Changes

Atrial fibrillation can occur in all species when there is '''atrial dilation''' secondary to other cardiac lesions.

Atrial fibrillation can occur in all species when there is '''atrial dilation''' secondary to other cardiac lesions.

==Clinical Signs==

==Clinical Signs==

===Horses===

===Horses===

This may be an '''incidental finding''' on clinical examination, especially if the horse is not used for highly athletic activities. If the horse is raced, hunted or an eventer, then signs may occur during exercise and include '''exercise intolerance''', reluctance to exercise or a poor performance during exercise. It can be associated with '''[[Exercise Induced Pulmonary Haemorrhage|exercise induced pulmonary haemorrhage]]''', so this can be a clinical sign of the condition.

This may be an '''incidental finding''' on clinical examination, especially if the horse is not used for highly athletic activities. The atrial contraction only contributes to around 15% of the ventricular filling, so signs of atrial fibrillation are only seen during vigorous exercise. If the horse is raced, hunted or an eventer, then signs may occur during exercise and include '''exercise intolerance''', reluctance to exercise or a poor performance during exercise. It can be associated with '''[[Exercise Induced Pulmonary Haemorrhage|exercise induced pulmonary haemorrhage]]''', so this can be a clinical sign of the condition.

 

===Cattle===

===Cattle===

Signs generally relate to the underlying disease process, which in cows can range from '''gastrointestinal diseases''' such as a [[LDA|left-displaced abomasum]], to uterine torsion.

Signs generally relate to the underlying disease process, which in cows can range from '''gastrointestinal diseases''' such as a [[LDA|left-displaced abomasum]], to uterine torsion.

===Small Animals===

===Small Animals===

Patients with primary atrial fibrillation are usually asymptomatic. However, there may be signs of haemodynamic compromise due to the rapid heart rate and a loss of atrial contribution to ventricular filling; which would usually account for up to 20% of cardiac output. This most commonly manifests as exercise intolerance.  

Patients with primary atrial fibrillation are usually asymptomatic. However, there may be signs of haemodynamic compromise due to the rapid heart rate and a loss of atrial contribution to ventricular filling; which would usually account for up to 20% of cardiac output. This most commonly manifests as exercise intolerance.  

* Ventricular rate variable

* Ventricular rate variable

* Sudden onset and termination

* Sudden onset and termination

====Atrial Fibrillation===

====Atrial Fibrillation====

* No P waves

* No P waves

* Coarse oscillation of the baseline (F-waves)

* Coarse oscillation of the baseline (F-waves)

There is a greater success with conversion in young horses and when conversion is attempted shortly following the onset of the arrythmia. If the arrythmia has been present for more than 4 months, therapeutic success is much less common and there is a higher recurrence rate.

There is a greater success with conversion in young horses and when conversion is attempted shortly following the onset of the arrythmia. If the arrythmia has been present for more than 4 months, therapeutic success is much less common and there is a higher recurrence rate.

Horses can also develop atrial fibrillation secondary to '''cardiac disease''', such as [[Mitral Valve Dysplasia|mitral valve insufficiency]], [[Tricuspid Valve Dysplasia|tricuspid valve insufficiency]], or any acquired or congenital disease leading to atrial hypertrophy. Horses will usually develop '''congestive heart failure''' and have a resting tachycardia. These underlying conditions should be diagnosed and the congestive heart failure treated with diuretics and inotropes. These horses will have a poor prognosis for return to function and treatment is mainly to slow progression of disease.

Horses can also develop atrial fibrillation secondary to '''cardiac disease''', such as [[Degenerative Mitral Valve Disease|mitral valve insufficiency]], [[Tricuspid Valve Dysplasia|tricuspid valve insufficiency]], or any acquired or congenital disease leading to atrial hypertrophy. Horses will usually develop '''congestive heart failure''' and have a resting tachycardia. These underlying conditions should be diagnosed and the congestive heart failure treated with diuretics and inotropes. These horses will have a poor prognosis for return to function and treatment is mainly to slow progression of disease.

===Cattle===

===Cattle===

===Small Animals===

===Small Animals===

In '''dogs''', '''digoxin''', is usually the first line of therapy in slowing conduction through the AV node. The goal is to keep the heart rate between 140 and 160 beats per minute. If the heart rate remains high, a calcium channel blocker such as '''diltiazem or a beta-blocker''' should be used as well.

 

In '''dogs''' with AF secondary to '''structural heart disease''', '''Digoxin''' is usually the first line of therapy. Digoxin slows conduction through the AV node. The goal is to keep the heart rate <150 bpm. Dogs should be re-assessed 5-7 days after starting Digoxin and serum Digoxin levels should be measured >8 hours post-administration. If the heart rate remains high and the serum Digoxin level is within target range, a calcium channel blocker such as '''Diltiazem''' can be added. If compliance is good and finances are not limited, there may be additional benefit of an ACE inhibitor, Spironolactone and Omega-3 fatty acids. These help reverse structural remodelling and modulate pro-inflammatory cytokines that perpetuate arrhythmias.  

High-dose '''oral quinidine or electrical cardioversion''' can be used in primary atrial fibrillation cases to convert the heart back to sinus rhythm. This requires experienced personnel, general anaesthesia and special equipment.

In '''dogs''' with '''primary 'lone' AF''', '''Amioderone''' should be administered if electric cardioversion is an option.  Amioderone increases the chances of remaining in sinus rhythm following cardioversion and some dogs may spontaneously convert to sinus rhythm with Amioderone alone. If electrical cardioversion is not an option, and the rate is >150bpm, then rate control is appropriate, using '''beta-blockers''' or '''Diltiazem'''. It is important to monitor these dogs for the development of structural cardiac disease, as AF may be seen in the occult phase of [[Dilated Cardiomyopathy|Dilated Cardiomyopathy]].

In '''cats''', '''diltiazem or atenolol''' are usually the drugs of choice. Digoxin can also be added if the heart rate is still high or there is evidence of heart failure.

In '''cats''', atrial fibrillation usually indicates advanced structural heart disease with atrial dilation and is associated with a poor prognosis. The first-line drug of choice is  '''Diltiazem'''.  

In '''rabbits''', '''digoxin''' has been used anecdotally to slow the heart rate.

In '''rabbits''', '''Digoxin''' has been used anecdotally to slow the heart rate.

In all cases with concurrent severe heart disease and possibly '''congestive heart failure''', efforts to control the disease by using diuretics such as '''frusemide''' can be helpful in improving clinical signs. Calcium channel blockers and beta-blockers, both negative inotropes, should be used carefully in animals with myocardial failure.

In all cases with concurrent severe heart disease and possibly '''congestive heart failure''', efforts to control the disease by using diuretics such as Furosemide can be helpful in improving clinical signs. Calcium channel blockers and beta-blockers, both negative inotropes, should be used carefully in animals with myocardial failure (systolic dysfunction).

== Prognosis ==

== Prognosis ==

In '''cattle''', prognosis depends on the underlying gastrointestinal condition and the treatment options chosen by the farmer.

In '''cattle''', prognosis depends on the underlying gastrointestinal condition and the treatment options chosen by the farmer.

In '''small animals''', cases with primary atrial fibrillation and normal ultrasound findings have a good prognosis. Animals with secondary atrial fibrillation associated with severe heart disease have a guarded to poor prognosis.

In '''small animals''', cases with primary atrial fibrillation and normal echocardiographic findings have a good prognosis. Animals with secondary atrial fibrillation associated with severe heart disease have a guarded to poor prognosis.

{{Learning

{{Learning

== References ==

== References ==

Boswood, A (2008) '''Cardiovascular System Study Guide''', ''Royal Veterinary College''.

Luis Fuentes, V, Johnson, L.R, Dennis, S. (2010) '''BSAVA Manual of Canine and Feline Cardiorespiratory Medicine (Second Edition)'''Boswood, A (2008) '''Cardiovascular System Study Guide''', ''Royal Veterinary College''.

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Ettinger, S.J. and Feldman, E. C. (2000) '''Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2''' (Fifth Edition), W.B. ''Saunders Company''.

Ettinger, S.J. and Feldman, E. C. (2000) '''Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2''' (Fifth Edition), W.B. ''Saunders Company''.

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Knottenbelt, D.C. '''A Handbook of Equine Medicine for Final Year Students''', ''University of Liverpool''.

Knottenbelt, D.C. '''A Handbook of Equine Medicine for Final Year Students''', ''University of Liverpool''.

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Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing''.  

Pasquini, C, Pasquini, S, Woods, P (2005) '''Guide to Equine Clinics Volume 1: Equine Medicine''' (Third edition), ''SUDZ Publishing''.  

Rose, R. J. and Hodgson, D. R. (2000) '''Manual of Equine Practice''' (Second Edition), ''Saunders''.  

Rose, R. J. and Hodgson, D. R. (2000) '''Manual of Equine Practice''' (Second Edition), ''Saunders''.  

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