Fainting (Syncope)
A syncope, commonly known as fainting, is a sudden, brief, and fully reversible loss of consciousness caused by temporary reduced blood flow to the brain. In this neurological phenomenon, acute cerebral hypoperfusion occurs, leading to an abrupt collapse of the animal. Unlike other disturbances of consciousness such as seizures or narcolepsy, syncope is typically of short duration (usually less than a minute) and is characterized by complete recovery without neurological residuals.
The prevalence of syncope is significantly higher in dogs than in cats. This is partly due to anatomical and physiological differences in the cardiovascular system as well as the varying frequency of predisposing underlying conditions. In cats, syncopes are a real rarity, while they are more commonly observed in dogs, especially in certain breeds with cardiological predispositions.
The pathophysiological basis of syncope is a reduction in cerebral blood flow by approximately 30-35% or a drop in systemic blood pressure below 60 mmHg. This critical hypoperfusion leads to a lack of oxygen and glucose in the brain, causing a temporary inability to maintain normal brain function.
Causes
Fainting (brief loss of consciousness, syncope) occurs when the brain is temporarily not supplied with enough blood and consequently suffers from oxygen deficiency.
The loss of consciousness is usually brief but can be an expression of a serious functional disorder of the heart. In most cases, cardiac arrhythmias or diseases of the pericardium are the cause.
Syncopes occur more often in dogs. In cats, they are a rarity.
Loss of consciousness can also occur after trauma or a fall.
Supplement
The etiology of syncope in small animals is diverse, with cardiovascular causes dominating. Basically, the causes can be categorized as follows:
Cardiac causes are predominant in dogs and include cardiac arrhythmias such as bradyarrhythmias (e.g., third-degree AV block, sinus node dysfunction), tachyarrhythmias (e.g., ventricular tachycardia, supraventricular tachycardia), as well as structural heart diseases like cardiomyopathies, heart valve diseases, or congenital heart defects. Especially brachycephalic breeds such as Pugs, French and English Bulldogs suffer more frequently from cardiogenic syncopes due to their anatomical peculiarities and predisposition to heart diseases.
In Dobermans, Boxers, and Cavalier King Charles Spaniels, syncopes occur more frequently due to breed-specific heart diseases such as dilated cardiomyopathy or mitral valve endocardiosis. Maine Coon and Ragdoll cats can also be affected due to their genetic predisposition for hypertrophic cardiomyopathy, although syncopes are generally rare in cats.
Non-cardiac causes include neurocardiogenic (vasovagal) syncopes triggered by a sudden drop in blood pressure due to a reflex, orthostatic hypotension during rapid position changes, as well as metabolic disorders such as hypoglycemia, severe anemia, or hypoxia. Diseases such as carotid sinus hypersensitivity, situational syncopes (e.g., during coughing, retching, or defecation), and medication side effects can also lead to syncopes.
Traumatic events such as traffic accidents or falls can also lead to temporary loss of consciousness, which is, however, pathophysiologically distinct from a classic syncope.
Symptoms
- Sudden onset
- Collapse of the animal
- Short duration
- No urination
The clinical presentation of syncope is characteristic and usually follows a typical pattern. The loss of consciousness occurs abruptly and leads to the sudden collapse of the animal. This event may be preceded by prodromal symptoms, which, however, are often only recognized retrospectively by the pet owner:
Before the actual syncope, signs such as restlessness, weakness, staggering, trembling, or brief disorientation may occur. During the syncope, the animal lies flat on its side, shows no reaction to external stimuli, and has pale-cyanotic mucous membranes. Breathing may be shallow or temporarily suspended, and the pulse is weak or barely palpable. Unlike epileptic seizures, tonic-clonic convulsions, involuntary urination or defecation, as well as pre-ictal and post-ictal phases are typically absent.
The duration of a syncope is mostly only a few seconds to a maximum of one to two minutes. Recovery occurs spontaneously and completely, with the animal appearing normal again immediately after the event or only briefly disoriented. In cardiogenic syncopes, episodes can be triggered or exacerbated by physical exertion, excitement, or stress.
Particularly important for differential diagnosis is the distinction from other disturbances of consciousness: Unlike vestibular syndrome in older animals, syncope does not involve head tilt and nystagmus. Unlike epileptic seizures, syncope does not lead to chewing movements, salivation, or a post-ictal phase with confusion. In narcolepsy, however, the animal is awakened by external stimuli, which is not the case with syncope.
First Aid
- Place your pet on its right side, remove the muzzle, open its mouth, and gently (!) pull the tongue forward.
- If there are no injuries and the animal is breathing, let it lie on its side on the floor until it wants to get up on its own. Do not carry it to the couch or similar. It could stagger and fall when trying to stand up.
- If you are out and about, immediately stop the walk. Give the animal plenty of time to recover on the spot. Loosen the collar.
- If your pet does not stand up on its own within one minute or shows severely bleeding injuries, try to take it to a veterinarian immediately. If necessary, call for help from other people.
- In case of very heavy bleeding after a fall or trauma from other causes (traffic accident), try to stop or reduce the bleeding by applying compression until you reach the veterinarian.
- If you detect no breathing and heart activity, you can also perform chest compressions and artificial respiration on the animal (see —> Resuscitation, Reanimation).
- Keep in mind that you are dealing with a small organism in some cases, and you should not use more force than you would with small children of comparable size.
- Apply pressure to the heart region just behind the elbow on the left side of the body while your pet is lying on its right side, and possibly hold against it with your other hand on the right side. After about 15 compressions, give one breath. Then repeat with about 15 compressions, and so on.
- When giving artificial respiration through the nostrils, use a cloth, tilt the animal’s head slightly backward, and don’t blow too forcefully. The chest should only rise slightly. If you don’t tilt the animal’s head backward, you might blow your breath into the animal’s stomach.
Diagnosis
Diagnosing syncope requires a systematic approach, starting with a thorough medical history. Particularly important are detailed information about the exact circumstances of the event, its duration, triggering factors, and the animal’s behavior before, during, and after the episode. Video recordings of the episodes by the owner can be extremely helpful in differentiating between syncope and other disturbances of consciousness.
The clinical examination includes a thorough cardiovascular and neurological evaluation. Auscultation to detect heart murmurs, arrhythmias, or changes in heart rate, as well as assessment of pulse quality and mucous membrane color, are necessary. The neurological examination serves to rule out primary neurological causes.
Further diagnostic procedures include:
An electrocardiogram (ECG) is essential for identifying cardiac arrhythmias. Since many arrhythmias occur intermittently, long-term ECG (Holter monitoring) over 24-48 hours or an implantable loop recorder may be necessary for rare episodes. Echocardiography allows assessment of heart structure and function and is particularly important when structural heart diseases or congenital defects are suspected.
Laboratory tests including complete blood count, serum biochemistry, electrolytes, and thyroid values help identify metabolic causes. A glucose tolerance test is indicated if hypoglycemia is suspected. Imaging procedures such as chest X-rays to assess heart size and lung structure, and in selected cases, advanced imaging (CT, MRI) when intracranial pathologies are suspected, can complement the diagnostics.
In complex cases, electrophysiological studies may be required for more precise characterization of cardiac arrhythmias, or a tilt table test for evaluation of neurocardiogenic syncopes. However, these specialized procedures are only available in cardiology referral centers.
The differential diagnosis includes epileptic seizures, narcolepsy/cataplexy, vestibular syndrome, collapse due to orthopedic problems, weakness from metabolic disorders, and transient ischemic attacks.
Further veterinary measures
Syncopes can have many causes. However, they are usually caused by reduced heart performance, so more detailed examinations of heart function are advisable. ECG, cardiac ultrasound, X-rays, and certain laboratory tests are the primary focus.
In some cases, neurological examinations are necessary.
Only after clarifying the cause is appropriate therapy possible.
Supplement
The treatment of syncopes is primarily based on the underlying cause and follows an individually tailored therapy concept. For cardiogenic syncopes, the treatment of heart disease is the main focus.
For bradyarrhythmias such as third-degree AV block or sinus node dysfunction, the implantation of a permanent pacemaker may be indicated. This treatment option is now available in specialized veterinary medical centers and shows good long-term results with careful patient selection. Alternatively, medications such as theophylline or terbutaline can be used to increase heart rate, although their effectiveness is limited.
For tachyarrhythmias, antiarrhythmic drugs are used. For ventricular tachycardias, sotalol, mexiletine, or amiodarone are often used, while for supraventricular tachycardias, beta-blockers (e.g., atenolol), calcium channel blockers (e.g., diltiazem), or digoxin are used. The choice of medication is based on the specific arrhythmia, comorbidities, and potential side effects.
Structural heart diseases are treated according to their type. For heart valve diseases, ACE inhibitors, diuretics, and pimobendan are used, while cardiomyopathies are treated with beta-blockers, calcium channel blockers, or heart failure therapy depending on the type.
For neurocardiogenic (vasovagal) syncopes, the focus is on avoiding triggering factors. Additionally, fludrocortisone can be used to increase blood volume or beta-blockers to dampen the cardiac reflex response.
Metabolic causes require specific therapy for the underlying condition, particularly the treatment of hypoglycemia by adjusting feeding or insulin therapy for insulinomas.
In addition to drug therapy, lifestyle adjustments are important. These include avoiding excessive physical exertion in cardiogenic syncopes, stress reduction, and the use of chest harnesses instead of collars in predisposed animals. In brachycephalic breeds, weight reduction can contribute to improving cardiorespiratory function.
Prognosis and aftercare
The prognosis for syncope varies considerably and depends largely on the underlying cause. Generally, syncopes of cardiogenic origin have a more cautious prognosis than those with non-cardiac causes.
For cardiac arrhythmias, the prognosis depends on the type of arrhythmia and treatment options. Patients with third-degree AV block who receive a pacemaker show significantly improved life expectancy with survival rates of 85-90% in the first year after implantation. For malignant ventricular arrhythmias, the prognosis is more guarded but can be improved with appropriate antiarrhythmic therapy.
Structural heart diseases such as dilated cardiomyopathy or advanced mitral valve endocardiosis are associated with a less favorable prognosis, as they often progress. Here, the median survival time after the onset of syncope is often only 6-18 months despite optimal medical therapy.
For neurocardiogenic syncopes, the prognosis is generally good if triggering factors can be identified and avoided. These patients often have a normal life expectancy with adequate management.
Follow-up care plays a crucial role in the management of patients with syncope. Regular check-ups are necessary to monitor the response to therapy and make adjustments if needed. For cardiogenic syncopes, cardiological check-ups with ECG and, if necessary, echocardiography are usually recommended every 3-6 months.
For patients with pacemakers, special check-ups are necessary to verify pacemaker function and battery capacity. Modern devices sometimes allow for telemedicine monitoring.
For pet owners, documenting the frequency and severity of syncope episodes is important. A diary can help recognize patterns and assess the success of therapy. Additionally, owners should be trained in recognizing warning signs that could indicate deterioration.
Summary
Syncope in dogs and cats is defined as a sudden, brief, and completely reversible loss of consciousness due to temporary cerebral hypoperfusion. It occurs significantly more often in dogs than in cats and can indicate various underlying diseases, with cardiovascular causes being dominant.
The symptoms are characterized by a sudden collapse of the animal with brief loss of consciousness without typical seizure activity and with complete recovery within a short time. The differentiation from other disturbances of consciousness such as epileptic seizures or vestibular syndrome is clinically significant.
The diagnosis requires a systematic approach with thorough anamnesis, clinical examination, and targeted cardiac diagnostics. Electrocardiography, long-term ECG, and echocardiography are central diagnostic procedures.
The therapy is directed at the underlying cause and includes, depending on the findings, antiarrhythmic medication, implantation of a pacemaker for certain bradyarrhythmias, or the treatment of structural heart diseases. Additionally, adjustments to lifestyle habits and regular follow-up examinations are necessary.
The prognosis varies considerably depending on the underlying disease. While neurocardiogenic syncopes often have a good prognosis, cardiogenic syncopes due to advanced heart diseases are associated with a more cautious prognosis.
Outlook on current research
Research in the field of syncope in small animals continues to evolve and focuses on several promising areas. Current studies are investigating genetic predispositions for cardiac arrhythmias in various dog breeds. Particularly in Boxers, Dobermans, and German Shepherds, genetic markers are being identified that are associated with an increased risk of arrhythmogenic syncopes. These findings could lead to targeted genetic screenings in the future to identify at-risk animals early.
In the field of diagnostics, miniaturized implantable long-term ECG recorders are being developed, specifically optimized for veterinary use. These devices enable continuous monitoring over months and can automatically detect and store arrhythmias. Initial clinical studies show promising results with significantly higher detection rates for intermittent arrhythmias compared to conventional Holter monitors.
The technology of pacemaker implantation for small animals is also being continuously improved. Newer devices are smaller, more durable, and have more advanced programming options that allow for more individualized adaptation to the patient’s needs. In addition, wireless monitoring systems are being developed that enable telemedicine monitoring of patients with a pacemaker, allowing complications to be detected earlier.
In the area of pharmacotherapy, new antiarrhythmic substances with a more favorable side effect profile are being investigated. Particularly promising are selective ion channel blockers that specifically target certain cardiac ion channels, potentially achieving a more targeted antiarrhythmic effect with fewer systemic side effects.
Last but not least, interventional electrophysiology is gaining importance in veterinary medicine. Catheter ablation procedures for the treatment of focal arrhythmias, which have mainly been used in human medicine until now, are increasingly being adapted for selected veterinary patients. Initial experience reports show encouraging results in the treatment of supraventricular tachycardias in dogs.
These research approaches promise significant advances in the understanding, diagnosis, and treatment of syncopes in dogs and cats in the coming years, which could ultimately lead to improved quality of life and prognosis for affected animals.
Frequently asked questions (FAQs)
- What is the difference between a syncope and an epileptic seizure in my pet?
During a syncope, there is a brief loss of consciousness without seizure activity, followed by immediate complete recovery. An epileptic seizure typically shows seizure activity (twitching, chewing movements), often urination or defecation, and a subsequent phase of confusion (postictal phase). - Are certain dog breeds particularly prone to syncope?
Yes, certain breeds have an increased risk. Brachycephalic breeds (Pugs, Bulldogs) due to their respiratory problems, Dobermans and Boxers because of predisposing heart diseases, and Cavalier King Charles Spaniels due to frequent mitral valve diseases are particularly at risk. - Can a single syncope be an emergency, or should I wait and see?
Any first syncope should be considered an emergency and should result in a prompt veterinary examination. Even if the animal recovers quickly, a potentially life-threatening underlying condition may be present. - As a pet owner, how can I distinguish between a syncope and simple stumbling or slipping?
During a syncope, the animal completely loses consciousness and does not respond to verbal cues or touch for a short time. When stumbling or slipping, the animal remains conscious and responds normally to its surroundings. - Can a syncope be triggered by stress or excitement?
Yes, especially neurocardiogenic (vasovagal) syncopes can be triggered by emotional stress, anxiety, or excitement. In animals with heart diseases, stress can also lead to a deterioration of heart function and thus to syncope. - What first aid measures should I take if my pet experiences a syncope?
Place your pet on its right side, ensure clear airways (gently stretch the head, carefully pull the tongue forward), keep it warm and calm. Avoid hectic movements and transport the animal carefully to the veterinarian after recovery. - Can an animal with recurrent syncopes lead a normal life?
With proper diagnosis and treatment, many animals can lead a good life. The prognosis depends on the underlying condition. Adjustments in daily life (e.g., avoiding overexertion, stress) may be necessary. - Are pacemakers a realistic option for pets?
Yes, pacemakers are successfully used in dogs and less frequently in cats. The technology has been adapted for small animals and shows good long-term results. However, this option is only available in specialized centers and is associated with significant costs. - How do syncopes in cats differ from those in dogs?
Syncopes are generally much less common in cats than in dogs. When they occur, they are more often associated with severe structural heart diseases such as hypertrophic cardiomyopathy. The clinical presentation is similar, but diagnosis in cats can be more difficult due to their more secretive behavior. - Can dietary supplements or special diets prevent syncopes?
For primarily cardiogenic syncopes, there are no specific dietary supplements for prevention. However, for heart diseases, low-sodium diets and certain supplements (e.g., taurine, omega-3 fatty acids) can be supportive. The primary treatment should always be medication-based.
Literature
- Sigrist, N.: Emergency Medicine for Dogs and Cats. Enke, 2017
- Rose, A. and S. Resch: The Syncope. What’s Going On When the Dog Collapses? Enke Verlag in Georg Thieme Verlag KG, 12(02): 20–23, 2016
- Killich, M. (Ed.): Small Animal Cardiology, Diagnosis and Therapy of Heart Diseases in Dogs, Cats, and Small Pets, Part 2 Diagnostics. Thieme Publishing Group, Stuttgart, New York, Delhi, 2019, DOI: 10.1055/b-0038-163915
- Löwe, G. and Löwe, O. (2021). Emergencies in Dogs and Cats – A Veterinary Guide. Kynos-Verlag. 208 p.
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- Pariaut R, Santilli RA, Moïse NS. Advances in the management of atrial fibrillation in dogs. Journal of Veterinary Cardiology. 2021;33:7-20.
- Sanders RA, Kurosawa TA, Sist MD. Ambulatory electrocardiographic evaluation of the occurrence of arrhythmias in healthy Doberman Pinschers with echocardiographically normal hearts. Journal of the American Veterinary Medical Association. 2018;253(1):98-102. doi:10.2460/javma.253.1.98
- Estrada AH, Maisenbacher HW, Prosek R. Evaluation of pacemaker implantation in dogs with high-grade atrioventricular block. Journal of Veterinary Cardiology. 2020;32:48-58. doi:10.1016/j.jvc.2020.10.004