Atrial Fibrillation

Question 1

Describe atrial fibrillation

Answer 1

electrical activity arising form the atria that leads to disordered conduction patterns

Question 2

In a patient with A-fib, is there conduction from the atria to the AV node?

Answer 2

Yes

Question 3

During A-fib, is pacemaker activity of the ventricles autonomous and entirely independent of electrical activity of the atria?

Answer 3

No

Question 4

Describe a pulse defecit

Answer 4

A heart beat not accompanied by a discernible pulse

Question 5

Can dropped beats be discerned in a healthy animal?

Answer 5

yes

Question 6

What heart chamber function can be responsible for a pulse defecit?

Answer 6

inadequate ventricular filling

Question 7

Quinidine acts by reducing the entry of Na to cardiac myocytes through VOSC, and does what to electrical membrane threshold?

Answer 7

increases membrane threshold of excitability in cardiac myocytes

Question 8

How does A-fib manifest in horses?

Answer 8

develops spontaneously with no evidence of cardiac disease

perhaps perpetuated by large heart size and high vagal tone, electrolyte imbalances

Question 9

How does A-fib manifest in dogs

Answer 9

associated with underlying cardiac disease that causes L atrial enlargement

Question 10

In horses, what is the goal of treatment of A-fib?

Answer 10

restore normal sinus rhythm

provided there is no underlying cardiac dz

Question 11

In dogs, what is the goal of treatment of A-fib?

Answer 11

slow the transmission of impulses through the AV node in order to allow more efficient ventricular filling & enhance output
It is generally not possible to restore normal sinus rhythm in dogs due to underlying pathology

Question 12

what is the first drug of choice used to treat A-fib in dogs

Answer 12

Digoxin –> slows conduction through AV nodes to work as anti-arrhythmic

*Ca channel blockers and B blockers sometimes used

Question 13

Why would a dog be treated with Digoxin PLUS furosemide and pimobendan

Answer 13

Pimo improves cardiac function (+ve inotrope)

Frusemide reduces secondary pulmonary oedema

Question 14

what particular pathologies is A-fib usually associated with in dogs and cats?

Answer 14

Dog- mitral valve failure

Cat- hypertrophic cardiomyopathy

Question 15

What would I use if I wanted to increase AV nodal refractoriness & depress slow fibre conduction

Answer 15

digoxin 
B blocker (propanolol)
Ca channel blocker (diltiazem, verapamil)

Question 16

What would I use if I wanted to increase atrial refractoriness

Answer 16

Na channel blocker (e.g. quinidine) for atrial fibrillation in horses