The Medical Effects of TASERs

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Learning Objectives: After reading this article, the physician should be able to:

1. Discuss the function of the TASER.
2. Describe the known cardiac effects from use of this device.
3. Summarize the pros and cons of the use of a TASER.

Release Date: February 2008

Emergency physicians understand the need for rapid control of acutely delirious and agitated patients in the ED, and in past columns I have suggested various rationales and proposed interventions. It is intuitively obvious that patients must be able to cooperate, or at minimum, no longer flail around like a hooked barracuda in the bottom of a Florida flats boat for even a modicum of medical evaluation and treatment to begin. Prolonged agitation and struggling, especially against restraints, leads to a pathologic downward spiral, replete with metabolic acidosis, hyperthermia, rhabdomyolysis, coagulopathy, ARDS, and multisystem failure. Fatalities from uncontrolled or prolonged agitation are rare but well documented, often occurring precipitously, unexpectedly, and without warning. The physiology is usually one of PEA/bradycardia/asystole rather than ventricular fibrillation; however, once cardiac arrest occurs, it may be very difficult for resuscitation to be successful, even if medical personnel are on the scene.

Physical restraints and/or a bevy of burly security guards are often necessary to initially incapacitate a raving lunatic bent on hurting himself and everyone around him. Nonetheless, it appears prudent to expeditiously institute pharmacological restraint with doses potent enough to get the job done. I had suggested that a combination of benzodiazepines and haloperidol is the time-honored first approach to the medically undifferentiated individual, and generally this combination is the safest and most effective regimen for agitated delirium. If there is predominantly underlying psychiatric disease, there is increasing support for using rapidly acting atypical parenteral antipsychotics, such as IM olanzapine (Zyprexa) or ziprasidone (Geodon). The exact pharmacologic cocktail that is prospectively best suited for each individual circumstance has not been identified, and there is likely little difference between regimens. The key is to provide rapid and effective tranquilization so that an organized medical evaluation can commence.

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Figure: Barbed TASER darts with wires attached often have to be removed. Local lidocaine and a small puncture at the entrance site with a #11 blade usually do the trick. Photo courtesy of Joseph D'Orazio, MD

Law enforcement authorities face similar challenges in the field. They are often first on the scene, and must make important decisions with regard to their safety and the safety of everyone involved. The etiology of the delirium, the individual's underlying medical problems or metabolic milieu, or the severe co-morbidity accompanying cocaine/amphetamines, not to mention the individual's personal arsenal of dangerous weapons, simply cannot be determined before incarceration, cooperation, or submission are mandated. Many chronic stimulant users, for example, have clandestine cardiac disease, waiting to emerge as a lethal dysrhythmia when the milieu is right.

Chokeholds, hastily delivered gunshots, hogtying, and clubbing have been largely abandoned, and generally are believed to constitute unnecessary and unusual force. First responders who must quickly incapacitate a dangerous criminal have turned to the conducted electrical weapon, often called a stun gun but most commonly called a TASER, which, besides being its brand name, is the device studied in virtually all medical research because of its widespread use by law enforcement. (The TASER was designed in 1969 by Jack Cover, and was named after a fictional teenage adventurer and inventor, Thomas Swift [Thomas A. Swift's Electric Rifle].)

Unfortunately, an altercation with police can occasionally lead to the death of an alleged perpetrator. Now a police action becomes a highly charged social, racial, and emotional conundrum, an event that can draft all involved, even the EP, onto the 6 o'clock news or precipitate a neighborhood riot. The particularly unlucky ones garner instant, albeit unwanted and usually unwarranted, worldwide stardom on YouTube.com.

This month's column will attempt to put the use of the TASER into medical perspective. The TASER is loved and embraced by police, hated and disdained by human rights groups and those who have been on the receiving end of its voltage, and likely misunderstood by most. I will attempt to cull out important medical issues, and eschew the omnipresent social and legal been implicated as a direct cause of death by some, this bad rap has not been medically proven to my analysis. Medical complications can occur, but well documented serious sequelae are actually few and far between. It is certainly difficult to differentiate direct TASER complications from many other complex confounding issues. In reality, there is surprisingly little medical information identifying exactly what true medical havoc a TASER discharge actually inflicts on a human recipient of the shock.

Cardiac Electrophysiological Consequences of Neuromuscular Incapacitating Device Discharges: Cardiovascular Consequences of Stun Gun, Manthakumar K, et al J Am College Cardiol 2006;48:798

This article from the Canadian Institute of Health Research and the University of Toronto evaluated the cardiac consequences of neuromuscular incapacitation with a TASER discharge in an experimental animal model. The aim was to determine if large voltage electrical discharges dispensed from a TASER pose risks for triggering lethal cardiac arrhythmias. Given the impossibility of performing this in humans, a pig model was used.

Anesthetized pigs were monitored with intracardiac catheters and blood pressure transducers prior to the application of TASER discharges. Two commercially available models were used, and discharges were of 5 and 15 seconds duration. The devices delivered pulses of 50,000 V, 11 us to 50 us in duration, at a rate of 16 to 20 pulses per second. Per the author's introduction, this short duration of stimulation has been expected to have only a small chance of stimulating the myocardium, but will capture and stimulate nerves and skeletal muscle. The discharging wires were placed to provide two different vectors of electrical discharge, one being thoracic and parallel to the long access of the heart, and the other non-thoracic, being away from the heart (over the abdomen). In addition, an intravenous infusion of epinephrine was instituted to simulate the adrenergic storm produced by a struggling, delirious, or uncontrolled individual.

A total of 150 discharges were delivered. None of the nonthoracic discharges stimulated the heart, but about 80 percent of the over-the-heart discharges did produce electrical capture of the myocardium. When the electrical device was discharging, mechanical capture produced heart rates in the 300 beats per minute range. Only one of the discharges produced VT and one produced VF, both occurring during the epinephrine infusions. The VT spontaneously converted. It is unclear whether the epinephrine infusion or the electricity produced the ventricular arrhythmias. The authors theorized that structural heart disease could predispose to catastrophic ventricular arrhythmias when a rapid ventricular stimulation is produced by the device. They concluded that electrical TASER discharge across the chest of their experimental animal can capture the myocardium and could produce ventricular fibrillation. The intracardiac catheters may have found abnormalities not reported in other studies where surface EKGs were disrupted by the electrical discharges.

The authors were careful to avoid postulating that VF could be precipitated in humans. They caution that their model only describes the worst-case scenario in which the discharge is vectored across the heart, and they believe that their model rules out arrhythmias as a cause of death when the vectors are not across the heart or when death occurs after the discharges. Importantly, this study demonstrated that the discharges across the chest caused electrical and mechanical capture of the myocardium in this model.

In their conclusion, the authors state that their experimental model suggests that electrical discharges across the chest can produce cardiac stimulation at high rates, possibly suggesting cardiac risk in humans. Importantly, they do not conclude that the device can cause ventricular fibrillation in humans.

Comment: TASERs are being increasingly used by law enforcement officers worldwide. They have often replaced the 9 mm police handgun as the intervention of choice when other measures have failed. The device is said to deliver 50,000 volts of electricity, arching between two propelled metal barbed darts that are imbedded in the skin when the device is discharged. In reality, significantly less voltage is actually delivered to the recipient, but the myth is perpetuated by many.

The electricity is delivered through the attached wires, and is intended to produce incapacitation by severe stimulation/contraction of skeletal muscle. There has never been definitive proof that the TASER can precipitate sudden death in humans, although sudden death temporally associated with these devices has been reported. Of course, sudden death after a police struggle was around long before the TASER was invented.

When EKG monitoring has been performed in human volunteers who have received a TASER application, significant adverse cardiac electrical physiological consequences have not been found. These authors believe that their intracardiac catheters were a unique addition to the study of this device. This model actually proves that the myocardium is directly stimulated and captured.

This study has been criticized as being an artificial circumstance, and creating an electrical event not possible in humans. (J Am Coll Cardiol 2007;49[6]:732.) It has been noted that swine may be more sensitive to electrical induction of arrhythmias. Although this article may show that there is myocardial capture, there was no conclusion, even from the authors, that these data can be extrapolated to humans.

Importantly, deaths related to TASER use often occur after the discharge has finished, rendering VF an unlikely culprit. Finally, those few deaths following acute delirium that have been electrically studied demonstrate bradyarrhythmias and asystole, rather than ventricular fibrillation. Although it seems evident that the TASER can stimulate the myocardium of the pig when the electrodes are directly over the heart (but not elsewhere), it's a far stretch to state that this device can cause VF in a human when used in the manner prescribed by the manufacturer.

Effective Cocaine Intoxication on Threshold for Stun Gun Induction of Ventricular Fibrillation, Lakkireddy D, et al J Am Coll Cardiol 2006;48(4):805

This manufacturer-sponsored study sought to evaluate the effect of cocaine on TASER-induced VF threshold in a pig model. Because violent subjects who are restrained or controlled by police are often intoxicated with cocaine or other drugs, the interaction of cocaine with a TASER, particularly with the production of VF, would be an important parameter to study. Again, the adult pig model was used.

A custom device (not an actual TASER) was attached to five locations on the animal's body, and standard discharges associated with the commercially available TASER were applied. No ventricular fibrillation was seen in any of the locations before or after cocaine infusion. The electrical discharges were then escalated above the level possible with the TASER until VF was induced. The VF threshold increased as the distance of the electrodes from the heart increased.

Interestingly, cocaine increased the required strength of the electrical discharge that was required to produce ventricular capture. The study demonstrated that cocaine actually increased the safety margin by one-and-a-half to two times from baseline. The authors conclude that the use of cocaine increases the safety margin (raises the VF threshold) by 50 percent to 100 percent above baseline with regard to potential vulnerability of the pig heart to VF from the TASER discharges.

Comment: Like the previous study, the TASER was demonstrated to produce ventricular capture as the device is discharging. The studies also found that once the shock stopped, myocardial capture was lost. Therefore, if an individual maintains vital signs but collapses minutes after the event, it seems intuitively reasonable to acquit the TASER as the prime suspect. This study showed, however, that VF cannot be induced using a standard TASER discharge when it was applied to the authors' definition of the most sensitive area of the body.

The conclusion that cocaine decreases the potential for TASER-induced VF in cocaine use is an interesting one. In this study, cocaine increased the safety margin of arrythmia up to two times baseline. There was less myocardial capture after cocaine infusion. As with other studies, these authors were unable to demonstrate any cardiac enzyme leak or injury to the heart by histopathological analysis.

The Safety of the TASER

It is difficult to separate unsubstantiated newspaper articles, emotionally charged TV reports, or current YouTube videos from scientific data with regard to the safety of the TASER. Likewise, so-called scientific studies, either on volunteers or animals, are not the same as the real issue at hand. Autopsy reports often assume that the TASER is “related” to the death just because it was used premortem and because no specific cause of death can be found (not uncommon in many deaths). In the past, medical examiners have related deaths to the TASER. Most quote reports from the 1990s before any true electrical data were available. (J Forensic Sci 1991;36:434; J Forensic Sci 1992;37:956.)

It should be noted that although studies on this device are very incomplete, there is no credible proof that the TASER induces cardiac arrest when used by law enforcement officials in a prescribed manner. In fact, the voltage required to induce VF has been calculated to be 15 to 42 times the charge possible to be delivered from the TASER. (Pacing Clin Electrophys 2005;28(Suppl 1):S284.) It has been stated that there have been no documented cases of VF directly caused by the device in more than 600,000 police uses. (J Am Coll Cardiol 2007;49[6]:732.)

Contrast this with lay press headlines that the TASER kills many people. (“167 Cases of Death Following Stun-Gun Use,” Arizona Republic, February 5, 2006.) If one reads the UpToDate database, the 2007 version states that the TASER is “capable of inducing fatal arrhythmias and other injuries.” My analysis: We simply don't know for sure, but many self-proclaimed authorities come down on both sides of the debate, many have a personal, financial, or social bias, and many simply don't read the literature.

Other injuries claimed to be associated with the TASER include burns, lacerations, testicular torsion, and miscarriage. Although the concepts may be believable, these are often anecdotal and poorly characterized reports. A miscarriage two weeks after a TASER application is hardly a scientific cause-effect. Thoracic spine compression fractures from the TASER in a volunteer who did not fall but experienced severe muscle contraction has recently been reported. (Ann Emerg Med 2007;50[5]:584.) Fracture and dislocation from electrical shock are well documented.

All articles that claim the TASER can cause VF reference a short letter to the editor by Kim and Franklin (New Engl J Med 2005;353:958) titled “Ventricular Fibrillation after Stun Gun Discharge.” If one actually reads this sketchy report, it is hardly proof of the article's title. This is clearly only a worrisome observation and certainly not quotable science based on my read. Specifically, a violently agitated subject was subdued with a TASER. Later he had VF but was resuscitated to normal with ACLS interventions. No drug screen or medical history was reported.

Kroll claims that this particular case was “misreported with serious omissions.” His version (personal communication: “Obtained from police records”) was that following submission of a violently agitated man with a TASER, paramedics found a normal pulse and respirations. Twenty some minutes after this episode, the subject experienced a cardiorespiratory collapse. It is my understanding that no ventricular fibrillation was documented until many minutes after TASER use, and after interventions including multiple medic-delivered cardiac shocks, atropine and epinephrine were administered. As stated, most agitated patients die via bradycardia. I am leery of this supposed documentation of VF after TASER discharge, yet it is universally quoted. So far, I have received no response from the author to my email query.

A theoretical discussion by Ideker (Am J Forensic Med Patho 2007;28[3]:195) states that fundamental laws of electrical stimulation predicted the TASER pulse will not stimulate an ectopic beat in a large majority of normal adults. It is unlikely, at least from a theoretical stance, that a TASER can initiate ventricular fibrillation. It's a nice theoretical discussion but hardly firm clinical evidence.

Ho et al recently reported on respiratory effects of prolonged electrical weapon application to human volunteers. (Acad Emerg Med 2007;14:197.) Human volunteers received a 15-second application of electrical current while wearing respiratory measurement devices. These were certainly brave volunteers. Respiratory parameters were collected during and after exposure. The aim of the article was to see if the TASER contributed to death by impairing respirations. In this study, respiratory measurements were taken pre-exposure, during electrical weapon exposure, and during the first and second minute after exposure. No respiratory impairment was demonstrated either during prolonged continuous or prolonged intermittent TASER discharge. There was no decrease in tidal volume nor was there hypercapnia, hypoxia, or apnea associated in this volunteer model.

Other work has failed to demonstrate any significant changes in cardiac serum markers, hyperkalemia, or acidosis following TASER application. Transient mild increases in CPK and lactate were observed, likely due to muscle contraction. (Acad Emerg Med 2006;13:589.) Shocking does not cause hyperthermia (Forensic Sci Int November 2007, abstract only), and minimal testing has shown no disruption of pacemakers, ICDs, or their leads when exposed to TASERs. (Europace 2007;9[7]:551.)

Conclusions

It may be difficult to convince family members that the death of their loved one following a TASER episode by police was not related to the use of this device. After all, lightning and the electric chair kill, and he was shocked and then died, and so likely was “electrocuted.” However, it is difficult to find any credible medical evidence that such is the case or even possible. These scenarios are always multifactorial, and frequently clouded by underlying unknown heart disease, drug overdose, massive stimulant use, alcohol withdrawal, or other unknown variables. Specifically, to my analysis, ventricular fibrillation has not been demonstrated as a direct result of TASER use in humans.

Certainly the TASER dart can cause physical damage, and I have had to dig out a few during my ED shifts; a dart in the eye would be potentially blinding. (Am J Ophthalmol 2005;139:713.) Injuries from falls during muscle incapacitation can be expected, so the emergency physician needs to be aware of occult injuries, particularly cervical spine injuries. Fractures and dislocations may occur secondary to intense muscular contractions.

Many police departments have protocols mandating that all subjects who have had TASER applied be brought to the ED for medical clearance. It has not been my experience that the police politely escort the suspect into the ED wearing a cervical collar, so C-spine precautions should be high on the list of priorities for the clinician.

When I took an informal poll of my colleagues and our residents, it was the common belief, almost unanimous, that the TASER can cause death and rather frequently. Referenced sources: YouTube, newspapers, and the 6 o'clock news. The American Civil Liberties Union and Amnesty International are passionate opponents of the TASER, viewing it as an anathema at its zenith. The National Institute of Justice is a firm supporter, citing the device's safety profile.

For those interested in the social debate, I suggest you Google the web sites of these organizations and surf YouTube. Some believe that the TASER violates civil rights, and is a prime example of unnecessary force and police brutality. Any police officer will tell you that the TASER is a rather remarkable device, and many of them have to experience the TASER firsthand prior to being issued the device. Newspapers report that police injuries and the number of shot suspects have plummeted following TASER introduction.

In my experience, these devices can certainly be overused by zealous police officers, but the general consensus by the law enforcement community is that fewer policemen are injured and fewer perpetrators are shot with conventional weapons. I certainly would not like to be the recipient of a TASER application, nor would I ever like to be a police officer called to the scene of a raving lunatic with lethal weapons who is capable of gargantuan physical acts.

A civilian TASER is now available (about $400 and requiring a background check performed by the company). These devices are illegal in Philadelphia, but my wife wants one.

Finally, Boseman (Ann Emerg Med 2005;46[3]:300) has likened the TASER to the now federally mandated automobile airbags: They may harm a small subset of individuals but save the lives of countless others. Is this a reasonable tradeoff? Importantly, research into the full adverse effects of the TASER is nascent, to say the least, so the bottom line is never say never until more data are available.

Bad Press for TASERs?

Jeffrey Ho, MD, Christian Sloane, MD, and Gary Vilke, MD, all of whom have extensively researched the medical effects of TASERs, wade through the hype looking for the truth, and distill the evidence into opinions you can count on. See p. 4.

Reader Feedback: Readers are invited to ask specific questions and offer personal experiences, comments, or observations on InFocus topics. Literature references are appreciated. Pertinent responses will be published in a future issue. Please send comments to [email protected]. Dr. Roberts requests feedback on this month's column, especially personal experiences with successes, failures, and technique.

TASER Trivia

• ▪ The TASER was designed in 1969 by Jack Cover, and the TASER was named after a fictional teenage adventurer and inventor, Thomas Swift (Thomas A. Swift's Electric Rifle).
• ▪ The devices are used worldwide by about 12,000 law enforcement agencies, and an estimated 600,000 people have been shocked.
• ▪ The only readily available TASER is produced by TASER International, Inc., in Scottsdale, AZ.
• ▪ Models are M26 (military) and X26 (police). A civilian model is now available (C2).
• ▪ Barbed dart-like electrodes are propelled by nitrogen, and wires attached to the darts deliver electricity to the subject. Although 50,000 V is often quoted, significantly less is actually delivered to the subject.
• ▪ Some models have cameras to record events, and some have laser sights.
• ▪ Electric source is 8 AA batteries in the device, which deliver a pulse of electricity for five seconds, but the duration of discharge can be prolonged by the operator to 15 seconds.
• ▪ Electricity arcs between electrodes, so direct skin penetration is not always needed to incapacitate subject. Older models required darts to penetrate skin to be effective, and clothing could interfere with effect.
• ▪ Systemic effects of shock usually last a few minutes after discharge has ended.
• ▪ Maximum range is about 20 to 30 feet.
• ▪ Some models have electrodes in the tip of the device so it can be held directly against the skin and discharged without need to fire darts, hence the name “stun gun.”
• ▪ Unwanted effects include eye injury and skeletal trauma from muscle contraction and falling.

TASER Clarifies Voltage in Weapon

Dr. Roberts: The peak open circuit voltage of the TASER X26 Electronic Control Device (ECD) is approximately 50,000 volts. This voltage represents the peak voltage potential across the probes when the circuit is in the open state, that is, when no current is flowing. The 50 KV is an important factor for calculating how much clothing and air gap the arc can penetrate (the higher the peak open circuit voltage, the greater the gap that the current can arc across).

While the 50 KV potential is important for calculating how far the arc can bridge across an air gap, however, it is not relevant to the bio-effect of the current on the target person. The human subject never experiences the 50 KV because the voltage drops as soon as the arc forms and current starts to flow. It's like a blocked water hose: While the hose is blocked, the pressure builds up inside. When the blockage breaks loose and the water begins to flow, the pressure drops immediately, and the pressure measured at the output of the hose never hits the peak pressures experienced within the hose prior to the blockage breaking free. The peak voltage during current flow through the body is about 1,200 volts, and the average voltage during the 100-microsecond duration of the pulse is about 400 volts. I hope this clarifies the operation of our technology. — Rick Smith, Chief Executive Officer, TASER International, Inc., Scottsdale, AZ

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