Dr Pedro Oliveira
DVM, MRCVS, Diplomate ECVIM-CA (Cardiology)
VVS Cardiology Specialist
Syncope or seizure?
The distinction between a seizure, a syncopal episode or simply falling over may be quite challenging. The distress of witnessing such an episode may also influence the ability of the carer of the pet to describe the events accurately.
A fit may be described as a sudden attack of a certain symptom or behaviour. It can be a normal event, such as a fit of coughing, or an abnormal symptom.
A seizure is an abnormal sudden event. When this event derives from abnormal brain activity, it is called an epileptic seizure and may range from mild signs to full-blown tonic-clonic motor activity. An enduring predisposition for having epileptic seizures is called epilepsy.
Fainting is caused by brain hypoxia that may result in transient weakness (pre-syncope) to loss of consciousness (syncope) for a short amount of time. It occurs due to a transient drop in blood perfusion to the brain associated with insufficient cardiac output (i.e. obstructive heart disease or inappropriately high or low heart rate) or poor regulation of blood pressure (i.e. vasovagal syncope).
Some dogs become recumbent, or fall over, during exercise and can’t or won’t get up. This is often interpreted as a pre-syncopal episode, or ‘collapse’ is usually described. It normally happens to older dogs with musculoskeletal problems, or dogs with respiratory problems such as brachycephalic breeds. It also occurs in dogs with neuromuscular disorders (i.e. myasthenia gravis).
How can I distinguish them?
|30 sec to 2-3 minutes||< 1 min||variable duration|
|Pre- and post-ictal signs||Sudden onset + full recovery||Gradual onset + quick recovery|
|Normally at rest||Normally on exercise, excitement, vomiting, coughing||During exercise|
|Abnormal mentation to loss of consciousness. involuntary limb movements, salivation, urination and/or defaecation||Loss of consciousness, Flaccid +/- opisthotonos (hyperextension of the neck and forelimbs)||No involuntary movements or loss of consciousness|
The investigation of episodic events in dogs or cats may be challenging and often requires a multidisciplinary approach; with a cardiologist, a neurologist, and an internal medicine specialist involved in the case. Case support for all of these disciplines is available from the VVS Specialist Team.
An accurate description of the sequence of events before, during, and after the episode may help determine the likely aetiology and direct the investigation. However, this is often lacking as the stress of witnessing such an event influences the perception of the carer in regard to the sequence and duration of events. To complicate things further, there may be overlap between the categories described above (i.e. prolonged brain hypoxia from a cardiac syncope may lead to a hypoxic seizure). For this reason, it is very important that a step-by-step approach is followed, without exception, in these cases. The VVS Team are on hand to assist with this.
- Clinical history
- What was the dog/cat doing at the time of collapse?
- Was there a trigger?
- Sudden or gradual onset?
- Did the patient fall or remain standing? Sternal or lateral?
- Was there loss of consciousness?
- Limb movements? Opisthotonos?
- Urination or defaecation?
- How long did it last?
- Was recovery sudden or gradual?
- What happened after the event?
- Compare events if multiple.
- Ask the client to record a video of an event with their mobile phone.
- Physical examination (including neurological examination)
- Blood/urine analyses and blood pressure
- Serum biochemistry
- Cardiac biomarkers
- Bile acid stimulation test
- Parasite screening (i.e. lungworm)
- Urine analysis
A number of systemic disorders may lead to episodic weakness or seizure activity. Some examples include anaemia, electrolyte disorders, hypoglycaemia, insulinoma, phaeochromocytoma, systemic hypertension, portosystemic liver shunts, etc. For this reason, it is important to perform comprehensive blood and urine analyses as well as blood pressure measurement early in the investigation. The assistance of an internal medicine specialist may be necessary, as the diagnosis and treatment of some of these disorders is not straightforward (e.g. insulinoma and phaeochromocytoma).
In the same way, it is always a good idea to consult a neurologist early on to determine if a neurological cause is likely and avoid any un-necessary tests. Based on the neurological examination findings and the description, or better yet, video of the episode, a decision is made as to whether a neurological investigation is appropriate, or if a cardiovascular assessment should be performed first.
The VVS Specialists enjoy working together as a multidisciplinary team; an approach usually restricted to referral hospital settings! VVS are proud to have turned this dynamic around, enabling the general practitioner to invite our team into their practice, so that we can care for their patients together.
Echocardiography is the best non-invasive diagnostic tool to assess the cardiac structure and function. It is always indicated whenever there is suspicion of underlying heart disease (i.e. a heart murmur or a gallop is present). In this case, the presence of obstructive heart diseases (e.g. pulmonic or aortic stenosis, some cases of hypertrophic cardiomyopathy or neoplasia occluding the pulmonic or aortic flow) may lead to episodic weakness or collapse and should be ruled out. It also allows the identification of pulmonary hypertension, a known cause of episodic collapse. The VVS Cardiology Team are available to guide you through live echocardiography to support you in confidently ruling in or out pulmonary hypertension in cases such as this, as well as any structural abnormalities.
Case study: dog echocardiography
Echocardiographic pictures from a 3-year-old dog with syncopal episodes that occurred most commonly during exercise or excitement. Pulmonary hypertension was confirmed via echocardiography. Lungworm testing and accompanying chest radiographs revealed that this was caused by lungworm infestation. This patient was treated with fenbendazole and sildenafil and showed significant improvement with resolution of clinical signs within 3 months.
- Resting ECG and Ambulatory ECG (Holter)
Cardiac arrhythmias are a major cause of episodic collapse. They are commonly associated with underlying heart disease (e.g. DCM, primary arrhythmias) but may also occur due to extra-cardiac disease (e.g. inflammatory disease, splenic neoplasia). A standard electrocardiogram should always be performed, especially if an arrhythmia is detected during examination. This should ideally include at least 6 leads and last for 5-10 minutes. Unfortunately, the intermittent nature of cardiac arrhythmias makes it difficult to document rhythm disturbances with just a normal ECG. In other words, this is not a sensitive test for intermittent arrhythmias, and is often normal during the 5-10 minute recording. A longer duration electrocardiogram is required, with a 24h (or longer) ambulatory ECG recording (Holter), ideally documenting the cardiac rhythm during an episode of collapse. The VVS Cardiology Team are on-hand to assist you in the use and interpretation of 6 lead ECGs and Holter monitors.
Case study: dog ECG (Holter Monitor)
Electrocardiogram recorded during a 7-day ambulatory-ECG in a 5 year old Boxer dog experiencing episodes of collapse with loss of consciousness and full recovery within 20-30 seconds. Sudden sinus bradycardia with long sinus pauses is seen following a sinus rhythm with approximately 130 bpm. This sudden drop in rate resulted in a collapse episode with the same characteristics as described above. Progressive slow recovery with a return to a normal heart rate is seen. Echocardiography did not show the presence of underlying structural heart disease in this case. This presentation is suggestive of a vasovagal event which is not uncommon in this breed. Alternatively, sinus node dysfunction could be present, however, other signs of abnormal sinus node function (i.e. sinus pauses/arrest) would have been expected in the remainder of the recording and were not present. This example illustrates that not all collapsing Boxers are experiencing ventricular tachycardia!
Unfortunately, an effective treatment does not exist for vasovagal syncope. Trying to avoid the triggering event (e.g. sudden excitement with the arrival of the postman!) is recommended although often impossible to achieve. Sympathomimetic or parasympatholytic drugs (i.e. atropine, theophylline) or an artificial pacemaker are often ineffective in preventing further episodes.
Case study: cat ECG
Electrocardiogram from a cat experiencing episodes of collapse with loss of consciousness and full recovery within 10 seconds. Additionally, signs of lethargy were also noticed. In this case a rapid supraventricular tachycardia (300 bpm) was identified as the underlying cause. Arrhythmias in cats are often associated with underlying structural heart disease which was also the case with this cat. A heart scan confirmed the presence of hypertrophic cardiomyopathy.
- Thoracic radiographs +/- abdominal ultrasound
If a cardiovascular cause has not been found at this stage, or if an extra-cardiac cause is suspected, chest radiographs and abdominal ultrasound should be performed (i.e. to rule out neoplasia, check for lung or abdominal disease…). The VVS Diagnostic Imaging Team are happy to assist with interpreting your images or if you are a VVS Partner Practice then we can live-guide you through an in-depth abdominal ultrasound examination.
- Neurological investigation with brain MRI and cerebrospinal fluid analysis (CSF)
If a cause has still not been found at this stage and a neurological event is on your differential list, then a neurological advanced imaging investigation can be performed. It is extremely important that before advanced imaging is performed, that careful neuroanatomical localisation and differential diagnoses are discussed. This crucial step avoids imaging the wrong localisation or choosing the wrong advanced imaging test.
This is normally the last step, as it requires general anaesthesia, expensive equipment and advanced imaging interpretation. If a neurological cause is suspected from the beginning, this step should be performed earlier in the investigation so that unnecessary tests may be avoided. The VVS Neurology Team are always happy to assist and advise.
As you can see, investigating episodes of weakness, collapse or seizure can be challenging and even Specialists may call on their multidisciplinary colleagues for assistance! The multidisciplinary VVS Team are here to support you and your clients at every step. By working together these challenging cases become simpler, more enjoyable and very rewarding.
If your practice becomes a VVS member practice, you will benefit from the VVS workstation and equipment within your practice, enabling all your veterinary team to seek Specialist support whenever they need it.
Benefits of the VVS Virtual system include:
- Patients receive world-class Specialist care.
- Patients are treated in their usual practice, by vets that know them and their owners.
- Patients and owners do not have to travel to referral centres.
- Vets keep cases (and revenues) in house.
- Vets are upskilled, as they learn from VVS Specialists.
- Time with a VVS Specialist counts towards CPD hours, meaning that vets gain CPD whilst also bringing in practice revenue and without having days away from the practice.
- Vets have reassurance that they never need work alone. VVS’s friendly Specialists become part of the practice team.
- COVID guidelines are easy to follow as all consults are virtual.
Cardiology cases can feel overwhelming to deal with in general practice, but VVS’ friendly world-class Cardiologists are on hand to support you and to enable you to bring outstanding clinical care to your patients and reassurance to their owners. Just click below to find out more – we’re here to help!
The author would like to thank his VVS colleague Dr Lisa Alves, DVM PhD Dip ECVN MRCVS RCVS and European Specialist in Veterinary Neurology, for her assistance with this article.