Arrhythmias (Abnormal Heart Rhythms)

Arrhythmias occur when the cycle of impulses that regulate your pet’s heartbeat are abnormal or “off”. As a result, the heart may beat too fast, too slow or possibly even skip beats. This is a fairly common condition in dogs and cats, and it can be a symptom of a serious underlying condition, so a visit to your veterinarian is recommended to be safe.

Arrhythmias are generally classified astachyarrhythmias (abnormally fast heart rate and rhythm)) or bradyarrhythmias (abnormally slow heart rate and rhythm)).

Tachyarrhythmias can be either ventricular, which involve the lower chambers of the heart, or atrial, which involve the upper chambers.

  • Ventricular Arrhythmias
    • Ventricular arrhythmias originate in the ventricular myocardium (heart muscle). They can happen in all breeds, but we commonly see them in Boxers, Doberman Pinschers, and Great Danes.
  • Atrial Fibrillation
    • Atrial fibrillation is an abnormal heart rhythm that originates in the atrial myocardium. We primarily see atrial fibrillation in larger breed dogs, but it can occur in any dog or cat. Dogs and cats usually develop atrial fibrillation as a result of advanced heart disease; however, it can occur in a non-diseased heart (a condition called lone atrial fibrillation). Atrial fibrillation results in a very fast irregular heartbeat which causes animals to feel weak and in many cases develop congestive heart failure.

Examples of bradyarrhythmias include:

  • Heart Block (Atrioventricular block)
    • In dogs and cats, the heartbeat (electrical activity) is initiated in the sinus node located in the right atrium. The electrical activity travels from the sinus node, down through the atrioventricular node, into the bundle branches. This is the mechanism by which the atria (top heart chambers) and the ventricles (bottom heart chambers) communicate causing the heart to contract. There are diseases that cause the communication path (atrioventricular node) from the atria to the ventricles to be delayed or even eliminated, which over time can lead to collapse and/or congestive heart failure.
  • Sick Sinus Syndrome/Sinus Node Dysfunction (Bradycardia-Tachycardia Syndrome)
    • In dogs with Sick Sinus Syndrome, the sinus node does not consistently fire to cause regular cardiac contractions. This leads to very long pauses (greater than 8 seconds) between contractions, which can result in collapse/fainting. Sometimes the long pauses are preceded by a very rapid heart rate. This is a disease that is common in Miniature Schnauzers, Cocker Spaniels, and West Highland White Terriers.

Common symptoms of arrhythmias include general weakness, fainting or sudden collapse, and heavy or rapid breathing. Arrhythmias can be diagnosed using both an electrocardiogram (ECG – rhythm analysis) as well as a Holter monitor (24-hour ECG). Once the type of arrhythmia is identified, available treatment options – such as medical therapy, pacemaker implantation, etc. – can be determined and discussed in greater detail.

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