Common Cardiovascular diseases in Equine Flashcards
How might a heart murmur be detected?
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)
What generally causes valvular murmurs in horses?
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
What usually causes significant valve murmurs in horses?
Mitral or aortic valve regurgitation
What is the unimportant left systolic murmur?
Aortic ejection
What is the important left systolic murmur?
Mitral insufficiency
What is the important left diastolic murmur?
Aortic insufficiency
What is the unimportant left diastolic murmur?
Ventricular filling
What is the important right systolic murmur?
VSD
What is the unimportant right systolic murmur?
Tricuspid insufficency
What is aortic flow?
usually short (early systole)
* grade 1-3/5
* PMI: high, under triceps
* localised
What is mitral regurgitation?
throughout systole
* grade 1-5/5
* PMI: often low
* radiates caudosorsally
What is the clinical significance of mitral insufficiency?
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
What is ventricular filling?
early diastole (squeak)
* 1-2/5
* low, towards apex
* localised
What is left diastolic aortic regurgitation?
- throughout diastole
- 1-5/5
- high, under triceps
- radiates caudoventrally
What is the clinical significance of aortic insufficiency?
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
What makes the prognosis poor for aortic insufficiency in horses?
- Young
- Have multiple murmurs
- VPCS
- Hyperkinetic pulses
- Pulse pressure >60mg
What is the clinical significance of ventricular septal defect?
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
What is a dysrhythmia
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
What is a common dysrhythmia?
2nd degree atrioventricular block
What is an uncommon dysrhythmia?
Premature supraventricular (atrial) contractions
Premature ventricular contractions
What is an occasional dsyrthmia?
atrial fibrillation
What is a second degree AV block?
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
What is a pathological AV block?
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
What are premature depolarisations?
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
What is the functional effect of atrial fibrillation?
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)
What is a premature depolarisation?
- Frequent premature beats are associated with exercise intolerance
- Ventricular contractions occur earlier than expected
- Compensatory pause afterwards
- Auscultation= irregular
