The influence of risk on the results of warm heart surgery: a substudy of a randomized trial
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G T Christakis1, S V Lichtenstein, K J Buth
1Division of Cardiovascular Surgery, Sunnybrook Health Science Centre, University of Toronto, Ontario, Canada.
Insights
Warm cardioplegia significantly reduces overall morbidity and mortality in heart surgery patients. However, this benefit was not significantly different across various patient risk levels, suggesting other factors influence outcomes in high-risk individuals.
Area of Science:
- Cardiovascular Surgery
- Cardiac Anesthesia
- Myocardial Protection
Background:
- The Warm Heart Investigators Trial showed warm cardioplegia reduces low output syndrome and myocardial infarction.
- This subanalysis focuses on high-risk patients to assess the benefits of warm heart surgery.
Purpose of the Study:
- To determine the effect of warm heart surgery on high-risk patients undergoing isolated coronary bypass.
- To analyze the influence of cardioplegia technique and predicted risk on patient outcomes.
Main Methods:
- A prospective subanalysis of 1374 patients from the Warm Heart Investigators Trial.
- Patients were randomized to warm or cold cardioplegia.
- Risk stratification used a multivariate model; composite outcome included death, low output syndrome, and enzymatic myocardial infarction.
Main Results:
- Warm cardioplegia significantly reduced overall morbidity and mortality (15.9% vs. 25.2%, P < 0.01).
- No significant differences in warm-cold cardioplegia effects were observed across risk terciles.
- Similar outcome improvements were seen in low-risk and high-risk patients with warm cardioplegia.
Conclusions:
- Warm cardioplegia offers overall benefits in reducing morbidity and mortality.
- The lack of differential benefit in high-risk patients suggests other clinical and technical factors are involved.
- Further research is needed to identify specific patient subgroups who benefit most from advanced myocardial protection techniques.
Objective:
The Warm Heart Investigators Trial randomized isolated coronary bypass patients to cold or warm cardioplegia, and demonstrated that warm cardioplegia significantly reduced the prevalence of low output syndrome and myocardial infarction (as defined by CKMB enzyme release). This study was designed prospectively as a subanalysis of the original 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 complete data for all outcomes were included, totalling 1374 patients (692 warm cardioplegia, 682 cold cardioplegia) who were randomized in the Warm Heart Investigators Trial. High medium and low risk patients were identified by a multivariate model of predicted risk for the study outcome.
Results:
Analysis of the independent and interactive influence of cardioplegia technique and predicted risk demonstrated that warm cardioplegia significantly reduced the overall prevalence of morbidity and mortality (warm: 15.9 versus cold: 25.2%, P < 0.01). However, no significant differences in warm-cold effects were detected among risk terciles. Cardioplegia technique had a similar differential influence 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%).
Conclusions:
Although our analysis confirms the overall benefits of warm cardioplegia, our unanticipated finding in high risk subjects may be explained by the fact that morbidity and mortality in that patient subgroup is caused not only by poor myocardial protection, but by other clinical and technical factors. Further studies are necessary to identify those patients who might benefit most from improved myocardial protection techniques.