Percutaneous coronary intervention and the need for an implantable cardioverter-defibrillator after out-of-hospital cardiac arrest

A successful strategy for secondary prevention for survivors of out-of-hospital cardiac arrest (OHCA) is based on the identification and effective management of the underlying diseases and co-morbidities. Cardiac diseases associated with sudden cardiac arrest (SCA) differ depending on age. Cardiomyopathies, channelopathies, myocarditis, and substance abuse are more common in adolescents and younger adults,1–3 while individuals beyond 40–50 years of age more frequently suffer from chronic degenerative cardiovascular diseases, including coronary artery disease (CAD), heart failure, and valvular heart diseases as the underlying cause of SCA.4,5 Accuracy in the identification of a single underlying cause of SCA may be challenging because older individuals may have multiple chronic cardiovascular conditions simultaneously.6 Approximately one-half of all OHCA patients have no known underlying heart disease, but most of them suffer from undiagnosed ischaemic heart disease.4 A case-based cohort analysis from the Framingham study revealed a 50% higher risk of sudden death in the presence of a family history of SCA.7 Additionally, familial sudden death occurs more frequently in individuals resuscitated from primary VF than in controls.8 These data suggest a genetic disposition for sudden death even without a known Mendelian disease. In patients with ischaemic heart disease, several tools have been proposed to predict the risk of SCA, including heart rate variability, baroreflex sensitivity, microvolt T-wave alternans, heart rate turbulence, QT interval dispersion, and programmed ventricular stimulation. Disappointingly, despite early positive results, none of these parameters influenced clinical decision-making. The only reliable predictor of SCA in ischaemic heart disease is left ventricular ejection fraction (LVEF).9 Over a mean follow-up of almost 3 years, the crude death rate was 36.4% in the patients treated medically.10 Treatment with antiarrhythmic drugs was either neutral (amiodarone) or increased the risk of SCA.11,12 Implantation of a cardioverter-defibrillator is associated with a 50% and a 28% reduction in arrhythmic mortality and total mortality, respectively.13 Based on these findings, current guidelines suggest that implantable cardioverter-defibrillator (ICD) implantation is recommended in patients with documented VF in the absence of reversible causes or within 48 h after myocardial infarction (MI) and who are receiving chronic optimal medical therapy and have a reasonable expectation of survival with a good functional status over more than 1 year.6 In the current issue of the journal, Sharifzadehgan et al.14 analysed data from the prospective Paris Sudden Death Expertise Center (Paris-SDEC) registry and included all patients with SCA related to a cardiac cause brought alive. They described the characteristics of patients discharged from the hospital without ICD after survival of OHCA. Out of the 4,314 SCA survivors admitted to the hospital, 1064 cardiac-related SCA survivors who were discharged were alive, and 356 patients (33.5%) underwent ICD implantation. The underlying cause of SCA among individuals who were discharged without an ICD was acute coronary syndrome (ACS) in 85% of them, chronic CAD in 5.8%, structural non-ischaemic heart disease in 6.8%, and non-structural heart disease in 2.4%. Among patients with ACS-related SCA, 93.8% were discharged without an ICD. Immediate coronary angioplasty in the setting of ACS was closely related to discharge without implantation of an ICD. This finding clearly challenges the precision and accuracy of the diagnosis of ACS (Figure 1). Percutaneous coronary interventions, residual SCD risk, and implantable cardioverter-defibrillators after out-of-hospital cardiac arrest (OCHA, out of hospital cardiac arrest; hsTnI, high sensitivity troponin I; HCM, hypertrophic cardiomyopathy; ACS, acute coronary syndrome; ICD, implantable cardioverter-defibrillator). The major strengths of this study are the large sample size of this multicentre registry and the exhaustive data analyses. However, there are some important limitations that have to be considered when translating results into clinical practice. First, the interventional cardiologist’s decision to perform PCI was a major factor that influenced the decision to implant or not to implant an ICD. Intracoronary imaging was not systematically performed. Additionally, detailed information regarding coronary lesion morphology is not available. Thus, it remains elusive if coronary lesions fixed by angioplasty have been the true culprit lesions. Some patients might have undergone stenting of lesions and might be considered ‘innocent bystanders’ without causing any impact on the outcome. Thus, additional chronic cardiovascular conditions might leave patients at high risk for recurrent SCA. Second, there is no information according to the type of MI. However, risk reduction associated with coronary revascularization may differ between Type 1 and Type 2 MI. Finally, completeness of revascularization is unknown. Residual myocardial ischaemia may influence future SCA risk and might influence the decision to perform ICD implantation. In the study by Sharifzadehgan et al.,14 13.1% of ACS patients who survived SCA had a prior history of CAD, and 28.6% had LVEF dysfunction at discharge. A total of 84.5% of individuals with a history of CAD were discharged without ICD implantation. Moreover, out of the 85.5% of ACS patients who survived SCA and underwent immediate coronary angioplasty, 9.5% were discharged with LVEF dysfunction (LVEF below 35%). Remarkably, 88.5% of individuals with impaired LVEF were discharged without an ICD. As already mentioned, current guidelines suggest that ICD implantation is recommended in patients with documented VF who receive chronic optimal medical therapy.6 Left ventricular ejection fraction may improve after revascularization and with guideline-directed medical therapy resulting in a reduction of the residual arrhythmogenic risk. However, this study emphasizes that the diagnosis of ACS may influence the decision-making in favour of withholding ICD implantation even with additional findings that may increase future SCA risk. Currently, the jury is still out on the debate on the appropriateness of ICD implantations in such patients, and additional prospective studies are needed to assess the risk of SCA in patients discharged without an ICD. According to current guidelines, ICD implantation is not indicated in OHCA survivors with documented VF when a reversible cause can be identified or within 48 h after MI. The present study14 found that ACS has been diagnosed in a large majority (85%) of OHCA survivors discharged without an ICD. Additionally, immediate coronary angioplasty in the setting of ACS was strongly related to discharge without implantation of an ICD. These decision pathways seem to be evidence-based and are supported by international guidelines.6 Acute coronary syndrome diagnosis in patients admitted for SCA is usually based on ECG changes and elevated cardiac biomarkers. However, the specificity of such findings may be lower soon after resuscitation for an SCA when compared with that for other individuals. Thus in OHCA patients, the accuracy of the diagnosis of an ACS might be impaired. The finding of a coronary artery stenosis and implantation of a coronary stent should not be a substitute for an appropriate adjudication of diagnosis, possibly by a multidisciplinary cardiac arrest team. A high degree of suspicion is warranted to identify additional or alternative causes of the SCA that may persist despite coronary angioplasty and could increase the residual risk for recurrent SCA when ICD implantation is omitted. Conflict of interest: None declared.