Common Cardiovascular diseases in Equine

Question 1

How might a heart murmur be detected?

Answer 1

A heart murmur is an abnormal noise that is heard during the
cardiac cycle
* They are generally caused by turbulent (rather than laminar) flow
of blood
* They are detected by auscultation and assessed further (if
necessary) with ultrasound (echocardiography)

Question 2

What generally causes valvular murmurs in horses?

Answer 2

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 3

What usually causes significant valve murmurs in horses?

Answer 3

Mitral or aortic valve regurgitation

Question 4

What is the unimportant left systolic murmur?

Answer 4

Aortic ejection

Question 5

What is the important left systolic murmur?

Answer 5

Mitral insufficiency

Question 6

What is the important left diastolic murmur?

Answer 6

Aortic insufficiency

Question 7

What is the unimportant left diastolic murmur?

Answer 7

Ventricular filling

Question 8

What is the important right systolic murmur?

Answer 8

VSD

Question 9

What is the unimportant right systolic murmur?

Answer 9

Tricuspid insufficency

Question 10

What is aortic flow?

Answer 10

usually short (early systole)
* grade 1-3/5
* PMI: high, under triceps
* localised

Question 11

What is mitral regurgitation?

Answer 11

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

Question 12

What is the clinical significance of mitral insufficiency?

Answer 12

Unpredictable:
 Mild regurgitation
 not uncommon in successful performance
horses
 often remain stable with no impact on
performance
 May (or may not):
 progress to left sided congestive heart failure?
 cause respiratory signs?
 develop atrial fibrillation?
 cause collapse – pulmonary artery rupture?
 Re-evaluate annually
 Monitor resting heart rate
 Should have echocardiography

Question 13

What is ventricular filling?

Answer 13

early diastole (squeak)
* 1-2/5
* low, towards apex
* localised

Question 14

What is left diastolic aortic regurgitation?

Answer 14

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

Question 15

What is the clinical significance of aortic insufficiency?

Answer 15

usually older horses
* usually clinically insignificant
* usually self limiting via increased
contractility
* bounding pulses reflect severe
regurgitation
* volume overload may lead to mitral
stretching and regurgitation
* susceptible to exercise induced
ventricular arrhythmias (VPCs)
* should have echocardiography and
ECG

Question 16

What makes the prognosis poor for aortic insufficiency in horses?

Answer 16

• Young
• Have multiple murmurs
• VPCS
• Hyperkinetic pulses
• Pulse pressure >60mg

Question 17

What is the clinical significance of ventricular septal defect?

Answer 17

usually immediately below
aortic/tricuspid valves
* flow generally left to right
* small defects (<2-2.5cm) are usually
well tolerated
* larger defects decrease cardiac output
and cause volume overload
* when discovered in an adult horse
then shouldn’t get worse
* when discovered in foals/young horses
require careful assessment

Question 18

What is a dysrhythmia

Answer 18

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 19

What is a common dysrhythmia?

Answer 19

2nd degree atrioventricular block

Question 20

What is an uncommon dysrhythmia?

Answer 20

Premature supraventricular (atrial) contractions
 Premature ventricular contractions

Question 21

What is an occasional dsyrthmia?

Answer 21

atrial fibrillation

Question 22

What is a second degree AV block?

Answer 22

very common (40% of normal horses?)
 not a problem (“physiologic”)
 caused by high vagal tone on the AV node
 eliminated by adrenaline (exercise or excitement), so disappears as rate
increases
 when the heart rate is low, horses tend to block occasional ventricular
contractions (at the AV node) as an alternative to simply slowing down the
overall heart rate
 heart rate will be low-to-normal (24-36 bpm)
 regular diastolic pauses (“regularly irregular”)
 isolated S4 is audible in the diastolic pause

Question 23

What is a pathological AV block?

Answer 23

Rarely seen
 May cause exercise intolerance or even collapse
 Caused by disease of the AV node – e.g. scarring (fibrosis) or inflammation)
 Advanced 2nd degree AV block:
 several (usually 2-4) consecutive beats blocked
 3rd degree block
 all beats blocked at AV node so the atria and ventricles contract independently of
one another
 Can try rest/anti-inflammatories but might require a pacemaker

Question 24

What are premature depolarisations?

Answer 24

Occasional premature beats can be normal (e.g. 1 every few hours)
 More frequent premature beats may be associated with exercise intolerance
 Ventricular contractions (QRS) occur earlier than expected
 Might have a compensatory pause afterwards
 Auscultation – irregularly irregular
 The premature QRS may be:
 Preceded by an early P wave = Supraventricular (atrial) Premature Depolarisations
 Driven by an excitable SA node
 The early PQRST looks normal
 SVPDs can predispose to atrial fibrillation
 Occur without a preceding P wave = Ventricular Premature Depolarisations
 Driven by an excitable ventricle
 The early QRS will look different to other QRS complexes in the ECG

Question 25

What is the functional effect of atrial fibrillation?

Answer 25

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)

Question 26

What is a premature depolarisation?

Answer 26

• Frequent premature beats are associated with exercise intolerance
• Ventricular contractions occur earlier than expected
• Compensatory pause afterwards
• Auscultation= irregular