Cardiology Flashcards
why are cardiac issues much less common in horses than dogs?
they have a huge cardiac reserve at rest
how do horses with cardiac disease generally present?
incidental at pre-purchase exam
poor performance
systemic illness
what valve does the most prominent beat occur on?
mitral
what is the apex beat of the horses heart over?
mitral valve
what valve is listened to on the right of the horse?
tricuspid
what is systole and diastole?
systole - contraction
diastole - relaxation
what causes S1?
ventricles contract and the AV valves close (mitral/tricuspid)
what causes S2?
ventricules relax and semilunar valves shut (aortic/pulmonic)
what causes S4?
atrial contraction
when is S4 heard?
just before S1
what causes S3?
end of rapid ventricular filling (difficult to hear)
when is S3 heard?
just after S2
why does mitral valve regurgitation cause a loud S3?
there is more blood in the atria due to the regurgitation so ventricular filling is even faster due to the pressure
how does the length of systole compare to diastole in the normal heart beat?
systole is much shorter
how does the length of systole compare to diastole with a fast heart beat?
systole and diastole become much similar in length
what is a murmur?
turbulent flow of blood
turbulence of blood is influence by Reynolds number, what is Reynolds number influenced by?
vessel diameter
blood velocity
blood density
how is a grade 1 murmur described?
barely audible
how is a grade 2 murmur described?
definite murmur quieter than S1 and S2
how is a grade 3 murmur described?
obvious loud murmur as loud and S1 and S2
how is a grade 4 murmur described?
very loud murmur louder than S1 and S2
how is a grade 5 murmur described?
very loud with a palpable thrill
how is a grade 6 murmur described?
audible with stethoscope just off chest wall
how can the timing of a murmur be described?
systolic
diastolic
continuous
(mid, early, late, pan, holo)
what ways can a murmur be described?
grade
timing
point of maximal intensity
radiation
shape of murmur
quality of murmur
how would a murmur from aortic valve regurgitation be described?
holodiastolic
between aorta and left ventricle
decrescendo
how would a murmur from mitral valve regurgitation be described?
holosystolic
between left atrium and ventricle
plateau
what are the two categories of murmurs?
physiological (functional)
pathological
when is an aortic flow murmur heard?
early-mid systole
where is an aortic flow murmur localised to?
heart base
what are the two main physiological murmurs?
flow and filling
when is a filling murmur heard?
early diastole
what animals is a filling murmur heard in?
fit young horses
what sound does a filling murmur make?
squeak/whoop
how would the murmur heard with mitral/tricuspid regurgitation be described?
holo/pansystolic
plateau or crescendo
PMI heart apex
why is tricuspid regurgitation less severe than mitral?
right side of heart (tricuspid) is under less pressure
how would a ventricular septal defect murmur be described?
loudest on right
pansystolic
radiates cranial/ventral
how would an aortic insufficiency murmur be described?
decrescendo (buzzing)
holodiastolic
PMI left heart base
what age horses is an aortic insufficiency murmur heart in?
teenage (moaning sound)
why is a patent ductus arteriosus murmur a constant murmur?
because there is always a pressure gradient
what age horses is patent ductus arteriosus murmur common in?
young horses (first 5 days of life)
what is oedema?
abnormal and excessive accumulation of fluid in the interstium
how does generalised oedema often present in horses?
accumulated in the lowermost part of the body (dependant oedema)
how is excess fluid drained from the interstitial space?
via the lymphatic system
what causes fluid to leave the vessels at the arterial end of capillaries?
hydrostatic pressure
what causes fluid to enter the vessel at the venous end of the capillary?
oncotic pressure
what are the four mechanisms that can cause oedema?
increased capillary hydrostatic pressure
decreased capillary oncotic pressure
lymphatic obstruction
increased capillary permeability
what are some possible causes of decreased oncotic pressure?
protein losing enteropathy
protein losing nephropathy
haemorrhage
chronic hepatopathy
what are some possible causes of lymphatic obstruction?
confinement (standing still for too long)
tumours
post-partum
lymphangitis
what are the three main causes of increased vascular permeability?
vasculitis
SIRS (endotoxaemia)
local inflammation
what happens to white blood cells in cases of SIRS?
they stick to the blood vessel walls
what happens when neutrophils stick to blood vessel walls in cases of SIRS?
causes damage to the wall
why do gums become congested in SIRS cases?
body loses ability to send blood to places that need them the most - generalise vasodilation
does losing a gram of globulin or albumin from blood have more effect on the oncotic pressure?
albumin (smaller molecule so more molecules are lost per gram)
what are some possible infectious causes of vasculitis?
infectious equine viral arteritis
herpes virus 1
infectious anaemia
Hendra
African horse sickness
what are the possible routes of transmission of infectious equine viral arteritis?
respiratory or venereal
what are the possible clinical signs of infectious equine viral arteritis?
pyrexia, dull, oedema, stiff gait, abortion, respiratory disease
what can cause an immune mediated vasculitis?
allergy/hypersensitivity
what is a severe generalised immune mediated vasculitis called?
purpura haemorrhagica
what types of hypersensitivity can cause a vasculitis?
1 - IgE
3 - immune complex
what parasite is associated with verminous vasculitis?
Stongylus vulgaris
what is the most common place for an aneurysm/rupture in stallions?
aortic root
what is thrombophlebitis?
blood clot that sticks to an inflamed vessel wall
where is thrombosis common in horses?
aortic-iliac
jugular from catheterisation
what is lymphangitis?
inflammation/infection of lymph vessels
how does lywmphantiis usually present?
swollen leg, painful on palpation but can bear weight
how is lymphangitis treated?
NSAIDs
possible antimicrobials
topical cleaning and cold treatment
encourage walking and movement
what is the function ion the AV node?
slow the wave of depolarisation down to prevent the atria and ventricles contracting at the same time
what is the point of the refractory period in cardiomyocytes?
to ensure it cannot contract again straight away
what factors can alter the resting and threshold potential of cells?
autonomic nervous system
potassium, sodium and calcium concentrations inside compared to outside of the cell
drugs
what effect will the parasympathetic system have on the heart?
triggers acetylcholine release which opens potassium channels on the pacemaker cells which lowers the resting potential meaning it will take longer to reach the threshold potential
where are the electrodes placed for equine ECG?
left arm (positive) - heart apex
right arm (negative) - mid right jugular furrow
what does the P wave show on ECG?
atrial depolarisation
what does the P-R interval of an ECG show?
AV node slowing the depolarisation
what does the QRS complex show on an ECG?
ventricular depolarisation (atria depolarises here)
what does the T wave of an ECG show?
ventricular repolarisation
what are the common arrhythmias in horses?
first/second degree AV block
sinus arrhythmias and tachycardia/bradycardia
atrial premature complexes
atrial fibrillation
ventricular premature complexes
ventricular tachycardia
what happens during second degree AV block?
regular SA node depolarisation and conduction pathway but AV node stops the spread of depolarisation every 3-4 beats
what heart sound can be heard when there is a dropped beat due to second degree AV block?
S4
is second degree AV block pathological or physiological in horses?
physiological - often clears with sympathetic tone (exercise….) - resting horses
is second degree AV block pathological or physiological in horses?
physiological - often clears with sympathetic tone (exercise….) - resting horses
what happens on an ECG during a first degree AV block?
prolonged P-R complex
what happens on an ECG with sinus arrhythmias?
P-R interval waxes and wanes
what does atrial fibrillation sound like?
trainers in a washing machine - all the beats but completely random
what are the most common presenting complaints of horses with atrial fibrillation?
poor performance
fading during a race
epistaxis
(incidental in low work horses)
what is the treatment for atrial fibrillation based on?
increasing the refractory period to prevent the wave being able to continue around the atria
what is the prognosis for horses with secondary atrial fibrillation?
poor - don’t bother treating
what are the main options for cardioversion to treat atrial fibrillation?
pharmacologic conversion (quinidine sulphate)
transvenous electrical cardioversion
what are the side effects for quinidine sulphate used to treat atrial fibrillation due to?
blockage of sodium channels (GI tract, nervous, muscles…)
why are currents for transverse electrical cardioversion placed on the skin?
would create too much heat as too higher current would be required so it would cook the animal
what is done to see if a horse with atrial fibrillation is safe to ride?
do an exercising ECG to look for rhythms and determine risk of collapse - looking to see if it alters the ventricular beats
what causes an atrial premature complex?
ectopic pacemaker in the atria (oddly shaped P wave)
how is it determined if the ectopic pacemaker is atrial or ventricular?
atrial - P wave effected
ventricular - QRS wave effected
