Defibrillation Pulse Research Articles

Evaluation of the influence of the duration of the pause between the phases of depolarizing biphasic half-sinusoidal and truncated exponential defibrillation pulses on their energy efficiency

Evaluation of the influence of the duration of the pause between the phases of depolarizing biphasic half-sinusoidal and truncated exponential defibrillation pulses on their energy efficiency

Subcutaneous Implantable Cardioverter Defibrillator: A Contemporary Overview.

The difference between subcutaneous implantable cardioverter defibrillators (S-ICDs) and transvenous ICDs (TV-ICDs) concerns a whole extra thoracic implantation, including a defibrillator coil and pulse generator, without endovascular components. The improved safety profile has allowed the S-ICD to be rapidly taken up, especially among younger patients. Reports of its role in different cardiac diseases at high risk of SCD such as hypertrophic and arrhythmic cardiomyopathies, as well as channelopathies, is increasing. S-ICDs show comparable efficacy, reliability, and safety outcomes compared to TV-ICD. However, some technical issues (i.e., the inability to perform anti-bradycardia pacing) strongly limit the employment of S-ICDs. Therefore, it still remains only an alternative to the traditional ICD thus far. This review aims to provide a contemporary overview of the role of S-ICDs compared to TV-ICDs in clinical practice, including technical aspects regarding device manufacture and implantation techniques. Newer outlooks and future perspectives of S-ICDs are also brought up to date.

Evaluation of the Influence of the Amplitude of the Second Phase of the Depolarizing Bipolar Half-Sinusoidal Defibrillation Pulse on Its Energy Efficiency

Evaluation of the Influence of the Amplitude of the Second Phase of the Depolarizing Bipolar Half-Sinusoidal Defibrillation Pulse on Its Energy Efficiency

Reduced motion external defibrillation: Reduced subject motion with equivalent defibrillation efficiency validated in swine.

External defibrillators are used for arrhythmia cardioversion and for defibrillating during cardiac arrest. During defibrillation, short-duration biphasic pulses cause intense motion due to rapid chest-wall muscle contraction. A reduced motion external defibrillator (RMD) was constructed by integrating a commercial defibrillator with a Tetanizing-waveform generator. A long-duration, low-amplitude, tetanizing waveform slowly stimulated the chest musculature before the biphasic pulse, reducing muscle contraction during the shock. The purpose of this study was to evaluate RMD defibrillation in swine for subject motion during defibrillation pulses and for defibrillation effectiveness. RMD defibrillation can reduce the duration of arrhythmia ablation therapy or simplify cardioversion procedures. The tetanizing unit delivered a triangular 1-kHz pulse of 0.25- to 2.0-second duration and 10- to 100-V peak amplitude, subsequently triggering the conventional defibrillator to output standard 1- to 200-J energy biphasic pulses at the next R wave. Forward limb motion was evaluated by measuring peak acceleration and limb work during RMD (tetanizing + biphasic) or biphasic pulse-only waveforms at 10-3-second sampling rate. Seven swine were arrested electrically and subsequently defibrillated. Biphasic pulse-only and RMD defibrillations were repeated 25-35 times per swine, varying tetanizing parameters and biphasic pulse energy. Defibrillation thresholds (DFTs) were established by measuring the minimum energy required to restore sinus rhythm with biphasic pulse-only or RMD defibrillations. Two forward-limb acceleration peaks occurred during both the tetanizing waveform and biphasic pulse, indicating rapid and slower nociceptic (pain sensation) nerve fiber activation. Optimal RMD tetanizing parameters (25-35 V, 0.25- to 0.75-second duration), relative to biphasic pulse-only defibrillations, resulted in 74% ± 10% smaller peak accelerations and 85% ± 10% reduced limb work. DFT energies were identical when comparing RMD to biphasic pulse-only defibrillations. Relative to conventional defibrillations, RMD defibrillations maintain rhythm restoration efficiency with drastically reduced subject motion.

Low-energy, single-pulse surface stimulation defibrillates large mammalian ventricles.

Strong electric shocks are the gold standard for ventricular defibrillation but are associated with pain and tissue damage. We hypothesized that targeting the excitable gap (EG) of reentry with low-energy surface stimulation is a less damaging and painless alternative for ventricular defibrillation. The purpose of this study was to determine the conditions under which low-energy surface stimulation defibrillates large mammalian ventricles. Low-energy surface stimulation was delivered with five electrodes that were 7 cm long and placed 1-2 cm apart on the endocardial and epicardial surfaces of perfused pig left ventricle (LV). Rapid pacing (>4 Hz) was used to induce reentry from a single electrode. A 2 ms defibrillation pulse ≤0.5 A was delivered from all electrodes with a varied time delay from the end of the induction protocol (0.1-5 seconds). Optical mapping was performed and arrhythmia dynamics analyzed. For mechanistic insight, simulations of the VF induction and defibrillation protocols were performed in silico with an LV model emulating the experimental conditions and electrodes placed 0.25-2 cm apart. In living LV, reentry was induced with varying complexity and dominant frequencies ranging between 3.5 to 6.2 Hz over 8 seconds postinitiation. Low-energy defibrillation was achieved with energy <60 mJ and electrode separations up to 2 cm for less complex arrhythmia. In simulations, defibrillation consistently occurred when stimulation captured >75% of the EG, which blocked reentry <2.9 mm in front of the leading reentrant wavefront. Defibrillation with low-energy, single-pulse surface stimulation is feasible with energies below the human pain threshold (100 mJ). Optimal defibrillation occurs when arrhythmia complexity is minimal and electrodes capture >75% of the EG.

The Purkinje network plays a major role in low-energy ventricular defibrillation

BackgroundDuring ventricular fibrillation (VF), targeting the excitable gap (EG) of reentry throughout the myocardium with low-energy surface stimulation shows promise for painless defibrillation. However, the Purkinje network may provide alternative pathways for reentry to evade termination. This study investigates the role of the Purkinje network in painless defibrillation. MethodsIn a computational human biventricular model featuring a Purkinje network, VF was initiated with 4 Hz epicardial pacing. Defibrillation was attempted by stimulating myocardial surface EG with a low-energy 2 ms duration pulse at 2x stimulus capture, which was administered at coupling intervals incremented by 0.25 s between 0.25 and 5 s after VF initiation. Defibrillation was accomplished if reentry ceased ≤ 1 s after the defibrillation pulse. The protocol was repeated with the Purkinje network and myocardial surface EG stimulated simultaneously, and again after uncoupling the Purkinje network from the myocardium. ResultsVF with the Purkinje network coupled and uncoupled had comparable dominant frequency in the left (3.81 ± 0.44 versus 3.77 ± 0.53 Hz) and right (3.80 ± 0.37 versus 3.76 ± 0.48 Hz) ventricles. When uncoupling the Purkinje network, myocardial surface EG stimulation terminated VF for all defibrillation pulses. When coupled, myocardial EG surface stimulation terminated VF for only 55% of the defibrillation pulses, but improved to 100% when stimulated simultaneously with Purkinje network EG. Defibrillation failures were attributed to EG evading stimulation in the Purkinje network. ConclusionsDefibrillation that exclusively targets myocardium can fail due to accessory pathways in the Purkinje network that allow for reentrant activity to evade termination and maintain VF. Painless defibrillation strategies should be adapted to include the Purkinje network.

Evaluation of the Effect of Chopping Modulation of a Defibrillation Pulse on Its Energy Efficiency Based on the Hypothesis of Guaranteed Defibrillation

Evaluation of the Effect of Chopping Modulation of a Defibrillation Pulse on Its Energy Efficiency Based on the Hypothesis of Guaranteed Defibrillation

Effect of defibrillation on the performance of an implantable vagus nerve stimulation system

BackgroundVagus Nerve Stimulation (VNS) delivers Autonomic Regulation Therapy (ART) for heart failure (HF), and has been associated with improvement in cardiac function and heart failure symptoms. VNS is delivered using an implantable pulse generator (IPG) and lead with electrodes placed around the cervical vagus nerve. Because HF patients may receive concomitant cardiac defibrillation therapy, testing was conducted to determine the effect of defibrillation (DF) on the VNS system.MethodsDF testing was conducted on three ART IPGs (LivaNova USA, Inc.) according to international standard ISO14708-1, which evaluated whether DF had any permanent effects on the system. Each IPG was connected to a defibrillation pulse generator and subjected to a series of high-energy pulses.ResultsThe specified series of pulses were successfully delivered to each of the three devices. All three IPGs passed factory electrical tests, and interrogation confirmed that software and data were unchanged from the pre-programmed values. No shifts in parameters or failures were observed.ConclusionsImplantable VNS systems were tested for immunity to defibrillation, and were found to be unaffected by a series of high-energy defibrillation pulses. These results suggest that this VNS system can be used safely and continue to function after patients have been defibrillated.

Areas of effectiveness of half-sine monophasic and biphasic depolarizing defibrillation pulses on the diagram of energy / phase of fibrillation cycle

The aim of this study is to compare the areas of effectiveness of half-sine monophasic and biphasic depolarizing defibrillation pulses in the diagram of energy / phase of fibrillation cycle. The study was carried out on the ten Tusscher-Panfilov 2006 model of the human ventricular myocyte under the influence of simulated fibrillation in the BeatBox simulation environment under the Fedora operating system. The simulation was carried out on a computer under the Windows 10 operating system, the Fedora operating system was implemented in the Oracle VM VirtualBox virtualization environment. The results of computer simulations have shown that the areas of effectiveness for monophasic and biphasic defibrillation pulses are significantly different. In a biphasic pulse, the fraction of a fibrillation cycle at which refractoriness is extended is significantly higher than that of a monophasic pulse at low defibrillation pulse energies. It can be assumed that this provides the energy advantage of a biphasic defibrillation pulse over a monophasic one.

Comparison of the energy efficiency of defibrillation pulses based on the hypothesis of guaranteed defibrillation

The aim of this study is to compare, on the basis of the guaranteed defibrillation hypothesis, the energy efficiency of a trapezoidal defibrillation pulse with fixed rise and fall times with the main types of defibrillation pulses: truncated exponential with the tilt of 50%, rectangular and half-sine. The study was carried out using the ten Tusscher–Panfilov 2006 human ventricular myocyte model subjected to simulated fibrillation in the BeatBox simulation environment. Depolarizing excitation stimuli with a high frequency were used to simulate fibrillation. The results of computer simulation based on the hypothesis of the guaranteed defibrillation showed that defibrillation pulses are energetically efficient (have low values of threshold energy of defibrillation) in a rather narrow range of phase duration values, beyond which a rapid increase in the threshold energy is observed. In terms of energy efficiency, the trapezoidal pulse with the sloping rise and fall is very close to the half-sine one, and at the same time it has a wider range of energetically effective durations. Significantly higher minimum threshold energy of guaranteed defibrillation is a characteristic of rectangular and truncated exponential pulses, while the truncated exponential pulse has a more uniform characteristic in the area of energetically effective durations. From the results obtained, it can be assumed that the maximum duration of the phases of the defibrillation pulse should be limited to the value of no more than 9ms. In this case, the nominal delivered energy at the load impedance of 175Ω should be at least 140J. The possibility of increasing the pulse duration without a significant drop in its energy efficiency will ensure the delivery of more energy in patients with high transthoracic impedance and, accordingly, a greater probability of successful defibrillation. The above will also increase the probability of successful defibrillation in patients with defibrillation electrodes placement errors.

Evaluation of the Influence of the Rise and Fall Times of a Monophasic Trapezoidal Defibrillation Pulse on Its Energy Efficiency Using the ten Tusscher–Panfilov Cardiomyocyte Model

The ten Tusscher–Panfilov 2006 cardiomyocyte model was subjected to simulated fibrillation to determine the dependence of the threshold energy of guaranteed defibrillation on the duration of the trapezoidal defibrillation pulse with sloping rise and fall for different rise and fall times. According to the guaranteed defibrillation hypothesis, the duration of the current refractory period of all myocardial myocytes after exposure to a defibrillation pulse should be no less than the duration of the period of the fibrillation waves. This can lead to the cessation of the propagation of fibrillation waves through the myocardium. Computer simulation showed that the threshold energy of guaranteed defibrillation decreases only with an increase in the pulse rise time until the threshold energy of the energy-optimal half-sine pulse is reached. An increase in the pulse fall time reduces the threshold defibrillation energy spread in the range of energy-efficient pulse durations. In this case, the range of energy-efficient pulse durations shifts toward greater values.

Effect of Defibrillation on the Performance of an Implantable Vagus Nerve Stimulation System

Background Vagus Nerve Stimulation delivers Autonomic Regulation Therapy (ART) for heart failure (HF), and in a pilot study has been associated with improvement in heart rate, heart rate variability, left ventricular function, 6-minute walk distance, NYHA class, and quality of life. VNS is delivered using an implantable pulse generator (IPG) and a lead placed around the cervical vagus nerve. Because patients with HF may receive concomitant cardiac defibrillation therapy, testing was conducted to determine the effect of defibrillation (DF) upon the VNS system. Methods DF testing was conducted on three Model 103 IPGs, which have identical hardware to the VITARIA™ system used to deliver ART for HF. DF testing evaluated whether DF had any permanent effects on the VNS system, and that programmed software settings and data capture were recoverable through reprogramming. Testing was conducted according to the methodology specified in the international standard ISO 14708-1 for active implantable medical devices. All of the testing equipment was verified to be in proper working order with current calibration. Each IPG was connected to a defibrillation pulse generator (MegaPulse Defib) and subjected to a series of voltage spikes, monophasic pulses, and biphasic pulses. The pulse amplitude was 140 V, and was connected to the device through a 300 Ω resistor. For each application of energy, three positive-polarity pulses were delivered 20 seconds apart, followed by a 60-second pause, and three negative-polarity pulses 20 seconds apart (Figure). Results The specified series of high-energy pulses were successfully delivered to each of the three devices. All three IPGs passed the electrical tests, and interrogation confirmed that software and data were unchanged from the pre-programmed values. No shifts in parameters or failures were observed. Conclusions Implantable VNS systems equivalent to VITARIA were tested for immunity to defibrillation, and were found to be unaffected by a series of high-energy defibrillation pulses. These results suggest that this VNS system can be used safely and continue to function after patients have been defibrillated.

Electromuscular Incapacitation Current Induced Neuromuscular Tissue Injury.

Electrical stun devices (ESDs) serve a basic role in law enforcement and provide an alternative to lethal options for target control by causing electromuscular incapacitation (EMI). A fundamental concern is the adverse health consequences associated with their use. The capability of EMI electric field pulses to disrupt skeletal muscle cells (i.e. rhabdomyolysis) was investigated over the operational range commonly used in commercial EMI devices. Functional and structural alteration and recovery of muscle and nerve tissue were assessed. In an anesthetized swine model, the left thigh was exposed to 2 min of electrical pulses, using a commercially available ESD or a custom-made EMI signal power amplifier. Serum creatinine phosphokinase (CPK), troponin, aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) levels were monitored intermittently for 6 h post-EMI exposure. A standard external cardiac defibrillator served as a positive control. Muscle and nerve tissue histology adjacent to the EMI contacts were examined. Post-EMI shock skeletal muscle function was evaluated by analyzing the compound muscle action potentials (CMAPs) of the rectus femoris muscle. Maximal energy cardiac defibrillator pulses resulted in rhabdomyolysis and marked elevation of CPK, LDH, and AST 6 h post-shock. EMI field pulses resulted in the animals developing transient acidosis. CMAP amplitudes decreased approximately 50% after EMI and recovered to near-normal levels within 6 h. Within 6 h post-EMI exposure, blood CPK was mildly increased, LDH was normal, and no arrhythmia was observed. Minimal rhabdomyolysis was produced by the EMI pulses. These results suggest that EMI exposure is unlikely to cause extremity rhabdomyolysis in normal individuals. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

Shaping of Biphasic Defibrillation Pulses with Stepwise Shape Regulation and Fixed Duration

A defibrillator pulse generator designed by E. E. Gorokhov-Miroshnikov for generation of biphasic defibrillation pulses with stepwise regulation of shape and optimum fixed duration (~10 ms) in the range of load impedance 25-175 Ω is presented. The generator, built using relatively low-cost electronic components, provides a high stored energy utilization coefficient. The main characteristics of the biphasic pulse generated by the prototype of generator are given. The design features of the generator are described.

Comparative Modeling of Biphasic Defibrillation Pulses: Quasi-sinusoidal and Trapezoidal with Sloping Rise and Fall

A model of a defibrillator power module generating pulses of arbitrary shape with load impedance of 25-250 Ω was used to obtain the characteristics of biphasic pulses: quasi-sinusoidal pulses (Gurvich–Venin pulses) and trapezoidal pulses with sloping rise and fall. At high load impedances (100-250 Ω), production of trapezoidal pulses, as compared with quasi-sinusoidal, produced larger mean first-phase currents (by 11-20%) and greater pulse energy (by 25-35%).

Defibrillation failure in patients undergoing replacement of subcutaneous defibrillator pulse generator

Defibrillation threshold (DFT) testing is commonly performed in patients undergoing subcutaneous implantable cardioverter-defibrillator (S-ICD) implantation. Growing evidence indicates that successful DFT testing correlates with the technique used for implantation of the defibrillation lead and pulse generator. However, evidence on whether DFT testing should be performed in patients undergoing S-ICD pulse generator replacement is lacking. The purpose of this study was to determine the outcome of DFT testing in patients undergoing replacement of an S-ICD pulse generator. A total of 357 S-ICD implantations were performed between November 2010 and July 2019. Twenty-five consecutive patients underwent S-ICD replacement between 2015 and 2019. Clinical data, perioperative medication, technical measurements, and PRAETORIAN score were assessed and grouped according to the outcome of DFT testing. In 5 of 25 patients (20%), induced ventricular fibrillation was not successfully terminated after the first or second 65-J shock after pulse generator replacement with need for external defibrillation. Repositioning of the pulse generator and/or capsulectomy at the pocket site were necessary to achieve effective DFT with 65 J in all cases. Shock impedance increased in all patients at the time of pulse generator replacement compared to first implantation and was significantly higher in patients with ineffective DFT (119 ± 17 Ω vs 93 ± 26 Ω; P = .03). Otherwise, no differences in clinical characteristics, comorbidities, body mass index, intraoperative medication, or PRAETORIAN score were predictive of defibrillation failure. The high proportion of patients with DFT failure after S-ICD pulse generator replacement indicates that DFT testing is mandatory to ensure safe function of the S-ICD.

Measuring defibrillator surface potentials: The validation of a predictive defibrillation computer model

Implantable cardioverter defibrillators (ICDs) are commonly used to reduce the risk in patients with life-threatening arrhythmias, however, clinicians have little systematic guidance to place the device, especially in cases of unusual anatomy. We have previously developed a computational model that evaluates the efficacy of a delivered shock as a clinical and research aid to guide ICD placement on a patient specific basis. We report here on progress to validate this model with measured ICD surface potential maps from patients undergoing ICD implantation and testing for defibrillation threshold (DFT). We obtained body surface potential maps of the defibrillation pulses by adapting a limited lead selection and potential estimation algorithm to deal with the limited space for recording electrodes. Comparison of the simulated and measured potential maps of the defibrillation shock yielded similar patterns, a typical correlation greater than 0.9, and a relative error less than 15%. Comparison of defibrillation thresholds also showed accurate prediction of the simulations. The high agreement of the potential maps and DFTs suggests that the predictive simulation generates realistic potential values and can accurately predict DFTs in patients. These validation results pave the way for use of this model in optimization studies prior to device implantation.

Control of electrical turbulence by periodic excitation of cardiac tissue.

Electrical turbulence in cardiac tissue is associated with arrhythmias such as life-threatening ventricular fibrillation. Recent experimental studies have shown that a sequence of low-energy electrical far-field pulses is able to terminate fibrillation more gently than a single high-energy pulse which causes severe side effects. During this low-energy antifibrillation pacing (LEAP), only tissue near sufficiently large conduction heterogeneities, such as large coronary arteries, is activated. In order to optimize LEAP, we performed extensive simulations of cardiac tissue perforated by blood vessels, employing two alternative cellular models that exhibit electrical turbulence at a similar length scale. Moreover, the scale of blood vessels in our two-dimensional simulations was chosen such that the threshold for single pulse defibrillation matches experimental values. For each of the 100 initial conditions, we tested different electrical field strengths, pulse shapes, numbers of pulses, and periods between the pulses. LEAP is successful for both models, albeit with substantial differences. One model exhibits a spectrum of chaotic activity featuring a narrow peak around a dominant frequency. In this case, the optimal period between low-energy pulses matches this frequency and LEAP greatly reduces the required energy for successful defibrillation. For pulses with larger energies, the system is perturbed such that underdrive pacing becomes advantageous. The spectrum of the second model features a broader peak, resulting in a less pronounced optimal pacing period and a decreased energy reduction. In both cases, pacing with five or six pulses which are separated by the dominant period maximizes the energy reduction.

Study of the Impact of Rectangular Current Pulses on the Ten Tusscher-Panfilov Model of Human Ventricular Myocyte

The behavior of the 2006 ten Tusscher-Panfilov model of human ventricular myocytes under the impact of periodic excitation impulses was studied in the BeatBox simulation environment. The cardiomyocyte model has a limited susceptibility to an forced higher frequency excitation rhythm. A high-frequency excitation rhythm can be forced by gradually increasing the frequency of excitation impulses. The mechanism of defibrillation pulse impact consists of presumably prolonging the refractoriness of cardiomyocytes which undermines their susceptibility for a long time to a forced high-frequency rhythm of fibrillation, as a result for which they hinder the propagation of a fibrillation wave. This is the only mechanism of defibrillation that was identified during the simulation. The threshold energy of a depolarizing defibrillation pulse prolonging the refractoriness of the cardio-myocyte varies depending on a delay relative to the excitation impulse (the excitation cycle phase) in a wide range (the maximum value exceeds the minimum by several thousand times). The results show differences in the mechanisms of impact on a cardiomyocyte between an excitation impulse and a monophasic defibrillation pulse.

Intermuscular technique for implantation of the subcutaneous implantable cardioverter defibrillator: long-term performance and complications.

The subcutaneous cardioverter defibrillator was designed to overcome electrode complications of transvenous defibrillation systems. While largely achieved, pocket complications have increased. Subcutaneous implantation of the pulse generator leaves it prone to erosion, extrusion, discomfort, and poor cosmesis. We use a demonstration electrode and pulse generator with fluoroscopy, prior to prepping and draping, to maximize the left ventricular mass between them. We adapted a submuscular abdominal ICD technique to implant the S-ICD intermuscularly between the anterior surface of serratus anterior and the posterior surface of latissimus dorsi. Surgery in our patients beyond the subcutaneous tissue was bloodless, as muscle layers were carefully separated but not incised, which also protected the long thoracic nerve. Two layers of muscle protect the pulse generator. We have implanted 82 consecutive patients with this technique, taking ∼65 min. All patients were converted with 65 J standard polarity shock during induced arrhythmia conversion testing, with six (7.3%) patients requiring a repositioning of the pulse generator prior to successful conversion. Seven spontaneous episodes of ventricular fibrillation were detected in three (3.6%) patients, all successfully converted back to sinus rhythm. Long-term patient outcomes have been good with low complication rates over the mean ± standard deviation 3.6 ± 1.2 years. Our intermuscular technique and implant methodology is successful for placement of the subcutaneous defibrillator pulse generator. Our technique leads to an excellent cosmetic result and high levels of patient satisfaction. Rates of first shock conversion during defibrillation testing, inappropriate shocks, and complications during follow-up compare favourably with previous published case series. There were no left arm movement limitations post-operatively.