ICM and NICM
Supported by strong evidences from RCTs, prophylactic implantation of an ICD, a class I recommendation in HF patient with ICM and reduced left ventricular systolic function, can reduce mortality compared with conventional drug therapy [36,37]. Contrarily, DANISH trials demonstrated that ICD for primary prevention in patients with heart failure caused by non-ischemic etiology did not improve survival benefits [38]. This meta-analysis presented a similar result that ICM patients with CRT indication can benefit from an additional ICD therapy rather than NICM patients. It may be explained by a higher risk of death from fatal arrhythmia in patients with ICM. Moreover, several studies reported that patients with NICM have a better improvement in LV systolic function and LV reverse remodeling compared with patients with ICM [39,40], which resulted in a further reduction of the risk of SCD and ventricular tachyarrhythmias [41]. Above all, it may suggest a less needed of an additional ICD for primary prevention in NICM patients due to a sufficiently reduction of fatal tachyarrhythmias by CRT-P alone.