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Y4 EQ - Cardio-Respiratory > Equine Arrhythmias > Flashcards

Equine Arrhythmias Flashcards

1
Q

Arrythmias are the same in the horse except?

A
  • Very large heart, with large myocardium
  • Huge excess capacity at rest, therefore very high vagal tone
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2
Q

The vagus nerve controls which parts of the heart? What is the effect of this?

A

SAN and AVN
Increased vagal tone affects these nodes

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3
Q

The cardiac action potential conduction system pacemaker and threshold potentials can be influenced by?

A

Autonomic Nervous system
K+, Na+ and Ca2+ concentrations
Drugs

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4
Q

What is the function of the AV node?

A

Slow down depolarisation between the atria and ventricles so they don’t contract at the same time

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5
Q

What is the resting potential?

A

The difference between positive and negative potential difference in the myocytes
Resting potential is negative

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6
Q

What is the refractory period?

A

The time when a cardiac myocyte cant carry another wave of depolarisation

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7
Q

How is the pacemaker action potential different to the cardiomyocyte action potential?

A

Pacemaker action potential has a creeping resting potential that slowly increases until threshold is reached and it has a dramatic increase
Regularly sends out waves of depolarisation

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8
Q

Describe how to carry out an equine ECG

A

Base apex lead:
- Left arm (+): heart apex
- Right arm (-): mid right jugular furrow
- Neutral: remote from heart

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9
Q

The P wave represents?

A

Atrial depolarisation starting at the SA node

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10
Q

The P-R segment on an ECG represents?

A

Delay at the AV node
Prevents synchronous atrial / ventricular contraction

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11
Q

The QRS complex represents?

A

Depolarisation that starts at the AV node

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12
Q

The T wave on an ECG represents?

A

Ventricular repolarisation
- can change morphology / polarity at different heart rates = normal

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13
Q

Describe the heart sounds in the horse

A

Arial depolarisation and contraction = S4 ‘B’
Ventricular depolarisation and contraction = S1 ‘LUB’
Ventricular repolarisation and relaxation = S2 ‘DUP’

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14
Q

What are the 2 consequences of depolarisation starting at an ectopic focus (spreads over the atria in a different direction)?

A

Different wave of depolarisation
Different shaped ECG (p-wave)

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15
Q

Describe how an ectopic ventricular pacemaker alters the ECG

A
  • Normally starts at the AV node and spreads down the conduction fibres.
  • If the ectopic focus starts at another location i.e. the ventricular wall, it spreads in a different direction and takes longer. So the ECG is wider and appears bizarre
  • Ectopic ventricular pacemaker close to conduction system: run of ventricular tachycardia
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16
Q

Name the 2 common physiological arrythmias in horses

A

1st and 2nd degree AV block
Sinus arrythmias/bradycardia/tachycardia

17
Q

Name the 4 common pathological arrythmias in horses

A

Atrial Premature complexes (APC)
Atrial fibrillation
Ventricular Premature complexes
Ventricular tachycardia

18
Q

Name the 4 less common pathological arrythmias in horses

A
  • Atrial tachycardia
  • Junctional escape complexes/premature contractions
  • Ventricular fibrillation
  • 3rd degree AV block
19
Q

Describe the features of second degree AV block in horses

A
  • Common physiological arrhythmia at rest
  • Regular SA node depol.
  • Conduction pathway normal
  • AV node stops spread of depolarisation to ventricles every 3 - 4 beats
20
Q

Describe the ECG of a horse with 2nd degree AV block

A
  • Regular R-R intervals
  • Pause is approx double R-R interval
  • Normal QRS morphology
  • Normal P waves (and therefore S4)
  • Dropped beat
21
Q

What change is seen on the ECG in a horse with 1st degree AV block?

A

Prolonged P-R interval

22
Q

What change is seen on the ECG in a horse with sinus arrythmia?

A

Periodic waxing and waning of the R-R interval

23
Q

What change is seen on the ECG in a horse with sinus block or arrest?

A
  • Occasional pauses of 2+ R-R intervals
  • No P or QRS T on ECG
24
Q

Describe how an ECG would appear if a horse has atrial fibrilation

A
  • Irregular R-R intervals
  • Absence of P waves
  • ‘F’ (fibrillation) waves
  • QRS normal morphology
25
Q

How is the heart rhythm affected by atrial fibrillation?

A

Becomes irregularly irregular
Long pauses
Premature beats
No 4th heart sound
Prominent S3

26
Q

If atrial fibrillation is suspected, how is it diagnosed?

A

Echocardiography
Check for underlying Pathology:
- Serum electrolytes / FE
- Complete Blood count
- Cardiac troponin

27
Q

How may a horse present if it has atrial fibrillation?

A

Poor performance
Fading during race
Epistaxis
Often Incidental finding in sedentary / low level athletes

28
Q

How can atrial fibrillation be differentiated from 2nd degree AV block?

A

Careful auscultation

29
Q

AF in the horse without any underlying cardiac pathology called …?

A

Lone atrial fibrillation

30
Q

Is atrial fibrillation a cause of heart failure?

A

No
AF can be an effect of other cardiac disease = ‘Secondary AF’

31
Q

What are the two main options for treating atrial fibrillation?

A
  1. Pharmacologic conversion –Quinidine sulphate
  2. Transvenous electrical cardioversion
32
Q

Describe how quinidine sulfate is used to treat AF

A

Oral
Main effect = increases refractory period for atrial cells
STOP if horse does not convert or shows severe side effects

33
Q

Is a horse with atrial fibrillation suitable to ride?

A
  • Low but still increased risk of collapse
  • Perform an exercising ECG up to/beyond level they will be ridden
  • Ectopic ventricular beats = not suitable
  • Only suitable for light work if in sustained AF
34
Q

Regular atrial premature contractions can lead to..?

A

Atrial fibrillation

35
Q

How many VPCs / APCs are significant?

A

> 2 isolated premature at peak exercise
5 pairs or paroxysms post exercise

Y4 EQ - Cardio-Respiratory (6 decks)

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