Wayne C. McDaniel

Transthoracic Ventricular Defibrillation in the 100 kg Calf with Symmetrical One-Cycle Bidirectional Rectangular Wave Stimuli

From 2760 fibrillation-defibrillation episodes in 100 kg calves, the effectiveness of reversing ventricular fibrillation of 30 s duration with symmetrical one-cycle bidirectional rectangular-wave shocks was determined. Pulse widths of 0.5-64 ms, pulse amplitudes of 35,50,70,100, and 140 A, and delivered pulse energies in the 93-1567 J range were employed in a primary study involving 39 animals. Families of curves relating percent successful defibrillation and the time intervals required for the return ofventricular activity and of normal sinus rhythm in the postdefibrillation electrocardiograms to the parameters of the delivered shocks were derived. In an eight-calf supplementary study involving 91-110 kg animals, the effectiveness of 50 A, 10 ms bidirectional rectangular wave shocks and 70 A, 6 ms unidirectional rectangular wave shocks were stringently compared by interlacing fibrillation-defibrillation episodes involving 120 bidirectional and 120 unidirectional shocks. When combined with previously published data for unidirectional wave shocks in 100 kg calves, our data suggest that pulse amplitude and pulse width specifications are considerably broader for successful bidirectional rectangular wave shocks than for unidirectional rectangular wave shocks, and that appreciably higher first-shock successful defibrillation (96-99 percent) can be achieved with bidirectional waveforms

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.

Superiority of biphasic shocks in the defibrillation of dogs by epicardial patches and catheter electrodes

Currently available internal cardiac defibrillators use a uniphasic, truncated exponential waveform morphology of about 6 msec in duration at an energy level of 23 to 33 joules. To determine if improved defibrillation could be achieved with a different waveform morphology, we implanted 4.5 cm2 titanium patches to the left and right ventricle of 28 dogs. After ventricular fibrillation was induced, defibrillation was attempted using 7, 12, 13, or 17 joules. A 5 msec rectangular uniphasic waveform morphology was compared with a 10 msec rectangular biphasic waveform with the lagging 5 msec pulse of half the amplitude of the leading 5 msec. In an additional seven dogs, a transvenous bipolar catheter was placed with the distal electrode in the right ventricular apex and the proximal electrode in the superior vena cava. Biphasic and uniphasic shocks were compared at 14 joules. In the patch-patch system, the biphasic waveform was superior to the uniphasic waveform at 7 joules (67% versus 35%, p less than 0.001) and at 12 joules (93% versus 78%, p less than 0.001). No statistically significant differences were achieved at 13 joules or 17 joules. In the catheter electrode system with a delivered energy of 14 joules, the biphasic waveform was more effective than the uniphasic waveform (87% versus 27%, p less than 0.001). Manufacturers of automatic implantable defibrillators should consider this information in the design of future automatic implantable defibrillators.

Adverse effects of permanent cardiac internal defibrillator patches on external defibrillation

At the time of left ventricular aneurysm resection, antiarrhythmic operations or other open-heart operative procedures in patients with ventricular dysrhythmia, permanent internal defibrillator patches may be inserted. Insertion of the energy source may be delayed due to its unavailability or to a desire for postoperative electrophysiologic study before its insertion. To assess the effects of permanent internal defibrillator patches on external defibrillation, 7 anesthetized calves were studied. Fibrillation-defibrillation studies were performed before and after insertion of permanent internal defibrillator patches (model L67, 27 cm2, Intec Systems), one on each ventricle. The values of percent successful defibrillation obtained before insertion of the patches, although much lower than values that would be expected in humans, are consistent with the results of an extensive earlier study involving this calf model. Similar values obtained after insertion of the patches are appreciably lower than the values obtained before implantation of the patches, and appreciably lower than the results predicted by the earlier study. A significant decrease in the percent of successful defibrillations (p less than 0.001) was observed for a shock intensity of approximately 400 J. Permanent internal cardiac defibrillator patches on the right and left ventricles reduce the probability of achieving successful defibrillation externally with unidirectional shocks. The wisdom of implanting permanent large internal cardiac defibrillator patches without the energy source is questioned.

Ultrahigh-energy hydrogen thyratron/SCR bidirectional waveform defibrillator

Presented here is a description of an ultrahigh-energy hydrogen thyratron/SCR bidirectional waveform research defibrillator having a sinusoidal voltage source for inducing fibrillation and three pulse generators for generating defibrillatory waveforms. The first pulse generator uses an 18 kJ capacitor bank at 0·8, 1·6 or 2·4 kV discharged through the chest by two series-connected silicon-controlled rectifiers (SCRs). Two other series-connected SCRs in parallel with the bank terminate the discharge. The second pulse generator uses an 18 kJ bank at 5, 10 or 15 kV. Ceramic-enveloped hydrogen thyratrons in series with the chest initiate the discharge, and in parallel with the bank terminate the discharge. The third pulse generator supplies a reverse-current pulse when used with either the first or second pulse generators to produce bidirectional waveforms. An 18 kJ bank at 2·5, 5 or 10 kV is discharged by an SCR chain in series with the chest. The discharge is terminated by an SCR chain in parallel with the bank. Symmetrical bidirectional rectangular, truncated exponential, and untruncated exponential waveforms are generated by the first and third pulse generators with their respective banks at 2·4 and 2·5 kV, the second and third pulse generators with their banks at 5 kV, or the second and third pulse generators with their banks at 10 kV. The full energy-storage capabilities of the capacitor banks can be used in the first two arrangements; usable energy storage in the third arrangement is limited to about 10 kJ per bank.

In vitro evaluation of five commercially available perfusion systems

An in vitro experiment was designed to examine and compare pump durability and stability, and hematologic derangements induced by four centrifugal pumps and one roller pump on fresh, unpooled citrated bovine blood. Pumps tested included St. Jude Medical Lifestream (n=7), Medtronic Bio-Pump® (n=7) and Carmeda Bio-Pump® (n=7), Sarns (n=7) centrifugal pump, and Sarns roller pump (n=7). Identical circuits consisted of equal inflow and outflow lengths of 3/8″ tubing connecting a 1 liter (L) reservoir to a pump head or roller region. Pump flow was controlled at 4.5 ± 0.3 L/min. All circuits (0.1 L lactated Ringers solution prime + 1 L blood) were tested for 24 h. Blood samples were drawn hourly for hours 1–6, every other hour for hours 8–12, and then at hour 24. Parameters monitored included pH, fibrinogen, plasma free hemoglobin (free Hb), lactate dehydrogenase (LDH), and platelet counts. Over the 24-h period, platelet counts decreased similarly among the perfusion systems. Free Hb and LDH rose significantly with the Sarns roller and centrifugal pumps after five hours of pumping. No significant changes in fibrinogen or pH were detected. Pump speed required to maintain flow with the Bio-pumps was significantly faster than with the Sarns and St. Jude Medical pumps.The authors conclude that these perfusion systems function reliably and satisfactorily during the first 4 h in an in vitro circuit. All centrifugal pumps were less hostile to red blood cells than the roller pump. Under these experimental conditions, the Sarns centrifugal pump caused more hemolysis than the other three centrifugal systems tested. There was no apparent advantage to the Carmeda Bio-Pump (heparin bonded) circuit in this trial.

Electrical parameters of projectile stun guns

Projectile stun guns have been developed as less-lethal devices that law enforcement officers can use to control potentially violent subjects, as an alternative to using firearms. These devices apply high voltage, low amperage, pulsatile electric shocks to the subject, which causes involuntary skeletal muscle contraction and renders the subject unable to further resist. In field use of these devices, the electric shock is often applied to the thorax, which raises the issue of cardiac safety of these devices. An important determinant of the cardiac safety of these devices is their electrical output. Here the outputs of three commercially available projectile stun guns were evaluated with a resistive load and in a human-sized animal model (a 72 kg pig).

Optimal Biphastc Waveform Duration For Canine Cardiac Defibrillatton With A "single Capacitor" Waveform And A Non-thoracotomy Electrode System

Previous studies have shown that biphasic waveforms are generally superior to uniphasic waveforms for achieving ventricular defibrilla- tion (1,2). However, the efficacy varies with the detailed structure of the waveform. In this paper, we present the results of a 720 episode study of a family of biphasic truncated exponen- tial waveforms in canine defibrillation with a non-thoracotomy electrode system. The family of waveforms all deliver nominally equal energies; have a final current equal to 25% of the initial current; and have the polarity reversal occur- ring so that the lagging phase of the waveform is 67 percent of the duration of the leading phase of the waveform. The total duration was varied from 5 to 25 milliseconds. The results show a broad plateau of successful defibrillation throughout the 5-12 millisecond range. We ob- served a significant deterioration of performance by the 20 millisecond duration.

General superiority of biphasic over uniphasic shocks in cardiac defibrillation

The comparative results of eight studies involving uniphasic and biphasic waveforms in 16383 transthoracic fibrillation-defibrillation episodes in 100-kg calves are critically summarized. A 1200-episode study of uniphasic and biphasic waveforms in epicardial and catheter defibrillation in dogs and two studies involving 733 defibrillation attempts using uniphasic and biphasic waveforms in the epicardial defibrillation of calves are presented. It is found that appropriate biphasic waveforms generally outperform uniphasic waveforms by (a) yielding a higher percent success, (b) requiring less energy to yield the peak possible value of success, and (c) furnishing quite successful results over a broader range of waveform parameters, thus making satisfactory performance less dependent on operator technique or patient-to-patient differences.<<ETX>>

Cardiac stimulation with electronic control device application.

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.