High Risk Of Sudden Cardiac Death Research Articles

Abstract 19577: Race and Sudden Cardiac Death: Findings From the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

Introduction: Blacks, as compared to whites, have a higher burden of cardiovascular disease (CVD) risk factors and CVD. Recent studies have reported a higher burden of sudden cardiac death (SCD) in blacks; however, it remains unclear whether this elevation in SCD risk is independent of racial differences in risk factor profiles and prevalent CVD. Methods: We examined the association between black race and SCD in participants with and without a history of CVD at baseline in the REGARDS study, a prospective, longitudinal cohort of 29,695 participants ≥45 years (55% women, 41% black) from across the United States. SCD was defined as sudden pulselessness from a presumed cardiac origin that occurred out of hospital or in the emergency room. Results: Over a median [IQR] of 6.0 [4.5-7.3] years of follow-up, 388 SCD events occurred. Compared to whites, blacks had less education, lower income and a higher burden of CVD risk factors. In the entire population, the age-adjusted SCD incidence rates per 1000 person-years were 2.6 (95% CI, 2.3-3.0) for blacks versus 1.7 (95% CI, 1.4-1.9) for whites, (HR=1.47; 95% CI 1.20-1.79). This elevated risk was attenuated after controlling for CVD risk factors and became non-significant after controlling for prevalent CVD (Table 1). Among the subgroup of 22,507 participants without CVD at baseline, SCD risk remained elevated in blacks (HR=1.90; 1.35-2.68) even after controlling for CVD risk factors and medication use (Table 1). In contrast, there was no elevation in SCD risk among the participants with prevalent CVD at baseline. The association between black race and SCD was stronger in those without compared to those with a history of CVD (p=0.001). Conclusions: The higher risk of SCD risk associated with black race, compared to whites, is partially explained by the higher prevalence of CVD and its risk factors in blacks. However, there remains a higher SCD risk associated with black race among those without CVD not explained by standard CVD risk factors.

Midwall Fibrosis: Cardiac Magnetic Resonance Imaging in Risk Stratifying Cardiomyopathies

The United Kingdom’s National Institute for Health and Care Excellence guidance on implantable cardiac defibrillator (ICD) therapy recommend ICD in those with left ventricular dysfunction and a high risk of sudden cardiac death (SCD). SCD accounts for 30% deaths in non-ischaemic dilated cardiomyopathy (DCM), however risk stratifying and predicting SCD in DCM is a major management challenge. We present two cases demonstrating the potential role of cardiac magnetic resonance imaging in risk stratifying DCM.

Implantable cardioverter-defibrillator and wait-list outcomes in pediatric patients awaiting heart transplantation

Implantable cardioverter-defibrillators (ICDs) reduce the incidence of sudden cardiac death (SCD) in adults with end-stage heart failure; however, their efficacy in pediatric patients awaiting heart transplantation is not well established. This study sought to investigate the role of ICDs in preventing SCD and waiting list mortality as well as to determine risk factors for SCD in pediatric patients listed for heart transplantation. We queried the United Network for Organ Sharing database for all pediatric patients (age ≤18 years) listed for heart transplantation (2005-2014). The Cox proportional hazards model was used to identify risk factors for SCD and all-cause mortality. A total of 5072 mostly White (55%) male (55%) patients (mean age 6.2 ± 6.5 years) were identified, of whom 426 (8.3%) had ICD at listing. At 6 months, 65% underwent heart transplantation, 15% died (4% died of SCD), and 20% were alive. In a multivariable model, United Network for Organ Sharing status 1B (hazard ratio [HR] 0.52; 95% confidence interval [CI] 0.29-0.95; P = .03), myocarditis (HR 0.19; 95% CI 0.05-0.77; P = .02), restrictive cardiomyopathy (HR 0.19; 95% CI 0.05-0.76; P = .02), and dilated cardiomyopathy (HR 0.32; 95% CI 0.20-0.52; P < .001) were associated with lower SCD risk, while younger age at listing (HR 0.94 per year; 95% CI 0.90-0.98; P = .003) was associated with higher SCD risk. ICD at listing was not associated with reduced SCD (P = .12), all-cause mortality, or delisting (P = .57). In pediatric patients listed for heart transplantation, the risk of SCD remains low and does not differ between patients with and without an ICD at listing.

Mutation and clinical relevance in a large cohort of unrelated Chinese patients with hypertrophic cardiomyopathy

To explore the genetic basis and phenotypic correlation with disease severity in a large cohort of Chinese patients with hypertrophic cardiomyopathy (HCM). A total of 179 unrelated Chinese HCM patients admitted to our department from 2002 to 2011 were enrolled in this study. Direct gene sequencing of β-myosin heavy chain (MYH7), myosin binding protein-C ( MYBPC3), and cardiac troponin T (TNNT2) were performed and clinical data were obtained in these patients. A total of 34 mutations were identified in 40 patients (22.3%), 79.4% (27/34) mutations occurred only once and a possible hot spot, A26 in MYH7, was found. Distribution of mutations was 52.9% (18/34) (MYBPC3), 35.3% (12/34) ( MYH7) and 11.8% (4/34) (TNNT2) respectively. Double mutations were identified in 2.2% (4/179) patients. Genotype-positive patients were associated with an earlier symptom onset, severer left ventricular hypertrophy, a higher incidence of syncope, and were more likely to have positive family history of HCM or sudden cardiac death (SCD) , and were more likely to progress into heart failure (24.2% vs. 5.0%, P = 0.002) and at a higher risk of SCD (9.1% vs. 0, P = 0.009) during the 6.5-year follow-up. No statistical difference in any clinical parameters and outcomes was found between patients carrying MYBPC3 and MYH7 mutations. Double mutations were associated with malignant clinical progression in this cohort. Different phenotype severity could be seen in HCM patients with same genotype (e. g. MYH7-1736T, TNNT2-R92W). MYBPC3 is the most predominant gene mutation in this HCM cohort. The presence of a sarcomere mutation in patients with HCM is associated with poor clinical outcome, although no specific genes or mutations can exactly predict the severity of clinical phenotypes.

Analysis of T-wave Alternans in ambulatory recordings using the ADTWA index.

Implantable cardioverter defibrillators (ICD) are the most effective way of preventing sudden cardiac death (SCD). However, the implantation of an ICD is an invasive procedure with associated risks and a high cost. Therefore, it is necessary to determine non-invasive risk markers that identify patients at a higher risk of suffering malignant arrhytmias. One of the most promising non-invasive indices is T-wave alternans (TWA). This work assesses T-wave alternans using the Amplitude of Dominant T-Wave Alternans (ADTWA), that is derived from the dominant T wave associated to a number of consecutive beats. Data from 650 patients with heart failure enrolled in the MUSIC study were analyzed. ADTWA have higher values increasing heart rate. ADTWA was also significantly higher in SCD patients than in survivors (survivors vs. SCD: 6.60±1.98 vs. 7.55±2.53, p=0.01). ADTWA seems a promising index to identify patients with heart failure at higher risk of SCD.

Consistency of heart rate–QTc prolongation consistency and sudden cardiac death: The Rotterdam Study

A prolonged heart rate-corrected QT (QTc) interval is a well-known risk indicator for sudden cardiac death (SCD) and a contraindication for drugs with potentially arrhythmogenic adverse effects. We aimed to study the consistency of QTc interval prolongation and whether a consistent QTc interval prolongation correlates differently with SCD than does an inconsistently prolonged QTc interval. We used a population-based cohort study of persons 55 years and older. We excluded participants using QTc-prolonging drugs or with bundle branch block. The QT interval was corrected for heart rate using Bazett and Fridericia formulas. Using a Cox regression model, we assessed the association between QTc interval prolongation consistency and the occurrence of SCD. A total of 3484 participants had electrocardiograms (ECGs) recorded on 2 consecutive visits. In 96%-98% of participants with a normal QTc interval on the first ECG, the QTc interval remained normal, but only in 27%-35% of those with a prolonged QTc interval, the QTc interval was prolonged on the second ECG after a median of 1.8 years. A consistently prolonged QTc interval was associated with an increased risk of SCD as compared with a consistently normal QTc interval (Bazett: hazard ratio 2.23; 95% confidence interval 1.17-4.24, Fridericia: hazard ratio 6.67; 95% confidence interval 2.96-15.06). A prolonged QTc interval preceded or followed by a normal QTc interval was not significantly associated with an increased risk of SCD. Persons with an inconsistently prolonged QTc interval did not have a higher risk of SCD than those with a consistently normal QTc interval. Persons with a consistently prolonged QTc interval did have a higher risk of SCD. Our results suggest that repeated measurements of the QTc interval could enhance risk stratification.

Clinical Dilemma: Recurrent Syncope With Isolated Left Ventricle Non-Compaction Cardiomyopathy and Preserved Ejection Fraction, a Case Report and Review of the Literature

Left ventricle non-compaction cardiomyopathy (LVNC) is an uncommon disorder characterized by the persistence of fetal myocardium of prominent trabecular meshwork, deep intertrabecular recesses, systolic dysfunction and left ventricular dilatation. It is thought to be caused by the arrest of normal endomyocardial morphogenesis. Here we present a case of a 27-year-old Caucasian female without past medical history who was presented to the emergency department because of syncope while she was working out. On further questioning, she relates that she has been having recurrent syncope for the last 9 years but she did not seek medical attention. Echocardiography and cardiac magnetic resonance imaging confirmed the diagnosis of LVNC and also showed a preserved ejection fraction. Implantable loop recorder showed recurrent non-sustained ventricular tachycardia. Although data were limited, an implantable cardioverter-defibrillator was prophylactically implanted because of the individual’s high sudden cardiac death risk. J Med Cases. 2015;6(2):77-80 doi: https://doi.org/10.14740/jmc2035w

The Entirely Subcutaneous Defibrillator – A New Generation and Future Expectations

Although conventional implantable cardioverter-defibrillators (ICDs) have proved effective in the prevention of sudden cardiac death (SCD), they still appear to be limited by non-trivial acute and long-term complications. The recent advent of an entirely subcutaneous ICD (S-ICD) represents a further step in the evolution of defibrillation technology towards a less-invasive approach. This review highlights some historical and current issues concerning the S-ICD that may offer a viable therapeutic option in selected patients at high risk of SCD and in whom pacing is not required. After the CE Mark and US Food and Drug Administration (FDA) approvals, the S-ICD is being implanted worldwide with growing clinical data regarding its safety and efficacy (the EFFORTLESS Registry). The recently developed new generation of S-ICD (EMBLEM, Boston Scientific) demonstrates favourable features including a smaller device, longer longevity and remote-monitoring compatibility. Further innovations in the S-ICD system and potential integration with leadless pacing may play an important role in defibrillation therapy and prevention of SCD in the near future.

SYNCOPE AS SUDDEN CARDIAC DEATH RISK FACTOR

The article analyses the link of syncope and sudden cardiac death risk with primary diagnosis. The data of dependency between syncope and risk of sudden cardiac death and mechanism of syncopal episodes is presented. The criteria of syncope with high sudden cardiac death risk are given. The article also provides an algorithm of syncopal episode diagnosis according to the ESC Guidelines (2009).

SUDDEN CARDIAC DEATH IN PATIENTS WITH DILATED CARDIOMYOPATHY

The review discusses accumulated to date scientific data on dilated cardiomyopathy: causative factors, clinical manifestations, sudden cardiac death in patients with the disease and its risk-stratification in the light of National guidelines on the definition of risk and prevention of sudden cardiac death (2012). A case of a patient with dilated cardiomyopathy and high-risk of sudden cardiac death is presented.

Exercise cardiac power and the risk of sudden cardiac death in a long-term prospective study

BackgroundLittle is known about exercise cardiac power and the risk of sudden cardiac death. The aim of this study was to examine the relationship of exercise cardiac power (ECP), defined as a ratio of directly measured maximal oxygen uptake with peak systolic blood pressure during exercise, with the risk for sudden cardiac death (SCD). MethodsThis prospective study was based on 2358 men who participated in exercise stress test at baseline. During an average follow-up of 20years 205 SCDs occurred. ResultsMen with ECP (<8.2mL/mmHg, lowest quartile) had a 4.6-fold (95% CI 2.8–7.5, p<0.001) increased risk of SCD as compared to with ECP in the highest quartile (>12.8mL/mmHg) after adjusting for age and examination years. Men with low ECP (<8.2mL/mmHg) had markedly increased risk of SCD (RR 3.9, 95% CI 2.19–7.14, p<0.001) after adjustment for conventional risk factors and left ventricular hypertrophy, whereas for progressive adjustment for resting systolic blood pressure, the respective risk among men with lowest ECP was 2.5 (95% CI 1.46–4.22, p<0.001). After adding ECP in the multivariate model, the Harrell C-index increased from 0.760 to 0.778 showing the significant incremental value of ECP in predicting SCD. The integrated discrimination improvement was 0.014 (p=0.004). ConclusionsLow ECP provides a non-invasive and easily available measure for the prediction of SCD and may help in identifying men with high risk for SCD.

Abstract 18946: A Complex Cardiac Rhythm and Conduction Abnormalities in Three Families Carrying a SCN5A Missense Mutation May Involve Single Nucleotide Polymorphisms in SCN5A and RYR2 genes

Background: Mutations in the gene encoding the cardiac sodium channel (SCN5A) have been implicated in arrhythmia syndromes including Brugada (BrS) and long-QT type 3 syndromes. Also, wide spectrums of mixed phenotypes, known as “overlap syndromes”, have been associated to SCN5A mutations. The contributions of single nucleotide polymorphisms (SNPs) add more complexity to the disease phenotype. Here we report a missense mutation in SCN5A (T1708N) in three Hispanic families with history of sudden cardiac death (SCD) and extensive variability and severity of symptoms, including syncope, atrial and ventricular tachycardia, and conduction abnormalities. Methods and Results: We used the Ion Torrent platform and AmpliSeq panel to sequence 19 genes associated with arrhythmia syndromes. In addition to SCN5A-T1708N mutation, the patients carry two common SNPs, SCN5A-H558R and the cardiac ryanodine receptor RYR2-Q2958R, which we previously reported to be highly prevalent (~30%) in Hispanics and to increase the risk of SCD in homozygous individuals. To study the functional properties of SCN5A-T1708N, the mutation was engineered by site-directed mutagenesis into SCN5A with or without the SCN5A-H558R and expressed in HEK cells for voltage clamp experiments. SCN5A-T1708N showed a significant increase of late INa compared to WT. Also, the kinetic properties of SCN5A-T1708N showed slower time constants of recovery and increase in slow inactivation, which would tend to reduce INa; these effects were not modified by the presence of SCN5A-H558R. On the other hand, INa density for SCN5A-T1708N was reduced compared to WT (289± 63 and 387± 62 pA/pF, respectively), yet, for the double mutant H558R-T1708N, INa was more severely depressed (145± 32 pA/pF). Conclusion: The profound biophysical phenotype of T1708N with loss and gain of function could account for the variability and the severity of the clinical phenotype in these families. The RYR2-Q2958R polymorphism may function as a pro-arrhythmic genetic modifier and it is conceivable that it may predispose to SCD in some members of these families. The study of these polymorphisms in large cohorts may identify common haplotypes associated to cardiac arrhythmias and facilitate identification of patients at high risk for SCD.

Abstract 18714: Role of 123 Iodine Metaiodobenzylguanidine Imaging in Prediction of Arrhythmic Events in Heart Failure Patients Candidate to ICD

Background: According to guidelines, implantable cardioverter defibrillator (ICD) is recommended in prevention of sudden cardiac death (SCD) in heart failure (HF) patients (pts). Guidelines have several limitations because ICD indication is based mainly on left ventricular ejection fraction (EF). Recent data showed that, independently from EF, 123-iodine metaiodobenzylguanidine imaging (123-I MIBG) could help to identify HF pts at high risk of SCD [heart/ mediastinum (H/M) ratio ≤1.6 and a summed score (SS) &gt; 26], who may benefit of ICD. Aim: Our aim is to assess, in a real world registry, the role of 123-I MIBG for the prediction of ventricular tachyarrhythmia (VT) causing appropriate ICD therapy in HF pts. Methods: We consecutively enrolled 97 patients admitted to our hospital with diagnosis of HF, left ventricular ejection fraction (LVEF) ≤35% and indication to ICD. All patients underwent MIBG imaging. The patients were classified into two groups: Group 1 with H/M≤1.6 , SS&gt; 26; Group2 with H/M&gt;1.6, SS &lt;26. All patients underwent 1 year follow-up. Results: 65 pts were included in group 1 and 32 pts in group 2. All baseline characteristics were similar in 2 groups apart from the etiology (table 1). In group 1, H/M ratio was 1.37±0.3 vs 1.8 ± 0.2 in group 2 (p=0.0002); SS was 37.5± 9.7 vs 16 ±6 in group 2 (p = 0.0001). At 1 year follow-up VTs causing appropriate ICD therapy in group 1 were 13.4% vs 1.28% in group 2(p=0.02); overall cardiac events were in group 1 16.4 % vs 1.92% in group 2 (p=0.02). Conclusion: Our results suggest that 123 I-MIBG can identify patients at increased risk for arrhythmic death and can be useful in the decision-making of ICD implantation independently from ejection fraction.

Abstract 14990: Sudden Death in Patients with Heart Failure and Preserved Ejection Fraction

Introduction: Severely reduced left ventricular ejection fraction (EF) is an established risk factor for sudden cardiac death (SCD), but has limited sensitivity and specificity. We evaluated the contribution of heart failure (HF) with preserved ejection fraction toward risk of SCD in the general population. Hypothesis: We hypothesized that HF would predict risk of SCD, even among patients with preserved EF. Methods: Subjects from an ongoing community-based study of SCD in the northwest US (pop. approx. one million) were included if age ≥18 (2002 - 2012) with clinical history and assessment of EF. Clinical history of heart failure (HF) was determined by physician report. Ejection fraction (EF) was determined from echocardiogram, angiogram, or multigated acquisition scan, and categorized as EF &lt;20%, 20-34%, 35-44%, 45-54%, and ≥55%. Laboratory values of brain natriuretic peptide (BNP) were obtained from routine clinical laboratory testing for a subset of patients. Results: Cases (n=628, mean age 69.9, 65% male) were more likely than controls (n = 580, mean age 66.8, 66% male) to have a history of clinically-recognized HF (58% vs. 24%, p&lt;0.0001) and to have an EF ≤ 35% (27% vs. 12%, p&lt;0.0001). At each EF level above 20%, HF was approximately twice as prevalent in cases compared to controls (Figure, p≤0.002). Median BNP levels were significantly higher for patients with HF vs. those without, across EF categories. Adjusting for age and sex, each category of decreasing EF was associated with an increased risk of SCD (OR 1.4, 95% CI 1.3 - 1.6, p&lt;0.0001), but the association was diminished by adjustment for HF, and for BNP. Odds of SCD were 4-fold higher (p&lt;0.0001) in the presence HF, adjusting for age and sex, across all categories of EF. Conclusions: In this population, the significant role of HF with preserved EF in SCD was confirmed by BNP level trends. Improvements in SCD prevention will require focused investigation of high risk SCD markers in patients with heart failure and preserved EF.

A prediction model for sudden cardiac death in patients with heart failure and preserved ejection fraction.

Sudden cardiac death (SCD) accounts for ∼ 25% of all deaths in heart failure with preserved ejection fraction (HFpEF). However, strategies to identify HFpEF patients at a higher risk of SCD have not been developed. We studied 4128 patients with HFpEF enrolled in the Irbesartan in Patients with Heart Failure and Preserved Ejection Fraction (I-PRESERVE) trial. All SCDs were adjudicated by a clinical endpoint committee. Cumulative incidences of SCD were estimated counting other deaths as competing risks. Cox regression analysis was used to generate a risk model for SCD. During a mean follow-up of 4.1 years, 231 (5.6%) patients died suddenly and 650 (15.7%) died non-suddenly. A multivariable model in 3480 patients including age, gender, history of diabetes and myocardial infarction, LBBB on ECG, and the natural logarithm of NT-proBNP identified a subgroup of 837 (24%) patients with ≥10% cumulative incidence of SCD over 5 years, accounting for other deaths as competing risk (Harrell's C index 0.75). The 5-year cumulative incidences of SCD in the higher and lower risk groups were 11% and 4%, respectively. In the higher risk group, 32% of deaths were SCD compared with 26% in the entire I-PRESERVE cohort. A multivariable prediction model identified patients with HFpEF who have a ≥10% risk of SCD over 5 years, similar to the risk of SCD in the Sudden Cardiac Death in Heart Failure (SCD-Heft) trial. This model may be useful for selecting patients with HFpEF for SCD prevention trials.

Abstract MP09: Deep Terminal Negativity of the P Wave in V1 is Associated with Sudden Cardiac Death in the Community: The Atherosclerosis Risk in Communities Study

Background: Deep terminal negativity of the P wave in V1 (P prime in V1, PPV1) defined as PPV1 ≤ -0.1mV in amplitude and ≥40 ms in duration (one small box on ECG grid) is sign of a left atrium enlargement, and a component in the Romhilt-Estes score of left ventricular hypertrophy (LVH). LVH is known to be associated with the risk of sudden cardiac death (SCD). Deep PPV1 negativity is also associated with atrial fibrillation (AF) and stroke; both have been linked to SCD as well. However, it is unknown whether or not PPV1 negativity is independently associated with SCD. Method: Baseline resting digital 12-lead ECGs of 13232 ARIC cohort participants (mean age 53.9±5.7 y; 5760 [43.5%] men; 9747 [73.7%] white) were analyzed. Individuals with prevalent baseline coronary heart disease (CHD), heart failure (HF), or QRS ≥ 120 ms were excluded. The ECGs were analyzed using a 12SL TM algorithm (GE Healthcare, Wauwatosa, WI, USA). Amplitude and duration of PPV1 was automatically measured. Results: Deep PPV1 negativity was observed in 97 (0.73%) participants. During a median follow-up of 14 years, 182 participants had SCD. In multivariable competing risks regression analysis, deep PPV1 negativity was significantly associated with SCD after adjustment for baseline risk factors of CHD and SCD (age, sex, race, diabetes, smoking, alcohol consumption, cholesterol, triglycerides, body mass index, serum creatinine, albumin, systolic blood pressure, use of antihypertensive, QT-prolonging medications, level of physical activity, mean heart rate, QTc, QRS duration, ECG-LVH by Cornell product), and incident HF, AF, stroke [subHR 3.8 (95%CI 1.88-7.69); P&lt;0.0001]. Deep PPV1 negativity showed 7% sensitivity and 99% specificity for SCD prediction. Conclusion: In apparently CV healthy, middle-aged individuals, deep terminal negativity of P-wave in V1 is associated with about 4-times higher risk of SCD during 14 years of follow-up. Further studies should explore the cardiac substrate underlying presence of this marker and its use for risk stratification.

The Brugada Syndrome - Diagnosis, Clinical Implications and Risk Stratification.

The Brugada syndrome (BrS) is a hereditary arrhythmic syndrome manifesting as syncope or sudden cardiac death (SCD) in individuals without overt structural heart disease. Currently, its diagnosis is mainly based on the presence of a spontaneous or Na+-channel blocker induced so-called "type 1" Brugada electrocardiographic (ECG) pattern typically seen in leads V1 and V2 recorded from the 4th to 2nd intercostal spaces. Presently the main unresolved clinical problem in the BrS is the identification of patients at high risk of SCD who need implantable cardioverter-defibrillator (ICD). Current guidelines recommend ICD implantation only in patients with spontaneous type 1 ECG pattern and either history of aborted cardiac arrest or documented sustained ventricular tachycardia (class I) or syncope of arrhythmic origin (class IIa) because they are at high risk of recurrent arrhythmias. However, the majority of BrS patients are asymptomatic when diagnosed and have generally low risk (0.5 % annually or lower) and therefore are not indicated for ICD. Most of SCD victims in the BrS have had no symptoms prior to the fatal event and therefore were not protected with an ICD. Currently there are no reliable methods to identify these potential victims of SCD. Although some ECG markers such as QRS fragmentation and infero-lateral early repolarisation have been demonstrated to signify increased arrhythmic risk their value still needs to be confirmed in large prospective studies. Novel risk assessment strategies need to be developed based on computerised quantitative ECG analysis of large digital ECG databases in patients with BrS and their relatives, and combined assessment of the most important factors of ventricular arrhythmogenesis.

Mechanisms of sudden cardiac death

Worldwide, sudden cardiac death (SCD) is a major problem. It is most frequently caused by ventricular tachyarrhythmias: Monomorphic and polymorphic ventricular tachycardia (VT), torsade de pointes (TdP), and ventricular fibrillation (VF). Beta blockade, ACE inhibition, coronary reperfusion and other treatments have reduced the incidence of VT butpulseless electrical activity (PEA) is increasingly seen, particularly in patients with advanced chronic heart disease. From existing data, bradyarrhythmia in the form of asystole(usually complete heart block without escape rhythm) causes only a minor proportion (10-15%) of SCD. In patients aged 50 years and more, coronary artery disease plays a dominant role causing more than 75% of SCD cases, either by acute ischemia and ventricular fibrillation or by chronic scar formation and reentrant VT. In younger patients, SCD may occur in patients with structurally normal hearts. A number of arrhythmogenic disorders with an increased risk of SCD have been detected and better understood recently, such as long and short QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and the early repolarization syndrome. Most importantly, ECG signs and clinical features indicating high risk for SCD have been identified. Knowledge of the exact electrophysiologic mechanisms of ventricular tachyarrhythmias at the cellular level has been improved and mechanisms such as phase 2 reentry and reflection proposed to better understand why and how SCD occurs.

Sudden cardiac death in patients with nonischemic cardiomyopathy

Sudden cardiac death (SCD) is an important cause of mortality worldwide. Although SCD is most often associated with coronary heart disease, the risk of SCD in patients without ischemic heart disease is well-established. Nonischemic cardiomyopathies, including idiopathic dilated cardiomyopathy, hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy represent three unique disease entities that have been shown to be highly associated with SCD and ventricular arrhythmias. A variety of risk stratification tools have been investigated, although the optimal strategy remains unknown. Identification of the arrhythmogenic substrate and treatment of ventricular arrhythmias in these subgroups can be challenging. Herein, we aim to discuss the current understanding of the anatomic and electrophysiologic substrate underlying ventricular arrhythmias and highlight features that may be associated with a higher risk of SCD in these 3 conditions.

Lack of difference in T wave variability between patients at risk of sudden cardiac death and healthy subjects

BackgroundT wave variability (Tvar) is a proposed method to predict sudden cardiac death (SCD). The purpose of this trial was to evaluate the reproducibility of Tvar measurements over time and demonstrate a difference in Tvar between patient populations at risk for ventricular arrhythmias and healthy subjects. MethodsSixty subjects were enrolled in into 3 groups: healthy subjects (Population I), patients at high risk of SCD (Population II), and patients with a recent ventricular tachyarrhythmia event (Population III). Recording and analysis of T wave amplitude variance (TAV) as a measure of Tvar was performed at baseline and 3months. ResultsTAV could not be interpreted in 12 of 43 patients in Populations II and III due to PVCs or noise. No subject had a TAV value suggestive of high risk of SCD as per a previously defined cutoff of >59μV. Median (range) values of TAV in μV at baseline for Populations I, II and III were 26 (15–39), 21 (13–43), and 24 (18–41), respectively (p=0.39). TAV was reproducible within population's from baseline to 3months (p=0.27, 0.53, 0.17 for Populations I, II and III, respectively). There was no significant difference between TAV values of high risk patients and healthy subjects. ConclusionTvar was reproducible primarily in patients with left ventricular dysfunction. However, the role of Tvar as a risk stratifying tool remains inconclusive.