A shock can cause muscle spasms
Muscles are stimulated by electricity. The effect depends on the intensity of the current and the type of muscle it travels through.
We’ve all felt a buzzing or tingling sensation that doesn’t cause injury. That’s the effect of a current as low as 0.25 milliamperes (mA) entering the body.
When a current above 10 mA travels through flexor muscles, such as the ones in our forearms that close the fingers, it causes a sustained contraction. The victim may be unable to let go of the source of the current, making the duration of the contact longer and increasing the severity of the shock.
When a current above 10 mA travels through extensor muscles, it causes a violent spasm. If the muscles affected are the hip extensors that lengthen the limbs away from the body, the victim may be propelled, sometimes many metres away!
Muscles, ligaments and tendons may tear as a result of the sudden contraction caused by an electric shock. Tissue can also be burned if the shock is lasting or the current is high.
A shock can cause cardiac arrest
If a current of 50 mA passes through the heart, it can cause cardiac arrest.
The heart is also a muscle, which beats to pump blood through the body. The rhythm of our heartbeat is controlled by electric impulses—it is these impulses that are monitored by an electrocardiogram. If a current from outside the body passes through the heart, it can mask these impulses and disturb the heart’s rhythm. This irregular heartbeat is called arrhythmia and can even manifest as a total disorganization of the rhythm, known as ventricular fibrillation.
When ventricular fibrillation occurs, the heart stops pumping and the blood stops circulating. The victim rapidly loses consciousness and dies if a healthy heartbeat is not restored with a device called a defibrillator.
The arrhythmia can occur at the time of the shock or in the hours following the electric shock.
A shock can cause burns to tissues and organs
When a current above 100 mA passes through the body, it leaves marks at the points of contact with the skin. Currents above 10,000 mA (10 A) cause serious burns that may require amputation of the affected limb.
Some burns are easy to recognize because they look like the burns you can get from contact with heat. Others may seem harmless but aren’t: tiny charred craters indicate the presence of much more serious internal burns.
Electrical burns often affect internal organs. They are caused by the heat generated from the body’s resistance to the current passing through it. Internal damage may be much more serious than the external injuries suggest.
Internal burns often have serious consequences: scarring, amputation, loss of function, loss of sensation and even death. For example, if a lot of tissue is destroyed, the large amount of waste generated can cause serious kidney or blood circulation disorders.
A shock can affect the nervous system
Nerves are tissue that offers very little resistance to the passage of an electric current. When nerves are affected by an electric shock, the consequences include pain, tingling, numbness, weakness or difficulty moving a limb. These effects may clear up with time or be permanent.
Electric injury can also affect the central nervous system. When a shock occurs, the victim may be dazed or may experience amnesia, seizure or respiratory arrest.
Long-term damage to the nerves and the brain will depend on the extent of the injuries and may develop up to several months after the shock. This type of damage can also cause psychiatric disorders.
A shock can have other unexpected consequences
Other disorders can appear in the weeks or months following the shock, depending on which organs the current passed through. For example, if the current passed through the eyes, cataracts may develop over time.