A Transcutaneous Electrical Nerve Stimulation (TENS) unit sends small electrical currents through the skin to manage pain. While considered safe for most people when used correctly, questions arise about its safety concerning the heart. For individuals without underlying health issues, there is no evidence that a properly used TENS unit can cause a heart attack. However, the device’s electrical signals can pose risks in certain situations, so specific precautions are necessary for particular individuals.
Understanding Electrical Interference with the Heart
A TENS unit functions by delivering low-voltage electrical currents through electrodes placed on the skin, stimulating nerve fibers to reduce the perception of pain. This process operates on the principle of blocking pain signals from reaching the brain and encouraging the body to release its own natural painkillers. The effectiveness of this therapy relies on the strategic placement of electrodes to target specific nerve pathways related to the source of pain.
The heart operates using its own sophisticated, internal electrical system. This natural system generates coordinated electrical impulses that cause the heart muscle to contract and pump blood, creating a regular heartbeat. An external electrical source, like a TENS unit, can interfere with this natural cardiac rhythm if the current passes through the chest cavity. This is similar to how a powerful radio signal can disrupt a weaker one, causing the heart’s own signals to be misinterpreted.
This interference is the primary reason for the guidelines regarding TENS unit use. If the external electrical signals from the device disrupt the heart’s intrinsic rhythm, it could lead to an arrhythmia, or irregular heartbeat. For a healthy heart, the risk is minimal, but for a heart with a pre-existing condition, such interference could be dangerous.
Contraindications for Individuals with Heart Conditions
Certain individuals are at a higher risk for complications and should avoid TENS therapy or use it only under direct medical supervision. A significant risk is for people with implanted medical devices like pacemakers or implantable cardioverter-defibrillators (ICDs). The electrical impulses from the TENS unit can be misinterpreted by these devices as the heart’s own signals, which can inhibit pacemaker function or trigger an unnecessary shock from an ICD.
Studies show that TENS signals can interfere with the function of these cardiac devices. In one study, interference was detected in some patients with ICDs, with the device misinterpreting the signals as abnormal heart rhythms. In a small percentage of those cases, the interference was significant enough to trigger a shock, making it important for individuals with these implants to avoid TENS therapy unless cleared by a cardiologist.
People with known heart rhythm problems, such as certain arrhythmias, or other unstable heart conditions should also exercise caution. The external electrical stimulation, even if not directly over the heart, could aggravate an existing condition. Anyone with a history of heart disease or any cardiac concerns should consult their doctor before using a TENS unit to ensure it is a safe option for them.
Safe TENS Unit Placement and Usage
Correct electrode placement is important for using a TENS unit safely. The primary rule is to never place electrode pads in locations that could allow the current to pass through the heart. Electrodes should not be placed across the chest, with one pad on the front and one on the back, as this trans-thoracic placement creates a direct path for the current through the chest cavity.
Other prohibited areas for electrode placement include:
- The front or sides of the neck. Placing electrodes near the carotid sinus, an area that helps regulate blood pressure, can cause a sharp drop in blood pressure.
- The head, over the eyes, or in the mouth.
- Over open wounds or infected tissue.
- Areas with numb skin.
General safety practices enhance safe use:
- Always start the TENS unit on its lowest intensity setting and gradually increase it to a level that is strong but comfortable.
- Do not use the device while sleeping, driving, or in water, such as in the bath or shower.
- Before applying the pads, ensure the skin is clean and dry for good adhesion and consistent electrical contact.
- Check the skin for redness or irritation after use.
The sensation should be a tingling, not a pain.