The contribution of observational studies to the knowledge of drug effectiveness in heart failure

Randomized controlled trials (RCTs) are the golden standard for the assessment of drug efficacy. Little is known about the add-on value of observational studies in heart failure (HF). We aimed to assess the contribution of observational studies to actual knowledge regarding the effectiveness of angiotensin-converting enzyme inhibitors (ACEI), and beta-blockers (BB) in HF.Observational studies that assessed the effectiveness of ACEI and BB in HF were identified by searching Medline, Embase, Cochrane Database (1990-2005) and the bibliographies of published articles. Cohort, case-control and time-series analysis studies were considered for inclusion. Studies with <100 patients and those who did not perform a multivariate analysis were excluded.A total of 23 cohort studies met the inclusion criteria. Studies of ACEI and BB showed a decrease in mortality with drug use in elderly patients with a broad range of ejection fraction (EF), and in those with depressed EF. Additionally, they showed a decrease in mortality in patients with renal insufficiency. The effect of ACEI and BB in HF with preserved EF was not clear, although last evidence suggests a potential benefit. Low-dose ACEI and BB may have beneficial effects. Target doses of ACEI seemed superior to low doses, but there was no clear dose-response relationship.Observational studies in HF validate the effectiveness of ACEI and BB in populations underrepresented or excluded from RCTs. Observational studies of drug effectiveness provide relevant additional information for clinical practice.