TASER is easy on the heart
Nov 26, 2007 9 comments
A study of the effect of TASERs on human and animal hearts suggests that he weapons are unlikely to harm the human heart. The work was done by researchers in the UK and involved laboratory experiments and computer simulations. The team concluded that the jolt from the weapon is not enough cause the heart to beat irregularly.
The TASER is a battery-operated electrical incapacitation weapon that works by firing two tethered barbs at a person -- and then sending pulses of high-voltage electricity through the tether wires. While this causes involuntary muscle contraction and intense pain in the unfortunate target, the TASER is used by many police forces as a less-lethal alternative to firearms. However, several people have died after being struck by a TASER, leading to some controversy and concern regarding the potential negative effects of the device on the heart.
Now, a multidisciplinary research collaboration led by the UK Defence Science and Technology Laboratory (Dstl) has examined the possibility that the strike from two commercial TASERs: the M26 and X26 can cause the human heart to beat irregularly – a condition called cardiac arrhythmia. To do this, the researchers applied the TASER waveforms to a digitized human-body representation and modelled the current flow within its heart. These simulated currents were then applied to a guinea-pig heart in vitro (Phys. Med. Biol. 52 7193 ).
The TASERS under investigation produce damped sinusoidal waves: the M26 generates a 50 kHz waveform with a current of 10-12 A, a peak voltage of nearly 1000 V and a 50 µs pulse duration; the X26 generates a 120 kHz wave with a peak voltage of around 300 V and a pulse duration of 120 µs. The research team applied these waveforms to the anterior chest wall of a numerical model of a human body using a dart separation of 225 mm - the distance that caused the highest current density on the heart.
By employing computational electromagnetic modelling, the team determined that the M26 TASER induced a peak absolute current density of 0.66 mA/mm2, spread over a circular region of approximately 25 mm in diameter on the right ventricle (beneath the upper probe). For the X26 TASER, the highest peak absolute current density was 0.11 mA/mm2, spread across a similar region.
The team then determined whether the TASER pulses could disrupt a beating guinea-pig heart. The choice of guinea-pig heart was partly based on the similarity of its electrocardiographic-wave configurations to those generated by a human heart.
The heart, which had been removed from the animal, was beating spontaneously. The M26 and X26 waveforms were applied to the surface of the heart using an electrode. At the maximum current densities predicted by the human model (0.66 and 0.11 mA/mm2), the pulses did not cause the heart to beat erratically. Indeed, the current densities of both devices had to be increased by at least a factor of 60 before erratic heartbeats were seen.
As a result of the simulations and experiments, the team concluded that there is a wide safety margin between the intensity of a TASER strike and the level at which a human heart would beat irregularly. The team did, however, caution that factors such as the consumption of alcohol or some drugs, or an existing heart condition could reduce this safety margin in some individuals.
"This paper provides an important first step in determining the bioelectric effects of TASERs on the heart," said Brad Roth, associate professor in the department of physics at Oakland University in Rochester, Michigan. "I have many concerns about TASERs, but the induction of a cardiac arrhythmia appears to be less of a problem than I would have initially guessed."
"Given the controversy surrounding the use of the TASER, there has been astonishingly little research into its safety," said Kenneth Foster, professor of bioengineering and electrical engineering at the University of Pennsylvania. "We could have guessed that the risks of cardiac events are rather low, since TASER International markets the weapon by sending them to police conventions and by now, hundreds of police officers have tased themselves without mishap. It is nevertheless reassuring see good studies being done that support this conclusion."
About the author
Tami Freeman is science editor on medicalphysicsweb.