Syncope in Dogs

Syncope (Fainting) in Dogs

By: PetPlace Veterinarians

Section: Information In-depth

Syncope (fainting) is a symptom related to a wide number of disorders.

  • Sometimes the cause is relatively simple, such as moderate to severe anemia, causing inadequate delivery of oxygen to the brain.

  • Severe respiratory dysfunction or airway obstruction (as with severe tracheal or windpipe collapse) can cause fainting, because the blood oxygen level will fall.

  • There are some problems with the involuntary (autonomic) nervous system that are difficult to diagnose, which can lead to fainting in pets. In most cases, however, the cause of syncope is traced to cardiovascular disease (abnormal function of the heart or blood vessels).

    Heart conditions that may cause syncope include:

  • Congenital heart defect (birth defects) that obstructs blood flow or prevents the normal movement of blood to the lungs.

  • Heart failure with inadequate heart action, leading to reduced blood flow (cardiac output).


  • Pulmonary hypertension (high resistance to blood flow in the lungs) such as that caused by heartworm disease or pulmonary thromboembolism (abnormal blood clot formation in the blood vessels of the lung).

  • Occasionally, disease of the pericardium (the space around the heart), the heart muscle (cardiomyopathy), the heart valves, or cardiac tumors lead to syncope.

  • Electrical disturbances of the heart, including pacemaker malfunction (sinus arrest), abnormal electrical impulse conduction (atrioventricular heart block) or excessively fast, abnormal heart rhythms (supraventricular and ventricular tachycardias).

  • Neurocardiogenic syncope (slow heart rate and abnormal dilation of blood vessels causing low blood pressure) may be precipitated by sudden standing, activity, excitement, urination, or pressure on the neck (hypersensitive carotid sinus).

  • Pressure on the neck or collar can cause fainting in some sensitive animals (hypersensitive carotid sinus syndrome).

  • High blood pressure (hypertension) that can lead to stoke or abnormal heart function.

    Some heart conditions are especially common in particular breeds, for example:

  • The Boxer dog, English bulldog, and Doberman pinscher are often affected with abnormal electrical rhythms, such as ventricular tachycardia (a rapid abnormal rhythm originating from the bottom of the heart) or neurocardiogenic syncope (characterized by a slow heart rate and excessive dilation of blood vessels).

  • The miniature schnauzer, the West Highland white terrier, and the cocker spaniel are breeds especially prone to disease of the heart "pacemaker" (the "sick sinus" syndrome).

  • The Labrador retriever is predisposed to supraventricular tachycardia (a rapid abnormal rhythm originating in the top chambers of the heart).

    •  
    Printable Version
     
    Have a Pet Question?
    Review the Most Frequent Questions
    Answered by Dr. Jon and His Staff of Veterinarians
    Ask Dr. Jon
    Dr. Jon's Newsletter
    Yes! Send Me the Latest Health Information, Pet Tips, Pet Stories and more...
     
     

    Related Articles

    • 1 Acute Collapse in Dogs

      If your dog suffers an acute collapse, he will sit down suddenly or lie down and won’t be able to get back up. He may even lose consciousness. Call or take your pet to your veterinarian immediately.

      Read MoreRead More
    Related Articles
    • 1Acute Collapse in Dogs

      If your dog suffers an acute collapse, he will sit down suddenly or lie down and won’t be able to get back up. He may even lose consciousness. Call or take your pet to your veterinarian immediately.

      Read MoreRead More
     

    Over 10,000 Veterinarian Approved Articles

    Dogs & Puppies
    Cats
    Related Articles
    • 1Acute Collapse in Dogs

      If your dog suffers an acute collapse, he will sit down suddenly or lie down and won’t be able to get back up. He may even lose consciousness. Call or take your pet to your veterinarian immediately.

      Read MoreRead More