Utility of current risk stratification tests for predicting major arrhythmic events after myocardial infarction

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.

Preimplantation B-type natriuretic peptide concentration is an independent predictor of future appropriate implantable defibrillator therapies

OBJECTIVE

To assess prospectively whether preimplantation B-type natriuretic peptide (BNP) and C reactive protein (CRP) concentrations predict future appropriate therapies from an implantable cardioverter-defibrillator (ICD).

DESIGN AND SETTING

Prospective cohort study conducted in a tertiary cardiac care centre.

METHODS

345 consecutive patients undergoing first time ICD implantation were prospectively studied. Serum BNP and CRP concentrations were obtained the day before ICD implantation. Patients were followed up with device interrogation to assess for appropriate shocks or antitachycardia pacing. Inappropriate therapies were excluded. Mean (SD) follow up was 13 (5) months.

RESULTS

Patients had ischaemic (71%), primary dilated (17%), and valvar or other cardiomyopathies (12%). About half (52%) had ICDs implanted for primary prevention. Sixty three (18%) received appropriate ICD therapies. Serum creatinine, beta blocker, statin, and angiotensin converting enzyme inhibitor usage did not differ between therapy and no therapy groups. By univariate comparison, ejection fraction (p = 0.048), not taking amiodarone (p = 0.033), and BNP concentration (p = 0.0003) were risk factors for ICD therapy. However, by Cox regression multivariate analysis, only BNP above the 50th centile was a significant predictor (hazard ratio 2.19, 95% confidence interval 1.07 to 4.71, p = 0.040). Median BNP was 573 ng/l versus 243 ng/l in therapy and no therapy patients, respectively (p = 0.0003). More patients with BNP above the 50th centile (27% v 10%, p = 0.006) received ICD therapies.

CONCLUSIONS

A single preimplantation BNP concentration determination is independently predictive of ICD therapies in patients with cardiomyopathies undergoing first time ICD implantation. CRP was not independently predictive of ICD therapies when compared with BNP.

Negative impact of depression on outcomes in patients with coronary artery disease: mechanisms, treatment considerations, and future directions

Depressive symptoms are common in coronary artery disease (CAD) patients, and are associated with increased cardiac risk. Although an important relation exists between depression and CAD prognosis, the underlying pathophysiological mechanisms are poorly understood. Additionally, evidence including the recently published ENRICHD (Enhancing Recovery in Coronary Heart Disease Patients) trial suggests that depression treatments do not lower recurrent cardiac risk. The reason for the observed lack of benefit with depression treatment in CAD patients is unclear. In this review, we discuss the impact of depression in CAD patients, the possible mechanisms involved, the studies that have examined the effects of psychological and antidepressant therapies on recurrent cardiac events, and the direction that future research should take.

The Use of Implantable Cardioverter Defibrillators for the Prevention of Sudden Cardiac Death: A Review of the Evidence and Implications

Sudden cardiac death (SCD) claims approximately 460,000 lives per year in the United States, and half of these deaths occur in people with a history of coronary artery disease. Patients with left ventricular dysfunction and a history of myocardial infarction are at especially high risk. There is now strong evidence from multiple well-designed randomized controlled trials that implantable cardioverter defibrillators (ICDs) save lives when used for both primary and secondary prevention. As indications for ICD implantation have broadened, considerable debate has taken place because of the substantial cost involved in widespread ICD utilization. This article summarizes the epidemiology of SCD, reviews the evidence supporting the use of ICDs in patients with ischemic cardiomyopathy, and explores some of the controversy surrounding ICD utilization that has arisen in the wake of recent trials that have utilized ICDs for the primary prevention of SCD.

Prediction of sudden cardiac death after acute myocardial infarction: role of Holter monitoring in the modern treatment era

AIMS

Current treatment may have changed the risk profiles of survivors of acute myocardial infarction (AMI). We evaluated the utility of Holter-based risk variables in the prediction of sudden cardiac death (SCD) among survivors of AMI treated with modern therapy.

METHODS AND RESULTS

A total of 2130 AMI patients (mean age 59 +/- 10 years) were included. The patients were treated with modern therapeutic strategies, for example, 94% were on beta-blocking therapy and 70% underwent coronary revascularization. Various risk parameters from Holter monitoring were analysed. During a median follow-up of 1012 days (interquartile range: 750-1416 days), cardiac mortality was 113/2130, including 52 SCDs. All Holter variables predicted the occurrence of SCD (P<0.01), but only reduced post-ectopic turbulence slope (TS) (P<0.001) and non-sustained ventricular tachycardia (P<0.01) remained as marked SCD predictors after adjustment for age, diabetes, and ejection fraction (EF). In a subgroup analysis, none of the Holter variables predicted SCD among those with an EF < or = 0.35, but many variables predicted SCD among those with an EF >0.35, particularly TS (hazard ratio 5.9; 95% CI 2.9-11.7, P<0.001).

CONCLUSION

Among the post-AMI patients treated according to the current guidelines, the incidence of SCD is low. Various Holter variables still predict the occurrence of SCD, particularly among the patients with preserved left ventricular function.

Cost-effectiveness of in-home automated external defibrillators for individuals at increased risk of sudden cardiac death

BACKGROUND/OBJECTIVE

In-home automated external defibrillators (AEDs) are increasingly recommended as a means for improving survival of cardiac arrests that occur at home. The current study was conducted to explore the relationship between individuals' risk of cardiac arrest and cost-effectiveness of in-home AED deployment.

DESIGN

Markov decision model employing a societal perspective.

PATIENTS

Four hypothetical cohorts of American adults 60 years of age at progressively greater risk for sudden cardiac death (SCD): 1) all adults (annual probability of SCD 0.4%); 2) adults with multiple SCD risk factors (probability 2%); 3) adults with previous myocardial infarction (probability 4%); and 4) adults with ischemic cardiomyopathy unable to receive an implantable defibrillator (probability 6%).

INTERVENTION

Strategy 1: individuals suffering an in-home cardiac arrest were treated with emergency medical services equipped with AEDs (EMS-D). Strategy 2: individuals suffering an in-home cardiac arrest received initial treatment with an in-home AED, followed by EMS.

RESULTS

Assuming cardiac arrest survival rates of 15% with EMS-D and 30% with AEDs, the cost per quality-adjusted life-year gained (QALY) of providing in-home AEDs to all adults 60 years of age is 216,000 dollars. Costs of providing in-home AEDs to adults with multiple risk factors (2% probability of SCD), previous myocardial infarction (4% probability), and ischemic cardiomyopathy (6% probability) are 132,000 dollars, 104,000 dollars, and 88,000 dollars, respectively.

CONCLUSIONS

The cost-effectiveness of in-home AEDs is intimately linked to individuals' risk of SCD. However, providing in-home AEDs to all adults over age 60 appears relatively expensive.

Incidence of nonsustained and sustained ventricular tachyarrhythmias in patients with an implantable cardioverter defibrillator

INTRODUCTION

Nonsustained ventricular tachycardia (NSVT) is a frequent phenomenon in some patients with heart disease, but its association with sustained ventricular tachycardias (ventricular tachycardia [VT]/ventricular fibrillation [VF]) is still not clear. The aim of this study was to determine whether NSVT incidence was associated with sustained VT/VF in patients with an implantable cardioverter defibrillator (ICD).

METHODS AND RESULTS

Retrospective data analysis was conducted in 923 ICD patients with a mean follow-up of 4 months. NSVT and sustained VT/VF were defined as device-detected tachycardias. The incidence rates of NSVT and sustained VT/VF as well as ICD therapies were determined as episodes per patient. The NSVT index was defined as the product of NSVT episodes/day times the mean number of beats per episode, i.e., total beats/day. The NSVT index peak was defined as the highest value on or prior to the day with sustained VT/VF episodes. Patients (n = 393) with NSVT experienced a higher incidence of sustained VT/VF (17.2 +/- 63.0 episodes/patient) and ICD therapies (15.2 +/- 61.4 episodes/patient) than patients (n = 530) without NSVT (sustained VT/VF: 0.5 +/- 6.6 and therapies: 0.5 +/- 5.6; P < 0.0001). Approximately 74% of NSVT index peaks occurred on the same day or <3 days prior to sustained VT/VF episodes. The index was higher for peaks < or =3 days prior to the day with sustained VT/VF (94.3 +/- 140.1 total beats/day) than for peaks >3 days prior to the day with sustained VT/VF (32.7 +/- 55.9 total beats/day; P < 0.0001).

CONCLUSION

ICD patients with NSVT represent a population more likely to experience sustained VT/VF episodes with a temporal association between an NSVT surge and sustained VT/VF occurrence.

Noninvasive risk stratification in postinfarction patients with severe left ventricular dysfunction and methodology of the MADIT II noninvasive electrocardiology substudy

Sudden cardiac death occurs as a result of a complex interplay of changes in myocardial substrate, imbalance of autonomic regulation of the heart, and myocardial vulnerability. Noninvasive electrocardiology serves as a comprehensive tool for investigating factors representing mechanistic pathways leading to cardiac events. Heart rate variability, nonlinear dynamics of heart rate, and heart rate turbulence provide insight into autonomic control of the heart. Prognostic value of these parameters in postinfarction patients is well established for predicting cardiac death, but there is less evidence for their association with sudden death or arrhythmic events. Electrical manifestation of changes in myocardial substrate include QRS and QTc prolongation, presence of conduction disturbances, presence of late potentials, abnormalities of repolarization morphology, and presence of nonsinus rhythm, namely atrial fibrillation. Electrocardiogram (ECG) measures reflecting myocardial vulnerability to arrhythmias include frequent ventricular premature beats, T wave alternans, or QT variability. Prognostic significance of these parameters is documented in studies focused mostly on them as individual markers of risk. The noninvasive electrocardiology substudy of the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) allows for simultaneous analysis of several of the above ECG markers of risk and will provide insight about relative contribution of mechanistic pathways leading to cardiac death in postinfarction patients with severe left ventricular dysfunction. Combination of a standard 12-lead ECG and 10-minute high-resolution Holter recordings serves to evaluate the prognostic significance of noninvasive electrocardiology parameters for mortality in patients randomized to conventional treatment and for arrhythmic events in patients randomized to implantable cardioverter defibrillator therapy.

Risk stratification in diabetic patients with a previous myocardial infarction

We used Kaplan-Meier 2-year survival analysis on CAST registry patients to estimate prognostic power of VPC frequency (> or =10/hr), presence of nonsustained ventricular tachycardia (NSVT), left ventricular ejection fraction, and presence of diabetes. We also used meta-analysis of reports in the literature to estimate prognostic power of signal-averaged electrocardiogram (SAECG) and electrophysiological tests (EPS) as well as VPCs, NSVT, and LVEF. Combined results from CAST analysis and literature meta-analysis yielded sensitivity and specificity for VPCs, NSVT, SAECG, LVEF, Diabetes, and EPS. The overall 2 year event rate for life-threatening arrhythmias or death was 7.88% for 51,144 cases in the combined CAST and literature data. After segmenting the population 21.3% were diabetic with a predicted 2 yr event rate of 13.5% and 78.7% were nondiabetic event rate of 6.4%. We defined low risk as <10% and high risk as > or =30%. Otherwise predicted event rate was classified as "unstratified." When all possible combination of noninvasive tests were applied, a prominent difference in the proportions of cases at risk between the diabetics and nondiabetics was revealed. When the unstratified cases were subsequently tested with EPS, the difference between the two groups was even more marked.

Prediction of sudden cardiac death after myocardial infarction in the beta-blocking era

OBJECTIVES

This study assessed the predictive power of arrhythmia risk markers after an acute myocardial infarction (AMI).

BACKGROUND

Several risk variables have been suggested to predict the occurrence of sudden cardiac death (SCD), but the utility of these variables has not been well established among patients using medical therapy according to contemporary guidelines.

METHODS

A consecutive series of 700 patients with AMI was studied. The end points were total mortality, SCD, and nonsudden cardiac death (non-SCD). Nonsustained ventricular tachycardia (nsVT), ejection fraction (EF), heart rate variability, baroreflex sensitivity, signal-averaged electrocardiogram (SAECG), QT dispersion, and QRS duration were analyzed (n = 675). Beta-blocking therapy was used by 97% of the patients at discharge and by 95% at one and two years after AMI.

RESULTS

During a mean (+/-SD) follow-up of 43 +/- 15 months, 37 non-SCDs (5.5%) and 22 SCDs (3.2%) occurred. All arrhythmia risk variables differed between the survivors and those with non-SCD (e.g., the standard deviation of N-N intervals was 98 +/- 32 vs. 74 +/- 21 ms [p < 0.001] and the QRS duration was 103 +/- 22 vs.89 +/- 16 ms [p < 0.001]). Sudden cardiac death was weakly predicted only by reduced EF (<0.40; p < 0.05), nsVT (p < 0.05), and abnormal SAECG (p < 0.05), but not by autonomic markers or standard ECG variables. The positive predictive accuracy of EF, nsVT, and abnormal SAECG as predictors of SCD was relatively low (8%, 12%, and 13%, respectively).

CONCLUSIONS

The common arrhythmia risk variables, particularly the autonomic and standard ECG markers, have limited predictive power in identifying patients at risk of SCD after AMI in the beta-blocking era.

Structural pathways and prevention of heart failure and sudden death

We review the macroscopic and microscopic anatomy of myocardial disease associated with heart failure (HF) and sudden cardiac death (SCD) and focus on the prevention of SCD in light of its structural pathways. Compared to patients without SCD, patients with SCD exhibit 5- to 6-fold increases in the risks of ventricular arrhythmias and SCD. Epidemiologically, left ventricular hypertrophy by ECG or echocardiography acts as a potent dose-dependent SCD predictor. Dyslipidemia, a coronary disease risk factor, independently predicts echocardiographic hypertrophy. In adult SCD autopsy studies, increases in heart weight and severe coronary disease are constant findings, whereas rates of acute coronary thrombi vary remarkably. The microscopic myocardial anatomy of SCD is incompletely defined but may include prevalent changes of advanced myocardial disease, including cardiomyocyte hypertrophy, cardiomyocyte apoptosis, fibroblast hyperplasia, diffuse and focal matrix protein accumulation, and recruitment of inflammatory cells. Hypertrophied cardiomyocytes express "fetospecific" genetic programs that can account for acquired long QT physiology with risk for polymorphic ventricular arrhythmias. Structural heart disease associated with HF and high SCD risk is causally related to an up-regulation of the adrenergic renin-angiotensin-aldosterone pathway. In outcome trials, suppression of this pathway with combinations of beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin-II receptor blockers, and mineralocorticoid receptor blockers have achieved substantial total mortality and SCD reductions. Contrarily, trials with ion channel-active agents that are not known to reduce structural heart disease have failed to reduce these risks. Device therapy effectively prevents SCD, but whether biventricular pacing-induced remodeling decreases left ventricular mass remains uncertain.

Effectiveness of implantable defibrillators for preventing arrhythmic events and death: a meta-analysis

OBJECTIVES

The aim of this study was to compare the effectiveness of the implantable cardioverter defibrillator (ICD) and medical strategies for prevention of arrhythmic events and death.

BACKGROUND

The ICD is a potential strategy to reduce mortality in patients at risk of sudden death.

METHODS

The MEDLINE, EMBASE, and Cochrane Library electronic databases were searched from January 1966 to April 2002. All published randomized controlled trials comparing ICD implantation with medical therapy were reviewed. Four independent reviewers extracted data on all-cause mortality, nonarrhythmic death, and arrhythmic death using a standardized protocol.

RESULTS

Nine studies including over 5,000 patients were synthesized using both fixed-effects and random-effects models. The primary and secondary prevention trials showed a significant benefit of the ICD with respect to arrhythmic death, with relative risks (RR) of 0.34 and 0.50, respectively (both p < 0.001). The mortality benefit of the ICD was entirely attributable to a reduction in arrhythmic death (all trials: p < 0.00001). Whereas the secondary prevention trials exhibited a robust decrease in all-cause ICD mortality (RR 0.75; p < 0.001), the pooled primary prevention trials demonstrated decreased all-cause ICD mortality (RR 0.66; p < 0.05) which was dependent on selected individual trials. The disparity in ICD-related mortality reductions in the primary prevention trials was related to variability in the incidence of arrhythmic death between individual studies.

CONCLUSIONS

Although the ICD decreases the risk of arrhythmic death, its impact on all-cause mortality is related to the underlying risk of arrhythmia-related death relative to competing causes. Given the cost of the device strategy, policies of targeted intervention based on the future risk of arrhythmia are warranted.

[Risk stratification after acute myocardial infarction]

In recent years, the characteristics of patients who suffer acute myocardial infarction without complications during hospitalization have changed. In addition, the range of non-invasive studies available for evaluating left ventricular systolic function, residual myocardial ischemia, and myocardial viability in these patients has improved. Left ventricular systolic function and residual ischemia should be evaluated in all patients before release. The non-invasive technique used (exercise test, echocardiography, nuclear cardiology, magnetic resonance imaging) depends on availability, experience, and results at each institution. Coronary arteriography should be performed in patients with significant ischemia or severe left ventricular systolic dysfunction in non-invasive studies. In these cases coronary angiography must be performed to determine if coronary arteries are suitable for revascularization before performing a test of myocardial viability.