Implantable devices for the treatment of cardiac arrhythmias

The development of implantable devices for the treatment of tachyarrhythmias has resulted in additional therapeutic choices for the affected patients. Technologic advances now permit one to choose from a wide variety of devices capable of intervening automatically in the presence of supraventricular or ventricular arrhythmias. Although all methods remain in the investigational stage at this time, sufficient evidence has been gathered to support the efficacy of certain devices in the presence of various arrhythmias. Pacemaker-energy pulses may be delivered in various sequences to interrupt re-entrant rhythms, and their reproducible success can be effectively demonstrated in the electrophysiology laboratory. Cardioverting and defibrillating devices are capable of recognizing and successfully interrupting malignant ventricular arrhythmias. The automatic defibrillator has already been reported to reduce 1-year arrhythmic mortality in high-risk patients. Although still in the infant stages of development, the continuing advances in device technology suggest that their future applications are indeed promising.     

Sequential pulse defibrillation for implantable defibrillators

A technique is described that reduces defibrillation threshold for automatic implantable defibrillators, permits either reducing the size of the pulse generator or increasing the effectiveness of the pulse generator, and provides an increased safety factor. Defibrillation threshold was compared in 12 anesthetized dogs with mean (+/- SD) body weight of 21.6 +/- 3.4 kg for two defibrillating modalities: 1) single pulse technique with current flowing from electrodes in the right ventricle to electrodes either in the superior vena cava or on the left ventricular epicardium, and 2) sequential pulse technique. The sequential pulse technique tested uses two pulses and three or four electrodes. Current of the first 5-ms pulse flows from the superior vena caval electrode to an electrode in the right ventricle, and after a 1-ms interval, current of the second pulse flows from electrodes on the left ventricular epicardium to the right ventricular electrode. Ventricular defibrillation threshold was reduced by 56% to 6.3 +/- 1.03 joules (mean +/- SEM) (P less than 0.01). Because defibrillation threshold is less for sequential pulse defibrillation than for conventional techniques, sequential pulse defibrillators can be smaller and more effective than previously available devices.     

Potassium efflux from myocardial cells induced by defibrillator shock

A transient, dose-dependent cardiac depression was produced by defibrillator shocks in an isolated, working canine heart preparation perfused with oxygenated arterial blood from a support dog. Accompanying this depression was an efflux of potassium (K+), forced out of the myocardial cells by the passage of defibrillating current. The transient increase in extracellular K+ concentration was recorded graphically in the venous outflow. It was found that 5-msec rectangular wave shocks, from three to ten times defibrillatory current threshold, released dose-related pulses of K+. It is concluded that because K+ is a myocardial depressant, at least part of the myocardial depression after defibrillation is caused by the release of K+ from the myocardial cells.     

简易新型除颤器的设计

提出一种采用80C196KC单片机识别心室纤颤的设计思想，并采用低能量的双相脉冲技术实现去纤颤，突破了传统去纤颤器在技术与应用方面的局限性。     

Relationship between pacemaker fibrillation thresholds and electrode area.

Energy thresholds for electrical pacing of the heart are lower with small electrodes than with large. Because pacing of the heart during the vulnerable period may produce ventricular fibrillation, it is also pertinent to know if fibrillation threshold is affected by the electrode size. Electrodes of different surface area but of the same material were implanted in 40 dogs and the pacing thresholds were recorded. Ventricular fibrillation was electrically induced by discharging a 2-msec d.c. cathodal pulse of progressively increasing energy into the vulnerable period. It was found that small electrodes required more energy to produce ventricular fibrillation than large electrodes, and the ratio of fibrillation to stimulation threshold was higher for the small-surface-area electrode. The difference between the thresholds and ratios obtained with the various electrodes was statistically significant. A similar experiment was performed in animals with chronically implanted electrodes, producing comparable results. The results indicate that, in regard to pacing and fibrillation thresholds, small electrodes are preferable to large.     

Sequential pulse defibrillation in man: comparison of thresholds in normal subjects and those with cardiac disease

We compared the parameters describing the defibrillation threshold in patients with normal hearts and in patients with ischemic heart disease, using a special electrode system and sequential pulses of current. Twenty-eight patients consented to the study (mean age: 36.6 +/- 10.1 years; mean mass: 80.7 +/- 13.8 kg). Twenty-one patients underwent surgery for Wolff-Parkinson-White syndrome (relatively normal hearts). Six patients had a history of previous myocardial infarction and aneurysm or coronary artery disease; and one patient had been resuscitated from an episode of sudden death, without evidence of consequent myocardial damage. For 26 patients, defibrillation thresholds were determined intraoperatively by passing sequential pulses through a catheter electrode and epicardial mesh electrode. For 2 patients defibrillation thresholds were determined during electrophysiologic study, after ventricular fibrillation was induced by programmed stimulation, by passing sequential pulses through a catheter and skin-patch electrode. Parameters for sequential pulse defibrillation thresholds between the two groups did not differ appreciably. Total energy for patients with normal hearts averaged 9.9 +/- 6.3 J compared to 8.9 +/- 4.6 J for patients with cardiac disease. No patient with cardiac disease had defibrillation parameters that exceeded the range of the normal patients. These results suggest that the presence of cardiac disease may not significantly alter the parameters necessary for successful defibrillation when using sequential pulses for delivery of energy.     

Electode catheter for transvenous defibrillation.

Development of an implantable automatic defibrillator is dependent on achieving a reduction in the energy required for defibrillation, which is related to an optimal electrode configuration. This study investigated the use of a transvenous catheter electrode utilizing the damped sinusoidal waveform; compared the defibrillation effectiveness of varying the configuration of the four electrode units and of using a catheter/subcutaneous metal plate combination; and determined the lowest energy level necessary for near consistent transvenous defibrillation.     

The mechanism underlying sudden death from electric shock

Much has been written on the effects of electric shock on the body. However, in those cases in which victims become pulseless and therefore die suddenly, the underlying event has assuredly been ventricular fibrillation. In this condition of the heart, all of the muscle fibers of the ventricles, the main pumping chambers, contract and relax randomly and pump no blood. Simple protracted cardiac arrest, in this circumstance, is most unlikely. It generally is believed that only low-frequency alternating current can induce ventricular fibrillation; this assumption is invalid, because a single pulse of current applied to the body, as well as high-frequency current, can induce ventricular fibrillation. The important variables are the type and magnitude of the current and the manner in which it is applied to the body. To date, the current pathway has received too little attention. This article reviews the various mechanisms by which a single shock or a train of pulses can induce ventricular fibrillation.     

The prediction of the impedance of the thorax to defibrillating current.

In this paper a technique for predicting thoracic impedance to defibrillator pulses is described. The impedance to low-current (1.0 mA) high-frequency (10-500kHz) sinusoidal current is used as an indicator of the impedance of the thorax to high-current, damped sinusoidal waveform pulses. Results from 71 dogs to which defibrillator shocks of 4 to 220 A peak current were applied show that thoracic impedance can be predicted by this method. This information indicates that it is possible to design a defibrillator that can automatically measure chest impedance prior to a defibrillation shock and deliver a predetermined peak current to the subject.     

A high-voltage cardiac stimulator for field shocks of a whole heart in a bath

Defibrillators are a critical tool for treating heart disease; however, the mechanisms by which they halt fibrillation are still not fully understood and are the subject of ongoing research. Clinical defibrillators do not provide the precise control of shock timing, duration, and voltage or other features needed for detailed scientific inquiry, and there are few, if any, commercially available units designed for research applications. For this reason, we have developed a high-voltage, programmable, capacitive-discharge stimulator optimized to deliver defibrillation shocks with precise timing and voltage control to an isolated animal heart, either in air or in a bath. This stimulator is capable of delivering voltages of up to 500 V and energies of nearly 100 J with timing accuracy of a few microseconds and with rise and fall times of 5 micros or less and is controlled only by two external timing pulses and a control computer that sets the stimulation parameters via a LABVIEW interface. Most importantly, the stimulator has circuits to protect the high-voltage circuitry and the operator from programming and input-output errors. This device has been tested and used successfully in field shock experiments on rabbit hearts as well as other protocols requiring high voltage.     

Impedance to transthoracic direct current discharge: a model for testing interface material

An in vitro method for screening the relative impedance of gels has been developed. A nonconductive chamber was built with 1-cm-diameter electrodes placed 1 cm apart. This chamber is filled with electrode gel to be tested. The defibrillator used delivers a half-sinusoidal waveform. When the same stored energy is discharged by this defibrillator into increasing impedance, the resultant delivered current wave decreases while the voltage wave increases. Thus, with increasing impedance, the delivered volt-time interval increases. Twelve electrode gels were studied; 10 measurements were made on each gel. There is a marked variation in the impedance to direct current discharge of commercially available electrode gels. A large number of commercially available electrode gels are not suitable for use as the interface between the paddle electrodes and the chest wall during elective cardioversion and emergency defibrillation.     

The automatic external defibrillator-pacemaker: clinical rationale and engineering design

Prompt defibrillation is the cornerstone of therapy for out-of-hospital sudden cardiac arrest. Overwhelming evidence indicates that victims whose cardiac arrest is witnessed and whose ECG rhythm is ventricular fibrillation can be successfully resuscitated, with significant prolongation of life. The automatic external defibrillator-pacemaker (AEDP) is designed to be used by family members of patients with known heart disease, by basic level technicians in emergency rescue systems, and by lay rescuers in corporate-industrial-public environments. The AEDP is designed for safety and ease of use. It incorporates a highly sensitive and specific electronic diagnostic logic. It defibrillates and paces with a unique tongue-chest electrode system or through two adhesive chest electrodes. The AEDP should be a cost-effective device for the treatment of sudden cardiac arrest and can play a major role in public health strategies for optimizing care for this enormous problem.     

用于低能量除颤的除颤器设计

设计了用于低能量除颤的,可灵活调节放电脉冲宽度和准确测量实际放电能量的除颤器.该除颤器的放电波形为双相指数截尾波,通过人工设置,可释放1～3组双相指数截尾波;放电脉冲的宽度、各脉冲之间的时间间隔可人工灵活调节,最小步长为0.1 ms;可测量放电前后储能电容电压,再根据储能电容的容值准确地计算出实际放电能量.该除颤器在双相指数截尾波的基础上,通过调节放电脉冲的宽度、各脉冲之间的时间问隔及脉冲数量,优化放电波形,达到低能量除颤的目的.已在20余例低能量除颤的动物实验中应用,各项功能符合设计要求.     

On-line impedance analysis system for studying the pulmonary vascular response to hypoxia.

The response of the pulmonary circulation to hypoxia is generally assessed in terms of cardiac output and pulmonary vascular resistance. However, due to pulsatility, the opposition to blood flow can be described accurately only by the input impedance to the pulmonary bed. For assessment of impedance, a system was developed consisting of implantable pressure transducers and an improved muitichannel continuous wave Doppler flow meter. A computer system was used to analyze the data, which was based on power output of the right heart, power dissipation in the pulmonary circulation, and impedance spectra. Data have been obtained from dogs exposed to various levels of acute hypoxia.     

Adaptive Gaussian Noise Image Removal Algorithm Using Filtering-Based Noise Estimation

This paper proposes a spatially denoising algorithm using filtering-based noise estimation for an image corrupted by Gaussian noise.The proposed algorithm consists of two stages:estimation and elimination of noise density.To adaptively deal with variety of the noise amount,a noisy input image is firstly filtered by a lowpass filter.Standard deviation of the noise is computed from different images between the noisy input and its filtered image.In addition,a modified Gaussian noise removal filter based on the local statistics such as local weighted mean,local weighted activity and local maximum is used to control the degree of noise suppression.Experiments show the effectiveness of the proposed algorithm.     

Electromagnetic Characteristic of Twin-wire Indirect Arc Welding

Traditional welding methods are limited in low heat input to workpiece and high welding wire melting rate. Twin-wire indirect arc(TWIA) welding is a new welding method characterized by high melting rate and low heat input. This method uses two wires: one connected to the negative electrode and another to the positive electrode of a direct-current(DC) power source. The workpiece is an independent, non-connected unit. A three dimensional finite element model of TWIA is devised. Electric and magnetic fields are calculated and their influence upon TWIA behavior and the welding process is discussed. The results show that with a 100 A welding current, the maximum temperature reached is 17 758 K, arc voltage is 14.646 V while maximum current density was 61 A/mm2 with a maximum Lorene force of 84.5 uN. The above mentioned arc parameters near the cathode and anode regions are far higher than those in the arc column region. The Lorene force is the key reason for plasma velocity direction deviated and charged particles flowed in the channel formed by the cathode, anode and upper part of arc column regions. This led to most of the energy being supplied to the polar and upper part of arc column regions. The interaction between electric and magnetic fields is a major determinant in shaping TWIA as well as heat input on the workpiece. This is a first study of electromagnetic characteristics and their influences in the TWIA welding process, and it is significant in both a theoretical and practical sense.     

Automatic generation of IGUN(C) input files for enhanced mesh resolution at the plasma meniscus

The plasma-beam interface (meniscus) is highly nonlinear and its correct simulation needs a mesh resolution of the order of the Debye length. In high intensity ion sources, the plasma density is usually too high and the Debye length is too small for a sufficient mesh resolution. A well established method to overcome this dilemma is the use of a field line and an equipotential line to be created in a first run, in order to dissect the simulation problem into a plasma part with much higher mesh resolution and a transport part with usual resolution. In the past many users of IGUN have found it difficult to perform this dissection. Therefore, a new feature has been added to IGUN to automatically write new input files for the dissected areas. For this a field line starting point needs to be defined as well as the potential of a pseudo electrode. The field line then is used for the plasma part as a slanted and curved Neumann boundary, while the pseudo electrode will act as the extraction electrode. The trajectory end data then are used in the automatically generated concatenating run as ion starting input without any need for the user to adjust for positions or different mesh resolutions. Here we show as an example the simulation of the well-known CHORDIS ion source, the calculated field line, the pseudo equipotential line, and the resulting simulations for the automatically generated input files for the plasma and the transport parts.     

Analysis of the current-density distribution from a tapered, gelled-pad external cardiac pacing electrode

We have designed a high-impedance (5000 omega-cm), tapered, gelled-pad, external cardiac pacing electrode that limits the migration of charges to the perimeter of a circular electrode and produces a more uniform current-density distribution than external cardiac pacing electrodes in clinical use. A computer simulation was developed that uses cylindrical coordinates to analyze the current-density distribution at the interface between the electrode and human tissue. Our computer simulation analyzed 32 different electrodes, and the results showed that the gelled-pad thickness, the gelled-pad taper, and the radius of the conducting disk were not significant parameters in determining the current-density distributions for low-resistivity electrodes. Those parameters were, however, significant for high-resistivity electrodes. We defined the optimum resistivity as that at which the tapered, gelled-pad electrode produces the most uniform current-density distribution and delivers the most current to human tissue. When evaluating electrodes at the optimum resistivity, we determined that the peak current density of the tapered, gelled-pad electrode was 50% lower than that of the clinically available electrodes, while delivering 58% more current to the human tissue.     

Impulse noise cancellation in image data using a two-output nonlinear filter

The quality of image data is often degraded by impulse noise caused by noisy sensors and/or transmission errors. To address this issue, a two-output nonlinear filtering architecture is presented. The proposed approach is based on the subsequent activation of two recursive filtering algorithms that operate on different subsets of input data. As a result, two pixel values are updated at each processing step producing a very effective cancellation of noise pulses. Impulse noise removal is based on rank ordered filtering. A nonlinear mechanism for error correction is also provided in order to avoid detail blur. Validation of the method is carried out by evaluating the quality of the filtered data with respect to two conflicting performance indexes: effectiveness of noise cancellation and accuracy of detail preservation. Results of computer simulations show that the proposed approach performs significantly better than well-known nonlinear methods in the literature including state-of-the-art operators.     

PULSE DISCRIMINATION FOR ELECTRICAL DISCHARGE MACHINING WITH ROTATING ELECTRODE

This article presents a new method for discrimination of various types of pulses generated during an electrical discharge machining process in presence of a rotating electrode. Existing pulse discrimination methods do not perform efficiently in an electrical discharge machine with rotating electrode, as arcs rarely occur during the machining process. Our method involves simultaneous comparison of the gap voltage and current signals with various thresholds. The main advantage of our proposed method is its efficient computation and significantly better accuracy in discriminating between various pulse classes for electrical discharge machining devices with rotating electrode. Experimental studies demonstrate a superior performance of our method in distinguishing normal pulses from harmful arcs, open circuit and short circuit pulses, compared with the state-of-art methods.