***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The publication of major studies dealing with the natural history of bradyarrhythmias and tachyarrhythmias and major advances in the technology of pacemakers and implantable cardioverter-defibrillators ( ICDs ) has m and ated this revision of the 1991 ACC/AHA Guidelines for Implantation of Pacemakers and Antiarrhythmia Devices . This executive summary appears in the April 7 , 1998 issue of Circulation . The full text of the guidelines , including the ACC/AHA Class I , II , and III recommendations , is published in the April 1998 issue of the Journal of the American College of Cardiology . Reprints of both the executive summary and the full text are available from both organizations . Following extensive review of the medical literature and related documents previously published by the American College of Cardiology , the American Heart Association , and the North American Society for Pacing and Electrophysiology , the writing committee developed recommendations that are evidence based whenever possible . Evidence supporting current recommendations is ranked as level A if the data were derived from multiple r and omized clinical trials involving a large number of individuals . Evidence was ranked as level B when data were derived from a limited number of trials involving comparatively small numbers of patients or from well- design ed data analysis of nonr and omized studies or observational data registries . Evidence was ranked as level C when consensus of expert opinion was the primary source of recommendation . The committee emphasizes that for certain conditions for which no other therapies are available , the indications for device therapies are based on years of clinical experience as well as expert consensus and are thus well supported , even though the evidence was ranked as level C. These guidelines include exp and ed sections on selection of pacemakers and ICDs , optimization of technology , cost , and follow-up of implanted devices . The follow-up sections are relatively brief because in many instances the type and frequency of follow-up examinations BACKGROUND We conducted a prospect i ve , multicenter , r and omized comparison of implantable cardioverter-defibrillator ( ICD ) versus antiarrhythmic drug therapy in survivors of cardiac arrest secondary to documented ventricular arrhythmias . METHODS AND RESULTS From 1987 , eligible patients were r and omized to an ICD , amiodarone , propafenone , or metoprolol ( ICD versus antiarrhythmic agents r and omization ratio 1:3 ) . Assignment to propafenone was discontinued in March 1992 , after an interim analysis conducted in 58 patients showed a 61 % higher all-cause mortality rate than in 61 ICD patients during a follow-up of 11.3 months . The study continued to recruit 288 patients in the remaining 3 study groups ; of these , 99 were assigned to ICDs , 92 to amiodarone , and 97 to metoprolol . The primary end point was all-cause mortality . The study was terminated in March 1998 , when all patients had concluded a minimum 2-year follow-up . Over a mean follow-up of 57+/-34 months , the crude death rates were 36.4 % ( 95 % CI 26.9 % to 46.6 % ) in the ICD and 44.4 % ( 95 % CI 37.2 % to 51.8 % ) in the amiodarone/metoprolol arm . Overall survival was higher , though not significantly , in patients assigned to ICD than in those assigned to drug therapy ( 1-sided P=0.081 , hazard ratio 0.766 , [ 97.5 % CI upper bound 1.112 ] ) . In ICD patients , the percent reductions in all-cause mortality were 41.9 % , 39.3 % , 28 . 4 % , 27.7 % , 22.8 % , 11.4 % , 9.1 % , 10.6 % , and 24.7 % at years 1 to 9 of follow-up . CONCLUSIONS During long-term follow-up of cardiac arrest survivors , therapy with an ICD is associated with a 23 % ( nonsignificant ) reduction of all-cause mortality rates when compared with treatment with amiodarone/metoprolol . The benefit of ICD therapy is more evident during the first 5 years after the index event Background —Implantable cardioverter defibrillator ( ICD ) use reduces mortality in patients with serious ventricular arrhythmias compared with antiarrhythmic drug ( AAD ) use . However , the relative impact of these therapies on self-perceived quality of life ( QoL ) is unknown . Methods and Results —Three self-administered instruments were used to measure generic and disease-specific QoL in  Antiarrhythmics  Versus  Implantable Defibrillators  trial participants . Generalized linear models were used to assess the relationships between self-perceived QoL and treatment ( AAD versus ICD ) and adverse symptoms and ICD shocks . To minimize the impact of missing data , only patients surviving 1 year were included in the primary analyses . Baseline characteristics among QoL participants ( n=905 ) and non participants ( n=111 ) were similar , but participants who survived 1 year ( n=800 ) were healthier at baseline than nonsurvivors ( n=105 ) . Of the 800 patients in the primary analysis , characteristics of those r and omized to AAD ( n=384 ) versus ICD ( n=416 ) were similar . Overall , ICD and AAD use were associated with similar alterations in QoL. The development of sporadic shocks and adverse symptoms were each associated with reduced physical functioning and mental well-being and increased concerns among ICD recipients , whereas development of adverse symptoms was associated with reduced physical functioning and increased concerns among AAD recipients . Conclusions —ICD and AAD therapy are associated with similar alterations in self-perceived QoL over 1-year follow-up . Adverse symptoms were associated with reduced self-perceived QoL in both groups , and sporadic shocks were associated with reduced QoL in ICD recipients OBJECTIVES The purpose of this multicenter r and omized trial was to compare total mortality during therapy with amiodarone or an implantable cardioverter-defibrillator ( ICD ) in patients with nonischemic dilated cardiomyopathy ( NIDCM ) and nonsustained ventricular tachycardia ( NSVT ) . BACKGROUND Whether an ICD reduces mortality more than amiodarone in patients with NIDCM and NSVT is unknown . METHODS One hundred three patients with NIDCM , left ventricular ejection fraction < or = 0.35 , and asymptomatic NSVT were r and omized to receive either amiodarone or an ICD . The primary end point was total mortality . Secondary end points included arrhythmia-free survival , quality of life , and costs . RESULTS The study was stopped when the prospect i ve stopping rule for futility was reached . The percent of patients surviving at one year ( 90 % vs. 96 % ) and three years ( 88 % vs. 87 % ) in the amiodarone and ICD groups , respectively , were not statistically different ( p = 0.8 ) . Quality of life was also similar with each therapy ( p = NS ) . There was a trend with amiodarone , as compared to the ICD , towards improved arrhythmia-free survival ( p = 0.1 ) and lower costs during the first year of therapy ( $ 8,879 US dollars vs. $ 22,039 US dollars , p = 0.1 ) . CONCLUSIONS Mortality and quality of life in patients with NIDCM and NSVT treated with amiodarone or an ICD are not statistically different . There is a trend towards a more beneficial cost profile and improved arrhythmia-free survival with amiodarone therapy More than 1 million Americans per year have acute myocardial infa rct ion ( 1 ) . Those who survive to hospital discharge have a 5 % to 10 % risk for dying suddenly within the first year ( 27 ) . Prevention of those sudden deaths is an important goal , and several approaches have been used to accomplish it . Secondary prevention with type I antiarrhythmic drugs has been unsuccessful ( 8) . Prophylactic use of amiodarone has significantly reduced death after myocardial infa rct ion in some but not all r and omized trials . Quantitative overviews of these studies suggest that amiodarone reduces mortality rates by 10 % to 20 % ( 9 , 10 ) . Recent studies of the implantable cardioverter defibrillator ( ICD ) in patients who have no history of sustained arrhythmia have also had mixed results , with positive results in patients with unsustained ventricular tachycardia ( 11 , 12 ) and negative results in patients with reduced ejection fraction and positive results on signal-averaged electrocardiography ( 13 ) . The use of prophylactic ICD has nevertheless attracted great interest because of the demonstrated efficacy of the device in patients who have had a documented episode of ventricular fibrillation or sustained ventricular tachycardia ( 1416 ) . Although ongoing or planned r and omized , controlled trials ( 17 , 18 ) will clarify the role of ICDs and amiodarone therapy in patients who have had myocardial infa rct ions , the results of these trials will not be available until late 2001 at the earliest . We previously showed that ICDs can be cost-effective in patients who have survived an episode of ventricular fibrillation or sustained ventricular tachycardia ( 19 ) . These findings can not be extrapolated to prophylactic use of ICDs in patients who have had myocardial infa rct ions because the risk for sudden death in such patients is lower . Indeed , the current st and ard of care for patients who have had myocardial infa rct ion does not include prophylactic antiarrhythmic therapy . With recent evidence of the efficacy of antiarrhythmia management in patients who have had myocardial infa rct ions , the potential cost-effectiveness of prophylactic antiarrhythmic therapy should be reassessed . In this study , we estimated survival and costs for patients with past myocardial infa rct ion who were treated with amiodarone , ICD , or no specific antiarrhythmic therapy . We evaluated the level of efficacy needed to make  prophylactic therapy  with an ICD or amiodarone  cost-effective in three groups of patients with past myocardial infa rct ion who were stratified by left ventricular ejection fraction . Methods We used a decision model to estimate the length of life and expenditures for patients who had myocardial infa rct ion without symptomatic , sustained ventricular arrhythmia and who received one of three treatment strategies : ICD , amiodarone therapy , or no antiarrhythmic therapy ( Figure 1 ) . We stratified patients into three groups according to ejection fraction : less than or equal to 0.3 , 0.31 to 0.4 , and greater than 0.4 . Although the ability of many clinical factors to predict the risk for sudden cardiac death has been analyzed and several independent risk factors have been identified ( 20 ) , ejection fraction has consistently been the single most powerful predictor of sudden cardiac death ( 2124 ) . Figure 1 . The decision model . The square node on the left represents a choice among three alternative treatments : implantable cardiac defibrillator ( ICD ) , amiodarone , and no antiarrhythmic treatment . Circles represent chance nodes . Patients who receive an ICD are at risk for death from the implant procedure . Patients who do not die of ICD implantation and patients who are receiving amiodarone or no treatment enter the Markov tree ( denoted by rectangles containing circles and an arrow ) . The Markov tree represents the clinical events that can occur during each 1-month period as a patient is followed until death . During each 1-month period , a patient may die from arrhythmic or nonarrhythmic cardiac causes and may also die of noncardiac causes . If none of these events occur , the patient remains well for the 1-month period . Patients who have an ICD may have a lead infection or failure that causes them to withdraw from treatment ( and to switch to no antiarrhythmic therapy ) . Patients who receive amiodarone are at risk for amiodarone toxicity . In our analysis , a patient may die of toxicity , withdraw from treatment ( and switch to no antiarrhythmic therapy ) , or have acute toxicity that does not require discontinuation . We adhered to the recommendations of the Panel on Cost-effectiveness in Health and Medicine ( 25 , 26 ) . We used a societal perspective to evaluate health benefits and costs , discounting each at a rate of 3 % per year . We performed one-way sensitivity analyses on all of the model variables , as well as selected two-way , three-way , and n-way ( Monte Carlo ) probabilistic sensitivity analyses ( 27 ) . Decision Model We developed a Markov model ( 28 , 29 ) ( SMLTree decision analysis software , version 2.9 , J. Hollenberg , New York , New York ) by modifying a model used previously to assess the cost-effectiveness of ICDs or amiodarone in patients who had experienced sustained ventricular arrhythmia ( 19 , 30 ) ( Figure 1 ) . Our current model includes the possibility of no antiarrhythmic therapy and uses data relevant to the lower-risk population of patients who have survived myocardial infa rct ion . The model tracks a cohort of patients who received prophylactic ICD ( implanted without a thoracotomy ) , amiodarone therapy , or no antiarrhythmic therapy .  Patients who received an ICD were at risk for procedural death . Patients who survived ICD implantation , patients treated with amiodarone , and patients who received no antiarrhythmic therapy  entered a Markov tree ( Figure 1 ) . Each month , these patients were at risk for sudden cardiac death , nons 
    Output:
    
Implantable cardioverter defibrillators prevent sudden cardiac death regardless of baseline risk .
However , their impact on total mortality is sensitive to baseline risk for arrhythmic death .