Mary Allen
Temporary loss of consciousness in dogs can have various causes.
General Description
The term syncope comes from the Greek meaning syn (“with”) and kopten (“to interrupt”) and is the medical term for fainting. Syncope is a temporary loss of consciousness with reduced muscle tension. This is caused by reduced blood flow and insufficient oxygen saturation in the cerebral vessels of the brainstem. The brainstem is responsible for maintaining breathing and circulation, among other things. Differentiating from a true syncope are other causes of loss of consciousness, such as epileptic seizures.
In principle, there are four major causes of syncope:
- Structural heart or lung disease
- Cardiac arrhythmias
- Acute transient oxygen deficiency
- Reflex-mediated syncope
Structural heart or lung diseases are understood to mean diseases that affect the heart muscle tissue or lung tissue and which are also morphologically changed (in terms of their shape). This includes congenital heart diseases, cardiac effusion with cardiac tamponade, or pulmonary hypertension due to various causes. In the case of cardiac arrhythmia, the generation and conduction of excitation in the heart muscle are abnormal. An acute, temporary lack of oxygen in dogs can be caused, for example, by obstruction of the upper respiratory tract or paralysis of the larynx (larynx paralysis). Reflex-mediated syncope is caused by a reflex that dilates blood vessels and/or decreases heart rate.
Symptoms
How do I distinguish syncope from other disorders of consciousness?
It is usually very difficult to distinguish syncope from another condition with loss of consciousness. It is important to differentiate between syncope and an epileptiform seizure (epilepsy/seizure). The behavior before, during, and after the episode is particularly important here. Syncope usually follows a triggering event such as exertion, excitement, or coughing. The animal’s muscle tone is usually flaccid during syncope and no urine or feces are passed. After syncope, the animals show normal behavior.
In cases where the syncope or seizure has occurred more frequently, it may be helpful to take a video of the seizure. Occasionally, it is also difficult to distinguish conscious weakness from the unconsciousness of the animal. Can the animal be retrieved or addressed? If one is not sure, other differential diagnoses for the symptom of weakness can also be considered. The symptoms of weakness can be caused by metabolism or, for example, by neuromuscular disease. In contrast to weakness, however, syncope develops episodically and the animal appears completely normal again after the syncope even without therapy. However, episodic weakness can also occur with hypoglycemia due to insulin administration or due to an insulin-producing tumor.
Diagnosis
Clinical examination of a patient with syncope is important to assess cardiovascular status, as this can be indicative of cardiac disease.
A blood test can diagnose other possible causes, such as weakness due to hypoglycemia (low blood sugar levels) or anemia (low blood count). Electrolyte disorders, such as hyperkalemia (elevated levels of potassium in the blood) can explain cardiac arrhythmia.
After these investigations, an electrocardiogram (ECG) is recommended in a patient with a history of syncope. This should be recorded for at least one minute. Since the most common cause of syncope in dogs is a cardiac arrhythmia and arrhythmias can also occur sporadically, there is the possibility of recording an ECG over 24 hours. A “Holter ECG” is used for this. This device can be fixed to the animal for 24 hours with a chest bandage and then analyzed. More detailed examinations of the heart such as chest X-ray and echocardiography with Doppler are necessary to investigate functional and structural heart diseases
Therapy
Treatment depends on the underlying condition of the syncope. If cardiac arrhythmias are present, antiarrhythmic drugs and/or the implantation of a cardiac pacemaker are necessary, depending on the type of arrhythmia. In the case of situation-related syncopes, such as coughing, the underlying cause must be treated.
Prognosis
The prognosis also depends on the underlying cause of the syncope. In general, however, cardiac causes have a more cautious prognosis than, for example, cough-related syncope.