This systematic review and meta-analysis demonstrate that patients with NCCM who are judged to be at increased risk for SCD may significantly benefit from ICD therapy. The pooled analysis, after adjusting for study population and follow-up time, demonstrates an appropriate ICD therapy rate of 11.95 per 100 person-years, and by that, almost certainly preventing SCD. The inappropriate therapy rate was 4.8 per 100 person-years. The cardiac mortality rate was 2.37 per 100 person-years. This study did not find any SCD incidents as a reason of mortality in the study population. Complications were observed in 10% of the patients, with lead-type complications as the most frequent complication; lead malfunctions and lead revisions were present in 4% of patients, lead displacement in 3%, infection in 2%, and pneumothorax in 2%.
Clearly, risk stratification of patients with NCCM is important for management decisions regarding pharmacological therapy and ICD implantation. The 2015 ESC guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death recommend the same approach for NCCM as dilated cardiomyopathy (DCM); patients with ventricular arrhythmias require optimum pharmacological treatment, and ventricular arrhythmia triggering causes should be treated. Patients with hemodynamically intolerable ventricular tachycardia or ventricular fibrillations with a life expectancy of more than one year (class 1A recommendation) or symptomatic heart failure with an LVEF of 35 percent or less despite at least three months of optimum pharmacological therapy may consider an ICD.
Ventricular arrhythmias are frequently reported, up to 47%, in patients with NCCM . Kaya et al. suggest prophylactic ICD implantation in patients with non-sustained ventricular tachycardia recordings on Holter in the setting of LV dysfunction (LVEF < 50%), familial history of SCD before 50 years, and early repolarization and/or fragmented QRS on ECG .
In clinical practice, an empiric individualized risk stratification for NCCM patients is utilized for decision-making. In secondary prevention of SCD, an ICD is always advised. The studies included in this meta-analysis used the ESC guidelines or comparable decision strategy for the implantation of ICDs in the included patients. In the present analysis, 66% received an ICD for primary prevention of SCD. Secondary prevention ICD implantation was performed in 34%.
Ertuğrul et al.  included pediatric patients in their study. They followed the ESC guidelines, which recommend ICD implantation in patients younger than sixteen years after a life-threatening ventricular arrhythmia. ICD implantation as primary prevention in patients younger than sixteen years is recommended when 2 or more major risk factors are present: severe left ventricular hypertrophy, syncope, NSVT, or a family history of sudden death .
The present analysis found appropriate ICD therapies were substantially more frequent than inappropriate ICD therapies, with a difference of 7.15 events per 100 person-years. This result, combined with zero events of SCD and a low cardiac mortality rate, shows the positive effects of ICD therapy on preventing SCD in NCCM patients as well as suggesting that no failure to shock occurred in any patient in this study.
However, the inappropriate therapy rate of 4.8 per 100 person-years together with a high incidence of complications is a serious concern, which necessitates a good counseling process before ICD implantation, especially because of the relatively young mean age (38.6 years) of the patient population.
Not all currently known risk factors of SCD were described in each study. However, most patients in this meta-analysis were at increased risk of SCD considering 29% had a family history of SCD, 19% had experienced ventricular tachycardia before ICD implantation, and 4 of the 6 studies, who measured the mean LVEF, had a mean LVEF of 35% or less.
Most of the patients in this pooled analysis received a conventional transvenous single chamber ICD system. Only 1 study included patients who received subcutaneous ICDs (S-ICD). An S-ICD could theoretically bring down the number of complications, considering the most frequent complications in this study were transvenous lead related. Only 3% of the patients in this study received a S-ICD; hence, more information on the use of S-ICD in NCCM is needed.
Firstly, this study included existing abstracts. This resulted in more studies with fewer information and outcomes than full-text articles, such as no description of which guidelines were used to implement an ICD. Secondly, five studies were excluded from the meta-analysis because these studies did not describe a specific follow-up duration for NCCM patients exclusively. Zero event studies could not be included in the meta-analysis. Both the appropriate ICD therapy and cardiac mortality meta-analysis results could therefore be higher in this study than in reality. Next, the decision strategy regarding the ICD implantation strategy was not specified. This meta-analysis did not exclude studies based on age and included one study with pediatric patients. ICD therapy in pediatric patients with NCCM is not well studied and an ICD may have other outcomes in these patients. Finally, the gap between the oldest and latest study is 11 years. Experience with ICD implantation and programming may have improved significantly during that time period.