Equine cardiology Flashcards
What cardiac issue is more likely to cause poor performance; rhythm disturbances or valvular disease
Rhythm disturbances
Horses have a high circulatory reserve capacity so it is rare for valvular disease to cause poor performance
What are the 3 mechanisms of oedema
- Changes in oncotic pressure; from hypoproteinaemia
- Changes in hydrostatic pressure e.g in congestive heart failure
- Vasculitis which allows more leakage
How common is congestive heart failure in horses c/f dogs
Uncommon
What type of oedema does L vs R sided heart failure cause
Left sided causes pulmonary oedema
Right sided causes peripheral oedema; more common presentation and noticed more
Causes of L sided heart failure
- Acute onset L sided disease e.g bacterial endocarditis, ruptures chorda tendinae
- Pulmonary hypertension
- Congenital disease
How to differential pulmonary oedema with L sided heart failure from asthma signs
Unlike asthma, horses with heart failure are tachcardic
What is a cause of right sided heart failre
Chronic endocardial disease
What severe consequence is pulmonary hypertension a risk factor for the development of
Vascular failure
What are primary and secondary causes of pulmonary hypertension
Primary = pulmonary disease from hypoxia
secondary = mitral valve regurgitation, aortic valve regurgitation, atrial fibrillation
Where to listen to mitral valve
LIC 5 (caudal on left side)
Where to listen to the aortic and pulmonic valves
LIC 4 i.e cranial on left side
How hard to press using stethoscope for high vs low freq sounds
Press lightly for low freq
Press hard for high freq
What are S4, S1, S2, S3 sounds assocaited with
S4 = onset of atrial systole
S1 = onset of ventricular systole with closure of AV valves (and opening of semilunar)
S2 = onset of diastole with closure of semilunar valve and opening of AV valves
S3 = assocaited with rapid ventricular filling in mid-diastole
Where is S1 loudest
Over LIC5 (i.e hear closing of mitral valve)
Where is S2 loudest
Over LIC 4; since listening to semilunar valves close
Where is S3 loudest
Over cardiac apex (towards sternum on LIC5) since listening to ventricular filling
When might we hear S4 and S3 heart sounds
S4 in 60% of TBs
S3 in 40% TBs
When might S1 be louder than normal
Hypertension, adrenaline, mitral valve disease
When might S2 be louder than normal
Fever, adrenaline, anaemia
What is a physiological murmur
One just caused by blood leaving the heart
= most common murmur
At which grade do we recommend that murmurs have further investigation
Grade 3
Grading system of heart murmurs
1 = quiet murmur that is hard to identify
2 = murmur quieter than heart sounds
3 = murmur at same volume of S1/S2
4 = murmur louder than S1/S2
5 = loud murmur with precordial thrill
6 = murmur audible with stethoscope off the thoracic wall
What direction does murmur radiate in AV regurgitation
Dorsally
What is a systolic vs diastolic murmur
Systolic = between S1 and S2
Diastolic = after S2
What does holo-systolic mean
Murmur filling time between S1 and S2
What does pan-sysolic mean
Murmur across heart sounds b/w S1 and S2
What does mid-systolic murmur mean
Murmur between S1/S2 but not filling whole time
What are two types of left sided systolic murmur
Physiological flow murmurs from aortic ejection
Mitral valve regurgitation
What are two types of right sided systolic murmurs
Tricuspic valve regurgitation
Ventricular septal defect
What are the types of diastolic murmurs
Aortic valve regurgitation
Physiological filling murmur
CHaracteristics of a left sided flow murmur
loudest cranially on left (because it is aortic ejection we hear)
Early/mid systolic
Low grade
Cranio-dorsal radiation
Characteristics of mitral valve insufficiency murmur
Loudest caudally on the left LIC5
Variable timing/intensity
Radiates caudo-dorsally
Band shaped
How can mitral valve insufficiency end up leading to poor performance
Via development of atrial fibrillation
- Because the jet of blood flowing backwards causes atrial expansion
What clinical signs can develop from mitral valve insufficiency
[usually incidental finding]
- Poor performance due to atrial fibrillation from atrial enlargement
- Louder third heart sound since more passive filling occurs once atrium has enlarged
Pulmonary hypertension which can get worse until the point of vessel failure; collapse and death if pulmonary artery
+ pulmonary hypertension leads to right sided failure
Can get acute onset left sided failure if there is chorda tendinae rupture or bacterial endocarditis
What does a louder third heart sound indicate
Large heart; since it represents more passive filling from enlarged atria
Negative prognostic signs on mitral valve insufficiency investigation; generally and on echo
> Grade 3 or above murmur
Loud third heart sound
Dysrhytmia (atrial fibrillation)
Congestive heart failure (may be left side or biventricular)
Bacterial endocarditis
+ on echo: pulmonary hypertension, left atrial enlargement
What is the only regurgitant lesion on the right side of the heart
tricuspid
Details of tricuspid regurgitation
Radiates dorsally
Common and largely well tolerated
= assocaited with fitness due to cardiac hypertrophy in training
What dysrhythmia can tricuspid regurgitation predispose to
Atrial fibrillation due to right atrial enlargement
- This can then impact performance
What murmur is associated with fitness
Tricuspid regurgitation due to cardiac hypertrophy
what grade do we investigate tricuspid regurgitation in TBs
Grade 4 (vs grade 3 in other breeds)
What should we consider as a rare but possible cause of a NEW tricuspid murmur
Bacterial endocarditis
e.g from septic jugular thrombosis due to catheter placement, from dental disease
Negative prognostic signs with tricuspid regurgitation
Loud murmur >4 in TB
Loud third heart sound
Dysrhythmia (atrial fibrillation)
Congestive heart failure (right side)
Bacterial endocarditis
Look on echo for right atrial enlargement and pulmonary hypertension
What breed is a ventricular septal defect common in
Welsh ponies
Characteristics of a ventricular septal defect
Systolic murmur in Right IC4 which is high grade and radiates sternally
Largely well tolerated
+ get concurrent systolic murmur on LIC4 due to relative pulmonic stenosis
It is SIZE of defect not murmur grade that indicates significance
Can go on to get a diastolic murmur which is a negative prognostic indicator
Why can horses with ventricular septal defect go on to get a concurrent diastolic murmur
Valves sucked through defect
What can induce a diastolic physiological murmur
Stress
Where can we hear physiological diastolic squeak best
LIC 5 often towards apex
Where do we hear aortic regurgitation and what are the characteristics
Loudest over LIC4 and radiates widely
Variable grade
Either early or holo diastolic
Decrescendo
Progressive condition
What other clinical sign might we find in horses with aortic regurgitation
Hyperkinetic pulses because the systolic pressure increases and diastolic decreases
What are some potential consequences of aortic regurgitation
Can develop secondary mitral valve regurgitation
Ventricular dilation can lead to ventricular arrhythmias e.g vtac and collapse
What do we advise for horses with aortic regurgitation that develop exercise induced ventricular arrhythmias
Stop riding them
What are negative prognostic indicators with aortic regurgitation
Secondary mitral valve regurgitation
High pulse pressure >60mmHg
Congestive heart failure (left sided or biventricular)
Bacterial endocarditis
+ left ventricular enlargement on echo
NB: murmur grade not a useful indicator
What extra test is a good idea with aortic regurgitation (safety)
Exercising electrocardiography to look for exercise induced ventricular arrhythmia
Characteristics of pulmonic regurgitation murmur
Rare and rarely affects performance
Loudest on LIC 3 or 4
Diagnose by excluding aortic regurgitation on echo
Long and musical sound
What consequences can develop from pulmonic insufficiency
Right ventricular hypertrophy leading to cor pulmonale
Pulmonary hypertension
+ eventually can get alveolar hypoxia and respiratory distress
What can cause a continuous heart murmur and what other clinical sign do we tend to see with it
Aortic root rupture or aortocardiac fistula
Tend to see ventricular tachycardia >100bpm due to disruption to interventricular conduction tissue
What signs can we see with bacterial endocarditis
Should suspect in any new murmurs assocaited with severe disease
- Acute onset heart failure
- Fever, tachypnoea, tachycardia, murmur
Hyperfibrinogenaemia, anaemia, leucocytosis
How to diagnose bacterial endocarditis
Blood culture 3X apart hourly via sterile procedure but still risk of false -ves
What do we need to be aware with colic and heart murmurs
Colic can make horses present with new murmurs and even atrial fibrillation but this goes away when colic treated
What makes us think that it is heart failure presenting as colic rather than colic presenting with a murmur
If the heart rate is much higher than would be expected for the clinical signs of pain
What does endocardial disease vs myocardial disease manifest as
Endocardial: as cardiac murmurs
Myocardial: cardiac dysrhythmias (so can get collapse/sudden death)
What conditions can lead to myocardial dysfunction
Electrolyte abnormalities e.g Ca2+, Mg2+, K+
Increased myocardial muscle mass
Increased heart chamber size
Myocarditis
What might we see on bloods that indicates myocardial dysfunction
Cardiac troponin 1 is released when cell membrane severely damaged
Creatinine kinase is released with less severe damage (cell membrane dysfunction)
What could cause myocarditis
Bacteria: S aureus, Strep equi equi, Clostridium, sepsis, pericarditis, endocarditis
Borrelia burdgdorferi
- Viruses: EIA, EVA, African Horse Sickness
- Parasites: Large strongyles, toxoplasma, sarcocystis
What can cause dilated cardiomyopathy
Myocarditis
Congenital
Toxic most common e.g ionophores, sycamores
How can we evaluate the myocardium
Echocardiography + mimic exercise via dobutamine-atropine stress echocardiography
Biopsies
ECG
What are the two indications for ECG
Rhythm disturbances detected
Tachycardia that can’t be explained by other finding s e.g stress, grass sickness, pain, hypovolvaemia
When must we be concerned about jockey safety in exercising ECG
Atrial fibrillation
Myocardial disease
Aortic valve regurg
What type of AV block is a physiological response to high blood pressure
2nd degree AV block
= vagally mediated baroreceptor response
How can we test if 2nd degree AVB is just physiological response
Cause a stress response to remove the vagal tone e.g bang stable door
This should eliminate the arrhthymia
What is 1st degree AVB
Lengthening of the PR interval
What is 3rd degree AVB
Where the atrium and ventricles are not coordinating their contractions
= always pathological
When is 2nd degree AVB indicative of pathology
If beats are blocked during exercise
What is atrial fibrillation
Where the atria are not contracting so don’t get the extra squeeze of blood into ventricles (~20% of heart function)
So can cause poor performance in athletes
What are the 3 types of atrial fibrillation
Lone spontaneous disease
Secondary to cardiac disease via atrial enlargement
Paroxysmal atrial fibrillation
ECG characteristics with atrial fibrillation
Absence of P waves
Normal QRS
See F waves of electrical activity instead
In horses it is a bradydysrhythmia (unlike in dogs)
When might a atrial fibrillation bradydysrhythmia suddenly chnage to tachydysrhythmia
With colic since lose vagal tone
What is paroxysmal atrial fibrillation
In fit horses at a gallop may convert to atrial fibrillation and heart rate increases massively to >220bpm meaning no time for diastolic filling from atria so get collapse
Only affects athletes since pleasure horses can cope without extra 20% of blood from atrial contraction and diastolic filling
Usually horses get back up quickly as heart rate reduces and they convert back to sinus rhythm within an hour
Signs of atrial fibrillation on ausculatation
Irregularly irregular rhythm
Normal or slow rate
No 4th heart sound
Loud 3rd heart sound
+ something about jugular pulses
Two treatment options for atrial fibrillation
Quinidine: riskier, only for acute <2-3 months
Transvenous cardioversion: safer; indicated with chronic AF, significant cardiac disease, ventricular tachycardia at exercise
What are the side effects of quinidine
Severe colic and diarrhoea
Cardiac side effects e.g supraventricular tachycardia, ventricular tachycardia
Vasodilation
Which dysrhythmias are not compatible with life
Asystole
VEntricular fibrillation
How much do atria contribute to cardiac output
~15% so most horses can cope with atrial fibrillation
When to treat ventricular tachycardia and how
WHen HR >100
Where there are multiple ventricular ectopic foci
When there is evidence of heart failure
Use lidocaine anti-dysrhythmic
Could start with magnesium sulphate since fewer side effects and ‘does no harm’
