Atrial fibrillation is a form of cardiac arrhythmia. In atrial fibrillation a pet’s heart rhythm is driven by chaotic electrical impulses within the atria (the upper chambers of the heart), rather than originating in the normal pacemaker of the heart (the sinus node).


In dogs and cats, atrial fibrillation is usually due to severe underlying heart disease (such as degenerative mitral valve disease, dilated cardiomyopathy or hypertrophic cardiomyopathy). Since the type and severity of underlying heart disease affects treatment options and prognosis, an echocardiogram to assess cardiac structure and function is strongly recommended for dogs and cats diagnosed with atrial fibrillation.


Atrial fibrillation interferes with the ability of the heart to fill normally and often results in a persistently rapid heart rate, which further impairs cardiac function and may trigger the onset of heart failure or worsen pre-existing heart failure. If a pet with atrial fibrillation has a rapid ventricular response rate (heart rate), medications will be prescribed to try to slow the heart rate down. Follow-up usually involves rechecking your pet’s heart rate via auscultation (listening to the heart with a stethoscope) and an in-hospital ECG to ensure the medication(s) are effective. Ideally a 24-hour at-home ECG (Holter monitor) would then be obtained to ensure the pet’s atrial fibrillation is well controlled over a longer period of time in his/her normal environment.


In some cases, a procedure called electrical cardioversion may be recommended. This involves delivery of electrical energy to the heart via special paddles placed on the chest. The goal of electrical cardioversion is to restore a normal sinus rhythm. This procedure requires a brief period of general anesthesia.


In rare cases a pet may be diagnosed with a condition called lone atrial fibrillation. This is generally only seen in giant breed dogs and is characterized by atrial fibrillation in the absence of any identifiable cardiac abnormalities on echocardiogram. The ventricular response rate (heart rate) is usually relatively slow in cases of lone atrial fibrillation, so heart-rate slowing medications may not be necessary. It should be noted that some dogs initially diagnosed with lone atrial fibrillation eventually develop structural/functional cardiac abnormalities, so follow-up echocardiography is still necessary.


Normal ECG


Atrial fibrillation