Warm versus cold blood cardioplegia in paediatric cardiac surgery: where do we stand 2 decades later?

In this issue of the European Journal for Cardio-thoracic Surgery, Stoica et al. [1] provide a detailed analysis of their single-centre randomized control trial on the effect of temperature of blood-based cardioplegia on myocardial protection in a moderate-risk group of paediatric patients undergoing open-heart surgery.

Over the last 20 years, the Bristol group has published several important articles on myocardial protection both in adults and more recently in paediatric patients [2, 3].

The use of normothermic cardiopulmonary bypass (CPB) in paediatric cardiac surgery was introduced in 1996 [4]. Since then, a few European centres led the initial clinical studies whereas a more conservative approach of mild/moderate hypothermic CPB was still the preferred strategy both in the USA and most European countries [5].

In 2001, based on their encouraging early clinical results, the leading French group combined normothermic CPB with intermittent warm blood cardioplegia in paediatric cardiac congenital surgery [6].

Two decades later, as underscored by Stoica et al., only a handful of clinical studies have adequately compared normothermic CPB and intermittent warm blood cardioplegia to one of the many other strategies used worldwide [5, 7].

In this study, specific biochemical and other surrogate markers of myocardial protection have been extensively evaluated and are presented in the manuscript and its appendices. Taken altogether, the authors demonstrate that intermittent warm blood cardioplegia provides similar myocardial protection to cold blood cardioplegia as assessed with cardiac troponin-T measurements. These results are in line with our own observations [8]. One should however keep in mind that immediate postoperative cardiac troponin measurements in congenital open-heart surgery are lesion and/or surgery dependent and that only concentrations at later time (beyond 24 h) may reflect myocardial ischaemia and/or necrosis [9].

As hypothesized by the authors, it is likely the unbalanced number of re-interventions for residual lesions in the warm blood cardioplegia group negatively influenced some of the end points but those differences are unlikely to be related to the method of myocardial protection.

Among details, the authors did not exclude troponin measurements in those patients who benefitted from intraoperative cardioversion or defibrillation. While the former is unlikely to result in an increased troponin release, the latter surely does [10].

Finally, though intermittent warm blood cardioplegia was previously shown to preserve stored energy metabolites in comparison to cold crystalloid cardioplegia, the authors did not perform cardiac biopsy, so the cellular mechanisms of their observations will remain unknown.

Unfortunately, existing randomized control trials, including current Stoica’s study, only enrolled moderate-risk paediatric congenital cardiac patients, with reasonable CPB and cross-clamp time, so it will remain unknown whether intermittent warm blood cardioplegia would be beneficial or detrimental in higher risk-adjusted congenital heart surgery score categories of patients.

Again, the Bristol group has to be complemented for pursuing well-designed studies on important topics within congenital cardiac surgery for which important heterogeneity exists among centres worldwide.

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