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 abnormal heart function.
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