Equine Cardiology 1 Flashcards
how fast can a horse run?
65km/h
equine heart size, and what this determines
- 0.9 - 1.1% BWT
- determines maximum stroke volume > cardiac output
> aerobic capacity > exercise performance
oxygen delivery to tissues in the horse depends on?
how important is the spleen?
- cardiac output
- oxygen carrying capacity
> spleen 12L or more of RBC
> spleen size increased in racing horses
> splenectomy reduces performance > no splenic contraction possible
systemic circulation horse volume, how much in veins and arteries at rest and with exercise? how much goes to skeletal muscle?
blood volume = 8-10% BWT
- 75% in circulation
> at rest, 60% in venous system, 15% arterial
- with exercise, redistribution
> skeletal muscle at rest 10-20%
> skeletal muscle with exercise 80-90%
equine heart rates and how they relate to parasympathetic / sympathetic systems
30-100 - parasympathetic withdrawl
100-204(-241) - sympathetic and catecholamine inputs
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241 is ~max HR
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- this is what happens as a horse starts to run
what happens with stroke volume as a horse goes from rest to running
rest: 2.0-2.5ml/kg, ~1L
running: 3/–4/0ml/Kg, ~2L
training response in horses
cardiovascular
- improved function
- increased cardiac output
> increased heart size
> increased stroke volume
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musculoskeletal
- increased vasculature
- increased intramyocyte oxidative enzyme proliferation
diagnostic evaluation of a horse should look at:
(esp. regarding racing/ cardio complaints)
- electrocardiogram limitations?
- history
> medications? ionophores?
<> - physical exam
> respiratory changes?
> check rest of body before heart
> check jugular
> listen to both sides of the heart
> cardiac enlargement, displacement, murmurs? cardiac silhouette?
<> - electrocardiogram
> rate, rhythm, complexes
> duration
> perkinje fibers in horse penetrate all the way through the myocardium, wheras in other animals only 2/3 through > makes it harder/ impossible to pick up chamber dilation
> can use devices to look over a longer time, or with exercise
<> - ultrasound
<> - routine blood analysis
<> - other
what is cardiac triponin I?
- specific isoenzyme we can pick up, low level released from myocytes all the time, increased level with breakdown, eg. with hypoxia
> used in humans, validated in horses
what do the S1, S2, S3, S4 heart sounds come from?
S1 - associated with AV valve closure
S2 - associated with aortic and pulmonic valve closure
S3 - associated rapid ventricular filling
S4 - associated with atrial contraction
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- sounds come from shifts in the volume of blood in the heart, not actually closure of valves
one way to place ECG leads
Base - apex lead
negative lead at minubrium
positive lead at xyphoid
ground lead on neck
what is a Q wave and what does it look like on an electrocardiogram? how is it placed relative to other waves?
depolarisation of the interventricular septum
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- must be a negative deflection
- must be the first deflection of the QRS complex
- must be followed by an R wave
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- there can only be one Q wave per QRS complex
what is an R wave and what does it look like on an electrocardiogram? how is it placed relative to other waves?
The R wave represents early ventricular depolarisation
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- positive deflection
- all positive deflections are R waves and only R waves (within the QRS complex)
- there can be several R waves per QRS complex
what is an S wave and what does it look like on an electrocardiogram? how is it placed relative to other waves?
signifies the final depolarization of the ventricles, at the base of the heart.
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- it must be a negative deflection
- it must follow an R wave
- there can be several S waves per WRS complex
what is a QS wave
- it must be a negative deflection
- there must be no R wave in the QRS complex
> therefore it describes a QRS complex with only one deflection and this deflection is negative
variations in normal P wave appearance on horse ECG
(what does it represent)
represents the electrical depolarization of the atria of the heart.
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- monophasic - one hump
> positive or negative - bifid - two humps
> positive or negative - biphasic
> positive then negative
> negative then positive
appearance of normal horse T wave
what does it represent
monophasic (positive, negative), biphasic
- horse can have tall wave
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T wave represents the repolarization of the ventricles
why can ther ebe multiple P waves in horse
atria are picking up just out of synch
sinus arrhythmia - is it ok? why?
-normal in horse, associated with respiration
what does first degree AV block look like on an electrocardiogram
prolonged P-R interval
types of second degree AV block, what they look like on ECG, why they might occur
type 1- Mobitz type-1 (Wenckebach phenomenon)
> increasing P-R interval successively, and then a dropped beat ie. P wave but no QRS following
> due to high vagal tone / parasympathetic input
> can try to increase sympathetic input by startling, running…
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type 2 - Mobitz type-2
> dont have progressive prolonging of P-R interval, just dropped beat
> more likely to be associated with pathology
what is a third degree AV block, what does it look like on ECG
complete block; A-V dissociation
> P wave not associated with QRS, T complexes
> infiltrative disease with heart, usually. Rarer.
wider and taller R & T wave is usually what?
- ventricular premature complex, not necessarily abnormal
atrial and ventricular premature contraction
- do we need to treat, if single vs multiple?
- singular, occasional complexes - no treatment needed
<><><> - multiple, frequent occurence:
- assess underlying condition
> electrolyte imbalances
> cardiac troponin I
> echocardiogram
> holter monitor
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> Can be viral induced
Tx - antiinflammatory therapy > NSAIDs, corticosteroids
