Influence of patient characteristics in the selection of patients for defibrillator implantation (the AVID Registry). Antiarrhythmics Versus Implantable Defibrillators

The role of multimodality imaging in the selection for implantable cardioverter-defibrillators in heart failure: A narrative review

Advanced pharmacologic and interventional therapies have improved survival in heart failure. Implantable cardioverter-defibrillators (ICD) have been shown to reduce mortality in patients with heart failure, but the benefit appears to be uneven in this population. We reviewed the evidence showing the benefit of ICD therapy in heart failure patients, the main issues arising from these studies, and the possible answers for a better risk stratification. In addition, we showed that multimodality imaging could improve patient selection for the implantation of ICDs, in both primary and secondary prevention, beyond the selection using only the left ventricular ejection fraction, by concentrating on arrhythmic substrate.

Evaluating sex differences in population-based utilization of implantable cardioverter-defibrillators: role of cardiac conditions and noncardiac comorbidities

BACKGROUND

The influence of age and comorbidities on sex-specific implantable cardioverter-defibrillator (ICD) use for primary or secondary prevention is undefined.

OBJECTIVE

The purpose of this study was to investigate the influence of age and comorbidities on sex-specific ICD use.

METHODS

Sex disparities and sex-specific trends in ICD implantation according to indication in patients with cardiac arrest (1998-2007) in Ontario, Canada, were examined. Use of ICDs for primary prevention in patients with myocardial infarction (2002-2007) or heart failure (2005-2007) also was examined.

RESULTS

Among 9,246 eligible secondary prevention patients (age 66.3 +/- 14.3 years; 3,577 women [39%]) with cardiac arrest, men were more likely to undergo ICD implantation, with an age-, comorbidity-, and arrhythmia-adjusted hazard ratio (HR) of 1.92 (95% confidence interval [CI]: 1.66-2.23). Among 105,516 patients with myocardial infarction (age 68.3 +/- 12.7 years; 42,987 women [41%]), men were threefold more likely to undergo ICD implantation, with an adjusted HR of 3.00 (95% CI: 2.53-3.55). Among 61,160 patients with heart failure (age 76.2 +/- 12.0 years; 31,575 women [52%]), ICD implantation was more likely in men, with an adjusted HR of 3.01 (95% CI: 2.59-3.50). The odds of ICD implant for secondary prevention increased over time by 21% (95% CI: 13%-30%) in women and by 6% (95% CI: 2%-11%) in men, but rates of ICD use in men for primary prevention indications were persistently higher.

CONCLUSION

Men were more likely to undergo defibrillator implant than were women for primary and secondary prevention. Age and comorbidities did not account for the observed sex differences. Although sex differences in secondary prevention are declining over time, disparities in primary prevention persist.

Amiodarone: what have we learned from clinical trials?

Amiodarone is an antiarrhythmic agent commonly used in the treatment of supraventricular and ventricular tachyarrhythmias. This paper reviews clinical trials in which amiodarone was used in one of the treatment arms. Key post-myocardial infarction trials include EMIAT and CAMIAT, both of which demonstrated that amiodarone reduced arrhythmic but not overall mortality. In patients with congestive heart failure (CHF), amiodarone was associated with a neutral survival in CHF/STAT and improvement in survival in GESICA. In patients with nonsustained ventricular tachycardia, the MADIT trial demonstrated that therapy with an implantable cardioverter-defibrillator (ICD) improved survival compared with the antiarrhythmic drug arm in such patients, most of whom were taking amiodarone. In sustained VT/VF patients, the CASCADE trial demonstrated that empiric amiodarone lowered arrhythmic recurrence rates compared with other drugs guided by serial Holter or electrophysiologic studies. Several trials including AVID, CIDS, and CASH have demonstrated the superiority of ICD therapy compared with empiric amiodarone in improving overall survival. Clinical implications of these trials are discussed.

Effect of Cardiac and Noncardiac Conditions on Survival After Defibrillator Implantation

OBJECTIVES

We sought to examine outcomes in recipients of implantable cardioverter-defibrillators (ICDs) and the effect of age, gender, and comorbidities on survival.

BACKGROUND

Age, gender, and comorbidities may significantly affect outcomes in ICD recipients.

METHODS

We examined factors associated with mortality in 2,467 ICD recipients in Ontario, Canada, using a province-wide database. Comorbidities were identified retrospectively by examining all diagnosis codes within the 3 years before implant.

RESULTS

Mean ages at ICD implant were 63.2 +/- 12.5 years (1,944 men) and 59.8 +/- 15.9 years (523 women). Mortality rates at one and 2 years were 7.8% and 14.0%. Older age at implant increased the risk of death with hazard ratios (HR) of 2.05 (95% confidence interval [CI] 1.70 to 2.47) and 3.00 (95% CI 2.43 to 3.71) for those 65 to 74 years and >/=75 years, respectively (both p < 0.001), but gender was not a predictor of death. Common noncardiac conditions associated with death included peripheral vascular disease (adjusted HR 1.50, 95% CI 1.18 to 1.91), pulmonary disease (adjusted HR 1.35, 95% CI 1.10 to 1.66), and renal disease (adjusted HR 1.57, 95% CI 1.25 to 1.99). Many ICD recipients had prior heart failure (46.2%) with an increased HR of 2.33 for death (95% CI 1.96 to 2.76; p < 0.001). Greater comorbidity burden conferred increased risk, with HRs adjusted for age, gender, and heart failure of 1.72 (95% CI 1.44 to 2.05), 2.79 (95% CI 2.15 to 3.62), and 2.98 (95% CI 1.74 to 5.10) for those with 1, 2, and 3 or more noncardiac comorbidities, respectively (all p < 0.001).

CONCLUSIONS

Age, noncardiac comorbidities, and prior heart failure influence survival outcomes in ICD recipients. These factors should be considered in the care of ICD recipients.

Implantable cardioverter-defibrillators should be used routinely in the elderly

Implantable cardioverter-defibrillators (ICDs) reduce mortality in selected high-risk populations by reducing the risk of sudden death. No clinical trial examining ICD efficacy has focused specifically on benefits and risks in the elderly, but all trials have included substantial numbers of older patients. The author addresses several issues: Is the risk of sudden death different for the elderly than in younger patients? Is ICD implantation feasible in the elderly? Is there evidence that ICD use in the elderly improves survival? The author's research indicates that while total mortality is higher for the elderly, there does not appear to be a specific predilection for arrhythmic death. Recent reports indicate that while ICDs can be implanted in a Medicare population, ICD implantation is associated with significant mortality (0.9%), as well as periprocedural complications (10.8%). In spite of the risks, both secondary and primary prevention trials demonstrate that the survival benefit associated with ICD use in the study populations was at least as great for elderly patients as for younger persons. Thus, published data support judicious ICD use in elderly patients at high risk for sudden death.

Disparities in the use of primary prevention and defibrillator therapy among blacks and women

OBJECTIVES

This study determines whether there are racial or gender disparities in the use of implantable cardioverter-defibrillator therapy for primary prevention of sudden cardiac death.

BACKGROUND

Primary prevention of sudden death with implantable cardioverter-defibrillator therapy has been shown to improve survival for high-risk patients with coronary artery disease and left ventricular dysfunction.

METHODS

The Center for Medicare and Medicaid Services Medicare database from the year 2002 was used to identify patients who were potential candidates for implantable cardioverter-defibrillator therapy on the basis of a combination of International Classification of Diseases, Ninth Revision, Clinical Modification codes that reflected the presence of an ischemic cardiomyopathy. This cohort was analyzed to determine which patients received implantable cardioverter-defibrillator therapy during the same year. The clinical characteristics of the potential implantable cardioverter-defibrillator candidates were compared with those who actually received an implantable cardioverter-defibrillator.

RESULTS

A total 132565 Medicare patients hospitalized during 2002 were identified as having an ischemic cardiomyopathy; 10370 (8%) of these patients underwent implantable cardioverter-defibrillator implantation during the same year. The percentage of patients who underwent implantable cardioverter-defibrillator implantation was higher for men compared with women (10.2% vs 3.5%; P<.001) and whites compared with blacks (8.1 vs 5.4; P<.001). After multivariate analysis, age, gender, and race remained independent predictors of implantable cardioverter-defibrillator implantation. Women with an ischemic cardiomyopathy were 65% less likely to receive implantable cardioverter-defibrillator therapy compared with men (P<.001), and black patients were 31% less likely to receive implantable cardioverter-defibrillator therapy compared with patients of other races (P < .001).

CONCLUSIONS

Use of implantable cardioverter-defibrillator therapy for primary prevention of sudden death among the elderly population identified as having an ischemic cardiomyopathy was significantly lower among women compared with men, and among blacks compared with whites. Further exploration of gender and racial barriers to appropriate implantable cardioverter-defibrillator use for primary prevention is needed.

Mortality Reduction by Implantable Cardioverter-Defibrillators in High-Risk Patients With Heart Failure, Ischemic Heart Disease, and New-Onset Ventricular Arrhythmia

OBJECTIVES

To investigate the generalizability of the reduction in mortality posed by implantable cardioverter-defibrillators, we examined the effectiveness of defibrillators as applied in routine medical practice.

BACKGROUND

Implantable cardioverter-defibrillators have been shown to be efficacious in the primary and secondary prevention of overall and cardiovascular mortality in clinical trials.

METHODS

Using the National Veterans Administration database, we identified a cohort of 6,996 patients from 1995 to 1999 with new-onset ventricular arrhythmia and pre-existing ischemic heart disease and congestive heart failure, of which 1,442 received a defibrillator, and followed them for three years to determine rates of mortality. With multivariate logistic regression analyses that adjusted for demographics, illness severity, and comorbidity, we assessed overall, cardiovascular, and noncardiovascular rates of mortality. To further address potential confounding, we also stratified the cohort by quintiles using a multivariable propensity score for each patient and determined mortality rates.

RESULTS

For the overall cohort, multivariate regression showed that those who received defibrillators had significantly lower all-cause (odds ratio [OR] 0.52; 95% confidence interval [CI] 0.45 to 0.60) and cardiovascular (OR 0.56; 95% CI 0.49 to 0.65)] rates of mortality at three years. No significant differences were noted between groups in their rates of noncardiovascular mortality (OR 0.92; 95% CI 0.77 to 1.10). Propensity score analysis demonstrated similar mortality reduction benefits at three years: risk ratio (RR) 0.72 (95% CI 0.69 to 0.79) for all-cause; RR 0.70 (95% CI 0.63 to 0.78) for cardiovascular; and RR 0.95 (95% CI 0.83 to 1.08) for noncardiovascular rates of mortality. These results suggest that one death is prevented in this patient population for every four to five patients receiving a defibrillator for three years.

CONCLUSIONS

Implantable cardioverter-defibrillators in routine medical practice significantly reduce cardiovascular and all-cause rates of mortality at levels similar to secondary prevention trials.

Management of ventricular arrhythmias in diverse populations in California

BACKGROUND

The use of coronary angiography and revascularization is lower than expected among black patients. It is uncertain whether use of other cardiac procedures also varies according to race and ethnicity and whether outcomes are affected.

METHODS

We analyzed discharge abstracts from all nonfederal hospitals in California of patients hospitalized for a primary diagnosis of ventricular tachycardia or ventricular fibrillation between 1992 and 1994. We compared mortality rates and use of electrophysiologic study (EPS) and implantable cardioverter-defibrillator (ICD) procedures according to the race and ethnicity of the patient.

RESULTS

Among 8713 patients admitted with ventricular tachycardia or ventricular fibrillation, 29% (n = 2508) had a subsequent EPS procedure, and 9% (n = 818) had an ICD implanted. After controlling for potential confounding factors, we found that black patients were significantly less likely than white patients to undergo EPS (odds ratio 0.72, CI 0.56-0.92) or ICD implantation (odds ratio 0.39, CI 0.25-0.60). Blacks discharged alive from the initial hospital admission had higher mortality rates over the next year than white patients, even after controlling for multiple confounding risk factors (risk ratio 1.18, CI 1.03-1.36). The use of EPS and ICD procedures was also significantly affected by several other factors, most notably by on-site procedure availability but also by age, sex, and insurance status.

CONCLUSIONS

In a large population of patients hospitalized for ventricular arrhythmia, blacks had significantly lower rates of utilization for EPS and ICD procedures and higher subsequent mortality rates.

Outcome studies with device therapy in patients with heart failure

Heart failure is a common debilitating condition for which pharmacologic therapy thus far has provided only partial relief. Despite, and sometimes because of, medical therapy, the overall prognosis remains poor, with high rates of sudden death and death from progressive heart failure. Device-based therapies offer considerable promise for relief of symptoms and for improving prognosis. It is clear that implantable defibrillators should be considered for patients with heart failure who have been resuscitated from ventricular fibrillation or sustained ventricular tachycardia. Several large studies currently are investigating the effects of implantable defibrillators on total mortality in patients with major left ventricular systolic dysfunction but without other risk factors for sudden death. Cardiac resynchronization is a promising new therapy that may relieve the symptoms of heart failure in appropriately selected patients resistant to optimal pharmacologic therapy. Two large trials (CARE-HF and COMPANION) currently are investigating the effects of cardiac resynchronization therapy (CRT) on morbidity and mortality. It is important that those involved in these trials enroll patients quickly and minimize device implantation into patients who have not been assigned this therapy (cross-overs). Overenthusiasm for the benefits that doctors believe devices might bring could destroy the future basis for our clinical practice, denying future generations of patients and the doctors themselves access to what they believe to be effective treatments.

Leakage of energy to the body surface during defibrillation shock by an implantable cardioverter-defibrillator (ICD) system--experimental evaluation during defibrillation shocks through the right ventricular lead and the subcutaneous active-can in canines

The leakage of electrical current to the body surface during defibrillation shock delivery by an implantable cardioverter-defibrillator (ICD) device (the Medtronic Jewel Plus PCD system) was evaluated in 5 dogs. The defibrillation shocks were delivered between the active-can implanted in the left subclavicular region and the endocardial lead placed in the right ventricle at the energy levels of 1, 2, 8, 12, 24 and 34 J. During each delivery, the electrical current leakage from the body surface was measured by electrodes connected to a circuit at 4 recording positions: (A) parallel-subcutaneous (the electrodes were fixed in the subcutaneous tissue of the left shoulder and the right lower chest, and the direction of the electrode vector was parallel to the direction of the defibrillation energy flow); (B) cross-subcutaneous (the electrodes were fixed in the subcutaneous tissue of the right shoulder and the left lower chest, and the vector of the electrodes was roughly perpendicular to the direction of the energy flow); (C) parallel-surface (the electrodes were fixed with ECG paste on the shaved skin surface at the left shoulder and the right lower chest); and (D) surface grounded (the electrodes were fixed on the shaved skin surface at the left shoulder and the left foot, which was grounded). The circuit resistance was set at a variable level (100-5,000 ohms) in accordance with the resistance measured through each canine body. Leakage energies were measured in 750 defibrillation shocks with each circuit resistance in 5 dogs. The leakage energy increased in accordance with the increase of the delivered energy and the decrease of the circuit resistance in all 4 recording positions. When the circuit resistance was set at 1,000 ohms, the leakage energy during shock delivery at 34 J was 32+/-17 mJ at position A, 5+/-9 mJ at B, 10+/-9 mJ at C, and 4+/-3 mJ at D (p=0.042). The peak current was highest at position A and was 87+/-22 mA with a circuit resistance of 1,000 ohms. The power of the leakage energy depended on the delivered energy and the impedance between the electrodes. The angle between the alignment of the recording electrodes and the direction of the energy flow was another important factor in determining the leakage energy. Although the peak current of the leakage energy reached the level of macro shock, the highest leakage energy from the body surface was considerably less because of the short duration of the shock delivery.

Do baseline characteristics accurately discriminate between patients likely versus unlikely to benefit from implantable defibrillator therapy? Evaluation of the Canadian implantable defibrillator study implantable cardioverter defibrillatory efficacy score in the antiarrhythmics versus implantable defibrillators trial

OBJECTIVE

Our purpose was to evaluate whether baseline characteristics predictive of implantable cardioverter defibrillator (ICD) efficacy in the Canadian Implantable Defibrillator Study (CIDS) are predictive in the Antiarrhythmics Versus Implantable Defibrillators (AVID) Trial.

BACKGROUND

ICD therapy is superior to antiarrhythmic drug use in patients with life-threatening arrhythmias. However, identification of subgroups most likely to benefit from ICD therapy may be useful. Data from CIDS suggest that 3 characteristics (age > or =70 years, ejection fraction [EF] < or =0.35, and New York Heart Association class >II) can be combined to reliably categorize patients as likely (> or =2 characteristics) versus unlikely to benefit (<2 characteristics) from ICD therapy.

METHODS

The utility of the CIDS categorization of ICD efficacy was assessed by Kaplan-Meier analysis and Cox hazards modeling. The accuracy of the CIDS score was formally tested by evaluating for interaction between categorization of benefit and treatment in a Cox model.

RESULTS

ICD therapy was associated with a significantly lower risk of death in the 320 patients categorized as likely to benefit (relative risk [RR] 0.57, 95% confidence interval [CI] 0.37-0.88, P =.01) and a trend toward a lower risk of death in the 689 patients categorized as unlikely to benefit (RR 0.70, 95% CI 0.48-1.03, P =.07). Categorization of benefit was imperfect, as evidenced by a lack of statistical interaction (P =.5). Although 32 of the 42 deaths prevented by ICD therapy in AVID were in patients categorized as likely to benefit, all 42 of these patients had EF values < or =0.35. Neither advanced age nor poorer functional class predicted ICD efficacy in AVID.

CONCLUSION

Of the 3 characteristics identified to predict ICD efficacy in CIDS, only depressed EF predicted ICD efficacy in AVID. Thus physicians faced with limited resources might elect to consider ICD therapy over antiarrhythmic drug use in patients with severely depressed EF values.

Amiodarone: clinical trials

Amiodarone is an antiarrhythmic agent commonly used in the treatment of supraventricular and ventricular tachyarrhythmias. This article reviews the results and clinical implications of primary and secondary prevention trials in which amiodarone was used in one of the treatment arms. Key post-myocardial infarction primary prevention trials include the European Myocardial Infarct Amiodarone Trial (EMIAT) and the Canadian Amiodarone Myocardial Infarction Trial (CAMIAT), both of which demonstrated that amiodarone reduced arrhythmic but not overall mortality. In congestive heart failure patients, amiodarone was studied as a primary prevention strategy in two pivotal trials: Grupo de Estudio de la Sobrevida en la Insuficiencia Cardiac en Argentina (GESICA) and Amiodarone in Patients With Congestive Heart Failure and Asymptomatic Ventricular Arrhythmia (CHF-STAT). Amiodarone was associated with a neutral overall survival and a trend toward improved survival in nonischemic cardiomyopathy patients in CHF/STAT and improved survival in GESICA. In post-myocardial infarction patients with nonsustained ventricular tachycardia and a depressed ejection fraction, the Multicenter Automatic Defibrillator Implantation Trial (MADIT) demonstrated that implantable cardioverter-defibrillators (ICD) statistically improved survival compared to the antiarrhythmic drug arm, most of whose patients were taking amiodarone. In patients with histories of sustained ventricular tachycardia or ventricular fibrillation, the Cardiac Arrest Study in Seattle: Conventional Versus Amiodarone Drug Evaluation (CASCADE) trial demonstrated that empiric amiodarone lowered arrhythmic recurrence rates compared to other drugs guided by serial Holter or electrophysiologic studies. However, arrhythmic death rates were high in both treatment arms of the study. Several secondary prevention trials, including the Antiarrhythmics Versus Implantable Defibrillators Study (AVID), the Canadian Implantable Defibrillator Study (CIDS), and the Cardiac Arrest Study Hamburg (CASH), have demonstrated the superiority of ICD therapy compared to empiric amiodarone in improving overall survival. Based on the above findings, amiodarone is safe to use in post-myocardial infarction and congestive heart failure patients that need antiarrhythmic therapy. Although amiodarone is effective in treating malignant arrhythmias, high-risk patients should be considered for an ICD as frontline therapy.

Beta-blocker use and survival in patients with ventricular fibrillation or symptomatic ventricular tachycardia: the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial

OBJECTIVES

To evaluate whether use of beta-adrenergic blocking agents, alone or in combination with specific antiarrhythmic therapy, is associated with improved survival in persons with ventricular fibrillation (VF) or symptomatic ventricular tachycardia (VT).

BACKGROUND

The ability of beta-blockers to alter the mortality of patients with VF or VT receiving contemporary medical management is not well defined.

METHODS

Survival of 1,016 randomized and 2,101 eligible, nonrandomized patients with VF or symptomatic VT followed in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial through December 31, 1996 was assessed using Cox proportional hazards analysis.

RESULTS

The 817 (28%) patients discharged from hospital receiving beta-blockers had less ventricular dysfunction, fewer symptoms of heart failure and a different pattern of medication use compared with patients not receiving beta-blockers. Before adjustment for important prognostic variables, beta-blockade was not significantly associated with survival in randomized or in eligible, nonrandomized patients treated with specific antiarrhythmic therapy. After adjustment, beta-blockade remained unrelated to survival in randomized or in eligible, nonrandomized patients treated with amiodarone alone (n = 1142; adjusted relative risk [RR] = 0.96; 95% confidence interval [CI] 0.64-1.45; p = 0.85) or a defibrillator alone (n = 1347; adjusted RR = 0.88; 95% CI 0.55 to 1.40; p = 0.58). In contrast, beta-blockade was independently associated with improved survival in eligible, nonrandomized patients who were not treated with specific antiarrhythmic therapy (n = 412; adjusted RR = 0.47; 95% CI 0.25 to 0.88; p = 0.018).

CONCLUSIONS

Beta-blocker use was independently associated with improved survival in patients with VF or symptomatic VT who were not treated with specific antiarrhythmic therapy, but a protective effect was not prominent in patients already receiving amiodarone or a defibrillator.

Implantable cardioverter-defibrillators

Implantable defibrillators have become the dominant therapeutic modality for patients with life-threatening ventricular arrhythmias. Current defibrillators are small (<60 mL) and implanted with techniques similar to standard pacemakers. They provide high-energy shocks for ventricular fibrillation and rapid ventricular tachycardia, antitachycardia pacing for monomorphic ventricular tachycardia, as well as antibradycardia pacing. Newer devices incorporating an atrial lead allow dual-chamber pacing and better discrimination between ventricular and supraventricular tachyarrhythmias. Randomized controlled trials have shown superior survival with implantable defibrillators than with antiarrhythmic drugs in survivors of life-threatening ventricular tachyarrhythmias and in high-risk patients with coronary artery disease. Complications associated with implantable defibrillator therapy include infection, lead failure, and spurious shocks for supraventricular tachyarrhythmias. Most patients adapt well to living with an implantable defibrillator, although driving often has to be restricted. Limited evidence suggests that implantable defibrillator therapy is cost-effective when compared with other widely accepted treatments. The use of implantable defibrillators is likely to continue to expand in the future. Ongoing clinical trials will define further prophylactic indications of the implantable defibrillator and clarify its cost-effectiveness ratio in different clinical settings.

A decade of clinical trial developments in postmyocardial infarction, congestive heart failure, and sustained ventricular tachyarrhythmia patients: from CAST to AVID and beyond. Cardiac Arrhythmic Suppression Trial. Antiarrhythmic Versus Implantable Defibrillators

Multiple trials using antiarrhythmic drugs, pharmacologic therapy, and implantable cardioverter defibrillators have been performed in an attempt to improve survival in patients: (1) postmyocardial infarction; (2) with congestive heart failure, with and without nonsustained ventricular tachycardia; and (3) with sustained ventricular tachycardia and those who have survived an out-of-hospital cardiac arrest. This article reviews some of the key findings and limitations of completed and ongoing trials. We also make recommendations for the current treatment of such patients based on the results of these trials.