THE INFLUENCE OF RISK ON THE RESULTS OF WARM HEART-SURGERY - A SUBSTUDY OF A RANDOMIZED TRIAL

Objective: The Warm Heart Investigators Trial randomized isolated coro nary bypass patients to cold or warm cardioplegia, and demonstrated th at warm cardioplegia significantly reduced the prevalence of low outpu t syndrome and myocardial infarction (as defined by CKMB enzyme releas e). This study was designed prospectively as a subanalysis of the orig inal trial, to determine the effect of warm heart surgery on high risk patients, who were anticipated to derive the major benefit from warm cardioplegia. Methods: The prespecified endpoint for this study was a composite outcome of morbidity and mortality (death and/or low output syndrome and/or enzymatic myocardial infarction). Only patients with c omplete data for all outcomes were included, totalling 1374 patients ( 692 warm cardioplegia, 682 cold cardioplegia) who were randomized in t he Warm Heart Investigators Trial. High, medium and low risk patients were identified by a multivariate model of predicted risk for the stud y outcome. Results: Analysis of the independent and interactive influe nce of cardioplegia technique and predicted risk demonstrated that war m cardioplegia significantly reduced the overall prevalence of morbidi ty and mortality (warm: 15.9 versus cold: 25.2%, P < 0.01). However, n o significant differences in warm-cold effects were detected among ris k terciles. Cardioplegia technique had a similar differential influenc e on mortality and morbidity in low risk patients (warm: 7.3, cold: 17 .4%) as it did in high risk patients (warm: 31.1, cold: 39.9%). Conclu sions: Although our analysis confirms the overall benefits of warm car dioplegia, our unanticipated finding in high risk subjects may be expl ained by the fact that morbidity and mortality in that patient subgrou p is caused not only by poor myocardial protection, but by other clini cal and technical factors. Further studies are necessary to identify t hose patients who might benefit most from improved myocardial protecti on techniques. (C) 1997 Elsevier Science B.V.