Defibrillation Fields Research Articles

Defibrillators: Selecting the Right Device for the Right Patient.

Advances in the field of defibrillation have brought to practice different types of devices that include the transvenous implantable cardioverter-defibrillator (ICD) with or without cardiac resynchronization therapy, the subcutaneous ICD (S-ICD), and the wearable cardioverter-defibrillator. To ensure optimal use of these devices and to achieve best patient outcomes, clinicians need to understand how these devices work, learn the characteristics of patients who qualify them for one type of device versus another, and recognize the remaining gaps in knowledge surrounding these devices. The transvenous ICD has been shown in several randomized clinical trials to improve the survival of patients resuscitated from near-fatal ventricular fibrillation and those with sustained ventricular tachycardia with syncope or systolic heart failure as a result of ischemic or nonischemic cardiomyopathy despite receiving guideline-directed medical therapy. Important gaps in knowledge regarding the transvenous ICD involve the role of the ICD in patient subgroups not included, or not well represented, in clinical trials and the need to refine the selection criteria for the ICD in patients who are indicated for it. S-ICDs were recently introduced into the clinical arena as another option for many patients who have an approved indication for a transvenous ICD. The main advantage of the S-ICD is a lower risk of infection and lead-related complications; however, the S-ICD does not offer bradycardia or antitachycardia pacing. The S-ICD may be ideal for patients with limited vascular access, high infection risk, or some congenital heart diseases. However, more data are needed regarding the efficacy and effectiveness of the S-ICD in comparison to transvenous ICDs, the extent of defibrillation testing required, and the use of the S-ICD with other novel technologies, including leadless pacemakers. Cardiac resynchronization therapy-defibrillators are indicated in patients with a left ventricular ejection fraction ≤35%, QRS width ≥130 ms, and New York Heart Association class II, III, or ambulatory IV symptoms despite treatment with guideline-directed medical therapy. Multiple randomized controlled trials have shown that the cardiac resynchronization therapy-defibrillator improves survival, quality of life, and several echocardiographic measures. One main challenge related to cardiac resynchronization therapy-defibrillators is the 30% nonresponse rate. Many initiatives are underway to address this challenge including improved cardiac resynchronization therapy and imaging technologies and enhanced selection of patients and device programming.

Sudden cardiac arrest on the football field of play—highlights for sports medicine from the European Resuscitation Council 2015 Consensus Guidelines

The European Resuscitation Council (ERC) 2015 Guidelines for Resuscitation were published recently. For the first time, these guidelines included a subsection on ‘cardiac arrest during sports activities’ in the section...

A shocking past: a walk through generations of defibrillation development.

Defibrillation is one of the most successful and widely recognized applications of electrotherapy. Yet the historical road to its first successful application in a patient and the innovative adaptation to an implantable device is marred with unexpected turns, political and personal setbacks, and public and scientific condemnation at each new idea. Driven by dedicated scientists and ever-advancing creative applications of new technologies, from electrocardiography to high density mapping and computational simulations, the field of defibrillation persevered and continued to evolve to the life-saving tool it is today. In addition to critical technological advances, the history of defibrillation is also marked by the plasticity of the theory of defibrillation. The advancing theories of success have propelled the campaign for reducing the defibrillation energy requirement, instilling hope in the development of a painless and harmless electrical defibrillation strategy.

Virtual 3D Heart Models to Aid Pacemaker Implantation in Children

Virtual 3D Heart Models to Aid Pacemaker Implantation in Children

Radiotherapy-induced pacemaker and implantable cardioverter defibrillator malfunction

It is well known that ionizing radiation can interfere with circuits in permanent pacemakers and implantable cardioverter defibrillators. Contemporary implantable cardiac devices use complementary metal-oxide silicon in combination with other very sensitive transistors. These sensitive components are especially susceptible to electromagnetic and ionizing radiation, which can potentially cause permanent damage. Electromagnetic interference is, in general, a transient phenomenon. Radiologic imaging tests have been implicated in rare cases of implantable device dysfunction and these events have been mostly transient. The American Association of Physicists in Medicine last published recommendations regarding irradiation of pacemakers in 1994. This publication is outdated and may not be pertinent for the current technology used both in the field of artificial cardiac pacing and defibrillation and in the field of radiation oncology. Updated guidelines are definitely needed.

Sudden Death Prevention With Implantable Devices

The “modern” era of the treatment of ventricular tachyarrhythmias with device-based therapy may have begun in 1899, when Prevost and Battelli noted, almost as an afterthought, that direct current shock could terminate ventricular fibrillation (VF) in dogs.1 Three decades later, pioneering work in the field of defibrillation concluded that the passage of electrical current across the heart can both initiate and terminate VF.2,3 Still, little attention was paid to this phenomenon, as evidenced by Paul Dudley White’s Heart Disease , which devoted less than half a page to VF and characterized the arrhythmia as “a condition of little importance so far as we know now.”4 In 1947, the thoracic surgeon Claude Beck saved the first human life by the successful use of cardiac defibrillation in a 14-year-old boy who developed VF during a thoracic surgical procedure and went on to achieve a full recovery.5 These early accomplishments provided the foundation for the landmark work of Mirowski and Mower that ultimately led to the development of the implantable cardioverter-defibrillator (ICD) and its introduction in humans in 1980.6 Pacing may prevent sudden cardiac death due to bradyarrhythmias and in certain circumstances such as torsade de pointes associated with congenital long-QT syndrome (LQTS) and pause-dependent ventricular tachycardia (VT). Although no controlled studies exist, retrospective analyses suggest that recurrent torsade de pointes in patients with LQTS may be prevented by continuous pacing.7 Early clinical data on small numbers of patients suggested that the combination of β-adrenergic blockade plus continuous pacing reduced the number of syncopal events and the anticipated rate of sudden death in high-risk LQTS patients.8 The beneficial effects of pacing may be limited to patients with LQT2 and LQT3, in which the transmural dispersion of repolarization worsens steeply during bradycardia.9 Genotype-phenotype correlation confirms that …

Implantation of systems for cardiac resynchronisation: tips and tricks ? cardiac surgeon's view

Specific problems of cardiosurgical implantation of biventricular devices for cardiac resynchronisation therapy are elucidated elaborately. In particular, the necessity and amount of intraoperative monitoring as well as the appropriate mode of anaesthesia are described. Furthermore, the sequence of lead placement, the technique of coronary sinus intubation using a guiding catheter as well as means to avoid thrombus formation in the coronary sinus are depicted. Biventricular ICD devices should be implanted from a left sided approach to integrate the device into the defibrillation field and to maintain the option of placing an additional subcutaneous array lead. It is of particular cardiosurgical interest that coronary vein leads are applicable for ventricular stimulation in patients after tricuspid valve replacement thus avoiding repeated surgical exposure of the heart.

Membrane polarization induced in the myocardium by defibrillation fields: an idealized 3-D finite element bidomain/monodomain torso model

This study develops a three-dimensional finite element torso model with bidomain myocardium to simulate the transmembrane potential (TMP) of the heart induced by defibrillation fields. The inhomogeneities of the torso are modeled as eccentric spherical volumes with both the curvature and the rotation features of cardiac fibers incorporated in the myocardial region. The numerical computation of the finite element bidomain myocardial model is validated by a semianalytic solution. The simulations show that rotation of fiber orientation through the depth of the myocardial wall changes the pattern of polarization and decreases the amount of cardiac tissue polarized compared to the idealized analytic model with no fiber rotation incorporated. The TMP induced by transthoracic and transvenous defibrillation fields are calculated and visualized. The TMP is quantified by a continuous measure of the percentage of myocardial mass above a potential gradient threshold. Using this measure, the root mean square differences in TMP distribution produced by reversing the electrode polarity for anterior-posterior and transvenous electrode configurations are 13.6 and 28.6%, respectively. These results support the claim that a bidomain model of the heart predicts a change of defibrillation threshold with reversed electrode polarity.

Finite element analysis of defibrillation fields in a human torso model for ventricular defibrillation.

In order to optimize defibrillation electrode systems for ventricular defibrillation thresholds (DFTs), a Finite Element Torso model was built from fast CT scans of a patient who had large cardiac dimensions (upper bound of normal) but no heart disease. Clinically used defibrillation electrode configurations, i.e. Superior Vena Cava (SVC) to Right Ventricle (RV) (SVC-RV), left pectoral Can to RV (Can-RV) and Can + SVC-RV, were analyzed. The DFTs were calculated based on 95% ventricular mass having voltage gradient > 5 V/cm and these results were also compared with clinical data. The low voltage gradient regions with voltage gradient < 5 V/cm were identified and the effect of electrode dimension and location on DFTs were also investigated for each system. A good correlation between the model results and the clinical data supports the use of Finite Element Analysis of a human torso model for optimization of defibrillation electrode systems. This correlation also indicates that the critical mass hypothesis is the primary mechanism of defibrillation. Both the FEA results and the clinical data show that Can + SVC-RV system offers the lowest voltage DFTs when compared with SVC-RV and Can-RV systems. Analysis of the effect of RV, SVC and Can electrode dimensions and locations can have an important impact on defibrillation lead designs.

Extracting isovolumes from three-dimensional torso geometry using PROLOG

Three-dimensional (3-D) finite element torso models are widely used to simulate defibrillation field quantities, such as potential, gradient, and current density. These quantities are computed at spatial nodes that comprise the torso model. These spatial nodes typically number between 10(5) and 10(6), which makes the comprehension of torso defibrillation simulation output difficult. Therefore, the objective of this study is to rapidly prototype software to extract a subset of the geometric model of the torso for visualization in which the nodal information associated with the geometry of the model meets a specified threshold value (e.g., minimum gradient). The data extraction software is implemented in PROLOG, which is used to correlate the coordinate, structural, and nodal data of the torso model. A PROLOG-based environment has been developed and is used to rapidly design and test new methods for sorting, collecting, and optimizing data extractions from defibrillation simulations in a human torso model for subsequent visualization.

Lead failure caused by twiddler's syndrome in subpectorally implanted unipolar single-lead cardioverter-defibrillators

Twiddler's syndrome, first described in 1968 by Bayless, Beanlands, and Baird 1 as a rare complication in patients with pacemakers, is characterized by dislodgment of transvenous leads by the twisting of pulse generators in the subcutaneous pocket, resulting in lead malfunction. As might be expected, similar complications could arise in the case of subpectorally placed implantable cardioverterdefibrillators (ICDs). Especially in unipolar defibrillation systems, which use the housing of the ICD itself as the second active defibrillation electrode, device migration could have a fatal influence on the defibrillation field. We report two cases of this rare complication. PATIENT 1. A 66-year-old male patient (body index 24.5 kg/m 2) with severe coronary artery disease and ventricular tachycardia was referred to our clinic. Bypass surgery was

Detailed 2-D and 3-D finite element modeling of the human body for the evaluation of defibrillation fields

Detailed finite-element modeling of the human body has been carried out for the evaluation of implanted electrode potential distributions and defibrillation fields. Modeling details have been achieved in 2-D and 3-D down to the arbitrary topologies of the human body and its organs. This type of analysis requires 2-D and 3-D mesh generators that can be used to discretize arbitrary shapes. The main objective of this study is to develop a highly accurate clinical tool to be used by physicians to determine the adequacy of operation of an implanted device across the human heart before surgery. Furthermore, the model could determine the optimum sizes and locations of the stimulation electrodes for achieving a successful defibrillation according to the physiological requirements regarding shock uniformity and strength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cardiac potential and potential gradient fields generated by single, combined, and sequential shocks during ventricular defibrillation.

Potential gradient field determination may be a helpful means of describing the effects of defibrillation shocks; however, potential gradient field requirements for defibrillation with different electrode configurations have not been established. To evaluate the field requirements for defibrillation, potential fields during defibrillation shocks and the following ventricular activations were recorded with 74 epicardial electrodes in 12 open-chest dogs with the use of a computerized mapping system. Shock electrodes (2.64 cm2) were attached to the lateral right atrium (R), lateral left ventricular base (L), and left ventricular apex (V). Four electrode configurations were tested: single shocks of 14-msec duration given to two single anode-single cathode configurations, R:V and L:V, and to one dual anode-single cathode configuration, (R+L):V; and sequential 7-msec shocks separated by 1 msec given to R:V and L:V (R:V----L:V). Defibrillation threshold (DFT) current was significantly lower for R:V----L:V than for the other configurations and markedly higher for L:V. Despite these differences, the minimum potential gradients measured at DFT were not significantly different (approximately 6-7 V/cm for each electrode configuration). Potential gradient fields generated by the electrode configurations were markedly uneven, with a 15-27-fold change from lowest to highest gradient, with the greatest decrease in gradient occurring near the shock electrodes. Although gradient fields varied with the electrode configuration, all configurations produced weak fields along the right ventricular base. Early sites of epicardial activation after all unsuccessful shocks occurred in areas in which the field was weak; 87% occurred at sites with gradients less than 15 V/cm. Ventricular tachycardia originating in high gradient areas near shock electrodes followed 11 of 67 successful shocks. These data suggest that 1) defibrillation fields created by small epicardial electrodes are very uneven; 2) achievement of a certain minimum potential gradient over both ventricles is necessary for ventricular defibrillation; 3) the difference in shock strengths required to achieve this minimum gradient over both ventricles may explain the differences in DFTs for various electrode configurations; and 4) high gradient areas in the uneven fields can induce ectopic activation after successful shocks.

Calculations of potential distributions produced by implanted electrodes in a man model by finite elements

The finite-element (FE) method is used to analyze and determine the potential distribution produced by implanted stimulating electrodes used in conjunction with an implanted defibrillator. These electrodes are used to deliver an energy shock to halt ventricular fibrillation during fatal arrhythmias in human beings. The FE solution was obtained by solving the Laplace equation using a Galerkin procedure. An infinite cylindrical model having three coaxial layers of tissue with two electrodes was used to show preliminary results of the FE model. An analytical procedure was developed and used to validate the FE results. The overall objective of this study is to develop a computer model for the study of defibrillation fields. This model can be used to estimate the potential distribution and potential gradients on the heart for various electrode sizes and configurations for a given shock strength. The most promising variation of these defibrillation-electrode configurations can be chosen for experimental testing in laboratory animals and possibly in human beings. >

A volume conductor model of the thorax for the study of defibrillation fields.

The authors develop a physiologically realistic volume conductor model for calculating epicardial potentials during transthoracic stimulation. The objective of the study is to measure cardiac potentials during a transthoracic stimulus and compare the measurements to calculated epicardial potentials obtained from the model. The results for all four stimulus configurations (anterior-posterior, neck-waist, precordial, and right-left) on the torso consistently yield correlation coefficients of about 0.90 and RMS errors of 47% between calculated and measured epicardial potentials for a homogeneous torso. Incorporating the effects of the skeletal muscle layer improves the agreement, i.e., correlation coefficients increase to about 0.914 and RMS errors decrease to about 42%. At the same time, the lungs and heart have little influence on the agreement between measured and calculated epicardial potentials. The results of the study demonstrate the importance of the skeletal muscle layer in physiologically realistic volume conductor models. >