Lightning injuries are usually thought to be caused by direct strike, side flash, or ground current;1,2 none of which explain lightning-related deaths where current does not apparently enter or leave the patient's body.
In June, 1996, a 32-year-old man and three other golfers stood under a tree during a lightning storm. When lightning struck the tree, the patient suffered a cardiac arrest. Cardiopulmonary resuscitation was given by a physician who was nearby. The patient was taken to hospital but remained comatose and died on the 18th day. Three other golfers under the same tree survived. One had surface burns on his head, neck, and abdomen at places where he wore metal objects: necklace, belt buckle, and metal button on a cap. The other two golfers had only brief loss of consciousness. This case and at least four other cases in the medical literature3 are unusual in that patients succumbed to lightning but there was no evidence of external damage from lightning currents. Lightning-related hypoxic encephalopathy secondary to cardiac arrest is often fatal.3 Most lightning casualties have external signs of damage from contact with electrical current, such as skin burns and Lichtenberg figures or "ferning".4,5 However, some patients have a cardiac arrest as the result of a lightning strike without external signs of electrical burns.
Lightning "bolts" have very high peak currents (100000 amps) which rise in µs and decay more slowly. They may produce intense nearby magnetic fields
(several millitesla at a distance of about 1 m), which may induce large but short-lived (<1 ms) currents in a human body. The induced current
wave-form is proportional to the change per time of the magnetic field. The lightning may induce a loop current within the human torso without
evidence of current entering the body. If these currents occur during a vulnerable part of the cardiac cycle, they could cause asystole or
ventricular fibrillation.*
This hypothesis may be tested on mice or rats exposed to rapidly rising magnetic field pulses that approximate the dynamics of lightning currents within cylindrical chambers enclosed by solenoid windings. This method would necessitate the use of fields on the order or ten times as great as the natural lightning fields. Our proposed mechanism may explain some unwitnessed and unexplained "heart attacks" among hikers found dead in the mountains.
Presented in part at the American Association of Physics Teachers Meeting in Denver, Colorado, August 14, 1997.
We thank Vincent W Vanek.
*Lightning stroke with peak current 100000 amp gives peak magnetic field (Bp):
Where µo=magnetic permeability of air 4(10-7) Webers/A*m Ip=peak current (amps). R=distance from
the lightning stoke (m).
For a distance of 1·0 m, Bp=2(10-2) Tesla. Lightning current rises to its peak in about 10-6 s, so the rate of rise of dB/dt is 2(104) Tesla/s. Electrical field induced in a cylindrical object (human torso)
Where E=electrical field (v/m) a=radius of the induced current path (m). Highest fields would be at the perimeter of the torso and the lowest
ones produced in the centre. With an estimate of a=0·1 m yields E of about 1000 V/m for dB/dt=2(104) Tesla, and
current density of about 1000 A/m2 through the ventricles (tissue resistivity 1 ohm/m). Long current pulses (of ms) or for
60 Hz, such a current density would lead to arrhythmias. For current pulses lasting a few µs, electrical impedance of cardiac-cell
membranes is due almost entirely to the membrane capacitance (Cm) which is on the order of 0·01 F/m2, the change
in membrane potential (Vm) is
For J=1000 A/m2, and the duration of the current pulse, 
t=10-6 s, predicts a Vm
of 100 mV. If the cardiac
cell is in a refractory state this current is not likely to re-trigger a discharge in the active phase corresponding to the ECG T wave. Ventricular
fibrillation or asystole may result.
1 Kleinschmidt-DeMasters BK. Neuropathology of lightning-strike injuries. Semin Neurol 1995; 15: 323-28.
2 Cooper MA. Emergent care of lightning and electrical injuries. Semin Neurol 1995; 15: 268-78.
3 Wetli CV. Keraunopathology: an analysis of 45 fatalities. Am J Forens Med Path 1996; 17: 89-98.
4 Cherington M, Yarnell PR, London SF. Neurological complications of lightning injuries. West J Med 1995; 162: 413-17.
5 ten Dius HJ, Klasen HJ, Nijsten MWN, Pietronero L. Superficial lightning injuries: their "fractal" shape and origin. Burns 1987; 13: 141-46.
Lightning Data Center, St Anthony Hospital, Denver, CO 80204, USA (M Cherington); Department of Neurology, University of Colorado School of Medicine, Denver; and Electrical and Computer Engineering Department, Boulder, CO