Cardiac Fibrillation Risks with TASER® Conducted Electrical Weapons · 2015-08-28 · • The overall theoretical VF risk was estimated not to exceed 1 in 2,873,147 • Thus, in

Cardiac Fibrillation Risks with TASER® Conducted Electrical

WeaponsDorin Panescu1, Ph.D., FIEEE, Mark Kroll2, Ph.D., FIEEE,

Michael Brave3, M.S., J.D. 1Advanced Cardiac Therapeutics, Santa Clara, CA, 2University of Minnesota, Minneapolis, MN, 3LAAW International, LLC, Scottsdale, AZ

Dr. Panescu is a paid consultant and retained expert to TASER International, Inc. (TASER)

Dr. Kroll is a paid consultant and retained expert to TASER, and a member of TASER’s Scientific and Medical Advisory Board (SMAB) and Corporate Board of Directors

Mr. Brave is an employee of TASER and legal advisor to the TASER SMAB and TASER Training Advisory Board

Disclosures

EMBC 2015: WeAT15.4 VF Risk Aug 26, 2015

Reports of arrest-related deaths (ARDs) in close temporal association with the use of CEWs raised speculation about potential direct electrical stimulation of the heart Incidents where CEW darts landed on suspects’ anterior chest,

where narrower dart-to-heart distances (DTH) may be presented

Previous studies have estimated the cardiac risk implied by TASER CEWs but have not included recent epidemiological data

Effects of partial and oblique dart penetration have never been considered before

It is important to understand the theoretical cardiac risk profile of CEWs in light of recent information

Introduction


Background: TASER® X26™ CEW


Output parameters: TASER X26 and X2 CEWs


Output parameters: TASER X26 and X2 CEWs


Computation of CEW cardiac risks:• Estimate CEW ventricular fibrillation thresholds (VFT)• Estimate the maximum distance from the tip of a typical 9 mm CEW dart to

the tissue region still exposed to VFT (MaxDTH) • Determine the distribution of minimum skin-to-heart distance (STH) for

anterior chest locations (from recent epidemiological data)• Compute overall CEW cardiac risk as• VFrisk = Pchest*PZone_MinSTH*PMaxDTHvsBMI*Pdart_penetrate

- VFrisk is the overall probability of VF induction with TASER X26 CEWs- Pchest is the probability of hitting the anterior chest with CEW darts, as per recent

epidemiological studies- PZone_MinSTH is the conditional probability of hitting the area of minimum STH- PMaxDTHvsBMI is the probability of STH being shorter than the length of the CEW dart plus

MaxDTH- Pdart_penetrate is the correction applied to account for partial or oblique dart penetration

Methods: Estimation of Cardiac Risk


Strength-duration curve adjusted for cardiac tissue stimulation with narrow duration pulses (0.1 ms):• VFTJ = Jrh*(1+c/d) – single pulse

• Per Sugimoto et al., the VFT may drop to as low as about 3 times the cardiac cell excitation threshold, if more than 4 premature ventricular beats occur

• Hence pvrVFTJ = Jexcite*(1+c/d) – for series of pulses which capture the heart– Where Jrh is the current density rheobase, c is chronaxie and d is stimulus duration– For VF induction: Jrh = 7 mA/cm2

– For excitation: Jexcite = 1.48 mA/cm2

– c = 1.2 ms– d = 0.1 ms

• Hence:– VFTJ = 7 mA/cm2*(1+1.2 ms/0.1 ms) = 91 mA/cm2

– pvr VFTJ = 3*1.48 mA/cm2*(1+1.2 ms/0.1 ms) = 58 mA/cm2

Methods: Ventricular Fibrillation Thresholds


Methods: 3-D Finite Element Model


Tissue regions: Skin: 2 mm thick Fat: 6 mm thick Pectoral Muscle (anisotropic): 7 mm thick Sternum/Rib/Intercostal muscle (anisotropic): 11 mm thick Lung and connective tissue: 8 mm thick Cardiac tissue: 11 mm thick 3-D Model was 24 cm long, 20 cm wide and 4.5 cm thick

General: CEW darts 15 cm apart and

9 mm embedded into tissue Voltage boundary conditions:

1700 V (TASE X26 CEW) Steady-state solution 36480 hexahedral elements. Resolution: 0.17 – 2.75 mm

Methods: 3-D Finite Element Model

Region Resistivity [Ω⋅cm]Skin 5000Fat 2500Pectoral muscle ρx = 1000; ρy=ρz=200Bone (sternum, rib) 1000000Intercostal muscle ρx = 1000; ρy=ρz=200Lung 1500Connective tissue 500Cardiac tissue 333Electrode 0.001


Methods: STH vs. BMI distributions(Wisconsin Group)


MinSTH vs. BMI and ARD subject BMI range(N = 55 males)

Methods: STH vs. BMI distributions(Cleveland Group)


MinSTH vs. BMI and ARD subject BMI range(N = 37 males)

Methods: CEW Chest Shot Distributions


CEW chest shot distributions from 24 cases in which X26 CEW darts were deployed to the anterior chest

Results: MaxDTH w/no Induction of VF or pvrVF


• 9 mm CEW dart fully embedded into tissue• MaxDTH = 3.5 mm, with VFTJ = 91 mA/cm2

• MaxDTH = 4.3 mm, with pvrVFTJ = 58 mA/cm2

• Hence to induce VF -> MinSTH ≤ 9 + 4.3 mm = 13.3 mm

Results: Effects of Fat, Sternum, Skeletal Muscle


• Fat, anisotropic skeletal muscle, sternum, rib layers and lung pose high electrical resistance to flow of currents towards the heart

• Over 200% combined attenuation of CEW currents

• Figure shows J distribution relative to the tip of a dart that landed over the 4th rib area

• Dart tip obliquely lodged in the subcutaneous layer

• Jmax in cardiac tissue layer was 0.6 mA/cm2

– safety margins of 150 x and 90 x with respect to VFTJ and pvrVFTJ

STH vs. BMI distributions: Given MinSTH ≤ 13.3 mm for any chance of VF induction Using Wisconsin and Cleveland combined STH vs. BMI distributions

PMaxDTHvsBMI = 1/(55 + 37) = 1/92 = 1.1%

Effects of partial or oblique-angle CEW dart penetration: Objective: find the oblique angle and the percent of partial penetration

that still have the closest heart point within MaxDTH from the dart tip inthe subject with the smallest STH (MinSTH = 12.7 mm)

k*Lengthdart*cos(α) + MaxDTH ≥ MinSTH Solution: 0 ≤ α ≤ 21° and 8.4/9 < k ≤ 1

Pdart_penetrate = 0.78%

Results: Risk Probability Computations


CEW anterior chest shots (recent epidemiological data):

Out of 1201 consecutive TASER X26 deployment cases, 178 cases involved dart locations on the anterior chest area

Pchest = 178/1201 = 14.8%

CEW shots to zone of MinSTH:

24 recent cases: 18 had their respective darts fall within the anterior chest area Out of these 2*18 = 36 dart locations, only one came close to

the left chest region where the MinSTH distance was met None of these cases had documented VF induction

PZone_MinSTH = 1/36 = 2.7%

Results: Risk Probability Computations


Overall theoretical VF risk combines the above probabilities:

VFrisk = Pchest*PZone_MinSTH*PMaxDTHvsBMI*Pdart_penetrate

VFrisk = 178/1201*1/36*1/92*0.0078 = 0.0000003481

Overall theoretical VF risk is less than 1 in 2,873,147cases

Results: Overall Theoretical VF Risk


• The overall theoretical VF risk was estimated not to exceed 1 in 2,873,147

• Thus, in general, CEWs should not be considered risk-free force options

• But, the use of TASER X26 CEWs implies an extremely low cardiac risk profile• Findings are consistent with prior modeling literature.• Findings are consistent with field epidemiological studies.• Findings are consistent with human and animal studies.

• Analysis above was presented for TASER X26 CEWs

• Newer CEW models, such as TASER X26P and X2 CEWs, have lower charge outputs, shorter pulse durations and are expected to pose even lower cardiac risk

Conclusions


Documents

Cardiac Fibrillation Risks with TASER® Conducted Electrical Weapons · 2015-08-28 · • The overall theoretical VF risk was estimated not to exceed 1 in 2,873,147 • Thus, in