Electrical injury

An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current.

The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or only produce a light tingling sensation. However, a shock caused by low and otherwise harmless current could startle an individual and cause injury due to jerking away or falling. A strong electric shock can often cause painful muscle spasms severe enough to dislocate joints or even to break bones. The loss of muscle control is the reason that a person may be unable to release themselves from the electrical source; if this happens at a height as on a power line they can be thrown off. Larger currents can result in tissue damage and may trigger ventricular fibrillation or cardiac arrest. If death results from an electric shock the cause of death is generally referred to as electrocution.

Electric injury occurs upon contact of a body part with electricity that causes a sufficient current to pass through the person's tissues. Contact with energized wiring or devices is the most common cause. In cases of exposure to high voltages, such as on a power transmission tower, direct contact may not be necessary as the voltage may "jump" the air gap to the electrical device.

Following an electrical injury from household current, if a person has no symptoms, no underlying heart problems, and is not pregnant, further testing is not required. Otherwise an electrocardiogram, blood work to check the heart, and urine testing for signs of muscle breakdown may be performed.

Management may involve resuscitation, pain medications, wound management, and heart rhythm monitoring. Electrical injuries affect more than 30,000 people a year in the United States and result in about 1,000 deaths.

Heating due to resistance can cause extensive and deep burns. When applied to the hand, electricity can cause involuntary muscle contraction, preventing the victim from untensing their hand muscles and releasing the wire, increasing the risk for serious burns. Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance or the square of the current multiplied by the resistance) available from the source. Damage due to current is through tissue heating and/or electroporation injury. For most cases of high-energy electrical trauma, the Joule heating in the deeper tissues along the extremity will reach damaging temperatures in a few seconds.

A domestic power supply voltage (110 or 230 V), 50 or 60 Hz alternating current (AC) through the chest for a duration longer than one second may induce ventricular fibrillation at currents as low as 30 milliamperes (mA). With direct current (DC), 90 to 130 mA are required at the same duration. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode), a much lower current of less than 1 mA (AC or DC) can cause fibrillation. If not immediately treated by defibrillation, ventricular fibrillation is usually lethal, causing cardiac arrest, because all of the heart muscle fibres move independently instead of in the coordinated action needed for successful cardiac cycle to pump blood and maintain circulation. Short single DC pulses induce VF dependent on the amount of charge (in mC) transferred to the body, which makes the amplitude of the electrical stimulus independent of the exact amount of current flowing through the body for very short pulse durations. DC shocks of short duration are usually better tolerated by the heart even at high currents and rarely induce ventricular fibrillation compared to lower currents with longer duration with both DC or AC. The amount of current can easily reach very high values as amperage is only of second order importance to fibrillation risk in the case of ultra short contact times with direct currents. But even if the charge itself is harmless, the amount of energy being discharged still can lead to thermal and chemical hazards if its value is high enough. One example of high current electric shock which may be usually harmless is an electrostatic discharge as experienced in everyday life on door handles, car doors etc. These currents can reach values up to 60 A without harmful effects on the heart as the duration is in the order of only several ns. Another example for dangerous electrostatic discharges even without flowing directly through the body are lightning strikes and high voltage arcs.

Mechanism of cardiac arrhythmias induced by electricity is not fully understood, but various biopsies have shown arrhythmogenic foci in patchy myocardial fibrosis which contained increased amount of Na+ and K+ pumps, possibly associated with transient and localized changes in sodium-potassium transport as well as their concentrations, resulting in changes in membrane potential.