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Cardiac Stimulation with Electronic Control Device Application
The Journal of Emergency Medicine, Vol. 47, No. 4, pp. 486–492, 2014 Copyright Ó 2014 Elsevier Inc. Printed in the USA. All rights reserved 0736-4679/$ - see front matter
http://dx.doi.org/10.1016/j.jemermed.2014.06.019
Brief Reports CARDIAC STIMULATION WITH ELECTRONIC CONTROL DEVICE APPLICATION Scott M. Koerber, DO,* Sivakumar Ardhanari, MD,* Wayne C. McDaniel, PHD,† Anand Chockalingam, MD,* Pawell Zymek, MD,* and Greg Flaker, MD* *Department of Internal Medicine and †Department of Electrical and Computer Engineering, University of Missouri, Columbia, Missouri Reprint Address: Greg Flaker, MD, Department of Internal Medicine, University of Missouri, One Hospital Drive, CE306, Columbia, MO 65212
, Abstract—Background: Electronic control devices (ECDs) are weapons used to incapacitate violent subjects. Subjects have died suddenly after ECD application, but because cardiac dysrhythmias have been inconsistently observed during ECD application in animals, the cause for death is uncertain. Objectives: The objective was to identify the factors contributing to cardiac stimulation during ECD application detected by transesophageal echocardiography. Methods: Four Yorkshire pigs were anesthetized, paralyzed with vecuronium, and restrained in a supine position. A GE 6T echo probe was placed in the esophagus to directly visualize left ventricular function. M-mode echocardiography was used to estimate heart rate. Two dart locations, chest and abdomen, were assessed. ECD applications were delivered from one of five commercially available devices (Taser X26, Singer S200 AT, Taser M26, Taser X3, and Taser C2) in random order to each pig, four times in each orientation. Results: Cardiac stimulation, characterized by multiple PVCs or the sudden increase in ventricular contraction rate during application, did not occur with abdominal dart location. With chest dart application in small pigs, cardiac stimulation occurred with all ECDs except with the Taser X3 (p < 0.0001). In large pigs, cardiac stimulation occurred only during chest application of the S200 AT (chest vs. abdomen: 207 beats/min, vs. 91 beats/min, p < 0.0001). Conclusion: Cardiac stimulation occurs during ECD application in pigs, and is dependent upon subject size, dart orientation, and ECD. The Taser X3 did not result in cardiac stimulation in small or large pigs. Ó 2014 Elsevier Inc.
INTRODUCTION Electronic control devices (ECDs) are electrical devices used by both law enforcement officials and citizens to incapacitate violent subjects. ECDs function by shooting two barbed probes into the subject’s skin or clothes. The probes are connected to the device by conductive wires, which deliver a series of rapid pulses of high-voltage electrical shocks that cause involuntary muscle contraction to subdue the subject. ECDs are emerging as one of several intermediate-force options available to law enforcement officers as an alternative to firearms. As of March 31, 2011, there have been an estimated 1.27 million uses of ECDs by law enforcement officers (1). Prior studies have found that the use of ECDs results in a decrease in injury rates among both criminals and police officers (2,3). Due to the delivery of electrical shocks to the thorax, concern has been raised that fatal cardiac dysrhythmias may result from ECD application. Over 400 deaths have been associated with their use from 2001 to 2008, but the exact cause of death is unclear (4). The induction of ventricular dysrhythmias has not been consistently observed in animal studies and it remains uncertain if cardiac stimulation occurs during ECD application in humans (5–8). Due to this, a number of other explanations for the ECD-associated deaths have been proposed. These include metabolic or electrolyte abnormalities, and excited delirium syndrome, which is described
, Keywords—TASER; electronic control device; cardiac stimulation; stun gun; dysrhythmia
RECEIVED: 25 January 2013; FINAL SUBMISSION RECEIVED: 17 March 2014; ACCEPTED: 30 June 2014 486
Effect of FFP Transfusion on INR
as agitation, incoherence, hyperthermia, and violent behavior (9). During experimental ECD application in animals, detection of cardiac stimulation has been challenging. Surface ECG tracings become saturated with electrical and motion artifact during ECD discharge, which complicates the detection of heart rate or cardiac rhythm. Transthoracic echocardiography has been used in some studies of ECD cardiac stimulation, but offers limited windows with further degradation of image quality due to chest muscle contraction. We hypothesized that ECD-induced cardiac stimulation could be detected and quantified better with transesophageal echocardiography (TEE). We further hypothesized that if cardiac stimulation did occur, it would vary depending on subject size, dart location, and the characteristics of the various waveforms of commercially available ECDs. METHODS This study was reviewed and approved by the appropriate Institutional Animal Care and Use Committee. Pigs were selected for the study due to their use in past studies of cardiac stimulation by ECDs (5–8). Five commercially available ECDs, the TASER M26, TASER X26, TASER X3, TASER C2 (all from TASER International, Scottsdale, AZ), and the Stinger S-200AT (Stinger Systems, Tampa, FL) were tested during these
Figure 1. Waveforms of each electronic control device.
487
experiments. The devices tested were supplied to the investigators by the Oakland Police Force, along with a grant to partially fund this study. These devices differ in output waveform, pulse duration, and amplitude (Figure 1, waveforms of each ECD). Each ECD was applied individually to a 400-U resistor to capture the images shown in Figure 1, and to allow us to assess the differences in output waveform. Four Yorkshire pigs: Group 1 (n = 2, 25 6 0 kg) and Group 2 (n = 2, 69.4 6 1.6 kg) were anesthetized, paralyzed with vecuronium, and restrained in a supine position. A femoral artery was cannulated to allow the monitoring of arterial blood pressure, and to allow collection of arterial blood samples. Arterial blood gas and electrolytes were monitored every 30 to 40 min, and corrected to maintain them within normal limits. A GE 6T echo probe was placed in the esophagus to directly monitor cardiac function, mitral valve function, and to assess heart rate during ECD application. Two dart locations, a chest orientation and an abdominal orientation, were assessed (Figure 2). In the chest orientation, two darts were placed subcutaneously to maximal depth (12 mm), with one dart 4–7 cm right of the sternal notch and one dart 7–10 cm left of the umbilicus. In the abdominal orientation, the darts were positioned 7–10 cm lateral to each side of the umbilicus. Each ECD was applied in random order to each pig, four times in the same orientation separated by at least
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Cardiac stimulation was not detected in any ECD application in the abdominal orientation, thus, this served as a baseline or resting heart rate (Figure 4). Cardiac stimulation did not occur in large animals except with the S200 AT in the chest orientation. Cardiac stimulation was dependent upon the ECD. The Taser X3 did not result in cardiac stimulation in any of the scenarios tested (Figure 4). Chest application of the Taser M26 in small pigs did result in cardiac stimulation, but at a much slower rate compared to the Taser X26, Taser C2, and Stinger S200 AT (Figure 4A). In total, there were 40 ECD applications in each pig, consisting of four from each device in the abdominal orientation and four from each device in the chest orientation. During the total of 160 ECD applications, ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) was not observed. DISCUSSION Figure 2. Recumbent anesthetized pig. Image adapted from Khaja et al. (8). SN = sternal notch; U = umbilicus; CO = cardiac orientation; AO = abdominal orientation.
2 min. Because each device had its own set of probes, which had to be inserted into the skin, all shocks from one device in one probe orientation were delivered in succession. After each device was applied in the first orientation, this process was repeated in the other orientation. The trigger was pulled one time and released during the application. Each device has a standard discharge duration ranging from 4–5 s. The TEE images of each ECD application were recorded to assess heart rate and function more closely. These TEE images were later interpreted by an author that was blinded to the pig size, type of ECD being applied, and the orientation being used. Heart rate was calculated by measuring left ventricular myocardial contractions using M-mode on the TEE for each ECD application. RESULTS Cardiac stimulation was detected by transesophageal echocardiography during some ECD applications. It was characterized by a spectrum of abrupt changes in heart rate, ranging from frequent ventricular ectopy to very rapid myocardial motion. It was followed by resumption of normal cardiac rhythm and heart rate after termination of the ECD application. An example of the heart rate determination during the ECD application using M-mode echocardiography is shown in Figure 3. In Figure 3A, the heart rate was estimated to be 239 beats/ min, whereas in Figure 3B, the heart rate was estimated to be 97 beats/min.
This study has three important findings. First, cardiac stimulation occurs with ECD applications in pigs, which can be quantified using TEE. Second, cardiac stimulation is dependent upon both subject size and dart location. Third, the type of ECD, with variation in pulse amplitude, pulse duration, and waveform characteristics is an important determinant of cardiac stimulation. There have been several animal studies, including ours, that have demonstrated cardiac stimulation resulting from ECDs (5–7,10,11). Many studies have used the surface ECG to assess heart rhythm during ECD application, but due to electrical interference from the ECD, the surface ECG is difficult to see clearly. By using TEE, left ventricular function and mitral valve motion could be visualized prior to, during, and after ECD applications. The ECD application resulted in abrupt changes in heart rate ranging from occasional myocardial capture to the onset of rapid myocardial motion similar to ventricular flutter. Based on the high temporal resolution of M mode, this ECD capture rate could be reproducibly measured. This methodology is the best way we have found to assess cardiac ECD stimulation. Valentino et al. previously studied the effect of dart location in cardiac stimulation with the TASER X26 by using transthoracic echocardiography (7). In their study, multiple dart locations were tested, and they found the transcardiac orientation to be the most likely to stimulate the heart. They reported that 85.2% of the ECD applications in the transcardiac orientation stimulated the heart (7). Our study found very similar results, in that 100% of the ECDs applications that resulted in cardiac stimulation occurred in the chest orientation. However, a criticism of Valentino’s study was the use of relatively small pigs ranging in weight from 25–36 kg.
Effect of FFP Transfusion on INR
489
Figure 3. M-mode echocardiography shows heart rate of Taser X26 in a small pig. (A) Chest orientation, heart rate 239 beats/min. (B) Abdominal orientation, heart rate 97 beats/min.
Our study, by looking at two different weight groups (mean weights 25 kg for small and 67 kg for large pigs), demonstrated that cardiac stimulation is dependent upon subject size, and is more likely to occur in smaller pigs. One possible explanation for smaller pigs being more susceptible to dysrhythmias from ECDs is the closer proximity of the darts to the pig’s heart. This effect was examined in multiple studies by Wu et al. and Lakkireddy et al. (12–14). Both groups reported that the risk of inducing VF decreased exponentially as the dart-to-heart distance increased. Smaller pigs have a smaller dart-toheart distance, and therefore are more likely to have cardiac stimulation resulting from ECD exposure. Despite multiple ECD applications that resulted in cardiac stimulation, no sustained VT or VF was observed in
our study. However, fatal dysrhythmias resulting from ECDs have been demonstrated in pigs (5,7,12). Multiple reported cases of in-custody deaths after ECD exposure have raised concern about the safety of these devices (4,15,16). A recent study by Zipes examined eight cases of ECD use leading to fatal dysrhythmias (VF, VT, or asystole) (15). In these cases, the fatal rhythm was established minutes after the ECD application, whereas the rhythm prior to and during ECD application was unknown. An estimated risk of VF from ECD exposure was calculated by Kroll et al. (17). Accounting for body mass index and gender, they reported a theoretical VF risk of 1 per 2.5 million ECD exposures for TASER devices. Differences in electrical output of ECDs influence their ability to stimulate the heart. The devices vary in
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Figure 4. Heart rate response during electronic control device application: (A) small pigs; (B) large pigs. *Chest vs abdominal p # 0.0001.
waveform shape, pulse amplitude, waveform duration, and pulse-repetition frequency. The TASER X3, characterized by a monophasic waveform, short pulse duration, and low amplitude, was the only device that did not stimulate the heart in any scenario tested, which suggests this output waveform could be the safest from a cardiac stimulation standpoint. However, given the number of variables between the devices, it is impossible to know which variable is most influential. More studies need to be done that reduce or eliminate some of the variables during ECD tests. For example, if we had the ability to generate an ECD waveform with a constant pulse duration, and we could vary the ECD pulse amplitude, then we could estimate a ‘‘threshold’’ of cardiac stimulation. Limitations Despite the statistically significant results, this study was done on a small sample size of only four subjects.
This study was designed to detect cardiac stimulation in an animal model, and these results will have to be extrapolated to humans. Typical scenarios possibly leading to fatal dysrhythmia in humans, such as illicit drug use and agitation, could not be recreated in our study. In addition, even though a device might not cause cardiac stimulation in an animal model, this might not be true in human applications. CONCLUSION Our data suggest that not all ECDs are created equal. Some ECDs generate shocks that make them more likely to stimulate the heart of experimental animals. Cardiac stimulation occurs during ECD applications, and this can be observed and quantified better using TEE than other experimental methods used in prior studies. Cardiac stimulation is dependent upon subject size, dart location, and ECD device.
Effect of FFP Transfusion on INR Acknowledgments—Department of Veterans Affairs, VISN 15 Research Award; and a research grant from the Oakland, CA Police Force.
REFERENCES 1. Brewer JE, Kroll MW. Field statistics overview. In: Kroll MW, Ho JD, eds. TASER conducted electrical weapons: physiology, pathology, and law. New York: Springer-Kluwer; 2009:283–301. 2. Jenkinson E, Neeson C, Bleetman A. The relative risk of police useof-force options: evaluating the potential for deployment of electronic weaponry. J Clin Forensic Med 2006;13:229–41. 3. Smith MR, Kaminski RJ, Rojek J, Alpert GP, Mathis J. The impact of conducted energy devices and other types of force and resistance on officer and suspect injuries. Policing 2007;30:423–46. 4. Swerdlow CD, Fishbein MC, Chaman L, Lakkireddy DR, Tchou P. Presenting rhythm in sudden deaths temporally proximate to discharge of TASER conducted electrical weapons. Acad Emerg Med 2009;16:726–39. 5. Dennis AJ, Valentino DJ, Walter RJ, et al. Acute effects of TASER X26 discharges in a swine model. J Trauma 2007;63:581–90. 6. Walter RJ, Dennis AJ, Valentino DJ, et al. TASER X26 discharges in swine produce potentially fatal ventricular arrhythmias. Acad Emerg Med 2008;15:66–73. 7. Valentino DJ, Walter RJ, Dennis AJ, et al. Taser X26 discharges in swine: ventricular rhythm capture is dependent on discharge vector. J Trauma 2008;65:1478–85. discussion 1485–7.
491 8. Khaja A, Govindarajan G, McDaniel W, Flaker G. Cardiac safety of conducted electrical devices in pigs and their effect on pacemaker function. Am J Emerg Med 2011;29:1089–96. 9. Di Maio TG, Di Maio VJM. Excited delirium syndrome cause of death and prevention. Boca Raton, FL: Taylor and Francis; 2006. 10. Dawes DM, Ho JD, Cole JB, et al. Effect of an electronic control device exposure on a methamphetamine-intoxicated animal model. Acad Emerg Med 2010;17:436–43. 11. McDaniel WC, Stratbucker RA, Nerheim M, Brewer JE. Cardiac safety of neuromuscular incapacitating defensive devices. Pacing Clin Electrophysiol 2005;28(Suppl 1):S284–7. 12. Wu JY, Sun H, O’Rourke AP, et al. Taser blunt probe dart-to-heart distance causing ventricular fibrillation in pigs. IEEE Trans Biomed Eng 2008;55:2768–71. 13. Lakkireddy D, Sun H, O’Rourke AP, et al. Taser blunt probe dart-toheart distance causing ventricular fibrillation in pigs. IEEE Trans Biomed Eng 2008;31:398–408. 14. Lakkireddy D, Wallick D, Ryschon K, et al. Effects of cocaine intoxication on the threshold for stun gun induction of ventricular fibrillation. J Am Coll Cardiol 2006;48:805–11. 15. Zipes DP. Sudden cardiac arrest and death following application of shocks from a TASER electronic control device. Circulation 2012; 125:2417–22. 16. Bozeman WP, Hauda WE 2nd, Heck JJ, Graham DD Jr, Winslow JE. Safety and injury profile of conducted electrical weapons used by law enforcement officers against criminal suspects. Ann Emerg Med 2009;53:480–9. 17. Kroll MW, Lakkireddy D, Rahko PS, Panescu D. Ventricular fibrillation risk estimation for conducted electrical weapons: critical convolutions. Conf Proc IEEE Eng Med Biol Soc 2011;2011:271–7.
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ARTICLE SUMMARY 1. Why is this topic important? Due to the increasing use of electronic control devices (ECDs), the number of deaths associated with their use is also increasing. Although some theories attempt to link the deaths to cardiac dysrhythmias resulting from the ECD, the exact mechanism is still unclear. 2. What does this study attempt to show? This study looks at different factors that may contribute to fatal dysrhythmias caused by ECD application. These factors include subject size, dart location, and specific differences in each ECD waveform. Once these factors are identified, a safer, more efficient ECD can be created. 3. What are the key findings? There are three key findings from this study. First, cardiac stimulation was detected during some ECD applications and was able to be quantified using transesophageal echocardiography. Second, cardiac stimulation was dependent not only upon subject size and dart location, but also on differences in the type of ECD. Cardiac stimulation occurred most frequently in small pigs with the dart placed across the heart. Third, despite proving cardiac stimulation can occur during ECD application, no fatal or sustained dysrhythmias were seen. 4. How is patient care impacted? Once the factors that contribute to cardiac stimulation are identified, it may be possible to create a safer and more efficient ECD. This will cut down on the number of deaths associated with ECD use. Once the exact mechanism is found, specific measures might be able to be taken to prevent fatal dysrhythmias.
http://dx.doi.org/10.1016/j.jemermed.2014.06.019
Brief Reports CARDIAC STIMULATION WITH ELECTRONIC CONTROL DEVICE APPLICATION Scott M. Koerber, DO,* Sivakumar Ardhanari, MD,* Wayne C. McDaniel, PHD,† Anand Chockalingam, MD,* Pawell Zymek, MD,* and Greg Flaker, MD* *Department of Internal Medicine and †Department of Electrical and Computer Engineering, University of Missouri, Columbia, Missouri Reprint Address: Greg Flaker, MD, Department of Internal Medicine, University of Missouri, One Hospital Drive, CE306, Columbia, MO 65212
, Abstract—Background: Electronic control devices (ECDs) are weapons used to incapacitate violent subjects. Subjects have died suddenly after ECD application, but because cardiac dysrhythmias have been inconsistently observed during ECD application in animals, the cause for death is uncertain. Objectives: The objective was to identify the factors contributing to cardiac stimulation during ECD application detected by transesophageal echocardiography. Methods: Four Yorkshire pigs were anesthetized, paralyzed with vecuronium, and restrained in a supine position. A GE 6T echo probe was placed in the esophagus to directly visualize left ventricular function. M-mode echocardiography was used to estimate heart rate. Two dart locations, chest and abdomen, were assessed. ECD applications were delivered from one of five commercially available devices (Taser X26, Singer S200 AT, Taser M26, Taser X3, and Taser C2) in random order to each pig, four times in each orientation. Results: Cardiac stimulation, characterized by multiple PVCs or the sudden increase in ventricular contraction rate during application, did not occur with abdominal dart location. With chest dart application in small pigs, cardiac stimulation occurred with all ECDs except with the Taser X3 (p < 0.0001). In large pigs, cardiac stimulation occurred only during chest application of the S200 AT (chest vs. abdomen: 207 beats/min, vs. 91 beats/min, p < 0.0001). Conclusion: Cardiac stimulation occurs during ECD application in pigs, and is dependent upon subject size, dart orientation, and ECD. The Taser X3 did not result in cardiac stimulation in small or large pigs. Ó 2014 Elsevier Inc.
INTRODUCTION Electronic control devices (ECDs) are electrical devices used by both law enforcement officials and citizens to incapacitate violent subjects. ECDs function by shooting two barbed probes into the subject’s skin or clothes. The probes are connected to the device by conductive wires, which deliver a series of rapid pulses of high-voltage electrical shocks that cause involuntary muscle contraction to subdue the subject. ECDs are emerging as one of several intermediate-force options available to law enforcement officers as an alternative to firearms. As of March 31, 2011, there have been an estimated 1.27 million uses of ECDs by law enforcement officers (1). Prior studies have found that the use of ECDs results in a decrease in injury rates among both criminals and police officers (2,3). Due to the delivery of electrical shocks to the thorax, concern has been raised that fatal cardiac dysrhythmias may result from ECD application. Over 400 deaths have been associated with their use from 2001 to 2008, but the exact cause of death is unclear (4). The induction of ventricular dysrhythmias has not been consistently observed in animal studies and it remains uncertain if cardiac stimulation occurs during ECD application in humans (5–8). Due to this, a number of other explanations for the ECD-associated deaths have been proposed. These include metabolic or electrolyte abnormalities, and excited delirium syndrome, which is described
, Keywords—TASER; electronic control device; cardiac stimulation; stun gun; dysrhythmia
RECEIVED: 25 January 2013; FINAL SUBMISSION RECEIVED: 17 March 2014; ACCEPTED: 30 June 2014 486
Effect of FFP Transfusion on INR
as agitation, incoherence, hyperthermia, and violent behavior (9). During experimental ECD application in animals, detection of cardiac stimulation has been challenging. Surface ECG tracings become saturated with electrical and motion artifact during ECD discharge, which complicates the detection of heart rate or cardiac rhythm. Transthoracic echocardiography has been used in some studies of ECD cardiac stimulation, but offers limited windows with further degradation of image quality due to chest muscle contraction. We hypothesized that ECD-induced cardiac stimulation could be detected and quantified better with transesophageal echocardiography (TEE). We further hypothesized that if cardiac stimulation did occur, it would vary depending on subject size, dart location, and the characteristics of the various waveforms of commercially available ECDs. METHODS This study was reviewed and approved by the appropriate Institutional Animal Care and Use Committee. Pigs were selected for the study due to their use in past studies of cardiac stimulation by ECDs (5–8). Five commercially available ECDs, the TASER M26, TASER X26, TASER X3, TASER C2 (all from TASER International, Scottsdale, AZ), and the Stinger S-200AT (Stinger Systems, Tampa, FL) were tested during these
Figure 1. Waveforms of each electronic control device.
487
experiments. The devices tested were supplied to the investigators by the Oakland Police Force, along with a grant to partially fund this study. These devices differ in output waveform, pulse duration, and amplitude (Figure 1, waveforms of each ECD). Each ECD was applied individually to a 400-U resistor to capture the images shown in Figure 1, and to allow us to assess the differences in output waveform. Four Yorkshire pigs: Group 1 (n = 2, 25 6 0 kg) and Group 2 (n = 2, 69.4 6 1.6 kg) were anesthetized, paralyzed with vecuronium, and restrained in a supine position. A femoral artery was cannulated to allow the monitoring of arterial blood pressure, and to allow collection of arterial blood samples. Arterial blood gas and electrolytes were monitored every 30 to 40 min, and corrected to maintain them within normal limits. A GE 6T echo probe was placed in the esophagus to directly monitor cardiac function, mitral valve function, and to assess heart rate during ECD application. Two dart locations, a chest orientation and an abdominal orientation, were assessed (Figure 2). In the chest orientation, two darts were placed subcutaneously to maximal depth (12 mm), with one dart 4–7 cm right of the sternal notch and one dart 7–10 cm left of the umbilicus. In the abdominal orientation, the darts were positioned 7–10 cm lateral to each side of the umbilicus. Each ECD was applied in random order to each pig, four times in the same orientation separated by at least
488
S. M. Koerber et al.
Cardiac stimulation was not detected in any ECD application in the abdominal orientation, thus, this served as a baseline or resting heart rate (Figure 4). Cardiac stimulation did not occur in large animals except with the S200 AT in the chest orientation. Cardiac stimulation was dependent upon the ECD. The Taser X3 did not result in cardiac stimulation in any of the scenarios tested (Figure 4). Chest application of the Taser M26 in small pigs did result in cardiac stimulation, but at a much slower rate compared to the Taser X26, Taser C2, and Stinger S200 AT (Figure 4A). In total, there were 40 ECD applications in each pig, consisting of four from each device in the abdominal orientation and four from each device in the chest orientation. During the total of 160 ECD applications, ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) was not observed. DISCUSSION Figure 2. Recumbent anesthetized pig. Image adapted from Khaja et al. (8). SN = sternal notch; U = umbilicus; CO = cardiac orientation; AO = abdominal orientation.
2 min. Because each device had its own set of probes, which had to be inserted into the skin, all shocks from one device in one probe orientation were delivered in succession. After each device was applied in the first orientation, this process was repeated in the other orientation. The trigger was pulled one time and released during the application. Each device has a standard discharge duration ranging from 4–5 s. The TEE images of each ECD application were recorded to assess heart rate and function more closely. These TEE images were later interpreted by an author that was blinded to the pig size, type of ECD being applied, and the orientation being used. Heart rate was calculated by measuring left ventricular myocardial contractions using M-mode on the TEE for each ECD application. RESULTS Cardiac stimulation was detected by transesophageal echocardiography during some ECD applications. It was characterized by a spectrum of abrupt changes in heart rate, ranging from frequent ventricular ectopy to very rapid myocardial motion. It was followed by resumption of normal cardiac rhythm and heart rate after termination of the ECD application. An example of the heart rate determination during the ECD application using M-mode echocardiography is shown in Figure 3. In Figure 3A, the heart rate was estimated to be 239 beats/ min, whereas in Figure 3B, the heart rate was estimated to be 97 beats/min.
This study has three important findings. First, cardiac stimulation occurs with ECD applications in pigs, which can be quantified using TEE. Second, cardiac stimulation is dependent upon both subject size and dart location. Third, the type of ECD, with variation in pulse amplitude, pulse duration, and waveform characteristics is an important determinant of cardiac stimulation. There have been several animal studies, including ours, that have demonstrated cardiac stimulation resulting from ECDs (5–7,10,11). Many studies have used the surface ECG to assess heart rhythm during ECD application, but due to electrical interference from the ECD, the surface ECG is difficult to see clearly. By using TEE, left ventricular function and mitral valve motion could be visualized prior to, during, and after ECD applications. The ECD application resulted in abrupt changes in heart rate ranging from occasional myocardial capture to the onset of rapid myocardial motion similar to ventricular flutter. Based on the high temporal resolution of M mode, this ECD capture rate could be reproducibly measured. This methodology is the best way we have found to assess cardiac ECD stimulation. Valentino et al. previously studied the effect of dart location in cardiac stimulation with the TASER X26 by using transthoracic echocardiography (7). In their study, multiple dart locations were tested, and they found the transcardiac orientation to be the most likely to stimulate the heart. They reported that 85.2% of the ECD applications in the transcardiac orientation stimulated the heart (7). Our study found very similar results, in that 100% of the ECDs applications that resulted in cardiac stimulation occurred in the chest orientation. However, a criticism of Valentino’s study was the use of relatively small pigs ranging in weight from 25–36 kg.
Effect of FFP Transfusion on INR
489
Figure 3. M-mode echocardiography shows heart rate of Taser X26 in a small pig. (A) Chest orientation, heart rate 239 beats/min. (B) Abdominal orientation, heart rate 97 beats/min.
Our study, by looking at two different weight groups (mean weights 25 kg for small and 67 kg for large pigs), demonstrated that cardiac stimulation is dependent upon subject size, and is more likely to occur in smaller pigs. One possible explanation for smaller pigs being more susceptible to dysrhythmias from ECDs is the closer proximity of the darts to the pig’s heart. This effect was examined in multiple studies by Wu et al. and Lakkireddy et al. (12–14). Both groups reported that the risk of inducing VF decreased exponentially as the dart-to-heart distance increased. Smaller pigs have a smaller dart-toheart distance, and therefore are more likely to have cardiac stimulation resulting from ECD exposure. Despite multiple ECD applications that resulted in cardiac stimulation, no sustained VT or VF was observed in
our study. However, fatal dysrhythmias resulting from ECDs have been demonstrated in pigs (5,7,12). Multiple reported cases of in-custody deaths after ECD exposure have raised concern about the safety of these devices (4,15,16). A recent study by Zipes examined eight cases of ECD use leading to fatal dysrhythmias (VF, VT, or asystole) (15). In these cases, the fatal rhythm was established minutes after the ECD application, whereas the rhythm prior to and during ECD application was unknown. An estimated risk of VF from ECD exposure was calculated by Kroll et al. (17). Accounting for body mass index and gender, they reported a theoretical VF risk of 1 per 2.5 million ECD exposures for TASER devices. Differences in electrical output of ECDs influence their ability to stimulate the heart. The devices vary in
490
S. M. Koerber et al.
Figure 4. Heart rate response during electronic control device application: (A) small pigs; (B) large pigs. *Chest vs abdominal p # 0.0001.
waveform shape, pulse amplitude, waveform duration, and pulse-repetition frequency. The TASER X3, characterized by a monophasic waveform, short pulse duration, and low amplitude, was the only device that did not stimulate the heart in any scenario tested, which suggests this output waveform could be the safest from a cardiac stimulation standpoint. However, given the number of variables between the devices, it is impossible to know which variable is most influential. More studies need to be done that reduce or eliminate some of the variables during ECD tests. For example, if we had the ability to generate an ECD waveform with a constant pulse duration, and we could vary the ECD pulse amplitude, then we could estimate a ‘‘threshold’’ of cardiac stimulation. Limitations Despite the statistically significant results, this study was done on a small sample size of only four subjects.
This study was designed to detect cardiac stimulation in an animal model, and these results will have to be extrapolated to humans. Typical scenarios possibly leading to fatal dysrhythmia in humans, such as illicit drug use and agitation, could not be recreated in our study. In addition, even though a device might not cause cardiac stimulation in an animal model, this might not be true in human applications. CONCLUSION Our data suggest that not all ECDs are created equal. Some ECDs generate shocks that make them more likely to stimulate the heart of experimental animals. Cardiac stimulation occurs during ECD applications, and this can be observed and quantified better using TEE than other experimental methods used in prior studies. Cardiac stimulation is dependent upon subject size, dart location, and ECD device.
Effect of FFP Transfusion on INR Acknowledgments—Department of Veterans Affairs, VISN 15 Research Award; and a research grant from the Oakland, CA Police Force.
REFERENCES 1. Brewer JE, Kroll MW. Field statistics overview. In: Kroll MW, Ho JD, eds. TASER conducted electrical weapons: physiology, pathology, and law. New York: Springer-Kluwer; 2009:283–301. 2. Jenkinson E, Neeson C, Bleetman A. The relative risk of police useof-force options: evaluating the potential for deployment of electronic weaponry. J Clin Forensic Med 2006;13:229–41. 3. Smith MR, Kaminski RJ, Rojek J, Alpert GP, Mathis J. The impact of conducted energy devices and other types of force and resistance on officer and suspect injuries. Policing 2007;30:423–46. 4. Swerdlow CD, Fishbein MC, Chaman L, Lakkireddy DR, Tchou P. Presenting rhythm in sudden deaths temporally proximate to discharge of TASER conducted electrical weapons. Acad Emerg Med 2009;16:726–39. 5. Dennis AJ, Valentino DJ, Walter RJ, et al. Acute effects of TASER X26 discharges in a swine model. J Trauma 2007;63:581–90. 6. Walter RJ, Dennis AJ, Valentino DJ, et al. TASER X26 discharges in swine produce potentially fatal ventricular arrhythmias. Acad Emerg Med 2008;15:66–73. 7. Valentino DJ, Walter RJ, Dennis AJ, et al. Taser X26 discharges in swine: ventricular rhythm capture is dependent on discharge vector. J Trauma 2008;65:1478–85. discussion 1485–7.
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ARTICLE SUMMARY 1. Why is this topic important? Due to the increasing use of electronic control devices (ECDs), the number of deaths associated with their use is also increasing. Although some theories attempt to link the deaths to cardiac dysrhythmias resulting from the ECD, the exact mechanism is still unclear. 2. What does this study attempt to show? This study looks at different factors that may contribute to fatal dysrhythmias caused by ECD application. These factors include subject size, dart location, and specific differences in each ECD waveform. Once these factors are identified, a safer, more efficient ECD can be created. 3. What are the key findings? There are three key findings from this study. First, cardiac stimulation was detected during some ECD applications and was able to be quantified using transesophageal echocardiography. Second, cardiac stimulation was dependent not only upon subject size and dart location, but also on differences in the type of ECD. Cardiac stimulation occurred most frequently in small pigs with the dart placed across the heart. Third, despite proving cardiac stimulation can occur during ECD application, no fatal or sustained dysrhythmias were seen. 4. How is patient care impacted? Once the factors that contribute to cardiac stimulation are identified, it may be possible to create a safer and more efficient ECD. This will cut down on the number of deaths associated with ECD use. Once the exact mechanism is found, specific measures might be able to be taken to prevent fatal dysrhythmias.