Genetic Determinants of Sudden Cardiac Death

Abstract

Sudden cardiac death (SCD) is the final common end point of multiple disease processes. It results from a complex interplay of structural, metabolic, and genetic determinants. Although epidemiological risk factors such as age, prior myocardial infarction, and low ejection fraction are well established, this syndrome also has a strong genetic component. An understanding of the genetic contributions to risk could add substantially to the prediction and prevention of SCD. In this review, we explore the epidemiology, heritability, and allelic architecture of SCD and provide a detailed overview of the genetics of inherited electrophysiological and structural heart diseases that are potent risk factors for SCD. At the population level, the conventional cardiac risk factors are powerful risk factors for SCD. For example, diabetes mellitus is associated with a marked increase in risk of SCD (odds ratioϭ1.7 without microvascular disease; odds ratioϭ2.7 with microvascular disease). 3 Among subjects with known coronary artery disease, smoking is linked to an increase in risk of SCD (hazard ratioϭ2.5). 4 In a multivariate analysis from the Paris Prospective Study, a 42-mg/dL increase in total cholesterol (1 SD of the sample variation) was associated with a 23% increased risk of SCD. In the same analysis, an increase of 20 mm Hg in systolic blood pressure was associated with a 23% increase in the risk of SCD. 5 Furthermore, data from the Framingham Heart Study demonstrate that left ventricular hypertrophy is a risk factor for ventricular arrhythmias 6 and SCD. 7 Regular high-intensity exercise appears to be associated with a lower rate of SCD, 8 although the risk is transiently increased in the 30 minutes immediately after vigorous exercise. 8 -10 Advances in the treatment of these risk factors may be partly responsible for the decline in cardiovascular mortality over the past 20 years, 11,12 but the burden of SCD remains high. The primary challenge to reducing the rate of SCD is that the bulk of events occur without warning and in patients with few identifiable risk factors (Figure 1). 13 For example, although an ejection fraction of Ͻ35% is a powerful risk factor for SCD and a current indication for implantable cardioverter-defibrillator implantation, only one third of SCD victims have a low ejection fraction. 14 The conventional coronary risk factors and presence of congestive heart failure are associated with SCD in the general population but have poor ability to predict SCD at the individual level because of their prevalence and comparatively modest effects on risk. Epidemiology of SCDAt the individual level, separating risk factors for all-cause cardiovascular mortality from risk factors for primary arrhythmia has been challenging. Among post-myocardial infarction patients who are known to be at risk of SCD, electrophysiological evaluation has been the most powerful tool in current clinical use to refine individual risk stratification. 15 Current measures that have been examined with varying predictive power include ...

Drug-Induced Arrhythmia

“…These classic forms of LQTS are associated with different T-wave morphologies and arrhythmic triggers based on the particular form of LQTS, although substantial overlap exists. 1 Other variants of genetic LQTS have been associated with proteins that affect trafficking or function of ion channels such as ankyrin 2 (LQT4) or a variety of proteins that affect ion channel kinetics (reviewed elsewhere 2,3 ). Additionally, the genetic short-QT syndrome has been described as being related to gain-of-function mutations in potassium channels or loss-of-function mutations in calcium channels.…”

“…[7][8][9] Furthermore, missense mutations in genes associated with the LQTS (encoding cardiac sodium and potassium channels) are relatively common in the general population, although the functional impact of most of these mutations is currently unknown. 3,10 Relatively common genetic variants in genes encoding cardiac ion channels have been associated with QTc prolongation, [11][12][13][14] and QTc effects have been noted to be associated with mutations in genes not associated with classic forms of LQTS such as NOS1AP. 15 Genetic forms of the LQTS therefore represent a wide spectrum of diseases.…”

Genetics of Sudden Cardiac Death

“…The bulk of mutations are reported in eight myofilament-associated genes including β-myosin heavy chain (MYH7) and myosin binding protein-C (MYBPC3), which account for 30-40 % of all cases [6]. Cardiac troponin T (TNNT2), tropomyosin (TPM1), cardiac troponin I (TNNI3), cardiac actin (ACTC), and the myosin light chains (MYL3, MYL2) represent only 1-5 % of cases [6,7]. Previous studies have shown that some mutations in the β-myosin heavy chain gene (Arg403Gln, Arg453Gln, and Arg719Trp) have nearly complete penetrance and lead to a severe early-onset disease with a high risk of SCD [8].…”

“…Impairment of these intercellular junctions and, thus, myocytes mechanical coupling are considered the primary underlying molecular defects. Other non-desmosomal proteins have also been reported to play a significant role in the pathogenesis of ARVC: ryanodine receptor 2 (cardiac) [ [6,7].…”

Mainstreaming Genetics: A Comparative Review of Clinical Services for Inherited Cardiovascular Conditions in the UK

“…ICCs include arrhythmias (for example long QT and Brugada syndromes), cardiomyopathies (for example hypertrophic cardiomyopathy and dilated cardiomyopathy), inherited arteriopathies (such as Marfan syndrome), muscular dystrophies, and familial hypercholesterolaemia (FH) [1,2,3,4,5]. In some cases, the first indication that an individual has an ICC is their sudden cardiac death, often in adolescence or early adulthood.…”