Common Equine Cardiovascular Conditions

Question 1

What are the general rules of equine murmurs?

Answer 1

valvular murmurs in horses are generally due to
regurgitation rather than stenosis
 pulmonary valve murmurs are very rare
 tricuspid valve (RAV) murmurs are rarely significant

Question 2

What are the three potentially significant murmurs in horses?

Answer 2

• Mitral LAV
• Aortic valve regurgitation
• Ventricular septal defect

Question 3

What are the two causes of left systolic?

Answer 3

• Aortic flow (unimportant)
• Mitral regurgitation (potentially important)

Question 4

When does mitral regurgitation occur?

Answer 4

throughout systole
* grade 1-5/5
* PMI: often low
* radiates caudosorsally

Question 5

What is aortic flow?

Answer 5

• Usually short
• Grades 1-3/5
• PMI- high (under the triceps)
• localised

Question 6

What are the two left diastolic issues?

Answer 6

1. Aortic regurgitation (important)
2. Ventricular filling (not important)

Question 7

What is left diastolic aortic regurgitation?

Answer 7

• occurs throughout diastole
• 1-5/5
• High, under triceps
• radiates caudoventrally

Question 8

What is left diastolic ventricular filling?

Answer 8

• early diastole
• 1-2/5
• low, towards the apex
• localised

Question 9

What is the clinical significance of aortic insufficency?

Answer 9

• Usually older horses
• Usually clinically insignificant
• self limiting via increased contractility
• bounding pulses reflect severe regurgitation
• volume overload may lead to mitral stretching

Question 10

What makes the aortic insufficency prognosis poor?

Answer 10

• Young
• With multiple murmurs
• Hyperkinetic pulses
• Pulse pressure > 60mmHg

Question 11

What are the two issues that cause right systolic?

Answer 11

• Tricuspid regurgitation (unimportant)
• Ventricular septal defect (potentially important)

Question 12

What is tricuspid regurgitation?

Answer 12

• occurs throughout systole
• 1-5/5
• high under triceps

Question 13

When does ventricular septal defect occur?

Answer 13

• throughout systole
• 3-5/5
• low, near the sternum

Question 14

What is the clinical significance of ventricular septal defect?

Answer 14

• ususally occurs immediately below the aortic/ tricuspid valves
• flow generally from left to right
• small defects are usually well tolerated
• larger defects decrease cardiac output and cause volume overload
• shouldnt get worse once discovered in an adult horse
• requires careful assessment when discovered in foals/ young horses

Question 15

What is a dysrhythmia?

Answer 15

A dysrhythmia (or arrhythmia) is an abnormality of the
cardiac rhythm
This MAY OR MAY NOT have an effect on cardiac output
They are detected by auscultation and further assessed with
electrocardiography (ECG)
bradydysrhythmias are associated with a delay or absence
of the expected regular beat
tachydysrhythmias are associated with premature or earlier
than expected beats

Question 16

What is the most common dysrhythmia?

Answer 16

2nd degree atrioventricular block

Question 17

What is the occasional dysrhythmia?

Answer 17

atrial fibrillation

Question 18

What is the uncommon dysrhythmia?

Answer 18

Premature supraventricular (atrial) contractions
Premature ventricular contractions

Question 19

What is the rare dysrhythmia?

Answer 19

Advanced 2nd degree AV block, 3rd degree AV block,
sinoatrial block, ventricular fibrillation

Question 20

What is the physiology of the 2nd degree AV block?

Answer 20

• very common and not usually a problem
• caused by high vagal tone on the AV node
• eliminated by adrenaline
• when the heart rate is low, horses tend to block occasional ventricular contractions
• heart rate is low to normal
• regular diastolic pauses
• isolated S4 is audible in the diastolic phase

Question 21

What is a pathologic AV block?

Answer 21

• rarely seen
• may cause exercise intolerance or collapse
• caused by disease of the av node e.g scarring fibrosis

Question 22

What are premature depolarisations?

Answer 22

• occasional premature beats can be normal
• more frequent premature beats may be associated with exercise intolerance
• ventricular contractions may occur earlier than expected
• compensatory pause afterwards

Question 23

What is atrial fibrillation?

Answer 23

• Most common abnormal rhythm
• Ventricular contractions become random
• overall heart rate is normal
• no atrial sound heard during pauses

Question 24

What is the functional effect of atrial fibrillation?

Answer 24

Prime effect = loss of atrial contraction
* no problem at low to moderate heart rates (ventricles have time to fill by gravity)
* there is poor ventricular filling at high heart rates (atrial contraction is needed to
fill ventricles quickly)
* occasionally more serious arrhythmias develop during exercise (should have
exercising ECG if going to be ridden)