Sudden Cardiac Death, Genes, and Arrhythmogenesis

Interaction effects between insomnia and depression on risk of out-of-hospital cardiac arrest: Multi-center study

BACKGROUND

Insomnia and depression have been known to be risk factors of several diseases, including coronary heart disease. We hypothesized that insomnia affects the out-of-hospital cardiac arrest (OHCA) incidence, and these effects may vary depending on whether it is accompanied by depression. This study aimed to determine the association between insomnia and OHCA incidence and whether the effect of insomnia is influenced by depression.

METHODS

This prospective multicenter case-control study was performed using Phase II Cardiac Arrest Pursuit Trial with Unique Registration and Epidemiology Surveillance (CAPTURES-II) project database for OHCA cases and community-based controls in Korea. The main exposure was history of insomnia. We conducted conditional logistic regression analysis to estimate the effect of insomnia on the risk of OHCA incidence and performed interaction analysis between insomnia and depression. Finally, subgroup analysis was conducted in the patients with insomnia.

RESULTS

Insomnia was not associated with increased OHCA risk (0.95 [0.64-1.40]). In the interaction analysis, insomnia interacted with depression on OHCA incidence in the young population. Insomnia was associated with significantly higher odds of OHCA incidence (3.65 [1.29-10.33]) in patients with depression than in those without depression (0.84 [0.59-1.17]). In the subgroup analysis, depression increased OHCA incidence only in patients who were not taking insomnia medication (3.66 [1.15-11.66]).

CONCLUSION

Insomnia with depression is a risk factor for OHCA in the young population. This trend was maintained only in the population not consuming insomnia medication. Early and active medical intervention for patients with insomnia may contribute to lowering the risk of OHCA.

Interactions between Sleep Apnea and Coronary Artery Disease on the Incidence of Sudden Cardiac Arrest: A Multi-Center Case-Control Study

PURPOSE

Sleep apnea (SA) is a risk factor for coronary artery disease (CAD), and SA and CAD increase the incidence of sudden cardiac arrest (SCA). This study aimed to investigate the effect of SA on the incidence of SCA and explore the effect of varying degrees of SA with or without CAD on the incidence of SCA.

MATERIALS AND METHODS

This prospective multi-center, case-control study was performed using the phase II Cardiac Arrest Pursuit Trial with Unique Registry and Epidemiologic Surveillance (CAPTURES-II) database for SCA cases and community-based controls in Korea. The matching ratio of cases to controls was 1:1, and they were randomly matched within demographics, including age, sex, and residence. The primary variable was a history of SA, and the second variable was a history of CAD. We conducted a conditional logistic regression analysis to estimate the effect of SA and CAD on the SCA risk, and an interaction analysis between SA and CAD.

RESULTS

SA was associated with an increased risk of SCA [adjusted odds ratio (AOR) (95% confidence interval, CI): 1.54 (1.16-2.03)], and CAD was associated with an increased risk of SCA [AOR (95% CI): 3.94 (2.50-6.18)]. SA was a risk factor for SCA in patients without CAD [AOR (95% CI): 1.62 (1.21-2.17)], but not in patients with CAD [AOR (95% CI): 0.56 (0.20-1.53)].

CONCLUSION

In the general population, SA is risk factor for SCA only in patients without CAD. Early medical intervention for SA, especially in populations without pre-existing CAD, may reduce the SCA risk. ClinicalTrials.gov (NCT03700203).

Genetics and genomics of arrhythmic risk: current and future strategies to prevent sudden cardiac death

A genetic risk of sudden cardiac arrest and sudden death due to an arrhythmic cause, known as sudden cardiac death (SCD), has become apparent from epidemiological studies in the general population and in patients with ischaemic heart disease. However, genetic susceptibility to sudden death is greatest in young people and is associated with uncommon, monogenic forms of heart disease. Despite comprehensive pathology and genetic evaluations, SCD remains unexplained in a proportion of young people and is termed sudden arrhythmic death syndrome, which poses challenges to the identification of relatives from affected families who might be at risk of SCD. In this Review, we assess the current understanding of the epidemiology and causes of SCD and evaluate both the monogenic and the polygenic contributions to the risk of SCD in the young and SCD associated with drug therapy. Finally, we analyse the potential clinical role of genomic testing in the prevention of SCD in the general population.

Airflow obstruction, impaired lung function and risk of sudden cardiac death: a prospective cohort study

BACKGROUND

Growing evidence suggests that compromised lung health may be linked to cardiovascular disease. However, little is known about its association with sudden cardiac death (SCD).

OBJECTIVES

We aimed to assess the link between impaired lung function, airflow obstruction and risk of SCD by race and gender in four US communities.

METHODS

A total of 14 708 Atherosclerosis Risk in Communities (ARIC) study participants who underwent spirometry and were asked about lung health (1987-1989) were followed. The main outcome was physician-adjudicated SCD. Fine-Gray proportional subdistribution hazard models with Firth's penalised partial likelihood correction were used to estimate the HRs.

RESULTS

Over a median follow-up of 25.4 years, 706 (4.8%) subjects experienced SCD. The incidence of SCD was inversely associated with FEV₁ in each of the four race and gender groups and across all smoking status categories. After adjusting for multiple measured confounders, HRs of SCD comparing the lowest with the highest quintile of FEV₁ were 2.62 (95% CI 1.62 to 4.26) for white males, 1.80 (95% CI 1.03 to 3.15) for white females, 2.07 (95% CI 1.05 to 4.11) for black males and 2.62 (95% CI 1.21 to 5.65) for black females. The above associations were consistently observed among the never smokers. Moderate to very severe airflow obstruction was associated with increased risk of SCD. Addition of FEV₁ significantly improved the predictive power for SCD.

CONCLUSIONS

Impaired lung function and airflow obstruction were associated with increased risk of SCD in general population. Additional research to elucidate the underlying mechanisms is warranted.

Relation of multicenter automatic defibrillator implantation trial implantable cardioverter-defibrillator score with long-term cardiovascular events in patients with implantable cardioverter-defibrillator

OBJECTIVE

To test the hypothesis that multicenter automatic defibrillator implantation trial (MADIT) - implantable cardioverter-defibrillator (ICD) scores predict replacement requirement and appropriate shock in a mixed population including both primary and secondary prevention and long-term adverse cardiovascular events.

METHODS

The study has a retrospective design. Patients who were implanted with ICD in the cardiology clinic of Atatürk University Faculty of Medicine between 2000 and 2013 were included in the study. For this purpose, 1394 patients who were implanted with a device in our clinic were reviewed. Then, those who were implanted with permanent pacemaker (n=1005), cardiac resynchronization treatment (CRT) (n=45) and CRT-ICD (n=198) were excluded.

RESULTS

A total of 146 patients (98 males, 67.1%) with a mean age of 61.1 (±14.8) years were recruited. The median follow-up time was 21.5 months (mean 30.6±25.9 months; minimum 4 months, and maximum 120 months). The median MADIT-ICD scores in the patients were 2. MADIT-ICD scores were categorized as low in 15.1%, intermediate in 57.5%, and high score in 27.4% of patients. Accordingly, MADIT-ICD scores (1.29 [1.00-1.68], p=0.050), hemoglobin (0.86 [0.75-0.99], p=0.047), and left ventricular ejection fraction (EF) (0.97 [0.94-0.99], p=0.023) were determined as independent predictors of major adverse cardiovascular events in the long-term follow-up of ICD-implanted population.

CONCLUSION

In this study, we showed that there was an independent association of long-term adverse cardiovascular events with MADIT-ICD score, hemoglobin, and EF in patients implanted with ICD.

Sleep Apnea and Sudden Cardiac Death

Sleep plays an integral role in maintaining health and quality of life. Obstructive sleep apnea (OSA) is a prevalent sleep disorder recognized as a risk factor for cardiovascular disease (CVD) and arrhythmias. Sudden cardiac death (SCD) is a common and devastating event. Out-of-hospital SCD accounts for the majority of deaths from cardiac disease, which is the leading cause of death globally. A limited but emerging body of research have further elaborated on the link between OSA and SCD. In this article, we aim to provide a critical review of the existing evidence by addressing the following: What epidemiologic evidence exists linking OSA to SCD? What evidence exists for a pathophysiologic connection between OSA and SCD? Are there electrocardiographic markers of SCD found in patients with OSA? Does heart failure represent a major effect modifier regarding the relationship between OSA and SCD? What is the impact of sleep apnea treatment on SCD and cardiovascular outcomes? Finally, we elaborate on ongoing research to enhance our understanding of the OSA-SCD association.

Notas sobre <em>Tanacetum corymbosum s. l.</em> (Asteraceae)

Se presenta un estudio nomenclatural y taxonómico sobre Chrysanthemum italicum L., C. achilleae L., C. tanacetifolium Pourr., Pyrethrum cinereum Griseb., P. clusii Fisch. ex Rchb., P. clusii Tausch, P. daucifolium Pers. y P. tenuifolium Ten., táxones que pertenecen al grupo crítico de Tanacetum corymbosum. Se propone una nueva clasificación infraespecífica de Tanacetum corymbosum (L.) Sch. Bip. s. l. y se reconocen cinco subespecies sobre la base de un estudio morfológico del material tipo y otros especímenes. Se proporciona una clave de diagnóstico de los táxones estudiados. Se propone también un cambio nomenclatural, i.e. Tanacetum corymbosum subsp. daucifolium (Pers.) Iamonico comb. nov. Se designan lectotipos para los nombres Chrysanthemum cinereum (espécimen conservado en GOET), Chrysanthemum achilleae (imagen de Micheli), Chrysanthemum italicum (en LINN), Pyrethrum clusii de Rechenbach (ilustración de Clusius), Pyrethrum tenuifolium (en G) y Pyrethrum clusii de Tausch (imagen de Clusius). Se designa un neotipo para Chrysanthemum tanacetifolium (en P).

Clues to the Pathophysiology of Sudden Cardiac Death in Obstructive Sleep Apnea

BACKGROUND

Risk assessment of sudden cardiac death (SCD) is multifactorial and complex, especially among individuals without established cardiovascular disease. There are insufficiently investigated conditions that can affect arrhythmogenesis. One such condition is obstructive sleep apnea (OSA) syndrome, which is not on the list of risk factors of the Russian National Society of Arrhythmology.

OBJECTIVE

The aim of this review article is to discuss clues to the pathophysiology of SCD in OSA subjects.

METHODS

We searched the literature for data reporting the impact of apnea on arrhythmogenesis. The preferred languages were English and Russian. The most important clinical reports, as well as biochemistry and pathophysiology guides, were selected for inclusion in the review.

RESULTS

It was clearly observed in the searched literature that OSA is the crucial aspect of arrhythmogenesis. Among the clues are intermittent nocturnal hypoxia, reactive oxygen species, cardiomyocyte metabolism disturbances, myocardial electric heterogeneity, and intrathoracic pressure changes.

CONCLUSION

This review emphasizes the importance of the inclusion of OSA in the list of risk factors of the Russian National Society of Arrhythmology.

Sudden Cardiac Death in Ischemic Heart Disease: Pathophysiology and Risk Stratification

Sudden cardiac death (SCD) accounts for approximately 360,000 deaths annually in the United States. Ischemic heart disease is the major cause of death in the general adult population. SCD can be due to arrhythmic or nonarrhythmic cardiac causes. Arrhythmic SCD may be caused by ventricular tachyarrhythmia or pulseless electrical activity/asystole. This article reviews the most recent pathophysiology and risk stratification strategies for SCD, emphasizing electrophysiologic surrogates of conduction disorder, dispersion of repolarization, and autonomic imbalance. Factors that modify arrhythmic death are addressed.

Using Zebrafish for High-Throughput Screening of Novel Cardiovascular Drugs

Cardiovascular diseases remain a major challenge for modern drug discovery. The diseases are chronic, complex, and the result of sophisticated interactions between genetics and environment involving multiple cell types and a host of systemic factors. The clinical events are often abrupt, and the diseases may be asymptomatic until a highly morbid event. Target selection is often based on limited information, and though highly specific agents are often identified in screening, their final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index, or substantial toxicities. Our understanding of complexity of cardiovascular disease has grown dramatically over the past 2 decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in cardiac or vascular disease. Despite these insights, the majority of active cardiovascular agents derive from a remarkably small number of classes of agents and target a very limited number of pathways. These agents have often been used initially for particular indications and then discovered serendipitously to have efficacy in other cardiac disorders or in a manner unrelated to their original mechanism of action. In this review, the rationale for in vivo screening is described, and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. An overview is provided of the complex mechanisms underlying most clinical cardiovascular diseases, and insight is offered into the limits of single downstream pathways as drug targets. The zebrafish is introduced as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology are discussed, including in vivo screening of zebrafish genetic disease models.

Efficient Generation of Cardiac Purkinje-like Cells from Embryonic Stem Cells by Activating cAMP Signaling

Strategies to derive cardiac conduction system (CCS) cells including Purkinje cells (PC) would facilitate models for mechanistic studies and drug discovery, and also provide new cellular materials for regenerative therapies. However, using current cardiac differentiation protocols, the differentiation efficiency of CCS cells is extremely low, typically below 1% of the culture. High-throughput chemical screening is a powerful strategy for identifying small molecules that can activate signaling pathways to enhance embryonic stem cell (ESC) differentiation. We describe how to carry out a high- throughput screen to identify small molecules that can efficiently promote CCS generation from mouse ESCs. We also describe several assays, including immunofluorescence staining, electrophysiology, FACS analysis and quantitative real- time PCR, to characterize the phenotype of ESC-derived PC. In summary, we describe an efficient way to identify small molecules that enhance cardiac PC generation. These protocols can be adapted to identify other rare cell lineages by directed differentiation from ESCs. © 2017 by John Wiley & Sons, Inc.

Efficient Generation of Cardiac Purkinje Cells from ESCs by Activating cAMP Signaling

Dysfunction of the specialized cardiac conduction system (CCS) is associated with life-threatening arrhythmias. Strategies to derive CCS cells, including rare Purkinje cells (PCs), would facilitate models for mechanistic studies and drug discovery and also provide new cellular materials for regenerative therapies. A high-throughput chemical screen using CCS:lacz and Contactin2:egfp (Cntn2:egfp) reporter embryonic stem cell (ESC) lines was used to discover a small molecule, sodium nitroprusside (SN), that efficiently promotes the generation of cardiac cells that express gene profiles and generate action potentials of PC-like cells. Imaging and mechanistic studies suggest that SN promotes the generation of PCs from cardiac progenitors initially expressing cardiac myosin heavy chain and that it does so by activating cyclic AMP signaling. These findings provide a strategy to derive scalable PCs, along with insight into the ontogeny of CCS development.

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A chemical screen was carried out for compounds that induce cardiac conduction cells

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Two ESC reporter lines were used to identify lead hits

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Sodium nitroprusside efficiently generated scalable amounts of PC-like cells

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By activating cAMP signaling, PCs are derived from cardiac progenitors

Risk stratification for sudden cardiac death: current status and challenges for the future

Sudden cardiac death (SCD) remains a daunting problem. It is a major public health issue for several reasons: from its prevalence (20% of total mortality in the industrialized world) to the devastating psycho-social impact on society and on the families of victims often still in their prime, and it represents a challenge for medicine, and especially for cardiology. This text summarizes the discussions and opinions of a group of investigators with a long-standing interest in this field. We addressed the occurrence of SCD in individuals apparently healthy, in patients with heart disease and mild or severe cardiac dysfunction, and in those with genetically based arrhythmic diseases. Recognizing the need for more accurate registries of the global and regional distribution of SCD in these different categories, we focused on the assessment of risk for SCD in these four groups, looking at the significance of alterations in cardiac function, of signs of electrical instability identified by ECG abnormalities or by autonomic tests, and of the progressive impact of genetic screening. Special attention was given to the identification of areas of research more or less likely to provide useful information, and thereby more or less suitable for the investment of time and of research funds.

Genetic isolation of stem cell-derived pacemaker-nodal cardiac myocytes

Dysfunction of the cardiac pacemaker tissues due to genetic defects, acquired diseases, or aging results in arrhythmias. When arrhythmias occur, artificial pacemaker implants are used for treatment. However, the numerous limitations of electronic implants have prompted studies of biological pacemakers that can integrate into the myocardium providing a permanent cure. Embryonic stem (ES) cells cultured as three-dimensional (3D) spheroid aggregates termed embryoid bodies possess the ability to generate all cardiac myocyte subtypes. Here, we report the use of a SHOX2 promoter and a Cx30.2 enhancer to genetically identify and isolate ES cell-derived sinoatrial node (SAN) and atrioventricular node (AVN) cells, respectively. The ES cell-derived Shox2 and Cx30.2 cardiac myocytes exhibit a spider cell morphology and high intracellular calcium loading characteristic of pacemaker-nodal myocytes. These cells express abundant levels of pacemaker genes such as endogenous HCN4, Cx45, Cx30.2, Tbx2, and Tbx3. These cells were passaged, frozen, and thawed multiple times while maintaining their pacemaker-nodal phenotype. When cultured as 3D aggregates in an attempt to create a critical mass that simulates in vivo architecture, these cell lines exhibited an increase in the expression level of key regulators of cardiovascular development, such as GATA4 and GATA6 transcription factors. In addition, the aggregate culture system resulted in an increase in the expression level of several ion channels that play a major role in the spontaneous diastolic depolarization characteristic of pacemaker cells. We have isolated pure populations of SAN and AVN cells that will be useful tools for generating biological pacemakers.

Obstructive sleep apnea and the risk of sudden cardiac death: a longitudinal study of 10,701 adults

OBJECTIVES

This study sought to identify the risk of sudden cardiac death (SCD) associated with obstructive sleep apnea (OSA).

BACKGROUND

Risk stratification for SCD, a major cause of mortality, is difficult. OSA is linked to cardiovascular disease and arrhythmias and has been shown to increase the risk of nocturnal SCD. It is unknown if OSA independently increases the risk of SCD.

METHODS

We included 10,701 consecutive adults undergoing their first diagnostic polysomnogram between July 1987 and July 2003. During follow-up up to 15 years, we assessed incident resuscitated or fatal SCD in relation to the presence of OSA, physiological data including the apnea-hypopnea index (AHI), and nocturnal oxygen saturation (O2sat) parameters, and relevant comorbidities.

RESULTS

During an average follow-up of 5.3 years, 142 patients had resuscitated or fatal SCD (annual rate 0.27%). In multivariate analysis, independent risk factors for SCD were age, hypertension, coronary artery disease, cardiomyopathy or heart failure, ventricular ectopy or nonsustained ventricular tachycardia, and lowest nocturnal O2sat (per 10% decrease, hazard ratio [HR]: 1.14; p = 0.029). SCD was best predicted by age >60 years (HR: 5.53), apnea-hypopnea index >20 (HR: 1.60), mean nocturnal O2sat <93% (HR: 2.93), and lowest nocturnal O2sat <78% (HR: 2.60; all p < 0.0001).

CONCLUSIONS

In a population of 10,701 adults referred for polysomnography, OSA predicted incident SCD, and the magnitude of risk was predicted by multiple parameters characterizing OSA severity. Nocturnal hypoxemia, an important pathophysiological feature of OSA, strongly predicted SCD independently of well-established risk factors. These findings implicate OSA, a prevalent condition, as a novel risk factor for SCD.

Out-of-hospital cardiac arrests and outdoor air pollution exposure in Copenhagen, Denmark

Cardiovascular disease is the number one cause of death globally and air pollution can be a contributing cause. Acute myocardial infarction and cardiac arrest are frequent manifestations of coronary heart disease. The objectives of the study were to investigate the association between 4 657 out-of-hospital cardiac arrests (OHCA) and hourly and daily outdoor levels of PM₁₀, PM_2.5, coarse fraction of PM (PM_10-2.5), ultrafine particle proxies, NO_x, NO₂, O₃ and CO in Copenhagen, Denmark, for the period 2000–2010. Susceptible groups by age and sex was also investigated. A case-crossover design was applied. None of the hourly lags of any of the pollutants were significantly associated with OHCA events. The strongest association with OHCA events was observed for the daily lag4 of PM_2.5, lag3 of PM₁₀, lag3 of PM_10-2.5, lag3 of NO_x and lag4 of CO. An IQR increase of PM_2.5 and PM₁₀ was associated with a significant increase of 4% (95% CI: 0%; 9%) and 5% (95% CI: 1%; 9%) in OHCA events with 3 days lag, respectively. None of the other daily lags or other pollutants was significantly associated with OHCA events. Adjustment for O₃ slightly increased the association between OHCA and PM_2.5 and PM₁₀. No susceptible groups were identified.

Comparison of ventricular tachyarrhythmia characteristics in patients with idiopathic dilated or ischemic cardiomyopathy and defibrillators implanted for primary prevention

BACKGROUND

Implantable cardioverter-defibrillator (ICD) therapy for primary prevention is well established in ischemic cardiomyopathy (ICM). Data on the role of ICDs in patients with dilated cardiomyopathy (DCM) and no history of ventricular tachyarrhythmia (VT/VF) are more limited.

HYPOTHESIS

DCM patients with an impaired left ventricular ejection fraction (LVEF) still represent a low arrhythmic risk subgroup in clinical practice.

METHODS

ICD stored data of DCM patients with an LVEF ≤35% was compared to data of ICM patients meeting Multicenter Automatic Defibrillator Implantation Trial (MADIT) eligibility criteria. VT/VF occurrences and electrical storm (ES) events were analyzed.

RESULTS

There were 652 patients followed for 50.9 ± 33.9 months. There were 1978 VT and 241 VF episodes analyzed in 66 out of 203 patients (32.5%) with DCM and in 118 out of 449 patients (26.3%, P = 0.209) with ICM. Freedom of appropriate ICD treatment due to VT/VF or ES events did not differ in both patient populations (log-rank, P>0.05). In patients presenting with VT/VF episodes, mean event rates were comparable in both patient populations (3.2 ± 14.1 for DCM and VT vs 3 ± 13.9 for ICM and VT [P = 0.855], 0.4 ± 1.3 for DCM and VF vs 0.4 ± 1.8 for ICM and VF [P = 0.763], and 0.2 ± 0.7 for DCM and ES vs 0.2 ± 1 for ICM and ES [P = 0.666]).

CONCLUSIONS

DCM patients with prophylactic ICDs implanted due to heart failure and patients fulfilling MADIT criteria reveal comparable patterns of VT/VF/ES events during long-term follow-up. Incidence, mean number of events, and time to first event did not differ significantly. Findings support the current guidelines for prophylactic ICD therapy in DCM patients with heart failure.

Effects of lüfukang capsules on coronary artery ligation-induced arrhythmia in dogs

OBJECTIVE

To observe the effects of Lüfukang Capsules on arrhythmia induced by ligation of coronary artery in dogs.

METHODS

Thirty dogs were randomly divided into 5 groups, the model group administrated with equal volume of distilled water, the positive control group administrated with Wenxin Granules, and the small, medium and large dosage LFKC groups, 6 dogs in each group. Thirty minutes after medication, electrocardiogram was conducted and the time of arrhythmia occurrence, times of ventricular premature beat (VP), and incidence rates of ventricular tachycardia (VT) and ventricular fibrillation (VF) were recorded in the model dogs with arrhythmia induced by ligation of coronary artery.

RESULTS

Compared with the model group, the occurrence time of arrhythmia induced by the coronary artery ligation in the medium and large LFKC groups was significantly delayed (20.45 +/- 9.10 and 19.92 +/- 3.78, respectively, both P < 0.05). The frequency of VP in the medium and large LFKC groups was also significantly decreased (8.17 +/- 6.62 and 3.83 +/- 2.79, respectively, both P < 0.01).

CONCLUSION

LFKC has anti-arrhythmic effects for the experimental arrhythmia induced by the ligation of coronary artery in dogs.

Genetic Polymorphisms as Risk Stratification Tool in Primary Preventive ICD Therapy

More and more implantable cardioverter-defibrillators (ICDs) are implanted as primary prevention of sudden cardiac death (SCD). However, major problem in practice is to identify high-risk patients for SCD. Different methods for noninvasive risk stratification do not have a sufficient positive or negative predictive value. Since current approaches lead to implantation of ICDs in a large number of patients who will never suffer an arrhythmic event and simultaneously patients still die of SCD who currently did not seem eligible for primary preventive ICD implantation, there is a need for additional tools for risk stratification. Epidemiological studies point to a hereditary risk of SCD. Different susceptibility of each person concerning arrhythmogenic events might be explained by genetic polymorphisms. By obtaining an individual “pattern” of polymorphisms of genes encoding for proteins which are important in arrhythmogenesis in one patient, risk stratification in primary prevention of SCD might by improved.

Changes in ventricular repolarization duration during typical daily emotion in patients with Long QT syndrome

OBJECTIVE

Intense emotions are known triggers of sudden cardiac death. However, the effect of typical daily emotion on repolarization has not been examined. We examined whether QT interval changes as a function of typical daily emotion in patients at risk for cardiac events in the context of emotion.

METHODS

We studied 161 patients (n = 114 females; mean age, 35 years) with the congenital form of the Long QT Syndrome during daily activities. Each day for 3 days, a 12-hour Holter recording was completed. Patients were paged ten times per day at random times and rated the intensity of 16 prespecified emotions during the preceding 5 minutes. Measurements of QT interval and interbeat intervals were synchronized with emotion ratings.

RESULTS

Low Arousal Positive Affect was associated with significant increases in QT interval corrected for heart rate (using Fridericia's QTc) (p < .001), whereas higher arousal Activated Positive Affect (p < .001) and Activated Negative Affect (p < .01) were associated with significant decreases in QTc. Changes in QTc as a function of daily emotion ranged from 5-ms increases to 11-ms decreases. High-frequency heart rate variability (vagal tone) was positively correlated with QTc (p < .001). The effects of each positive emotion variable on QTc were greater in LQT2 than LQT1 patients (p < .001).

CONCLUSION

Ventricular repolarization duration (QTc) changes dynamically as a function of daily emotion. These changes are relatively small and do not constitute a risk in themselves. In the context of other risk factors, however, they may contribute to ventricular arrhythmias in vulnerable populations.

Quantitative trait loci for electrocardiographic parameters and arrhythmia in the mouse

Cardiac arrhythmias associated with sudden death are influenced by multiple biological pathways and are modulated by numerous genetic and environmental factors. Elevated heart rate and prolonged ECG indices of conduction and repolarization have been associated with risk of sudden death. Insight into the genetic underpinnings of these parameters thus provides an important means to the dissection of the genetic components modulating risk of sudden cardiac death. In this study we mapped quantitative trait loci (QTL) modulating heart rate, ECG indices of conduction and repolarization, and susceptibility to arrhythmia, in a conduction disease-sensitized F(2) mouse population. Heart rate, P-duration, PR-, QRS- and QT-interval were measured at baseline (n=502) and after flecainide administration (n=370) in mutant F(2) progeny (F(2)-MUT) resulting from the FVB/NJ-Scn5a1798(insD/+) X 129P2-Scn5a1798(insD/+) mouse cross. Episodes of sinus arrhythmia and ventricular tachyarrhythmia occurring post-flecainide were treated as binary traits. F(2)-MUT mice were genotyped using a genome-wide 768 single nucleotide polymorphism (SNP) panel. Interval mapping uncovered multiple QTL for ECG parameters and arrhythmia. A sex-interacting scan identified QTL displaying sex-dependency, and a two-dimensional QTL scan unmasked locus-locus (epistasis) interactions influencing ECG traits. A number of QTL coincided at specific chromosomal locations, suggesting pleiotropic effects at these loci. Through transcript profiling in myocardium from the parental mouse strains we identified genes co-localizing at the identified QTL that constitute highly relevant candidates for the observed effects. The detection of QTL influencing ECG indices and arrhythmia is an essential step towards identifying genetic networks for sudden, arrhythmic, cardiac death.

Defining a new paradigm for human arrhythmia syndromes: phenotypic manifestations of gene mutations in ion channel- and transporter-associated proteins

Over the past 15 years, gene mutations in cardiac ion channels have been linked to a host of potentially fatal human arrhythmias including long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia. More recently, a new paradigm for human arrhythmia has emerged based on gene mutations that affect the activity of cardiac ion channel- and transporter- associated proteins. As part of the Circulation Research thematic series on inherited arrhythmias, this review focuses on the emerging field of human arrhythmias caused by dysfunction in cytosolic gene products (including ankyrins, yotiao, syntrophin, and caveolin-3) that regulate the activities of key membrane ion channels and transporters.

Cardiac Arrhythmia: In vivo screening in the zebrafish to overcome complexity in drug discovery

IMPORTANCE OF THE FIELD: Cardiac arrhythmias remain a major challenge for modern drug discovery. Clinical events are paroxysmal, often rare and may be asymptomatic until a highly morbid complication. Target selection is often based on limited information and though highly specific agents are identified in screening, the final efficacy is often compromised by unanticipated systemic responses, a narrow therapeutic index and substantial toxicities. AREAS COVERED IN THIS REVIEW: Our understanding of complexity of arrhythmogenesis has grown dramatically over the last two decades, and the range of potential disease mechanisms now includes pathways previously thought only tangentially involved in arrhythmia. This review surveys the literature on arrhythmia mechanisms from 1965 to the present day, outlines the complex biology underlying potentially each and every rhythm disturbance, and highlights the problems for rational target identification. The rationale for in vivo screening is described and the utility of the zebrafish for this approach and for complementary work in functional genomics is discussed. Current limitations of the model in this setting and the need for careful validation in new disease areas are also described. WHAT THE READER WILL GAIN: An overview of the complex mechanisms underlying most clinical arrhythmias, and insight into the limits of ion channel conductances as drug targets. An introduction to the zebrafish as a model organism, in particular for cardiovascular biology. Potential approaches to overcoming the hurdles to drug discovery in the face of complex biology including in vivo screening of zebrafish genetic disease models. TAKE HOME MESSAGE: In vivo screening in faithful disease models allows the effects of drugs on integrative physiology and disease biology to be captured during the screening process, in a manner agnostic to potential drug target or targets. This systematic strategy bypasses current gaps in our understanding of disease biology, but emphasizes the importance of the rigor of the disease model.

Early identification of risk factors for sudden cardiac death

Sudden cardiac death (SCD) is a global health issue. The unexpected nature of this devastating condition compounds the urgency of discovering methods for early detection of risk, which will lead to more effective prevention. However, the complex and dynamic nature of SCD continues to present a considerable challenge for the early identification of risk factors. Measurement of the left ventricular ejection fraction (LVEF) is currently the only major risk factor used for stratification in clinical practice. Severely decreased LVEF is likely to manifest late in the natural history of SCD, however, and may only affect a small subgroup of patients who will suffer SCD. A growing body of literature describes novel risk markers and predictors of SCD, such as high-risk phenotypes, genetic variants and biomarkers. This Review will discuss the potential utility of these markers as early identifiers of risk, and suggests a framework for the conduct of future studies for the discovery, validation, and deployment of novel SCD risk factors.

Sudden cardiac death: epidemiology and risk factors

Sudden cardiac death (SCD) is an important public-health problem with multiple etiologies, risk factors, and changing temporal trends. Substantial progress has been made over the past few decades in identifying markers that confer increased SCD risk at the population level. However, the quest for predicting the high-risk individual who could be a candidate for an implantable cardioverter-defibrillator, or other therapy, continues. In this article, we review the incidence, temporal trends, and triggers of SCD, and its demographic, clinical, and genetic risk factors. We also discuss the available evidence supporting the use of public-access defibrillators.

Neurohormonal regulation of cardiac ion channels in chronic heart failure

Alteration of neurohormonal homeostasis is a hallmark of the pathophysiology of chronic heart failure (CHF). In particular, overactivation of the renin-angiotensin-aldosterone system and the sympathetic catecholaminergic system is consistently observed. Chronic overactivation of these hormonal pathways leads to a detrimental arrhythmogenic remodeling of cardiac tissue due to dysregulation of cardiac ion channels. Sudden cardiac death resulting from ventricular arrhythmias is a major cause of mortality in patients with CHF. All the drug classes known to reduce mortality in patients with CHF are neurohormonal blockers. The aim of this review was to provide an overview of how cardiac ion channels are regulated by hormones known to play a central role in the pathogenesis of CHF.

Long QT Syndrome

The hereditary Long QT syndrome (LQTS) is a genetic channelopathy with variable penetrance that is associated with increased propensity for polymorphic ventricular tachyarrhythmias and sudden cardiac death in young individuals with normal cardiac morphology. The diagnosis of this genetic disorder relies on a constellation of electrocardiographic, clinical, and genetic factors. Accumulating data from recent studies indicate that the clinical course of affected LQTS patients is time-dependent and age-specific, demonstrating important gender differences among age groups. Risk assessment should consider age-gender interactions, prior syncopal history, QT-interval duration, and genetic factors. Beta-blockers constitute the mainstay therapy for LQTS, while left cardiac sympathetic denervation and implantation of a cardioverter defibrillator should be considered in patients who remain symptomatic despite beta-blocker therapy. Current and ongoing studies are also evaluating genotype-specific therapies that may reduce the risk for life-threatening cardiac events in high-risk LQTS patients.

A genetic framework for improving arrhythmia therapy

Abnormalities in heart rhythm continue to cause high rates of illness and death. Better treatment could be provided by solving two main challenges: the early identification of patients who are at risk, and the characterization of molecular pathways that culminate in arrhythmias. By analysing mechanisms that increase susceptibility to arrhythmia in individuals with genetic syndromes, it might be possible to improve current therapies and to develop new ways to treat and prevent common arrhythmias.

Preventing tomorrow's sudden cardiac death today: part I: Current data on risk stratification for sudden cardiac death

Accurate and timely prediction of sudden cardiac death (SCD) is a necessary prerequisite for effective prevention and therapy. Although the largest number of SCD events occurs in patients without overt heart disease, there are currently no tests that are of proven predictive value in this population. Efforts in risk stratification for SCD have focused primarily on predicting SCD in patients with known structural heart disease. Despite the ubiquity of tests that have been purported to predict SCD vulnerability in such patients, there is little consensus on which test, in addition to the left ventricular ejection fraction, should be used to determine which patients will benefit from an implantable cardioverter defibrillator. On July 20 and 21, 2006, a group of experts representing clinical cardiology, cardiac electrophysiology, biostatistics, economics, and health policy were joined by representatives of the US Food and Drug administration, Centers for Medicare Services, Agency for Health Research and Quality, the Heart Rhythm Society, and the device and pharmaceutical industry for a round table meeting to review current data on strategies of risk stratification for SCD, to explore methods to translate these strategies into practice and policy, and to identify areas that need to be addressed by future research studies. The meeting was organized by the Duke Center for the Prevention of SCD at the Duke Clinical Research Institute and was funded by industry participants. This article summarizes the presentations and discussions that occurred at that meeting.

Runs of ventricular and supraventricular tachycardia triggered by air pollution in patients with coronary heart disease

OBJECTIVE

The authors conducted an investigation of the association between air pollution and arrhythmia.

METHODS

A prospective panel study (October 2000-April 2001) was conducted in Erfurt, Germany. Fifty-seven men with coronary heart disease were subjected to six 24-hour electrocardiogram recordings. Runs of supraventricular and ventricular tachycardia were associated with continuous ultrafine particle counts (UFP), accumulation mode particle counts (ACP), PM2.5, and gaseous pollutants. Poisson and linear regression models were applied adjusting for trend, weekday, and meteorologic data.

RESULTS

Elevated concentrations of UFP, ACP, PM2.5, and nitrogen dioxide increased the risk for supraventricular runs and the number of ventricular runs at almost all lags. Statistically significant associations were found predominantly in the previous 24 to 71 hours and with the 5-day moving average.

CONCLUSION

Elevated concentrations of fine and ultrafine particle increased the risk of arrhythmia in men with coronary heart disease.

Implantable cardioverter defibrillators for prevention of sudden cardiac death

Despite the multiple advances in the field of cardiovascular medicine, the incidence of sudden cardiac death (SCD) continues to rise. Of all SCDs, <25% occur in individuals deemed at high risk by current risk-stratification algorithms; hence, these risk-stratification algorithms are not satisfactory. Until better markers are identified to risk stratify patients, we will see an increasing use of implantable cardioverter defibrillators (ICDs). However, even with the increase in defibrillator use, the impact on overall incidence of SCD may only be modest, as many individuals experience SCD as the first manifestation of cardiovascular disease. Another important challenge is widespread availability of automated external defibrillators and effective utilization of public access defibrillation programs for timely and appropriate management of out-of-hospital victims with cardiac arrest. This review discusses the current understanding on SCD, risk stratification, and management aimed at reducing SCD, particularly with the use of ICDs.

Spectrum and prevalence of cardiac sodium channel variants among black, white, Asian, and Hispanic individuals: implications for arrhythmogenic susceptibility and Brugada/long QT syndrome genetic testing

OBJECTIVES

The purpose of this study was to determine the prevalence and spectrum of nonsynonymous polymorphisms (amino acid variants) in the cardiac sodium channel among healthy subjects.

BACKGROUND

Pathogenic mutations in the cardiac sodium channel gene, SCN5A, cause approximately 15 to 20% of Brugada syndrome (BrS1), 5 to 10% of long QT syndrome (LQT3), and 2 to 5% of sudden infant death syndrome.

METHODS

Using single-stranded conformation polymorphism, denaturing high-performance liquid chromatography, and/or direct DNA sequencing, mutational analysis of the protein-encoding exons of SCN5A was performed on 829 unrelated, anonymous healthy subjects: 319 black, 295 white, 112 Asian, and 103 Hispanic.

RESULTS

In addition to the four known common polymorphisms (R34C, H558R, S1103Y, and R1193Q), four relatively ethnic-specific polymorphisms were identified: R481W, S524Y, P1090L, and V1951L. Overall, 39 distinct missense variants (28 novel) were elucidated. Nineteen variants (49%) were found only in the black cohort. Only seven variants (18%) localized to transmembrane-spanning domains. Four variants (F1293S, R1512W, and V1951L cited previously as BrS1-causing mutations and S1787N previously published as a possible LQT3-causing mutation) were identified in this healthy cohort.

CONCLUSIONS

This study provides the first comprehensive determination of the prevalence and spectrum of cardiac sodium channel variants in healthy subjects from four distinct ethnic groups. This compendium of SCN5A variants is critical for proper interpretation of SCN5A genetic testing and provides an essential hit list of targets for future functional studies to determine whether or not any of these variants mediate genetic susceptibility for arrhythmias in the setting of either drugs or disease.

Association between short term exposure to fine particulate matter and heart rate variability in older subjects with and without heart disease

BACKGROUND

Short term increases in exposure to particulate matter (PM) air pollution are associated with increased cardiovascular morbidity and mortality. The mechanism behind this effect is unclear, although changes in autonomic control have been observed. It was hypothesised that increases in fine PM measured at the subjects' home in the preceding hour would be associated with decreased high frequency heart rate variability (HF-HRV) in individuals with pre-existing cardiac disease.

METHODS

Two hundred and eighty five daily 20 minute measures of HRV (including a paced breathing protocol) were made in the homes of 34 elderly individuals with (n = 21) and without (n = 13) cardiovascular disease (CVD) over a 10 day period in Seattle between February 2000 and March 2002. Fine PM was continuously measured by nephelometry at the individuals' homes.

RESULTS

The median age of the study population was 77 years (range 57-87) and 44% were male. Models that adjusted for health status, relative humidity, temperature, mean heart rate, and medication use did not find a significant association between a 10 microg/m3 increase in 1 hour mean outdoor PM2.5 before the HRV measurement and a change in HF-HRV power in individuals with CVD (3% increase in median HF-HRV (95% CI -19 to 32)) or without CVD (5% decrease in median HF-HRV (95% CI -34 to 36)). Similarly, no association was evident using 4 hour and 24 hour mean outdoor PM2.5 exposures before the HRV measurement.

CONCLUSION

No association was found between increased residence levels of fine PM and frequency domain measures of HRV in elderly individuals.

Repolarization changes induced by air pollution in ischemic heart disease patients

Epidemiologic studies report associations between particulate air pollution and cardiovascular morbidity and mortality, but the underlying pathophysiologic mechanisms are still unclear. We tested the hypothesis that patients with preexisting coronary heart disease experience changes in the repolarization parameters in association with rising concentrations of air pollution. A prospective panel study was conducted in Erfurt, East Germany, with 12 repeated electrocardiogram (ECG) recordings in 56 males with ischemic heart disease. Hourly particulate and gaseous air pollution and meteorologic data were acquired. The following ECG parameters reflecting myocardial substrate and vulnerability were measured: QT duration, T-wave amplitude, T-wave complexity, and variability of T-wave complexity. Fixed effect regression analysis was used adjusting for subject, trend, weekday, and meteorology. The analysis showed a significant increase in QT duration in response to exposure to organic carbon; a significant decrease in T-wave amplitude with exposure to ultrafine, accumulation mode, and PM2.5 particles (particles < 2.5 microm in aerodynamic diameter); and a corresponding significant increase of T-wave complexity in association with PM2.5 particles for the 24 hr before ECG recordings. Variability of T-wave complexity showed a significant increase with organic and elemental carbon in the same time interval. This study provides evidence suggesting an immediate effect of air pollution on repolarization duration, morphology, and variability representing myocardial substrate and vulnerability, key factors in the mechanisms of cardiac death.

Post-transcriptional alterations in the expression of cardiac Na+ channel subunits in chronic heart failure

Clinical and experimental evidence has recently accumulated about the importance of alterations of Na(+) channel (NaCh) function and slow myocardial conduction for arrhythmias in infarcted and failing hearts (i.e., heart failure, HF). The present study evaluated the molecular mechanisms of local alterations in the expression of NaCh subunits which underlie Na(+) current (I(Na)) density decrease in HF. HF was induced in five dogs by sequential coronary microembolization and developed approximately 3 months after the last embolization (left ventricle (LV), ejection fraction = 27 +/- 7%). Five normal dogs served as a control group. Ventricular cardiomyocytes were isolated enzymatically from LV mid-myocardium and I(Na) was measured by whole-cell patch-clamp. The mRNA encoding the cardiac-specific NaCh alpha-subunit Na(v)1.5, and one of its auxiliary subunits beta 1 (NaCh beta 1), were analyzed by competitive reverse transcription-polymerase chain reaction. Protein levels of Na(v)1.5, NaCh beta 1 and NaCh beta 2 were evaluated by western blotting. The maximum density of I(Na)/C(m) was decreased in HF (n = 5) compared to control hearts (33.2 +/- 4.4 vs. 50.0 +/- 4.9 pA/pF, mean +/- S.E.M., n = 5, P < 0.05). The steady-state inactivation and activation of I(Na) remained unchanged in HF compared to control hearts. The levels of mRNA encoding Na(v)1.5, and NaCh beta 1 were unaltered in FH. However, Na(v)1.5 protein expression was reduced about 30% in HF, while NaCh beta 1 and NaCh beta 2 protein were unchanged. We conclude that experimental HF in dogs results in post-transcriptional changes in cardiac NaCh alpha-subunit expression.

Ventricular Dysrhythmias in Heart Failure

Left-ventricular systolic dysfunction, or heart failure (HF), is a chronic, progressive condition with a poor prognosis. Approximately 50% of deaths, especially in mild to moderate cases, are sudden. Most sudden deaths are thought to be due to ventricular tachycardia; however, premature ventricular contractions and couplets parallel severity of HF and have been associated with increased mortality risk as opposed to dysrhythmic death. Ventricular arrhythmogenesis results from many mechanisms (afterdepolarizations, reentry, and enhanced automaticity) and preconditions (electrophysiologic abnormalities, neuroendocrine activation, electrolyte imbalances, scar from an ischemic event in ischemic cardiomyopathy, fibrosis in dilated cardiomyopathy, hemodynamic abnormalities, and HF medical management). Nurses are key caregivers in optimally managing HF, either by direct actions or by using advocacy, communication, and collaboration skills to promote positive outcomes. Ventricular dysrhythmia management consists of facilitating core HF pharmacologic and nonpharmacologic medical therapies, using amiodarone to improve symptoms, as needed, and utilizing implantable cardioverter-defibrillator therapy to reduce the risk of sudden cardiac death.

Genotype-phenotype correlation in congenital heart disease

PURPOSE OF REVIEW

The understanding of the etiology of congenital cardiac lesions is rapidly progressing from the recognition of embryologic origins to insight into the genetic basis for these disorders. Concurrently, in this era, great effort is being expended to gather data that will generate clinically useful genotype-phenotype correlation. This rapidly evolving area of inquiry, in which the clinical implications of mutation status are fully explored, makes available information applicable to those involved in all aspects of congenital cardiac disease.

RECENT FINDINGS

Three syndromes with cardiovascular phenotypes were selected for review. Each has received a great deal of attention in the recent past based on improved understanding of the range of mutations expressed and the relation of these mutations to clinical findings. These three syndromes--Noonan, Marfan, and long QT syndrome--span the range of congenital heart disease and provide examples of genotype-phenotype correlation.

SUMMARY

Better understanding of the clinical implications of specific mutations should allow not only for more sensitive and specific diagnoses to be made but also for improvements in therapeutic options and efficacy.

PET measures of pre- and post-synaptic cardiac beta adrenergic function

Positron Emission Tomography was used to measure global and regional cardiac beta-adrenergic function in 19 normal subjects and 9 congestive heart failure patients. [(11)C]-meta-hydroxyephedrine was used to image norepinephrine transporter function as an indicator of pre-synaptic function and [(11)C]-CGP12177 was used to measure cell surface beta-receptor density as an indicator of post-synaptic function. Pre-synaptic, but not post-synaptic, function was significantly different between normals and CHF patients. Pre-synaptic function was well matched to post-synaptic function in the normal hearts but significantly different and poorly matched in the CHF patients studied. This imaging technique can help us understand regional sympathetic function in cardiac disease.

Noninvasive risk stratification in postinfarction patients with severe left ventricular dysfunction and methodology of the MADIT II noninvasive electrocardiology substudy

Sudden cardiac death occurs as a result of a complex interplay of changes in myocardial substrate, imbalance of autonomic regulation of the heart, and myocardial vulnerability. Noninvasive electrocardiology serves as a comprehensive tool for investigating factors representing mechanistic pathways leading to cardiac events. Heart rate variability, nonlinear dynamics of heart rate, and heart rate turbulence provide insight into autonomic control of the heart. Prognostic value of these parameters in postinfarction patients is well established for predicting cardiac death, but there is less evidence for their association with sudden death or arrhythmic events. Electrical manifestation of changes in myocardial substrate include QRS and QTc prolongation, presence of conduction disturbances, presence of late potentials, abnormalities of repolarization morphology, and presence of nonsinus rhythm, namely atrial fibrillation. Electrocardiogram (ECG) measures reflecting myocardial vulnerability to arrhythmias include frequent ventricular premature beats, T wave alternans, or QT variability. Prognostic significance of these parameters is documented in studies focused mostly on them as individual markers of risk. The noninvasive electrocardiology substudy of the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) allows for simultaneous analysis of several of the above ECG markers of risk and will provide insight about relative contribution of mechanistic pathways leading to cardiac death in postinfarction patients with severe left ventricular dysfunction. Combination of a standard 12-lead ECG and 10-minute high-resolution Holter recordings serves to evaluate the prognostic significance of noninvasive electrocardiology parameters for mortality in patients randomized to conventional treatment and for arrhythmic events in patients randomized to implantable cardioverter defibrillator therapy.

Risk stratification and management of sudden cardiac death: a new paradigm

Risk Stratification and Management of SCD. Management of SCD is undergoing radical change in direction. It is becoming increasingly appreciated that besides depressed left ventricular systolic function and the conventional risk stratification tools, new markers for plaque vulnerability, enhanced thrombogenesis, specific genetic alterations of the autonomic nervous system, cardiac sarcolemmal and contractile proteins, and familial clustering may better segregate patients with atherosclerotic coronary artery disease who are at high risk for SCD from those who may suffer from nonfatal ischemic events. Better understanding of pathophysiologic processes, such as postmyocardial infarction remodeling, the transition from compensated hypertrophy to heart failure, and the increased cardiovascular risk of coronary artery disease in the presence of diabetes or even a prediabetic state will help to improve both risk stratification and management. The rapidly developing fields of microchips technology and proteomics may allow rapid and cost-effective mass screening of multiple risk factors for SCD. The ultimate goal is to identify novel methods for risk stratification, risk modification, and prevention of SCD that could be applied to the general public at large.