The National Institute for Clinical Excellence (NICE) has recommended that implantable cardioverter defibrillators should be routinely considered for patients who have survived ventricular fibrillation or ventricular tachycardia with haemodynamic compromise for secondary prevention of arrhythmic death. It also recommends it in certain patients who have not yet had a serious arrhythmic event but who are at high risk of sudden cardiac death as primary prevention. This second group comprises mainly patients who have survived a myocardial infarction. Only a tiny minority of these patients is currently being investigated and treated with implantable defibrillators.
After an infarction, impaired ventricular function with an ejection fraction of 35% or less, non-sustained ventricular tachycardia (three beats or more) on ambulatory 24 hour monitoring, and inducible ventricular tachycardia at electrophysiological testing identify a subgroup of patients at high risk of sudden death. Paradoxically, antiarrhythmic drugs increase the risk of death and should be avoided in patients with significantly impaired ventricular function.1 At best, amiodarone decreases the risk of sudden death slightly but does not affect overall mortality, with a risk reduction of 13%-15%.2
Two prospective randomised controlled trials of preventive strategies have shown the benefit of the implantable cardioverter defibrillator in this high risk group. The multicentre automatic defibrillator trial, or MADIT, compared the implantable cardioverter defibrillator with best medical treatment, which included amiodarone in 74% of the control group.3 It was a relatively small study, justified by its sequential trial design. The multicentre unsustained tachycardia trial, or MUSTT, compared an electrophysiologically guided strategy with no antiarrhythmic therapy.4 The strategy involved serial drug testing—antiarrhythmic drugs were given, and the electrophysiology study repeated to determine if ventricular tachycardia could still be induced. Suppression of induction of ventricular tachycardia was deemed a success. If not, antiarrhythmic drugs were withdrawn and an implantable cardioverter defibrillator implanted. Although this was not a trial of the implantable cardioverter defibrillator itself, benefit was seen only in those patients treated with defibrillators.
Both these trials have shown that implantable cardioverter defibrillators confer a relative risk reduction of 54%-60% in all-cause mortality. Using this evidence the American College of Cardiology, American Heart Association,5 National Institute for Clinical Excellence,6 and European Society of Cardiology7 have all recommended using an implantable cardioverter defibrillator as a primary prevention strategy in such high risk patients. In addition, NICE recommends that screening programmes should be put in place so that these patients can be identified.
Screening requires assessment of ventricular function, 24 hour ambulatory monitoring in those with an ejection fraction of less than 35%, and an electrophysiological study in those with non-sustained ventricular tachycardia aimed at provoking sustained ventricular tachycardia. Despite the recommendation in September 2000 that screening programmes be put in place, there seems to be none in the United Kingdom. Screening should be undertaken as a cascade as identification requires all three criteria. Assessment of ventricular function is already required by the national service framework for heart disease, for which extra resource should be available, but only a minority of post-infarction patients undergo ambulatory monitoring and extremely few undergo electrophysiological studies.
Best guesses suggest that after an infarction about 1% of patients will fulfil all three criteria and therefore be considered for cardioverter defibrillator implantation.8–11 These estimates are based on a variety of assumptions—that 4%-16% of post-infarction patients will have an ejection fraction of 35% or less,8,10,11 of these 12%-16% will have non-sustained ventricular tachycardia on ambulatory monitoring,8,10 and that sustained ventricular tachycardia will be inducible at electrophysiological study in 22%-35% of these.11,12 There are 300 000 myocardial infarctions each year in the United Kingdom; over half the patients survive. Using these assumptions, over 1500 patients each year should be considered for an implantable cardioverter defibrillator as a primary prevention strategy. If the recommendations made by NICE are adopted many patients should be screened after infarction. About 24 000 should undergo ambulatory monitoring; 16%, or about 4000, should undergo electrophysiological study, and 1%, or about 250, should have a cardioverter defibrillator implanted.
Since the guidance from NICE was published, a further primary prevention trial (MADIT 2) has shown a relative reduction in mortality of 31% in post-infarction patients treated with an implantable cardioverter defibrillator compared with the control group receiving usual treatment.13 This trial used a much simplified selection criterion—ejection fraction less than 30% after myocardial infarction—obviating the need for the screening cascade described by NICE. It does suggest, however, that at least five times as many patients as fulfil the current NICE criteria might benefit from an implanted defibrillator.
Increasing the number of patients being investigated and treated according to the guidance from NICE will need much additional resource. Till then few British patients will receive the care recommended by NICE and widely available in the Western world.
Footnotes
JMM and AJC have received research grants and speaking fees from manufacturers of implantable cardioverter defibrillators. Both contributed advice to the health technology appraisal committee of NICE.
References
- 1.Cardiac Arrhythmia Suppression Trial (CAST) Investigators. Preliminary report: effect of encainide and flecainide on mortality in a randomized trial of arrhythmia suppression after myocardial infarction. N Engl J Med. 1989;321:406–412. doi: 10.1056/NEJM198908103210629. [DOI] [PubMed] [Google Scholar]
- 2.Connolly S. Evidence based analysis of amiodarone efficacy and safety. Circulation. 1999;100:2025–2034. doi: 10.1161/01.cir.100.19.2025. [DOI] [PubMed] [Google Scholar]
- 3.Moss A, Hall W, Cannom D, Daubert J, Higgins S, Klein H, et al. for the multicenter automatic defibrillator implantation trial investigators. Improved survival with an implantable defibrillator in patients with coronary disease at high risk for malignant ventricular arrhythmia N Engl J Med 19963351933–1940. [DOI] [PubMed] [Google Scholar]
- 4.Buxton A, Lee K, Fisher J, Josephson M, Prystowsky E, Hafley M. A randomized study of the prevention of sudden cardiac death in patients with cornary artery disease. N Engl J Med. 1999;341:1882–1890. doi: 10.1056/NEJM199912163412503. [DOI] [PubMed] [Google Scholar]
- 5.Gregatoros G, Cheitlin M, Connill A al e. ACC/AHA guidelines for implantation of cardiac pacemakers and antiarrhythmia devices. A report of the ACC/AHA task force on practice guidelines (committee on pacemaker implantation) J Am Coll Cardiol. 1998;31:1175–1206. doi: 10.1016/s0735-1097(98)00024-2. [DOI] [PubMed] [Google Scholar]
- 6.National Institute for Clinical Excellence. Guidance on the use of implantable cardioverter defibrillators for arrhythmias. London: National Institute for Clinical Excellence; 2000. [Google Scholar]
- 7.Hauer R, Aliot E, Block M, Capucci A, Luderitz B, Santini M, et al. Indications for implantable cardioverter defibrillator (ICD) therapy Study group on guidelines on ICDs of the working group on arrhythmias and the working group on cardiac pacing of the European Society of Cardiology. Eur Heart J. 2001;22:1074–1081. doi: 10.1053/euhj.2001.2584. [DOI] [PubMed] [Google Scholar]
- 8.Maggioni A, Zuanetti G, Franzosi M, Rovelli F, Santoro E, Stazewsky L, et al. Prevalence and prognostic significance of ventricular arrhythmias after acute myocardial infarction in the fibrinolytic era GISSI-2 results. Circulation. 1993;87:312–322. doi: 10.1161/01.cir.87.2.312. [DOI] [PubMed] [Google Scholar]
- 9.Every N, Hlatky M, McDonald K, Weaver W, Hallstrom A. Estimating the proportion of post myocardial infarction patients who may benefit from prophlactic implantable defibrillator placement from analysis of the CAST Registry. Am J Cardiol. 1998;82:683–685. doi: 10.1016/s0002-9149(98)00417-2. [DOI] [PubMed] [Google Scholar]
- 10.Hohnloser S, Klingenheben T, Zabel M, Shopperl M, Mauss O. Prevalence, characteristics and prognostic value during long term follow up of nonsustained ventricular tachycardia after myocardial infarction in the thrombolytic era. J Am Coll Cardiol. 1999;33:1895–1902. doi: 10.1016/s0735-1097(99)00108-4. [DOI] [PubMed] [Google Scholar]
- 11.Schmitt C, Barthel P, Ndrepepa G, Schreieck J, Plewan A, Schomig A, et al. Value of programmed ventricular stimulation for prophylactic internal cardioverter-defibrillator implantation in postinfarction patients preselected by noninvasive risk stratifiers. J Am Coll Cardiol. 2001;37:1901–1907. doi: 10.1016/s0735-1097(01)01246-3. [DOI] [PubMed] [Google Scholar]
- 12.Buxton A, Lee K, DiCarlo L, Gold M, Greer G, Prystowsky E, et al. for the multicenter unsustained tachycardia trial investigators. Electrophysiologic testing to identify patients with coronary artery disease who are at risk for sudden death. N Engl J Med. 2000;342:1937–1945. doi: 10.1056/NEJM200006293422602. [DOI] [PubMed] [Google Scholar]
- 13.Moss AJ, Zareba W, Hall WJ, Klein H, Wilber DJ, Cannom DS, et al. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med. 2002;346:877–883. doi: 10.1056/NEJMoa013474. [DOI] [PubMed] [Google Scholar]