John C. Schuder

Transthoracic Ventricular Defibrillation in the Dog with Truncated and Untruncated Exponential Stimuli

From 10 560 transthoracic fibrillation-defibrillation episodes in large anesthetized dogs, the effectiveness of 88 types of untruncated and truncated exponential waveforms in reversing ventricular fibrillation was evaluated. The study involved waveforms which could be generated with stored energy levels (in the simple capacitor-switch sense) of 60, 90, 120, and 180 J and initial current levels of 10, 20, 30, 40, 60, 80, and 100 A. The 10-A waveforms were untruncated or truncated at final current values of 5, 7.5, and 9 A. The 20-, 30-, and 40-A waveforms were untruncated or truncated at 5, 10, and 15 A. The 60-, 80-, and l00-A waveforms were untruncated or truncated at the 15-A level.

An Inductively Coupled RF System for the Transmission of 1 kW of Power Through the Skin

In systems in which inductive coupling between a pancake-shaped coil on the surface of the body and a similar coil within the body is utilized for the transport of electromagnetic energy, the minimization of temperature rise in the tissue is intimately related to the achievement of minimum losses in the region of the implanted coil. A detailed theoretical analysis indicates the design considerations for achieving minimum losses in the vicinity of the implanted coil and predicts relevant internal losses of about one-half of 1 percent of the transported power. Experimental verification of theoretical expectations has involved an operating frequency of 428 kHz for the transmission of 1 kW of power between a simple water-cooled coil on the surface of the chest and a coil implanted in the chest wall of a dog. A maximum tissue temperature of 103.5° F was observed. Since 1-h operation per day at the 1-kW level would supply the anticipated energy requirements for a patient with an artificial heart, the system may find application in the charging of internal energy storage units of artificial heart systems.

Transthoracic Ventricular Defibrillation with Triangular and Trapezoidal Waveforms

From 7, 200 fibrillation-defibrillation episodes in anesthetized dogs, the effectiveness of 6 classes of unidirectional shocks in reversing ventricular fibrillation of 30-sec duration was determined. The shocks lasted for 1 to 256 msec. Three waveforms (ascending ramp triangular, descending ramp triangular, and trapezoidal) were studied at peak currents of 10 amp and 20 amp. Families of curves of per cent success vs. energy were derived from the data for the 6 classes of waveforms studied and from corresponding curves for 3 classes of unidirectional square-wave shocks previously studied by our group. The families of curves were used as a basis for an analysis of the influence of various parameters on the effectiveness of shocks. We conclude that an appropriate energy content is a necessary, but not sufficient condition for effective ventricular defibrillation, that long, low-amplitude tails on shocks are detrimental and that excessive energy content is detrimental.

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

The Role of an Engineering Oriented Medical Research Group in Developing Improved Methods and Devices for Achieving Ventricular Defibrillation: The University of Missouri Experience

Physical scientists and engineers have played important roles in helping to expand our understanding of the factors that influence the defibrillation process and in developing improved methods and devices for achieving cardiac ventricular defibrillation. The long‐term experience of one engineering oriented group, based in a clinical department of a medical school, is summarized. Emphasized are the features of a series of research defibrillators that facilitated the generation of an extensive experimental database from studies in dogs and calves, the development of the first automatic implantable defibrillator to be successfully used in dogs, and studies that furnished the rationale for the widespread use of the uniphasic truncated exponential waveform and for the increasing interest in a variety of biphasic and multiphasic waveforms. Also considered are studies concerning the scaling of the defibrillatory shock with subject size and the role of compound units, defibrillation threshold, and contour graphs in the presentation and interpretation of data.

Ventricular defibrillation in the dog using implanted and partially implanted electrode systems.

Abstract Two totally implanted and two partially implanted electrode systems were studied in 2,100 fibrillation-defibrillation episodes in large anesthetized dogs. In one of the totally implanted systems, two metal disks, 7.6 cm in diameter, were implanted between the pectoralis major muscle and the rib cage, with the right electrode high on the chest and slightly to the right of midline and the left electrode over the apex of the heart. In the other totally implanted system, a unipolar catheter electrode positioned in the right atrium and superior vena cava was used together with a 7.6 cm disk electrode over the apex of the heart. In the partially implanted systems, a unipolar catheter electrode in the right atrium and superior vena cava was used together with either a 7.6 cm disk electrode or a 6.3 by 20.3 cm rectangular sheet electrode placed on the surface of the chest over the apex of the heart. Four types of unidirectional shocks were used in evaluating the twin disk system. Nine types of shocks were used with systems involving the catheter electrode. Derived curves indicate that the 90 percent level of successful defibrillation is achieved with 38 joules on the day of implantation and 54 joules 32 weeks after implantation for the twin disk system, 12 joules on the day of implantation and 19 joules 33 weeks after implantation for the catheter-internal disk system, 15 joules for the catheter-external disk system and 24 joules for the catheter-external sheet system.

Transthoracic Ventricular Defibrillation with Square-wave Stimuli: One-Half Cycle, One Cycle, and Multicycle Waveforms

A very high powered amplifier for experimental transthoracic ventricular defibrillation has been described. The effectiveness of both one-half-cycle unidirectional and one-cycle bidirectional square waves in terminating ventricular fibrillation first increases, then reaches a maximum and finally decreases as the duration of the shock is increased. With 10- and 20-ampere unidirectional shocks and 10-ampere bidirectional shocks, a maximal effectiveness of substantially 100% was found under the chosen experimental conditions. Five-ampere unidirectional and bidirectional shocks yielded maximal effectiveness of 70%. The effectiveness of a 128-millisecond, 5-ampere, multicycle square-wave shock is a strong function of frequency and has a maximal value of approximately 70%.

Transthoracic ventricular defibrillation in the 100 kg calf with unidirectional rectangular pulses.

The effectiveness in reversing ventricular fibrillation of 30 seconds duration of unidirectional rectangular-wave shocks having pulse widths of 0.5 through 64 msec, pulse amplitudes of 35, 50, 70, 100, and 140 amp, and pulse energies of 109 through 1,660 J was studied in 3,303 transthoracic fibrillation-defibrillation episodes in 100 kg calves. A total of 38 animals were used in the study. Postdefibrillation electrocardiograms were recorded. Families of curves of percent successful defibrillation vs pulse duration, percent successful defibrillation vs pulse energy, duration of postdefibrillation complete block or standstill vs energy, and time required for a return to normal sinus rhythm vs energy were derived. The most effective waveform studied (70 amp -8 msec - 862 J) yielded defibrillation on the initial attempt in 93% of 120 episodes. In general, the duration of complete block or standstill and the time required for a return to normal sinus rhythm increased with increasing pulse current and pulse energy.

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.

Incidence of Arrhythmias in the Dog Following Transthoracic Ventricular Defibrillation with Unidirectional Rectangular Stimuli

The incidence of the various types of arrhythmia induced by defibrillation in anesthetized dogs that had had continous ventricular fibrillation for 30 seconds was studied as a function of the current strengh and the duration of the unidirectional rectangular pulse used to terminate the fibrillation. Shocks at 10, 20, 40, 80, and 100 amp with durations in the range of 80 μsec through 64 msec were used. At any given energy level the incidence of induced arrhythmias was much larger for the 40-, 80-, and 100-amp shocks than for the 10- and 20-amp shocks. At 10 and 20 amp, the incidence of induced arrhythmias increased with increasing energy content. Premature ventricular contractions were observed at nearly all levels of energy and current, in contrast to other types of arrhythmias that appear to be strongly related to energy content or current amplitude or both.