Implantable Cardioverter-defibrillator Therapy For Primary Prevention Research Articles

IMPAIRED HYPEREMIC MYOCARDIAL BLOOD FLOW IS ASSOCIATED WITH INDUCIBILITY OF VENTRICULAR ARRHYTHMIA IN ISCHEMIC CARDIOMYOPATHY

Risk stratification for ventricular arrhythmias (VA) is important to refine selection criteria for primary prevention implantable cardioverter-defibrillator therapy. Impaired hyperemic myocardial blood flow (MBF) is associated with increased mortality rate in ischemic and non-ischemic cardiomyopathy

Controversy surrounding the best time for ICD implantation after myocardial infarction

Controversy surrounding the best time for ICD implantation after myocardial infarction

Survival benefit of primary prevention implantable cardioverter-defibrillator therapy after myocardial infarction: does time to implant matter? A meta-analysis using patient-level data from 4 clinical trials.

Whether there is an optimal time to place an implantable cardioverter-defibrillator (ICD) more than 40 days after myocardial infarction (MI) in guideline-eligible patients is unknown. To evaluate the effect of time from MI to randomization on mortality, rehospitalizations, and complications. Individual data on patients enrolled in 9 primary prevention ICD trials were provided. Clinical trials were eligible for the current analysis if they enrolled patients with an MI more than 40 days prior to randomization to primary prevention ICD therapy vs usual care: Multicenter Automatic Defibrillator Implantation Trial I, Multicenter UnSustained Tachyardia Trial, Multicenter Automatic Defibrillator Implantation Trial II, and Sudden Cardiac Death in Heart Failure Trial. ICD recipients died less frequently than nonrecipients at 5 years across all subgroups of time from MI to randomization. In unadjusted Cox proportional hazards regression, a survival benefit was evident in most subgroups. Adjusted Bayesian Weibull survival modeling yielded hazard ratio (HR) 0.50, 95% posterior credible interval (PCI) 0.20-1.25 41-180 days after MI; HR 0.98, 95% PCI 0.37-2.37 181-365 days after MI; HR 0.22, 95% PCI 0.07-0.59>1-2 years after MI; HR 0.42, 95% PCI 0.17-0.90>2-5 years after MI; HR 0.55, 95% PCI 0.25-1.15>5-10 years after MI; and HR 0.48, 95% PCI 0.20-1.02>10 years after MI. There was no evidence of an interaction between time from MI and all-cause mortality, rehospitalizations, or complications. In this meta-analysis, there was scant evidence that the efficacy of primary prevention ICD therapy depends on time to implantation more than 40 days after MI. Similarly, there was no evidence that the risks of rehospitalizations or complications depend on time more than 40 days after MI.

Scar heterogeneity on cardiovascular magnetic resonance as a predictor of appropriate implantable cardioverter defibrillator therapy.

BackgroundDespite the survival benefit of implantable-cardioverter-defibrillators (ICDs), the vast majority of patients receiving an ICD for primary prevention do not receive ICD therapy. We sought to assess the role of heterogeneous scar area (HSA) identified by late gadolinium enhancement cardiovascular magnetic resonance (LGE-CMR) in predicting appropriate ICD therapy for primary prevention of sudden cardiac death (SCD).MethodsFrom September 2003 to March 2011, all patients who underwent primary prevention ICD implantation and had a pre-implantation LGE-CMR were identified. Scar size was determined using thresholds of 4 and 6 standard deviations (SD) above remote normal myocardium; HSA was defined using 3 different criteria; as the region between 2 SD and 4 SD (HSA2-4SD), between 2SD and 6SD (HSA2-6SD), and between 4SD and 6SD (HSA4-6SD). The end-point was appropriate ICD therapy.ResultsOut of 40 total patients followed for 25 ± 24 months, 7 had appropriate ICD therapy. Scar size measured by different thresholds was similar in ICD therapy and non-ICD therapy groups (P = NS for all). However, HSA2-4SD and HSA4-6SD were significantly larger in the ICD therapy group (P = 0.001 and P = 0.03, respectively). In multivariable model HSA2-4SD was the only significant independent predictor of ICD therapy (HR = 1.08, 95%CI: 1.00-1.16, P = 0.04). Kaplan-Meier analysis showed that patients with greater HSA2-4SD had a lower survival free of appropriate ICD therapy (P = 0.026).ConclusionsIn primary prevention ICD implantation, LGE-CMR HSA identifies patients with appropriate ICD therapy. If confirmed in larger series, HSA can be used for risk stratification in primary prevention of SCD.

Longitudinal Study of Implantable Cardioverter-Defibrillators

Implantable cardioverter-defibrillators (ICDs) are increasingly used for primary prevention after randomized, controlled trials demonstrating that they reduce the risk of death in patients with left ventricular systolic dysfunction. The extent to which the clinical characteristics and long-term outcomes of unselected, community-based patients with left ventricular systolic dysfunction undergoing primary prevention ICD implantation in a real-world setting compare with those enrolled in the randomized, controlled trials is not well characterized. This study is being conducted to address these questions. The study cohort includes consecutive patients undergoing primary prevention ICD placement between January 1, 2006 and December 31, 2009 in 7 health plans. Baseline clinical characteristics were acquired from the National Cardiovascular Data Registry ICD Registry. Longitudinal data collection is underway, and will include hospitalization, mortality, and resource use from standardized health plan data archives. Data regarding ICD therapies will be obtained through chart abstraction and adjudicated by a panel of experts in device therapy. Compared with the populations of primary prevention ICD therapy randomized, controlled trials, the cohort (n=2621) is on average significantly older (by 2.5-6.5 years), more often female, more often from racial and ethnic minority groups, and has a higher burden of coexisting conditions. The cohort is similar, however, to a national population undergoing primary prevention ICD placement. Patients undergoing primary prevention ICD implantation in this study differ from those enrolled in the randomized, controlled trials that established the efficacy of ICDs. Understanding a broad range of health outcomes, including ICD therapies, will provide patients, clinicians, and policy makers with contemporary data to inform decision-making.

Use of implantable cardioverter-defibrillators for primary prevention in older patients: A systematic literature review and meta-analysis

Randomized clinical trials (RCTs) have demonstrated the efficacy of implantable cardioverter-defibrillators (ICDs) in reducing sudden cardiac death (SCD) in specific patient populations. However, patients ≥ 65 years were under-represented in these trials and the overall benefit of ICDs may be diminished in older patients due to competing risks for death. We evaluate the published data on ICD efficacy at reducing all-cause mortality in patients ≥ 65 years and in patients ≥ 75 years. We searched MEDLINE to identify RCTs and observational studies of ICDs that provided age-based outcome data for primary prevention of SCD. The primary endpoint was mortality evaluated by a meta-analysis of the RCTs using a random-effects model. Secondary endpoints included operative mortality, long-term complications and quality of life. The enrollment of patients ≥ 65 years in RCTs was limited (range: 33% in DEFINITE to 56% in MUSTT). Combining data from four RCTs (n = 3,562) revealed that primary prevention ICD therapy is efficacious in reducing all-cause mortality in patients ≥ 65 years (HR 0.66; 95% CI 0.50-0.87; test of heterogeneity: X(2) = 5.26; p = 0.15). For patients ≥ 75 years, combining data from four RCTs (n = 579) revealed that primary prevention ICD therapy remains efficacious in reducing all-cause mortality (HR 0.73; 95% CI 0.51-0.974; p = 0.03). There appears to be no difference in ICD-related, operative, in-hospital, or long- -term complications among older patients compared to younger patients, although it remains unclear if older patients have a better quality of life with an ICD than younger patients. Although the overall evidence regarding ICD efficacy in patients ≥ 65 years is limited and divergent, and the evidence available for patients ≥ 75 years is even more sparse, our meta-analysis suggests that primary prevention ICDs may be beneficial in older patients. Our findings need to be validated by future studies, particularly ones examining ICD complications and quality of life.

Implantable Cardioverter-Defibrillator therapy for primary prevention of sudden cardiac death in patients with severe Chagas cardiomyopathy

Sudden cardiac death (SCD) affects about half of patients who died of Chagas disease followed at a referral center, and may victim up to 20% of patients without any evidence of heart disease [1]. In the vast majority of cases, SCD is caused by either sustained ventricular tachycardia (VT) degenerating into ventricular fibrillation (VF) or direct VF [1]. In patients with non-Chagas disease dilated cardiomyopathy and left ventricular ejection fraction b35%, Implantable CardioverterDefibrillator (ICD) delivered-therapy has been recommended by international guidelines to avert SCD [2]. Conversely, the impact of ICD therapy in patients with Chagas cardiomyopathy and a left ventricular ejection fraction b35% is unknown. Accordingly, we report herein our initial experience with ICD-delivered therapy in patients with severe Chagas cardiomyopathy. From January, 2006 to December, 2009, a total of 32 patients routinely followed at the Cardiomyopathy Outpatient Service of our Institution received ICD therapy for primary prevention of SCD. The study was approved by the Local Ethical Committee (protocol 3626/ 2010). Inclusion criteria were a left ventricular ejection fraction b35% at radionuclide ventriculography, receiving standard therapy for chronic systolic heart failure, and to have a reasonable expectation of 1-year survival after device implantation [2]. All patients were on New York Heart Association class II at the time of ICD implantation and none had syncope before device implantation. Nineteen (59%) patients had a positive serology for Chagas disease and were considered to have Chagas cardiomyopathy, whereas the remaining 13 (41%) patients had non-Chagas disease dilated cardiomyopathy. Device therapy consisted of antitachycardia pacing (ATP) or shock. ATP was the initial therapy for VT. Shock was the initial therapy when heart rate was higher than 200 beats per minute (VF zone), when ATP accelerated VT heart rate, or when ATP failed to abolish VT. Baseline characteristics of the study population are given in Table 1. It is noteworthy that 87% patients were on Beta-Blocker therapy. Sustained VT was detected in 4 (21%) of 19 patients with Chagas cardiomyopathy and in 2 (15%) patients with non-Chagas cardiomyopathy (pN0.05). VF was observed in 4 Chagas cardiomyopathy (21%) patients and in 2 (15%) non-Chagas cardiomyopathy patients (pN0.05). Overall, 10 (31%) patients were shocked. In total, shock occurrence was necessary to terminate 136 out of 172 (79%) episodes of VT/VF. Inappropriate shock occurred in 4 (12%) patients; 2 (10%) in Chagas and 2 (14%) in non-Chagas cardiomyopathy patients (pN0.05). A total of 101 episodes of VFwere observed in 6 patients. Median of episodes per patient was 6.5 (3, 38). Ninety-four episodes of VF were observed in four Chagas and 7 episodes of VF in two non-Chagas cardiomyopathy patients (p=0.03). Median time to first event was 78 (34, 151) days in Chagas and 173 (71, 593) days in non-Chagas cardiomyopathy patients (pb0.005). Median time to VF was 80 (22, 147) days in Chagas cardiomyopathy patients and 151 (43, 804) days in non-Chagas cardiomyopathy patients (pb0.005). Probability of freedom from shock occurrence was similar in Chagas and non-Chagas cardiomyopathy patients (Fig. 1). Median follow upwas 292 (78, 845) days in Chagas and 654 (158, 987) days in non-Chagas cardiomyopathy patients (pb0.005). Three (9%) patients died during the study period; 2 in Chagas and 1 in non-Chagas patients (pN0.05). The frequency of shock occurrence observed in our Chagas cardiomyopathy cohort in this study was similar to that reported in patients with non-Chagas cardiomyopathy [3]. The lower mortality rate observed in our study in comparison to studies of secondary prevention of SCD [4] in Chagas disease patients may partially be explained by the lower frequency of shock occurrence. Also, the frequency of shock episodes observed in this investigation was lower than that seen in Chagas disease patients receiving ICD therapy for secondary prevention of SCD [4–6]. This can account, at least in part, for the similarity of mortality rate observed in our study in comparison to that seen in non-Chagas cardiomyopathy patients [7]. The higher frequency of VF episodes/per patient observed in Chagas cardiomyopathy patients in this study can also reflect the characteristics of the pathogenesis of Chagas disease [8]. In patients with Chagas cardiomyopathy, foci of confluent fibrosis intermingled with mononuclear cell infiltrate disseminated throughout the myocardium are frequently seen. Moreover, myocardial ischemia

The Contradiction of Appropriate Shocks in Primary Prevention ICDs

> Do I contradict myself? Very well, then I contradict myself, I am large, I contain multitudes. > > —Walt Whitman1 It is a common fault of true believers to celebrate successful reinforcement of their belief system and to dismiss failures. Such has been the case with the evolution of implantable cardioverter-defibrillator (ICD) therapy. Evidence-based guidelines, national health care coverage determinations (CAG-00157R3, January 27, 2005), and clinical practice have been transformed by large randomized clinical trials demonstrating that ICDs reduce mortality in patients with reduced left ventricular ejection fraction (EF), regardless of etiology or accompanying symptoms of heart failure, and with no history of sustained ventricular tachyarrhythmia (VTA) or cardiac arrest.1a,2 This reduction in mortality is due entirely to prevention of sudden cardiac death (SCD) by VTA.3 Consequently, primary prevention ICDs have become an important healthcare industry, with heavily invested stakeholders (implanting physicians, medical device manufacturers, and hospitals) pursuing the same relentless mission: how can we get more ICDs into qualifying patients? Article see p 2645 A few years ago, in an editorial arguing for national coverage determinations to align with evidence-based medicine, I wrote that in an earlier era intellectual opposition to the idea of the ICD was antivisionary.4,5 However, it now seems that contemporary application of primary prevention ICD therapy has become an anti-intellectual endeavor. Twenty years later, the translation to clinical practice has devolved to low EF, needs ICD. The problem with this declaration is that it is wrong on both points. At least 50% of SCD occurs in nonqualifying patients with normal or near-normal range EFs, and need is difficult to accept when absolute risk reduction is 1% to 3%1,2 and the morbidity consequences of ICD therapy are substantial. Nonetheless, primary prevention ICDs are here to stay and efforts to refine …

Driving Guidelines and Restrictions in Patients With a History of Cardiac Arrhythmias, Syncope,or Implantable Devices

The need to drive is universal in many countries. Patients with syncope, cardiac arrhythmias, or implantable cardioverter-defibrillators (ICDs) have an ongoing risk of sudden incapacitation that may cause harm to themselves and/or others when driving. Restrictions on driving and driving guidelines have been developed with the intent to reduce and prevent motor vehicle accidents, thereby improving personal and public safety. Several guidelines and consensus statements recently were updated. This review focuses on the syncope-related driving guidelines and restrictions. Driving issues related to other causes of loss of consciousness, such as drug or alcohol intoxication, epilepsy, or metabolic disorders, are not included in this review. Approximately 1% to 3% of all motor vehicle accidents are caused by the driver's sudden incapacitation; of these accidents, 5% to 10% are related to cardiac causes, with or without syncope. Major cardiac causes of syncope are neurally mediated mechanisms, bradycardia, and tachycardia. When the cause of syncope is determined and adequately treated, no driving restrictions are usually required after treatment is implemented. Patients who receive ICD therapy for primary or secondary sudden cardiac death prevention are at risk for future device discharges and sudden incapacitation whether or not they are driving. When the cause of syncope is unknown, the response to treatment is uncertain (such as treating the neurocardiogenic/vasovagal syncope), or ICD discharge is possible, driving recommendations are based on the estimation of "risk of harm while driving" and the general consensus on the threshold of "acceptable risk of harm." The annual risk of harm while driving can be estimated by the following formula: driving time (%) × vehicle type (commercial to private) × annual risk of syncope or incapacitation × probability of injury or accident.

Cost-effectiveness of implantable cardioverter defibrillators in patients ≥65 years of age

More than 80% of sudden cardiac deaths (SCDs) occur in patients >or=65 years old; the cost-effectiveness of implantable cardioverter defibrillator (ICD) therapy in older patients remains unclear. We sought to examine the cost-effectiveness of ICD therapy in at-risk patients >or=65 years old.We developed a Markov model to evaluate lifetime costs and benefits of ICD therapy compared with optimal medical therapy in patients >or=65 years of age with left ventricular dysfunction. Data were derived from the literature and existing clinical trials of primary prevention of SCD. Outcome measures included life years, quality-adjusted life years, costs, and incremental cost-effectiveness.Benefits and costs of ICD therapy in older individuals varied widely by clinical-trial population. In the 5 trials considered, for patients >or=65 years of age, ICDs demonstrated a life expectancy benefit compared with control therapy (incremental cost-effectiveness ratios ranging from $37,031-$138,458 per quality-adjusted life year). For 75-year-old patients, the findings were qualitatively similar, although cost-effectiveness was reduced in all trial populations. In sensitivity analyses, cost-effectiveness of ICD therapy in older individuals depended upon the trial population, quality of life, device cost, and frequency of generator replacement. Sensitivity analyses on other variables did not change the results substantially.The cost-effectiveness of ICD therapy for primary prevention in older patients varies widely among trials. Given an aging US population and the high risk of SCD in these individuals, further studies of ICD therapy and their cost-effectiveness-specifically in older patients-are needed.

Implantable defibrillator therapy for ventricular tachyarrhythmia in left ventricular assist device patients

Ventricular arrhythmias (VA) occur frequently after permanent left ventricular assist device (LVAD) implantation in end stage heart failure. Left ventricular assist device patients require rhythm control in contrast to patients with biventricular support. However, the rationale for implantable cardioverter-defibrillator (ICD) utilization in LVAD patients remains unclear. This study investigated the safety and efficacy of primary prevention ICD therapy and the rate of appropriate ICD interventions in LVAD patients. We prospectively collected data from patients receiving LVADs. Patients without previous ICD received an ICD after LVAD implantation for primary prevention. Sixty-one patients with LVAD and ICD were followed prospectively for 365 +/- 321 days. Nine patients died from thromboembolism or haemorrhage. Overall, the rate of appropriate ICD interventions was 34%, mostly for treatment of monomorphic VT in 52%, polymorphic VT in 13%, and VF in 35%. Seventy-one percent of VA were terminated by overdrive pacing, 29% by shock. Patients with a history of VA before LVAD implantation had a significantly higher 1-year rate for ICD therapy compared with LVAD patients with a primary prevention ICD indication LVAD patients (50 vs. 24%). Similarly, patients with non-ischaemic cardiomyopathy had a significantly higher risk for ICD therapy than patients with ischaemic heart disease (50 vs. 22%). Implantable cardioverter-defibrillator therapy is safe and effective in LVAD patients. Ventricular arrhythmias leading to ICD intervention occur frequently in 34% of LVAD patients after 1 year, with large variations depending on the underlying cardiac disease and previous arrhythmia history. Primary prevention ICD indication after LVAD implantation yields high rates of ICD intervention. A history of previous VA strongly predicts future use of ICD treatment after LVAD implantation.

Noninvasive Arrhythmia Risk Assessment in Guiding Pharmacologic Therapy for Prevention of Sudden Cardiac Death: Where Do We Stand? Where Do We Go?

Noninvasive Arrhythmia Risk Assessment in Guiding Pharmacologic Therapy for Prevention of Sudden Cardiac Death: Where Do We Stand? Where Do We Go?

Clinical Summaries

Clinical Summaries

Update on primary prevention implantable cardioverter-defibrillator therapy

Although the death rate from cardiovascular disease has decreased, nearly 2400 Americans die from cardiovascular disease each day (an average of one person every 37 seconds). Sudden cardiac death (SCD) affects individuals in the prime of their lives, with resuscitation rates successful in only a minority of patients, in part due to absent defibrillation by lay responders. After the publication of positive trials, the Centers for Medicare & Medicaid Services approved the implantable cardioverter-defibrillator (ICD) for the primary prevention of SCD. More recently, ICD therapy also has been shown to be effective for the primary prevention of SCD in patients with systolic heart failure, sometimes with the addition of cardiac resynchronization therapy. This article reviews the current status of primary prevention ICD therapy.

Current status of implantable cardioverter-defibrillator therapy in heart failure

Sudden cardiac arrest is one of the leading causes of death in patients with heart failure (HF). The implantable cardioverter-defibrillator (ICD) is the only evidence-based treatment strategy for patients who have survived a life-threatening ventricular arrhythmic event. Randomized clinical trials have shown that specific subsets of HF patients with ischemic and nonischemic dilated cardiomyopathy benefit from ICD therapy for primary prevention of sudden cardiac arrest. Cardiac resynchronization therapy has become the device-based therapy of choice for improving symptoms and survival in severe HF patients with evidence of ventricular dyssynchrony. This review summarizes the current status of ICD therapy in treating HF patients based on randomized clinical trials and current practice guidelines.

Do some implant too many defibrillators or others too few?

Since the landmark trials MADIT II, SCD-HeFT, and COMPANION have reported their positive results in 2002–05,1–3 the indications for the use of implantable cardioverter-defibrillators (ICDs) have substantially broadened. However, the ‘MADIT II shock’ affected many physicians and it has repeatedly been questioned if and how these results should be translated into daily clinical practice. Major concerns are listed in Table 1 . View this table: Table 1 Objective and subjective reasons for not providing patients with an indication for primary prevention of sudden cardiac death with an ICD Some more recent publications have fuelled the impression that at least in Europe and the USA, there may be too many ICD implantations. An important post hoc analysis of MADIT II suggests that patients who are (apart from their severely depressed left ventricular function) ‘too healthy’ and those who have too many co-morbidities (renal failure, atrial fibrillation, etc.) may not benefit from ICD implantation.4 Also in patients with severely depressed left ventricular function after myocardial infarction, it seems as if all-cause mortality cannot be reduced significantly if the ICD is implanted within the first month after the event.5 In addition, device and lead recalls and safety alerts question the safety of ICD therapy. Finally, a post hoc analysis of SCD-HeFT found an association between ICD shock discharges and mortality.6 Therefore, the euphoria about ICD therapy for primary prevention of … *Corresponding author. Tel: +49 521 772 77525, Fax: +49 521 772 77526, Email: c.w.israel{at}em.uni-frankfurt.de

Arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVCM) is a genetically determined disease characterized by the progressive replacement of cardiomyocytes by fibrofatty tissue, predominantly in the right ventricle. It leads to electrical instability and is therefore a major cause of sudden cardiac death (SCD) in apparently healthy young individuals, particularly in athletes. The diagnosis of ARVCM can be challenging and is based on a set of major and minor criteria which include structural, functional, histological, imaging, electrocardiographic and anamnestic parameters. ARVCM can be diagnosed, when two major criteria, or one major and two minor criteria, or four minor criteria from different categories are present. An implantable cardioverter defibrillator (ICD) should be used in patients who were resuscitated from SCD or who present with sustained ventricular tachycardia or otherwise unexplained syncope. The role of ICD therapy in primary prevention of SCD is a matter of ongoing debate and has to be decided on an individualized basis. Due to the familial accumulation of the disease, the screening of relatives is important. For the symptomatic treatment of arrhythmias, beta-blockers, sotalol, amiodarone and catheter ablation can be used. Arrhythmias in patients with ARVCM often occur in conjunction with physical exercise. Patients with ARVCM should therefore abstain from competitive sports or leisure-time activities where any possible loss of consciousness poses an increased hazard (scuba diving, hang gliding, parachuting, etc.).

Cost Effectiveness of Implantable Cardioverter-Defibrillators for Primary Prevention in a Belgian Context

Implantable cardioverter-defibrillator (ICD) therapy was traditionally applied in patients who survived a cardiac arrest or who experienced a symptomatic ventricular tachyarrhythmia. Its use in primary prevention (i.e. in patients who have yet to experience a serious arrhythmic event, but who are considered at high risk for sudden cardiac death) has become more common, and policy makers question whether ICD therapy should be reimbursed in these instances. To assess the cost effectiveness of primary prevention ICD therapy versus conventional therapy from the perspective of the Belgian health insurance system. A lifetime 1-month cycle Markov model was constructed and populated with clinical and effectiveness data from the SCD-HeFT study and real-world Belgian cost data expressed in year 2005 values. Probabilistic modelling and sensitivity analyses were performed. ICD therapy results in 1.22 life-years gained (LYG) or 1.03 QALYs gained. The lifetime cost-effectiveness and cost-utility ratios were euro 59,989 (95% CI 35 873, 113 518) per LYG and euro 71 428 (95% CI 40 225, 134 623) per QALY gained, respectively. A cost-effectiveness ratio <euro 50,000 per QALY gained was obtained in 15.5% of 1000 simulations. Increasing the service life of the device from 5 to 7 years would improve the cost effectiveness to euro 57,229 (95% CI 32 568, 106 410) per QALY gained. ICD therapy may not be judged cost effective for the primary prevention of death in patients with a SCD-HeFT profile in the Belgian context using current technology and patient selection. A combination of price reductions and increased service life of the device may alter this conclusion.

Is Microvolt T-Wave Alternans the Answer to Risk Stratification in Heart Failure?

Despite recent advances in the prevention and treatment of cardiovascular disease, sudden cardiac death (SCD) still accounts for ≈50% of all cardiovascular deaths in developed countries, thus accounting for a significant proportion of annual death worldwide.1 Reduction of the incidence of SCD depends on identification of those at most risk. In the present review we will concentrate on the challenges of risk stratification for SCD in chronic heart failure (CHF). We evaluate the utility of microvolt T-wave alternans (MTWA) as a tool for predicting SCD and consider whether MTWA is currently a valid means of selecting which patients should, or should not, receive an implantable cardioverter-defibrillator (ICD). Until recently, attempts to prevent SCD relied on pharmacological therapy. β-Blockers,2 angiotensin-converting enzyme inhibitors,3 angiotensin receptor blockers4 and aldosterone antagonists5 modestly reduce the risk of SCD in patients with CHF and after myocardial infarction (MI), whereas antiarrhythmic therapy has largely failed.6 Despite such treatments, these patients remained at high risk until the advent of the ICD. Although ICDs have further reduced the risk of SCD, they are expensive and can be associated with significant morbidity; therefore, precisely targeting their use is crucial. Implantation of ICDs for secondary prevention is clear. Prior sustained ventricular arrhythmia confers high risk and the benefit/risk balance is clearly favorable.7 Also, the secondary prevention population is relatively small and readily identified, thus the financial costs are not insurmountable. Primary prevention ICD therapy is an entirely different scenario. Large, randomized controlled trials have shown a mortality benefit with ICDs in patients with a low left ventricular ejection fraction (LVEF) and a history of MI or CHF.6,8 However, 2 major concerns have restricted implementation of this strategy. First, although analyses have estimated an acceptable cost-effectiveness profile,9 the immediate cost of implanting devices …

Sex Differences in the Use of Implantable Cardioverter-Defibrillators for Primary and Secondary Prevention of Sudden Cardiac Death

Previous studies of sex differences in the use of implantable cardioverter-defibrillators (ICDs) predate recent expansions in Medicare coverage and did not provide patient follow-up over multiple years. To examine sex differences in ICD use for primary and secondary prevention of sudden cardiac death. Analysis of a 5% national sample of research-identifiable files obtained from the US Centers for Medicare & Medicaid Services for the period 1991 through 2005. Patients were those aged 65 years or older with Medicare fee-for-service coverage and diagnosed with acute myocardial infarction and either heart failure or cardiomyopathy but no prior cardiac arrest or ventricular tachycardia (ie, the primary prevention cohort [n = 65,917 men and 70,504 women]), or with cardiac arrest or ventricular tachycardia (ie, the secondary prevention cohort [n = 52,252 men and 47,411 women]), from 1999 through 2005. Receipt of ICD therapy and all-cause mortality at 1 year. In the 2005 primary prevention cohort, 32.3 per 1000 men and 8.6 per 1000 women received ICD therapy within 1 year of cohort entry. In multivariate analyses, men were more likely than women to receive ICD therapy (hazard ratio [HR], 3.15; 95% confidence interval [CI], 2.86-3.47). Among men and women alive at 180 days after cohort entry, the hazard of mortality in the subsequent year was not significantly lower among those who received ICD therapy (HR, 1.01; 95% CI, 0.82-1.23). In the 2005 secondary prevention cohort, 102.2 per 1000 men and 38.4 per 1000 women received ICD therapy. Controlling for demographic variables and comorbid conditions, men were more likely than women to receive ICD therapy (HR, 2.44; 95% CI, 2.30-2.59). Among men and women alive at 30 days after cohort entry, the hazard of mortality in the subsequent year was significantly lower among those who received ICD therapy (HR, 0.65; 95% CI, 0.60-0.71). In the Medicare population, women are significantly less likely than men to receive ICD therapy for primary or secondary prevention of sudden cardiac death.