Sudden death due to cardiac arrhythmias

CPR in medical schools: learning by teaching BLS to sudden cardiac death survivors--a promising strategy for medical students?

BACKGROUND

Cardiopulmonary resuscitation (CPR) training is gaining more importance for medical students. There were many attempts to improve the basic life support (BLS) skills in medical students, some being rather successful, some less. We developed a new problem based learning curriculum, where students had to teach CPR to cardiac arrest survivors in order to improve the knowledge about life support skills of trainers and trainees.

METHODS

Medical students who enrolled in our curriculum had to pass a 2 semester problem based learning session about the principles of cardiac arrest, CPR, BLS and defibrillation (CPR-D). Then the students taught cardiac arrest survivors who were randomly chosen out of a cardiac arrest database of our emergency department. Both, the student and the Sudden Cardiac Death (SCD) survivor were asked about their skills and knowledge via questionnaires immediately after the course. The questionnaires were then used to evaluate if this new teaching strategy is useful for learning CPR via a problem-based-learning course. The survey was grouped into three categories, namely "Use of AED", "CPR-D" and "Training". In addition, there was space for free answers where the participants could state their opinion in their own words, which provided some useful hints for upcoming programs.

RESULTS

This new learning-by-teaching strategy was highly accepted by all participants, the students and the SCD survivors. Most SCD survivors would use their skills in case one of their relatives goes into cardiac arrest (96%). Furthermore, 86% of the trainees were able to deal with failures and/or disturbances by themselves. On the trainer's side, 96% of the students felt to be well prepared for the course and were considered to be competent by 96% of their trainees.

CONCLUSION

We could prove that learning by teaching CPR is possible and is highly accepted by the students. By offering a compelling appreciation of what CPR can achieve in using survivors from SCD as trainees made them go deeper into the subject of resuscitation, what also might result in a longer lasting benefit than regular lecture courses in CPR.

Treatment of early heart failure: an ACEI or a beta-blocker first?

The basis of modern chronic heart failure (CHF) treatment is a combination of optimum doses of a beta-blocker and an angiotensin-converting enzyme inhibitor (ACEI); however, patients cannot be started on full doses of both drugs and treatment has to be initiated one way or the other. By tradition and according to guideline recommendations, an ACEI is usually initiated first, followed by a beta-blocker after a varying time period based on clinical judgement. Early beta-blockade has several theoretical advantages, and two surrogate end point studies have indicated that initiation of CHF treatment with a beta-blocker may be superior to an ACEI. The Cardiac Insufficiency Bisoprolol III trial was the first trial investigating the optimum sequence of initiating treatment of CHF in terms of mortality and morbidity. The results indicated that, in stable, mildly to moderately symptomatic patients with systolic CHF, initiation of therapy with the beta-blocker bisoprolol followed by the ACEI enalapril was similarly efficacious to the opposite sequence in terms of combined mortality and all-cause hospitalisation. However, initiating therapy with bisoprolol showed a trend towards better survival, but also towards further worsening of CHF. This review aims to put these recent findings into clinical perspective.

Lifetimes of epicardial rotors in panoramic optical maps of fibrillating swine ventricles

During ventricular fibrillation (VF), electrical activation waves are fragmented, and the heart cannot contract in synchrony. It has been proposed that VF waves emanate from stable periodic sources (often called "mother rotors"). The objective of the present study was to determine if stable rotors are consistently present on the epicardial surface of hearts comparable in size to human hearts. Using new optical mapping technology, we imaged VF from nearly the entire ventricular surface of six isolated swine hearts. Using newly developed pattern analysis algorithms, we identified and tracked VF wave fronts and phase singularities (PS; the pivot point of a reentrant wave front). We introduce the notion of a compound rotor in which the rotor's central PS can change and describe an algorithm for automatically identifying such patterns. This prevents rotor lifetimes from being inappropriately abbreviated by wave front fragmentation and collision events near the PS. We found that stable epicardial rotors were not consistently present during VF: only 1 of 17 VF episodes contained a compound rotor that lasted for the entire mapped interval of 4 s. However, shorter-lived rotors were common; 12.2 (SD 3.3) compound rotors with lifetime >200 ms were visible on the epicardium at any given instant. We conclude that epicardial mother rotors do not drive VF in this experimental model; if mother rotors do exist, they are intramural or septal. This paucity of persistent rotors suggests that individual rotors will eventually terminate by themselves and therefore that the continual formation of new rotors is critical for VF maintenance.

Implantable Cardioverter- Defibrillator Therapy in Clinical Practice

Pharmacologic treatment of heart failure has led to dramatic improvements in survival and quality of life. Nonetheless, heart failure often progresses despite treatment with diuretics, angiotensin-converting enzyme inhibitors, beta-adrenergic blockers, aldosterone antagonists, and digoxin. Further, despite a steady decline in the risk of death from pump failure, many patients remain at high risk for sudden cardiac death. The annual incidence of sudden cardiac death in the U.S. alone has been estimated at 184,000 to over 400,000 cases. During the past decade, substantial advances have been made in the use of device-based therapy for this population. The role of the implantable cardioverter-defibrillator (ICD) continues to evolve in routine heart failure management. The current status of ICD therapy in the treatment of heart failure patients based on randomized clinical trial results and published practice guidelines is summarized in this review.

Increased Intra-QRS Fragmentation in Magnetocardiography as a Predictor of Arrhythmic Events and Mortality in Patients with Cardiac Dysfunction After Myocardial Infarction

INTRODUCTION

Increased intra-QRS fragmentation score (FRA) in magnetocardiography (MCG) has shown association with sustained ventricular arrhythmias in post-MI patients suggesting its relation to arrhythmia substrate. The aim of this study was to investigate whether increased FRA in MCG predicts arrhythmic events and mortality after acute myocardial infarction (MI) with cardiac dysfunction.

METHODS AND RESULTS

A series of 158 patients with acute MI and left ventricular ejection fraction (LVEF) <50% were studied. Their age was 60 +/- 10 years and LVEF 40 +/- 6%. MCG was registered and FRA was computed. For comparison, QRS duration in 12-lead ECG was measured. In a mean follow-up of 50 +/- 15 months, 32 (20%) patients died and 18 (11%) had an arrhythmic event. Both arrhythmic event rate and all-cause mortality were significantly higher in patients with increased FRA (P < 0.001 for both). In contrast, increased QRS duration in ECG predicted all-cause mortality (P < 0.05) but not arrhythmic events. In multivariate analysis, FRA was an independent predictor of both arrhythmic events and all-cause mortality. Using a combined criterion of increased FRA and LVEF < 30% yielded positive and negative predictive accuracies of 50% and 91% for arrhythmic events.

CONCLUSION

In post-MI patients with left ventricular dysfunction, increased intra-QRS fragmentation in high-resolution magnetocardiography predicts arrhythmic events, whereas QRS duration in 12-lead ECG predicts all-cause mortality. Analysis of intra-QRS fragmentation by MCG may assist in guiding therapy of post-MI patients, for example, by selecting those who would benefit most from prophylactic implantable cardioverter-defibrillator therapy.

Implications of CIBIS III: a commentary

Combined therapy with optimum doses of a beta-blocker and an angiotensin-converting enzyme inhibitor (ACE-I) is the mainstay for the treatment of chronic heart failure (CHF). However, patients cannot be started on full doses of both drugs and treatment has to be initiated one way or the other. The Cardiac Insufficiency Bisoprolol Study (CIBIS) III was the first trial investigating the optimum sequence of initiating treatment of CHF, in terms of mortality and morbidity. CIBIS III compared randomised, open-label initial monotherapy with bisoprolol or enalapril for six months, followed by their combination for six to 24 months, in 1,010 patients at least 65 years of age, with stable, mildly or moderately symptomatic, systolic CHF. The two strategies were similarly efficacious in terms of the combined primary endpoint of mortality or all-cause hospitalisation, and showed similar safety. The bisoprolol-first approach showed a 28% lower mortality at the end of the monotherapy phase (p=0.24) and a 31% lower mortality at the end of the first year (p=0.06), but a 25% increase in worsening of CHF events (p=0.23). The main conclusion is that, CHF therapy may be started with bisoprolol or enalapril in patients like those in CIBIS III. However, it may be argued that the primary therapeutic goal in the early phase of CHF should be improved survival, whereas the long-term aim, achievable during combined therapy with optimum doses of several drugs, should be improved quality of life, physical function, morbidity and survival. In such case, the CIBIS III findings would tend to support starting CHF therapy with bisoprolol rather than enalapril in stable patients with mild or moderate symptoms.

Preserved heart rate variability identifies low-risk patients with nonischemic dilated cardiomyopathy: Results from the DEFINITE trial

BACKGROUND

The recent expansion of indications for prophylactic implantable cardioverter-defibrillator (ICD) placement in subjects with nonischemic dilated cardiomyopathy has raised concerns about the cost-effectiveness of this therapy.

OBJECTIVES

The purpose of this study was to identify low-risk patients with nonischemic dilated cardiomyopathy who may not require prophylactic ICD placement.

METHODS

This was a prospective study of 274 participants in the Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) trial, a randomized controlled trial that evaluated the role of prophylactic ICD placement in patients with nonischemic dilated cardiomyopathy. The patients underwent 24-hour Holter recording for analysis of heart rate variability (HRV). The primary HRV variable was the standard deviation of normal R-R intervals (SDNN). Patients with atrial fibrillation and frequent ventricular ectopy (>25% of beats) were excluded from HRV analysis (23% of patients). SDNN was categorized in tertiles, and Kaplan-Meier analysis was performed to compare survival in the three tertiles and excluded patients.

RESULTS

The study population was 73% male, with a mean age of 59 +/- 12 years and mean left ventricular ejection fraction of 21% +/- 6%. After 3-year follow-up, significant differences in mortality rates were observed: SDNN >113 ms: 0 (0%), SDNN 81-113 ms: 5 (7%), SDNN <81 ms: 7 (10%), excluded patients: 11 (17%) (P = .03). There were no deaths in the tertile with SDNN >113 ms regardless of treatment assignment (ICD vs control).

CONCLUSION

Patients with nonischemic dilated cardiomyopathy and preserved HRV have an excellent prognosis and may not benefit from prophylactic ICD placement. Patients with severely depressed HRV and patients who are excluded from HRV analysis because of atrial fibrillation and frequent ventricular ectopy have the highest mortality.

Sudden death is associated with a widened paced QRS complex in noncoronary cardiac disease

INTRODUCTION

Recent experimental and clinical trials have provided evidence that increased duration of right ventricular electrogram in response to premature extrastimuli correlates with the risk of ventricular fibrillation in noncoronary heart disease. The aim of the present study was to investigate the duration of the surface QRS complex at short coupling intervals of extrastimuli as a new indicator for major arrhythmic events.

METHODS

32 patients all with nonischemic heart diseases and well preserved left ventricular function in sinusrhythm were included into the study. Fifteen had witnessed sudden death due to ventricular fibrillation or polymorphic ventricular tachycardia (VF/VT group). The control group comprised seventeen patients without a history of ventricular arrhythmias (control group). All subjects underwent programmed ventricular stimulation and QRS-durations S1-S2-S3 directly above the ventricular refractory period were analyzed.

RESULTS

Both groups had a comparable basic QRS complex of 85 +/- 9 (VF/VT) vs. 87 +/- 13 ms (control), p = 0.83. The stimulated QRS complex S3 was significantly wider in the VF/VT group compared to the control group at pacing rates of 500 and 430 ms (500 ms: 256 +/- 22 vs. 235 +/- 32 ms, p = 0.04; 430 ms: 258 +/- 23 vs. 226 +/- 27 ms, p = 0.001). No differences with regard to the ventricular effective refractory period and the ventriculoatrial conduction could be observed beween the groups.

CONCLUSIONS

Our results indicate that the duration of the paced QRS complex may be a valuable parameter to predict arrhythmic risk in patients with nonischemic heart disease. Further prospective studies in larger trials are necessary to corroborate this investigation.

Allelic variants of SCN5A and risk of sudden cardiac arrest in patients with coronary artery disease

BACKGROUND

Most sudden cardiac arrests occur in patients who have associated significant coronary artery disease (CAD), but current methods of risk stratification are inadequate.

OBJECTIVES

The purpose of this study was to evaluate whether allelic variation of SCN5A could determine risk of sudden cardiac arrest among patients with CAD.

METHODS

This case-control study was conducted as part of the ongoing Oregon Sudden Unexpected Death Study (Ore-SUDS). Cases of sudden cardiac arrest with associated CAD were identified among residents of Multnomah County, Oregon (population 660,486). Geographically matched control subjects had significant CAD but no history of cardiac arrest, ventricular arrhythmia, or syncope. DNA was extracted from blood samples, and all 28 exons of SCN5A were screened for allelic variants using denaturing high-performance liquid chromatography. All identified variants were confirmed by direct sequencing.

RESULTS

Sixty-seven cases (mean age 65 +/- 13 years, 18% female) and 91 controls (mean age 66 +/- 12 years, 30% female) were compared. Race was known in 94% of all patients; 92% of case subjects and 89% of control subjects were Caucasian. No patient had clinically manifest familial long QT syndrome. Nonsynonymous nucleotide changes were found in 4% of cases and 1% of controls (P = .31), with one novel mutation (G1291A) identified in one case subject. Synonymous nucleotide changes were found in 27% of cases and 21% of controls (P = .45).

CONCLUSION

The overall prevalence of amino acid-altering polymorphisms of the SCN5A gene was relatively low in both groups. Allelic variants of SCN5A did not contribute to risk of sudden cardiac arrest in this primarily Caucasian population with significant CAD.

Population-based analysis of sudden cardiac death with and without left ventricular systolic dysfunction: two-year findings from the Oregon Sudden Unexpected Death Study

OBJECTIVES

We sought to evaluate the contribution of left ventricular (LV) dysfunction toward occurrence of sudden cardiac death (SCD) in the general population, and to identify distinguishing characteristics of SCD in the absence of LV dysfunction.

BACKGROUND

Patients who manifest warning symptoms and signs are more likely to undergo evaluation before SCD. Although prevalence of LV dysfunction in this subgroup may overestimate the prevalence in overall SCD, this is the only means of assessment in the general population.

METHODS

All cases of SCD in Multnomah County, Oregon (population 660,486; 2002 to 2004) were prospectively ascertained in the ongoing Oregon Sudden Unexpected Death Study. We retrospectively assessed LV ejection fraction (LVEF) among subjects who underwent evaluation of LV function before SCD (normal: > or =55%; mildly to moderately reduced: 36% to 54%; and severely reduced: < or =35%). Of a total of 714 SCD cases (annual incidence 54 per 100,000), LV function was assessed in 121 (17%).

RESULTS

The LVEF was severely reduced in 36 patients (30%), mildly to moderately reduced in 27 (22%), and normal in 58 (48%). Patients with normal LVEF were distinguishable by younger age (66 +/- 15 years vs. 74 +/- 10 years; p = 0.001), higher proportion of females (47% vs. 27%; p = 0.025), higher prevalence of seizure disorder (14% vs. 0%; p = 0.002), and lower prevalence of established coronary artery disease (50% vs. 81%; p < 0.001).

CONCLUSIONS

In this community-wide study, only one-third of the evaluated SCD cases had severe LV dysfunction meeting current criteria for prophylactic cardioverter-defibrillator implantation. The SCD cases with normal LV function had several distinguishing clinical characteristics. These findings support the aggressive development of alternative screening methods to enhance identification of patients at risk.

Frequency of sudden cardiac death among acute myocardial infarction survivors with optimized medical and revascularization therapy

The epidemiologic pattern of sudden cardiac death (SCD) may have changed in the modern treatment era of patients after an acute myocardial infarction (AMI). We evaluated the effect of optimized medical and revascularization therapy on the incidence of SCD after an AMI. A total of 2,130 consecutive patients (mean age 59 +/- 10 years) with an AMI from 2 European centers (Germany and Finland) was included in the study. In this population, 1,004 patients (47%) were treated with an optimized medical and revascularization strategy (defined as treatment with revascularization, beta blockers, aspirin, statins, and angiotensin-converting enzyme inhibitors). Nonoptimized treatment, defined as a lack of any optimized treatment, was received by 1,126 patients (53%). During the mean follow-up of 2.9 +/- 1.3 years, the incidence of SCD was very low among patients who received optimized treatment (1.2%, annual incidence 0.4%) compared with those who did not (3.6%, annual incidence 1.4%, p <0.01). The treatment strategy that had the greatest effect on differences in the SCD rate was revascularization therapy, with the hazard ratio of SCD being 2.1 (95% confidence interval 1.2 to 3.7, p <0.01) for SCD among nonrevascularized patients. Nonoptimized treatment was more often received by older patients, women, diabetic patients, and those with depressed left ventricular function. In conclusion, the incidence of SCD is low in the modern treatment era of patients after an AMI. Coronary revascularization seems to have a great effect on altered the epidemiologic pattern of SCD.

Asthma deaths and the athlete

Asthma has recently become more prevalent, more severe, and more deadly. Approximately 4500 individuals die from asthma annually in the United States, an unacceptable number for a condition that can be managed effectively. Sudden death with exercise may result from a variety of causes, including previously unrecognized cardiac conditions. Asthma has also been recognized as a cause of death in association with sports. Recent data indicate those who suffer from mild to moderate asthma are also at risk for asthma fatality. The absolute magnitude of the increase in risk of death from asthma during sports, however, is very small. For this reason, individuals with asthma should not be discouraged from active participation in sports. Rather, this should reinforce the message that asthma is a condition that may be potentially serious, but can, and should be, well controlled with proper management.

The impact of age, body mass index, and fish intake on the EPA and DHA content of human erythrocytes

n-3 FA are beneficial for cardiovascular health, reducing platelet aggregation, TG levels, and the risk of sudden death from myocardial infarction. The percentage of EPA + DHA in red blood cells (RBC), also known as the Omega-3 Index, has recently been proposed as a risk marker for death from coronary heart disease (CHD). The purpose of this study was to begin to explore the factors that can influence RBC EPA + DHA. We collected information on the number of servings of tuna or nonfried fish consumed per month, as well as on age, gender, ethnicity, smoking status, the presence of diabetes, and body mass index (BMI) in 163 adults in Kansas City who were not taking fish oil supplements. The average RBC EPA + DHA in this population was 4.9 +/- 2.1%. On a multivariate analysis, four factors significantly and independently influenced the Omega-3 Index: fish servings, age, BMI, and diabetes. The Index increased by 0.24 units with each additional monthly serving of tuna or nonfried fish (P < 0.0001), and by 0.5 units for each additional decade in age (P < 0.0001). The Index was 1.13% units lower in subjects with diabetes (P = 0.015) and decreased by 0.3% units with each 3-unit increase in BMI (P = 0.001). Gender or smoking status had no effect, and the univariate relationship with ethnicity vanished after controlling for fish intake. Given the importance of n-3 FA in influencing risk for death from CHD, further studies are warranted to delineate the nondietary factors that influence RBC EPA + DHA content.

Dyslipidemia is Associated with Ventricular Tachyarrhythmia in Patients with Acute ST-Segment Elevation Myocardial Infarction

BACKGROUND

Ventricular tachyarrhythmia developing in the acute stage of myocardial infarction (MI) is an important cause of sudden cardiac death. The aim of this study was to determine whether dyslipidemia is associated with the occurrence of ventricular tachycardia/fibrillation (VT/VF) during the acute stage of ST-segment elevation MI (STEMI).

METHODS

A total of 58 patients experiencing VT/VF within 24 hours after the onset of MI were selected as the study group. A group of 58 patients with MI but without VT/VF was selected as the control group matched for sex (overall, 104 males), age (overall, 58 +/- 10 years), and the use of thrombolytic therapy (n = 82). The lipid profiles including total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglyceride were measured during the first week and at the third month after the index MI. Other coronary risk factors, and clinical, hemodynamic and angiographic characteristics were also included in the assessment.

RESULTS

During the acute stage, patients with VT/VF had higher levels of LDL-C and lower blood pressure on initial arrival at our hospital. At the 3-month follow-up, those patients with VT/VF showed higher levels of TC, LDL-C and triglyceride. Multivariate analysis revealed that LDL-C (p < 0.001) at the 3-month follow-up, mean blood pressure on arrival (p < 0.01), and the difference in triglyceride levels between the first week and the third month (p < 0.05) were independent predictors for the occurrence of VT/VF in the acute stage of MI.

CONCLUSION

This study suggests that dyslipidemia imposes a higher risk of developing tachyarrhythmia in the acute phase of STEMI.

High-precision guidance of ablation catheters to arrhythmic sites using electrocardiographic signals

Hemodynamically unstable ventricular arrhythmias are frequently untreatable with radio-frequency ablation due to the difficulty of rapidly and accurately localizing the site of origin of an arrhythmia with current technologies. We demonstrate a new catheter guidance method that will direct the tip of an ablation catheter to the site of origin of an arrhythmia and reduce the time needed to locate the site such that a patient need only be maintained in the arrhythmia for a few beats. The algorithm, based on a single-equivalent moving dipole (SEMD) model, is used to identify the bioelectric dipole corresponding to a site of origin of an arrhythmia. If a current dipole is produced at the ablation catheter tip, the tip position may also be calculated using this algorithm, and the catheter can be guided towards the site of origin of the arrhythmia. We present a method to compensate for the effect of systematic non-idealities, such as boundary effects, on the accuracy of this algorithm. In simulations, this method is able to guide the catheter tip to within 1.5 mm of the arrhythmic site at any location within the model torso with almost 100% success and with a realistic number of movements of the ablation catheter. These results suggest that this method has great potential to direct radio-frequency ablation procedures, especially in the significant patient population that is currently untreatable.

A multi-country health economic evaluation of highly concentrated N-3 polyunsaturated fatty acids in secondary prevention after myocardial infarction

BACKGROUND

Patients who survive an acute myocardial infarction (MI) are at an increased risk of subsequent major cardiovascular events and (often sudden) cardiac death. The use of highly concentrated and purified omega-3 polyunsaturated fatty acids (n-3 PUFAs), in addition to standard secondary prevention after MI, results in a significant reduction in the risk of sudden death versus no n-3 PUFAs. This study assessed the cost effectiveness of adding n-3 PUFAs to the current secondary prevention treatment versus standard prevention alone after acute MI in five countries: Australia, Belgium, Canada, Germany and Poland.

METHODS

Based on the clinical outcomes of GISSI-P (Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico - Prevenzione) [MI, stroke, revascularisation rate and mortality], a decision model was built in DataProtrade mark. The implications of adding n-3 PUFAs to standard treatment in patients aged 59 years with a recent history of MI were analysed from the healthcare payer's perspective. The time horizon was 3.5 years (identical to GISSI-Prevenzione) but the effects on life expectancy through avoidance of cardiac events were calculated lifelong. Event costs were based on literature data. Life expectancy data for survivors of cardiac disease were taken from the Saskatchewan database and then adjusted by country. Results are expressed as extra cost (Euro) per life-year gained (LYG). Annual discounting of 5% was applied to health effects and costs.

RESULTS

Treatment with highly concentrated n-3 PUFAs yielded between 0.261 (Poland) and 0.284 (Australia) LYG, at an additional cost of 787 Euros(Canada) to 1,439 Euros(Belgium). The ICER varied between 2,788 Euros(Canada) and 5,097 Euros(Belgium) per LYG. Sensitivity analyses on effectiveness, cost of complications and discounting proved the robustness of the results. A second-order Monte Carlo simulation based on the 95% confidence intervals obtained from GISSI-P suggests that highly concentrated n-3 PUFAs are cost effective in 93% of simulations in Poland and in >98% of simulations in the other countries, assuming the country-specific societal willingness-to-pay threshold. Total costs were considerably increased by including healthcare costs incurred during the remaining life-years, but this had no impact on the ICER-based treatment recommendation.

CONCLUSIONS

Adding highly concentrated n-3 PUFAs to standard treatment in the secondary prevention of MI appears to be cost effective versus standard treatment alone in the five countries studied.

Microvolt T-wave alternans and the risk of death or sustained ventricular arrhythmias in patients with left ventricular dysfunction

OBJECTIVES

This study hypothesized that microvolt T-wave alternans (MTWA) improves selection of patients for implantable cardioverter-defibrillator (ICD) prophylaxis, especially by identifying patients who are not likely to benefit.

BACKGROUND

Many patients with left ventricular dysfunction are now eligible for prophylactic ICDs, but most eligible patients do not benefit; MTWA testing has been proposed to improve patient selection.

METHODS

Our study was conducted at 11 clinical centers in the U.S. Patients were eligible if they had a left ventricular ejection fraction (LVEF) < or =0.40 and lacked a history of sustained ventricular arrhythmias; patients were excluded for atrial fibrillation, unstable coronary artery disease, or New York Heart Association functional class IV heart failure. Participants underwent an MTWA test and then were followed for about two years. The primary outcome was all-cause mortality or non-fatal sustained ventricular arrhythmias.

RESULTS

Ischemic heart disease was present in 49%, mean LVEF was 0.25, and 66% had an abnormal MTWA test. During 20 +/- 6 months of follow-up, 51 end points (40 deaths and 11 non-fatal sustained ventricular arrhythmias) occurred. Comparing patients with normal and abnormal MTWA tests, the hazard ratio for the primary end point was 6.5 at two years (95% confidence interval 2.4 to 18.1, p < 0.001). Survival of patients with normal MTWA tests was 97.5% at two years. The strong association between MTWA and the primary end point was similar in all subgroups tested.

CONCLUSIONS

Among patients with heart disease and LVEF < or =0.40, MTWA can identify not only a high-risk group, but also a low-risk group unlikely to benefit from ICD prophylaxis.

Mechanisms of sudden cardiac death

Despite recent advances in preventing sudden cardiac death (SCD) due to cardiac arrhythmia, its incidence in the population at large has remained unacceptably high. Better understanding of the interaction among various functional, structural, and genetic factors underlying the susceptibility to, and initiation of, fatal arrhythmias is a major goal and will provide new tools for the prediction, prevention, and therapy of SCD. Here, we review the role of aberrant intracellular Ca handling, ionic imbalances associated with acute myocardial ischemia, neurohumoral changes, and genetic predisposition in the pathogenesis of SCD due to cardiac arrhythmia. Therapeutic measures to prevent SCD are also discussed.

Adding clopidogrel to aspirin improves outcome in ST-elevation myocardial infarction patients receiving fibrinolytic therapy

Acute coronary syndromes result from the rupture of an atherosclerotic plaque with superimposed thrombosis. In an ST-elevation myocardial infarction, the thrombus occludes the coronary vessel, leading to an abrupt decrease in myocardial perfusion. The focus of initial management is the timely restoration of flow in the infarct-related artery via fibrinolytic therapy or percutaneous coronary intervention. Adjunctive therapy aimed at inhibition of platelets and the coagulation cascade is critical to establish and maintain vessel patency. Clopidogrel, an oral antiplatelet agent, has recently been shown to offer significant clinical benefit in STEMI (ST-elevation myocardial infarction) and is a welcome addition to standard fibrinolytic therapy.

Drug-induced q-T prolongation

Drug therapy may induce Q-T prolongation by alteration of potassium ion currents in cardiac cells, resulting in abnormal repolarization. Q-T prolongation, whether congenital or acquired, has been associated with the development of the malignant dysrhythmia Torsade de Pointes (TdP), which may result in sudden death. Re-cent regulatory actions and drug withdrawals due to Q-T prolongation or TdP have focused attention on this issue. Although our understanding of the pathophysiology continues to evolve, both patient and medication factors contribute to the individual risk of drug-induced Q-T prolongation or TdP. The clinician should be aware of these issues when prescribing new drugs and should weigh the risks and benefits carefully when prescribing drugs known to prolong the Q-T interval.

Epidemiology and stratification of risk for sudden cardiac death

Sudden cardiac death (SCD) is a major cause of mortality in the United States. Approximately 65% of cases of SCD occur in patients with underlying acute or chronic ischemic heart disease. The incidence of SCD increases 2- to 4-fold in the presence of coronary disease and 6- to 10-fold in the presence of structural heart disease. Ventricular fibrillation (VF) precipitated by ventricular tachycardia (VT) is a common mechanism of cardiac arrest leading to SCD. Triggers for SCD include electrolyte disturbances, heart failure, and transient ischemia. Although a large percentage of patients with out-of-hospital SCD do not survive, successful resuscitation to hospitalization has improved in recent years. One of the challenges for preventing SCD lies in identifying individuals at highest risk for SCD within a lower-risk population. The progression from conventional risk factors of coronary artery disease to arrhythmogenesis and SCD can be represented as a cascade of changes associated with levels of increasing risk. At the first level is atherogenesis, followed by changes in atherosclerotic plaque anatomy, which may be mediated by inflammatory processes. Disruption of active plaque formed during a transitional state initiates the thrombotic cascade and acute occlusion, after which acute changes in myocardial electrophysiology become the immediate trigger for arrhythmogenesis and SCD. Each level of the cascade offers different opportunities for risk prediction. Among the classes of risk predictors are clinical markers, such as ECG measures and ejection fraction. Transient risk markers, such as inflammatory markers, are potentially useful for identifying triggers for SCD. In the future, genetic profiling is expected to allow better assessment of individual risks for SCD.

Effect on survival and hospitalization of initiating treatment for chronic heart failure with bisoprolol followed by enalapril, as compared with the opposite sequence: results of the randomized Cardiac Insufficiency Bisoprolol Study (CIBIS) III

BACKGROUND

In patients with chronic heart failure (CHF), a beta-blocker is generally added to a regimen containing an angiotensin-converting-enzyme (ACE) inhibitor. It is unknown whether beta-blockade as initial therapy may be as useful.

METHODS AND RESULTS

We randomized 1010 patients with mild to moderate CHF and left ventricular ejection fraction < or =35%, who were not receiving ACE inhibitor, beta-blocker, or angiotensin receptor blocker therapy, to open-label monotherapy with either bisoprolol (target dose 10 mg QD; n=505) or enalapril (target dose 10 mg BID; n=505) for 6 months, followed by their combination for 6 to 24 months. The 2 strategies were blindly compared with regard to the combined primary end point of all-cause mortality or hospitalization and with regard to each of these end point components individually. Bisoprolol-first treatment was noninferior to enalapril-first treatment if the upper limit of the 95% confidence interval (CI) for the absolute between-group difference was <5%, corresponding to a hazard ratio (HR) of 1.17. In the intention-to-treat sample, the primary end point occurred in 178 patients allocated to bisoprolol-first treatment versus 186 allocated to enalapril-first treatment (absolute difference -1.6%, 95% CI -7.6 to 4.4%, HR 0.94; 95% CI 0.77 to 1.16). In the per-protocol sample, 163 patients allocated to bisoprolol-first treatment had a primary end point, versus 165 allocated to enalapril-first treatment (absolute difference -0.7%, 95% CI -6.6 to 5.1%, HR 0.97; 95% CI 0.78 to 1.21). With bisoprolol-first treatment, 65 patients died, versus 73 with enalapril-first treatment (HR 0.88; 95% CI 0.63 to 1.22), and 151 versus 157 patients were hospitalized (HR 0.95; 95% CI 0.76 to 1.19).

CONCLUSIONS

Although noninferiority of bisoprolol-first versus enalapril-first treatment was not proven in the per-protocol analysis, our results indicate that it may be as safe and efficacious to initiate treatment for CHF with bisoprolol as with enalapril.

Effects of acetyl-L-carnitine on cardiac dysautonomia in Rett syndrome: prevention of sudden death?

There is a higher incidence of sudden death in patients with Rett syndrome than individuals in the general population. Previous studies have implicated cardiac dysautonomia and a long QT interval as causative factors. Because carnitine plays a critical role in cellular metabolism and may have beneficial effects on cardiac and nerve function, we investigated the effects of long-term treatment with acetyl-L-carnitine on heart rate variability and electrocardiographic abnormalities in 10 girls with Rett syndrome and compared the results with 12 control patients (girls with Rett syndrome who were not treated). The age range of the subjects was 2-21 years. The study design called for the evaluation of heart rate variability, corrected QT interval, and QTc dispersion. In the 10 Rett girls treated with acetyl-L-carnitine, a significant increase in heart rate variability was observed. To explain these results, we hypothesize that acetyl-L-carnitine has a neurotrophic action on the cardiac autonomic nervous system. This effect may reduce the risk of sudden death in patients with this syndrome.

Late potentials and ventricular arrhythmias in acromegaly

BACKGROUND

Sudden death and increased prevalence of ventricular arrhythmias have already been described in acromegaly. Although late potentials (LPs) have been proved to be a new technique in detecting patients at risk for ventricular tachyarrhythmias its use in acromegaly is still unknown.

METHODS

We studied 70 acromegalic patients [32 males, 38 females; age 49+/-12 years (mean+/-S.D.)] and 70 control subjects age- and sex-matched [(35 males and 35 females; 46+/-12 years (mean+/-S.D.)]. Besides hormonal tests, we performed the following cardiovascular investigations: ECG, 24-h ECG Holter monitoring, echocardiography, and signal-averaged ECG (SAECG) time-domain analysis.

RESULTS

LPs occurrence was significantly higher in acromegalic patients as compared to the control group (22.9% vs. 2.9%; p=0.001). A greater duration of disease in patients with positive LPs compared to negative ones was pointed out (18 vs. 12 years; p=0.024). In the group of acromegalic patients with positive LPs we observed a significant association with premature ventricular complexes (PVCs) detected by means of 24-h Holter ECG recording (13 out of 15 patients: 86.7%; p=0.024). The positivity or negativity of LPs proved to be significantly associated with Lown scale PVC trends recorded by 24-h Holter ECG (p=0.014). In the group of patients with left ventricular hypertrophy a significant and pathological worsening of SAECG signals (QRS, LAS, RMS) was documented.

CONCLUSIONS

We observed a higher prevalence of LPs in acromegaly which significantly correlated with Lown scale of PVCs.

Acute exercise increases the ventricular arrhythmia threshold via the intrinsic adenosine receptor system in conscious hypertensive rats

Coronary artery occlusion-induced tachyarrhythmias that culminate in ventricular fibrillation are the leading cause of death in developed countries. The intrinsic adenosine receptor system protects the heart from an ischemic insult. Thus the increased functional demands made on the heart during exercise may produce protective adaptations mediated by endogenous adenosine. Therefore, we tested the hypothesis that a single bout of dynamic exercise increases the ventricular arrhythmia threshold (VAT) induced by coronary artery occlusion in conscious hypertensive rats via the intrinsic adenosine receptor system. To test this hypothesis, we recorded the VAT before and on an alternate day after a single bout of dynamic treadmill exercise (12 m/min, 10% grade for 40 min). A single bout of dynamic exercise significantly reduced postexercise arterial pressure (Δ−24 ± 4 mmHg) and increased VAT (Δ+1.95 ± 0.31 min). Adenosine receptor blockade with the nonselective adenosine receptor antagonists theophylline or aminophylline (10 mg/kg) attenuated the cardioprotective effects of a single bout of dynamic exercise. Results suggest that strategies that increase myocardial ATP requirements leading to adenosine production provide protection against coronary artery occlusion.

Mechanism of sudden cardiac death in pigs with viable chronically dysfunctional myocardium and ischemic cardiomyopathy

Pigs with viable chronically dysfunctional myocardium and ischemic cardiomyopathy are at high risk of sudden cardiac death (SCD). We sought to identify the arrhythmic mechanism of SCD, the relation to changes in left ventricular (LV) function, and inducibility of malignant arrhythmias before SCD. Juvenile pigs (n = 72) were instrumented with chronic stenoses on proximal left anterior descending and circumflex arteries. Survival was only 29% 3 mo after instrumentation, and all deaths were sudden and without prodromal symptoms of heart failure. Triphenyltetrazolium chloride staining demonstrated necrosis in only nine animals averaging 2.3 +/- 0.9% of the LV, with no difference between SCD animals and survivors. Implantable loop recorders (n = 13) documented both ventricular fibrillation (n = 6) and bradyasystole (n = 2) as the arrhythmic mechanism of death. Although regional and global function were depressed [anteroseptal wall thickening 1.8 +/- 0.2 vs. 4.2 +/- 0.2 mm in Sham animals (P < 0.001); fractional shortening 21 +/- 2 vs. 31 +/- 1% in Sham animals (P < 0.01)], there were no differences between SCD animals and survivors. LV mass increased in animals with ischemic cardiomyopathy and was greater in animals with SCD (4.0 +/- 0.2 vs. 3.1 +/- 0.1 g/kg in survivors; P < 0.001). Serial programmed ventricular stimulation failed to induce any sustained arrhythmias. We conclude that pigs with viable dysfunctional myocardium and globally reduced LV function have a high rate of SCD with a spectrum of arrhythmias similar to patients with ischemic cardiomyopathy. The risk is independent of necrosis but appears to increase with LV hypertrophy. Like patients with ischemic cardiomyopathy, programmed stimulation is insensitive to predict SCD when viable dysfunctional myocardium is the pathological substrate.

Enhanced Coagulation Activation by In Vitro Lipopolysaccharide Challenge in Patients with Ventricular Fibrillation Complicating Acute Myocardial Infarction

BACKGROUND

Indicators of coagulation and inflammation are elevated in patients with coronary heart disease. A role of coagulation activation in ventricular fibrillation during acute myocardial infarction has not been described.

METHODS AND RESULTS

Whole blood samples of 21 patients with a history of acute myocardial infarction complicated by ventricular fibrillation and whole blood samples of 18 patients without ventricular fibrillation were incubated with lipopolysaccharide (LPS). In both groups, the in vitro blood coagulation time was measured with the ReoRox, a viscometric whole blood coagulometer. CD62P expression on platelets, tissue-factor binding on monocytes, and platelet-monocyte aggregates were measured with flow cytometry. Without LPS, no difference in the coagulation times were observed in both patient groups. After incubation with LPS, patients with a history of ventricular fibrillation showed a significantly decreased coagulation time compared to patients without ventricular fibrillation. The decrease of coagulation time after incubation with LPS also differed significantly in both groups. Expression of CD62P on platelets was significantly higher in patients with a history of ventricular fibrillation after incubation with LPS. Although in each patient group incubation with LPS induced a significantly increased amount of tissue factor on monocytes and a significantly increased the number of platelet-monocyte aggregates, the two groups did not differ significantly concerning tissue factor binding on monocytes and the amount of platelet-monocyte aggregates.

CONCLUSIONS

After in vitro LPS challenge, patients with a history of ventricular fibrillation during myocardial infarction show an enhanced coagulation activation, which may partly be due to an enhanced platelet activation.

Implementation of community-based public access defibrillation in the PAD trial

BACKGROUND

The Public Access Defibrillation (PAD) Trial was a randomized, controlled trial designed to measure survival to hospital discharge following out-of-hospital cardiac arrest (OOH-CA) in community facilities trained and equipped to provide PAD, compared with community facilities trained to provide cardiopulmonary resuscitation (CPR) without any capacity for defibrillation.

OBJECTIVES

To report the implementation of community-based lay responder emergency response programs in 1,260 participating facilities recruited for the PAD Trial in the United States and Canada.

METHODS

This was a descriptive study of the characteristics of participating facilities, volunteers, and automated external defibrillator (AED) placements compiled by the PAD Trial, and a qualitative study of factors that facilitated or impeded implementation of emergency lay responder programs using focus groups of PAD Trial site coordinators.

RESULTS

The PAD Trial enrolled 1,260 community facilities (14.8% residential), with 20,400 lay volunteers (mean +/- standard deviation = 13.4 +/- 10.7 per facility) trained to respond to OOH-CA. The 598 locations randomized to receive AEDs required 2.7 +/- 1.8 AEDs per facility. Volunteer attrition was high, 36% after two years. Barriers to recruitment and implementation included identification of appropriate "at-risk" facilities, lack of interest or fear of litigation by a facility key decision maker, lack of motivated potential volunteer responders, training and retraining resource requirements, and lack of an existing communication/response infrastructure.

CONCLUSIONS

These data indicate that implementation of community-based lay responder programs is feasible in many types of facilities, although these programs require substantial resources and commitment, and many barriers to implementation of effective PAD programs exist.

Inhibition of cardiac HERG channels by grapefruit flavonoid naringenin: implications for the influence of dietary compounds on cardiac repolarisation

Flavonoids are naturally occurring food ingredients that have been associated with reduced cardiovascular mortality in epidemiological studies. In a previous study, we demonstrated for the first time that flavonoids are inhibitors of cardiac human ether-à-go-go-related gene (HERG) channels. Furthermore, we observed that grapefruit juice induced mild QTc prolongation in healthy subjects. HERG blockade by grapefruit flavonoid naringenin is most likely to be the mechanism underlying this effect. Therefore, the electrophysiological properties of HERG blockade by naringenin were analysed in detail. HERG potassium currents expressed in Xenopus oocytes were measured with a two-microelectrode voltage clamp. Naringenin blocked HERG potassium channels with an IC50 value of 102.6 microM in Xenopus oocytes. The onset of blockade was fast. The effect was completely reversible upon wash-out. Naringenin binding to HERG required aromatic residue F656 in the putative pore binding site. Channels were blocked in the open and inactivated states but not in the closed states. Naringenin did not affect HERG current activation. However, the half maximal inactivation voltage was shifted by 14.9 mV towards more negative potentials and current inactivation at negative potentials was accelerated. No frequency dependence of blockade was observed. Naringenin inhibits HERG channels with pharmacological characteristics similar to those of well-known HERG antagonists. From a clinical point of view, this effect could have both proarrhythmic and antiarrhythmic consequences. This may have important implications for phytotherapy and for dietary recommendations for cardiologic patients. Therefore, electrophysiological effects of flavonoids deserve further investigation.

Cardiovascular device development: lessons learned from pacemaker and implantable cardioverter-defibrillator therapy

Pacemaker (PM) and implantable cardioverter-defibrillator (ICD) therapy are two examples of remarkable technological advances that have revolutionized cardiovascular device therapy. Understanding the history of early PM and ICD device development, recognizing the importance of the clinical data that was required to launch the current "era" of exponential device use, and appreciating the challenge of maintaining device innovation without sacrificing device reliability, are important lessons that may offer insights into future cardiovascular device development.

[Resuscitation in ventricular fibrillation: what is essential?]

Prognosis of prehospital cardiac arrest due to ventricular fibrillation is dependent on the first minutes, as survival decreases by 10% for each minute by which resuscitation attempts are delayed. Thus, early defibrillation plays a key role in improving outcome of cardiac arrest victims. The effectiveness of automated external defibrillators (AEDs) in this setting has been proven by several clinical trials. There remains controversy with regard to using AEDs in the in-hospital setting, as well as the approach of "public access" defibrillation. Whereas the use of intravenous antiarrhythmic drugs, particularly amiodarone, remains controversial, new data support the use of vasopressine instead of epinephrine as vasopressor drug in cardiac arrest patients. The present review aims to focus on the above mentioned aspects as well as on the changes to the present ILCOR guidelines which have led to modification of the resuscitation guidelines of the European Resuscitation Council (ERC).

[Epidemiology of sudden cardiac death]

Sudden cardiac death remains a major challenge that we are still facing today. The complexity of the trigger mechanisms makes it difficult to achieve a reliable identification of high-risk patients. Three suggestions are made that might help to overcome this epidemiological catastrophe "Sudden Cardiac Death". 1. In patients with known heart disease risk stratification has to be improved by developing new methods to identify specifically those individuals, who are at risk for sudden rather than non-sudden cardiac death. 2. The general population contains an unknown proportion of individuals with advanced coronary disease, which is commonly asymptomatic. In these so called "normal population" classical risk stratification does not work. However, since there is a close relationship between the prevalence of risk factors for coronary disease and sudden death, a consequent treatment of risk factors should have a positive effect on sudden death rate as well. 3. The success rate of resuscitation has to be improved by strengthening each single link of the "chain of survival". Laypersons trained in basic and advanced life support techniques have to play a much major role on this scene.

Epicardial organization of human ventricular fibrillation

OBJECTIVE

The objective of this study was to test the hypothesis that on the epicardium of the in vivo human heart, ventricular fibrillation (VF) consists of chaotic small wavefronts that constantly change paths.

BACKGROUND

Despite the significance of VF to cardiovascular mortality, little is known about the wavefronts that constitute VF in humans.

METHODS

In 9 patients undergoing cardiac surgery, a single VF episode was induced by rapid pacing immediately after institution of cardiopulmonary bypass while recordings were made from 504 electrodes spaced 2 mm apart in a 20 cm(2) plaque held against the anterior left ventricle epicardium. A total of 26 segments of VF, each 2 s long, were analyzed. A computer algorithm identified individual wavefronts and classified them into groups that followed similar activation sequences.

RESULTS

The mean activation rate was 5.8 +/- 1.8 (mean +/- SD) cycles/s. The wavefronts during each epoch were grouped into 9.4 +/- 7.1 different activation pathways, and 8.3 +/- 2.3 wavefronts followed each pathway. Individual wavefronts spread to activate an area of 5.1 +/- 3.0 cm(2) in the mapped region. The majority of the wavefronts propagated into the mapped region and/or propagated out of the mapped region into adjacent tissue, suggesting that the wavefronts were larger than 5.1 cm(2). Reentry was identified in only 16 of the 26 (62%) 2-s segments, always completed <2 cycles, and lasted for 9.5 +/- 6.6% of these 16 epochs, which is 5.8% of the total duration of all the segments analyzed.

CONCLUSION

VF wavefronts on the human epicardium are usually large, repeatedly follow distinct pathways, and only occasionally reenter. If these results for the left ventricular epicardium are representative of those for the entire ventricular mass, they do not support the hypothesis that human VF consists of small, constantly changing wavefronts, but rather suggest that there is significant organization of human VF.

The pathology of sudden cardiac death in patients with ischemic heart disease—arrhythmology for anatomic pathologists

The goal of this review is to help anatomic pathologists interpret the significance of pathologic changes in the hearts of patients with coronary artery disease who died suddenly of spontaneous ventricular arrhythmias. Attention is focused on dynamic interactions between triggering events, such as acute ischemia, and stable anatomic substrates of arrhythmias, such as healed myocardial infarcts. A basic knowledge of arrhythmia mechanisms is necessary to understand the role of pathologic anatomy in the pathophysiology of sudden death.

Microvolt T-Wave Alternans for the Risk Stratification of Ventricular Tachyarrhythmic Events

OBJECTIVES

The objective of this study was to perform a meta-analysis of the predictive value of microvolt T-wave alternans (MTWA) testing for arrhythmic events in a wide variety of populations.

BACKGROUND

Previous studies describing the use of MTWA as a predictor of ventricular tachyarrhythmic events have been limited by small sample sizes and disparate populations.

METHODS

Prospective studies of the predictive value of exercise-induced MTWA published between January 1990 and December 2004 were retrieved. Data from each article were abstracted independently by two authors using a standardized protocol. Summary estimates of the predictive value of MTWA were made using a random-effects model.

RESULTS

Data were accumulated from 19 studies (2,608 subjects) across a wide range of populations. Overall, the positive predictive value of MTWA for arrhythmic events was 19.3% at an average of 21 months' follow-up (95% confidence interval [CI] 17.7% to 21.0%), the negative predictive value was 97.2% (95% CI 96.5% to 97.9%), and the univariate relative risk of an arrhythmic event was 3.77 (95% CI 2.39 to 5.95). There was no difference in predictive value between ischemic and nonischemic heart failure subgroups. The positive predictive value varied depending on the population of patients studied (p < 0.0001).

CONCLUSIONS

Microvolt T-wave alternans testing has significant value for the prediction of ventricular tachyarrhythmic events; however, there are significant limitations to its use. The predictive value of MTWA varies significantly depending on the population studied. Careful standardization is needed for what constitutes abnormal MTWA. The incremental prognostic value of MTWA when used with other methods of risk stratification is unclear.

Ejection fraction and QRS width as predictors of event rates in patients with implantable cardioverter defibrillators

OBJECTIVES

The Multicenter Automatic Defibrillator Implantation Trial II in 2002 recommended implantable cardioverter defibrillators (ICDs) prophylactically for all patients with a prior myocardial infarction and ejection fraction (EF) of 30% or less. In June of 2003, the Centers for Medicare and Medicaid Services approved reimbursement for ICD placement in patients with an EF of 30% or less who have a QRS interval greater than 120 ms. The purpose of this study was therefore to determine the value of QRS duration in predicting the occurrence of ventricular arrhythmias within the first year after ICD implantation. These ICDs were placed over the past 5 years for various indications.

METHODS

EF cut points of 30% or less and 31% or greater and QRS duration of 120 ms or less and 121 ms or greater were used to assess the risk of events.

RESULTS

There was a significant increase in events in subjects with EF of 30% or less, compared with patients with EF of 31% or greater (P < 0.05), and there was a trend toward increased likelihood of arrhythmias in patients with widened QRS width.

CONCLUSIONS

This study confirms the conclusion of the Multicenter Automatic Defibrillator Implantation Trial II and implies that the Centers for Medicare and Medicaid Services criteria for reimbursement may not be scientifically valid.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Sudden death in patients with myocardial infarction and left ventricular dysfunction, heart failure, or both

BACKGROUND

The risk of sudden death from cardiac causes is increased among survivors of acute myocardial infarction with reduced left ventricular systolic function. We assessed the risk and time course of sudden death in high-risk patients after myocardial infarction.

METHODS

We studied 14,609 patients with left ventricular dysfunction, heart failure, or both after myocardial infarction to assess the incidence and timing of sudden unexpected death or cardiac arrest with resuscitation in relation to the left ventricular ejection fraction.

RESULTS

Of 14,609 patients, 1067 (7 percent) had an event a median of 180 days after myocardial infarction: 903 died suddenly, and 164 were resuscitated after cardiac arrest. The risk was highest in the first 30 days after myocardial infarction--1.4 percent per month (95 percent confidence interval, 1.2 to 1.6 percent)--and decreased to 0.14 percent per month (95 percent confidence interval, 0.11 to 0.18 percent) after 2 years. Patients with a left ventricular ejection fraction of 30 percent or less were at highest risk in this early period (rate, 2.3 percent per month; 95 percent confidence interval, 1.8 to 2.8 percent). Nineteen percent of all sudden deaths or episodes of cardiac arrest with resuscitation occurred within the first 30 days after myocardial infarction, and 83 percent of all patients who died suddenly did so in the first 30 days after hospital discharge. Each decrease of 5 percentage points in the left ventricular ejection fraction was associated with a 21 percent adjusted increase in the risk of sudden death or cardiac arrest with resuscitation in the first 30 days.

CONCLUSIONS

The risk of sudden death is highest in the first 30 days after myocardial infarction among patients with left ventricular dysfunction, heart failure, or both. Thus, earlier implementation of strategies for preventing sudden death may be warranted in selected patients.

Electrophysiological and histopathological characteristics of progressive atrioventricular block accompanied by familial dilated cardiomyopathy caused by a novel mutation of lamin A/C gene

Conduction defect caused by lamin A/C gene mutation.

INTRODUCTION

Mutations of lamin A/C gene (LMNA) cause dilated cardiomyopathy (DCM) with atrioventricular (AV) conduction defect, although the electrophysiological and histological profiles are not fully understood.

METHODS AND RESULTS

We analyzed a large Japanese family (21 affected and 203 unaffected members) of DCM with AV block. The responsible LMNA mutation of IVS3-10A>G was novel and caused an aberrant splicing. The first clinical manifestation was low-grade AV block or atrial fibrillation (AF), which developed in affected members aged >or=30 years. We observed that the AV block progressed to third-degree within several years. The electrophysiological study of the four affected members revealed an impairment of intra-AV nodal conduction. Because of advanced AV block, pacemakers were implanted in 14 out of 21 affected members at the mean age of 44 years. Three affected members died suddenly and two affected members died of heart failure and/or ventricular tachycardia (VT) even after the pacemaker implantation. Postmortem examination showed conspicuous fibrofatty degeneration of the AV node. Endomyocardial biopsies showed remarkably deformed nuclei and substantial glycogen deposits in the subsarcolemma.

CONCLUSION

The clinical phenotype in this family was characterized by (1) the first manifestation of the prolonged PQ interval or AF in adolescence, (2) progressive intra-AV nodal block to the third degree in several years, and (3) progressive heart failure after pacemaker implantation. Histological study revealed preferential degeneration at the AV node area and novel cellular damages in the working myocardium.

Conditional mineralocorticoid receptor expression in the heart leads to life-threatening arrhythmias

BACKGROUND

Life-threatening cardiac arrhythmia is a major source of mortality worldwide. Besides rare inherited monogenic diseases such as long-QT or Brugada syndromes, which reflect abnormalities in ion fluxes across cardiac ion channels as a final common pathway, arrhythmias are most frequently acquired and associated with heart disease. The mineralocorticoid hormone aldosterone is an important contributor to morbidity and mortality in heart failure, but its mechanisms of action are incompletely understood.

METHODS AND RESULTS

To specifically assess the role of the mineralocorticoid receptor (MR) in the heart, in the absence of changes in aldosteronemia, we generated a transgenic mouse model with conditional cardiac-specific overexpression of the human MR. Mice exhibit a high rate of death prevented by spironolactone, an MR antagonist used in human therapy. Cardiac MR overexpression led to ion channel remodeling, resulting in prolonged ventricular repolarization at both the cellular and integrated levels and in severe ventricular arrhythmias.

CONCLUSIONS

Our results indicate that cardiac MR triggers cardiac arrhythmias, suggesting novel opportunities for prevention of arrhythmia-related sudden death.

Microvolt T-wave alternans during exercise and pacing in patients with acute myocardial infarction

Cardiac Arrhythmias and Risk Stratification after Myocardial infarction (CARISMA) is a prospective multicenter trial designed to document the incidence of cardiac arrhythmias after acute myocardial infarction (AMI), and to assess the predictive accuracy of various arrhythmic risk markers. In this substudy of the CARISMA trial, microvolt T-wave alternans (TWA) was assessed with specific equipment 6 weeks after AMI during bicycle exercise, atrial (A) pacing, and simultaneous ventricular and atrial (V + A) pacing in 80 patients with left ventricular ejection fraction (LVEF) <40%. The agreement between the acute test results was determined by overall proportion of concordance and the kappa statistic. Sustained TWA was observed in 24, 45, and 50% of the patients during the exercise test, A pacing, and V + A pacing, respectively. The number of indeterminate TWA was significantly lower during V + A pacing (n = 7) than exercise test (n = 34). The TWA concordance rate was 71% between exercise and V + A pacing (kappa= 0.53, P = 0.001), 79% between exercise and A pacing (kappa= 0.54, P < 0.001), and 95% between the two pacing modes (kappa= 0.89, P < 0.001). Patients with positive TWA in all tests had lower LVEF (28 +/- 7% vs 35 +/- 9%, P < 0.01) and wider QT dispersion (99 +/- 44 ms vs 67 +/- 38 ms, P < 0.01) than those with inconsistent test result. The low number of indeterminate tests and high concordance between the test results indicate that V + A pacing may provide a valuable means to assess TWA in patients who cannot complete the exercise test.

Association of air pollution with increased incidence of ventricular tachyarrhythmias recorded by implanted cardioverter defibrillators

Epidemiologic studies have demonstrated a consistent link between sudden cardiac deaths and particulate air pollution. We used implanted cardioverter defibrillator (ICD) records of ventricular tachyarrhythmias to assess the role of air pollution as a trigger of these potentially life-threatening events. The study cohort consisted of 203 cardiac patients with ICD devices in the Boston metropolitan area who were followed for an average of 3.1 years between 1995 and 2002. Fine particle mass and gaseous air pollution plus temperature and relative humidity were measured on almost all days, and black carbon, sulfate, and particle number on a subset of days. Date, time, and intracardiac electrograms of ICD-detected arrhythmias were downloaded at the patients' regular follow-up visits (about every 3 months). Ventricular tachyarrhythmias were identified by electrophysiologist review. Risk of ventricular arrhythmias associated with air pollution was estimated with logistic regression, adjusting for season, temperature, relative humidity, day of the week, patient, and a recent prior arrhythmia. We found increased risks of ventricular arrhythmias associated with 2-day mean exposure for all air pollutants considered, although these associations were not statistically significant. We found statistically significant associations between air pollution and ventricular arrhythmias for episodes within 3 days of a previous arrhythmia. The associations of ventricular tachyarrhythmias with fine particle mass, carbon monoxide, nitrogen dioxide, and black carbon suggest a link with motor vehicle pollutants. The associations with sulfate suggest a link with stationary fossil fuel combustion sources.

Noninvasive sudden death risk stratification by ambulatory ECG-based T-wave alternans analysis: evidence and methodological guidelines

Extensive experimental and clinical evidence supports the utility of T-wave alternans (TWA) as a marker of risk for ventricular fibrillation. This entity appears to reflect the fundamental arrhythmogenic property of enhanced dispersion of repolarization. This relationship probably accounts for its relative ubiquity in patients with diverse types of cardiac disease, as has been recognized with the development of analytical tools. A basic premise of this review is that ambulatory ECG monitoring of TWA as patients experience the provocative stimuli of daily activities can expose latent electrical instability in individuals at heightened risk for arrhythmias. We will discuss the literature that supports this concept and summarize the current state of knowledge regarding the use of routine ambulatory ECGs to evaluate TWA for arrhythmia risk stratification. The dynamic, nonspectral modified moving average analysis method for assessing TWA, which is compatible with ambulatory ECG monitoring, is described along with methodological guidelines for its implementation. Finally, the rationale for combined monitoring of autonomic markers along with TWA will be presented.