This review concluded that the use of modern therapy with β-blocking medication is associated with a reduced absolute mortality benefit of ICD therapy in patients with depressed left ventricular systolic function. In view of multiple limitations in the review process as well as reporting, the authors' conclusions need to be interpreted very cautiously.

To evaluate the association between the use of β-blocking medication and the reduction of absolute mortality from implantable cardioverter (ICD) therapy compared with the conventional medical therapy.

MEDLINE (from 1995 to 2005) and EMBASE were searched. Search terms were reported.

Randomised controlled trials (RCTs) which compared ICD with medical therapy in patients resuscitated after cardiac arrest, with documented or symptomatic sustained ventricular tachyarrhythmia, or with depressed ventricular function deemed to be at high risk of developing lethal cardiac arrhythmia, were eligible for inclusion. The primary outcome was all cause mortality.

It appears that both primary and secondary prevention studies were included. Number of participants in the included trials ranged from 103 to 2,521. Mean age of the participants ranged from 58 to 66 years. Mean ejection fraction of the trial participants ranged from 0.21 to 0.45.

The included studies were assessed for adequacy of randomisation, completeness of follow up and the objectivity of the outcome.

The authors did not state how the validity assessment for performed.

Data regarding the two year mortality in the ICD and control groups as well as the percentage of participants in the individual trials using β-blocking medication were extracted.

The authors did not state how the data were extracted for the review, or how many reviewers performed the data extraction.

Meta-regression was used to calculate and assess the statistical significance of the correlation coefficient r for the relationship between the use of β-blocking medication and two year mortality benefit of ICD in the included trials. An a priori decision was made to combine trials of primary and secondary prevention, and heterogeneity was not further explored.

Ten randomised controlled trials (n=7,851) were included. Some details of the trial participants were given in a table format. Number of participants in the included trials ranged from 103 to 2,521. The mean duration of follow-up ranged from 18 to 57 months.

Analysis of the selected trials showed a strong negative association between the use of β-blocking medication and the absolute reduction in two year mortality secondary to ICD therapy (r = -0.81, p <0.01). There was weak association between the use of angiotensin converting enzyme inhibitors and the absolute reduction in two-year mortality secondary to ICD therapy ( r= -0.66, p = 0.051).

The use of modern therapy with β-blocking medication is associated with a reduced absolute mortality benefit of ICD therapy in patients with depressed left ventricular systolic function.

The review addressed a well defined question in terms of study design, participants, interventions and outcomes assessed. It is not clear how many reviewers were involved in any stage of the review process, which raises the possibility of reviewer error and bias. The authors searched two relevant databases but did not report systematically searching for unpublished studies, increasing the possibility of publication bias and the exclusion of some relevant studies. An appropriate validity assessment was conducted but the results were neither reported nor used to inform the synthesis. The review was poorly reported with few details of primary studies, summary statistics or statistical methods used in the synthesis. In view of multiple limitations in the review process as well as reporting, the authors' conclusions need to be interpreted very cautiously.

The authors did not state any implications for practice or further research.

Medical Council of the Academy of Science, Helsinki; Foundation for Cardiovascular Research, Helsinki; Paulo Foundation; Paavo Nurmi Foundation, Helsinki, Finland.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.