Organization Of Electrical Activity Research Articles

Abstract 240: Comparison of Hemodynamics Generated by Synchronized and Interposed Compressions During Treatment of Pseudo Electro-mechanical Dissociation

Introduction: Pseudo electro-mechanical dissociation (P-EMD) is a cardiac arrest variant characterized by a life-threatening reduction in cardiac output in the presence of organized electrical activity. Synchronization of chest compressions to the R-wave in the ECG may be preferable to the delivery of standard CPR. However, in the bradycardic P-EMD state, synchronization may result in inadequate blood flow due to the low compression/heart rate. This pilot study examined the hemodynamic effect of interposing additional chest compressions between synchronized chest compressions during bradycardic P-EMD to increase the compression rate. Methods: P-EMD was induced via hypoxia in three female swine (~30 kg) and treated with synchronized compressions until the onset of asystole (HR<12 BPM). Interposed compressions were added when the heart rate fell below 60 BPM. A chest compression was classified as synchronized or interposed depending on the presence or absence of a co-incident R-wave. Hemodynamic parameters were integrated or averaged over each compression interval. Results: Synchronized compressions tended to produce larger aortic pressures, larger carotid blood flows, and lower right atrial pressures than interposed compressions. Data from one experiment are shown in Figure 1. The relative hemodynamic benefit of a synchronized chest compression appears to depend on the effectiveness of the underlying heart contraction. The interposed chest compressions generated forward carotid blood flow and increased the compression rate during bradycardia. Discussion: During bradycardic P-EMD, synchronized compressions may generate better hemodynamics than interposed compressions, and the combination of synchronized and interposed compressions may result in more blood flow than the delivery of synchronized compressions alone. Figure 1. Comparison of hemodynamics generated by synchronized compressions (blue) and interposed compressions (red).

A New Classification Algorithm With Guaranteed Sensitivity and Specificity for Medical Applications

We propose a novel algorithm to construct binary classifiers, in the spirit of the recently proposed guaranteed error machine (GEM) but with a-posteriori assessment of the “support” instances and without the need for a ternary output. We provide rigorous guarantees on the probability of misclassification; differently from GEM, such guarantees aim to bound the conditional probability of error given the true value of the classified instance. The proposed classifier can be tuned in order to give more importance to one of the two kinds of error, and to balance their ratio also in the presence of unbalanced training sets. Guaranteeing the conditional probabilities of error is crucial in many classification problems, in particular medical diagnoses, where being able to push the tradeoff between sensitivity (conditional probability of detecting a “true positive”) and specificity (conditional probability of detecting a “true negative”) toward higher sensitivity is of paramount importance. The application that first motivated our study is the classification of ventricular fibrillation (VF) into cases where restoration of an organized electrical activity is achieved immediately after a defibrillatory shock (“positive”), and cases where prompt resuscitation does not happen (“negative”). We provide experimental evidence that our approach is promising by testing it against three well-known medical datasets, against some data on VF that are available to the authors, and with Monte Carlo simulations.

Does the choice of definition for defibrillation and CPR success impact the predictability of ventricular fibrillation waveform analysis?

BackgroundQuantitative analysis of ventricular fibrillation (VF), such as amplitude spectral area (AMSA), predicts shock outcomes. However, there is no uniform definition of shock/cardiopulmonary resuscitation (CPR) success in out-of-hospital cardiac arrest (OHCA). The objective of this study is to investigate post-shock rhythm variations and the impact of shock/CPR success definition on the predictability of AMSA. MethodsA total of 554 shocks from 257 OHCA patients with VF as initial rhythm were analyzed. Post-shock rhythms were analyzed every 5s up to 120s and annotated as VF, asystole (AS) and organized rhythm (OR) at serial time intervals. Three shock/CPR success definitions were used to evaluate the predictability of AMSA: (1) termination of VF (ToVF); (2) return of organized electrical activity (ROEA); (3) return of potentially perfusing rhythm (RPPR). ResultsRhythm changes occurred after 54.5% (N=302) of shocks and 85.8% (N=259) of them occurred within 60s after shock delivery. The observed post-shock rhythm changes were (1) from AS to VF (24.9%), (2) from OR to VF (16.1%), and (3) from AS to OR (12.1%). The area under the receiver operating characteristic curve (AUC) for AMSA as a predictor of shock/CPR success reached its maximum 60s post-shock. The AUC was 0.646 for ToVF, 0.782 for ROEA, and 0.835 for RPPR (p<0.001) respectively. ConclusionsPost-shock rhythm is unstable in the first minute after the shock. The predictability of AMSA varies depending on the definition of shock/CPR success and performs best with the return of potentially perfusing rhythm endpoint for OHCA.

Abstract 11969: Effects of Definition of Defibrillation Success on Predictability of Ventricular Fibrillation Waveform Analysis

Introduction: Quantitative analysis of ventricular fibrillation (VF) waveform has the potential to optimize the timing of defibrillation by predicting defibrillation outcome. However, there is no consensus on the definition of defibrillation success in out-of-hospital settings. In the present study, we used a registry data of out-of-hospital cardiac arrest (OHCA) to investigate the effects of different definitions of defibrillation success on the predictability of amplitude spectrum area (AMSA). Methods: A total of 581 shocks from 264 OHCA patients with VF as the first recorded rhythm were included in this study.We determined the presence of VF, asystole or organized rhythm 120 seconds after shock delivery as the final outcome. In order to identify how different definitions of defibrillation success affect the predictive value of AMSA, we used 3 different definitions that were previously described in the literatures. (1) Termination of VF: A successful shock is defined as no presence of VF for 5 seconds or longer. (2) Return of organized electrical activity (ROEA): A successful shock is defined by an organized rhythm observed for at least 5 seconds after delivery of the shock. (3) Return of a potentially perfusing rhythm: An organized rhythm is restored with a heart rate greater than 40 beats/min, commencing within 60 seconds after shock delivery. Results: A total of 153 cases (26.3%) had an final outcome of organized rhythm. The defibrillation success rates were 72.1%, 49.2% and 27.0% when the 3 different definitions were used. The area under the receiver-operating-characteristic curve was 0.563 for termination of VF, 0.706 for organized rhythm, and 0.814 for return of potentially perfusing rhythm (p&lt;0.001). Conclusion: AMSA’s ability to predict shock success varied strongly depending on which definition of shock success was used. Termination of VF may be a good measure of defibrillation efficacy for new onset of VF, while return of a potentially perfusing rhythm is clinically more relevant as a definition for defibrillation success in OHCA. AMSA had the highest predictive value when used with the outcome of potentially perfusing rhythm. This supports the assumption that AMSA is, at least to some extent, a measure of myocardial viability.

End-of-life electrical surges

We read the study by Borjigin et al. about postcardiac arrest electrical activity and the possible explanation for near death experiences (NDEs) with great interest (1). Our research group at The George Washington University Medical Center published an observation of end-of-life electrical surges (ELES) in 2009 (2). In that study, we proposed that ELES could be responsible for NDEs, and this new study largely confirms that hypothesis. However, it is important to recognize that nothing has been definitively proven. Nonetheless, the findings of multiple research groups confirm that organized electrical activity can emanate from the brain at the time of death (3, 4). Our ongoing research here at The George Washington University Medical Center suggest that about half of patients who succumb in the intensive care unit display an ELES, and the waveform is at a higher frequency than that observed in animals. The significance of ELES remains unknown and is the source of significant controversy.

Inverse Relationship Between Fractionated Electrograms and Atrial Fibrosis in Persistent Atrial Fibrillation: Combined Magnetic Resonance Imaging and High-Density Mapping

This study sought to evaluate the relationship between fibrosis imaged by delayed-enhancement (DE) magnetic resonance imaging (MRI) and atrial electrograms (Egms) in persistent atrial fibrillation (AF). Atrial fractionated Egms are strongly related to slow anisotropic conduction. Their relationship to atrial fibrosis has not yet been investigated. Atrial high-resolution MRI of 18 patients with persistent AF (11 long-lasting persistent AF) was registered with mapping geometry (NavX electro-anatomical system (version 8.0, St. Jude Medical, St. Paul, Minnesota)). DE areas were categorized as dense or patchy, depending on their DE content. Left atrial Egms during AF were acquired using a high-density, 20-pole catheter (514 ± 77 sites/map). Fractionation, organization/regularity, local mean cycle length (CL), and voltage were analyzed with regard to DE. Patients with long-lasting persistent versus persistent AF had larger left atrial (LA) surface area (134 ± 38 cm(2) vs. 98 ± 9 cm(2), p = 0.02), a higher amount of atrial DE (70 ± 16 cm(2) vs. 49 ± 10 cm(2), p = 0.01), more complex fractionated atrial Egm (CFAE) extent (54 ± 16 cm(2) vs. 28 ± 15 cm(2), p = 0.02), and a shorter baseline AF CL (147 ± 10 ms vs. 182 ± 14 ms, p = 0.01). Continuous CFAE (CFEmean [NavX algorithm that quantifies Egm fractionation] <80 ms) occupied 38 ± 19% of total LA surface area. Dense DE was detected at the left posterior left atrium. In contrast, the right posterior left atrium contained predominantly patchy DE. Most CFAE (48 ± 14%) occurred at non-DE LA sites, followed by 41 ± 12% CFAE at patchy DE and 11 ± 6% at dense DE regions (p = 0.005 and p = 0.008, respectively); 19 ± 6% CFAE sites occurred at border zones of dense DE. Egms were less fractionated, with longer CL and lower voltage at dense DE versus non-DE regions: CFEmean: 97 ms versus 76 ms, p < 0.0001; local CL: 153 ms versus 143 ms, p < 0.0001; mean voltage: 0.63 mV versus 0.86 mV, p < 0.0001. Atrial fibrosis as defined by DE MRI is associated with slower and more organized electrical activity but with lower voltage than healthy atrial areas. Ninety percent of continuous CFAE sites occur at non-DE and patchy DE LA sites. These findings are important when choosing the ablation strategy in persistent AF.

Prediction of Defibrillation Outcome by Ventricular Fibrillation Waveform Analysis: A Clinical Review

The most frequent initial rhythm in out-of-hospital witnessed cardiac arrest is ventricular fibrillation (VF) and electrical defibrillation is still the only effective therapy for the termination of this life-threatening cardiac arrhythmia. Even though earlier defibrillation is greatly emphasized during cardiopulmonary resuscitation (CPR), unnecessary or repetitive high energy defibrillations are associated with decreased post-resuscitation myocardial function. Optimizing the timing of defibrillation is of great importance in order to discriminate patients should receive immediate defibrillation versus alternate therapies such as CPR. Since characteristics of VF waveform changes over time and with CPR, which exhibit predictable ability of defibrillation success, quantitative analysis of VF waveform has the potential to guide defibrillation. This article reviewed methods developed for VF waveform analysis (including time domain, frequency domain, time-frequency domain, nonlinear analysis, and combination analysis techniques) and their performances for the prediction of defibrillation outcomes in clinical settings. The retrospective meta-analysis confirmed that VF waveform could predict the return of organized electrical activity, restoration of spontaneous circulation, and survival reliably. Additionally, predictors based on time-frequency and nonlinear methods were superior to other methods on the whole. However, no prospective studies have been performed to identify the optimal time of defibrillation utilizing VF waveform analysis until now. Therefore, the value of VF waveform analysis to guide clinical countershock management still needs further investigation.

Features of the organization of the cerebral cortex bioelectric potentials and visceral state in neurotic depression

Studies were conducted with the participation of 20 patients with different classical variants of neurotic depression. The spatial organization of the bioelectrical activity of the brain was studied with the method of cross-correlation and coherent analysis. The autonomic-visceral state was assessed by the results of the auricular cryoreflex test (measurement of the cold sensibility of auricular points). The clinical picture of neurotic depression was shown to be reflected in the structure of the EEG spatial organization, which is modified depending on the degree of neurotic depression and the concomitant anxiety and asthenic syndromes. In the group with depressive syndrome without concomitant asthenic or anxiety manifestations, most changes were revealed in the right frontotemporal-left posterotemporal region. A cross-correlation and coherence decrease in the frontotemporal regions of both hemispheres and markedly increased cross-correlations in the right posterotemporal region were revealed in the depression + associated anxiety group. In the group where the depressive and anxiety syndromes were associated with marked asthenic manifestations, decreased cross-correlation and coherent relations in the frontotemporal regions of both hemispheres were observed. The clinical picture of neurotic disorders is reflected in a specific pattern of variations in the spatial organization of electrical activity of the cerebral cortex and in variations in the autonomic visceral state parameters. The development of negative emotional states in humans is accompanied by changes in the visceral functions. Variations in the central brain structures involve the zones of representation of emotional reactions and the zones of cortical representation of the organs. Insignificant central variations may cause autonomic dysfunction.

Onset dynamics of ventricular tachyarrhythmias as measured by dominant frequency

Differences in dominant frequency (DF), a measure of electrical activation rate, were used to characterize and classify ventricular tachyarrhythmias (VTA) at onset. In canine 3- to 5-day-old infarct border zone, monomorphic re-entrant ventricular tachycardia (MVT) was repeatedly induced by programmed electrical stimulation (14 experiments, total of 23 instances used for analysis). Ventricular fibrillation (VF) and polymorphic ventricular tachycardia (PVT) occasionally occurred (total of 23 and 4 episodes, respectively, for all experiments). For each of 196 to 312 border zone bipolar electrode recordings, the DF and DF spatial derivative (DFD) were calculated to assess electrical activity organization and were used to classify VTAs at onset. For classification, measurements were made at 1.5 and 3 seconds from last stimulus for all recording sites, and at 2.25 and 3 seconds for 3- to 7-site subsets as a test with limited data. At 1.5 seconds after stimulus end, the DF/DFD magnitudes were ordered: MVT < PVT < VF (P < .001). DF/DFD trended upward in VF, downward in MVT, and lacked trend in PVT (P < .001). Based on DF/DFD magnitudes/trends, the MVT/VF classifier accuracy was 94.6% (all sites/1.5 s), 97.9% (all sites/3 s), 82.6% (subset sites/2.25 s), and 86.3% (subset sites/3 s). VTAs are distinguishable at early onset by degree and trend in organization of electrical activity as estimated by DF and DFD. VF becomes increasingly disorganized, MVT becomes increasingly organized, and PVT remains intermediate. It may be possible to apply this technique for analysis and classification in a clinical setting using currently available special mapping catheters.

A novel application of sample entropy to the electrocardiogram of atrial fibrillation

Nowadays, several non-linear regularity estimators have been successfully applied to invasive atrial electrograms in order to characterize the atrial electrical activity organization during atrial fibrillation (AF). This arrhythmia is the most common encountered in clinical practice, accounting for approximately one-third of all the hospitalizations for cardiac rhythm disturbances. However, from a clinical point of view, it would be more desired to evaluate atrial activity (AA) organization from surface electrocardiographic (ECG) recordings, since they can be obtained easily and cheaply and the risks associated with invasive recordings could be avoided. In this work, Sample Entropy (SampEn) is proposed to assess the organization degree of the AA obtained from surface ECGs. To this respect, a reliable and non-invasive organization estimator would allow the prediction of spontaneous AF termination, since invasive studies have shown more organized electrical activity signals during the preceding instants of AF termination. The proposed method computed SampEn over the AA obtained from TQ segments, free of QRST complexes, and was validated with a database containing a training set of 20 AF recordings, with known termination properties, and a test set of 30 recordings. A simulation study showed that patients with heart rates of 130 bpm and above must be handled with care, because TQ intervals could be considerably reduced (<50 ms). As an overall result, spontaneous AF termination in 90% of the learning and test recordings was correctly predicted through this novel approach. As a conclusion, this work introduces the application of a non-linear regularity index able to assess significative differences in AA organization from surface ECG recordings during AF.

Rescue shock outcomes during out-of-hospital cardiac arrest

Questions remain about the optimal timing and method for treating ventricular fibrillation (VF) during out-of-hospital cardiac arrest, and a variety of treatment protocols are used. Detailed description of rescue shock outcomes during actual patient care under different protocols would allow rational comparison of treatment strategies. The purpose of this study is to describe rescue shock outcomes in a single system using a specific defibrillation protocol. Patient care records were examined for all adult (age> or =18 years) out-of-hospital cardiac arrest cases treated by an urban paramedic system during a 52-month interval. The immediate outcomes of monophasic rescue shocks were determined from the record and were classified as asystole, VF, restoration of organized electrical activity (ROEA), or restoration of spontaneous circulation (ROSC). Among 1496 cases of cardiac arrest, 654 received a median of 3 (IQR 1,5) rescue shocks. Of these cases, 408 (28%) had an initial rhythm of VF whereas VF developed later during resuscitation in the remainder. For an initial series of three escalating rescue shocks, most cases of ROSC (9%) and ROEA (12%) occurred after the first shock. The likelihood that a rescue shock would result in ROSC or ROEA increased with witnessed collapse, and rescue shock number. An initial rhythm of asystole was associated with a decreased likelihood that a rescue shock would result in ROEA. Witnessed collapse and an initial rhythm other than asystole were associated with an increased likelihood of rescue shock success. There is a small but real incremental gain in ROSC and ROEA from delivering three rescue shocks in rapid succession. The greater incidence of rescue shock success with later rescue shocks suggests that VF responds favorably to ongoing resuscitation.

Calcium-induced calcium release mechanism contributes to disorganization of VF dynamics during evolving global ischemia

Background: Defibrillation success as well as organization of electrical activity rapidly deteriorates with time after onset of VF leading to global ischemia. The mechanism underlying the evolution of VF organization remains speculative and poorly understood. Recently, intracellular Ca fluctuations mediated by the calcium-induced calcium release (CICR) mechanism have been implicated in wave fragmentation during VF. We hypothesized that the role of CICR in VF dynamics increases as VF/ischemia progresses. Methods: Pig hearts were Langendorff-perfused with blood. Coronary perfusion was interrupted after electrical induction of VF. Di-4-ANEPPS fluorescence movies were recorded from the anterior wall of the left ventricle during 0-7 minutes of VF/ischemia in the absence (control, n 7) and presence (n 5) of CICR channel blocker ryanodine (10 mol/l). Dominant frequency (DF) and the power at the DF (PDF) were computed for each pixel. Average PDF over the mapped area was used to assess the degree of periodicity during VF. We used Hilbert transform to detect trajectories of wavebreaks (WBs). The number of WBs per movie was used to quantify the complexity of VF. Results: PDF exhibited a biphasic dynamics in both groups, but ryanodine postponed the descending phase and caused a consistent increase in periodicity between 3 and 7 min of VF/ischemia (p 0.01, Figure). A transient decrease in the number of WBs was seen at minute two of ischemia in both control and ryanodine groups. Subsequently, WBs increased at minute 3 reaching a plateau at minute 4 in control animals. This effect was absent in the ryanodine group (p 0.001, Figure). Conclusion: CICR mechanism contributes selectively to disorganization of VF dynamics after 3 minutes of VF/ischemia, without any significant effect during earlier phases of VF.

Late-Breaking Clinical Trial Abstracts

Late-Breaking Clinical Trial Abstracts

Two-dimensional analysis of ventricular fibrillation in the guinea pig

Cardiac arrhythmias are undesirable electrical activity in the heart. Ventricular fibrillation (VF) is a fatal cardiac arrhythmia and is characterized by the breakdown of organized electrical activity in the ventricular myocardium. However, little is known about VF, partially because it is difficult to study and understand an apparently disorganized activity. One method for discovering the nature of VF is processing the epicardial electrical signals by using cardiac mapping techniques. These techniques involve the study of propagation patterns seen in VF. In this project, we used guinea pigs to study the spatial organization of the epicardial electrical activity during VF. VF was induced in 9 open chest guinea pigs and epicardial electrode data were acquired by using a square array of 192 electrodes for 4 seconds every minute. The mean correlation length and dominant frequency were measured in each recorded segment. Correlation length is a measure of the spatial order in a system and dominant frequency is the frequency corresponding to the spectral maximum. The mean correlation length was found to vary between 1-7 mm and the dominant frequency was in the range of 1-14 Hz. This study suggests that guinea pig VF exhibits a level of organization equivalent to or greater than that seen in previous studies.

Life span of ventricular fibrillation frequencies.

The nature and organization of electrical activity during ventricular fibrillation (VF) are important and controversial subjects dominated by 2 competing theories: the wavebreak and the dominant mother rotor hypothesis. To investigate spatiotemporal characteristics of ventricular fibrillation (VF), transmembrane potentials (V(m)) were recorded from multiple sites of perfused rabbit hearts using a voltage-sensitive dye and a photodiode array or a CCD camera, and the time-frequency characteristics of V(m) were analyzed by short-time fast Fourier transform (FFT) or generalized time-frequency representation with a cone-shaped kernel. The analysis was applied to all pixels to track VF frequencies in time and space. VF consisted of blobs, which are groups of contiguous pixels with a common frequency and an ill-defined shape. At any time t, several VF frequency blobs coexisted in the field of view, and the number of coexisting blobs was on average 5.9+/-2.1 (n=8 hearts) as they appeared and disappeared discontinuously with time and were not fixed in space. The life span of frequency blobs from birth to either annihilation or breakup to another frequency had a half-life of 0.39+/-0.13 second (n=4 hearts). The Ca2+ channel blocker nifedipine increased the stability of VF frequencies and reduced the number of frequency blobs progressing to a single frequency. In conclusion, VF consists of dynamically changing frequency blobs, which have a short life span and can be modified by pharmacological interventions, suggesting that VF is maintained by dynamically changing multiple wavelets.

Different patterns of atrial activation in idiopathic atrial fibrillation: simultaneous multisite atrial mapping in patients with paroxysmal and chronic atrial fibrillation

OBJECTIVESWe aimed to evaluate: 1) the behavior of electrical activity simultaneously in different atrial regions during atrial fibrillation (AF); 2) the difference of atrial activation between paroxysmal and chronic AF; 3) the atrial refractoriness dispersion; and 4) the correlation between the effective refractory periods (ERPs) and the FF intervals.BACKGROUNDLittle data exist on the electrophysiologic characteristics of the different atrial regions in patients with AF. A more detailed knowledge of the electrical activity during AF may provide further insights to improve treatment of AF.METHODSRight and left atria were extensively mapped in 30 patients with idiopathic AF (18 paroxysmal and 12 chronic). In different atrial locations, we analyzed 1) the FF interval duration; and 2) the grade of organization and, in case of organized electrical activity, the direction of atrial activation. Furthermore, in patients with paroxysmal AF, we determined the atrial ERP, evaluated the ERP dispersion and assessed the presence of a correlation between the ERPs and the FF intervals.RESULTSIn patients with chronic AF, we observed a shortening of the FF intervals and a greater prevalence of disorganized activity in all the atrial sites examined. In patients with paroxysmal AF, a significant dispersion of refractoriness was observed. The right lateral wall showed longer FF intervals and more organized atrial activity and, unexpectedly, the shortest mean ERPs. In contrast, the septal area showed shorter FF intervals, greater disorganization and the longest mean ERPs.CONCLUSIONSElectrical activity during AF showed a significant spatial inhomogeneity, which was more evident in patients with paroxysmal AF. The mean FF intervals did not correlate with the mean ERPs.

Spatial organization of electrical processes in the brain: problems and solutions.

Theoretical questions of the spatial organization of electrical activity in the brain are discussed in terms of a multilevel realization of the synergetic principle for formation of functional systems underlying behavior and mental function. The role of the spatial-temporal superimposition of coherent structures of biopotentials in generating fields of increased activity in the cerebral cortex is discussed, these being responsible for integrative and associative functions. A hypothesis is proposed regarding the relationship between the energy and information factors of coherent structures as one of the important characteristics describing the efficiency of energy-informational processes. Emphasis is placed on the need for considering not only linear, but also nonlinear associations of biopotentials in considerations of the form and functional sense of their spatial organization.

Dynamics of high-frequency (up to 200 Hz) components of brain electrical activity during learning reflect the functional mosaicism of the neocortex.

This study was undertaken with the aim of identifying frequency bands with correlated changes in the spectral power amplitudes of brain electrical activity, including high-frequency components (the 1-200 Hz band) in four dogs, using one-dimensional analysis. Factor and cluster analysis of the spectral densities of various parts of the cortex and the olfactory bulb were carried out. The ratios of factors in different parts of the brain, both in terms of the proportions of the total dispersity and in terms of weightings, provided data on regional and individual differences in electrical activity. During learning (development of a motor habit consisting of pressing a feeder pedal), the factor organization of electrical activity became more, complex, particularly in the high-frequency part of the spectrum (40-170 Hz). The changes consisted of the appearance of narrower frequency sub-bands, each of which was present at high weighting (0.7-0.9) for one of the factors. The use of high-frequency components allowed functional mosaicism of the neocortex to be detected.

An estimation of the spatial organization of electrical activity in the heart during ventricular fibrillation in humans

An estimation of the spatial organization of electrical activity in the heart during ventricular fibrillation in humans

Torsades de Pointes

Torsades de Pointes. Torsades de pointes are typically characterized by an ECG pattern of polymorphous but organized electrical activity of ventricular origin that occurs in the setting of a long QT interval, long‐coupled bigeminy, and has specific precipitating causes and therapeutic responses. Torsades de pointes can result from congenital (adrenergic dependent) and acquired (pause dependent) factors and may have similar cardiac substrates with different precipitating events. (J Cardiovasc Electrophysiol, Vol. 3, pp. 281–292, June 1992)