Syncope (Fainting) in Dogs

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Overview of Syncope (Fainting) in Dogs

The term syncope (or fainting) refers to a brief period of unconsciousness due a lack of blood flow or oxygen to the brain. Syncope causes collapse, which may last from seconds to minutes. Most fainting “spells” are due to low blood pressure or lack of oxygen delivery to the brain (cerebral hypoxia). Syncope is a clinical sign, not a diagnosis or primary form of heart disease.

Blood pressure depends mostly on heart and blood vessel function. Accordingly, disorders of the heart or vessels (cardiovascular system) are the most common causes of syncope. Often, the cause is an electrical disturbance of the heart (slow or irregular heart activity). At other times, there is a structural problem of the heart (such as an abnormality of the heart muscle or a valve) or pericardial disease (the sac around the heart). Recurrent syncopal attacks may cause brain injury.

Other conditions that can lead to syncope include: severe respiratory disease or severe coughing; metabolic (body chemistry) disease; endocrine (hormonal) disorders; dysautonomia (abnormal function of the involuntary nervous system); anemia and drug therapy. The brief event ends with rapid and complete recovery, in most cases.

What To Watch For

  • Sudden weakness – Syncope often begins with sudden weakness that quickly progresses to ataxia (incoordination); ending with a transient loss of consciousness. Often fainting is precipitated by sudden activity or exercise.
  • Crying out – Some pets vocalize (cry out) immediately prior to losing consciousness and there may be a “distant” or “glassy-eyed” appearance to the face.
  • Leg rigidity – The forelimbs may briefly become rigid and the head may be pulled back, causing confusion with a seizure disorder (such as epilepsy).
  • Incontinence – which is loss of urinary or bowel control.
  • Diagnosis of Syncope in Dogs

    Diagnostic studies should include:

  • A history (including medication review) and physical examination with an emphasis on stethoscope examination (auscultation) of the heart and lungs.
  • Exercise test – pre- and post-exercise heart examination
  • Measurement of blood pressure
  • Blood tests, including a blood glucose, blood biochemical tests, and complete blood count
  • Electrocardiogram (EKG) – this can include a routine EKG, an ambulatory (tape-recorded) EKG, or an “event monitor” (an EKG activated by the pet’s owner). The latter two EKG examinations often require referral to a specialist.
  • A chest X-ray (thoracic radiograph) – especially when indicated from history and physical examination
  • Pulse oximetry, if there is evidence of lung disease
  • Heartworm test in appropriate areas
  • Ultrasound examination of the heart (echocardiogram)
  • Additional laboratory (blood) tests, such as those evaluating endocrine (hormone) function
  • Treatment of Syncope in Dogs

    The treatment of syncope must be tailored to the underlying cause. In most cases, syncope is an historical complaint, but the cause of the problem must be sought and managed to prevent further occurrences.

    Home Care

    Optimal treatment for a pet with syncope requires a combination of home and professional veterinary care. Follow-up can be critical. Administer prescribed medication(s) as directed, and be certain to alert your veterinarian if you are experiencing problems treating your pet. Exact follow-up depends upon the cause.

    Prevention of Syncope in Dogs

  • In general, syncope cannot be prevented unless the precipitating event can be avoided. Try to avoid possible precipitating events, such as excitement or vigorous exercise.
  • Avoid collars which pull around the neck.
  • Your veterinarian may also recommend stool softeners or cough suppressants, if needed.
  • In-depth Information on Syncope in Dogs

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

    Causes  of Syncope in Dogs

  • 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).
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