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Proceedings of the IEEE

Issue 3 • Date March 1996

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Displaying Results 1 - 16 of 16
  • Special Issue on Electrical Therapy of Cardiac Arrhythmias

    Publication Year: 1996
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    Freely Available from IEEE
  • Strategic Technology Management [Book Reviews]

    Publication Year: 1996
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    Freely Available from IEEE
  • John G. Brainerd and Project PX (ENIAC) [Scanning the Past]

    Publication Year: 1996
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    Fifty years ago this month, the Proceedings of the Radio Engineers (IRE) included an article by John G. Brainerd on Project PX or ENIAC, which had recently been completed at the University of Pennsylvania, USA. The author had served as supervisor of the wartime project and was a professor of electrical engineering at the university. ENIAC was an acronym for Electronic Numerical Integrator and Computer and the article characterized it as a "mathematical robot" and "the first all-electronic general purpose computer." Brainerd mentioned that the machine occupied a 30 x 50 foot room and contained approximately 18 000 electron tubes. He explained that ENIAC had been conceived originally as a machine to solve ballistics equations more quickly and accurately but was now being discussed "in connection with problems which were not even thought of when development began." the author continues with a brief biography of Mr. Brainerd and notes that a historical symposium celebrating the 50th anniversary of the ENIAC is scheduled to be held at the University of Pennsylvania on May 17-18, 1996. View full abstract»

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  • The mechanism of defibrillation and cardioversion

    Publication Year: 1996 , Page(s): 392 - 403
    Cited by:  Papers (10)  |  Patents (1)
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    Sudden cardiac death due to ventricular fibrillation is responsible for over 400,000 deaths per year in the United States alone. The only treatment for this fatal arrhythmia is electrical defibrillation of the ventricle. During the initial seconds of ventricular fibrillation, multiple reentry circuits cause action potentials to occur rapidly with a cycle length determined primarily by the cellular refractory period. A successful defibrillation shock stimulates cells during the refractory period to produce a prolonged postshock response throughout the ventricle. The ventricle is then refractory to propagating fibrillation wavefronts and fibrillation ceases. Biphasic defibrillator waveforms, formed by reversing the polarity partway through the shock, lower defibrillation threshold significantly thereby allowing nonthoracotomy implantation of implantable cardioverter-defibrillators (ICDs). These waveforms appear to defibrillate at lower shock intensities primarily because sodium channel recovery from inactivation by the first phase of the waveform allows the shock to produce the required prolonged responses at these lower intensities. Defibrillation becomes much more difficult at the longer fibrillation durations encountered in “out-of-hospital” cardiac arrest, due to changes in fibrillation morphology. Recent studies suggest that sodium channel recovery produced by biphasic waveforms may also have the potential to increase probability of successful resuscitation under these more stringent conditions View full abstract»

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  • Ablation for the treatment of arrhythmias

    Publication Year: 1996 , Page(s): 404 - 416
    Cited by:  Papers (21)  |  Patents (20)
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    Surgical ablation of supraventricular cardiac arrhythmias has been rendered obsolete by the various modalities of electromagnetic transcatheter ablation techniques. Any ablation technique, including surgery is essentially the controlled destruction of a substrate which is acting as a source or a critical circuit limb of an arrhythmia. The most successful and popular modality is radio frequency (RF) ablation although other modalities such as dc shock, laser, microwave, and ultrasound are also being investigated. This review discusses the role of electrical ablation, especially RF ablation, as a treatment for supraventricular tachyarrhythmia and reviews the engineering principles and biological responses to ablation. A brief synopsis of the results of electrical catheter ablation procedures is presented. RF catheter ablation is a successful technique in clinical arrhythmia management, with reported success rates of greater than 95% in many series. The indications for clinical RF catheter ablation continue to broaden View full abstract»

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  • Detrimental effects of electrical fields on cardiac muscle

    Publication Year: 1996 , Page(s): 366 - 378
    Cited by:  Papers (25)
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    The use of controlled electrical shock as a therapy to manage cardiac arrhythmia is a practice commonly used today. High intensity electrical fields are generated near the shock electrodes, and if the electrodes are placed directly on or inside the heart as is often the case, tissue injury and dysfunction may result if the shock intensity is too high. Many factors influence the degree of dysfunction, including the intensity of the shock poise, duration of the pulse, waveform shape, size and position of the electrodes, and physiological state of the heart. One of the most immediate indications of aberrant cardiac function is an abnormality in the electrocardiogram, which results from field-induced changes in cellular electrophysiology. This article reviews results obtained primarily from animal experiments which delineate the intensities of electrical field that produce electrical dysfunction at various structural levels of the heart. Possible mechanisms underlying the detrimental effects of electrical fields are presented with the main focus on electroporation of the cell membrane. Other mechanisms that are described include formation of oxygen-derived free radicals, conformational damage to ionic pumps/channels, barotrauma, and hyperthermia. Differences between cathodal and anodal shock effects, as well as factors which may ameliorate electrical field-induced cardiac dysfunction, are also discussed View full abstract»

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  • The effect of externally applied electrical fields on myocardial tissue

    Publication Year: 1996 , Page(s): 379 - 391
    Cited by:  Papers (11)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1308 KB)  

    The explanation of the response to electrical stimulus by macroscopic regions of cardiac tissue in terms of the behavior of membrane ion channels requires mathematical models that span the range of spatial scales from the single cardiac cell to the entire heart. This is accomplished by the bidomain model, which successfully characterizes the electrical properties of the heart and the effect of externally applied electric fields on myocardial tissue, Recently the bidomain model has been used to make several specific, testable predictions: (1) a 4-fold symmetric magnetic field pattern is associated with an expanding wave front, (2) a region of positive interstitial potential precedes an expanding wave front in the direction parallel to the myocardial fibers, (3) the rate of rise of an action potential depends on the direction of propagation in superfused tissue, (4) the wave front in superfused strands of tissue is curved (5) a “dog bone” shaped region of depolarization exists under a unipolar cathode, (6) depolarized regions along the fiber direction adjacent to a unipolar anode are responsible for anodal stimulation, (7) interactions between adjacent depolarized and hyperpolarized tissue cause anode-break and cathode-break stimulation, (8) reentry can be induced by successive stimulation using a single unipolar cathode, and (9) a mechanism for far field stimulation depends on fiber curvature. These predictions have been verified qualitatively in every case where they have been tested experimentally. In some cases, such as the mechanisms for reentry induction and far field stimulation, the necessary experiments have not yet been performed View full abstract»

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  • Implantable pacemakers

    Publication Year: 1996 , Page(s): 480 - 486
    Cited by:  Papers (21)
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    Advances in cardiac pacing have greatly reduced the size of pacemakers, while improving their longevity and reliability, expanding their clinical applications and increasing their sophistication in terms of programming and automatic features. Significant reductions in the size of pacing systems have been mainly due to improvements in power sources, increased circuit integration, hybrid packaging, and the development of smaller leads and lead connectors. The use of sophisticated microprocessors has transformed some pacemakers into implantable computers. The incorporation of memory is enabling modern pacing devices to become more like Holter monitors, able to store significant amounts of intracardiac data. A trend toward the use of sensor technology has enabled pacemakers to provide rate response, taking the place of a damaged sinus node View full abstract»

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  • Using computer models to understand the roles of tissue structure and membrane dynamics in arrhythmogenesis

    Publication Year: 1996 , Page(s): 334 - 354
    Cited by:  Papers (40)
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    The merging of hypotheses and techniques from physics, mathematics, biomedical engineering, cardiology, and computer science is helping to form increasingly more realistic computer models of the heart. These models complement experimental and clinical studies that seek to elucidate the mechanisms of arrhythmogenesis and improve pharmacological and electrical therapies. This paper reviews the current state of the art of computer models for investigating normal and abnormal conduction in cardiac muscle. A brief introduction to the mathematical foundations of continuous (monodomain and bidomain) and discrete tissue structure models and to ionic current based and FitzHugh-Nagumo membrane models is presented. The paper summarizes some of the recent contributions in validating tissue structure models, modeling unidirectional block and reentry in a 1-D loop, and applying generic spiral wave theory to cardiac arrhythmias View full abstract»

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  • Implantable cardioverter defibrillators

    Publication Year: 1996 , Page(s): 468 - 479
    Cited by:  Papers (22)
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    The electrical design challenges for implantable defibrillators are discussed based on the following criteria: device evolution, system architecture, therapy delivery, mid heart activity sensing circuits. The discussion includes the incidence of sudden cardiac death and the clinical requirements of device hardware. System architecture includes the three dependent entities that define the system mid the functional components of the implanted device View full abstract»

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  • Experimental techniques for investigating cardiac electrical activity and response to electrical stimuli

    Publication Year: 1996 , Page(s): 417 - 427
    Cited by:  Papers (3)
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    One of the goals of experimental research in the areas of cardiac electrical activity and effects of stimulation has been to understand basic physiological responses of the heart to electrical stimulation. It is thought that electrical stimulation produces a distribution of current or an electric field in the heart that alters the transmembrane voltages of heart cells. This leads to changes in states of transmembrane voltage-dependent ionic currents, altered electrophysiological behavior of cells, and finally alteration of the electrophysiological behavior of the heart. The research has employed standard electrophysiological measurement techniques and new techniques that have been developed to study specific effects. This paper discusses some of the techniques View full abstract»

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  • Electrical behavior of defibrillation and pacing electrodes

    Publication Year: 1996 , Page(s): 446 - 456
    Cited by:  Papers (4)
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    This article discusses the electrodes and their interfaces for internal and external defibrillation and external pacing applications. Of primary concern is the nature of the current delivery and distribution at the electrode-tissue interface and the techniques that may be used to generate a uniform distribution of current density in order to minimize pain and burning. The cost of achieving a uniform current distribution is tolerable for external pacing applications, but questionable for defibrillation applications. In the process of examining the nature of the electrode interface, we also discuss various models of its behavior, including analytic, equivalent circuit, numerical, and empirical models View full abstract»

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  • The laws of electrical stimulation of cardiac tissue

    Publication Year: 1996 , Page(s): 355 - 365
    Cited by:  Papers (4)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB)  

    Classic description of the criteria for cardiac stimulation is by the strength-duration curve which may be presented for current, energy, or charge. Minima for each of these occur at different waveform durations. The fundamental mechanism by which the stimulus is effective is altering the polarization potential of the cell membranes in the heart. Partial depolarization of these cells initiates a cascade leading to complete depolarization which in turn triggers cardiac cell contraction. Active propagation of the depolarization from cell to cell is the mechanism for activation of the entire heart when stimulation is used for pacemaking. For depolarization with much stronger shocks, this depolarization mechanism in some cells is combined with hyperpolarization in other cells. The hyperpolarization causes anodal block of propagation. Two methods are used to study cardiac stimulation, the threshold concept and the probability concept, and each method has advantages and limitations. Many variables affect the capability of an electrical shock to stimulate the heart to a desired response. These include the current waveform the characteristics of the electrodes used to inject the current into the tissue, the disorder being treated, the mass of cells required to be effected, metabolic variables (such as temperature or pH of the the tissue), drugs, and the geometric arrangements of electrodes and body organs. Of particular engineering interest are different effectiveness of different electrical waveforms, and the electrode characteristics of half-cell potentials, polarization potentials and materials. Equivalent circuits are presented for the complex and nonlinear, interactive behavior of the electrical shock, electrodes, and tissues View full abstract»

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  • Cardiac pacing electrodes

    Publication Year: 1996 , Page(s): 457 - 467
    Cited by:  Papers (4)
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    On the surface, the cardiac pacing lead is just a simple cable that connects the pulse generator to the heart. The simple appearance of the lead is very misleading, however. The size, longevity, and features of the pulse generator and the patient's safety depend to a large extent on the performance of the lead. The pacemaker must assure that the heart will contract with each stimulus. Thus the pacemaker must deliver a pulse of sufficient voltage and duration to stimulate with a sufficient safety factor to cope with any minute-to-minute variations that may occur in daily life. At the same time, it is necessary to use as little current as possible to maintain as long a battery longevity as is practical. The most common approaches to the problem of reliably delivering a stimulus with adequate safety margin while decreasing the current drained from the battery have traditionally centered around electrode size, materials, surface structure, shape, and more recently glucocorticosteroid sustained release. Relatively little effort has been directed reward optimizing the stimulus waveform for treatment of Brady arrhythmias View full abstract»

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  • Detection algorithms in implantable cardioverter defibrillators

    Publication Year: 1996 , Page(s): 428 - 445
    Cited by:  Papers (22)  |  Patents (2)
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    Presents a review of the evolution of tachycardia fibrillation detection algorithms designed for implantable cardioverter defibrillators (ICD) including those that have been incorporated into first, second, and third generation devices. The major emphasis of this review is an overview of the development of new and innovative means for improved detection in next-generation devices. Time-domain and frequency-domain methods of electrogram analyses are described, limitations are cited and promising new proposals for increased specificity which address the false shock incidence are presented View full abstract»

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  • External defibrillators and emergency external pacemakers

    Publication Year: 1996 , Page(s): 487 - 499
    Cited by:  Papers (8)  |  Patents (1)
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    The first experimental defibrillation occurred in 1900. Zoll first achieved external defibrillation of a human heart in 1956 and the first commercial external manual defibrillators were introduced in 1961. The author discusses the steady improvements in manual defibrillator performance which have occurred since 1961, particularly relating to added functionality, event documentation, and telecommunications, and speculate on likely trends in the next few years. The author then considers the most important developments of the last 30 years, i.e., the development and successful use of smart automatic or advisory external defibrillators (AEDs) which are capable of accurately analyzing the ECG and of making reliable shock decisions. The first generation AEDs were intended for use by paramedics or nurses. There is growing interest in developing very simple, reliable, and low cast AEDs for widespread use by minimally trained first responders (e.g., fire fighters) and even lay persons (“public access defibrillation”) and existing of forthcoming AEDs for that application are discussed. Finally, the author briefly discusses external pacemakers and self-adhesive electrodes which have become common features of modern defibrillators View full abstract»

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