Sudden cardiac death: The larger problem... The larger genome

Sudden Cardiac Death Among Hemodialysis Patients

Hemodialysis patients carry a large burden of cardiovascular disease; most onerous is the high risk for sudden cardiac death. Defining sudden cardiac death among hemodialysis patients and understanding its pathogenesis are challenging, but inferences from the existing literature reveal differences between sudden cardiac death among hemodialysis patients and the general population. Vascular calcifications and left ventricular hypertrophy may play a role in the pathophysiology of sudden cardiac death, whereas traditional cardiovascular risk factors seem to have a more muted effect. Arrhythmic triggers also differ in this group as compared to the general population, with some arising uniquely from the hemodialysis procedure. Combined, these factors may alter the types of terminal arrhythmias that lead to sudden cardiac death among hemodialysis patients, having important implications for prevention strategies. This review highlights current knowledge on the epidemiology, pathophysiology, and risk factors for sudden cardiac death among hemodialysis patients. We then examine strategies for prevention, including the use of specific cardiac medications and device-based therapies such as implantable defibrillators. We also discuss dialysis-specific prevention strategies, including minimizing exposure to low potassium and calcium dialysate concentrations, extending dialysis treatment times or adding sessions to avoid rapid ultrafiltration, and lowering dialysate temperature.

Sudden cardiac death in CKD patients

The risk of sudden cardiac death (SCD) is high in chronic kidney disease patients, and it increases with the progression of kidney function deterioration. The most common causes of SDC are the following: ventricular tachycardia, ventricular tachyarrhythmia, tachycardia torsade de pointes, sustained ventricular fibrillation and bradyarrhythmia. Dialysis influences cardiovascular system and results in hemodynamic disturbances as well as electrolyte shifts altering myocardial electrophysiology. Studies suggest that this procedure exerts both detrimental (poor volume control can exacerbate hypertension and left ventricle hypertrophy) and beneficial effects (associated with fluid removal and subsequent decrease in left ventricle stretch). Dialysis-related vulnerability to serious arrhythmias is the result of sudden shifts in fluid status and electrolytes, particularly potassium, which alter the physiological milieu. Also Ca(2+) ions, in which concentration alters during dialysis, are of key importance in the contraction of vascular smooth muscle cells and cardiac myocytes, thus exerting significant effects on hemodynamics. Due to the fact that SCD occurs with similar frequency in peritoneal dialysis and in hemodialysis patients, it seems that end-stage renal disease factors are more important than the specific ones associated with dialysis type. The results of randomized trials suggested that hemodialysis patients may not derive the same benefit of cardiovascular disease therapy including beta-blockers, calcium channel blockers and angiotensin-converting enzyme inhibitors as the general population with normal kidney function. Noninvasive tests used to stratify SCD risk in HD patients have poor positive value, and thus, combining tests including HRV, baroreceptor sensitivity and effectiveness index as well as its function indices and heart rate turbulence should be implemented. There are only few large randomized placebo-controlled trials assessing the influence of cardioprotective medications or implantable cardioverter defibrillator (ICD) implantation in dialysis patients on life quality and survival, and their results are sometimes contradictory. The decision concerning treatment and/or ICD implantation in this group of patients should be made on the basis of careful assessment of individual risk factors. Moreover, due to the high hazard of cardiovascular mortality including SCD in dialysis patients, physicians should concentrate on the early selection of high-risk patients, monitoring them and introduction of preventive measures.

The interplay between CKD, sudden cardiac death, and ventricular arrhythmias

CKD patients face an increased risk of cardiovascular disease mortality, and the risk of sudden cardiac death (SCD) increases as kidney function declines. Risk factors for SCD are poorly understood and understudied among CKD patients. In the general population, coronary heart disease-associated risk factors are the most important determinants of SCD risk, but among CKD patients, there is evidence that these factors play a much smaller role. Complex relationships between CKD-specific risk factors, structural heart disease, and arrhythmic triggers contribute to the high risk of SCD and ventricular arrhythmias and modulate the effectiveness of available therapies. This review examines recent data on the epidemiology, pathophysiology, and mechanisms of SCD among CKD patients and examines current evidence regarding the use of pharmacologic and device-based therapies for management of SCD risk.

Sudden cardiac death and diabetes mellitus

Sudden cardiac death (SCD) affects a significant percentage of diabetic patients. SCD in these patients can be due to several factors, such as diastolic dysfunction, heart failure, altered platelet function, inflammation, sympathetic nervous stimulation and other factors. In the present review, we discuss the association between diabetes mellitus and SCD.

Circuit-wide structural and functional measures predict ventromedial prefrontal cortex fear generalization: implications for generalized anxiety disorder

The ventromedial prefrontal cortex (vmPFC) plays a critical role in a number of evaluative processes, including risk assessment. Impaired discrimination between threat and safety is considered a hallmark of clinical anxiety. Here, we investigated the circuit-wide structural and functional mechanisms underlying vmPFC threat-safety assessment in humans. We tested patients with generalized anxiety disorder (GAD; n = 32, female) and healthy controls (n = 25, age-matched female) on a task that assessed the generalization of conditioned threat during fMRI scanning. The task consisted of seven rectangles of graded widths presented on a screen; only the midsize one was paired with mild electric shock [conditioned stimulus (CS)], while the others, safety cues, systematically varied in width by ±20, 40, and 60% [generalization stimuli (GS)] compared with the CS. We derived an index reflecting vmPFC functioning from the BOLD reactivity on a continuum of threat (CS) to safety (GS least similar to CS); patients with GAD showed less discrimination between threat and safety cues, compared with healthy controls (Greenberg et al., 2013b). Using structural, functional (i.e., resting-state), and diffusion MRI, we measured vmPFC thickness, vmPFC functional connectivity, and vmPFC structural connectivity within the corticolimbic systems. The results demonstrate that all three factors predict individual variability of vmPFC threat assessment in an independent fashion. Moreover, these neural features are also linked to GAD, most likely via an vmPFC fear generalization. Our results strongly suggest that vmPFC threat processing is closely associated with broader corticolimbic circuit anomalies, which may synergistically contribute to clinical anxiety.

Association of CASQ2 polymorphisms with sudden cardiac arrest and heart failure in patients with coronary artery disease

BACKGROUND

Abnormal calcium handling plays a crucial role in arrhythmias, sudden cardiac arrest (SCA), and congestive heart failure (CHF). Calsequestrin 2 (CASQ2) mutations affect calcium release and initiate malignant ventricular arrhythmias (VAs) and SCA syndromes. Common single nucleotide polymorphisms (SNPs) in CASQ2 may be associated with SCA in patients with coronary artery disease (CAD).

OBJECTIVE

The purpose of this study was to examine the association of common CASQ2 SNPs with the risk of SCA in patients with CAD.

METHODS

CASQ2 SNPs (n = 14) were genotyped and analyzed in a case control study comparing 114 patients with CAD and SCA due to VA to 311 CAD controls without VA or SCA.

RESULTS

Multivariate logistic regression adjusting for age and CHF status identified an association between rs7521023 with SCA (odds ratio [OR] 2.72, 95% confidence interval [CI] 1.44-5.13, P = .002). The substantial impact of CHF on SCA in the model (OR 26.6, 95% CI 13.40-52.70, P <.001) led us to further examine the relationship between CHF, SCA, and CASQ2 SNPs. We identified 2 CASQ2 variants (rs7521023: OR 0.4, 95% CI 0.25-0.76, P = .003; rs6684209: OR 19.8, 95% CI 3.63-108.2, P <.001) associated with CHF after adjusting for SCA, age, gender, and hypertension.

CONCLUSION

We observed association between a CASQ2 polymorphism and SCA due to VA in patients with CAD adjusting for CHF and independent associations between CASQ2 SNPs and CHF adjusting for SCA. Further investigation in independent cohorts is needed to confirm these findings.

A common NOS1AP genetic polymorphism, rs12567209 G>A, is associated with sudden cardiac death in patients with chronic heart failure in the Chinese Han population

BACKGROUND

Variants in NOS1AP associated with cardiac repolarization and sudden cardiac death (SCD) in coronary artery disease have been reported. Whether they are related to mortality and QTc interval in chronic heart failure (CHF) has not been investigated.

METHODS AND RESULTS

A total of 1,428 patients with CHF and 480 control subjects were genotyped for 6 SNPs of NOS1AP, and the genetic associations with mortality as well as QTc interval were analyzed. During a median follow-up period of 52 months, 467 patients (32.70%) died, of which deaths 169 (36.19%) were SCD. The A allele of rs12567209 was associated with greater risk of all-cause death and SCD (hazard ratio [HR] 1.381, 95% confidence interval [CI] 1.124-1.698 [P = .002], and HR 1.645, 95% CI 1.184-2.287 [P = .003], respectively). After adjusting for other risk factors, significant differences remained (HR 1.309, 95% CI 1.054-1.624 [P = .015], and HR 1.601, 95% CI 1.129-2.271 [P = .008]). The A allele was also associated with prolongation of QTc interval by 4.04 ms in the entire population (P = .026).

CONCLUSIONS

The A allele of rs12567209 in NOS1AP may serve as an independent predictor of all-cause death and SCD in patients with CHF, it is also associated with prolonged QTc interval in the Chinese Han population.

Genetics can contribute to the prognosis of Brugada syndrome: a pilot model for risk stratification

Brugada syndrome is an inherited arrhythmogenic disorder leading to sudden death predominantly in the 3-4 decade. To date the only reliable treatment is the implantation of a cardioverter defibrillator; however, better criteria for risk stratification are needed, especially for asymptomatic subjects. Brugada syndrome genetic bases have been only partially understood, accounting for <30% of patients, and have been poorly correlated with prognosis, preventing inclusion of genetic data in current guidelines. We designed an observational study to identify genetic markers for risk stratification of Brugada patients by exploratory statistical analysis. The presence of genetic variants, identified by SCN5A gene analysis and genotyping of 73 candidate polymorphisms, was correlated with the occurrence of major arrhythmic events in a cohort of 92 Brugada patients by allelic association and survival analysis. In all, 18 mutations were identified in the SCN5A gene, including 5 novel, and statistical analysis indicated that mutation carriers had a significantly increased risk of major arrhythmic events (P=0.024). In addition, we established association of five polymorphisms with major arrhythmic events occurrence and consequently elaborated a pilot risk stratification algorithm by calculating a weighted genetic risk score, including the associated polymorphisms and the presence of SCN5A mutation as function of their odds ratio. This study correlates for the first time the presence of genetic variants with increased arrhythmic risk in Brugada patients, representing a first step towards the design of a new risk stratification model.

The prevalence of mutations in KCNQ1, KCNH2, and SCN5A in an unselected national cohort of young sudden unexplained death cases

INTRODUCTION

Sudden unexplained death account for one-third of all sudden natural deaths in the young (1-35 years). Hitherto, the prevalence of genopositive cases has primarily been based on deceased persons referred for postmortem genetic testing. These deaths potentially may represent the worst of cases, thus possibly overestimating the prevalence of potentially disease causing mutations in the 3 major long-QT syndrome (LQTS) genes in the general population. We therefore wanted to investigate the prevalence of mutations in an unselected population of sudden unexplained deaths in a nationwide setting.

METHODS

DNA for genetic testing was available for 44 cases of sudden unexplained death in Denmark in the period 2000-2006 (equaling 33% of all cases of sudden unexplained death in the age group). KCNQ1, KCNH2, and SCN5A were sequenced and in vitro electrophysiological studies were performed on novel mutations.

RESULTS

In total, 5 of 44 cases (11%) carried a mutation in 1 of the 3 genes corresponding to 11% of all investigated cases (R190W KCNQ1, F29L KCNH2 (2 cases), P297S KCNH2 and P1177L SCN5A). P1177L SCN5A has not been reported before. In vitro electrophysiological studies of P1177L SCN5A revealed an increased sustained current suggesting a LQTS phenotype.

CONCLUSION

In a nationwide setting, the genetic investigation of an unselected population of sudden unexplained death cases aged 1-35 years finds a lower than expected number of mutations compared to referred populations previously reported. We therefore conclude that the prevalence of mutations in the 3 major LQTS associated genes may not be as abundant as previously estimated.

Sudden cardiac death in hemodialysis patients: a comprehensive care approach to reduce risk

Sudden cardiac death is a major problem in hemodialysis patients, and our understanding of this disease is underdeveloped. The lack of a precise definition tailored for use in the hemodialysis population limits the reliability of epidemiologic reports. Efforts should be directed toward an accurate classification of all deaths that occur in this vulnerable population. The traditional paradigm of disease pathophysiology based on known cardiac risk factors appears to be inadequate to explain the magnitude of sudden cardiac death risk in chronic kidney disease, and numerous unique cofactors and exposures appear to determine risk in this population. Well-designed cohort studies will be needed for a basic understanding of disease pathophysiology and risk factors, and randomized intervention trials will be needed before best management practices can be implemented. This review examines available data to describe the characteristics of the high-risk patient and suggests a comprehensive common sense approach to prevention using existing cardiovascular medications and reducing and monitoring potential dialysis-related arrhythmic triggers. Other unproven cardiovascular therapies such as implantable cardioverter defibrillators should be used on a case-by-case basis, with recognition of the associated hazards that these devices carry among hemodialysis patients.

Cardiac levels of NOS1AP RNA from right ventricular tissue recovered during lead extraction

BACKGROUND

There is a scarcity of cardiac tissue available for research.

OBJECTIVE

(1) To investigate the feasibility of obtaining myocardial tissue from extracted pacemaker and defibrillator leads for gene expression analysis and (2) to examine the nitric oxide 1 adaptor protein (NOS1AP) RNA expression as a function of patient genotype.

METHODS

Seventeen patients (age = 56 ± 20 years; 12 men; 5 pacemakers; 12 defibrillators) undergoing lead extractions for standard indications (5 device erosion; 1 vascular occlusion; 11 lead malfunction or recall) were genotyped for 2 NOS1AP single nucleotide polymorphisms-rs10494366 (T to G) and rs10918594 (C to G)-and had RNA levels measured by real-time polymerase chain reaction for collagen I, troponin I, Ca(v)1.2, Kv4.3, HERG, KvLQT1, connexin 43, NOS1AP, and sodium-calcium exchanger. Ventricular tissue obtained from 3 failing hearts at transplantation served as reference.

RESULTS

A high ratio of cardiac troponin I/collagen I RNA identified 9 of the 17 patient samples (muscle rich), in which the gene expression profile was similar to that of the reference ventricular samples and significantly different (P < .003) from the expression profile of samples with a low troponin I/collagen ratio (muscle poor). TT and CC polymorphisms were associated with significantly lower NOS1AP RNA levels (P < .01 compared with the GG genotype).

CONCLUSIONS

Performing gene expression analyses on right ventricular tissue samples extracted with pacemaker and defibrillator leads is feasible. A significant number of samples contain cardiomyocytes that express troponin I and ion channels at levels comparable to those seen in explanted hearts. Decreased NOS1AP expression in rs10494366 TT and rs10918594 CC homozygotes may underlie shorter repolarization times.

Mutation analysis ion channel genes ventricular fibrillation survivors with coronary artery disease

BACKGROUND

Observations from population-based studies demonstrated a strong genetic component of sudden cardiac death. The aim of this study was to test the hypothesis that ion channel genes mutations are more common in ventricular fibrillation (VF) survivors with coronary artery disease (CAD) compared to controls.

METHODS

The entire coding sequence of KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes was analyzed in 45 (five females) CAD individuals-survivors of documented VF and in 90 matched healthy controls. In another control group of 141 matched patients with CAD without malignant arrhythmias, the exons containing rare coding variants found in the VF survivors were sequenced.

RESULTS

The carrier frequency of all the rare sequence variants was significantly higher in the VF survivors (8/45, 17.8%) than in CAD controls (3/141, 2.2%, P = 0.001). In VF survivors, four coding variants in eight individuals were found. Three in KCNH2 gene: R148W and GAG186del are novel; P347S was previously related to long QT syndrome. In SCN5A gene, P2006A variant was found in five unrelated males. This variant has been demonstrated previously to have small effect on sodium channel kinetics. No rare coding variants were found in the healthy controls. The P2006A variant was found in three CAD controls.

CONCLUSION

The prevalence of selected, rare coding variants in five long QT genes was significantly higher in cases versus controls, confirming a mechanistic role for these genes among a subgroup of patients with coronary disease and VF.

Targeting device therapy: genomics of sudden death

This article discusses the development and use of genomic predictors to define the population at risk for sudden cardiac death, which is usually defined as death from cardiac causes within an hour of symptom onset. The identification of genetic predictors of sudden death in heart failure is in its earliest stages. Mutations in ion channels have been shown to cause inherited forms of sudden death; there is, however, little evidence that mutations or rare single nucleotide polymorphisms (SNPs) in those genes are important causes of the common forms of sudden death. Other common variants in ion channels and related genes are associated with sudden death in the setting of acute myocardial infarction or heart failure. Ultimately, we hope to identify a handful of SNPs that modulate the risk of sudden death in heart failure and to develop an algorithm to predict risk based on genotype.

The genetics of cardiovascular disease: new insights from emerging approaches

The prospect that sequencing the human genome would see rapid translation of a greater understanding of cardiovascular genetics into novel diagnostics and therapeutics has so far met with only limited success. However, diverse technological advances and exploitation of novel animal models of cardiovascular development and disease are providing ever more insight into cardiovascular diseases and development, and bring closer the prospect of 'post-genomic' diagnostics and therapies. Here we review some of these emerging approaches (genome wide association studies, deep sequencing, microRNA regulation, and zebrafish as a model of cardiovascular disease and development) and discuss their potential for finally fulfilling the promise of application to clinical cardiovascular medicine.