Serious adverse events from TENS are rare. Occasional reports of mild electrical burns with TENS-like devices are due to an inappropriate technique. Some patients experience mild autonomic responses and minor skin irritation beneath electrodes. TENS can interfere with monitoring equipment and should not be placed close to transdermal drug delivery systems.
Guidelines produced by the UK Chartered Society of Physiotherapy list cardiac pacemakers and bleeding disorders as contraindications.4 TENS manufacturers list cardiac pacemakers, pregnancy, and epilepsy as contraindications because it may be difficult to exclude TENS as a potential cause of a problem from a legal perspective. Many centres regard these as contraindications. However, some specialists believe that it is possible to use TENS in these patient groups, providing that it is not applied locally and the situation is discussed with the relevant medical specialist and patient. Patient progress should be carefully monitored.
Pacemakers and cardiovascular problems
TENS has been shown to interfere with pacemaker function. For example, Holter monitoring has demonstrated interference with a cardiac pacemaker; in both instances, the sensitivity of the pacemaker was reprogrammed to resolve the problem. The manufacturers regard TENS as a contraindication in this situation and many centres have adopted this. Some specialists will utilize TENS in the presence of a pacemaker, providing that it is applied away from the chest area, but it is recommended that this is done in close consultation with a cardiologist and not undertaken by non-specialists. TENS is often used over the chest for angina with much success; again, the situation should be discussed with a cardiologist.
Electrodes should never be applied on anterior and posterior areas of the chest as this may compromise pulmonary ventilation due to excessive stimulation of the intercostal muscles. Electrodes should not be placed over areas where there has been recent haemorrhage as the currents may cause further haemorrhage. TENS should not be applied directly over ischaemic tissue, thrombosis, or both because of the potential for embolism.
TENS should not be administered over the abdomen or pelvis during pregnancy because the effects of TENS on fetal development are still unknown and currents could inadvertently cause uterine contractions and induce premature labour. Potential hazards away from these sites seem minimal, but many still regard this as a contraindication.
Practitioners should be cautious when giving TENS to patients with epilepsy and should not apply electrodes to the neck or head. TENS-induced seizures in a post-stroke patient have been reported, so TENS should be used with care in these patients.
Inappropriate electrode sites
TENS should not be applied over the anterior neck as this may produce a hypotensive response, laryngeal spasm, or both. TENS should not be delivered over the eyes as it may cause an increase in intraocular pressure.
It is advised not to apply TENS directly over areas of active malignancy except in palliative care and under the supervision of a specialist. A recent case series highlighted the potential benefit of TENS for cancer bone pain.5
Dermatological conditions or frail skin
TENS electrodes should not be applied on areas of broken or damaged skin, such as open wounds, although they can be applied over healthy tissue surrounding a wound.
TENS should not be applied to skin with diminished sensation because nerve damage is likely to diminish TENS effectiveness and the patient may be unaware that high-intensity currents are causing skin irritation. Caution is needed when using TENS in the presence of mechanical allodynia as TENS may exacerbate the pain.