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Cardio > Equine arrhythmias > Flashcards

Equine arrhythmias Flashcards

1
Q

Why are arrhythmias in the horse a problem?

A

hemodynamic: effect on BP, tissue perfusion and CO
saftey: can induce severe/fatal rhytm disturbance, syncope or sudden death

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2
Q

What are causes for arrhythmias in horses?

A

isolated electrical disorders
OR secondary to:
- structural heart dz
- metab and endoc factors
- systemic infl.
- hypotension, haemorrhage, anaemia, ischaemia
- autonomic influences
- toxicosis
- drugs

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3
Q

What are the goals when investigating arrhythmias?

A

confirm whether myocardial disease/dysfunction is present
identify specific or underlying causes

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4
Q

Whate are the diagnostic techniques used to investigate arrhythmias?

A

Clin hx, exam
clin. path.
echocardiography
ECG!!

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5
Q

What clinical pathology can indicate arrhythmias?

A

Hepatic and renal parameters of haematology and cbc
acid-base and electrolytes
Cardiac tropinin I and T
cardiac isoenzymes (creatine kinase, lactate dehydrogenase)
selenium and glutathione peroxidase
viral serology
blood bact culture (endocarditis)

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6
Q

What is the use of echocardiography in arrhythmia cases?

A

identifies global myocardial disfunction
rules out concurrent valvular dz or congenital heart dz

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7
Q

What does ECG in horses indicate?

A

cardiac rate and rhythm only
QRS size and duration doesn’t reflect the shape and size of ventricular myocardium like in small animals

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8
Q

How is the purkinje fibre system different in large animals?

A

the system is extensive, branches from endocardium to epicardium
depolarising wave is done by purkinje = less cell-cell spread through myocardium
= small wave fronts which are less influenced by myocardial mass than in SA

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9
Q

What does the horse ECG look like?

A

P is sometimes a double humo
No Q
T wave is vert variable

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10
Q

What is a telemetric ECG?

A

ECG monitor is attached to horse with surface contact electrodes
ECG is streamed to a distant monitor, instantaneous
can be used during exercise, intensive care, foetal monitoring

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11
Q

What are the physiologic cardiac arrhythmias in horses?

A

sinus arrhythmia
sinus bradycardia
sinus arrest/block
AV block (1st or 2nd degree)

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12
Q

What are the pathologic cardiac arrhythmias in horses?

A

atrial arrhythmia
ventricular arrhythmia
conduction disturbances (advanced 2nd degree AV block, 3rd degree AV block)

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13
Q

What is a first degree atrioventricular block?

A

physiological
delayed conduction through the AV node
causes a prolonged PR interval
slow, slightly variable heart rate

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14
Q

What is a second degree atrioventricular block?

A

physiological
intermittent block of conduction through the AV node (high vagal tone)
slow HR with pauses at regular intervals
Isolated, normally timed P waves on ECG without a following QRST
4th heart sound audible

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15
Q

What does a first degree AV block look like on an ECG?

A

longer PR intervals

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16
Q

What does a second degree AV block look like on an ECG?

A

P waves without QRST at normal time and normal shape
frequency of block is 1in3 and upwards

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17
Q

What is a third degree atrioventricular block?

A

pathological
complete block of conduction (dissociation)
due to pathology at the AV node (intoxication, uroperitoneum, electrode disturbance)
very slow ventricular rate, syncope and weakness

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18
Q

What is the treatment for 3rd degree AV block in horses?

A
  • vagolytic drugs in emergency, ex: atropine
  • corticosteroids? to reduce infl. around the AV node
  • pacemaker
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19
Q

What is an atrial premature depolarisation?

A

premature electrical cycle
occasional APD normal at rest, frequency increases during recovery phase after strenuous exercise but frequent APD during exercise is not normal

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20
Q

How do we investigate and treat APD?

A

rule out underlying cause
most idiopathic: often managed with coriticosteroids and rest
rarely require anti-arrhythmic therapy as ventricular rate is not increased

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21
Q

What is atrial fibrillation?

A

most common pathological arrhythmia
supraventrical tachyarrhythmia: uncoordinated atrial depolarisation due to multiple chaotic re-entry waves

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22
Q

What are the types of atrial fibrillation?

A

Paroxysmal: spontaneously converts to sinus rhythm (24-48h)
Sustained persistent: requires treatment to convert to sinus rhythm
Sustained permanent: does not respond to tx

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23
Q

What are the causes for AF?

A

Cardiac dz
idiopathic: “lone AF” no underlying dz

24
Q

What does initiation of AF require?

A

Large atrial mass (normal horses, atrial enlargement)
Slow SA node rate (high vagal tone)
Variable refractory periods (effect of high vagal tone, also in myocardial dz, electrolyte/pH change, allows re-entry to occur)

25
Q

What is the clinical significance of AF in horses?

A

frequently spontaneous and not due to cardiac dz (lone AF doesn’t cause heart failure but can be secondary to heart failure)
atrial contraction contributes 10-15% of ventricular filling, loss only affects CO at high intensity exercise
incidental finding in many types of horses

26
Q

What are the clinical signs of AF?

A

Depends on use of horse: none if low level exercise, exercise intolerance/poor performance in high level exercise

irregularly irregular rhythm, variable number with variable pauses, no fourth heart sound
variable pulse quality
variable intensity of heart sounds
exercise-induced pulmonary haemorrhage - epistaxis

27
Q

What do we investigating when deciding if we need to treat AF?

A

establish if there is an underlying heart disease (usually spontaneous or an effect not cause of heart dz)

check for signs of heart failure

28
Q

What are the signs of heart failure in horses?

A

resting tachycardia (>60bpm)
valve regurg. (murmur) especailly mitral/tricuspid
venous distention
oedema

29
Q

When do we treat AF and what do we treat with?

A

Incidental finding = no tx
Competition horse w/ exercise intolerance = quinidine, transvenous electrical cardioversion
Heart failure = palliative furosemide, digoxin, ACE inhibitors

30
Q

What is the use of Quinidine sulphate?

A

Prolongs the effective refractory period
Its a Class ! antiarrhythmic: slows the Na+ fast channels
Promotes the electrical homogeneity in the atria

31
Q

What are some of the (unwanted) effects of Quinidine Sulphate?

A

Vagolytic (ventricular tachycardia)
Alpha-adrenergic antagonist (hypotension)
Negative inotrope (decreases CO)
Other arrhythmias (possibly fatal)
GI ulceration (diarrhoea, colic)
Nasal oedema
Laminitis
Neuro signs, ataxia
Penile protrusion

32
Q

What is transvenous electroconversion?

A

intra-cardiac electrodes placed
shock delivered across atria
95% success rate
32% recurrence rate

33
Q

What determines the prognosis of a horse with AF?

A

underlying cardiac dz (don’t tx AF in heart failure cases, they will relapse)
duration of AF prior to tx (less than 3 months 15% recurrence, over 3months 60% recurrence with more side effects)

34
Q

What is Ventricular premature depolarisations?

A

Pathologic
1-3 abnormal consecutive beats
can be cause of poor performance if occurs during exercise (heart is emptying faster)

35
Q

What is the difference between VPD and ventricular tachycardia?

A

VPD: 1-3 abnormal consecutive heart beats
Ventricular tach: more than 3 consecutive VPDs

36
Q

What do we need to investigate and how to we treat VPD?

A

Establish is arrhythmia occurs at rest only, exercise only or both
if idiopathic: corticosteroids and rest
V. arrhythmias more likely to progress into fatal

37
Q

What are the signs and risks of ventricular tachycardia?

A

horses with systemic inflammation, electrolyte, acid/base disturbances, hypoxia
risk that rhythm will destabilise to ventricular fibrillation (death)

38
Q

When should we consider anti-arrhythmic therapy in horses with Ventricular Tachycardia?

A

clinical signs of low CO
Ventricular rate is greater than 100bpm
polymorphic complexes
R on T phenomenon

39
Q

What is a polymorphic complex on an ECG?

A

When there is 2 different types of ectopic complexes, P wave dissociated from QRS

40
Q

What is an R on T phenomenon on an ECG?

A

R waves occurring immediately after the preceding T wave

41
Q

What are the possible treatments for ventricular arrhythmias?

A

Magnesium sulphate (physiological calcium channel blocker)
Lidocaine
Propranolol (rarely effective in horses)
Procainamide
Quinidine gluconate

42
Q

What should we know about lidocaine as a tx for ventricular arrhythmias?

A

causes seizures at high doses
drug of choice under anaesthesia

43
Q

What are the causes of Ventricular arrhythmias?

A

isolated electrical disorders
OR
Secondary to
- structural heart dz
- metab and endocrine factors
- systemic infl.
- hypotension, haemorrhage, anaemia, ischaemia
- autonomic influences
- toxicosis
- drugs

44
Q

What is the pathogenesis causes of primary myocardial dz and dysfunction?

A

infectious causes (viral, bact. parasite)
nutritional (vit E, selenium deficiency)
cardiomyopathy
neoplasia
immune mediated
toxic
idiopathic

45
Q

What are the pathogenesis causes of secondary myocardial disease and dysfunction?

A

systemic inflammation (SIRS)
electrolyte disturbances
acid-base disturbances
hypoxia
catecholamine-induced
vagally-induced

46
Q

What are examples of viral causes of primary myocarditis in horses?

A

equine influenza
equine herpes virus
equine viral arteritis
african horse sickness
equine infectious anaemia

47
Q

What are examples of bacterial causes of primary myicarditis in horses?

A

s. aureus
clostridium chauvoei
mycobacterium
strep equi equi
actinobacillus
rhodococcus equi
borrelia burgdorferi (lyme dz)

48
Q

What are examples of parasitic causes of primary myocarditis in horses?

A

strongyles
onchocerca
toxoplasma
cysticerca
sarcocysta

49
Q

What is nutritional myodegeneration?

A

white muscle dz
selenium deficiency from pasture being deficient
oxidative injury to muscle
2 forms: cardiac and skeletal

50
Q

What is the difference between cardiac and skeletal white muscle dz?

A

cardiac: neonates, acute/per-acute, severe debilitation or sudden death, resp. signs, arrhythmias
skeletal: slightly older animals, weakness, stiffness and debilitation, signs precipitated by stress

51
Q

How do we diagnose white muscle dz?

A

whole blood selenium concentrations
glutathione peroxidase concentrations

52
Q

What is the treatment for nutritional myodegeneration?

A

vit E and selenium supplementation, IM injection

53
Q

What is the post mortem appearance of nutritional myodegeneration?

A

pale streaky muscles
degeneration and fibrosis of muscles

54
Q

What are the causes for hypoxia also causing secondary myocardial dz?

A

blood loss, haemoabdomen
upper airway obstruction
red maple leaf toxicity

55
Q

What are electrolyte abnormalities causing secondary myocardial dz?

A

potassium
calcium
magnesium

56
Q

What are the most important equine arrhythmias?

A

second degree Av block
A fib
V Tach

57
Q

When are anti-arrhythmic agents most likely to be used?

A

for some ventricular arrhythmias and atrial fibrillation

Cardio (11 decks)

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