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P ACING
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Editorial by Kim, et al.
High Energy Cardioversion of Atrial Fibrillation by Alaeddini, et al.
Magnetocardiography in Coronary Artery Disease by Hailer, et al.
Effects of Sensor Optimization by Erol-Yilmaz, et al.
ECG of Fasciculoventricular Pathway by Choi, et al.
Diagnostic Value of Nitrate Stimulated Tilt Testing by Aerts, et al.
Transcristal Conduction in Patients with AFL by Yang, et al.
Prevalence and Management of Inappropriate Detection by Chugh, et al.
Coronary Sinus Lead Extraction by Kasravi, et al.
Changes in QT in Patients with Edematous States by Madias
Intrinsic RV by Olshansky, et al.
Elderly Woman with AV Block by Indik, et al.
Musings by Grubb
Accessory Pathway In Right Atrial Diverticulum by Chiu, et al.
Letters to the Editor

THE OFFICIAL JOURNAL OF THE INTERNATIONAL CARDIAC PACING AND ELECTROPHYSIOLOGY SOCIETY
AND THE ASIAN-PACIFIC WORKING GROUP ON CARDIAC PACING AND ELECTROPHYSIOLOGY

This study did not address the safety index as it relates to individuals with arrhythmias, pacemakers, or implantable cardiac defibrillators.

Cardiac Safety of Neuromuscular Incapacitating
Defensive Devices
WAYNE C. McDANIEL,* ROBERT A. STRATBUCKER,† MAX NERHEIM,†
and JAMES E. BREWER‡
From the *University of Missouri-Columbia, Columbia, Missouri, †TASER® International, Scottsdale, Arizona,
and ‡Brewer Consulting, Minneapolis, Minnesota

McDANIEL, W.C., ET AL.: Cardiac Safety of Neuromuscular Incapacitating Defensive Devices. Neuromuscular incapacitation (NMI) devices discharge a pulsed dose of electrical energy to cause muscle contraction
and pain. Field data suggest electrical NMI devices present an extremely low risk of injury. One risk of
delivering electricity to a human is the induction of ventricular fibrillation (VF). We hypothesized that
inducing VF would require a significantly greater NMI discharge than a discharge output by fielded devices. The cardiac safety of NMI discharges was studied in nine pigs weighing 60 ± 28 kg. The minimum
fibrillating level was defined as the lowest discharge that induced VF at least once, the maximum safe level
was defined as the highest discharge which could be applied five times without VF induction, and the VF
threshold was defined as their average. A safety index was defined as the ratio of the VF threshold to the
standard discharge level output by fielded NMI devices. A VF induction protocol was applied to each pig
to estimate the VF threshold and safety index. The safety index for stored charge ranged from 15X to 42X
as weight increased from 30 to 117 kg (P < 0.001). Discharge levels above standard discharge and weight
were independently significant for predicting VF inducibility. The safety index for an NMI discharge was
significantly and positively associated with weight. Discharge levels for standard electrical NMI devices
have an extremely low probability of inducing VF. (PACE 2005; 28:S284–S287)
neuromuscular incapacitation, ventricular fibrillation, electrical safety
Introduction
Neuromuscular incapacitation (NMI) devices
discharge electrical energy at high peak voltage,
low average current, in 10–100 µs pulses delivered in 10–19 per-second trains.1 Parameters for
the electrical discharge of NMI devices have been
empirically determined to maximize neuromuscular stimulation, cause pain and muscle contractions, and temporarily incapacitate a human
subject.2
TASER® (Taser International, Scottsdale, AZ)
is an electrical NMI defensive device which has
been widely tested.3−7 There has been no report
directly related to its risk of inducing ventricular fibrillation (VF), although preliminary findings
suggest that the likelihood of inducing VF by an
NMI discharge is extremely low.2,8,9 We hypothesized that the induction of VF would require significantly greater discharge levels than delivered
by electrical NMI devices fielded by law enforcement agencies.

Partial funding received from the Office of Naval Research, contract N00014–02-C-0059.
Address for reprints: Wayne C. McDaniel, Ph.D., Technology
and Special Projects, University of Missouri-Columbia,
475 McReynolds Hall, Columbia, MO 65211; e-mail:
mcdanielwc@missouri.edu

S284

Methods
Study Design
The cardiac safety of the electrical discharge
by NMI devices was studied in a prospective controlled trial design with the standard NMI discharge as control, compared with discharges that
induced VF in a large pig. The animals were anesthetized with isoflurane, their arterial blood pressure, oxygen saturation, respiration, and heart rate
were continuously monitored until sacrifice.
Experimental Device and Electrodes

A custom device was built to deliver an
NMI electrical discharge that matched the waveform characteristics of the commercially available
TASER® , model X26 device. The experimental device allows the output capacitance to vary as a multiple of the nominal capacitance (and charge) for
a standard NMI device (0.008 µF, Fig. 1). All experimental NMI discharges were delivered with a
fixed voltage of 6000 V. The waveform, as a shortelectrical pulse, was delivered at a repetition rate
of 19 pulses per second for 5 seconds. The standard
NMI stored charge for the experiment control was
(0.008 µF × 6,000 V) = 48 µC. The standard NMI
discharge represented the same amount of charge
(coulombs) delivered by fielded NMI devices. The
pulses were discharged across the thorax of the animal, using metallic barbs that matched darts deployed in fielded NMI devices. One pulse delivery

January 2005, Supplement 1

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SAFETY OF NEUROMUSCULAR INCAPACITATING DEVICE

Figure 1. Experimental NMI waveforms compared to waveforms discharged by standard NMI
devices (standard waveform, black). Experimental waveforms are shown for 16 times standard
discharge (µA, green) and for 48 times standard discharge (µA, red). The waveforms represented
a single pulse of a two-stage capacitor discharge; standard NMI devices apply 19 pulses per
second for 5 seconds. The two-stage incapacitation discharge was designed to first penetrate high
impedance barriers (AC-like portion of waveform) and then to incapacitate neurological and
muscular activity (pedestal portion of waveform).

probe was placed at the sternal notch and another
on the anterolateral thorax at the point of maximum impulse.
Threshold Procedure

NMI discharges were applied in an up-down
method to determine a threshold for VF induction, beginning with a standard NMI discharge. Increasing stored charges were applied to the animal
until VF was induced. The stored charge was increased in steps by increasing the size of the experimental NMI device capacitor. Each stepped stored
charge had a capacitor value equal to a multiple
of the standard capacitance unit (0.008 µF), using
an increasing number of charge multiples (2 and
multiples of 4 from 4 to 48). Following the first
VF induction, a decreasing series of capacitancestepped discharges were then applied until VF
was no longer induced by five discharges of equal
stored charge. The animals were defibrillated with
an automatic external defibrillator. A recovery period of at least 90 seconds was allowed after discharges that did not induce VF. If a discharge did
induce VF, a recovery period of at least 5 min was
allowed following defibrillation.
Study Endpoints and Safety Index

The primary study endpoint was the determination of a safety index for each animal based on its
PACE, Vol. 28

weight. Discharge data were collected during the
experiment for each NMI discharge applied during the VF threshold procedure. Minimum fibrillating discharge level determined by the VF threshold procedure was defined as the lowest discharge
that induced VF at least once; maximum safe level
was defined as the highest discharge which could
be applied five times without induction of VF; VF
threshold was defined as their average. The safety
index was defined as the ratio of the VF threshold
to the standard NMI discharge (48 µC).
Statistical Analysis

All continuous variables are expressed as
mean ± standard deviation. Two sample t-tests for
samples with equal variance were used to compare
mean values. For all comparisons, a P ≤ 0.05 was
considered statistically significant.
Institutional Review

The study protocol received approval from the
Institutional Animal Care and Use Committee of
Sinclair Research Farms. All animals received humane care.
Results
Nine experiments were completed. The average weight of the swine was 60 ± 28 kg, ranging from 30 to 117 kg. All animals remained

January 2005, Supplement 1

S285

McDANIEL, ET AL.

Figure 2. Example of blood pressure before and during
an NMI discharge.

hemodynamically stable throughout the experimental procedures, despite an average of 26 ± 12
NMI discharges per animal (Fig. 2).
The safety index for stored charge ranged
from 15X to 42X as weight increased from 30 to
117 kg (P < 0.001, Table I, Fig. 3). The VF induction threshold level (1339 ± 463 µC stored charge)
was significantly higher than the standard level for
applied charge (48 µC stored charge, P < 0.0001).
The charge multiple at the VF induction threshold was 28 ± 10 compared to the standard charge
multiple of 1 (P < 0.0001, Table I). The maximum
safe charge multiple was 26 ± 9 with an average
stored charge of 1,227 ± 423 µC, and the minimum
VF inducing charge multiple was 30 ± 11 with an
average stored charge of 1,451 ± 509 µC.
The maximum safe levels and minimum VFI
levels of stored charge for experimental data were
regressed linearly for significant trends. The relationship between stored charge as a function
of weight (kg) was compared to experimental
stored charge for minimum VF induction discharge. The maximum safe discharge was modeled by 12.5*[weight (kg)] + 473 (n = 9, r2 =

0.69) and the minimum VF induction discharge
was modeled by 16.5*[weight (kg)] + 460 (n = 9,
r2 = 0.82). The analysis revealed a linear, increasing relationship of maximum safe and minimum VFI discharge multiples (and therefore safety
index) as a function of weight (kg). The relationship further confirmed a significantly greater
discharge required to induce VF compared to
standard discharge levels for a fielded NMI
device.
Logistic regression showed that the mean
charge multiple for a 50% likelihood of VF induction was 24 ± 13, with an odds ratio of 0.85 after
adjustment for weight (95% Wald confidence limits: 0.83, 0.88, P < 0.0001). Therefore, an increasing
charge multiple was shown to be independently
related to an increase in VF induction.
Discussion
This study confirmed the cardiac safety of an
experimental NMI device emulating the performance of commercially used devices. An NMI discharge that could induce VF required 15–42 times
the charge of the standard NMI discharge. Furthermore, this study demonstrated a safety index
strongly correlated with increasing weight. In addition, the observation of the hemodynamic stability of the animals suggests that these devices
may be safely applied multiple times if needed.
Discharge levels output by fielded NMI devices
have an extremely low probability of inducing
VF.
This study used adult domestic pigs chosen
to simulate a range of adult human body weights
between 30 and 120 kg, likely to be encountered
in police work. Our results suggest a safety index

Table I.
Experimental Outcomes for 19 Pulse per Second Discharges

Pig
1
2
4
5
6
7
8
9
10

Weight
(kg)

Max Safe
Multiple

Safe Stored
Charge (µC)

Min VFI
Multiple

VFI Stored
Charge (µC)

Threshold
Charge (µC)

Safety
Index

83
54
48
81
49
42
37
117
30
60 ± 28

28
28
28
40
20
20
16
36
14
26 ± 9

1344
1344
1344
1920
960
960
768
1728
672
1227 ± 423

32
32
32
44
24
24
20
48
16
30 ± 11

1536
1536
1536
2112
1152
1152
960
2304
768
1451 ± 509

1440
1440
1440
2016
1056
1056
864
2016
720
1339 ± 463

30
30
30
42
22
22
18
42
15
28 ± 10

µC = microcoulombs; VFI = ventricular fibrillation induction.

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January 2005, Supplement 1

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SAFETY OF NEUROMUSCULAR INCAPACITATING DEVICE

Figure 3. NMI safety index ( , triangle)
in relationship to weight (kg). The safety
index is the ratio of VF induction threshold discharge to fielded NMI discharge.

≥20 for human adults >45 kg. The standard NMI
devices may therefore have a safety index significantly >20 for field applications to adult humans.

The minimum discharge that would cause fibrillation was approximately 15 times the charge of the
standard pulse when used on the smallest pig.

References
1.

Murray J, Resnick B. A Guide to Taser Technology. Whitewater,
CO: Whitewater Press, 1997.
2. Stratbucker R, Roeder R, Nerheim M. Cardiac safety of high voltage
TASER X26 waveform. Proc Annu Int Conf IEEE Eng Med Biol Soc
2003; 3261–3262. Cancun, Mexico.
3. Koscove EM, The TASER® weapon: A new emergency medicine
problem. Ann Emerg Med 1985; 14:1205–1208.
4. Ordog GJ, Wasserberger J, Schlater T, et al. Electric gun (TASER® )
injuries. Ann Emerg Med 1987; 16:73–78.
5. Fish R, Electric shock, Part III: Deliberately applied electric shocks
and the treatment of electric injuries. J Emerg Med 1993; 11:599–
603.

PACE, Vol. 28

6.
7.
8.
9.

Robinson MN, Brooks CG, Renshaw GD. Electric shock devices
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Kornblum RN, Reddy SK. Effects of the TASER in fatalities
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Fish RM, Geddes LA. Effects of stun guns and tasers. Lancet 2001;
358:687–688.
McDaniel WC, Stratbucker RA, Smith RW. Surface application
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IL.

January 2005, Supplement 1

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