- Cause : primary in large-breed or giant-breed dogs. Secondary to atrial enlargement in small and medium-sized breeds.
- Signs : may be non-specific or signs of underlying pathology.
- Diagnosis : auscultation, electrocardiography.
- Treatment : conversion back to sinus rhythm (primary AF) or ventricular rate control (secondary AF).
- Prognosis : depends on cause - primary AF has good prognosis, secondary AF has poor prognosis.
Print off the owner factsheet on ( Heart rhythm disturbance atrial fibrillation) to give to your client.
- Auscultation of the heart gives a typical sound - chaotic heart rhythm, sometimes described as 'tennis shoes in the dryer'. May be other auscultation findings, eg murmur or respiratory crackles.
- Tachycardia (heart rate often >180 BPM), if secondary to heart disease.
Large and giant breed dogs with primary atrial fibrillation usually have ventricular rate within normal range (80-100 BPM).
- Marked pulse deficit or variable pulse intensity if tachycardic.
- Signs associated with underlying cardiac disease:
- Pulmonary edema.
- Pallor due to poor peripheral perfusion.
- Atrial premature contractions (APCs) .
- Supraventricular tachycardia with AV block.
- Primary AF: may be good if ventricular rate is not too fast initially or can be controlled with mediciation. Dogs with primary AF may remain asymptomatic for many years after diagnosis.
- Secondary AF: prognosis is often poor due to severe nature of underlying heart disease. In general, presence of AF is a negative prognostic sign in dogs with mitral valve disese or dilated cardiomyopathy.
Expected response to treatment
- Slower ventricular heart rate.
- It is rare for atrial fibrillation to convert to normal sinus rhythm but ventricular rate on ECG should slow.
- Improved exercise tolerance/demeanor.
- Improved ability to treat congestive heart failure .
Reasons for treatment failure
- Incorrect diagnosis.
- Severe underlying pathology.
- Inadequate doses of drug given or unacceptable side-effects associated with medication.