PATHOLOGY - Equine Heart Murmurs Flashcards
What are the two classifications of heart murmurs in horses?
Functional murmurs
Pathological murmurs
What are functional murmurs?
A functional murmur is where there is no heart disease detected and there is a plausable physiological explanation for the murmur
What are the seven characteristics of functional murmurs in horses?
- Short duration
- Systolic murmur
- Decrescendo murmur
- Grade I or II
- No other associated abnormal heart sounds
- Common in young, fit horses
- Variable intensity at different heart rates
What are five possible causes of functional murmurs in horses?
Young, fit horses
Anaemia
Thrombocytopenia
Colic
Endotoxaemia
Why do young fit horses often present with functional murmurs?
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
How does anaemia and thrombocytopenia cause a functional murmur in horses?
Anaemia and thrombocytopenia reduce blood viscocity, causing increased blood flow velocity and turbulent blood flow, resulting in a functional murmur
Why should you re-auscultate a horse after they have recovered from colic?
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
Why is tachycardia at rest particularly significant in horses?
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
At what intensity are heart murmurs in horses usually pathological?
Grade three heart murmus and above tend to be pathological in horses
What is the most common cause of a pathological murmur in horses?
Tricuspid valve regurgitation
What kind of mumur is heard with tricuspid valve regurgitation?
Right sided apical systolic plateau murmur with dorsocaudal radiation
What is the prognosis for a horse with tricuspid valve regurgitation with a grade I or II murmur?
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
At what grade should you do echocardiography in a horse with tricuspid valve regurgitation?
Grade III and above
(T/F) Tricuspid valve regurgitation commonly affects athletic performance in horses
FALSE. Tricuspid valve regurgitation rarely affects athletic performance in horses unless it is a severe defect
What are some poor prognostic signs of tricuspid valve regurgitation on clinical exam?
Pulsating, distended jugular
Short jugular refill time
Peripheral oedema
Atrial fibrillation
Signs of right sided congestive heart failure
What are some poor prognostic signs of tricuspid valve regurgitation on echocardiography?
Tricuspid valve thickening
Right atrial dilatation
Right ventricular eccentric hypertrophy
Why should you always check for evidence of left sided heart disease and pulmonary disease in horses with tricuspid valve regurgitation?
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
What kind of murmur is heard with mitral valve regurgitation?
Left sided apical systolic plateau murmur with dorsal radiation
What can be indicated by a buzzing sound heard on ausculation in a horse with mitral valve regurgitation?
A buzzing sound on regurgitation can indicate valve leaflet vibration due to chordae tendinae rupture
What is the prognosis for a horse with mitral valve regurgitation with a grade I or II murmur?
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
At what grade should you do echocardiography in a horse with mitral valve regurgitation?
Grade III and above
What is the prognosis for a horse with mitral valve regurgitation with a grade III or above murmur?
It is advised that these horses should not be purchased or used for athletic use unless there are no structural changes on echocardiography
Why is there a worse prognosis for horses with structural changes on echocardiography with mitral valve regurgitation?
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
What are some poor prognostic signs of mitral valve regurgitation on echocardiography?
Mitral valve thickening
Left atrial enlargement
Left ventricular eccentric hypertrophy
What can you use to measure cardiac contractility on echocardiography?
Calculate the fractional shortening on M mode echocardiography
At what fractional shortening value is mitral valve regurgitation classified as severe?
Less than 30% fractional shortening
What kind of murmur is heard with ventricular septal defects?
Grade IV or V left sided systolic murmur that radiates widely and ends up being louder on the right side
Which breeds of horse are predisposed to ventricular septal defects?
Arabs
Welsh ponies
What is the prognosis for horses with ventricular septal defects?
Horses cannot be used for breeding
Horses are not suitiable for high intensity athletic use
What should you do if you suspect a horse has a ventricular septal defect?
Echocardiography
What are good prognostic indicators for ventricular septal defects on echocardiography?
Small defect (less than 2.5cm)
High velocity jet
No significant structural changes to the heart
At what size of ventricular septal defect will horses live relatively normal lives?
Ventricular septal defect less than 5mm
What are poor prognostic indicators for ventricular septal defects on echocardiography?
Large defect (more than 2.5cm)
Low velocity jet
Increase left atrial and left ventricular dimension
Significant concurrent aortic or mitral regurgitation
When do horses typically present with clinical signs of a ventricular septal defect?
Within the first 5 years of life, unless that defect is small enough that it is not clinically significant
What is the general prognosis for horses showing clinical signs of a ventricular septal defect?
Euthanasia
What is the most common cause of pathological diastolic murmurs in horses?
Aortic valve regurgitation
Describe the pathophysiology of aortic valve regurgitation
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
What is the typical signalement for aortic valve regurgitation in horses?
Older horses
Why is aortic valve regurgitation particularly significant in young horses?
Aortic valve regurgitation is much more likely to severely progress and result in acute collapse in young horses
Which murmur is heard with aortic valve regurgitation?
Left sided basal diastolic plateau murmur
Why should you also listen for a systolic murmur if you suspect a horse has aortic valve regurgitation?
There can be concurrent mitral valve regurgitation with aortic valve regurgitation
What further testing should you do if you suspect a horse has aortic valve regurgitation?
Echocardiography
Why is it so important to do further investigation in horses with possible aortic valve regurgitation?
There is a high risk of acute collapse in horses with aortic valve regurgitation which will make them unsafe to ride
What are some poor prognostic signs of aortic valve regurgitation on clinical exam?
Tachycardia at rest (over 40bpm)
Atrial fibrillilation
Weak or bounding pulses
Signs of left sided congestive heart failure
What are some poor prognostic signs of aortic valve regurgitation on echocardiography?
Aortic valve thickening
Left ventricular eccentric hypertrophy
Left atrial dilatation
Enlargement of the aortic root
Concurrent mitral valve regurgitation
Why is there a worse prognosis for horses with structural changes on echocardiography with aortic valve regurgitation?
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
What can be used to assess if a horse with aortic valve regurgitation has developed ventricular arrhythmias at exercise?
Exercise holter ECG
(T/F) You can rarely ausculate a murmur associated with pulmonic valve regurgitation
TRUE.
Which heart valve is most commonly affected by endocarditis in horses?
Aortic valve
Unless the endocarditis is secondary to thrombophlebitis due to venous catheterisation, then it will be the tricuspid valve
What can be used to diagnose endocarditis in horses?
Echocardiography
Blood culture
What are the signs of pericardial effusion on auscultation?
Muffled heart sounds
