Diagnostic Electrophysiology

Electricity in the body

Nerves and muscles (including the heart muscles) produce electrical signals when they are working. These signals can be detected by sensitive electronic equipment and the results used to determine whether things are functioning normally. The most frequently used electrophysiological examination is electrocardiography (ECG).

Electrocardiography

ECG's may be viewed on screens, especially when they are being used for anaesthetic monitoring, but for diagnostic use they are typically recorded onto paper using a machine like the one shown here.

Investigation of heart problems will often also include radiography and ultrasound scanning.

Other electrodiagnostic tests

In addition to electrocardiography, AMCRS offers a range of electrodiagnostic tests which are often essential for investigating animals with peripheral nerve abnormalities (eg. nerve conduction velocity tests), muscle (electromyography) or neuromuscular junction disease (eg. evoked motor responses). Electophysiological techniques are also used to evaluate hearing ability in young dogs (BAER tests) and sight in dogs with retinal degeneration (electroretinography). See below for more information. In order to get a full understanding of the disease process, these electrodiagnostic tests are often integrated with other diagnostic methods including imaging, blood samples, nerve and muscle biopsies.

Electromyography

This is used to record muscle activity. The test is usually carried out under a general anaesthetic as background voluntary muscle activity is usually silent in the anaesthetised dog . However, diseased muscle will make characteristic "sounds". EMGs allow us to localise the problem area and give us some indication of diagnosis.

Motor nerve conduction studies

These are performed in an anaesthetised animal and allow us to determine the speed with which an impulse travels down a nerve. Nerves that have lost their surrounding insulation or have a reduced number of axons (fibres) will send impulses at a slower speed than normal nerves. By testing along the length of the nerve it is possible to determine whether the problem is at the root or distal end.

Brain evoked auditory response

This is used to test hearing ability. In young puppies it can usually be carried out while they are simply asleep but older dogs sedation is usually required.

The test measures brainstem and brain activity in response to repetitive clicks in one ear while noise is blocked out in the other ear. It allows us to determine if there is a problem in the hearing apparatus or in the nerves that conduct the information to the brain. This test can also be used in coma patients to determine if they are brain dead.

Electroretinogram

This is similar to the hearing test but instead measures brain activity in response to repetitive bright light flashes in the eye. It allows us to determine if blindness initiates from the retina or further within the optic pathway and brain. This is also usedwhen there are cataracts to see if theer is still some retinal function because there is no point in treating the cataract if the patient will not be able to see because there are retinal or deeper problems.