External validity of ST elevation myocardial infarction trials: the Zwolle studies.

Background: Guidelines are mainly based upon results of randomised controlled clinical trials. However, due to low external validity of these trials, their results can not reasonably be applied to all patients in routine practice. In our hospital, all patients with ST-elevation myocardial infarction (STEMI) are eligible for inclusion in one of our ongoing trials or registries. To asses differences between patients enrolled versus not-enrolled in a trial or registry, we evaluated all patients with a discharge diagnose of STEMI during the study period.
Methods: Retrospectively, individual patient data from all patients with a discharge diagnosis of STEMI between Jan 2001 and Dec 2001 were evaluated. Follow-up data were obtained until Dec 2004.
Results: A total of 583 patients were discharged with a diagnosis of STEMI. About 455 (78%) patients were enrolled in one of the ongoing clinical trials or registry and 128 were not. Not-enrolled patients were significantly older; more often had a history of previous MI and had higher risk profiles. Multivariate analysis revealed that higher age was the only independent predictor for non enrollment. Not-enrolled patients were more often treated conservatively and had a higher mortality rate (36% vs. 6%, P << 0.001). After multivariate analysis, non-enrollment (OR: 95% CI) 4.02 (1.98-8.16), age 1.07 (1.04-1.12), and diabetes 2.39 (1.17-4.89) were the only independent predictors of long term mortality.
Conclusions: This study shows important differences in baseline characteristics, treatment, and prognosis between patients with STEMI who were enrolled or not in a trial. To better reflect daily clinical practice, guidelines should also consider results of observational studies of unselected patients.