PATHOLOGY - Equine Heart Murmurs

Question 1

What are the two classifications of heart murmurs in horses?

Answer 1

Functional murmurs
Pathological murmurs

Question 2

What are functional murmurs?

Answer 2

A functional murmur is where there is no heart disease detected and there is a plausable physiological explanation for the murmur

Question 3

What are the characteristics of functional murmurs in horses?

Answer 3

1. Short duration
2. Systolic murmur
3. Decrescendo murmur
4. Grade I or II
5. No other associated abnormal heart sounds
6. Common in young, fit horses
7. Variable intensity at different heart rates

Question 4

What are five possible causes of functional murmurs in horses?

Answer 4

Young, fit horses
Anaemia
Thrombocytopenia
Colic
Endotoxaemia

Question 5

Why do young fit horses often present with functional murmurs?

Answer 5

Young fit horses have a considerably increased cardiac output to meet the oxygen demand required for intense exercise and a larger blood vessel diameter which causes increased velocity and turbulent blood resulting in a functional murmur

Question 6

How does anaemia and thrombocytopenia cause a functional murmur in horses?

Answer 6

Anaemia and thrombocytopenia reduce blood viscocity, causing increased blood flow velocity and turbulent blood flow, resulting in a functional murmur

Question 7

Why should you re-auscultate a horse after they have recovered from colic?

Answer 7

You should re-auscultate a horse after they have recovered from colic to see if the murmur has persisted. If it has, this suggests this is a pathological murmur rather than a functional murmur

Question 8

Why is tachycardia at rest particularly significant in horses?

Answer 8

In response to decreased cardiac output, horse’s tend to increase cardiac contractility rather than heart rate as a compensatory mechanism, so if there is tachycardia at rest this can indicate the horse is in congestive heart failure

Question 9

At what intensity are heart murmurs in horses usually pathological?

Answer 9

Grade three heart murmus and above tend to be pathological in horses

Question 10

What is the most common cause of a pathological murmur in horses?

Answer 10

Tricuspid valve regurgitation

Question 11

What kind of mumur is heard with tricuspid valve regurgitation?

Answer 11

Right sided apical systolic plateau murmur with dorsocaudal radiation

Question 12

What is the prognosis for a horse with tricuspid valve regurgitation with a grade I or II murmur?

Answer 12

It is unlikely that this murmur will cause significant effect on athletic performance at this time. However, the finding should be noted in the horse’s clinical record so that it can be re-evaluated at subsequent check-ups

Question 13

At what grade should you do echocardiography in a horse with tricuspid valve regurgitation?

Answer 13

Grade III and above

Question 14

(T/F) Tricuspid valve regurgitation commonly affects athletic performance in horses

Answer 14

FALSE. Tricuspid valve regurgitation rarely affects athletic performance in horses unless it is a severe defect

Question 15

What are some poor prognostic signs of tricuspid valve regurgitation on clinical exam?

Answer 15

Pulsating, distended jugular
Short jugular refill time
Peripheral oedema
Atrial fibrillation
Signs of right sided congestive heart failure

Question 16

What are some poor prognostic signs of tricuspid valve regurgitation on echocardiography?

Answer 16

Tricuspid valve thickening
Right atrial dilatation
Right ventricular eccentric hypertrophy

Question 17

Why should you always check for evidence of left sided heart disease and pulmonary disease in horses with tricuspid valve regurgitation?

Answer 17

Tricuspid valve regurgitation can be caused secondary to pulmonary hypertension and if this is the case there is a much higher chance this will affect athletic performance

Question 18

What kind of murmur is heard with mitral valve regurgitation?

Answer 18

Left sided apical systolic plateau murmur with dorsal radiation

Question 19

What can be indicated by a buzzing sound heard on ausculation in a horse with mitral valve regurgitation?

Answer 19

A buzzing sound on regurgitation can indicate valve leaflet vibration due to chordae tendinae rupture

Question 20

What is the prognosis for a horse with mitral valve regurgitation with a grade I or II murmur?

Answer 20

It is unlikely that this murmur will cause significant effect on athletic performance at this time. However, the finding should be noted in the horse’s clinical record so that it can be re-evaluated at subsequent check-ups

Question 21

At what grade should you do echocardiography in a horse with mitral valve regurgitation?

Answer 21

Grade III and above

Question 22

What is the prognosis for a horse with mitral valve regurgitation with a grade III or above murmur?

Answer 22

It is advised that these horses should not be purchased or used for athletic use unless there are no structural changes on echocardiography

Question 23

Why is there a worse prognosis for horses with structural changes on echocardiography with mitral valve regurgitation?

Answer 23

Mitral valve regurgitation causes volume overload and enlargement of the left atrium which increases the risk of atrial fibrillation. There will also be eccentric hypertrophy of the left ventricle which will eventually reduce cardiac contractility and cardiac output, as well as a backup of blood into the pulmonary veins, causing congestive heart failure and pulmonary hypertension

Question 24

What are some poor prognostic signs of mitral valve regurgitation on echocardiography?

Answer 24

Mitral valve thickening
Left atrial enlargement
Left ventricular eccentric hypertrophy

Question 25

What can you use to measure cardiac contractility on echocardiography?

Answer 25

Calculate the fractional shortening on M mode echocardiography

Question 26

At what fractional shortening value is mitral valve regurgitation classified as severe?

Answer 26

Less than 30% fractional shortening

Question 27

What kind of murmur is heard with ventricular septal defects?

Answer 27

Grade IV or V left sided systolic murmur that radiates widely and ends up being louder on the right side

Question 28

Which breeds of horse are predisposed to ventricular septal defects?

Answer 28

Arabs Welsh mountain ponies

Question 29

What is the prognosis for horses with ventricular septal defects?

Answer 29

Horses cannot be used for breeding Horses are not suitiable for high intensity athletic use

Question 30

What should you do if you suspect a horse has a ventricular septal defect?

Answer 30

Echocardiography

Question 31

What are good prognostic indicators for ventricular septal defects on echocardiography?

Answer 31

Small defect (less than 2.5cm) High velocity jet No significant structural changes to the heart

Question 32

At what size of ventricular septal defect will horses live relatively normal lives?

Answer 32

Ventricular septal defect less than 5mm

Question 33

What are poor prognostic indicators for ventricular septal defects on echocardiography?

Answer 33

Large defect (more than 2.5cm) Low velocity jet Increase left atrial and left ventricular dimension Significant concurrent aortic or mitral regurgitation

Question 34

When do horses typically present with clinical signs of a ventricular septal defect?

Answer 34

Within the first 5 years of life, unless that defect is small enough that it is not clinically significant

Question 35

What is the general prognosis for horses showing clinical signs of a ventricular septal defect?

Answer 35

Euthanasia

Question 36

What is the most common cause of pathological diastolic murmurs in horses?

Answer 36

Aortic valve regurgitation

Question 37

Describe the pathophysiology of aortic valve regurgitation

Answer 37

Aortic valve regurgitation results in blood regurgitation from the aorta back into the left ventricle and eventually the left atrium. This regurgitation eventually results in volume overload and left ventricular compensatory eccentric hypertrophy and left atrial dilatation. The hearts ability to pump blood effectively will progressively worsen along with the volume overload, this eccentric hypertrophy will also cause dilation of the valvular annular ring, resulting in mitral valve regurgutation and a worsening volume overload which will eventually cause a backup of blood into the pulmonary veins, causing increased hydrostatic pressure resulting in pulmonary oedema and left-sided congestive heart failure. This can also progress to right-sided congestive heart failure as pulmonary hypertension will increase the afterload on the right side of the heart, resulting in pressure overload, concentric hypertrophy of the right ventricle and eventual right-sided congestive heart failure

Question 38

What is the typical signalement for aortic valve regurgitation in horses?

Answer 38

Older horses

Question 39

Why is aortic valve regurgitation particularly significant in young horses?

Answer 39

Aortic valve regurgitation is much more likely to severely progress and result in acute collapse in young horses

Question 40

Which murmur is heard with aortic valve regurgitation?

Answer 40

Left sided basal diastolic plateau murmur

Question 41

Why should you also listen for a systolic murmur if you suspect a horse has aortic valve regurgitation?

Answer 41

There can be concurrent mitral valve regurgitation with aortic valve regurgitation

Question 42

What further testing should you do if you suspect a horse has aortic valve regurgitation?

Answer 42

Echocardiography

Question 43

Why is it so important to do further investigation in horses with possible aortic valve regurgitation?

Answer 43

There is a high risk of acute collapse in horses with aortic valve regurgitation which will make them unsafe to ride

Question 44

What are some poor prognostic signs of aortic valve regurgitation on clinical exam?

Answer 44

Tachycardia at rest (over 40bpm) Atrial fibrillilation Weak or bounding pulses Signs of left sided congestive heart failure

Question 45

What are some poor prognostic signs of aortic valve regurgitation on echocardiography?

Answer 45

Aortic valve thickening Left ventricular eccentric hypertrophy Left atrial dilatation Enlargement of the aortic root Concurrent mitral valve regurgitation

Question 46

Why is there a worse prognosis for horses with structural changes on echocardiography with aortic valve regurgitation?

Answer 46

Aortic valve regurgitation causes volume overload and enlargement of the left atrium which increases the risk of atrial fibrillation. There will also be eccentric hypertrophy of the left ventricle which will eventually reduce cardiac contractility and cardiac output, as well as a backup of blood into the pulmonary veins, causing congestive heart failure and pulmonary hypertension. Aortic valve regurgitation can also eventually result in myocardial hypoxia due to the increased heart rate an contractility at exercise, resulting in oxygen demand exceeding oxygen supply which can result in ventricular tachycardia which can progress to ventricular fibrillation which is fatal

Question 47

What can be used to assess if a horse with aortic valve regurgitation has developed ventricular arrhythmias at exercise?

Answer 47

Exercise holter ECG

Question 48

(T/F) You can rarely ausculate a murmur associated with pulmonic valve regurgitation

Answer 48

TRUE.

Question 49

Which heart valve is most commonly affected by endocarditis in horses?

Answer 49

Aortic valve ## Footnote Unless the endocarditis is secondary to thrombophlebitis due to venous catheterisation, then it will be the tricuspid valve

Question 50

What can be used to diagnose endocarditis in horses?

Answer 50

Echocardiography Blood culture

Question 51

What are the signs of pericardial effusion on auscultation?

Answer 51

Muffled heart sounds

Question 52

What should be evaluated if the cardiovascular system is not the cause of poor performance?

Answer 52

Evaluate the musculoskeletal system for lameness. If sound, recommend an investigation of the respiratory system to rule out a dynamic upper airway problem or lower airway problem