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J C Schuder

Publications and source records attributed to J C Schuder.

At least 19 recordsLinked to original sources
PubMed1999

Double pulse transthoracic defibrillation in the calf using percent fibrillation cycle length as spacing determinate.

Recent studies have found that when multiple pulses of energy are used for defibrillation with implantable electrodes, the spacing between these pulses is better determined as a percentage of the fibrillation cycle length (CL), rather than as a fixed function of time. Here, this concept is further tested in the transthoracic defibrillation of calves, which are approximately the size of heavy humans. Eleven 90-110 kg calves (101 +/- 6 kg) were used in evaluating the effectiveness in achieving transthoracic ventricular defibrillation of ten double pulse waveforms (two 50 A 4-ms rectangular monopulses) having leading edge-to-edge spacings of 4 ms (a 50 A 8-ms rectangular monopulse) and 50, 60, 70, 80, 90, 100, 110, 120, 130 percent fibrillation CL, respectively. In each of these waveforms, the total time when 50 A current was flowing (on time) was 8 ms. Our results show an unequivocal adverse interaction between the pulses, when the spacing is around 60%-70% fibrillation CL; but that the two pulses combined to defibrillate as effectively as a single 8-ms pulse when the spacing is around 110%-130% fibrillation CL. Electrocardiographic analysis suggests that the adverse interaction is due to a refibrillation phenomenon. This study confirms that double pulses can interact and have a negative effect on defibrillation efficacy. Our data suggests that the mechanism of this interaction involves the second pulse reinitiating fibrillation when the pulse separation is in a critical range of values. Our results are also compatible with the hypothesis that the spacing of multiple pulses is better determined as a percentage of the fibrillation CL than as absolute time, although more study is necessary to fully test this hypothesis.

Animals↗
PubMed1998

Relationship between efficacy of defibrillation shocks and frequency characteristics of shock waveforms.

INTRODUCTION: Using the Fourier transform, it is possible to replace each time domain representation of a defibrillatory shock by a unique frequency domain representation in which the shock waveform is defined in terms of a complex number function of frequency and typically described as an amplitude in amperes per hertz (or, closely related, joules per hertz) and an associated frequency-dependent phase angle. METHODS AND RESULTS: The present article describes the conceptual basis of the Fourier transform, sketches a simplified mathematical framework for deriving frequency domain parameters, considers properties crucial to interpreting defibrillatory-type shocks when expressed in the frequency domain, and then presents a series of shock waveforms in the frequency domain. Although not definitive, knowledge of the energy distribution with frequency alone, usually presented in joules per hertz, is shown to yield considerable insight into the probable comparable efficacy of uniphasic/biphasic rectangular, untruncated/truncated uniphasic exponential, and various biphasic "single capacitor" waveforms. CONCLUSION: In general, efficacy in achieving ventricular defibrillation is improved by parameter changes that shift a larger percentage of the delivered energy into a mid-frequency range (very roughly, 40 to 160 Hz). With further study, the frequency domain approach may prove to be a useful tool in the a priori selection of optimal defibrillatory shock waveforms.

Animals↗
PubMed1993

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.

Animals↗
PubMed1989

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.

Animals↗
PubMed1989

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.

Animals↗
PubMed1987

The cardiac ventricular defibrillation threshold: inherent limitations in its application and interpretation.

A quantity termed the "threshold" has been used to describe the results of electrical ventricular defibrillation studies, with the implication of a clear distinction between ineffective and effective shock intensities. Although several definitions of the threshold have been suggested, and various methods have been used to quantify it, no comparison of the accuracies of the various methods could be found in the literature. This article, after presenting a method of applying basic probability theory to an assumed distribution relating probability of successful defibrillation to current amplitude, uses the method to examine several popular algorithms for defibrillation-threshold determination. The results show that where a sharp transition exists from ineffective to effective current amplitudes, most algorithms yield fairly good results. Where that transition is gradual (as it appears to be in all of the published reports examined), the algorithms are shown to be inadequate.

Algorithms↗
PubMed1987

Is the effectiveness of cardiac ventricular defibrillation dependent upon polarity?

Studies involving 240 fibrillation-defibrillation episodes via epicardial patch electrodes in 21-27-kg dogs and 480 transthoracic episodes in 100-kg calves are reported. In dogs, 120 episodes involving shocks by a 3.7-A, 5-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes of the reverse polarity. When the upper right ventricular patch was positive with respect to the left ventricular apex patch, 85% of the episodes yielded defibrillation; 78% defibrillated with the reverse polarity. In one series in calves, 120 episodes involving shocks by a 42-A, 4-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes involving the reverse polarity. In a second series, 59-A, 4-ms shocks were employed. In the 42-A series, 38% of the episodes were successful when the upper right electrode was positive with respect to the electrode over the apex, and 28% were successful with the reverse polarity. Corresponding results in the 59-A series were 80% and 68%, respectively. On an unpaired basis, the three p values were 0.19, 0.14, and 0.04, respectively. On a paired basis, all three comparisons yielded significant differences (p less than 0.05). We conclude that in these cases, at least, there is a moderate dependence upon electrode polarity and that our results appear to warrant clinical studies.

Animals↗
PubMed1984

Defibrillation of 100 kg calves with asymmetrical, bidirectional, rectangular pulses.

The effectiveness in reversing ventricular fibrillation of 30 s duration of asymmetrical, bidirectional, rectangular waveforms in which the lagging half-cycle has the same duration but lower amplitude than the leading portion of the waveform was evaluated in a 2160-episode study involving anaesthetised calves. An additional 480-episode auxiliary study involved the interlacing of unidirectional and bidirectional wave episodes. The leading half-cycles of the 18 bidirectional waveforms evaluated were 35 A at 8 and 16 ms, 50 A at 4 and 8 ms, and 70 A at 2 and 4 ms. Associated with each of the six leading half-cycle configurations were lagging half-cycles having reverse current levels of 1/8th, 1/4th, and 1/2 of the leading half-cycle current amplitudes. Six waveforms were successful in 97% or more of the transthoracic episodes. Of these, three were 100% successful. Our data, when combined with those from earlier unidirectional and symmetrical, bidirectional, rectangular waveform studies, suggest that a broad category of bidirectional rectangular shocks are superior to the most favourable unidirectional rectangular shock.

Animals↗
PubMed1982

Transthoracic defibrillation in 100-kg calves with sequentially applied pulses.

The effectiveness of up to five 50-A, 4-ms rectangular pulses (each nominally 50% successful) followed, when required, by up to six 70-A, 6-ms pulses applied at 15-s intervals in reversing ventricular fibrillation in 100-kg calves was studied in 600 episodes in which 50-A, 6-ms; 70-A, 3-ms; 70-A, 6-ms; 70-A, 12-ms; or 100-A, 6-ms prefibrillation shocks had been delivered 5 s before the induction of fibrillation and in another 600 episodes in which the prefibrillation shock was omitted. We found that 1) there was a modest adverse influence of the prefibrillation shock upon the outcome of the 50-A, 4-ms portion of the sequential shock effort; 2) The 50-A, 4-ms shocks remained reasonably successful throughout the five-shock sequence; 3) when the prefibrillation shock was omitted, the time intervals for a return of a ventricular complex and normal sinus rhythm in the postdefibrillation electrocardiogram increased rapidly with the number of shocks required for defibrillation; and 4) if defibrillation was not achieved with the five-shock sequence, a single 70-A, 6-ms shock was about 94% successful and the sequence of up to six shocks was 100% successful.

Animals↗
PubMed1979

Scaling current and energy with body weight: requirements for the transthoracic ventricular defibrillation of calves as they grow from 50 to 150 kg.

To test the hypothesis that the effectiveness of a shock in achieving ventricular defibrillation is relatively independent of body weight if electrode diameter is proportional to the one-third power and current is proportional to the two-thirds power of weight, we studied defibrillation rates in 10 calves as they increased weight. At 50 kg, each calf was subjected to 20 fibrillation-defibrillation episodes using 10.3-cm diameter electrodes and 32-amp, 4-msec rectangular pulses for defibrillation. Two days after the original study, each calf underwent 20 additional episodes involving 44-amp pulses. With the specified scaling of electrode diameter and pulse amplitude, the two studies were repeated at weight intervals of 25 kg as the animals grew. Six calves survived. In the study that started with 32-amp pulses, first-shock success values of 28%, 49%, 66%, 51% and 23% were found in the six surviving calves at 50, 75, 100, 125 and 150 kg, respectively. The corresponding values were 93%, 96%, 93%, 94% and 91% in the study that started with 44-amp pulses. While the results of the 32-amp study fail to support our initial hypothesis, those obtained in the 44-amp current study appear compatible with the hypothesis.

Animals↗