Unrealistic expectations arising from mortality data reported in the cardiothoracic journals

Abstract

Background: This study was undertaken to ascertain whether mortality data in the cardiac surgical literature mirror data reported in national databases. Methods: This was a review of articles with 50 or more subjects reporting single-center mortality data for coronary artery bypass or aortic or mitral valve replacement published in the three major cardiothoracic surgical journals from 1997 through 2000. Mortality data and trends were examined. Results: One hundred sixty-nine articles were found (coronary artery bypass, n = 119; aortic valve replacement, n = 34; mitral valve replacement, n = 16). Articles were predominantly case series (N = 95), with smaller numbers of comparative retrospective studies (n = 34), randomized trials (n = 29), and prospective noncomparative studies (n = 11). The median mortality figures for these studies were 1.5% (interquartile range, 0.3%-2.6%) for coronary artery bypass, 3.4% (interquartile range, 2.0%-5.3%) for aortic valve replacement, and 4.7% (interquartile range, 2.1%-6.9%) for mitral valve replacement. In contrast, the national registry mortallity figures were 2.9%, 4.0%, and 6.0%, respectively, in the United States and 2.6%, 4.5% and 6.3%, respectively, in the United Kingdom. Coronary bypass studies with samples smaller than 100 patients reported lower mortality figures (median 0%) than did those with more than 100 patients (1.8%). Exploration with graphical plots suggested a bias toward reporting and publication of studies with below average mortality. Conclusions: Particularly for coronary artery bypass, published data tend to under-represent the risk of death as seen in most centers. Outcomes and magnitudes of effects as reported in these research studies may not be replicable to the same degree in most centers. In particular, extreme caution should be taken in extrapolating results from studies with fewer than 100 patients to larger surgical populations.