Changes

==Introduction==

==Introduction==

The temporary or permanent '''lack of atrial activity''' resulting from a '''failure of atrial depolarisation'''.  The ventricles still function normally.

Atrial standstill is the temporary or permanent '''lack of atrial activity''' resulting from a '''failure of atrial depolarisation'''.  The ventricles still function normally.

==Aetiology==

==Aetiology==

The '''atrial muscle fails to depolarise''', despite the production of an impulse from the sinoatrial node. So instead impulses pass from the '''sinoatrial node''' to the '''atrioventricular node''' by '''internodal pathways'''. This produces a '''sinoventricular rhythm'''. This can be caused by '''electrolyte abnormalities''' (especially hyperkalaemia), '''cardiomyopathies, muscular dystrophy, hypoadrenocorticism and toxicity'''.  

The '''atrial muscle fails to depolarise''', despite the production of an impulse from the sinoatrial node. So instead impulses pass from the '''sinoatrial node''' to the '''atrioventricular node''' by '''internodal pathways'''. This produces a '''sinoventricular rhythm'''. This can be caused by '''electrolyte abnormalities''' (especially '''hyperkalaemia''' - which can develop secondary to a number of conditions including [[Hypoadrenocorticism|Addison’s disease]], [[Acute Renal Failure|oliguric renal failure]] and [[Urogenital Disease and Anaesthesia|urethral obstruction]]), '''[[Cardiomyopathy|cardiomyopathies]], [[Muscular Dystrophy|muscular dystrophy]] (causing persistent atrial standstill - most commonly seen in the Springer Spaniel), and drug toxicity'''.  

==Clinical Signs==

==Clinical Signs==

==Diagnosis==

==Diagnosis==

Diagnosis can be confirmed by '''ECG''' or '''fluoroscopy'''.  

Diagnosis can be confirmed by '''[[ECG]]''' or '''fluoroscopy'''. With persistent atrial standstill cases, the heart rate will not increase upon administration of atropine. Underlying causes should be investigated, electrolyte abnormalities in particular.

===ECG===

===ECG===

An ECG should show an '''absence of P waves'''. '''Heart rate is regular''' but normally '''slow''', due to the presence of an '''escape rhythm'''. The '''QRS complexes are normal or slightly wide'''.  

An ECG should show an '''absence of P waves'''. '''Heart rate is regular''' but normally '''slow''', due to the presence of an '''[[Escape Rhythms|escape rhythm]]'''. The '''QRS complexes are normal or slightly wide'''.  

It is important to have an artefact-free ECG of diagnostic quality to confirm atrial standstill.  

It is important to have an artefact-free[[ ECG]] of diagnostic quality to confirm atrial standstill.  

==Treatment==

==Treatment==

Treat the '''underlying cause'''.

Treat the '''underlying cause'''. If this fails to resolve the condition or persistent atrial standstill is diagnosed a '''permanent ventricular pacemaker''' should be implanted.

{{Learning

{{Learning

|flashcards = [[Feline Medicine Q&A 01]]

|flashcards = [[Feline Medicine Q&A 01]]<br>[[Small Animal Soft Tissue Surgery Q&A 08]]

}}

}}

==References==

==References==

Martin, M (2002) '''ECG interpretation in small animals : 2. Abnormalities in the conduction system''' ''In Practice 2002 24: 194-20''

Martin, M (2002) '''ECG interpretation in small animals : 2. Abnormalities in the conduction system''' ''In Practice 2002 24: 194-20''