Are TASERs Safe for the Heart?

The TASER and How It Works

Electrical stun guns or neuromuscular incapacitating devices are increasingly being used by law enforcement to subdue suspects. The TASER is the most popular kind of these devices (TASER International, Inc., Scottsdale, AZ).¹ Its name is an acronym for the Thomas A. Swift Electric Rifle; the product was invented in the USA by Jack Cover, a NASA researcher, in the 1960s.² Different models of these devices have been introduced by the manufacturer. Among these, two models (M26c and X26c) are the ones most commonly used by police.³ A newly-introduced model, the X3, is capable of firing three cartridges in a "semi-automatic" mode.⁴ Moreover, TASER International has produced a model for civilians called the C2.⁵

The TASER resembles a handgun; however, instead of bullets, it ejects barbs which attach to the victim’s clothing or skin.

Then, a high-frequency, high-voltage, low-amplitude current is delivered via these barbs, causing involuntary muscle contraction and neuromuscular incapacitation.^1,2 Typically, this painful current stops suspects abruptly and drops them immediately to the ground. The TASER can also be deployed by holding it directly against the suspect’s body. This is called “drive stun” or “dry TASERing,” and is intended to cause pain without incapacitating the target.⁶

Although TASERs are acknowledged to be a safer alternative to firearms, there is some evidence that suggests the TASER might not be safe enough to be used widespread by law enforcement officials.¹

The TASER Debate

Even though many studies and reports have been published regarding the TASER’s safety, there is still no consensus. Some studies suggest that the TASER can directly pace the heart into ventricular fibrillation (VF). In North America, over 440 deaths have been reported immediately following TASER use.⁷ Two mechanisms have been previously proposed for inducing VF with electrical currents⁸: 1) Delivering a high-charge shock into the T-wave during the cardiac cycle; and 2) Delivering a lower level current for a longer time (e.g., 1–5 seconds). Current electrical safety standards are based on this knowledge. Kroll et al have presented another mechanism by which VF can be induced. This third newly presented mechanism involves the delivery of a continuous current causing high-rate cardiac capture. This eventually decreases the cardiac output, leading to ischemia and ultimately lowering the threshold of VF to the level at which the continuous current can induce VF.⁸ In summary, if the TASER could capture and pace heart muscle, there are several ways that VF could be induced.

Animal studies in pigs have shown that TASERs can indeed capture ventricular myocardium when the electrical vector is near the heart.^9-11 Other animal studies have been able to show induction of VF with standard TASER discharges.^11-13 Critics charge that these animal studies are artificially created situations in non-human subjects that make the TASER appear more dangerous than they are in the real world.¹⁴ However, case reports of humans being TASERed suggest that there is true risk of ventricular myocardium capture and induction of VF. One case report demonstrated capture of ventricular myocardium at high rates,¹⁵ and another described a victim who was found in VF after TASER application.¹⁶ Further evidence that electrical stun guns can capture ventricular myocardium and thereby induce VF comes from TASER International, Inc. funded research, in which they tested a new generation TASER that is able to eject multiple barbs simultaneously. In this study, subjects were exposed to two probes near the heart, and an apparent brief episode of cardiac capture was observed. Testing was immediately halted, and the manufacturer was notified. After redesigning the device, the study continued with a new version of the next generation TASER.¹⁷ Although testing with the new device showed no cardiac capture, this research seems to prove that cardiac capture is possible with these types of devices in real-world type situations.

Supporters of the TASER have pointed at numerous human studies that have shown no apparent harm from the device. However, in most of these studies, the current is applied to the back of resting, healthy volunteers.^18-21 Critics of the TASER contend that these experiments with subjects in a controlled environment are a poor approximation of the real-world situations in which the TASER is used. In the real world, police suspects resisting arrest likely have some specific conditions including hyperadrenergic state, being trapped in restraints, multiple TASER applications near the heart on the torso, and external influences (illicit drugs), any of which may put them at higher risk for sudden death.

While most researchers are evaluating the possible cardiac effects of TASERs by determining whether TASERs can directly pace the heart into a lethal ventricular tachyarrhythmia, either by extreme rapid pacing or discharge during the vulnerable period in the cardiac cycle, there are other investigators who believe that TASERs may also increase the risk of sudden death by another mechanism termed excited delirium.²² Excited delirium is a much-debated condition, which may result in sudden death after a violent struggle, often with police forces.^23,24 The exact mechanism of excited delirium is unknown, but it is likely that a surge in adrenergic tone, hyperthermia, or acidosis may decrease the threshold for life-threatening arrhythmia.^22,24 Another possible contributory factor in excited delirium is the severe pain during TASER application, which would lead to an increase in adrenergic tone. In addition, studies in both animal models and in humans have shown that TASER deployment can cause transient acidosis, which might play a role in development of excited delirium.^25,26 Therefore, excited delirium may be another potential mechanism by which TASERs may harm suspects. There are critics of the connection between TASERs and excited delirium; they argue that since the mechanism of this entity has not been clearly elucidated, it is unfair to cite the TASER as a contributor.²⁷

In addition, there are two reports describing the occurrence of myocardial infarction (MI) after TASER deployment.^28,29 Traumatic events after the TASER application have also been described, including ocular injuries, which mostly happen as a consequence of penetrating barbs. Injuries can include eyelid trauma, mydriasis, iritis, cataracts, macular cysts, optic neuritis, and globe penetration.²

There is a lack of epidemiological data regarding the safety of the TASER. The data collection concerning the use of the TASER and its consequences is not uniform, and is done sporadically by police departments. Nevertheless, we did a study in which we collected data from several police departments in California using the TASER. Our results showed a statistically significant 6.4-fold increase in the rate of in-custody sudden deaths not involving lethal (firearm) force in the first full year of TASER deployment compared to the predeployment period. There was no decrease in the rate of officer injuries as one might expect with the introduction of TASERs to the officers. Notably, the rate of in-custody sudden deaths did go back down to predeployment levels after the first full year of TASER use.¹

Recently, the controversy over TASERs has become even more contentious with the finding that there may be bias in the TASER literature. In a recently published article, we showed that among studies in which an author was affiliated with TASER International, Inc., 96% of the studies concluded the device was unlikely harmful (26%) or not harmful (70%). In contrast, among the studies of which none of the authors had an affiliation with the company, only 55% concluded that TASERs are unlikely harmful (29%) or not harmful (26%). The studies in which the author was affiliated with TASER International, Inc. had 18 times higher odds of concluding that the device was safe, suggesting that the literature may be severely biased.³⁰

The Next Step

The deficiencies in our current knowledge about TASER safety can be summarized into three main problems: 1) Lack of TASER studies where real-world situations are replicated; 2) Lack of epidemiological data about the TASER application and in-custody sudden deaths; and 3) Possible bias in the TASER literature. To address these problems, we have to design studies in which the conditions tested resemble the real world. Performing tests only in resting and fully anesthetized animal models seem to be insufficient. We need to collect accurate epidemiological data and devise a uniform data-gathering system and registry. To achieve this goal, police departments need to cooperate and disclose the cases of in-custody sudden deaths. Finally, due to the importance of this issue, we need to find ways to support independent researchers to do TASER-related research.

Conclusion

At this point, there is no consensus on whether TASERs are safe enough for widespread use by law enforcement. Some studies and case reports describe the possibility of the TASER pacing the heart into VF and causing sudden death. Despite these findings, other investigators claim that this risk is low enough for TASERs to be added to the options police have to subdue suspects. As the TASER is becoming more common among law enforcement, more research is highly recommended.

Disclosure. The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript.

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