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Canadian Journal of Cardiology

Implantable Cardioverter-Defibrillators in Sudden Cardiac Death Survivors: Are We Doing All We Can?

Published:September 06, 2017DOI:https://doi.org/10.1016/j.cjca.2017.07.016
      Sudden cardiac death (SCD) refers to sudden circulatory collapse leading to death, caused by a dangerous ventricular arrhythmia that is unheralded or occurs within 1 hour of the onset of symptoms. SCD is a leading cause of death in Canada and in the Western world, killing 40,000 Canadians each year, affecting men and women alike. It is projected to be the number one cause of mortality in the world by 2020.
      • Murray C.J.
      • Lopez A.D.
      Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study.
      SCD is the leading cause of potential life-years lost, estimating the burden of premature death for men to be 2.04 million potential life-years lost in the United States, and 1.29 million life-years for women.
      • Stecker E.C.
      • Reinier K.
      • Marijon E.
      • et al.
      Public health burden of sudden cardiac death in the United States.
      This burden of years of life lost is greater than that for all individual cancers, and other leading causes of death.
      SCD can be aborted if an electrical shock is administered within a few minutes of a ventricular arrhythmia. Unfortunately, < 10% of people who experience SCD outside of the hospital setting are successfully resuscitated, despite community awareness campaigns and wide distribution of automated external defibrillators.
      • Stiell I.G.
      • Wells G.A.
      • Field B.
      • et al.
      Advanced cardiac life support in out-of-hospital cardiac arrest.
      Patients who survived an out-of-hospital cardiac arrest are at high risk of recurrence, when reversible causes for the cardiac arrest are not contributory. Implantable cardioverter-defibrillator (ICD) therapy is able to rapidly detect ventricular arrhythmia and terminate it. ICDs are proven to be effective in reducing SCD in patients at high risk, and are associated with a significant survival benefit in the population, as evidenced by several randomized trials.
      Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators
      A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias.
      • Kuck K.H.
      • Cappato R.
      • Siebels J.
      • Ruppel R.
      Randomized comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from cardiac arrest: the Cardiac Arrest Study Hamburg (CASH).
      • Connolly S.J.
      • Gent M.
      • Roberts R.S.
      • et al.
      Canadian implantable defibrillator study (CIDS): a randomized trial of the implantable cardioverter defibrillator against amiodarone.
      ICD therapy rapidly treats ventricular arrhythmia, virtually eliminating neurological impairment, and decreases the risk of death by more than 30%. Practice guidelines recommend ICDs be used in patients who have survived a cardiac arrest, not found to be due to a reversible cause; this was a class I indication in the 2005 Canadian Cardiovascular Society device guidelines, most recently updated in 2016.
      • Tang A.S.
      • Ross H.
      • Simpson C.S.
      • et al.
      Canadian Cardiovascular Society/Canadian Heart Rhythm Society position paper on implantable cardioverter defibrillator use in Canada.
      • Bennett M.
      • Parkash R.
      • Nery P.
      • et al.
      Canadian Cardiovascular Society/Canadian Heart Rhythm Society 2016 implantable cardioverter-defibrillator guidelines.
      Previous studies from a decade ago reported that the ICD implantation rate in survivors of out of hospital cardiac arrest in the province of Ontario was low, ranging from 12% to 26.7%.
      • Parkash R.
      • Tang A.
      • Wells G.
      • et al.
      Use of implantable cardioverter defibrillators after out-of-hospital cardiac arrest: a prospective follow-up study.
      • Birnie D.H.
      • Sambell C.
      • Johansen H.
      • et al.
      Use of implantable cardioverter defibrillators in Canadian and US survivors of out-of-hospital cardiac arrest.
      This utilization rate was lower than that of the United States, where in the study by Birnie et al., it was reported to be 30.2%, over the same time period of study.
      • Birnie D.H.
      • Sambell C.
      • Johansen H.
      • et al.
      Use of implantable cardioverter defibrillators in Canadian and US survivors of out-of-hospital cardiac arrest.
      The study by Dorian et al., in this issue of the Canadian Journal of Cardiology, provides important, contemporary data on this issue.
      • Ho E.C.
      • Cheskes S.
      • Angaran P.
      • et al.
      on behalf of the Rescu Epistry Investigators
      Implantable cardioverter defibrillator implantation rates after out of hospital cardiac arrest: are the rates guideline-concordant?.
      Dorian et al. used the Toronto Epistry study to identify a cohort of patients who survived a cardiac arrest in the greater Toronto area, and subsequently determined the rate of in-hospital ICD implantation. Rescu Epistry is comprised of data from the Resuscitation Outcomes Consortium Epistry-Cardiac Arrest database and the Strategies for Post Arrest Care database.
      • Morrison L.J.
      • Nichol G.
      • Rea T.D.
      • et al.
      Rationale, development and implementation of the Resuscitation Outcomes Consortium Epistry-Cardiac Arrest.
      The study was conducted between 2011 and 2014 in the greater Toronto area, in a catchment area of 6.6 million people and 42 hospitals. Using registry data, the authors made an excellent attempt to carefully identify a “likely ICD-eligible” population, defined as those with all 3 criteria: (1) a shockable initial rhythm (ventricular tachycardia/fibrillation); (2) no definite ischemia; and (3) a good neurologic outcome. They reported that the ICD implantation rate in this cohort was 57%. Although ICD utilization increased from 46.3% of “likely ICD-eligible” patients in 2011 to 63.8% in 2014 (P = 0.05); this rate remains lower than would be expected for a population of patients who have survived an out of hospital cardiac arrest (particularly where Dorian et al.
      • Ho E.C.
      • Cheskes S.
      • Angaran P.
      • et al.
      on behalf of the Rescu Epistry Investigators
      Implantable cardioverter defibrillator implantation rates after out of hospital cardiac arrest: are the rates guideline-concordant?.
      made a thorough attempt at identifying the “likely ICD-eligible” population).
      There are, however, some important limitations to this study. The definition of “likely ICD-eligible” lacked information on other patient comorbidities, exact circumstances of the arrest, and whether a reversible cause was truly present. Because of this lack of additional data in this study, there is the possibility of misclassification bias. In addition, this study was performed in an urban region, where the findings might not be generalizable to a rural setting. Nevertheless, the overall ICD implantation rate in patients who have survived out of hospital cardiac arrest in this study remains abysmally low overall (23.9%) in this contemporary setting, with some light at the end of the tunnel if the ICD-eligible group is in fact accurately described. This study, and others, have identified factors that affect ICD utilization in primary as well as secondary prevention cohorts of ICD-eligible patients. The hospital location (urban vs rural), teaching vs nonteaching, and the ability to implant an ICD on-site have an effect on the appropriate use of these devices.
      • Parkash R.
      • Wightman H.
      • Miles G.
      • et al.
      Primary prevention of sudden cardiac death with device therapy in urban and rural populations.
      • Sadarmin P.P.
      • Wong K.C.
      • Rajappan K.
      • Bashir Y.
      • Betts T.R.
      Barriers to patients eligible for screening investigations and insertion of primary prevention implantable cardioverter defibrillators.
      Despite this study being performed in a primarily urban region, patients who presented to hospitals that were not able to implant ICDs were less likely to receive ICDs (odds ratio, 0.63; 95% confidence interval, 0.44-0.89) than those who presented to an ICD-capable institution.
      The authors conclude that ICD utilization in this population is not guideline-compliant, and further work is required to determine the factors behind this observation. This study highlights the importance of implementation of guidelines with knowledge translation programs that might assist in identifying truly eligible patients for primary as well as secondary prevention ICDs, and thus providing this life-saving therapy where a significant effect would occur on the rate of SCD in Canada. Programs targeting easier access to automatic external defibrillators and knowledge of cardiopulmonary resuscitation have led to improvements in survival from out of hospital cardiac arrest, in jurisdictions such as King County, Washington, The Netherlands, and Denmark.
      • Nichol G.
      • Cobb L.A.
      • Yin L.
      • et al.
      Briefer activation time is associated with better outcomes after out-of-hospital cardiac arrest.
      • Wissenberg M.
      • Lippert F.K.
      • Folke F.
      • et al.
      Association of national initiatives to improve cardiac arrest management with rates of bystander intervention and patient survival after out-of-hospital cardiac arrest.
      • Blom M.T.
      • Beesems S.G.
      • Homma P.C.
      • et al.
      Improved survival after out-of-hospital cardiac arrest and use of automated external defibrillators.
      In Canada, the Cardiac Arrhythmia Network of Canada (CANet; https://canet-nce.ca) has set one of its many goals as reduction of SCD. The findings from Dorian et al. provide strong support for the importance of the activities of a network like CANet. With the collective improvement of public awareness of SCD in Canada through the efforts of groups like CANet, as well as better risk factor identification of SCD, and improved knowledge translation to patients and care givers, SCD could be significantly reduced. The study by Dorian et al.
      • Ho E.C.
      • Cheskes S.
      • Angaran P.
      • et al.
      on behalf of the Rescu Epistry Investigators
      Implantable cardioverter defibrillator implantation rates after out of hospital cardiac arrest: are the rates guideline-concordant?.
      provides critical context in identifying the issue of ICD utilization in a population of patients at high risk for SCD, and provides important justification for increasing programs to improve our treatment of survivors from SCD.

      Disclosures

      The authors have no conflicts of interest to disclose.

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