Lecture Topic 3.1.1

Electrical activity of heart (ECG)

The ECG is the most important test for interpretation of the cardiac rhythm, conduction system abnormalities, and the detection of myocardial ischemia. The ECG is also of great value in the evaluation of other types of cardiac abnormalities including valvular heart disease, cardiomyopathy, pericarditis, and hypertensive disease. Finally, the ECG can be used to monitor drug treatment (specifically antiarrhythmic therapy) and to detect metabolic disturbances.

An ECG can help detect:

• arrhythmias – where the heart beats too slowly, too quickly, or irregularly
• coronary heart disease – where the heart’s blood supply is blocked or interrupted by a build-up of fatty substances
• heart attacks – where the supply of blood to the heart is suddenly blocked
• cardiomyopathy – where the heart walls become thickened or enlarged

How an ECG is carried out

Small, sticky sensors called electrodes are attached to your arms, legs and chest. These are connected by wires to an ECG recording machine.

You do not need to do anything special to prepare for the test. You can eat and drink as normal beforehand.

Before the electrodes are attached, you’ll usually need to remove your upper clothing. Your chest may need to be shaved or cleaned. Once the electrodes are in place, you may be offered a hospital gown to cover yourself.

The test itself usually only lasts a few minutes. You should be able to go home soon afterwards or return to the ward if you’re already staying in hospital.

Types of ECG

There are 3 main types of ECG:

• a resting ECG – carried out while you’re lying down in a comfortable position
• a stress or exercise ECG – carried out while you’re using an exercise bike or treadmill
• an ambulatory ECG – the electrodes are connected to a portable machine worn at your waist – your heart can be monitored at home for 1 or more days. This type of ECG is usually called a Holter monitor.

The type of ECG you have will depend on your symptoms and the heart problem suspected.

An exercise ECG may be recommended if your symptoms are triggered by physical activity. An ambulatory ECG may be more suitable if your symptoms are unpredictable and occur in random, short episodes.

Getting your results of your ECG

An ECG will show your heart rhythm and electrical activity as a graph displayed electronically or printed on paper.

For an ambulatory ECG, the ECG machine will store the information about your heart electronically. This can be checked by a doctor when the test is complete.

You may not be able to get the results of your ECG immediately. The recordings may need to be looked at by a specialist doctor to see if there are signs of a potential problem. Other tests may also be needed before it’s possible to tell you if there’s a problem.

You may need to visit the hospital, clinic or your GP a few days later to discuss your results with a doctor.

Risks and side effects of an ECG

An ECG is a quick, safe and painless test. No electricity is put into your body while it’s carried out.

There may be some slight discomfort when the electrodes are removed from your skin. It will be like removing a sticking plaster. Some people may develop a mild rash where the electrodes were attached.

An exercise ECG is performed under controlled conditions. The person carrying out the test will watch you. They’ll stop the test if you experience any symptoms or start to feel unwell.

Electromyography (EMG)

Electromyography (EMG) is a diagnostic procedure that evaluates the health condition of muscles and the nerve cells that control them. EMG results can help diagnose muscle disorders, nerve disorders, and disorders affecting the connection between nerves and muscles.

What is electromyography?

Electromyography (EMG) is a diagnostic procedure that evaluates the health condition of muscles and the nerve cells that control them. These nerve cells are known as motor neurons. They transmit electrical signals that cause muscles to contract and relax. An EMG translates these signals into graphs or numbers, helping doctors to make a diagnosis.

A doctor will usually order an EMG when someone is showing symptoms of a muscle or nerve disorder. These symptoms may include tingling, numbness, or unexplained weakness in the limbs. EMG results can help the doctor diagnose muscle disorders, nerve disorders, and disorders affecting the connection between nerves and muscles.

Some doctors may refer to electromyography as an electrodiagnostic exam.

Why is electromyography performed?

Your doctor may perform an EMG if you’re experiencing symptoms that may indicate a muscle or nerve disorder. Some symptoms that may call for an EMG include:

• tingling
• numbness
• muscle weakness
• muscle pain or cramping
• paralysis
• involuntary muscle twitching (or tics)

The results of an EMG can help your doctor determine the underlying cause of these symptoms. Possible causes could include:

• muscle disorders, such as muscular dystrophy
• disorders that affect the ability of the motor neuron to send electrical signals to the muscle, such as myasthenia gravis
• radiculopathies
• peripheral nerve disorders that affect the nerves outside the spinal cord, such as carpal tunnel syndrome
• nerve disorders, such as amyotrophic lateral sclerosis

How do I prepare for electromyography?

Make sure to notify your doctor about any over-the-counter or prescription medications you may be taking. It’s also important to tell your doctor if you have a bleeding disorder, or if you have a pacemaker or implantable defibrillator. You may not be able to have an EMG if you have any of these medical conditions or devices.

If you’re able to have an EMG, you should do the following beforehand:

• Avoid smoking for at least three hours before the procedure.
• Bathe or take a shower to remove any oils from the skin. Don’t apply any lotions or creams after washing.
• Wear comfortable clothing that doesn’t obstruct the area that your doctor will be evaluating. You may be asked to change into a hospital gown right before the procedure.
• What happens during an electromyography?
• You will be asked to lie down on an examination table or to sit in a reclined chair. Your doctor may ask you to move into different positions during the procedure.There are two components to an EMG test: the nerve conduction study and needle EMG. The nerve conduction study is the first part of the procedure. It involves placing small sensors called surface electrodes on the skin to assess the ability of the motor neurons to send electrical signals. The second part of the EMG procedure, known as needle EMG, also uses sensors to evaluate electrical signals. The sensors are called needle electrodes, and they’re directly inserted into muscle tissue to evaluate muscle activity when at rest and when contracted.The nerve conduction study is performed first. During this portion of the procedure, your doctor will apply several electrodes to the surface of your skin, usually in the area where you’re experiencing symptoms. These electrodes will evaluate how well your motor neurons communicate with your muscles. Once the test is complete, the electrodes are removed from the skin.After the nerve conduction study, your doctor will perform the needle EMG. Your doctor will first clean the affected area with an antiseptic. Then, they will use a needle to insert electrodes into your muscle tissue. You may feel slight discomfort or pain while the needle is being inserted.The needle electrodes will evaluate the electrical activity of your muscles when contracted and when at rest. These electrodes will be removed after the test is over.During both parts of the EMG procedure, the electrodes will deliver tiny electrical signals to your nerves. A computer will translate these signals into graphs or numerical values that can be interpreted by your doctor. The entire procedure should take between 30 and 60 minutes.

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Lecture Topic 3.1.2

Electroencephalogram (EEG)

What is an EEG?

An EEG is a test that detects abnormalities in your brain waves, or in the electrical activity of your brain. During the procedure, electrodes consisting of small metal discs with thin wires are pasted onto your scalp. The electrodes detect tiny electrical charges that result from the activity of your brain cells. The charges are amplified and appear as a graph on a computer screen, or as a recording that may be printed out on paper. Your healthcare provider then interprets the reading.

During an EEG, your healthcare provider typically evaluates about 100 pages, or computer screens, of activity. He or she pays special attention to the basic waveform, but also examines brief bursts of energy and responses to stimuli, such as flashing lights.
Evoked potential studies are related procedures that also may be done. These studies measure electrical activity in your brain in response to stimulation of sight, sound, or touch.

Why might I need an EEG?

The EEG is used to evaluate several types of brain disorders. When epilepsy is present, seizure activity will appear as rapid spiking waves on the EEG.

People with lesions of their brain, which can result from tumors or stroke, may have unusually slow EEG waves, depending on the size and the location of the lesion.

The test can also be used to diagnose other disorders that influence brain activity, such as Alzheimer’s disease, certain psychoses, and a sleep disorder called narcolepsy.

The EEG may also be used to determine the overall electrical activity of the brain (for example, to evaluate trauma, drug intoxication, or extent of brain damage in comatose patients). The EEG may also be used to monitor blood flow in the brain during surgical procedures.

There may be other reasons for your healthcare provider to recommend an EEG.

What are the risks of an EEG?

The EEG has been used for many years and is considered a safe procedure. The test causes no discomfort. The electrodes record activity. They do not produce any sensation. In addition, there is no risk of getting an electric shock.

In rare instances, an EEG can cause seizures in a person with a seizure disorder. This is due to the flashing lights or the deep breathing that may be involved during the test. If you do get a seizure, your healthcare provider will treat it immediately.

Other risks may be present, depending on your specific medical condition. Be sure to discuss any concerns with your healthcare provider before the procedure.

Certain factors or conditions may interfere with the reading of an EEG test. These include:

• Low blood sugar (hypoglycemia) caused by fasting
• Body or eye movement during the tests (but this will rarely, if ever, significantly interfere with the interpretation of the test)
• Lights, especially bright or flashing ones
• Certain medicines, such as sedatives
• Drinks containing caffeine, such as coffee, cola, and tea (while these drinks can occasionally alter the EEG results, this almost never interferes significantly with the interpretation of the test)
• Oily hair or the presence of hair spray
• How do I get ready for an EEG?Ask your healthcare provider to tell you what you should do before your test. Below is a list of common steps that you may be asked to do.
  • Your healthcare provider will explain the procedure to you and you can ask questions.
  • You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.
  • Wash your hair with shampoo, but do not use a conditioner the night before the test. Do not use any hair care products, such as hairspray or gels.
  • Tell your healthcare provider of all medicines (prescription and over-the-counter) and herbal supplements that you are taking.
  • Discontinue using medicines that may interfere with the test if your healthcare provider has directed you to do so. Do not stop using medicines without first consulting your healthcare provider.
  • Avoid consuming any food or drinks containing caffeine for 8 to 12 hours before the test.
  • Follow any directions your healthcare provider gives you about reducing your sleep the night before the test. Some EEG tests require that you sleep through the procedure, and some do not. If the EEG is to be done during sleep, adults may not be allowed to sleep more than 4 or 5 hours the night before the test. Children may not be allowed to sleep for more than 5 to 7 hours the night before.

What happens during an EEG?

1. You will be asked to relax in a reclining chair or lie on a bed.
2. Between 16 and 25 electrodes will be attached to your scalp with a special paste, or a cap containing the electrodes will be used.
3. You will be asked to close your eyes, relax, and be still.What happens after an EEG?

Skin irritation or redness may be present at the locations where the electrodes were placed, but this will wear off in a few hours.

Your healthcare provider will inform you when you may resume any medicines you stopped taking before the test.

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Lecture Topic 3.1.3

Electroretinogram

The electroretinogram (ERG) is a diagnostic test that measures the electrical activity of the retina in response to a light stimulus. The ERG arises from currents generated directly by retinal neurons in combination with contributions from retinal glia. Importantly, the ERG is an objective measure of retinal function that can be recorded non-invasively under physiological conditions. The first known ERG was recorded from amphibian retina in 1865 by the Swedish physiologist Alarik Frithiof Holmgren. James Dewar of Scotland subsequently recorded the ERG in humans in 1877. 

Preparation of the patient

According to ISCEV 2015 full-field ERG guidelines:

• Avoid fundus phtography, fundus autofluorescence, fluorescein angiography, and other intense illumination before ERG recording. If this is unavoidable, allow at least 30 min recovery time in ordinary room illumination.
• Maximally dilate the pupils (note pupil size before testing).
• There is no need to correct refractive error.
• Before dark-adapted protocols: 20 min of dark-adaptation.
• Before light-adapted protocols: 10 min of light-adaptation.
• If corneal contact lens electrodes are inserted after dark-adaptation, this should be performed under dim red light. Allow 5 min of extra dark adaptation after insertion of contact lens electrodes.
• Present low strength flashes before stronger flashes to avoid partial light adaptation from strong flashes.
• Request the patient to fixate steadily and not move his/her eyes. Ocular movements introduce large electrical artifacts, change electrode position, and may cause blockage of light by the eyelids/electrode.
• Protect corneal surface with non-irritating ionic conductive solution (artificial tears or contact lens solutions containing sodium chloride and no more viscous than 0.5% methyl cellulose). Improper installation of contact lens electrodes can cause corneal abrasions.

Electrooculogram

The electroocoulogram (EOG) is an elecrophysiologic test that measures the existing resting electrical potential between the cornea and Bruch’s membrane. The mean transepithelial voltage of bovine Retinal pigment epithelium is 6 millivolts (mV).
The EOG was described and named by Elwin Marg in 1951. Clinical applications were described first by Geoffrey Arden in 1962, who realized that the most valuable information was the comparison of the amplitudes under light and dark-adapted states (the Arden ratio).

The patient should be in stable indoor lighting for at least 30 min before the test. Strong retinal illumination including retinal imaging (fluorescein angiogram, fundus photography and others) and indirect ophthalmoscopy should be avoided during this period.

The patient is told to remain still other than moving his/her eyes back and forth. Four recording skin electrodes (silver-silver chloride or gold-disk) are placed at the medial and lateral canthi of both eyes, and the grounding electrode is placed on the forehead. The difference of electrical potential of the anterior and posterior part of the eyeball is called the standing potential.^[2] Standing potential indirectly measures the transepithelial potential (TEP) of the retinal pigment epithelium (RPE). TEP is the difference of membrane potential of basolateral and apical membranes of RPE.

Components of the EOG

The light-insensitive component accounts for the dark trough and is dependent on the integrity of the retinal pigment epithelium (RPE) as well as the cornea, lens, and ciliary body. The light-sensitive component is the slow light rise of the EOG and is generated by the depolarization of the basal membrane of the RPE.

The EOG is abnormal in:

• Best vitelliform macular dystrophy (early stage) and in carriers
• Stargardt macular dystrophy (advanced stage)
• Pattern dystrophies (normal or modestly subnormal)
• Membranoproliferative glomerulonephritis with electron dense material deposition in the choriocapillaris (normal or subnormal)
• Ectodermal dysplasia, ectrodactyly, and macular dystrophy, EEM syndrome (markedly reduced)
• Retinitis pigmentosa and rod-cone dystrophies
• Acquired cone and cone-rod dystrophies
• Oguchi disease
• Fundus Albipunctatus (no notable light rise with dark adaptation of 15 minutes)

The EOG is normal in:

• Dominantly inherited drusen of Bruch’s membrane
• Congenital achromatopsia
• Progressive diffuse cone dystrophy
• Autosomal recessive and X-linked recessive congenital stationary nyctalopia