Arrhythmias

Question 1

Horses have a very large heart with a huge myocardium. How does this affect vagal tone?

Answer 1

High vagal tone

Question 2

What is the P wave on an ECG?

Answer 2

Atrial depolarisation

+ contraction, S4

Question 3

What is the QRS wave on an ECG?

Answer 3

Ventricular depolarisation

+ contraction, S1

Question 4

What is the T wave on an ECG?

Answer 4

Ventricular repolarisation

+ relaxation, S2

Question 5

Where does the equine ECG attach to horses?

Answer 5

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

Question 6

What is the purpose of the P-R segment on an ECG?

Answer 6

Delay impulse at AV node

Prevent synchronous contraction of atria and ventricles

Question 7

Which part of an ECG wave may be positive or negative?

Answer 7

T wave

QRS normally negative in horse

Question 8

Which types of AV block are physiological arrhythmias and which are pathological?

Answer 8

1st and 2nd degree AV block = physiological

3rd degree AV block = pathological

Question 9

Does 2nd degree AV block occur at exercise or at rest?

Answer 9

At rest

AV node stops spread of depolarisation to ventricles every 3-4 beats

Question 10

Which physiological arrhythmia has no P wave and variable R-R intervals?

Answer 10

Sinus block

Question 11

Which common physiological arrhythmia has P waves followed by a pause of 2X R-R interval, every 3-4 beats?

Answer 11

2nd degree AV block

Question 12

Atrial fibrillation may present as poor performance, fading during a race and epistaxis. Why does AF cause epistaxis?

Answer 12

Pulmonary hypertension

Causes EIPH

Question 13

What is the most common arrhythmia causing poor performance in horses? It is often an incidental finding.

Answer 13

Atrial fibrillation

Question 14

Atrial fibrillation can be primary/lone AF (without underlying cardiac pathology) or secondary to cardiac pathology. Give an example of a condition that leads to secondary AF

Answer 14

Mitral regurgitation

Causing LA dilation

Question 15

Is atrial fibrillation a cause of heart failure?

Answer 15

NO

If a case of AF has heart failure, look for underlying cause

Question 16

Give the 3 clinical signs of heart failure in horses

Answer 16

HR >50bpm
Peripheral oedema
Jugular distension

Question 17

A horse has had a recent onset of atrial fibrillation in the last 12 hours. What treatment should be performed?

Answer 17

None - may revert to sinus rhythm within 24-48 hours

Question 18

What are the 2 conversion options for treating atrial fibrillation?

Answer 18

Pharmacological conversion - quinidine

Transvenous electrical cardioversion

Question 19

Quinidine sulphate is used for atrial fibrillation in horses. How is it administered? What if it is not succesful?

Answer 19

PO - nasogastric tube
Every 2 hours until conversion (maximum of 5 doses)
Prolong treatment interval and add in digoxin if needed - stop if side effects or not converting

Question 20

When using transvenous electrical cardioversion for atrial fibrillation, when should you NOT give the shock?

Answer 20

T wave - fatal

Question 21

Regular atrial premature contractions can lead to what other arrhythmia…

Answer 21

Atrial fibrillation

Question 22

What are atrial premature complexes?

Answer 22

Premature complexes with a different shaped P wave

Question 23

In general, what does a different shaped P wave suggest?

Answer 23

Atrial contraction originating somewhere other than SAN

Question 24

In general, what does a different shaped QRS or T suggest?

Answer 24

Ventricular contraction originating somewhere other than AVN

Question 25

2nd degree AV block is common in a lot of horses at rest. It is associated with what tone?

Answer 25

High vagal tone

Question 26

What tone can cause 2nd degree AV block to be abolished?

Answer 26

Increased sympathetic tone

Question 27

How is ventricular tachycardia defined?

Answer 27

4+ VPCs in a row