The meaning of early mortality after CABG.

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Abstract
Objective: Investigations of early mortality after coronary artery bypass grafting (CABG) are predominantly based on 30-day mortality or hospital mortality. The advantages, disadvantages, and usefulness of hospital mortality and 30-day mortality analyses to investigate the early risk after CABG are evaluated. Methods: A total of 4985 patients underwent isolated CABG from June 1988 to June 1997. A follow-up was performed 180 days after CABG (response rate: 98.6%). Results: The mean hospital stay was 13.5±9.6 days, the range was 0 to 142 days (25% quartile, 9 days; median, 12 days; 75% quartile, 15 days). The hospital mortality was 5.3%. The 30-day mortality was 5.6%. The non-parametric Kaplan–Meier curve of the time interval 0–180 days postoperatively proves the persistence of the still decreasing behaviour of the survival curve beyond the 30th day until about the 60th postoperative day. Stratified by era of operation, the 'early phase' after CABG seems to be prolonged beyond 30 days at least for the more recent operation era since 1991. Risk stratification proves that the higher the risk group, the more the early phase tends towards a prolongation. Conclusions: The hospital mortality reflects institutional habits concerning postoperative patient care. Therefore, a systematic underestimation of early mortality is likely. In contrast to hospital stay, the evaluation of 30-day mortality requires a follow-up procedure but allows interinstitutional comparisons. Nevertheless, 30-day mortality systematically underestimates the early risk, at least in the more recent CABG period. So, a standardized evaluation of a longer time period (p.e. 180 days) is recommended.