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Atrial Fibrillation and Atrial Flutter in Dogs

A dog's heart is divided into four chambers. The two top chambers are called the atria (single: atrium) whereas the bottom chambers are called the ventricles. Valves are provided between each atrial and ventricular pair, each on the left and right side. The valve between the right atrium and right ventricle is called the tricuspid valve, where the valve between the left atrium and left ventricle is called the mitral valve. The heart works with exceptional synchronization between the various atrial and ventricular structures, resulting in a consistent rhythmic pattern.

In both atrial fibrillation and atrial flutter this rhythm is disturbed and synchronization is lost between the atria and ventricles. Both conditions refer to a rhythm problem that originates in the upper chambers of the heart, that is, the atria. Atrial flutter is often a precursor to atrial fibrillation. In atrial flutter there is a premature electrical impulse that arises in the atria, resulting in a faster than normal heart rate, either regular or irregular in frequency, whereas in atrial fibrillation there is quivering type of contraction of the heart muscles, resulting in a rapid and abnormally paced heart rhythm, also referred to as arrhythmia. In atrial fibrillation the atria beat chaotically, resulting in irregular rhythms of the ventricle as well. Atrial fibrillation can occur with or without underlying heart disease. On an electrocardiogram (ECG), which measures the electrical activity of the heart, a distinct pattern can be differentiated in atrial fibrillation and atrial flutter.

Symptoms and Types

Atrial fibrillation is categorized by relevance, including:

• Primary atrial fibrillation
  • No underlying cardiac disease involved – cause not identified
• Secondary atrial fibrillation
  • Severe underlying cardiac disease like CHF is usually involved
• Paroxysmal atrial fibrillation
  • Periodic, recurrent episodes, which last for a short period of time (less than seven days), with the heart returning to its normal rhythm on its own
• Persistent atrial fibrillation
  • Arrhythmia lasts for more than 48 hours, only responds to treatment
• Permanent atrial fibrillation
  • Ongoing arrhythmia, cannot be treated

The symptoms generally relate to an underlying disease like congestive heart failure (CHF). Following are few of the symptoms related to atrial fibrillation.

• Galloping heart
• Exercise intolerance
• Weakness
• Cough
• Dyspnea (Difficult breathing)
• Tachypnea (Rapid respiratory rate)
• Lethargy
• Syncope/Loss of consciousness (rare)

Causes

• Chronic disease of the heart involving the valves
• Enlargement of the heart
• Cardiomyopathy (heart muscle disease)
• Congenital heart disease
• Neoplasia
• Digoxin toxicity (drug commonly used to treat various heart diseases)
• As a sequel congestive heart failure (CHF)
• Cause may remain unknown

Diagnosis

After taking a detailed history from you, including your dog's background health history and onset of symptoms, your veterinarian will perform a complete physical examination. Laboratory tests include a complete blood profile, with a biochemical profile, complete blood count, and urinalysis. It is possible that the results of these tests may not reveal much information related to this disease, but they may be helpful for accessing an overall picture of your dog's health and reveal other diseases, if present. Additional diagnostic tools include echocardiography (ECG), X-ray imaging, and color Doppler to help in characterizing the type and severity of any underlying heart disease.