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............................................................................................................................................................................. 6.1.1 Secondary prevention of sudden cardiac death Compared with amiodarone treatment, ICDs reduce mortality in survivors of cardiac arrest and in patients who have experienced sustained symptomatic ventricular arrhythmias. An ICD is recommended in such patients when the intent is to increase survival; the decision to implant should take into account the patient’s view and their QOL, the LVEF (survival benefit is uncertain when LVEF >35%) and the absence of other diseases likely to cause death within the following year.162164,184

6.1.2 Primary prevention of sudden cardiac death In an analysis of over 40 000 patients from 12 pivotal HF trials, rates of sudden cardiac death decreased by 44% over the 20-year period (from the mid-1990s to 2015).160 This is almost certainly due to advances in HF treatment, as many key guideline-recommended therapies, including beta-blockers, MRAs, sacubitril/valsartan, and CRT pacemakers (CRT-P), reduce the risk of sudden death. While the afore-mentioned HF therapies have been shown to reduce mortality in patients with HFrEF, amiodarone has not.161 However, if it is to be used, it should be with caution due to its significant side-effect profile. Conversely, dronedarone185 and the class I antiarrhythmic agents disopyramide, encainide, and flecainide186 should not be used for prevention of arrhythmias due to the increase in mortality seen in clinical studies. Although an ICD reduces the rate of sudden arrhythmic death in patients with HFrEF,187 it would be expected that, in well-managed patients, the additional benefit afforded by an ICD would be lower. In the DANISH trial, rates of sudden death were low in patients with nonischaemic cardiomyopathy (NICM); only 70 patients out of 1116 followed up over 5 years had sudden death.166 Whilst there was a modest absolute reduction in sudden death with a defibrillator-containing device, this did not significantly improve the overall risk of mortality. However, subgroup analysis suggested there was a benefit in those <_70 years.188 In a recent meta-analysis of studies that examined the effect of ICDs in NICM a survival benefit was still seen, although the effect was significantly weakened by the inclusion of the DANISH trial.167 On average, patients with IHD are at greater risk of sudden death than patients with NICM and therefore, although the relative benefits are similar, the absolute benefit is greater in patients with IHD.187 Two RCTs showed no benefit in patients who had an ICD implanted within 40 days after a MI.177,178 Although sudden arrhythmic deaths were reduced, this was balanced by an increase in non-arrhythmic deaths. Accordingly, an ICD for primary prevention is contraindicated in this time period. Furthermore, ICD implantation is recommended only if a minimum of 3 months of OMT has failed to increase the LVEF to >35%. OMT ideally includes the use of Class I recommended drugs for HFrEF. However, the ICD trials we cite predate the use of ARNI and SGLT2 inhibitors. Whether implantation of ICDs reduces mortality in those with an LVEF >35% is unknown. There is an ongoing trial of ICD therapy in such patients with the presence of scar on CMR imaging.189

6.1.3 Patient selection for implantable cardioverterdefibrillator therapy Patients with HFrEF and a QRS duration >_130 ms can be considered for CRT with a defibrillator (CRT-D) rather than ICD. See the section on CRT for further details (section 6.2). In patients with moderate or severe HF, a reduction in sudden death may be partially or wholly offset by an increase in death due to worsening HF.161 As such, ICD therapy is not recommended in patients in NYHA class IV, with severe symptoms refractory to pharmacological therapy, who are not candidates for a ventricular assist device (VAD) or cardiac transplantation. Such patients have a very limited life expectancy and are likely to die from pump failure. Similarly, patients with serious comorbidities who are unlikely to survive substantially more than 1 year with good QOL are unlikely to obtain substantial benefit from an ICD.179183

Although the DANISH trial did not show a significant benefit from ICD therapy in patients with NICM, it should be remembered that NICM is a heterogeneous condition, and certain subgroups (e.g. laminopathies, sarcoidosis) are at higher risk of sudden death and therefore merit careful consideration of ICD implantation. Tools to help risk stratification (e.g. scar burden on magnetic resonance imaging) can be helpful in that regard.190192 Patients should be counselled as to the purpose of an ICD and involved in the decision-making process. They should also be aware of the potential complications related to implantation, any additional implications for driving, and the risk of inappropriate shocks. Furthermore, patients should be informed about the circumstances where the defibrillator (or defibrillator component of a CRT-D) might be deactivated (e.g. terminal disease) or explanted (e.g. infection or recovery of LV function).193 Subsequent timely conversations regarding defibrillator deactivation should be held with the patient and caregiver(s). When an ICD generator reaches its end of life or requires explantation, it should not be replaced automatically. Rather, shared decision making should be undertaken.168172 Patients should be carefully evaluated by an experienced cardiologist as treatment goals may have changed since implantation (the risk of fatal arrhythmia may be lower, or the risk of non-arrhythmic death may be higher). It is a matter of some controversy whether patients whose LVEF has greatly improved and who have not required device therapy during the lifetime of the ICD should have another device implanted.168172

6.1.4 Implantable cardioverter-defibrillator programming Routine defibrillation threshold testing is no longer performed following implantation of an ICD or CRT-D as it does not improve shock efficacy or reduce arrhythmic death.194 Conservative programming with long delays195 between detection and the ICD delivering therapy dramatically reduces the risk of both inappropriate and appropriate but unnecessary shocks.194,196,197 Generally, for primary prevention, defibrillators are programmed to minimize pacing (e.g. ventricular demand pacing VVI at 40/min), and with a tachycardia treatment zone >200/min.194,198 Ultimately—and particularly for secondary prevention—programming should be adapted according to the patient’s specific needs.

6.1.5 Subcutaneous and wearable implantable cardioverter-defibrillators Subcutaneous ICDs (S-ICDs) appear to be as effective as conventional transvenous ICDs with a similar complication rate. Although the risk of inappropriate shocks appeared to be higher initially, Downloaded from academic.oup.com/eurheartj/article/42/36/3599/6358045 by guest on 07 October 2026