Limiting the analysis to patients randomized within 3 hours eliminated the overall excess in mortality in the treatment group, but significant heterogeneity persisted. Contrary to what a superficial reading of the results would lead one to believe, the choice of thrombolytic agent alone was not enough to explain the differences between trials. These agents appeared to confer a worse prognosis when added to lytic therapy. Author's discussion The authors draw a number of conclusions from their results. They feel that thrombolytic therapy is potentially beneficial, but that the exact patient groups and treatment strategies that will provide the most benefit remain unclear.
Early treatment appears to convey benefit.
The concept of trial heterogeneity is interesting and its application is well illustrated by this review. When a number of trials studying the same question are performed, they are unlikely to have the exact same outcomes, simply on the basis of sampling error. Just as a small difference between two treatment groups may be due to chance alone, a difference between two trials may also be due to chance. What we need to know is whether discrepancies between trials are greater than we would expect by chance. If so, further exploratory analyses can help elucidate the specific factors that are at the root of these differences.