The ability of an electrocardiogram to predict fatal and non-fatal cardiac events in asymptomatic middle-aged subjects

INTRODUCTION

The long-term prognostic value of a standard 12-lead electrocardiogram (ECG) for predicting cardiac events in apparently healthy middle-aged subjects is not well defined.

MATERIALS AND METHODS

A total of 9511 middle-aged subjects (mean age 43 ± 8.2 years, 52% males) without a known cardiac disease and with a follow-up 40 years were included in the study. Fatal and non-fatal cardiac events were collected from the national registries. The predictive value of ECG was separately analyzed for 10 and 30 years. Major ECG abnormalities were classified according to the Minnesota code.

RESULTS

Subjects with major ECG abnormalities (N = 1131) had an increased risk of cardiac death after 10-years (adjusted hazard ratio [HR] 1.7; 95% confidence interval [95% CI], 1.1-2.5, p = 0.009) and 30-years of follow-up (HR 1.3, 95% CI, 1.1-1.5, p < 0.001). Model discrimination measured with the C-index showed only a minor improvement with the inclusion of ECG abnormalities: 0.851 versus 0.853 and 0.742 versus 0.743 for 10- and 30-year follow-up, respectively. ECG did not predict non-fatal cardiac events after 10-years or 30-years of follow-up.

DISCUSSION

Major ECG abnormalities are associated with an increased risk of short and long-term cardiac mortality in middle-aged subjects. However, the improvement in discrimination between subjects with and without fatal cardiac events was marginal with abnormal ECG.

KEY MESSAGES

Abnormalities observed on 12-lead electrocardiogram are shown to have prognostic significance for cardiac events in elderly subjects without known cardiac disease. Our results suggest that ECG abnormalities increase the risk of fatal cardiac events also in middle-aged healthy subjects.

High plasma leptin levels are associated with impaired diastolic function in patients with coronary artery disease

BACKGROUND AND AIMS

Obese subjects have elevated leptin levels, which have been associated with increased risk of cardiovascular events. Because leptin has direct cellular effects on various tissues, we tested the hypothesis that leptin levels are associated with cardiac structure or function in patients with coronary artery disease (CAD).

METHODS AND RESULTS

The study population consisted of 1 601 CAD patients, of whom 42% had type 2 diabetes mellitus. Plasma leptin was measured in fasted state and an echocardiography performed. Leptin levels were not related to LV dimensions or LV ejection fraction (NS for all), but higher leptin levels were associated with elevated E/E' (9.43 vs. 11.94 in the lowest and the highest leptin quartile, respectively; p=0.018 for trend). Correspondingly, a decreasing trend was observed in E/A (1.15 vs. 1.06; p=0.037). These associations were independent of obesity and other relevant confounding variables.

CONCLUSION

We conclude that elevated plasma leptin levels are associated with impaired left ventricular diastolic function in patients with CAD independently of obesity and other confounding variables. Leptin may be one of the mechanistic links explaining the development of congestive heart failure in obese subjects.

12-Lead electrocardiogram as a predictor of sudden cardiac death: from epidemiology to clinical practice

Sudden cardiac death (SCD) causes a high burden of premature deaths in the population affecting subjects of all ages. The identification of subjects at high risk for SCD is of great importance as the prevention of many of these events would be possible with the treatment of underlying cardiac diseases and the use of implantable cardioverter-defibrillators (ICD). However, the current selection of patients for ICD therapy is based solely on left ventricular ejection fraction, and thus a substantial portion of patients at high risk does not qualify for the therapy. Role of the standard electrocardiogram (ECG) in SCD risk stratification has been under active research during the last decade and multiple abnormalities of depolarization and repolarization on the ECG associated with an increased risk of SCD have been identified. In this review, we describe the basic pathophysiological principles behind these changes. We also review the current knowledge of the prognostic significance of ECG predictors of SCD in the general population, and in patients with coronary heart disease (CHD), heart failure, cardiomyopathies, and in inheritable arrhythmia syndromes. Also, insights into the novel digital ECG signal processing techniques are provided.

Temporal Trends in the Clinical and Pathological Characteristics of Victims of Sudden Cardiac Death in the Absence of Previously Identified Heart Disease

Background—

Coronary artery disease is identified in ≈80% of victims of sudden cardiac death (SCD). Because the prevention strategies and public awareness have changed during the past decades, we studied the temporal trends in the pathogenesis of SCD.

Methods and Results—

FinGesture (n=4031) is a prospective study designed to classify the phenotype and genotype profiles of SCD in a consecutive series of victims of SCD in Northern Finland. On the basis of Finnish law, all subjects who die suddenly undergo autopsy. We analyzed the characteristics of SCD victims and autopsy findings in 1998 to 2002, 2003 to 2007, and 2008 to 2012. Among victims of SCD as a first cardiac event (n=2697), the proportion with coronary artery disease decreased during the 2008 to 2012 time period, compared with the 2 preceding 5-year periods: 74.0% in 1998 to 2002, 73.1% in 2003 to 2007, and 66.4% in 2008 to 2012 ( P <0.001). Proportion of SCDs associated with hypertensive heart disease with left ventricular hypertrophy in the absence of coronary artery disease increased from 1.7% in 1998 to 2002 to 5.8% in 2003 to 2007 and 8.9% in 2008 to 2012 ( P <0.001). Similarly, myocardial fibrosis in the absence of myocarditis or left ventricular hypertrophy, or other known pathogeneses, was 6.7% in the past 5-year period compared with 2 previous 5-year periods (3.7% and 4.0%; P <0.001 between 1998–2002 and 2008–2012 and between 2003–2007 and 2008–2012).

Conclusions—

The proportion of SCDs attributable to coronary artery disease, in the absence of a history of heart disease, has decreased, whereas the proportion associated with hypertensive heart disease and idiopathic fibrosis has increased during the past 15 years.

Diabetes, glucose tolerance, and the risk of sudden cardiac death

BACKGROUND

Diabetes predisposes to sudden cardiac death (SCD). However, it is uncertain whether greater proportion of cardiac deaths are sudden among diabetes patients than other subjects. It is also unclear whether the risk of SCD is pronounced already early in the course of the disease. The relationship of impaired glucose tolerance (IGT) and SCD is scarcely documented.

METHODS

A general population cohort of 10594 middle-aged subjects (mean age 44 years, 52.6 % male, follow-up duration 35-41 years) was divided into diabetes patients (n = 82), subjects with IGT (n = 3806, plasma glucose ≥9.58 mmol/l in one-hour glucose tolerance test), and controls (n = 6706).

RESULTS

Diabetes patients had an increased risk of SCD after adjustment confounders (hazard ratio 2.62, 95 % confidence interval 1.46-4.70, p = 0.001) but risk for non-sudden cardiac death was similarly increased and the proportion of SCD of cardiac deaths was not increased. The SCD risk persisted after exclusion of subjects with baseline cardiac disease or non-fatal cardiac events during the follow-up. Subjects with IGT were at increased risk for SCD (univariate hazard ratio 1.51; 95 % confidence interval 1.31-1.74; p < 0.001) and also for non-sudden cardiac deaths and non-fatal cardiac events but adjustments for other risk factors attenuated these effects.

CONCLUSIONS

Diabetes was associated with increased risk of SCD but also the risk of non-sudden cardiac death was similarly increased. The proportion of cardiac deaths being sudden in subjects with diabetes was not increased. The higher SCD risk in diabetes patients was independent of known cardiac disease at baseline or occurrence of non-fatal cardiac event during the follow-up.

Usefulness of Highly Sensitive Troponin as a Predictor of Short-Term Outcome in Patients With Diabetes Mellitus and Stable Coronary Artery Disease (from the ARTEMIS Study)

The aim of this study was to test the hypothesis that novel biomarkers may predict cardiac events in diabetic patients with stable coronary artery disease (CAD). Serum levels of highly sensitive troponin T (hs-TnT), B-type natriuretic peptide, highly sensitive C-reactive protein (hs-CRP), galectin-3, and soluble suppressor of tumorigenicity-2 (sST2) were analyzed in 1,137 patients with CAD and with type 2 diabetes, impaired glucose tolerance, or fasting glycaemia (diabetic group) and in 649 patients with normal glucose state. Cardiac death or hospitalization for congestive heart failure was the major end point during the follow-up of 2 years. Forty patients in the diabetic group (3.5%) and 9 patients in the nondiabetic group (1.4%) reached the primary end point. High hs-TnT level (≥14 ng/l) was the strongest predictor of the primary end point with hazard ratio of 24.5 (95% confidence interval 8.7 to 69.0; p <0.001) and remained so when adjusted for clinical variables, ejection fraction, renal, lipid, and glycemic status and other biomarkers (hazard ratio 9.9, 95% confidence interval 3.2 to 30.8; p <0.001). In the multivariate model, hs-CRP, B-type natriuretic peptide, and sST2 also predicted the primary end point in the diabetic group (p <0.01 for all). Only sST2 (p <0.001) and hs-CRP (p = 0.02) predicted the primary end point in nondiabetic group. The inclusion of hs-TnT in the model significantly improved discrimination (integrated discrimination improvement 0.050) and reclassification of the patients (net reclassification index 0.21). In conclusion, hs-TnT is a strong predictor of cardiac death or hospitalization for heart failure independently from traditional risk markers or other biomarkers in diabetic patients with stable CAD.

Body Mass Index as a Predictor of Sudden Cardiac Death and Usefulness of the Electrocardiogram for Risk Stratification

Evidence of the role of body mass index (BMI) as a risk factor for sudden cardiac death (SCD) is conflicting, and how electrocardiographic (ECG) SCD risk markers perform in subjects with different BMIs is not known. In this study, a general population cohort consisting of 10,543 middle-aged subjects (mean age 44 years, 52.7% men) was divided into groups of lean (BMI <20, n = 374), normal weight (BMI 20.0 to 24.9, n = 4,334), overweight (BMI 25.0 to 29.9, n = 4,390), and obese (BMI >30, n = 1,445) subjects. Cox proportional hazards models adjusted for confounders were used to assess the risk for SCD associated with BMI and the risk for SCD associated with ECG abnormalities in subjects with different BMIs. The overweight and obese subjects were at increased risk for SCD (hazard ratios [95% CIs] were 1.33 [1.13 to 1.56], p = 0.001 and 1.79 [1.44 to 2.23], p <0.001 for overweight and obese subjects, respectively). The risk of non-SCD had a similar relation with BMI as SCD. Hazard ratios associated with ECG abnormalities were 3.03, 1.75, 1.74, and 1.34 in groups of lean, normal weight, overweight, and obese subjects, respectively, but no statistical significance was reached in the obese. ECG abnormalities improved integrated discrimination indexes and continuous net reclassification indexes statistically significantly only in the normal weight group. In conclusion, the overweight and obese are at increased risk for SCD but also for non-SCD, and ECG abnormalities are associated with increased risk of SCD also in normal weight subjects presenting with less traditional cardiovascular risk factors.

Antiepileptic medications and the risk for sudden cardiac death caused by an acute coronary event: a prospective case-control study

BACKGROUND

Epilepsy is associated with sudden death, but the reasons for this association are not well known. Objective We studied the role of antiepileptic drugs (AEDs) as a factor contributing to sudden cardiac death (SCD) in The Finnish Study of the Genotype and Phenotype Characteristics of Sudden Cardiac Death (FinGesture).

METHODS AND RESULTS

The FinGesture study compares the characteristics of victims of SCD caused by an autopsy-verified acute coronary event (cases) vs. survivors of an acute coronary event (ACS) (controls). The study population comprised 3737 cases (mean age 64 ± 12 y) and 3081 controls (mean age 66 ± 12 y). The use of AED was obtained from death certificates, autopsy/hospital records, national drug imbursement register, and interviews with the relatives. AEDs were more commonly used by the victims of SCD vs. controls (5.5% vs. 2.2%, adjusted odds ratio 2.7, 95% CI; 1.9-3.9; p < 0001). The use of AED for non-epilepsy indications was also more common in the cases than in controls (1.5% vs. 1.0%, p = 0.005).

CONCLUSION

A higher rate of AED was observed in victims of SCD than in a control group of ACS patients. Concomitant use of AED could be responsible for a small fraction of deaths due to acute coronary events. Key message Epilepsy has been associated with sudden cardiac death. The use of antiepileptic drugs seems to be associated with an increased risk of sudden cardiac death during a coronary event. Physicians should be aware of the risk related to antiepileptic drugs especially when used for other reasons than epilepsy.

Exercise capacity and heart rate responses to exercise as predictors of short-term outcome among patients with stable coronary artery disease

Although exercise capacity (EC) and autonomic responses to exercise predict clinical outcomes in various populations, they are not routinely applied in patients with coronary artery disease (CAD). We hypothesized that the composite index of EC and exercise heart rate responses would be a powerful determinant of short-term risk in CAD. Patients with angiographically documented stable CAD and treated with β blockers (n = 1,531) underwent exercise testing to allow the calculation of age- and gender-adjusted EC, maximal chronotropic response index (CRI), and 2-minute postexercise heart rate recovery (HRR, percentage of maximal heart rate). Cardiovascular deaths and hospitalization due to heart failure, registered during a 2-year follow-up (n = 39, 2.5%), were defined as the composite primary end point. An exercise test risk score was calculated as the sum of hazard ratios related to abnormal (lowest tertile) EC, CRI, and HRR. Abnormal EC, CRI, and HRR predicted the primary end point, involving 4.5-, 2.2-, and 6.2-fold risk, respectively, independently of each other. The patients with intermediate and high exercise test risk score had 11.1-fold (95% confidence interval 2.4 to 51.1, p = 0.002) and 25.4-fold (95% confidence interval 5.5 to 116.8, p <0.001) adjusted risk for the primary end point in comparison with the low-risk group, respectively. The addition of this risk score to the established risk model enhanced discrimination by integrated discrimination index and reclassification by categorical and continuous net reclassification index (p <0.001 for all). In conclusion, the composite index of EC and heart rate responses to exercise and recovery is a powerful predictor of short-term outcome in patients with stable CAD.

Electrocardiographic T Wave Abnormalities and the Risk of Sudden Cardiac Death: The Finnish Perspective

The identification of patients at risk for sudden cardiac death (SCD) is still a significant challenge to clinicians and scientists. Noninvasive identification of high-risk patients has been of great interest, and several ventricular depolarization and repolarization abnormalities in the standard 12-lead electrocardiogram (ECG) have been associated with increased vulnerability to lethal ventricular arrhythmias. Several benign and pathological conditions can induce changes in repolarization detected as alteration of the ST segment or T wave. Changes in the ST segment and T waves can be early markers of an underlying cardiovascular disease, and even minor ST-T abnormalities have predicted reduced survival and increased risk of SCD in the adult population. In this review, we will discuss the current knowledge of the SCD risk with standard 12-lead ECG T wave abnormalities in the general population, and possible T wave changes in various cardiac conditions predisposing to SCD.

Serum PINP, PIIINP, galectin-3, and ST2 as surrogates of myocardial fibrosis and echocardiographic left venticular diastolic filling properties

Objectives and Background: Serum biomarkers have been proposed to reflect fibrosis of several human tissues, but their specific role in the detection of myocardial fibrosis has not been well-established. We studied the association between N-terminal propeptide of type I and III procollagen (PINP, PIIINP, respectively), galectin-3 (gal-3), soluble ST2 (ST2), and myocardial fibrosis measured by late gadolinium enhanced cardiac magnetic resonance imaging (LGE CMR) and their relation to left ventricular diastolic filling properties measured by tissue Doppler echocardiography (E/e') in patients with stable coronary artery disease (CAD).

Methods and Results: We determined the PINP, PIIINP, gal-3, and ST2 serum levels and performed LGE CMR and echocardiography on 63 patients with stable CAD without a history of prior myocardial infarction. Myocardial late gadolinium enhancement T1 relaxation time was defined as a specific marker of myocardial fibrosis. ST2, PINP, and PIIINP did not have a significant correlation with the post-LGE T1 relaxation time tertiles (NS for all), but the lowest post-LGE T1 relaxation time tertile had significantly higher gal-3 values than the other two tertiles (p = 0.002 and 0.002) and higher E/é-values (p = 0.009) compared to the highest T1 relaxation time tertile. ST2 (p = 0.025 and 0.029), gal-3 (p = 0.003 and < 0.001) and PIIINP (p = 0.001 and 0.007) levels were also significantly higher in the highest E/é tertile, compared to the other two tertiles.

Conclusions: Elevated serum levels of gal-3 reflect the degree of myocardial fibrosis assessed by LGE CMR. Gal-3, ST2, and PIIINP are also elevated in patients with impaired LV diastolic function, suggesting that these biomarkers are useful surrogates of structural and functional abnormality of the myocardium.

Effects of physical activity and exercise training on cardiovascular risk in coronary artery disease patients with and without type 2 diabetes

OBJECTIVE

Leisure-time physical activity (LTPA) and exercise training are essential parts of current guidelines for patients with coronary artery disease (CAD). However, the contributions of LTPA and exercise training to cardiovascular (CV) risk in CAD patients with type 2 diabetes (T2D) are not well established.

RESEARCH DESIGN AND METHODS

We examined the effects of LTPA (n = 539 and n = 507; with and without T2D, respectively) and 2-year controlled, home-based exercise training (n = 63 plus 64 control subjects with T2D and n = 72 plus 68 control subjects without T2D) on the CV risk profile and composite end point among CAD patients.

RESULTS

During the 2-year follow-up, patients with reduced LTPA at baseline had an increased risk of CV events (adjusted hazard ratio 2.3 [95% CI 1.1-5.1; P = 0.033], 2.1 [1.1-4.2; P = 0.027], and 2.0 [1.0-3.9; P = 0.044] for no LTPA, LTPA irregularly, and LTPA two to three times weekly, respectively) compared with those with LTPA more than three times weekly. Among patients who completed the 2-year exercise intervention, exercise training resulted in favorable changes in exercise capacity both in CAD patients with T2D (+0.2 ± 0.8 vs. -0.1 ± 0.8 MET, P = 0.030) and without T2D (+0.3 ± 0.7 vs. -0.1 ± 0.5 MET, P = 0.002) as compared with the control group but did not have any significant effects on major metabolic or autonomic nervous system risk factors in CAD patients with or without T2D.

CONCLUSIONS

There is an inverse association between habitual LTPA and short-term CV outcome, but controlled, home-based exercise training has only minor effects on the CV risk profile in CAD patients with T2D.

Clinical aspects of inherited J-wave syndromes

Presence of J-point elevation with rapidly ascending ST segment in the anterior leads of the 12-lead electrocardiogram has been generally considered a benign phenomenon. The concept of benign nature of J-waves has changed as data emerged on variants of J-waves that were associated with the increased risk of sudden cardiac death. Two specific inherited arrhythmia syndromes, such as Brugada syndrome and early repolarization syndrome, have been recognized that carry an increased risk for ventricular fibrillation. The current review is aimed at discussing the clinical aspects of these syndromes and the implications of incidental recognition of the J-waves in a randomly recorded electrocardiogram of asymptomatic subjects.

Increased type I collagen synthesis in victims of sudden cardiac death due to idiopathic myocardial fibrosis

AIMS

Idiopathic myocardial fibrosis (IMF) was observed to be the most prevalent autopsy finding in the victims of sudden cardiac death (SCD) under the age of 40 years in the FinGesture cohort. To elucidate further the mechanisms of IMF, we examined the collagen composition from the myocardial samples taken from the victims of IMF-associated SCD.

METHODS

Eighteen cases with IMF as a cause of death, confirmed by autopsy, were selected for the analysis. Controls (n = 27) included were cases in whom no cardiac or non-cardiac disease could be found as a cause of unexpected death at autopsy. In addition to conventional histological examination, immunohistochemical staining of procollagens I and III (PINP and PIINP), mature collagen III (IIINTP), and the cross-linked collagen I degradation product (ICTP) were performed.

RESULTS

Increased accumulation of PINP was observed in the fibrotic tissue of the IMF cases in comparison with control samples. In contrast, type III collagen was not as frequently expressed in the fibrotic areas.

CONCLUSION

Myocardial accumulation of PINP in the victims of IMF-associated SCD indicates increased type I collagen synthesis. Future studies on the role of circulating type I collagen biomarkers are needed to study further the implications of the described association.

Early repolarization as a predictor of arrhythmic and nonarrhythmic cardiac events in middle-aged subjects

BACKGROUND

Early repolarization (ER) in the inferior/lateral leads predicts mortality, but whether ER is a specific sign of increased risk for arrhythmic events is not known.

OBJECTIVE

The purpose of this study was to study the association of ER and arrhythmic events and nonarrhythmic morbidity and mortality.

METHODS

We assessed the prognostic significance of ER in a community-based general population of 10,846 middle-aged subjects (mean age 44 ± 8 years). The end-points were sustained ventricular tachycardia or resuscitated ventricular fibrillation (VT-VF), arrhythmic death, nonarrhythmic cardiac death, new-onset atrial fibrillation (AF), hospitalization for congestive heart failure, or coronary artery disease during mean follow-up of 30 ± 11 years. ER was defined as ≥0.1-mV elevation of J point in either inferior or lateral leads.

RESULTS

After including all risk factors of cardiac mortality and morbidity in Cox regression analysis, inferior ER (prevalence 3.5%) predicted VF-VT events (n = 108 [1.0%]) with a hazard ratio (HR) of 2.2 (95% confidence interval [CI] 1.1-4.5, P = .03) but not nonarrhythmic cardiac death (n = 1235 [12.2%]), AF (n = 1659 [15.2%]), congestive heart failure (n = 1752 [16.1%]), or coronary artery disease (n = 3592 [32.9%]) (P = NS for all). Inferior ER predicted arrhythmic death in cases without other QRS complex abnormalities (multivariate HR 1.68, 95 % CI 1.10-2.58, P = .02) but not in those with ER and other coexisting abnormalities in QRS morphology (HR 1.30, 95% CI 0.86-1.96, P = .22).

CONCLUSION

ER in the inferior leads, especially in cases without other QRS complex abnormalities, predicts the occurrence of VT-VF but not nonarrhythmic cardiac events, suggesting that ER is a specific sign of increased vulnerability to ventricular tachyarrhythmias.

Comparison of inferolateral early repolarization and its electrocardiographic phenotypes in pre- and postadolescent populations

Inferolateral early repolarization (ER) patterns on standard electrocardiogram (ECG) are associated with increased risk for cardiac and arrhythmic death in general adult population cohorts. We sought to determine the prevalence of inferolateral ER on surface ECG in multiracial pre- and postadolescent populations and to analyze its association with age, race, gender, and ST-segment patterns. A retrospective review was conducted of all ECGs recorded from preadolescent (aged 8-12 years, n = 719) and postadolescent (aged 21-25 years, n = 755) patients seen at a large academic medical center between January 1, 2009, and December 31, 2010. The overall prevalence of inferolateral ER was similar in the preadolescent and postadolescent populations (17% vs 16%, NS). The prevalence of ER increased after puberty in male patients (16% to 25%, p <0.001) and decreased in female patients (18% to 9%, p <0.001). Prevalence of ascending early repolarization (benign variant) also increased in males after puberty (15% to 23%, p <0.004) and decreased in females (11% to 4%, p <0.001). There were no differences in the prevalence of the risk-associated horizontal/descending pattern (3% in both groups). Subgroup analysis was performed on ECGs from the cohort of outpatients without cardiac disease, and the statistical trends remained the same. In conclusion, the overall prevalence of inferolateral ER was higher in pre- and postadolescent populations than in adult populations. However, the prevalence of the risk-associated horizontal/descending ST-segment pattern was only 3%, comparable to prevalence rates in the adult population. The variations in prevalence by gender and age suggest a possible influence of reproductive hormones.

Risk markers of sudden cardiac death in standard 12-lead electrocardiograms

The annual incidence of sudden cardiac death (SCD) is estimated at 1 per 1,000 for adults over the age of 35 years, and 1 per 100,000 for adolescents and young adults. Although the overall incidence of unexpected SCD among previously healthy persons is small, the emotional impact of these events is devastating. The 12-lead electrocardiogram (ECG) has been used as a risk assessment tool from healthy occupational applicants and athletes to patients with cardiovascular disorders. The ECG is also routinely recorded in the majority of patients hospitalized for non-cardiovascular causes. Thus, it is a widely used tool intended for identification of unsuspected heart disease generally, as well as for diagnosing specific disorders predisposing to fatal arrhythmias in subjects who have not experienced such events but who are at increased risk. Recognition of specific ECG features is of importance for prevention of SCD in asymptomatic persons. The purpose of this review is to catalog the disorders associated with SCD that may be reflected in 12-lead ECGs seen in office or hospital practices and to discuss their prevalence and the magnitude of risks. The focus is on ECG findings suggesting increased SCD risk among the asymptomatic subjects without previously diagnosed cardiac disease.

FTO genotype is associated with phenotypic variability of body mass index

There is evidence across several species for genetic control of phenotypic variation of complex traits, such that the variance among phenotypes is genotype dependent. Understanding genetic control of variability is important in evolutionary biology, agricultural selection programmes and human medicine, yet for complex traits, no individual genetic variants associated with variance, as opposed to the mean, have been identified. Here we perform a meta-analysis of genome-wide association studies of phenotypic variation using ∼170,000 samples on height and body mass index (BMI) in human populations. We report evidence that the single nucleotide polymorphism (SNP) rs7202116 at the FTO gene locus, which is known to be associated with obesity (as measured by mean BMI for each rs7202116 genotype), is also associated with phenotypic variability. We show that the results are not due to scale effects or other artefacts, and find no other experiment-wise significant evidence for effects on variability, either at loci other than FTO for BMI or at any locus for height. The difference in variance for BMI among individuals with opposite homozygous genotypes at the FTO locus is approximately 7%, corresponding to a difference of ∼0.5 kilograms in the standard deviation of weight. Our results indicate that genetic variants can be discovered that are associated with variability, and that between-person variability in obesity can partly be explained by the genotype at the FTO locus. The results are consistent with reported FTO by environment interactions for BMI, possibly mediated by DNA methylation. Our BMI results for other SNPs and our height results for all SNPs suggest that most genetic variants, including those that influence mean height or mean BMI, are not associated with phenotypic variance, or that their effects on variability are too small to detect even with samples sizes greater than 100,000.

A meta-analysis of genome-wide association studies of the electrocardiographic early repolarization pattern

BACKGROUND

The early repolarization pattern (ERP) is common and associated with risk of sudden cardiac death. ERP is heritable, and mutations have been described in syndromatic cases.

OBJECTIVE

To conduct a meta-analysis of genome-wide association studies to identify common genetic variants influencing ERP.

METHODS

We ascertained ERP on the basis of electrocardiograms in 3 large community-based cohorts from Europe and the United States: the Framingham Heart Study, the Health 2000 Study, and the KORA F4 Study. We analyzed genome-wide association studies in participants with and without ERP by logistic regression assuming an additive genetic model and meta-analyzed individual cohort results. We then sought to strengthen support for findings that reached P ≤ 1 × 10(-5) in independent individuals by direct genotyping or in-silico analysis of genome-wide data. We meta-analyzed the results from both stages.

RESULTS

Of 7482 individuals in the discovery stage, 452 showed ERP (ERP positive: mean age 46.9 ± 8.9 years, 30.3% women; ERP negative: 47.5 ± 9.4 years, 54.2% women). After meta-analysis, 8 single nucleotide polymorphisms reached P ≤ 1 × 10(-5): The most significant finding was intergenic rs11653989 (odds ratio 0.47; 95% confidence interval 0.36-0.61; P = 6.9 × 10(-9)). The most biologically relevant finding was intronic to KCND3: rs17029069 (odds ratio 1.46; 95% confidence interval 1.25-1.69; P = 8.5 × 10(-7)). In the replication step (7151 individuals), none of the 8 variants replicated, and combined meta-analysis results failed to reach genome-wide significance.

CONCLUSIONS

In a genome-wide association study, we were not able to reliably identify genetic variants predisposing to ERP, presumably due to insufficient statistical power and phenotype heterogeneity. The reported heritability of ERP warrants continued investigation in larger well-phenotyped populations.

Comparison of Family History of Sudden Cardiac Death in Nonischemic and Ischemic Heart Disease

Background—

Recent studies have identified the presence of familial clustering of ischemic sudden cardiac death (SCD) as a clinical expression of coronary artery disease. The purpose of this study was to determine whether nonischemic SCD has a similar familial background, which would be evidence of a genetic predisposition.

Methods and Results—

The retrospective case-control study included (1) consecutive victims of nonischemic SCD (n=223), (2) consecutive victims of ischemic SCD (n=596), whose deaths and diagnosis were verified at medicolegal autopsy, and (3) control subjects without heart disease (n=475). In each study group, the family history of SCD among the first-degree relatives was determined and verified from death certificates. The prevalence of SCD in ≥1 first-degree relative was significantly higher in victims of ischemic (34.2%) than nonischemic SCD (13.4%; P <0.001) or controls (17.6%; P <0.001). The history of SCD in first-degree relatives did not differ from controls in nonischemic SCD victims ( P =0.155). In a subgroup analysis of victims of ischemic SCD, the prevalence of family history of SCD in first-degree relatives did not differ between those with or without a prior infarct scar at autopsy (33.1% versus 29.9%, respectively; P =0.222).

Conclusions—

Ischemic SCD has a strong familial background both in cases with and without a prior myocardial infarction. The family history of SCD is not significantly increased in victims of nonischemic SCD, suggesting a larger role of sporadic occurrence than inherited traits as the cause of nonischemic SCD.

Association of early repolarization and sudden cardiac death during an acute coronary event

BACKGROUND

Electrocardiographic early repolarization (ER) pattern has been previously associated with arrhythmic mortality and with an increased risk of ventricular fibrillation. We hypothesized that there is an association between ER and sudden cardiac death (SCD) during an acute coronary event.

METHODS AND RESULTS

The present study included 432 consecutive victims of SCD because of acute coronary event and 532 survivors of such an event, in whom 12-lead ECGs recorded before and unrelated to the event could be evaluated. SCDs were verified by medicolegal autopsy to be because of acute coronary event. ER was defined as an elevation of the QRS-ST junction in at least 2 inferior or lateral leads, manifested as QRS notching or slurring. The prevalence of ER pattern ≥0.1 mV was more common in cases (62/432; 14.4%) than controls (42/532; 7.9%) (P=0.001). The victims of SCD were younger, were more commonly men and smokers, had lower body mass index, had elevated heart rate, had prolonged QRS complex, and had lower prevalence of history of prior cardiovascular disease than controls. After adjustments for baseline differences, the odds ratio for J waves without ST-segment elevation in the SCD group was 2.15 (95% CI, 1.20-3.85; P=0.01).

CONCLUSIONS

Higher prevalence of ER in a standard 12-lead ECG in victims of SCD than in survivors of an acute coronary event suggests that the presence of ER increases the vulnerability to fatal arrhythmia during acute myocardial ischemia and provides a plausible mechanistic link between this ECG pattern and higher arrhythmic mortality of middle-aged/elderly subjects.

Association of early repolarization and sudden cardiac death during an acute coronary event

BACKGROUND

Electrocardiographic early repolarization (ER) pattern has been previously associated with arrhythmic mortality and with an increased risk of ventricular fibrillation. We hypothesized that there is an association between ER and sudden cardiac death (SCD) during an acute coronary event.

METHODS AND RESULTS

The present study included 432 consecutive victims of SCD because of acute coronary event and 532 survivors of such an event, in whom 12-lead ECGs recorded before and unrelated to the event could be evaluated. SCDs were verified by medicolegal autopsy to be because of acute coronary event. ER was defined as an elevation of the QRS-ST junction in at least 2 inferior or lateral leads, manifested as QRS notching or slurring. The prevalence of ER pattern ≥0.1 mV was more common in cases (62/432; 14.4%) than controls (42/532; 7.9%) (P=0.001). The victims of SCD were younger, were more commonly men and smokers, had lower body mass index, had elevated heart rate, had prolonged QRS complex, and had lower prevalence of history of prior cardiovascular disease than controls. After adjustments for baseline differences, the odds ratio for J waves without ST-segment elevation in the SCD group was 2.15 (95% CI, 1.20-3.85; P=0.01).

CONCLUSIONS

Higher prevalence of ER in a standard 12-lead ECG in victims of SCD than in survivors of an acute coronary event suggests that the presence of ER increases the vulnerability to fatal arrhythmia during acute myocardial ischemia and provides a plausible mechanistic link between this ECG pattern and higher arrhythmic mortality of middle-aged/elderly subjects.