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Chronic Refractory Angina

Nursing Guidance for Transcutaneous Electrical Nerve Stimulation (TENS) for the treatment of chronic refractory angina

These Guidance lines have been produced in accordance with the NHS Executive publication "Clinical Guidelines" (May 1996) and incorporate those standards produce by the King's Fund for evidence based clinical practice.

Produced for the National Refractory Angina Centre
E-mail Dave.Trenbath@ccl-tr.nwest.nhs.uk
Tel:0044 (0)151 293 2201 + voice mail

Transcutaneous Electrical Nerve Stimulation (TENS)
One of a series of guidance notes
*TENS
* Patient Counselling
* Stellate Ganglion Block
* Paravertebral block
* Spinal Cord Stimulation
* High Thoracic Epidural
* Intrathecal pumpSynchromed
* Intrathecal pump Algomed

TENS: GUIDANCE FOR THE TREATMENT OF CHRONIC REFRACTORY ANGINA

Note TENS should only be prescribed following a full clinical evaluation and counselling
Transcutaneous Electrical Nerve Stimulation (TENS) is a highly effective therapy used for the relief of pain and has been proven beneficial when used in the treatment of neck pain, low back pain, sciatica, arthritis oestioarthritis(1) and labour(2). TENS therapy can ameliorate symptoms in chronic refractory angina and is routinely prescribed in patients attending our centre where conventional treatment with surgery or angioplasty is not possible (see clinical chapter). We always recommend that TENS is used in conjunction with relaxation techniques and after full counselling. It is helpful if patients and carers understand the basic principles of TENS and how TENS interferes with the angina angina reflex.
Essentially TENS involves the application of low voltage electrical current via pads placed on the skin in the area of pain. The stimulation selectively activates specialised vibration nerve fibres that compete with the pain fibres for space in the spinal cord. TENS works because there is not enough space in the spinal cord to allow both pain and vibration to travel on up top the brain. So far as the spinal cord is concerned vibration is considered more important than pain and will allow vibration impulses to pass up to the brain to be felt as a buzzing sensation whilst blocking out the pain signals. But that is not the end of it. One of the important negative consequences of all pain (including angina) is the initiation of the "fight or flight" response. For most sorts of pain the "fight or flight" response can be helpful but in angina the "fight or flight" response is invariably unhelpful because it makes the heart work harder whilst reducing its blood supply. So by blocking anginal pain TENS prevents the brain from making its reflex mistake of releasing adrenaline.

The three main components of the TENS machine are:

A box with battery and controls (about the size of a walkman)
A set of wires
Electrodes (which can be either disposable and adhesive or carbon rubber and reusable).

An electrode jelly is used as a conductive agent when carbon rubber electrodes are used.
When using TENS the skin should be clean, dry and free of grease or talc to ensure that conduction is not impaired. The electrodes are placed on the chest so that the main area where the patient experiences pain lies between them. They must be more than 1cm apart. The electrodes are connected to the TENS machine which is set to a continuous stimulation at a frequency of 70Hz and the intensity is set to a level immediately below that producing discomfort(3). It can be helpful to explain the use of TENS to patients in terms of the way in which patients are used to using nitrates. Patients are advised to use TENS for at least one hour three times a day whether or not pain is present (like long acting nitrates) and are encouraged to use it during acute attacks (like short acting nitrates). A higher level of intensity may be required to enable the spinal cord to block out the pain impulses. The intensity is increased until the pain of angina is no longer uncomfortable or distressing (repeated nitro spray or buccal nitrates). The usual rules apply to progressively worsening symptoms despite treatment and patients are advised to seek medical advice.

Safety

As a therapy TENS is very safe but contact dermatitis, can occur this is an inflammatory response of the skin that arises from touching a substance to which the person is sensitive. The type of electrodes, jelly and adhesive tape can all be the cause(4). Prior to the application of a TENS machine, it is very important to ensure the area of skin the electrodes are to be applied to is cleaned thoroughly before and then after application. There are rare cases reported of interference with electrocardiogram (ECG) readings due to electrical interference which could lead to a misinterpretation of the reading, it is advisable therefore not to use the machine whilst having an ECG. The use of a permanently implanted cardiac pacemaker device does not mean TENS cannot be used(5). However care must be taken when placing the electrodes as they should not be positioned directly over the pacemaker device. We routinely check the effect of TENS on pacemaker function in the ECG department. There is one report of TENS being misinterpreted by an implantable cardiac defibrillator this resulted in the patient receiving an inappropriate shock. Therefore TENS should always be used with great caution in such patients(6).
TENS should not be used whilst driving or operating machinary because movements of the pads can produce and unpredicatable and distracting jolts of current.

References