Angerlike behavioral state potentiates myocardial ischemia-induced T-wave alternans in canines

Stress, the autonomic nervous system, and sudden death

The existence of an important relationship between stress, the autonomic nervous system, and sudden cardiac death (SCD) has been long recognized. In the present essay we review the large number of conditions, acting at individual or at population level, that have been causally associated to SCD and discuss the mechanistic and translational value of the studies exploring such associations. These conditions include external stressors (earthquakes, wars) and internal stressors (anger, fear, loss of a loved one) and emotions of even opposite sign. Most situations confirm the time-honored view that increases in sympathetic activity are proarrhythmic whereas increases in vagal activity are protective; however, we will also show and discuss a condition in which the culprit appears to be the excess of vagal activity. The physiologic rationale underlying the most typical situations is on one hand the profibrillatory effect of the increase in the heterogeneity of repolarization secondary to the release of norepinephrine, and on the other the combined effect of acetylcholine to lower heart rate and to antagonize the cardiac effects of norepinephrine at ventricular level. An interesting facet of this potentially lethal relationship is that the elements involved are by no means always exceptional, and they can actually represent part of our everyday life.

Psychological factors and cardiac repolarization instability during anger in implantable cardioverter defibrillator patients

Background

Evidence indicates that emotions such as anger are associated with increased incidence of sudden cardiac death, but the biological mechanisms remain unclear. We tested the hypothesis that, in patients with sudden death vulnerability, anger would be associated with arrhythmic vulnerability, indexed by cardiac repolarization instability.

Methods

Patients with coronary artery disease (CAD) and an implantable cardioverter defibrillator (ICD; n = 41) and healthy controls (n = 26) gave an anger‐inducing speech (anger recall), rated their current (state) anger, and completed measures of trait (chronic) levels of Anger and Hostility. Repolarization instability was measured using QT Variability Index (QTVI) at resting baseline and during anger recall using continuous ECG.

Results

ICD patients had significantly higher QTVI at baseline and during anger recall compared with controls, indicating greater arrhythmic vulnerability overall. QTVI increased from baseline to anger recall to a similar extent in both groups. In ICD patients but not controls, during anger recall, self‐rated anger was related to QTVI (r = .44, p = .007). Trait (chronic) Anger Expression (r = .26, p = .04), Anger Control (r = −.26, p = .04), and Hostility (r = .25, p = .05) were each associated with the change in QTVI from baseline to anger recall (ΔQTVI). Moderation analyses evaluated whether psychological trait associations with ΔQTVI were specific to the ICD group. Results indicated that Hostility scores predicted ΔQTVI from baseline to anger recall in ICD patients (β = 0.07, p = .01), but not in controls.

Conclusions

Anger increases repolarization lability, but in patients with CAD and arrhythmic vulnerability, chronic and acute anger interact to trigger cardiac repolarization lability associated with susceptibility to malignant arrhythmias.

Evaluation of salivary vasopressin as an acute stress biomarker in healthy dogs with stress due to noise and environmental challenges

Background

Stress is associated with various detrimental changes in physiological health that affect an animal’s quality of life. The hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic-adreno-medullar (SAM) axis are two main physiological pathways that constitute the stress response of an organism. Arginine vasopressin (AVP) is a mediator of the HPA axis and is known to be related to social behaviours and stress. The serum concentration of AVP is higher in more aggressive dogs and humans with post-traumatic stress disorder. Salivary biomarker analysis is a non-invasive method to assess stress. The purpose of this study was to evaluate the possibility of using salivary AVP as an acute stress biomarker in dogs. Salivary AVP concentration was measured before and after exposure to all relevant environmental stimuli (i.e. car trip to the lab, physical examination by the veterinarian, and sampling procedure,) and then after 30 min of vacuum noise exposure. Behavioural assessments, physiologic parameter assessments, and serum cortisol analysis were conducted in combination. Statistical analysis was conducted separately in the total study population, the less stressed group, and the more stressed group, respectively.

Results

Based on stress behaviour analysis scores, 28 dogs were classified into less or more stressed groups. All four physiologic parameters (blood pressure, body temperature, heart rate, and respiratory rate) were significantly increased after noise and environmental challenges, in the more stressed group. Serum cortisol did not show any significant change. Salivary AVP significantly decreased after noise and environmental stimulation in the more stressed group but not in the less stressed group. Salivary AVP and blood pressure changes were negatively correlated in the more stressed group.

Conclusion

Salivary AVP may be a potential acute stress biomarker in dogs.

Contemplative Practices: A Strategy to Improve Health and Reduce Disparities

Health has many dimensions, and intolerance and lack of compassion may contribute to the poor health and disparities in our nation. Tolerance can convey an inherent paradox or dissonance that can be associated with stress. However, tolerance has a dimension of acceptance, an acknowledgement and acceptance of what "is" at the present moment, that can relieve tension associated with differing beliefs and practices. Compassionate consideration of others can be combined with acceptance to create harmony within and across individuals. In this article, we explore how contemplative practices can cultivate tolerance and compassion and contribute to improvements in individual and population health.

Perceived Discrimination and Longitudinal Change in Kidney Function Among Urban Adults

OBJECTIVE

Perceived discrimination has been associated with psychosocial distress and adverse health outcomes. We examined associations of perceived discrimination measures with changes in kidney function in a prospective cohort study, the Healthy Aging in Neighborhoods of Diversity across the Life Span.

METHODS

Our study included 1620 participants with preserved baseline kidney function (estimated glomerular filtration rate [eGFR] ≥ 60 mL/min/1.73 m) (662 whites and 958 African Americans, aged 30-64 years). Self-reported perceived racial discrimination and perceived gender discrimination (PGD) and a general measure of experience of discrimination (EOD) ("medium versus low," "high versus low") were examined in relation to baseline, follow-up, and annual rate of change in eGFR using multiple mixed-effects regression (γbase, γrate) and ordinary least square models (γfollow).

RESULTS

Perceived gender discrimination "high versus low PGD" was associated with a lower baseline eGFR in all models (γbase = -3.51 (1.34), p = .009 for total sample). Among white women, high EOD was associated with lower baseline eGFR, an effect that was strengthened in the full model (γbase = -5.86 [2.52], p = .020). Overall, "high versus low" PGD was associated with lower follow-up eGFR (γfollow = -3.03 [1.45], p = .036). Among African American women, both perceived racial discrimination and PGD were linked to lower follow-up kidney function, an effect that was attenuated with covariate adjustment, indicating mediation through health-related, psychosocial, and lifestyle factors. In contrast, EOD was not linked to follow-up eGFR in any of the sex by race groups.

CONCLUSIONS

Perceived racial and gender discrimination are associated with lower kidney function assessed by glomerular filtration rate and the strength of associations differ by sex and race groups. Perceived discrimination deserves further investigation as a psychosocial risk factors for kidney disease.

Electromuscular incapacitating devices discharge and risk of severe bradycardia

Electromuscular incapacitating devices (EMDs) are high-voltage, low-current stimulators causing involuntary muscle contractions and sensory response. Existing evidence about cardiac effects of EMD remains inconclusive. The aim of our study was to analyze electrocardiographic, echocardiographic, and microvolt T-wave alternans (MTWA) changes induced by EMD discharge.

We examined 26 volunteers (22 men; median age 30 years) who underwent single standard 5-second duration exposure to TASER X26 under continuous echocardiographic and electrocardiographic monitoring. Microvolt T-wave alternans testing was performed at baseline (MTWA-1), as well as immediately and 60 minutes after EMD exposure (MTWA-2 and MTWA-3, respectively).

Mean heart rate (HR) increased significantly from 88 ± 17 beats per minute before to 129 ± 17 beats per minute after exposure (P < 0.001). However, in 2 individuals, an abrupt decrease in HR was observed. In one of them, interval between two consecutive beats increased up to 1.7 seconds during the discharge. New onset of supraventricular premature beats was observed after discharge in 1 patient. Results of MTWA-1, MTWA-2, and MTWA-3 tests were positive in one of the subjects, each time in a different case.

Standard EMD exposure can be associated with a nonuniform reaction of HR and followed by heart rhythm disturbances. New MTWA positivity can reflect either the effect of EMD exposure or a potential false positivity of MTWA assessments.

Acute Stress Decreases but Chronic Stress Increases Myocardial Sensitivity to Ischemic Injury in Rodents

Cardiovascular disease (CVD) is the largest cause of mortality worldwide, and stress is a significant contributor to the development of CVD. The relationship between acute and chronic stress and CVD is well evidenced. Acute stress can lead to arrhythmias and ischemic injury. However, recent evidence in rodent models suggests that acute stress can decrease sensitivity to myocardial ischemia-reperfusion injury (IRI). Conversely, chronic stress is arrhythmogenic and increases sensitivity to myocardial IRI. Few studies have examined the impact of validated animal models of stress-related psychological disorders on the ischemic heart. This review examines the work that has been completed using rat models to study the effects of stress on myocardial sensitivity to ischemic injury. Utilization of animal models of stress-related psychological disorders is critical in the prevention and treatment of cardiovascular disorders in patients experiencing stress-related psychiatric conditions.

Psychogenic Stress in Hospitalized Dogs: Cross Species Comparisons, Implications for Health Care, and the Challenges of Evaluation

Simple Summary

The effects of stress on health outcomes in animals are well documented. Veterinary clinicians may be able to improve their patients’ care by better understanding how to recognize and reduce stress in those patients. This review will describe the physiology of the mammalian stress response and known health consequences of psychogenic, rather than physical, stress; as well as methods of measuring stress in animals. While the review will address stress in a range of domestic species, it will specifically focus on dogs.

Abstract

Evidence to support the existence of health consequences of psychogenic stress has been documented across a range of domestic species. A general understanding of methods of recognition and means of mitigation of psychogenic stress in hospitalized animals is arguably an important feature of the continuing efforts of clinicians to improve the well-being and health of dogs and other veterinary patients. The intent of this review is to describe, in a variety of species: the physiology of the stress syndrome, with particular attention to the hypothalamic-pituitary-adrenal axis; causes and characteristics of psychogenic stress; mechanisms and sequelae of stress-induced immune dysfunction; and other adverse effects of stress on health outcomes. Following that, we describe general aspects of the measurement of stress and the role of physiological measures and behavioral signals that may predict stress in hospitalized animals, specifically focusing on dogs.

Stress and the kidney

The prevalence of CKD has increased considerably over the past 2 decades. The rising rates of CKD have been attributed to known comorbidities such as diabetes, hypertension, and obesity; however, recent research has begun to explore the degree to which social, economic, and psychological factors have implications for the prevalence and progression of CKD, especially among high-risk populations such as African Americans. It has been suggested that stress can have implications for CKD, but this area of research has been largely unexplored. One contributing factor associated with the paucity of research on CKD is that many of the social, psychological, and environmental stressors cannot be recreated or simulated in a laboratory setting. Social science has established that stress can have implications for health, and we believe that stress is an important determinant of the development and progression of CKD. We draw heavily from the social scientific and social epidemiologic literature to present an intersectional conceptual frame specifying how stress can have implications for kidney disease, its progression, and its complications through multiple stressors and pathways.

Quantitative T-wave alternans analysis for guiding medical therapy: an underexploited opportunity

Reducing the toll of sudden cardiac death (SCD) remains a major challenge in cardiology, as it is the leading cause of adult mortality in the industrially developed world, claiming 310,000 lives annually in the United States alone. The main contemporary noninvasive index of cardiovascular risk, left ventricular ejection fraction (LVEF), has not proved adequately reliable, as the majority of individuals who die suddenly have relatively preserved cardiac mechanical function. Monitoring of T-wave alternans (TWA), a beat-to-beat fluctuation in ST-segment or T-wave morphology, is an attractive approach to risk stratification on both scientific and clinical grounds, as this ECG phenomenon has been shown using the FDA-cleared Spectral and Modified Moving Average methods to assess risk for cardiovascular mortality including SCD in studies enrolling >12,000 individuals with depressed or preserved LVEF. The evidence supporting TWA as a therapeutic target is reviewed.

Controlled exposure study of air pollution and T-wave alternans in volunteers without cardiovascular disease

BACKGROUND

Epidemiological studies have assessed T-wave alternans (TWA) as a possible mechanism of cardiac arrhythmias related to air pollution in high-risk subjects and have reported associations with increased TWA magnitude.

OBJECTIVE

In this controlled human exposure study, we assessed the impact of exposure to concentrated ambient particulate matter (CAP) and ozone (O3) on T-wave alternans in resting volunteers without preexisting cardiovascular disease.

METHODS

Seventeen participants without preexisting cardiovascular disease were randomized to filtered air (FA), CAP (150 μg/m3), O3 (120 ppb), or combined CAP + O3 exposures for 2 hr. Continuous electrocardiograms (ECGs) were recorded at rest and T-wave alternans (TWA) was computed by modified moving average analysis with QRS alignment for the artifact-free intervals of 20 beats along the V2 and V5 leads. Exposure-induced changes in the highest TWA magnitude (TWAMax) were estimated for the first and last 5 min of each exposure (TWAMax_Early and TWAMax_Late respectively). ΔTWAMax (Late-Early) were compared among exposure groups using analysis of variance.

RESULTS

Mean ± SD values for ΔTWAMax were -2.1 ± 0.4, -2.7 ± 1.1, -1.9 ± 1.5, and -1.2 ± 1.5 in FA, CAP, O3, and CAP + O3 exposure groups, respectively. No significant differences were observed between pollutant exposures and FA.

CONCLUSION

In our study of 17 volunteers who had no preexisting cardiovascular disease, we did not observe significant changes in T-wave alternans after 2-hr exposures to CAP, O3, or combined CAP + O3. This finding, however, does not preclude the possibility of pollution-related effects on TWA at elevated heart rates, such as during exercise, or the possibility of delayed responses.

Anger, emotion, and arrhythmias: from brain to heart

Strong emotion and mental stress are now recognized as playing a significant role in severe and fatal ventricular arrhythmias. The mechanisms, although incompletely understood, include central processing at the cortical and brain stem level, the autonomic nerves and the electrophysiology of the myocardium. Each of these is usually studied separately by investigators from different disciplines. However, many are regulatory processes which incorporate interactive feedforward and feedback mechanisms. In this review we consider the whole as an integrated interactive brain-heart system.

Biological pacemakers in canines exhibit positive chronotropic response to emotional arousal

BACKGROUND

Biological pacemakers based on the HCN2 channel isoform respond to beta-adrenergic and muscarinic stimulation, suggesting a capacity to respond to autonomic input.

OBJECTIVE

The purpose of this study was to investigate autonomic response to emotional arousal in canines implanted with murine HCN2-based biological pacemakers using gene therapy.

METHODS

An electronic pacemaker was implanted with its lead in the right ventricular apical endocardium (VVI 35 bpm). An adenoviral HCN2/GFP construct (Ad-HCN2, n = 7) or saline (control, n = 5) was injected into the left bundle branch on day 2 after radiofrequency ablation of the atrioventricular node to induce complete atrioventricular block. Emotional arousal was achieved by presenting food following an overnight fast. Autonomic control was evaluated with Poincaré plots of R-R(N) against R-R(N+1) intervals to characterize heart rate variability (HRV) and with continuous RR interval assessment via 24-hour ambulatory ECG. The 24-hour ECG and Poincaré plot shape were analyzed.

RESULTS

During day 1 after biological pacemaker implantation, Poincaré HRV parameters and RR intervals were unchanged with food presentation. However, on day 7, food presentation was accompanied by an increase in HRV (SD1, p < 0.07, and SD2, p < 0.05) and shortening of RR interval (P < .05) in dogs with Ad-HCN2 but not in controls.

CONCLUSION

This is the first demonstration that biological pacemakers are capable of responding to natural arousal stimuli to elicit appropriate chronotropic responses, a potential advantage over electronic pacemakers.

Usefulness of T-wave alternans in sudden death risk stratification and guiding medical therapy

Visible T-wave alternans (TWA), a beat-to-beat alternation in the morphology and amplitude of the ST segment or T wave, has been observed for over a century to occur in association with life-threatening arrhythmias in patients with acute coronary syndrome, heart failure, and cardiac channelopathies. This compelling linkage prompted development of quantitative techniques leading to FDA-cleared commercial methodologies for measuring nonvisible levels of TWA in the frequency and time domains. The first aim of this review is to summarize evidence from more than a hundred studies enrolling a total of >12,000 patients that support the predictivity of TWA for cardiovascular mortality and sudden cardiac death. The second focus is on the usefulness of TWA in guiding therapy. Until recently, TWA has been used primarily in decision making for cardioverter-defibrillator implantation. Its potential utility in guiding pharmacologic therapy has been underappreciated. We review clinical literature supporting the usefulness of TWA as an index of antiarrhythmic effects and proarrhythmia for different drug classes. Beta-adrenergic and sodium channel-blocking agents are the most widely studied drugs in clinical TWA investigations, with both reducing TWA magnitude; the exception is patients in whom sodium channel blockade discloses the Brugada syndrome and provokes macroscopic TWA. An intriguing possibility is that TWA may help to detect beneficial effects of nonantiarrhythmic agents such as the angiotensin II receptor blocker valsartan, which indirectly protects from arrhythmia through improving myocardial remodeling. We conclude that quantitative analysis of TWA has considerable potential to guide pharmacologic intervention and thereby serve as a therapeutic target.

Social environmental stressors, psychological factors, and kidney disease

Kidney disease is one of the most striking examples of health disparities in American public health. Disparities in the prevalence and progression of kidney disease are generally thought to be a function of group differences in the prevalence of kidney disease risk factors such as diabetes, hypertension, and obesity. However, the presence of these comorbidities does not completely explain the elevated rate of progression from chronic kidney disease (CKD) to end-stage renal disease among high-risk populations such as African Americans. We believe that the social environment is an important element in the pathway from CKD risk factors to CKD and end-stage renal disease. This review of the literature draws heavily from social science and social epidemiology to present a conceptual frame specifying how social, economic, and psychosocial factors interact to affect the risks for and the progression of kidney disease.

Anger-induced T-wave alternans predicts future ventricular arrhythmias in patients with implantable cardioverter-defibrillators

OBJECTIVES

This study sought to determine whether T-wave alternans (TWA) induced by anger in a laboratory setting predicts future ventricular arrhythmias in patients with implantable cardioverter-defibrillators (ICDs).

BACKGROUND

Anger can precipitate spontaneous ventricular tachycardia/ventricular fibrillation and induce TWA. Whether anger-induced TWA predicts future arrhythmias is unknown.

METHODS

Sixty-two patients with ICDs underwent ambulatory electrocardiography during a mental stress protocol, 3 months after the ICD was implanted. T-wave alternans was analyzed using time-domain methods. After a > or =1 year follow-up, ICD stored data was reviewed to determine incidence of ICD-terminated ventricular tachycardia/ventricular fibrillation.

RESULTS

Patients with ICD-terminated arrhythmias during follow-up (n = 10) had higher TWA induced by anger, 13.2 microV (interquartile range [IQR] 9.3 to 16 microV), compared with those patients without future ventricular arrhythmias, 9.3 microV (IQR 7.5 to 11.5 microV, p < 0.01). Patients in the highest quartile of anger-induced TWA (>11.9 microV, n = 15) were more likely to experience arrhythmias by 1 year than those in the lower quartiles (33% vs. 4%) and during extended follow-up (40% vs. 9%, p < 0.01 for both). In multivariable regression controlling for ejection fraction, prior clinical arrhythmia, and wide QRS, anger-induced TWA remained a significant predictor of arrhythmia, with likelihood in the top quartile 10.8 times that of other patients (95% confidence interval: 1.6 to 113, p < 0.05).

CONCLUSIONS

Anger-induced TWA predicts future ventricular arrhythmias in patients with ICDs, suggesting that emotion-induced repolarization instability may be 1 mechanism linking stress and sudden death. Whether there is a clinical role for anger-induced TWA testing requires further study.

Basis for sudden cardiac death prediction by T-wave alternans from an integrative physiology perspective

Detection of microvolt levels of T-wave alternans (TWA) has been shown to be useful in identifying individuals at heightened risk for sudden cardiac death. The mechanistic bases for TWA are complex, at the cellular level involving multiple mechanisms, particularly instabilities in membrane voltage (i.e., steep action potential duration restitution slope) and disruptions in intracellular calcium cycling dynamics. The integrative factors influencing TWA at the systemic level are also multifold. We focus on three main variables: heart rate, autonomic nervous system activity, and myocardial ischemia. Clinically, there is growing interest in extending TWA testing to include ambulatory ECG monitoring as well as exercise. The former modality permits assessment of the influence of diverse provocative stimuli of daily life, including physical activity, circadian factors, mental stress, and sleep-state related disturbances in respiratory and cardiovascular function. Two major emerging concepts in clinical TWA testing are discussed: quantitative analysis of TWA level to complement the current binary classification scheme, and risk stratification of patients with preserved left ventricular function, the population with the largest absolute number of sudden cardiac deaths.

Comparison of microvolt T-wave alternans measurements using atrial pacing compared to atropine administration

BACKGROUND

Microvolt T-wave alternans (MTWA) has been associated with malignant ventricular arrhythmias in patients (pts) with structural heart disease. MTWA has been shown to be a strong heart rate-dependent arrhythmia marker. However, in clinical practice some pts in which MTWA should be assessed are unable to perform physical exercise to increase heart rate due to various reasons.

METHODS

In this study, we investigated the feasibility of noninvasive MTWA measurement by using intravenous atropine to increase heart rate and compared the results to MTWA measurement by right atrial (RA) pacing during electrophysiologic (EP) study in 27 consecutive pts (53 +/- 14 years; nine women). Determining the arrhythmia event-rate, a follow-up of 18 months was performed in all pts.

RESULTS

Using atropine, five pts (18%) did not reach the target heart rate (105 bpm). In the remaining group of pts, concordant results for MTWA assessment could be found in 21 pts (96%). Comparing MTWA positive tests there were slightly higher amplitudes using right atrial (RA) pacing than atropine (7.0 +/- 2.3 microV vs 6.3 +/- 2.2 microV, P = 0.03; r = 0.97). During follow-up all pts with a positive MTWA test had documented ventricular arrhythmias. There were no arrhythmic events in the MTWA negative group.

CONCLUSION

Whenever target heart rate for MTWA evaluation is obtained by intravenous atropine, the results are comparable to RA pacing. In using atropine there has been observed no pharmacologically influenced increase of MTWA voltage leading to false positive MTWA results. Therefore the use of atropine can be recommended as a safe, non-invasive, and reliable method for MTWA assessment.

Depressive symptoms predict recurrence of atrial fibrillation after cardioversion

OBJECTIVE

The aim of this study was to evaluate whether depressive symptoms and the type-D personality are predictive of early recurrence of atrial fibrillation (or atrial flutter; AF) after successful electrical cardioversion (CV).

BACKGROUND

Depressive symptoms are associated with an adverse prognosis in patients with coronary artery disease, congestive heart failure, and ventricular arrhythmias. Anger and hostility have been shown to be predictive of development of AF. However, little is known about the effects of depression on AF.

METHODS

Fifty-four patients with persistent AF completed the Hospital Anxiety and Depression Scale (HADS) and the Type D Scale (DS-14) prior to elective electrical CV. Patients with a successful CV were followed for 2 months.

RESULTS

During the follow-up period, 27 patients (50%) had recurrence of the arrhythmia. Depressive mood (HADS depression scale >7) was the only significant nonsomatic predictor of recurrence, which was observed in 85% of depressed versus 39% of nondepressed patients [odds ratio=8.6; 95% confidence interval (CI)=1.7-44.0, P=.004]. HADS anxiety scores and the presence of the type-D personality pattern were not associated with recurrence of AF. On multivariate Cox regression analysis, including variables with a prevalence >10% of the total study population and a univariate discriminative effect yielding a P value of <.2, a HADS depression score >7 was found to be the only independently predictive variable of arrhythmia recurrence (hazard ratio=2.7; 95% CI=1.05-7.2; P=.046).

CONCLUSIONS

Our results indicate that depressive mood is a major risk factor for recurrence of AF after electrical CV. Heightened adrenergic tone and a proinflammatory state are possible mechanisms responsible for the observed association. Identification of depression may be of value prior to the decision to perform electrical CV.

Emotional triggers of acute coronary syndromes: strength of evidence, biological processes, and clinical implications

Emotional triggers of acute coronary syndromes include population-level events such as earthquakes and terrorist attacks, and individual experiences of acute anger, stress and depression. The methodology of studying emotional triggers has developed markedly over recent years, though limitations remain. The biological processes underlying triggering include acute autonomic dysregulation, neuroendocrine activation, hemostatic and inflammatory responses which, when associated with plaque disruption, promote myocardial ischemia, cardiac dysrhythmia and thrombosis formation. Prevention and management strategies for ameliorating emotional triggering remain to be effectively developed.

Acute volume overload elevates T-wave alternans magnitude

The objective of this study was to determine whether acute volume loading elevates T-wave alternans (TWA) in dogs with structurally normal hearts. TWA predicts sudden cardiac arrest in patients with left ventricular dysfunction and congestive heart failure. However, volume load and ventricular stretch may themselves precipitate arrhythmias. It is unclear to what extent volume load causes TWA. In six male mongrel dogs [25.8 kg (SD 4.2)] under general anesthesia, we measured TWA during progressive atrial pacing to 160 beats/min. Pacing was performed at baseline, at the midpoint and peak of a saline infusion designed to induce acute CHF, and then during diuresis. Dog 1 was hypothermic throughout the protocol and excluded from analysis. For dogs 2– 6, 102 ml/kg (SD 30) were infused over 315 min (SD 50), causing pulmonary capillary wedge pressure to rise from 9.6 (SD 3.5) to 21.2 mmHg (SD 1.6) ( P < 0.01), and heart rate variability to fall ( P < 0.01). TWA magnitude (Valt) rose in all dogs with volume load ( P < 0.001). Compared with baseline, TWA at peak infusion had higher magnitude [Valt 3.4 (SD 1.95) vs. 0.5 μV (SD 0.35); P = 0.011] and occurred at lower heart rates [128 (SD 6) vs. 151 beats/min (SD 12); P = 0.008]. Net volume load was linearly related to Valt ( P < 0.01), with each 10 ml/kg net volume load increasing Valt by 0.23 μV. Acute volume overload elevates TWA in normal canine hearts. Although dramatic, however, this effect may contribute clinically to abnormal TWA only in patients with marked volume overload. Future studies should examine the interaction of fluid overload, myocardial disease, and arrhythmia susceptibility.

Electrophysiologic characteristics of anger-triggered arrhythmias

BACKGROUND

Anger can precipitate ventricular arrhythmias in patients with implantable cardioverter-defibrillators (ICDs). Determining electrophysiologic characteristics of anger-triggered arrhythmias may help elucidate the mechanisms that link emotion and arrhythmia.

OBJECTIVES

We sought to compare the morphology and initiation pattern between ventricular arrhythmias that are triggered by anger and those that are not.

METHODS

At the time of shock, patients with ICDs recorded levels of defined mood states preceding the shock in a diary. Stored intracardiac electrograms (EGMs) were retrieved and analyzed in relation to corresponding mood states. The EGMs from 56 appropriate shocks in 24 patients (18 male, mean age 66 years, 74% with coronary artery disease) were reviewed and analyzed for morphology, mechanism of initiation (sudden onset vs. premature ventricular contraction [PVC]), pause dependence, and other characteristics.

RESULTS

Polymorphic ventricular tachycardia was more common in anger-triggered events, occurring in three (37.5%) of eight anger-triggered events compared with five (10.4%) of 48 of non-anger-triggered events (P <.05). Anger-triggered events were more likely to have PVC initiation, occurring in eight (100%) of eight, compared with 30 (68%) of 44 of non-anger-triggered events (P <.05). More anger-triggered events were pause dependent: five (62.5%) of eight versus seven (15%) of 37 non-anger-related events (P <.01). No difference in response to initial therapy was observed in anger-triggered arrhythmias.

CONCLUSION

Ventricular arrhythmias occurring in the setting of anger are more likely pause dependent and polymorphic. This suggests that in predisposed populations anger may create an arrhythmogenic substrate susceptible to more disorganized rhythms, a possible mechanism linking emotion and sudden death.

Mental stress and coronary artery disease: a multidisciplinary guide

Research suggests that acute and chronic stress are risk factors for the development and progression of coronary artery disease. Much of this work is multidisciplinary, using unfamiliar concepts deriving from disciplines other than cardiology and medicine. This article addresses and clarifies, for the cardiologist, some of the key concepts and issues in this area and provides an overview of evidence linking acute and chronic stress to cardiac pathology. Areas addressed include definitions and measurement of mental stress, methodological issues in stress research, and distinctions between stress and variables such as personality, emotion, and depression. Mental stress is a multifactorial process involving the environment, individual experiences and coping, and a set of neuroendocrine, autonomic, cardiovascular, and other systemic physiologic responses. There are difficulties identifying a single consensus physiologic stress measure because of individual differences in perceptions and physiologic response patterns. Nonetheless, important associations exist between mental stress and clinically relevant cardiovascular end points. As multidisciplinary research in this area continues, one major goal is the better integration of psychosocial knowledge and measures with cardiology research and practice.

Microvolt T-wave alternans: a review of techniques, interpretation, utility, clinical studies, and future perspectives

Microvolt T-wave alternans (TWA) testing involves measuring variation in the morphology of the T-wave on an every other beat basis. The magnitude of the variation observed is typically on the order of a few microvolts. Thus in order to detect microvolt TWA, specialized recording and signal processing methods must be employed for reliable measurement. Additionally, microvolt TWA is not generally present at rest even in patients at risk of ventricular tachyarrhythmias and therefore exercise stress, pharmacologic stress, or atrial pacing must be utilized in order to elevate the heart rate. A positive MTWA test is one in which sustained TWA is present with an onset heart rate < or = 110 bpm. With current instrumentation, microvolt TWA represents an inexpensive, convenient non-invasive testing modality. Microvolt TWA has been evaluated prospectively in a variety of patient populations as a means of predicting occurrence of ventricular tachyarrhythmic events and its association with the genesis of ventricular arrhythmias has been demonstrated. Future role of microvolt TWA testing in noninvasive risk stratification is awaiting results of ongoing clinical trials. In this article, we tried to review the techniques, interpretation, indications, clinical studies, and future perspectives of microvolt TWA.

The Influence of beta-Adrenergic Agonists and Antagonists on T-Wave Alternans in Patients with and Without Ventricular Tachyarrhythmia

BACKGROUND

T-wave alternans (TWA) is an important noninvasive measurement of ventricular tachyarrhythmia (VT) and is known to be influenced by the sympathetic nervous system. We examined the correlation between TWA measurement and the sympathetic nervous system in patients with and without VT.

METHODS AND RESULTS

Thirty-five patients (28 men, 7 women; mean age, 59 +/- 15 years) with tachyarrhythmia were assigned to two groups: VT group (n = 15) and supraventricular tachyarrhythmia (SVT) group (n = 20). Alternans voltage in lead vector magnitude (eVM) was measured during atrial pacing (90, 110 beats/min (bpm)). After eVM was measured at baseline, propranolol was administered, and eVM was measured again. In a subset of 18 patients (10 with VT and 8 with SVT), isoproterenol was administered prior to propranolol infusion. After propranolol infusion, eVM of both the VT and the SVT groups decreased significantly compared to baseline. The changes in absolute value of eVM at 110 bpm after propranolol infusion were greater in the VT group than in the SVT group (-1.3 +/- 0.8 microV vs -0.5 +/- 0.8 microV, P < 0.05). The eVM values of both the VT and the SVT groups increased after administration of isoproterenol compared to the baseline value. The changes in absolute value and percentile of eVM after isoproterenol infusion were smaller in the VT group than in the SVT group (2.0 +/- 1.8 microV vs 3.9 +/- 3.5 microV, P < 0.05; 21 +/- 18% vs 48 +/- 36%, P < 0.05).

CONCLUSIONS

The sympathetic nervous system has an influence over microvolt-level TWA. Administration of a beta-adrenergic antagonist caused a significant decrease in TWA, particularly in the VT group. This may partially explain the mechanism by which adrenergic antagonists inhibit VTs.

Noninvasive sudden death risk stratification by ambulatory ECG-based T-wave alternans analysis: evidence and methodological guidelines

Extensive experimental and clinical evidence supports the utility of T-wave alternans (TWA) as a marker of risk for ventricular fibrillation. This entity appears to reflect the fundamental arrhythmogenic property of enhanced dispersion of repolarization. This relationship probably accounts for its relative ubiquity in patients with diverse types of cardiac disease, as has been recognized with the development of analytical tools. A basic premise of this review is that ambulatory ECG monitoring of TWA as patients experience the provocative stimuli of daily activities can expose latent electrical instability in individuals at heightened risk for arrhythmias. We will discuss the literature that supports this concept and summarize the current state of knowledge regarding the use of routine ambulatory ECGs to evaluate TWA for arrhythmia risk stratification. The dynamic, nonspectral modified moving average analysis method for assessing TWA, which is compatible with ambulatory ECG monitoring, is described along with methodological guidelines for its implementation. Finally, the rationale for combined monitoring of autonomic markers along with TWA will be presented.

The effect of mental stress on the non-dipolar components of the T wave: modulation by hypnosis

OBJECTIVE

Mental or emotional stress-induced ventricular arrhythmias and sudden cardiac death are thought to be mediated by the autonomic nervous system and ischemia. In the absence of ischemia, increased inhomogeneity of repolarization is thought to be important. We tested the hypotheses that in the absence of ischemia, mental stress may modulate repolarization by changing autonomic balance; and mental relaxation induced by hypnosis may offset the potentially adverse effects of stress on the cardiac electrophysiology.

METHODS

Twelve healthy volunteers (6 male, age 18-35, mean 25 years) experienced a series of different emotions intended to induce a wide range of autonomic response (42 test epochs) on two separate occasions, with and without hypnosis, with continuous electrocardiogram recording. Low- (LF) and HF (high-frequency) heart rate variability was measured and ventricular repolarization was assessed using the relative T-wave residua (proportion of nondipolar components of the T wave) calculated for the T-onset - T peak (TWR-peak T), T peak -T end (TWR-end T), and the whole T wave (TWR).

RESULTS

Emotionally induced changes in LF and LF/HF ratio correlated with changes in TWR, e.g., (R = 0.51, p < .001; R = 0.59, p < .0001; and R = 0.59, p < .0003, for LF/HF versus TWR, TWR-Peak T, and TWR-end T, respectively. Mental relaxation induced by hypnosis increased LF power (1,205 ms2) versus 624 ms2, p < .003 for hypnotized versus nonhypnotized state), HF power (1,619 ms2 versus 572 ms2), p < .0004), and reduced LF/HF ratio (1.0 versus 1.5, p = .052) and was associated with a marked reduction in the changes in repolarization in response to emotion, e.g., 10.7 x 10(-6) versus 5.0 x10(-6), p < .03 for TWR.

CONCLUSIONS

a) Mental stress in the absence of ischemia altered repolarization inhomogeneity via change in the autonomic balance. b) Mental relaxation induced by hypnosis greatly reduced the effect of mental stress on repolarization. c) These findings may have implications for arrhythmogenesis.

Effects of Acute Mental Stress and Exercise on T-Wave Alternans in Patients With Implantable Cardioverter Defibrillators and Controls

BACKGROUND

Malignant cardiac arrhythmias can be triggered by exercise and by mental stress in vulnerable patients. Exercise-induced T-wave alternans (TWA) is an established marker of cardiac electrical instability. However, the effects of acute mental stress on TWA have not been investigated as a vulnerability marker in humans.

METHODS AND RESULTS

TWA responses to mental stress (anger recall and mental arithmetic) and bicycle ergometry were evaluated in patients with implantable cardioverter defibrillators (ICDs) and documented coronary artery disease (n=23, age 62.1+/-12.3 years) and controls (n=17, age 54.2+/-12.1 years). TWA was assessed from digitized ECGs by modified moving average analysis. Dual-isotope single photon emission computed tomography was used to assess myocardial ischemia. TWA increased during mental stress and exercise (P values <0.001), and TWA responses were higher in ICD patients than in controls (arithmetic Delta=8.9+/-1.4 versus 4.3+/-2.2 microV, P=0.043; exercise Delta=21.4+/-2.8 versus 13.8+/-3.2 microV, P=0.038). TWA increases with mental stress occurred at substantially lower heart rates (anger recall Delta=9.7+/-7.7 bpm, arithmetic Delta=14.3+/-13.3 bpm) versus exercise (Delta=53.7+/-22.7 bpm; P values <0.001). After adjustment for heart rate increases, mental stress and exercise provoked increased TWA in ICD patients (P values <0.05), but not in controls (P values >0.2). Ejection fraction and stress-induced myocardial ischemia were not associated with TWA.

CONCLUSIONS

Mental stress can induce cardiac electrical instability, as assessed via TWA, among patients with arrhythmic vulnerability and occurs at lower heart rates than with exercise. Pathophysiological mechanisms of mental stress-induced arrhythmias may therefore involve central and autonomic nervous system pathways that differ from exercise-induced arrhythmias.

Autonomic aspects of arrhythmogenesis: the enduring and the new

PURPOSE OF REVIEW

Recent progress in understanding the role of the autonomic nervous system in the development of cardiac arrhythmias is reviewed. The focus is on the translation of basic principles of neural control of heart rhythm that have emerged from experimental studies to clinical applications.

RECENT FINDINGS

Recent studies have made significant strides in defining the function of intrinsic cardiac innervation and the importance of nerve sprouting in electrical remodeling. A recurring theme is that heterogeneity of sympathetic innervation in response to injury is highly arrhythmogenic. In addition, both sympathetic and parasympathetic influences on ion channel activity have been found to accentuate electrical heterogeneities and thus to contribute to arrhythmogenesis in the long QT and Brugada syndromes. In the clinic, heart rate variability continues to be a useful tool in delineating pathophysiologic changes that result from the progression of heart disease and the impact of diabetic neuropathy. Heart rate turbulence, a noninvasive indicator of baroreceptor sensitivity, has emerged as a simple, practical tool to assess risk for cardiovascular mortality in patients with ischemic heart disease and heart failure. Evidence of the proarrhythmic influence of behavioral stress has been further bolstered by defibrillator discharge studies and ambulatory ECG-based T-wave alternans measurement.

SUMMARY

The results of recent investigations underscore the importance of the autonomic influences as triggers of arrhythmia and provide important mechanistic insights into the ionic and cellular mechanisms involved.

Catecholamine-provoked microvoltage T wave alternans in genotyped long QT syndrome

Macrovoltage T wave alternans (TWA) has been described in congenital long QT syndrome (LQTS). Microvoltage T wave alternans (microV-TWA) at low heart rate (HR) is a marker of arrhythmogenic risk in many conditions, but its significance in LQTS has not been established. Twenty-three genotypically heterogeneous patients with LQTS and 16 control subjects were studied at rest and during phenylephrine and dobutamine provocation. Genotyping was established by PCR amplification and DNA sequencing of the three most common LQTS genes; KCNQ1/KVLQT1 (LQT1), KCNH2/HERG (LQT2), and SCN5A (LQT3). microV-TWA was determined using Fast Fourier transform. Precluded by ectopy, microV-TWA could not be assessed in 8 of 23 patients with LQTS. In the remaining 15 patients with LQTS, microV-TWA occurred at lower HR in LQTS than in controls (117 +/- 49 vs 153 +/- 37 beats/min; P < 0.05). Patients with LQTS developed microV-TWA at HR < 150 beats/min more often than controls (10/15 vs 2/16; P = 0.003). However, microV-TWA was not detected in the 3 individuals with a history of out-of-hospital cardiac arrest including a 14-year-old male with an F339del-KVLQT1 mutation (LQT1) who had dobutamine-provoked polymorphic ventricular tachycardia requiring external defibrillation. Catecholamine-provoked microV-TWA occurs at lower HR in patients with LQTS than in healthy people but does not identify high risk subjects.

Ambulatory electrocardiogram-based tracking of T wave alternans in postmyocardial infarction patients to assess risk of cardiac arrest or arrhythmic death

INTRODUCTION

This is the first study to assess T wave alternans (TWA) analyzed from routine ambulatory electrocardiograms (AECGs) to identify postmyocardial infarction (post-MI) patients at increased risk for arrhythmic events.

METHODS AND RESULTS

The new method of modified moving average (MMA) analysis was used to measure TWA magnitude in 24-hour AECGs from ATRAMI, a prospective study of 1,284 post-MI patients. Using a nested case-control approach, we defined cases as patients who experienced cardiac arrest due to documented ventricular fibrillation or arrhythmic death during the follow-up period of 21 +/- 8 months. We analyzed 15 cases and 29 controls matched for sex, age, site of MI, left ventricular ejection fraction, thrombolysis, and beta-blockade therapy. TWA was reported as the maximum 15-second value at three predetermined times associated with cardiovascular stress: maximum heart rate, 8:00 A.M., and maximum ST segment deviation. TWA increased significantly from baseline in both leads at each time point (P <<0.01) in cases and controls. TWA in V5 increased more in cases than controls during peak heart rate (P = 0.005) and at 8:00 A.M. (P = 0.02). A 4- to 7-fold higher odds of life-threatening arrhythmias was predicted by TWA level above the 75th percentile during maximum heart rate in leads V1 (odds ratio [OR] 4.2, 95% confidence interval [CI]: 1.1-16.3, P = 0.04) and V5 (OR 7.9, 95% CI: 1.9-33.1, P = 0.005). TWA at 8:00 A.M. also predicted risk in leads V1 (OR = 5.0, 95% CI: 1.2-20.5, P = 0.02) and V5 (OR = 4.2, 95% CI: 1.1-16.3, P = 0.04).

CONCLUSION

TWA measurement from routine 24-hour AECGs is a promising approach for risk stratification for cardiac arrest and arrhythmic death in relatively low-risk post-MI patients.

Clinical value of T-wave alternans assessment

Microvolt-level T-wave alternans (TWA) is a new arrhythmia risk marker to assess subtle changes in repolarization that has been introduced for arrhythmia risk stratification. Recent experimental studies have demonstrated that it reflects a heartrate dependent increased spatial dispersion of repolarization associated with unidirectional conduction block, and reentry that may result in the occurrence of ventricular fibrillation. Clinical studies have convincingly demonstrated that TWA is closely related to arrhythmia induction in the electrophysiology (EP) laboratory as well as to the occurrence of spontaneous ventricular tachyarrhythmias in patients undergoing EP study. Subsequent studies showed that TWA-assessed noninvasively-is predictive of future arrhythmic events in patients with implanted ICDs as well as for ventricular tachyarrhythmias in patients with congestive heart failure without a prior history of arrhythmias. There is still controversy, however, about the predictive value of TWA in patients following acute myocardial infarction (MI). Several studies which differ in patient selection, pharmacologic treatment of the patients, and endpoint definitions, have reported conflicting results. Therefore, studies with a large number of unselected patients after acute MI on optimal treatment according to contemporary therapeutic guidelines as well as of patients with reduced left ventricular ejection fraction following MI are needed to define its role with regard to identifying patients who may benefit from primary preventive ICD therapy. Future research should also focus on evaluation of alternative methods to increase heart rate (i.e., pharmacological stimulation) in an attempt to reduce the proportion of incomplete tests in patients with insufficient increase in heart rate during exercise testing.

Progressive increases in complexity of T-wave oscillations herald ischemia-induced ventricular fibrillation

T-wave alternans (TWA), an ABAB oscillation, has been postulated as the initial pattern in a stepwise progression to higher-order oscillations, culminating in sudden arrhythmic death. The present study is the first to provide experimental evidence to support this intriguing concept. Epicardial and endocardial ECGs from 12 dogs were monitored during 8-minute left anterior descending coronary artery occlusion with right atrial pacing at 150 bpm. TWA magnitude was measured by modified moving average beat analysis, and the complexity of T-wave oscillations was assessed by complex demodulation. In 6 animals with subsequent ventricular fibrillation (VF), TWA achieved a threshold of 5.00+/-1.30 mV in epicardial ischemic-zone electrograms, which then exhibited a stepwise increase in T-wave oscillation complexity to quadrupling (ABCDABCD, 3 cases) or tripling (ABCABC, 2 cases) and to more complex forms (5 cases) preceding VF (6 cases). In dogs without VF, peak TWA levels did not increase from baseline, measuring a maximum of 0.35+/-0.10 mV (P=NS), or only 7% the value of those with VF, and T-wave multupling was not observed (0 of 6 versus 5 of 6, P<0.005). Discordant TWA episodes, with T waves alternating out of phase, were associated with increased T-wave complexity and fibrillation in 4 of 6 dogs with VF but in none of the 6 dogs without VF (P<0.025). TWA appears to be the first step in an orderly progression of T-wave complexity, episodes of discordant TWA, and VF. This demonstrated increase in T-wave complexity points to a fundamental mechanistic link underlying the ability of TWA to predict lethal arrhythmias.

Emotional and physical precipitants of ventricular arrhythmia

BACKGROUND

Observational studies have suggested that psychological stress increases the incidence of sudden cardiac death. Whether emotional or physical stressors can trigger spontaneous ventricular arrhythmias in patients at risk has not been systematically evaluated.

METHODS AND RESULTS

Patients with implantable cardioverter-defibrillators (ICDs) were given diaries to record levels of defined mood states and physical activity, using a 5-point intensity scale, during 2 periods preceding spontaneously occurring ICD shocks (0 to 15 minutes and 15 minutes to 2 hours) and during control periods 1 week later. ICD-stored electrograms confirmed the rhythm at the time of shock. A total of 107 confirmed ventricular arrhythmias requiring shock were reported by 42 patients (33 men; mean age, 65 years; 78% had coronary artery disease) between August 1996 and September 1999. In the 15 minutes preceding shock, an anger level > or =3 preceded 15% of events compared with 3% of control periods (P<0.04; odds ratio, 1.83; 95% confidence intervals, 1.04 to 3.16) Other mood states (anxiety, worry, sadness, happiness, challenge, feeling in control, or interest) did not differ. Patients were more physically active preceding shock than in control periods. Anger and physical activity were independently associated with the preshock period.

CONCLUSIONS

Anger and physical activity can trigger ventricular arrhythmias in patients with ICDs. Future investigations of therapies aimed at blocking a response to these stressors may decrease ventricular arrhythmias and shocks in these patients.

Pathophysiological basis and clinical application of T-wave alternans

We review the contemporary understanding of the pathophysiology of repolarization alternans and present a perspective on the use of T-wave alternans (TWA) as a risk stratification marker of malignant ventricular arrhythmias. Several studies have demonstrated a high correlation of susceptibility to ventricular arrhythmias and sudden cardiac death with the existence of TWA. We describe a number of cellular and molecular alterations in the diseased heart that may provide a link between electrical and mechanical alternans and arrhythmia susceptibility. Repolarization alternans is likely the result of distinct and diverse cellular and molecular alterations that are associated with exaggerated regional repolarization heterogeneity, which renders the heart susceptible to malignant arrhythmias.

Psychosocial influences on the development and course of coronary heart disease: current status and implications for research and practice

Psychosocial characteristics predict the development and course of coronary heart disease (CHD). In this review, the authors discussed human and animal research on psychophysiological mechanisms influencing coronary artery disease and its progression to CHD. They then reviewed literature on personality and characteristics of the social environment as risk factors for CHD. Hostility confers increased risk, and a group of risk factors involving depression and anxiety may be especially important following myocardial infarction. Social isolation, interpersonal conflict, and job stress confer increased risk. Psychosocial interventions may have beneficial effects on CHD morbidity and mortality, although inconsistent results and a variety of methodological limitations preclude firm conclusions. Finally, they discussed implications for clinical care and the agenda for future research.

Effects of psychological and social factors on organic disease: a critical assessment of research on coronary heart disease

An extensive research literature in the behavioral sciences and medicine suggests that psychological and social factors may play a direct role in organic coronary artery disease (CAD) pathology. However, many in the medical and scientific community regard this evidence with skepticism. This chapter critically examines research on the impact of psychological and psychosocial factors on the development and outcome of coronary heart disease, with particular emphasis on studies employing verifiable outcomes of CAD morbidity or mortality. Five key variables identified as possible psychosocial risk factors for CAD are addressed: acute and chronic stress, hostility, depression, social support, and socioeconomic status. Evidence regarding the efficacy of psychosocial interventions is also presented. It is suggested that, taken as a whole, evidence for a psychological and social impact on CAD morbidity and mortality is convincing. However, continued progress in this area requires multidisciplinary research integrating expertise in cardiology and the behavioral sciences, and more effective efforts to communicate research findings to a biomedical audience.

Effects of selective autonomic blockade on T-wave alternans in humans

BACKGROUND

T-wave alternans (TWA) is an important noninvasive measure of ventricular arrhythmia vulnerability. This study tested the hypothesis that the autonomic nervous system influences TWA measurement in high-risk subjects with coronary artery disease.

METHODS AND RESULTS

T-wave alternans was measured in 60 patients with coronary artery disease, left ventricular dysfunction, and inducible sustained ventricular tachycardia during electrophysiological studies. All patients had TWA measured at baseline with atrial pacing at 100 bpm (600 ms), 109 bpm (550 ms), and 120 bpm (500 ms). After a 10-minute recovery period, TWA was measured again after sympathetic blockade (esmolol, n=20), parasympathetic blockade (atropine, n=20), or no intervention (control subjects, n=20). The prevalence of significant TWA was unchanged compared with baseline after atropine infusion and in the control group. In contrast, the amplitude of TWA in the vector magnitude lead was significantly reduced after esmolol infusion (P<0.001), and the number of positive TWA tests was reduced by 50% (70% versus 35%, P<0.05).

CONCLUSIONS

Our findings have important implications for the use of TWA to risk-stratify patients for life-threatening ventricular arrhythmias and provide a new potential mechanism for the reduction in sudden cardiac death conferred by beta-blockers among patients with coronary artery disease and congestive heart failure.

Modified moving average analysis of T-wave alternans to predict ventricular fibrillation with high accuracy

T-wave alternans is a marker of cardiac electrical instability with the potential for arrhythmia risk stratification. The modified moving average method was developed to measure alternans in settings with artifacts, noise, and nonstationary data. Algorithms were developed and performance characteristics were validated with simulated electrocardiograms (ECGs). Experimental laboratory ECGs with dynamically changing alternans values were analyzed. Alternans values estimated by modified moving average analysis correlated strongly with input alternans values (r(2) = 0.9999). Rapidly changing alternans levels and phase reversals did not perturb the measurement. When heart rate was increased from 60 to 180 beats/min, with T-wave alternans apex moving from 237 to 103 ms after the R wave, the measured alternans peak varied <5% from input value. Simulated 50- to 1,000-microV motion artifact spikes typical of treadmill ECGs produced inaccuracies <2%. Alternans values in experimental laboratory study using standard electrodes tracked vulnerability to myocardial ischemia-induced ventricular fibrillation with 100% sensitivity and specificity at a cut point of 0.75 mV. Modified moving average analysis is a robust method that precisely measures T-wave alternans in settings with artifacts, noise, and nonstationary data typical of clinical ECGs and yields an accurate estimate of risk for ventricular fibrillation.