Fainting (syncope) does occur in dogs but is less common than in people. When a dog faints it briefly loses consciousness and falls to the ground motionless but in most cases recovers within a few moments without treatment. It is important, but often difficult, to differentiate between fainting and fitting because the causes and treatments for the two conditions are very different. In addition, some other medical problems (for example, reduced blood levels of glucose, or certain diseases of the nerves and muscles) can cause episodes of weakness or collapse. If your dog collapses for whatever reason contact your vet immediately for further advice.
Fainting occurs when there is an insufficient blood supply to the brain. When a person is standing up the head is higher than the heart and therefore blood has to be pumped uphill and so if there are any problems with the circulation it is made more obvious. In dogs their head is almost in line with the heart – this is why fainting is less common in dogs than people.
During a fainting episode your dog will fall to the ground, usually on its side. It may show involuntary muscle twitching and lose control of its bladder or bowels – these features can also be seen during a seizure and this is why some owners mistake a fainting episode for a seizure. However, during a faint, the body as a whole may be limp and floppy and the tongue and gums may be much paler than normal for your dog – these features are not typically seen during a seizure.
There are a number of different causes of reduced blood supply to the brain. Generally, reduced blood supply to the brain is caused by episodes of low blood pressure. This can be caused by the heart beating at an abnormally rapid or slow heart rate, or even stopping completely for a few seconds. Low blood pressure can also result from very weak contractions of the heart or from narrowing or excessive leakage of the heart valves.
Fainting is more common in some breeds of dog, e.g. Miniature Schnauzers, Westies, Boxers and Dobermanns because these breeds are more likely to suffer from specific cardiac diseases that can cause fainting. Many of the medical conditions that can cause fainting are more prevalent in older dogs. In younger animals fainting is occasionally associated with congenital heart disease. However, it is important to stress that some dogs, especially Boxers, can faint at any age in the absence of underlying heart disease. This often happens following excitement or a specific set of circumstances.
Some drugs can increase the likelihood of your pet fainting. If your pet is taking any medication be sure to mention it to your vet, even if you think they will already know about it.
Your vet will first want to be sure that your pet is fainting and not having a seizure. First your vet will want to know about the episodes – when they happen and what the dog is doing at the time. Although it can be very frightening the first time your dog faints you should try to stay calm and record as much information as you can to pass on to your vet.
Try to time how long your dog is unconscious (it always seems much longer than it really is) and what your dog was doing before and immediately after the episode. In between fainting episodes most animals are completely normal and so your vet may be unable to detect anything on clinical examination. If you are able to capture one of the episodes on video (for example, on your mobile phone) this can be useful for the vet.
There are enough different causes of fainting that your vet will not usually be able to tell what is wrong with your dog just by looking at them. Cardiac testing will normally be required and an ECG recording (electrical recording of the heart beat) is a vital component of this, often accompanied by ultrasound and sometimes x-rays of the heart. It is likely that blood tests will also be required.
Tests can sometimes go on for weeks or months, depending on how often your dog is fainting. In some cases your vet may arranage for your dog to be fitted with a heart monitor to wear at home. In some cases nothing abnormal will ever show up on the tests, offering reassurance that it is unlikely that a serious medical or cardiac problem was causing the fainting
The treatment for fainting depends on the underlying cause. In some cases there is no treatment and dogs may continue to have intermittent fainting episodes throughout their lives. It may be possible to determine when attacks are likely to occur (eg a dog may always have an attack when it gets very excited) and it might then be possible to avoid circumstances likely to trigger episodes.
In specific cases drug treatment may be available which will help minimise the problem and some conditions may require a surgical procedure (for example, implantation of a pacemaker) to help reduce the problem.
However, the good news is that many fainting episodes are not linked to serious underlying disease and in these dogs the frequency of episodes can often be reduced by careful management. When they do occur the episodes last less than a minute with a rapid full recovery to normal behaviour almost immediately. The biggest concern is to rule out any serious underlying disease that may be a threat to your pet and for your vet to be able to recommend the best treatment in individual cases.
If you have any concerns about your dog contact your vet for further advice.