Reanalysis of systematic reviews: The case of invasive strategies for acute coronary syndromes
Authors: Kuukasjärvi Pekka , Nordhausen Klaus , Malmivaara Antti 
Published: September 2006

Objectives: The objective of this study was to collect all systematic reviews on invasive strategies for acute coronary syndromes (ACS) and reanalyze the data in these reviews to reach combined estimates, as well as to make predictions on the effectiveness and risk of harm so as to facilitate relevant decision making in health care.

Methods: The data sources used were the following electronic databases, searched from 1994 to September 2004: Cochrane Database of Systematic Reviews; Cochrane Central Register of Controlled Trials; DARE, HTA, EED (NHS CRD); MEDLINE(R) In-Process, Other Non-Indexed Citations, MEDLINE(R), and PubMed (2000 to 2004). References to the identified systematic reviews were checked. An ancillary search to identify recent randomized controlled trials (RCTs) covering the period from January 2003 to January 2006 was done in MEDLINE(R). We included systematic reviews of RCTs on patients with ACS. In unstable angina and non–ST-elevation myocardial infarction (UA/NSTEMI), eligible reviews had to compare early routine invasive strategy with early selective invasive strategy. In ST-elevation myocardial infarction (STEMI), a comparison between primary percutaneous coronary intervention (PCI) and thrombolytic therapy was required. The methodological quality of the reviews was assessed, and a standardized data extraction form was used. Results for the main outcomes of the RCTs in the reviews were reanalyzed. An additional search of those RCTs not included in the meta-analyses was performed for UA/NSTEMI and short-term morality data on STEMI. Bayesian models were constructed to estimate the uncertainty about a possible treatment effect and to make predictions and probability statements. Main results are based on these analyses. Mortality was considered as the primary outcome measure.

Results: One systematic review on invasive strategies was identified for UA/NSTEMI and nine on invasive strategies for STEMI. Five reviews of the latter that were published after the year 2000 were included for the final analysis. The median quality score was 10.5 (range, 7–13; n = 6) on a scale from 0 to 18 points. An updated literature search identified one further RCT on UA/NSTEMI. Regarding NSTEMI and mortality, the average risk difference favoring an early invasive treatment strategy compared with early conservative strategy was .6 percent (95 percent credible interval [CrI], −2.1 to 1.0). Predicted risk (relative risk/risk difference scales) of doing harm was 26.7/26.6 percent. Regarding STEMI and mortality, the absolute risk reduction in favor of primary PCI over thrombolysis was 4.1 percent (95 percent CrI, −7.1 to −1.1) when PCI was compared with streptokinase and 1.2 percent (95 percent CrI, −2.7 to .2) when compared with fibrin-specific thrombolytics. Predicted risk of harm was 8.9/5.3 percent and 8.0/13.3 percent, respectively.

Conclusions: There seems to be at present no solid evidence for survival benefit on early invasive strategy for UA/NSTEMI as a broad diagnostic group, and the risk of doing harm should be considered. Also, the evidence for PCI to decrease early mortality after STEMI is scanty. Estimations of predicted harm may further aid decisions on whether to implement the new treatment over the old one. It may also give an additional dimension for interpreting the results of any meta-analysis.