Heart Beat Problems (Fibrillation and Flutter) in Dogs

Atrial fibrillation and atrial flutter are conditions characterized by abnormal heart rhythm (arrhythmia). To understand the two phenomena, it is important to know how heart works.

The heart is made up of four chambers, upper two are called atria (singular = atrium) and lower two chambers are ventricles. Valves are present between each atrial and ventricle pair on each side of the heart. Right sided atriam-ventricle valve is called tricuspid valve while valve between left atrium and left ventrical is called mitral valve. The normal constant rhythmic pattern of the heart is achieved through remarkable synochronization of various atrial and ventricl structures in the heart.

The electrical impulse that signals the heart to contract begins in the sinoatrial node (also called the sinus node or SA node) in the right atrium. The signal leaves the SA node and travels through the two upper chambers of the heart (atria). Then the signal passes through another node (the AV node), and finally, through the lower chambers (ventricles).

Atrial fibrillation and atrial flutter (AF & AFL), both conditions refer to an abnormal rhythm problem that occurs in the upper chambers of the heart. The atria beat very fast. This is because the electrical impulse does not travel in an orderly fashion through the atria. Instead, many impulses begin simultaneously and spread through the atria and compete for a chance to travel through the AV node. The firing of these impulses results in a very rapid and disorganized heartbeat. 

Main difference between atrial fibrillation and atrial flutter is that in atrial fibrillation,the electrical impulse of the heart is not regular. The atria contract very quickly and not in a regular pattern. This makes the ventricles beat abnormally, leading to an irregular (and usually fast) pulse. As a result, the heart cannot pump as much blood as the body needs. In atrial fibrillation the atria beat chaotically, resulting in irregular rhythms of the ventricle as well.

In atrial flutter, the ventricles may beat very fast, but in a regular pattern. Atrial flutter is often a precursor to atrial fibrillation.

Atrial fibrillation can occur with or without underlying heart disease. On an electrocardiogram (ECG), a distinct pattern can be differentiated in atrial fibrillation and atrial flutter.

The atrial fibrillation can be divided into different categories based on relevance.

Primary atrial fibrillation is when no underlying heart disease is present and cause is unknown. Secondary atrial fibrillation is due to severe underlying condition such as congestive heart failure. Paroxysmal atrial fibrillation is when periodic, recurrent episodes of AF occur, 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 is when arrhythmia lasts for more than 48 hours and responds only to treatment. Last but not the least, permanent atrial fibrillation which is an ongoing arrhythmia which cannot be treated.

Common signs associated with atrial fibrillation and atrial flutter include

Heart palpitation

Exercise intolerance



Dyspnea (Difficult breathing)

Tachypnea (Rapid respiratory rate)


Syncope/Loss of consciousness (rare)

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