The Taser® weapon: A new emergency medicine problem

CONCEPTS, COMPONENTS & CONFIGURATIONS electrical injury, Taser®; injury, Taser®; Taser ® weapon, injury

The Taser ® Weapon: A N e w Emergency Medicine Problem The Taser ® is an electrical law enforcement and self-defense weapon that is being used with increasing frequency. The weapon is described and its effects and ballistic and electrical considerations are reviewed. Clinical aspects of Taser ® injury, including weapon-fired barb injury, barb removal methods, injury secondary to electrical current, ventricular fibrillation, possible interactions with implanted pacemakers, and injuries secondary to weapon-induced falls, are discussed. Taser ® injuries are a n e w and increasingly frequent emergency medicine problem. [Koscove EM: The Taser ® weapon: A n e w emergency medicine problem. Ann Emerg Med December 1985;14:1205-1208.] INTRODUCTION The Taser ® (short for Thomas A Swift's Electric Rifle) is an electronic immobilization and defense weapon that has been available commercially since 1974. Only recently has it been used widely in the Los Angeles area. According to the manufacturer (Taser® Industries, Inc, Monrovia, California), the Taser ® currently is used or is being tested on a limited basis by more than 350 law enforcement agencies or facilities in the United States, as well as internationally. The popularity of this weapon is based on its reduced lethality with respect to immobilization when compared to the standard issue police handgun, the latter of which can inflict significant penetrating and life-threatening injury. It therefore is likely that an increasing number of "Tasered" patients will present to emergency departments as use of this device by law enforcement agencies becomes more popular. Most patients presenting to the ED have been Tasered because of violent or erratic behavior, often as a result of drug intoxication (particularly with phencyclidine [PCP]) or as a result of a psychiatric disturbance.

Eric M Koscove, MD Los Angeles, California From the Department of Emergency Medicine, Los Angeles County University of Southern California Medical Center, Los Angeles, California. Received for publication February 20, 1985. Accepted for publication May 16, 1985. Address for reprints: Eric Koscove, MD, Department of Emergency Medicine, LACUSC Medical Center, 1200 North State Street, Los Angeles, California 90033.

THE TASER ®

Two models of the Taser ® are marketed and in use. One is available primarily to law enforcement agencies. The other is available to the general public after appropriate-local firearm registration measures, if any, have been followed. The police model differs from the public model only in that its power output is twice that of the public model. The Taser ® is a hand-held device that weighs approximately 0.63 kg (Figure 1). It contains a power source (nickel-cadmium batteries), electronic circuitry, a flashlight, and two cartridges. Each cartridge contains two darts. Each dart, weighing 1.4 g, consists of a 4 - m m fish hook barb on a 5.5-mm by 1-mm shaft imbedded in a 2.38-cm metal and plastic cylinder. The cylinder is connected to the Taser ® by a 4.6-m wire (Figure 2). When a trigger bar on the Taser ® is depressed, a gunpowder charge is exploded, firing the two darts from a cartridge. When both darts are imbedded in the victim's skin or clothing, a high-voltage electrical pulse train of eight to 13 pulses per second is transmitted to the victim through the wires. An accessory device added to the weapon can be used in lieu of barbs. The device's two antennae, separated by 0.3 m at the distal tip, deliver the electrical pulse train when touched to the victim. The pulse train is transmitted as long as the trigger bar is depressed, with the only time limitation being 14:12 December 1985

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Fig. 1. T h e Taser ® weapon. Fig. 2. T h e Taser ® barb. that of the battery life (108 seconds in current models). Most Taser ® victims fall to the ground and experience rhythmic muscular contractions while the current is delivered. The exact mechanism of the fall and the contractions remains unclear. They are believed to result from tonic and clonic muscular contraction, a peripheral neuromuscular phenomenon, rather than from central nervous system stimulation. Most Taser ® patients have been persons under the influence of PCP, making reliable subjective impressions difficult to elicit. In a recent field trial, several prison guards volunteered to be Tasered. All remained awake; most felt "stunned" during the entire event; and all fell to the ground immediately (personal communication, Sergeant Anthony Lamarque, October 1984). A few reported a tingling sensation in an area approximately 4 cm in diameter under the dart that lasted two to three minutes after being Tasered. Most reported that the experience was unpleasant and declined to be reTasered.

M E C H A N I S M OF EFFECT An important concept in electrical injuries is that of the "let-go" current, defined as the m a x i m u m current a person can tolerate as evidenced by volitional use of muscles directly stimulated by that current. A person receiving a shock with a current exceeding the "let-go" current threshold cannot release a hand-held conductor transmitting the current.I, 2 It has been conjectured that the Taser ® delivers a current that exceeds the let-go current threshold, resulting in the Tasered patient being unable to free himself from the device as long as the current is delivered. Let-go c u r r e n t thresholds, derived from experiments 110/1206

with single-frequency currents at 60 Hz (household current) had a median of 16 mA for men and 10.5 mA for women. 3 The Taser ® current output in earlier public models has been estimated to be equivalent to a 60-Hz shock of approximately 3 mA.4 Therefore, based on the available literature, the mechanism of action of the Taser ®is unclear. Of interest is the fact that the weapon is capable of immobilizing a victim even if the two barbs are imbedded only in the clothing; that is, subcutaneous penetration is not necessary for an immobilizing effect to occur. BALLISTIC C O N S I D E R A T I O N S The ballistic output of the Taser ® is that of its two darts. The range of the weapon is 4.6 m and is limited by the conducting wires. The initial velocity of each dart is approximately 55 m/s. This velocity is slowed to approximately 30 m/s at 4 m, partly due to the inertia of the conducting wire leads. The initial velocity is substantially less than that of a BB gun (91 m/s) or .38 special handgun (332 m/s). The kinetic energy delivered by the Taser ® dart, proportional to its mass x velocityz, is very low. Hence the dart is ballistically a very low-velocity, lowenergy weapon.S The manufacturer reports that darts fired point-blank into the bare chest of a man resulted in only the barb and needle portion of the dart becoming imbedded in the skin. CLINICAL CONSIDERATIONS Despite the low ballistic output of the Taser ®, some important body areas may be prone to low-velocity injury by this weapon. Because the length of the dart needle is only 9.5 m m and this is probably the extent of depth of penetration into skin, the number of skin-covered vital structures potentially injured by the dart is limited. Annals of Emergency Medicine

The barb itself could lodge in any surface area, with the chest, abdomen, and legs being the areas encountered most frequently in clinical practice. Penetration into a major blood vessel (eg, carotid artery) has not been reported publicly. In addition, law enforcement personnel are instructed to fire the weapon at such major body surface areas as the chest and abdomen, rather than at the head and neck. Except for laceration and crushing, the only other ballistic mechanism of tissue damage by the dart probably is that caused by shock waves, s Given the low velocity and kinetic energy of the dart, this factor probably is insignificant, although there are no data to support this contention. The greatest--yet least intended-potential injury is that of dart penetration of the eye with subsequent rupture of the globe. Whether total loss of vision (from globe rupture or from t r a n s m i s s i o n of electrical current through the eye) would result is unknown. Clinical m a n a g e m e n t of a penetration of the eye should consist of leaving the dart in place, placement of a protective metal eye shield, and immediate ophthalmologic consultation. In addition, as with any penetration of the body surface by the dart, appropriate tetanus i m m u n i z a t i o n should be given. One of three methods may be used to remove Taser ® barbs from the skin. In descending order of ease they are: 1) grasping the wire connected to the dart and firmly pulling it away from the skin; 2) placing a 16-gauge needle over the barb portion of the dart and gently backing the dart out of the skin; and 3) prepping the skin, infiltrating locally with lidocaine, cutting down to the barb with a sterile scalpel, and removing the barb through the incision. The first method is well tolerated by the typical patient. The disadvantage is the p r o d u c t i o n of more irregular wound margins. Given 14:12 December 1985

the small skin area involved, however, poor cosmesis is not a major consideration. The second and particularly the third methods produce a wound margin with sharper edges and, hence, better healing and cosmesis. It is unknown if any particular method of extraction results in a higher rate of wound infection. Patients typically are not placed on antibiotic prophylaxis for these minor wounds. Local wound irrigation and cleansing, as well as appropriate tetanus prophylaxis, are reasonable measures. Although the Taser ® dart has a fish hook barb, an often-used modified technique for fish hook removal cannot be used. This modified method involves pushing the barb through the skin, removing the barb head by clipping, and withdrawing the barb shaft by backing it out of the entrance wound. 6 The dart shaft is too short to allow the entire barb head to be exposed by pushing it out through the distal skin, and therefore the barb cannot be clipped off using this method.

GENERAL CONSIDERATIONS Discussion of the electrical output of the Taser ® and its clinical consequences necessitates an understanding of available clinical and experimental information. Much of the data on which national electrical safety standards are based have been derived from experiments using 60-Hz sinusoidal power sources. The Taser ® produces a pulse train of damped sinusoidal waves. There are no current experimental data on the clinical effects of a train of damped sinusoidal waves as a function of pulse frequency, pulse duration, amplitude, current, and frequency of the damped sinusoid. As can be demonstrated by Fourier analysis, this train of damped sinusoidal current pulses can be represented by a sum of sinusoidal currents whose frequencies are multiples of the pulse frequency. 7 It is not known if simultaneous application of several frequencies has any different physiological effects (eg, in regard to fibrillation threshold) when compared to the sum of the effect of each frequency current applied individually. Nonetheless, it is known, based on experiments of single frequencies, that the let-go threshold of currents with frequencies of more than 1 kHz is significantly less than those of currents less than 1 kHz. t One of the major issues in electrical 14:12 December 1985

safety standards concerns fibrillatory current, the current that produces ventricular fibrillation. For externally applied current, the fibrillatory current in human beings is believed to be a function of the duration, frequency, and magnitude of the current, as well as the patient's body weight3,8, 9 The threshold of ventricular fibrillation for men (for an externally applied, 60-Hz current) has been proposed to be 500 mA for shocks of less than 200 ms duration and 50 mA for shocks of more than two seconds, lo Another possible cause of morbidity and mortality in electrical injuries is respiratory arrest or asphyxiation. 11-13 The respiratory effects of accidental electric shock in animals and human beings have not been studied extensively. 1446 Research has suggested that p e r m a n e n t respiratory arrest could occur, particularly with head or neck electrode placement that produces current flow across the medullary respiratory center, or with electrodes on two limbs)S, 17 In rabbits, current applied to two limbs caused temporary or permanent respiratory arrest; however, the latter was thought to be a consequence of circulatory arrest induced by a prolonged respiratory arrest. 18 Asphyxia by tetanic respiratory muscle contraction has been theorized. A 60-Hz current of 18 mA has stopped respiratory movements in human beings; a systematic study of 60-Hz current in animals proposed an "asphyxia threshold" of 40 mA.3A8 The energy output of the public-use Taser ® model is 0.3 J per pulse (personal c o m m u n i c a t i o n , Jack Cover, October 1984). The current output was estimated to range from 8.7 to 10.9 m A ) 9 Subsequent recalculation reduced the estimate to 3InA. 4 Several electrical engineering assumptions, some unsubstantiated, were used in the calculations. On the basis of these calculations, the current produced by the Taser ® appears to be under the proposed fibrillatory threshold and under the theorized asphyxia threshold. Therefore, if these estimations are correct, it appears unlikely that a Tasered victim with normal cardiopulmonary function will develop ventricular fibrillation or paralysis of respiratory muscles. The effects of the device on individuals with coronary artery disease, conduction defects (eg, sick sinus syndrome), Wolff-Parkinson-White syndrome, or preexisting arrhythmias, or on patients under the Annals of Emergency Medicine

influence of alcohol or other drugs are unknown. A single study on a Tasered human volunteer with continuous monitoring of pulse and blood pressure, and ECG monitoring has been performed (personal communication, Frank Summers, MD, October 1984). In this study the volunteer was subjected to a three-second Taser ® shock. The volunteer developed a mild elevation of blood pressure that lasted approximately two minutes and a mild increase in heart rate that lasted three to five m i n u t e s . No s i g n i f i c a n t arrhythrnias were noted. Continuous physiological monitoring of a human being during and after a Taser ® shock of more than three seconds has not been reported. No case of a Tasered victim with an implanted cardiac pacemaker has been reported. Several interactions could occur in this situation, although shielding of m o d e r n p a c e m a k e r s might preclude or minimize some of them. One of the most unlikely, yet most lethal, possibilities is that the Taser ® current could be conducted into the pacemaker catheter lead with current then flowing directly into the heart. The danger lies in the extremely low fibrillatory threshold when current is applied directly to the endocardium.2O-22 Ventricular fibrillation has been produced by 15 ~A of 60-Hz current applied to the endocardium through a standard pacemaker lead.23 Another possible interaction between Taser ® current and a demandinhibited pacemaker is the inhibition of the pacemaker as a result of the Taser® current being sensed by the pacemaker as normal and adequate cardiac electrical activity.24, 2s Induction of a very rapid ventricular-paced rate in a Tasered patient with a triggered p a c e m a k e r is a third possibility. 24 In addition, the soft warebased m e m o r y in m o r e m o d e r n pacemakers may be disrupted. A fractured pacemaker lead, resulting from sudden arm and shoulder motion secondary to accidental electrical shock, has been reported. 26 In this study, a symptomatic bradycardia ensued from the pacemaker failure to capture. The effect of Taser ® current in h u m a n beings wearing other electrical or biomechanical devices is unknown. A host of potential electrical injuries is possible. 27-3o Most of the injuries reviewed (eg, neurologic, renal, 1207/111

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vascular) have occurred as a result of exposure to c u r r e n t i n t e n s i t i e s far greater t h a n t h a t p r o d u c e d by t h e Taser ®. It appears less l i k e l y t h a t these more serious injuries (eg, rhabdomyolysis, severe bums) would occur in a Taser ® victim. In light of the lack of m o r e e x t e n s i v e h u m a n c l i n i c a l data, however, acute life-threatening problems (eg, potential cardiac injury or a r r h y t h m i a s ) should be assessed, particularly in patients w i t h k n o w n cardiac disease. 31-35 The necessity of hospital admission for postTaser cardiac evaluation or m o n i t o r i n g is unk n o w n . O n e series of e l e c t r i c a l l y shocked (not Tasered) p a t i e n t s had r e s o l u t i o n of a r r h y t h m i a s after 36 hours, g6 An easily overlooked aspect of injury in a Taser ® victim is that of the fall from a standing position. Potential injuries include contusions, lacerations, fractures, and i n t r a c r a n i a l hemorrhage. A l t h o u g h s i g n i f i c a n t damage seems unlikely, cervical spine injury is possible, and appropriate cervical spine precautions should be taken. A thorough physical examination, w i t h particular emphasis on injuries seco n d a r y to t h e fall, s h o u l d be performed. In addition, u n t i l further data are available, a postTaser ECG appears to be advisable. CONCLUSION The Taser ~ presents a new and increasingly frequent emergency medicine problem. Unlike such other k n o w n m e c h a n i s m s of injury as bullet wounds, e l e c t r o c u t i o n from household or industrial currents, and falls from heights, the Taser ® presents several unknowns. Major injuries, either primary to the current (cardiovascular or pulmonary) or secondary to the fall, have not been reported. Acute injuries in most patients have been limited to contusions, abrasions, and skin penetration by the darts. Whether there are any long-term sequelae to being Tasered remains to be determined.

The author thanks Theodore Bernstein, PhD, Department of Electrical Engineering, University of Wisconsin, Madison; Jack Cover, Taser ® inventor, Newport Beach, California; and James Niemann, MD, Department of Emergency Medicine, Harbor/UCLA Medical Center, Torrance, California, for their advice and assistance. 112/1208

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