaments

cause contraction, cell division, migration, and intracellular transport

Actin

• globular protein that polymerizes to form long, thin filaments.

• Contains binding sites for myosin heads.

• Key role in cell shape, movement, and division

Once Threshold reached

– Na+ influx

– K+ efflux

– Via the T-tubules the Sarcoplasmic Reticulum releases

Calcium

Tropomysin

Tropomyosin is an actin-binding, rod-shaped coiled-coil protein that regulates muscle contraction and acts as a major regulator of the cytoskeleton in non-muscle cells. In muscles, it blocks myosin-binding sites on actin, preventing contraction until calcium ions trigger a conformational shift

Troponin I, T, and C

Troponin I, T, and C are regulatory proteins within cardiac and skeletal muscle that control contraction

Troponin I, T, and C types

Troponin C (cTnC): Binds calcium ions to initiate muscle contraction. It is not specific to the heart.

Troponin I (cTnI): Inhibits myosin and actin interaction; specifically cardiac-specific, making it highly sensitive for heart muscle damage.

Troponin T (cTnT): Binds the troponin complex to tropomyosin. Primarily found in cardiac muscle, with minor, limited presence elsewhere.

Muscle Contraction

• Release of Calcium starts the contraction

• Calcium binds to Troponin C

• This binding causes tropomyosin to move off of the

actin binding site

• Myosin head then binds to actin.

• Myosin head then bends with ATP.

• Cycle is repeated many times

What is a sarcomere?

a muscle unit with myosin and actin fibers

Cortenary artery

provides blood to the heart muscle
every cell has a capillary that feeds it and takes away waste

horse lying on ground, blood from both nostrils

blood out both nostrils and that violent usually means lungs blew up, or larenx has problems

horse nostril bleeding

1 nostril, doctor did it, accidentally hit their tooth, or rotten tooth

PDA Patent Ductus Arteriosus.

Normal in foals for the first 72 hours of life

– Shunt from pulmonary artery to aorta in utero

– Washing machine murmur, turbulence

in utero no lungs are needed, bypass during that is the shunt
but as soon as the baby is born, starts to breath, pda should shut down

Atrial Septal Defect and Ventricular Septal Defect.

– Causes de-oxygenated blood to be pumped to body

– Murmur

– Exercise intolerance

wall between left and right heart sides, can have defect, high pressure blood squirts into the low blood pressure side, oxygenated blood doesn’t get around as much

Valvular Insufficiency

– All four can be effected (usually not at once)

– Murmur

– Ruptured Chordae Tendineae

• Leads to valvular insufficiency: a heart condition where valves fail to close completely, causing blood to flow backward, decreasing cardiac efficiency

Endocarditis

Endocarditis is an infection of the heart's inner lining, chambers, or valves, most commonly caused by bacteria that enter the bloodstream and attach to damaged heart tissue

Atrial Fibrillation or afib

– Most common arrhythmia

– Exercise intolerance

– Irregularly- irregular, everything discharge when they want, not good

– Can treat with Quinidine

standard bred racehorses, whoosh bum sound

Congestive Heart Failure

Congestive Heart Failure

– Dilated cardiomyopathy: a serious heart condition where the heart's main pumping chamber (left ventricle) enlarges and weakens, making it harder to pump blood, which often leads to heart failure

– Seen with COPD: Chronic Obstructive Pulmonary Disease (COPD) is a progressive lung disease causing airflow obstruction, with symptoms including shortness of breath, chronic cough, and mucus production

a chronic condition where the heart cannot pump enough blood to meet the body's needs, causing fluid to build up in the lungs and body

blood composition

plasma 55%, white blood cells and platelets <1%, red blood cells 45%

Blood

8% of body weight.

• Adult horse has aprox. 10 gallons of blood

• Transports oxygen and carbon dioxide

• Transports nutrients from GI

• Transports waste to kidneys

• Transports hormones from glands to target

• Aids in thermoregulation

• Key component of Immune System

• Clotting Cascade

red blood cells

No nuclei

• Hemoglobin in conjunction with iron carries oxygen

from lungs to tissues and carbon dioxide from tissues

to be expelled in lungs

• Produced in bone marrow

• Circulate 3 – 4 months then removed

• Large reserve in spleen, horse can contract spleen

when increased oxygen carrying capacity is needed, can squeeze and dump out RBCs, usually for escape, higher and more common in wild horses

baby horse is colic, laying down like a dog

nuconium compaction, use enema to treat it, soapy water, nuconium from fluids of baby getting embryonic fluids which are protein, eating it and feces

blood loss

Reproductive tract

– Breeding

– Post delivery

– Umbilical stump

broad ligament can rupture and bleed and mother horse can bleed out

proud flesh

lower wounds, excessive granulation, bulging over the skin, can cut it back and pressure wrap it, or burn it with copper sulfate to burn it back, caustic powder

lacerations

foreheads bleed a lot, but with blood flow there is healing
legs do not have great blood flow
distal limbs should be wrapped up
old wounds should be let to drain

Lacerations on distal limbs should be wrapped.

• If first bandage becomes soaked.

• Apply second bandage over first.

• Only remove bandages when primary repair is to

occur

How does clotting work?

muscles will spasm and cause clotting, but humans can then give pressure, there is a cellulose based clotting agents for soldiers

laceration treatments

betadine: stains you brown, less cytoxins used in hospitals
nolvasan: stains you blue, usually surgical

lidocaine for pain does also dilate the blood vessels so will bleed

old wounds can be tacted together

what is epistaxis?

nosebleed, lung rupture, or vet hit something and bleed

Exertion

– Exercise-induced pulmonary hemorrhage

• Trauma

– NGT

• Sinuses

– Ethmoid hematoma

dehydration

brain and heart have priority, sucks all fluid for that
Mucus Membranes dry up as dehydration progresses.

• GI sounds decrease as dehydration progresses, constipation or compaction, leading to gasses building, intestinal stretches, horses get anxious and feel painful, flight or fight mode, cecum fills out, sounds like a drum, skin stretched, constant gas production and horse balloon up

• Skin Tenting, check the eyelids, pinch on eyelids, see if stays, very subjective

Protein calculation

use a refractometer: measure total protein concentration in blood serum or plasma.

anemia

lack of RBC
–Decreased production: stop making them

– Loss

– Increased destruction, something is killing them

ex: tick borne illness, parasite, causes body to attack RBC

red maple trees, if branch falls off and a horse eats rotten leaves, horses can get renal failure, red blood cells clogging the kidneys
black walnuts, shavings can also cause failure

PVC determination

Packed Cell Volume (PCV) determination, or hematocrit, measures the percentage of red blood cells (RBCs) in a blood sample, typically through centrifugal separation
put the blood sample in a thin plastic tube with a stopper
RBC and plasma will separate after spinning, you measure the percentages based on how high the RBC level is in the thin tube
- Dehydration causes pcv to increase
- Anemia causes pcv to decrease

Where to draw blood from a horse?

jugular, if the horse is moving around a lot, you have to aim the needle downward to poke in

carotid artery is right on top of the jugular the further up the neck you go, the artery and vein separate and that gap gets bigger

What does the carotid artery do?

It gives blood to the brain, if injured, horses can backflip and then just lie on back having seizures, can only wait it out, they may die or get better

Where is the jugular vein?

it stands above the trachea, if you squeeze the neck muscles, it will fill up

Why blood tests?

check for drugs, but also, if a horse crosses state lines, equine infectious anemia exists, Dr. Cogins came up with test for this

"swamp fever," is an incurable, often fatal, viral disease of equids (horses, mules, donkeys) characterized by fever, severe anemia, and swelling
via blood-sucking insects or contaminated equipment, infected horses become lifelong carriers, requiring permanent isolation or euthanasia

What is the gutteral pouch?

Guttural pouches in horses are paired, air-filled sacs (outpouchings of the Eustachian tubes) located in the throatlatch region
used for thermo regulation

there is also a vessel inside to warm the air as it is breathed in

prone to mycosis (fungal plaques), empyema (pus), or tympany (air entrapment)

How do the legs thermoregulate?

Arterial blood is cooled by exchanging its heat to the returning venous blood in the legs

What is the starling equation?

What is interstitial pressure?

Interstitial pressure (or Interstitial Fluid Hydrostatic Pressure, IFHP) is the pressure within the fluid-filled spaces between cells (interstitial space) that influences fluid movement between these tissues and blood capillaries, typically acting as an opposing force to fluid exiting capillaries

What is osmotic pressure?

Osmotic pressure in blood is the force exerted by solutes (electrolytes, proteins) that draws water into the bloodstream, maintaining fluid balance between blood vessels and surrounding tissues

Plasma albumin

is the most abundant protein in human blood plasma, synthesized by the liver, playing critical roles in maintaining oncotic pressure (keeping fluid within blood vessels) and transporting hormones, drugs, and fatty acids. Normal levels (3.5–5.0 g/dL) indicate healthy liver/kidney function, while low levels (hypoalbuminemia) suggest disease, malnutrition, or inflammation.

low levels cause edema
pull water into bloodstream

Plasma globulins

Plasma globulins are a group of essential proteins in blood plasma—categorized as alpha, beta, and gamma—that play critical roles in immune defense, blood clotting, and the transport of nutrients, hormones, and lipids. Produced largely in the liver (alpha/beta) and by immune cells (gamma), they maintain osmotic pressure and fight infections.

Plasma electrolytes

Plasma electrolytes are essential minerals (like sodium, potassium, chloride, calcium, magnesium) dissolved in blood plasma that carry electrical charges, crucial for fluid balance, nerve signals, muscle function, and pH regulation, with imbalances indicating various health conditions. Clinically, tests measure levels of sodium, potassium, chloride, and bicarbonate, often alongside urea and creatinine, to assess hydration and organ function

plasma clotting factors

The clotting factors are Factor I (fibrinogen), Factor II (prothrombin), Factor III (tissue thromboplastin or tissue factor), Factor IV (ionized calcium), Factor V (labile factor or proaccelerin), Factor VII (stable factor or proconvertin), and Factor VIII (antihemophilic factor).

White Blood Cells

• Neutrophil: acting as the body's first responders to infections, especially bacterial and fungal, by engulfing germs and healing wounds

• Lymphocytes: Lymphocytes are crucial white blood cells—primarily T cells, B cells, and natural killer cells—that defend the body against infections, viruses, and tumors

• Monocyte: Monocytes are a type of white blood cell and key component of the innate immune system, comprising 2–10% of total leukocytes in human blood. They function by migrating into tissues to become macrophages or dendritic cells, aiding in pathogen defense, inflammation regulation, and tissue repair, low means bone marrow issues

• Basophil: Basophils are a type of white blood cell (leukocyte) that make up less than 1% of circulating white blood cells (normal range: ~0–300 cells/µL, or 0-1% of total WBC count). They play a crucial role in allergic reactions, inflammatory responses, and defense against parasites by releasing histamine, heparin, and other enzymes.

• Eosinophil: Eosinophils are a type of white blood cell crucial for fighting parasites and managing allergic reactions, killing cells, inflammatory responses

– Circulate, respond to chemotactic agents

– Diapedesis: or leukocyte extravasation, is the crucial process where white blood cells (neutrophils, monocytes, lymphocytes) pass through intact capillary walls into surrounding tissues to combat infection or inflammation. It is the final, active step of emigration, occurring after leukocyte adhesion and rolling, often driven by cytokines in postcapillary venules

What is blood doping?

Blood doping is a prohibited, illicit practice used by athletes to artificially increase their red blood cell count, enhancing oxygen delivery to muscles to improve endurance and performance

It typically involves blood transfusions (using one’s own or a donor’s blood) or the use of drugs like Erythropoietin (EPO) to stimulate RBC production. (synthetic oxygen carriers)

blood doping is dangerous and banned by the World Anti-Doping Agency (WADA). It significantly increases blood viscosity (thickness), which can lead to:

Strokes, heart attacks, and blood clots.

Infections from unsafe transfusion practices.

Increased pressure on the heart and lungs.

What is a milkshake for horses?

A "milkshake" is a performance-enhancing mixture given to racehorses that primarily contains sodium bicarbonate (baking soda), along with water, sugar, and electrolytes (salts). This illegal practice, known as "bicarbonate loading" or "milkshaking," is designed to counteract the buildup of lactic acid during intense exercise, so they do not feel the burn

tube into the stomach, this is illegal
but high dose of sodium bicarbonate acts as a buffer, raising the pH of the blood and extracellular fluid. This higher alkalinity is theorized to draw the excess hydrogen ions (from lactic acid) out of the muscle cells and into the bloodstream, where they are neutralized.

can cause death hours later, injury to nasal passages and throat, also cause accidental death and pneumonia from insertion into trachea instead of esophagus

Banamine testing

Banamine (flunixin meglumine) testing in horses is used to detect non-steroidal anti-inflammatory drug (NSAID) levels in blood or urine, typically to ensure compliance with competition rules.

How can you change protein levels?

you use IV plasma
hypertonic saline, pull water out of cells and tissues all of the vessels, reduces edema
Epsom salt (magnesium sulfate) acts as a strong saline laxative to clear the bowels for a colonoscopy, sometimes used as an adjunct to or component of prep kits. It works by pulling water into the intestine to flush out waste.