This paper was on Taser International's webpage under the heading "Cardiac Safety".
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Prepared by: Mark W. Kroll, PhD, FACC, FHRS
Published: 3/25/2007
The TASER ECD Affects the Nerves and Muscles but not the Heart
The TASER ECD delivers a rapid series of shocks. Each has less current than a strong static electricity shock that one could get from a doorknob on a winter day. Just as a strong static shock temporarily incapacitates someone, this series of 19 strong — but very short — shocks per second from the TASER X26 will likely temporarily incapacitate a violent criminal resisting arrest so that law enforcement officers will not have to use greater levels of physical force, multiple officer restraint techniques, chemical agents, clubs, or firearms.
Discussion
The high-voltage, ultra-short electrical pulses applied by the TASER ECDs are intended to stimulate A-a motor neurons, which are the nerves that control skeletal muscle[1] contraction, without stimulating cardiac muscle. Three types of factors contribute to the cardiac safety of these devices: the anatomic location of the heart, the short durations of the pulse, and the high currents required to induce a fatal VF.
The Strength-Duration Relationship
Nerve and cardiac electrical stimulation is accurately described by the strength-duration curve applied to average current.[2] The threshold for stimulation with pulses of infinite duration is the lowest and is called the “rheobase.” The threshold for shorter stimulation pulses then rise up from the rheobase (minimal) levels of current as the pulse is shortened. The duration at which the required field doubles is called the “chronaxie,” abbreviated dc. Pulses with duration near the chronaxie are most efficient for stimulation.
Figure 1 shows a representative strength-duration curve for widespread transcutaneous stimulation of A-a motor neurons which control skeletal muscle contraction. The rheobase for a motor neurons is approximately 1 A (ampere) with a chronaxie of 100 µs (microseconds). In contrast, the cardiac chronaxie, for transcutaneous stimulation, is 3–5 ms (milliseconds), 30–50 times longer in pulse duration.
Figure 2 shows the relative energy requirements to capture the A-a motor neurons with different pulse widths. Note that the most efficient pulse width is about 100 µs.
Figure 1 The threshold in amperes for the capture of the A-a motor neurons as a function of the pulse duration. Note that narrow pulses require much more current.
Figure 2 The threshold in millijoules for the capture of the A-a motor neurons as a function of the pulse duration. Note that the most efficient capture obtains at the 100 µs pulse width of the TASER X26 pulse.
TASER® Electronic Control Devices Electrical Characteristics
The TASER Waveforms
The TASER X26 ECD is a battery- (lithium camera-type) operated, pistol-shaped device that shoots two tethered darts and delivers 19 short pulses per second with a typical peak voltage of 1300 V (1000-1500 V) for a five-second burst. The device also generates an open-circuit voltage of up to 50,000 V to arc across thick clothing but that voltage is never seen in the body. Briefly, the pulse generated is a specially designed short pulse with a pulse duration of about 100 ms to efficiently capture alpha motor neurons while having minimal cardiac effects.[3],[4] (These devices should not be confused with a generic “stun gun” which uses various high frequency electrical currents, over a short fixed-electrode vector, to cause pain without skeletal muscle capture.)
The typical charge delivered is 100 µC (microcoulombs) giving an average net current of approximately 2 mA (milliamperes) (=19 pulses per second • 100 µC). As seen in Figure 3, the peak current of the normal pulse (labeled 1X) is 3.3 amperes (typical range of 3.0-3.6 A). With the typical inter-dart body impedance of 400 Ω (ohms), this corresponds to the peak voltage of 1300 V.
Figure 3 Output waveform of X26 weapon in tissue. The output circuit attempts to deliver a constant charge per pulse. Thus the output current is largely load independent.
The TASER M26 and TASER X26 ECD devices use compressed nitrogen to fire two small probes at distances up to 7.7 meters (25 feet). TASER cartridge models are available to reach out to 11 m (35 feet), as well. These probes, which will pierce most light clothing, are discharged from the cartridge at a velocity of approximately 200 feet per second and can penetrate the body to a depth of no more than 9 mm. The TASER X26 is 60% smaller, 60% lighter, and consumes one fifth (1/5th) the power of the TASER M26. Yet, the direct incapacitating effect of the X26 has been estimated to be 5% greater than that of the M26 due to the more optimal pulse duration.
The M26 TASER delivers damped sine wave current pulses, each having a peak amplitude of about 18 amperes and a fundamental frequency of 50 kHz (kilohertz) as seen in Figure 4. The output voltage will vary with contact impedance and may exceed 50,000 volts to arc through clothing when the probes are not directly contacting the body; dropping to about a 3,000–5,000 volts when directly contacting the body. The first, main cycle is about 10 µs long and delivers the charge to cause the A-a motor neuron capture. The charge in this phase is about 85 µC. The other phases do not appear to contribute to the contraction and may actually slightly cancel some of the effects of the principle phase.[5] This is why the X26 was developed to have one primary large phase.
Figure 4 M26 output waveform into a typical load. Due to the short duty cycle, the net average effective current is < 1 mA compared to the instantaneous peak current of 15 amperes or more. Figure 5 Voltage from the M26 and the proportional membrane response for possible electroporation. Due to the 10 µs time constant of electroporation, the effective peak voltage is less that half of the actual M26 peak voltage. Introduction to the Concept of Electrocution Electrocution is the induction of a cardiac arrest by electrical shock. This is theoretically how a TASER ECD, could have killed a criminal suspect.[i] It is an immediate death — on the order of seconds[ii] — as electricity does not build up in the body like a poison.[iii] There are five basic components to such an electrocution death: 1. There is an immediate loss of physical strength for continued resistance. 2. Collapse occurs within 5-15 seconds. 3. VF (ventricular fibrillation) rhythm results. Rhythm of asystole or PEA (pulseless electrical activity) is never induced. 4. Pulse disappears immediately. 5. Immediate defibrillation is usually successful. The TASER ECD PULSE CANNOT STOP THE HEART Summary The TASER ECD cannot stop the heart. While it has brief high currents, just like a strong static electricity shock, the pulses are significantly too short in duration to affect the heart. Since the pulses are each too weak to affect the heart a series of them will not affect it either. The safety of the TASER devices has been verified in numerous human and animal studies. It is doubtful that any law enforcement use-of-force technique or tool has been tested so thoroughly for safety. Safety Margin Calculations The best evidence for the cardiac safety of the device lies in the 210,000 voluntary training exposures and 340,000 suspect uses (total of 559,000 human uses) without any credible evidence of a resulting cardiac arrhythmia. Nevertheless, we can quantify the safety margin of the TASER device outputs by comparing them to published scientific data on the electrical induction of VF (the main cause of cardiac arrest). There are two primary ways to deliver an electrical shock to induce VF. The first is to deliver a single short shock (less than 1/20 second long) exactly during a particularly vulnerable point in the heartbeat cycle. The vulnerable spot is called the “T-wave.” The suggestion that the TASER device could induce VF (ventricular fibrillation) by shocking into the vulnerable period has been referred to as “Russian Roulette” or the “Lightning Lottery.” For short duration pulses, such as those from the TASER ECDs, the critical parameter for cardiac stimulation is the net delivered charge.[iv] The second way to deliver a shock to induce VF is to deliver either continuous or nearly continuous current for a longer period of time. For this scenario the critical parameter is the average current. The following analysis will calculate the safety margin for both scenarios. Safety Margin for a Single Pulse in the Vulnerable Zone The TASER M26 main phase delivered charge is about 85 microcoulombs (µC) and the TASER X26 delivers about 100 µC. It has been known for over a century that the critical parameter of electrical stimulation by short pulses is the electrical charge.[v] This has been more recently confirmed for cardiac stimulation with short duration pulses, such as those from the TASER ECDs.1 Green Model Green investigated the VF induction threshold for canines stimulated along their long axis.[vi] He found that the lowest threshold occurred with a 5 millisecond (ms) quarter sine wave and was 2 amperes (A). Integrating, we find a minimum required charge of 6.5 millicoulombs (mC). On the basis of many studies, it is common practice to use a normalization factor of 2 to 1 to go from canine results to human as humans are so much larger than the small dogs typically used in these laboratory experiments.[vii] This suggests a human VF threshold of 13 mC. With the TASER X26 charge of 100 µC we can calculate the safety margin as: SM = 13 mC ¸ 100 µC = 130:1 For the TASER M26 the safety margin would then be even higher at: SM = 13 mC ¸ 85 µC = 153:1 Peleska Model Peleska studied capacitor discharges into the T-wave and found a minimum required charge of 5 mC to induce VF.[viii] This suggests a human threshold of 10 mC. The safety margin is thus: 100:1 = 10 mC ¸ 100 µC for the X26 and: 118:1 = 10 mC ¸ 85 µC for the TASER M26 International Safety Standards International safety standards (e.g. IEC 479) are primarily based on the 50-60 Hz wall outlet frequencies and the classical but misleading RMS current measurements. However, revisions to IEC-479 are being considered which would include more scientific measurements directly related to the risk of fibrillation such as the charge in microcoulombs.[ix] The proposal refers to 100 µC as “disagreeable” and 10,000 µC as “ventricular fibrillation likely.” Note that this second number is 100 times greater than the TASER ECD charge. The updating of international standards is painfully slow as many countries input editing changes and the changes then require approvals around the globe. Nevertheless, it is encouraging that these standards are starting to move in the correct direction scientifically. Conclusion No pulse from the TASER X26 or the M26 could ever induce VF by affecting the heart during the “sensitive” spot. The charge in the device pulses is too low by factors of at least 100:1. The “lightning lottery” and “Russian roulette” theories are simply not possible. Multiple Pulses from the TASER ECD Cannot Stop the Heart Since it is clear that no single pulse from a TASER ECD can induce VF, it is important to analyze the impact of the stream of 19 pulses per second (PPS). For the continuous current modeling, we need to calculate the “continuous” current level. With a charge of 100 µC delivered 19 times per second we have 1.9 mC per second delivered, which is an average current of 1.9 milliamperes (mA) for the TASER X26. The pulse rate for the TASER M26 varies from 15 to 20 PPS depending on the battery voltage. With the charge of 85 µC the average current varies from 1.3-1.7 mA. The more conservative 1.7 mA is so close to the typical 1.9 mA from the TASER X26 that we can simplify calculations by using a conservative 1.9 mA for both devices. (Counting both positive and negative phases of the M26 and X26 gives slightly higher numbers of 3.6 mA and 2.1 mA. In my opinion, the lower numbers are the most appropriate metric for indicating the ability of the pulses to affect the heart as the polarity changing phases merely offer cancellation effects.) Knickerbocker Model Knickerbocker studied the VF threshold with 20 Hz (hertz or cycles-per-second) AC (alternating current).[x] He found a threshold of 70 mA for canines in the long axis and a 2-second connection. This suggests a human threshold of 140 mA. This gives a safety margin of 74:1 = 140 mA ¸ 1.9 mA for the X26 and M26. Beigelmeier Model Beigelmeier’s model holds that long-term AC (5 seconds or more) requires 1/20th of the current to fibrillate as does a single 20 millisecond (ms) pulse (which single pulse would have to be into the T-wave).[xi]We can predict the single pulse VF threshold from the Jones and Geddes study which found a ratio of 52:1 for a 10 ms pulse (the widest they investigated). This would give a single 10 ms pulse a VF threshold of 1.4 A = 52 · 27 mA. Dividing this by Beigelmeier’s ratio of 20 gives a predicted AC threshold of 70 mA. Doubling this for humans gives us a human threshold of 140 mA and a safety margin of: 74:1 for the TASER X26 and TASER M26 (which matches the results from the Knickerbocker model) Dalziel Model Dalziel performed a meta-analysis of VF thresholds for mammals.[xii] This is shown in Figure 1. Conservatively, he included swine which are very easy to fibrillate due to subtle cardiac conduction system differences. The average current required to cause fibrillation is given by the formula: I = 3.68W + 28.5 mA Where W is the body weight in kilograms. For pounds the formula is: I = 1.67W + 28.5 mA For a typical difficult arrestee of 190 lbs (86 kg) the average current required to fibrillate would be: I = 346 mA which gives an average safety margin of 182. However, Dalziel recognized that sensitivities to electrical currents vary and he thus performed a statistical analysis. He plotted the lower limit of sensitivity as the middle line in the figure. Note that this middle line gives a fibrillating current of over 160 mA for our 190 lb resisting human subject. This gives a safety margin of: 84 = 160 mA ¸ 1.9 mA Figure 1. Fibrillating currents as a function of body weight. The GFI Safety Outlet for Guidance Finally, let us consider the lessons from the ground-fault interrupter (GFI) outlets that are in everyone’s bathroom, under current electrical codes in the United States. The TASER ECD level of current (1.9 mA) is so low that it will not trip the GFI safety outlet in your bathroom which requires between 4 and 6 milliamperes.[xiii] The GFI specification is written in terms of root-mean square (RMS) current which will be discussed later. Nevertheless, the actual circuitry in the GFI outlets measure average current[xiv] which is also how TASER devices have to be rated. The GFI outlet designers recognize that RMS current measures the heating capability in a power source and not the fibrillating capability. Conclusion We have analyzed the risk of the induction of VF from the TASER X26 and M26 ECD with the two scenarios known for cardiac risk. For the risk of delivering a pulse into the vulnerable period of the cardiac cycle we find that the charge required is about 100–130 times that which the TASER X26 delivers. The TASER M26 safety margin was calculated at an even higher range of 118-153:1. We also analyzed the risk for the delivery of “continuous” current. We found a safety margin of 140:1 by two different methodologies for the TASER X26 and TASER M26. It appears that the TASER device output is incapable of inducing VF in adult human beings. Animal Results Show that the TASER ECD Cannot Harm the Heart TASER sponsored a study at the University of Missouri, Columbia, to determine the safety margin of the TASER X26 ECD. This institution has a well founded reputation for leading research in defibrillation going back decades. This study used pigs for the testing as pigs — pound for pound — are probably the easiest mammals to put into VF (ventricular fibrillation or cardiac arrest) by electricity.[xv] Also, the anesthetic used, isoflurane, is known to increase the risk of VF[xvi],[xvii] and thus this study was extremely conservative. Even with the smallest pigs (only 60 pounds) the output of the TASER X26 had to be increased by a factor of 15 to ever cause VF. In fact, a 200-pound pig required over 30 times the X26 output to ever cause VF. This safety margin of 30:1 is far higher than that of many over-the-counter medications. For example, acetaminophen (the active ingredient in many headache and pain medications) has a safety margin of only about 10:1 for the recommended dosage.[xviii],[xix] These ground breaking results were peer-reviewed and published in the leading journal Pacing and Clinical Electrophysiology (PACE).[xx] This study was done with careful scientific procedures and set a new standard for use of force weapons research. No one has been able to make a credible criticism of the methodology or principles of this study. And — importantly — no other studies have contradicted the results. On the contrary, other completed studies now in the publication-review process strongly support those results. In fact, the data was validated by a multi-year, multi-million dollar study completed by the United Kingdom government in 2005 when they found an even higher safety margin.[xxi] One researcher failed to induce VF in pigs and was finally forced to surgically open the skin, and move the fat and muscle insulating the heart. Then he poured a conductive gel (which conducted about 8 times better than the removed fat and the muscle against its grain) in until it directly contacted the heart. Only then was he able to induce VF by inserting a barb into the conductive gel within 5/8 inch of the heart.[xxii] This was a very useful result as it showed the great lengths that one had to go to in order to get VF from a TASER device. Unfortunately, this researcher perhaps went a bit too far by trying to analogize his extreme experiment to humans even though the thinnest humans have 1.2 inches between their skin and the heart which is filled with highly insulative muscle and fat. Human Studies Show that the TASER ECD Does Not Affect the Heart The following study was performed under the auspices of the University of Minnesota.[xxiii] Adult volunteers (n=66, age 40.3 ± 6.8 years, 65 male, 1 female) had typical cardiovascular histories: 6 hypertension, 6 hypercholesterolemia, 1 each of myocardial infarction and bypass grafting, heart failure, coronary disease, transient ischemic attack, and diabetes with 51 reporting no significant history. Each was shot in the back with standard TASER device barbs and received the full five-second application from the law enforcement model TASER X26. Each had blood drawn before, immediately after, and at 16 and 24 hours post-exposure. Troponin I, potassium, CK, lactate, and myoglobin were tested. A 12-lead ECG was recorded in 32 randomly chosen subjects at each venipuncture. A blinded cardiologist read all 128 ECGs in random order.[xxiv] There were no significant changes in any of the serum markers. Thirty of the 32 ECG subgroup had normal ECGs for all four recordings. One subject had all four recordings interpreted as left ventricular hypertrophy and another had occasional sinus pauses in all four recordings. The TASER ECD did not affect cardiac or skeletal serum markers or cause serial ECG changes. In other words, no sign of any effect on the heart was found in any of the volunteers. Another human study, through the University of California at San Diego, found no negative effects on the heart in the 49 volunteers exposed to the TASER devices.[xxv] The world’s expert on fibrillation is Raymond Ideker, MD, PhD, who has over 300 indexed manuscripts on the topic and over 1000 total papers and abstracts. He analyzed the TASER X26 output and calculated that it should have a 28:1 safety margin for the typical adult human.[xxvi] How Can the TASER ECD Affect the Muscles Without Affecting the Heart? The fact that the electrical pulses generated by the TASER X26 are too small and too short to stimulate the heart raises the question of why these same pulses are able to cause skeletal (external) muscle contraction. The electrical pulses stimulate the A-a motor nerves which in turn cause the skeletal muscle to contract.[xxvii] The time constant for stimulation of motor neurons from electrodes on the chest of dogs is approximately 0.24 ms, much shorter than the 3.6 ms for cardiac muscle.[xxviii] Other studies give time constants and chronaxies even shorter and nearer to 100 µs. The second reason why the motor neurons are excited by the TASER pulse—while the heart muscle is not—is that the motor neurons are much closer to the electrodes than is the heart. This also explains why the muscles most affected are those nearest to the electrodes of the TASER device. The different electrical resistivities of the various body tissues, and the relative insulating effect of the air-filled lungs, also cause the electric field to be many times smaller in the heart than in the surface tissues near the electrodes. In fact, the amount of current that passes through the heart from electrical pulses delivered to the chest wall is only about 4–10% of the total current delivered through chest electrodes.[xxix],[xxx] Most of the current flows around the chest between the two electrodes in the intercostal muscles. Electrical current prefers to flow with the grain of a muscle vs. against the grain by a factor of 10:1. Also, the 4–10% value occurs when electrodes are optimally placed to affect the heart. When the electrodes are elsewhere on the body, as they are in the large majority of cases when the TASER device is used, the percent of applied current that traverses the heart is even less. The TASER ECD is Safer than Many Headache Remedies Acetaminophen (also sold as paracetamol in the United Kingdom) has caused fatalities in adults with dosages of 15 grams or 30 extra-strength acetaminophens.[xxxi],[xxxii] One in 10 United States poisonings is acetaminophen alone. There are around 250 US deaths annually from acetaminophen. In the UK, it is even more popular and it accounts for every second poisoning. What is the safety margin for acetaminophen? The bottle labeled safe dose for a single day is eight tablets. The safety margin for someone taking the daily dose in one sitting is thus only 4:1. [xxxiii] To be generous, let us assume that people always followed the timing instructions, which recommend only two tablets every four hours. (People with bad headaches and other pains do not follow these limits and that is one reason there are so many acetaminophen poisonings.) After four hours the last two tablets are largely metabolized thus they are counted as — effectively — only one in the body. Now add in the two new tablets. The body now sees an effective ingestion of three tablets, or 1.5 grams. With a lower lethal limit of 15 g, there is now a safety margin of only 10:1. According to the conservative University of Missouri pig study, the TASER ECD safety margin for a full-sized adult is 30 times, thus a TASER device is indeed far safer than acetaminophen. How about body size effects? The threshold acetaminophen dose requiring treatment is 150 mg/kg of body weight. Assume a 110 pound young person. Such an individual’s body weight is 50 kg, giving a threshold acetaminophen dose of 7.5 grams, or 15 tablets. The safety margin (for the three tablets in four hours) is 5:1. At this weight, a TASER device has a safety margin of 22:1 by the McDaniel study. Regardless of body weight, the TASER device is around three to four times safer than acetaminophen. Note that this analysis does not include the risk that criminals struck by the TASER device may fall and hit their heads on a hard object, thus risking possible death from the secondary head trauma. This analysis deals only with death and not injury such as that from a barb hitting the eye or an increased risk of certain cancers associated with acetaminophen. Long TASER ECDs Applications Do Not Affect the Heart. Summary Electricity does not build up in the body like poison. If an electrical current does not electrocute someone in 2–5 seconds, it will not electrocute the person with a longer application. Thus, longer applications have no materially different effect on the heart. It is well known that VF can be induced by current flowing through the body. The current that is required to cause VF is dependent on the length of time for which the current is applied, and it is well established that the induction threshold decreases for the first few seconds and does not decrease further.[xxxiv],[xxxv],[xxxvi],[xxxvii] In other words, if you are not electrocuted by a certain level of electrical current after five seconds, you will not be electrocuted by a 60 second exposure either. If one ping-pong ball hit to the head does not kill you, 1,000 probably cannot either.
A recent study in smaller pigs (110 lbs) looked at an “extreme scenario” by burying the TASER barbs under the skin and placing a barb over the most sensitive part of the heart. With 15 second durations they were able to record some temporary and harmless effect on the heart. However, they saw the same effect 96% of the time with only a 5 s application.[xxxviii]
Both the International Electrotechnical Commission (IEC)[xxxix] and Underwriters Laboratories (UL)[xl] regulations recognize that electrocution either happens in the first second (or two) or does not happen. 4 Currents that will not induce VF in one second will not induce VF in one minute as shown in Figure 1 taken from Chilbert p 496.
Figure 2 shows that the TASER ECDs are literally off the charts as their currents are too low to fall on the graph.
Figure 2. Short applications (less than 1 second) require increasing current levels to induce VF. The lines on this graph represent worst case scenarios with extremely low probabilities of VF and are less than 1/10 the current typically required to electrocute an adult human being.
[1] Skeletal muscles are the ones that bodybuilders work on. This excludes the myriad of little muscles throughout the body that control valves and pumps, etc.
[2] Lapicque L. Recherches quantitatives sue l’excitation electrique des nerfs traitee comme une polarization.. J Physiol Paris 1907 ;9:620-–635.
[3] Voorhees CR, Voorhees WD 3rd, Geddes LA, Bourland JD, Hinds M. The chronaxie for myocardium and motor nerve in the dog with chest-surface electrodes. IEEE Trans Biomed Eng 1992 Jun;39(6):624–8.
[4] Alon GL, Inbar GF. Optimization of pulse duration and pulse charge during transcutaneous electrical nerve stimulation. Austral J Physiotherapy 29(6):195–201.
[5] It is highly likely that the other phases have a cancellation effect which increases cardiac safety. Regardless of whether they cancel or not, the charge delivered is far away from what is required to affect the heart.
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[ii] Weirich J, Hohnloser S, Antoni H. Factors determining the susceptibility of the isolated guinea pig heart to ventricular fibrillation induced by sinusoidal alternating current at frequencies from 1 to 1000 Hz. Basic Res Cardiol 1983 Nov–Dec;78(6):604–16.
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[xiii] ulstandardsinfonet.ul.com/scopes/0943b.html.
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[xxi] Wilkinson DI. PSDB Further evaluation of TASER devices. 2005. Publication No. 19/2005. Page-101. Home office, Police Scientific Development Branch, Sandridge, UK. Accessed http://www.homeoffice.gov.uk/docs3/psdb09-02.pdf.
[xxii] http://www.engr.wisc.edu/bme/faculty/webster_john/EB2006Final.pdf.
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[xxv] Saul D. Levine, C.S., Theodore Chan, Gary Vilke and James Dunford, Monitoring of Subjects Exposed to the Taser. Academic Emergency Medicine 2005. 12(5): p. Suppl-1 71.
[xxvi] Raymond E. Ideker, and Derek J. Dosdall. Can the Direct Cardiac Effects of the Electric Pulses Generated by the TASER X26 Cause Immediate or Delayed Sudden Cardiac Arrest in Normal Adults? 2006 in press.
[xxvii] Sweeney JD. Skeletal muscle response to electrical stimulation. IN: Reilly JP, ed. Electrical Stimulation and Electropathology New York, NY: Cambridge University Press, 1992:pp.285–327.
[xxviii] Voorhees CR, Voorhees WD, Geddes LA, et al. The chronaxie for myocardium and motor nerve in the dog with chest-surface electrodes. IEEE Trans Biomed Eng. 1992;39(6):624–627.
[xxix] Lerman BB, Deale OC. Relation between transcardiac and transthoracic current during defibrillation in humans. Circ Res. 1990;67:1420–1426.
[xxx] Camacho MA, Lehr JL, Eisenberg SR. A three-dimensional finite element model of human transthoracic defibrillation: Paddle placement and size. IEEE Trans Biomed Eng. 1995;42(6):572–578.
[xxxi] Wallace CI, et al. Paracetamol poisoning: an evidence based flowchart to guide management. Emerg Med J. 2002.
[xxxii] Jones AL. Recent advances in the management of late paracetamol poisoning. Emerg Med (Aust) 2000.
[xxxiii] There are many different parameters to measure the relative safety of drugs. The calculations here are not the same as the classical “Therapeutic Index” or the “Normalized Safety Margin.”
[xxxiv] Weirich J, Hohnloser S, Antoni H. Factors determining the susceptibility of the isolated guinea pig heart to ventricular fibrillation induced by sinusoidal alternating current at frequencies from 1 to 1000 Hz. Basic Res Cardiol 1983 Nov–Dec;78(6):604–16.
[xxxv] Younossi K, Rudiger HJ, Haap K, Antoni H. [Experimental studies on the threshold for fibrillation produced by direct or sinusoidal alternating current in the isolated guinea-pig heart] Basic Res Cardiol 1973 Nov-Dec;68(6):551–68.
[xxxvi] Hohnloser S, Weirich J, Antoni H. Influence of direct current on the electrical activity of the heart and on its susceptibility to ventricular fibrillation. Basic Res Cardiol 1982 May–Jun;77(3):237–49.
[xxxvii] Roy OZ, Park GC, Scott JR. Intracardiac catheter fibrillation thresholds as a function of the duration of 60 Hz current and electrode area. IEEE Trans Biomed Eng 1977 Sep;24(5):430–5.
[xxxviii] Nanthakumar K, Billingsley IM, Masse S, Dorian P, Cameron D, Chauhan VS, Downar E, Sevaptsidis E. Cardiac Electrophysiological Consequences of Neuromuscular Incapacitating Device Discharges. J Am Coll Cardiol 2006;48:798–804).
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[1] There are many different parameters to measure the relative safety of drugs. The calculations here are not the same as the classical “Therapeutic Index” or the “Normalized Safety Margin.”
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Source:
Mark W. Kroll, PhD, FACC, FHRS
Last Updated: 4/27/2007 7:22 AM