Different pathophysiological mechanisms during prolonged and moderate ischemia in pediatric cardiac surgery

Introduction

In recent decades, numerous techniques for cardioplegia have been developed with the aim of optimizing myocardial protection during pediatric cardiac surgery. Consequently, the question for the most suitable cardioplegia solution remains fraught with unanswered questions, as the ideal choice for safeguarding the hearts of pediatric patients continues to be a subject of contention, despite the plethora of available options.

Aim

Study objective: the aim of this study was to investigate mitochondrial respiratory pathway changes after a moderate ischemic period (after 1 hour) and a prolonged ischemic period (after 3 hours).

Methods

39 male Wistar albino rats (up to 1 month old) underwent median sternotomy, and Custodiol HTK, del Nido, or St. Thomas was infused into the aorta. Hearts were incubated for 1 h and 3 h, then transferred, cut, and homogenized. The homogenate underwent two centrifugations. Mitochondrial energy metabolism was tested using 2 mg equivalents, titrating substrates. Measurements included mitochondrial basal respiration (Mit), ATP-production coupled mitochondrial respiration (ADP), carbonyl cyanide p-trifluoromethoxy phenylhydrazone for maximal respiration (FCCP), and the ratio of cytochrome C complex to ATP-production coupled mitochondrial respiration (CytC/ADP). Three experiments were performed without cardioplegic solution (CP0 group). For moderate and long ischemic periods, 6 experiments each were performed in CP1 (St. Thomas), CP2 (Custodiol HTK), and CP3 (del Nido) groups.

Results

After 1 hour of ischemia, mitochondrial respiratory parameters showed strong and significant positive correlations, indicating preserved functional coupling. Basal respiration correlated with cytochrome C–dependent respiration (r=0.478), maximal uncoupled respiration (FCCP; r=0.608), and azide-sensitive respiration (r=0.883; all p<0.05). ATP-production–coupled respiration (ADP) demonstrated very strong correlations with cytochrome C (r=0.866), FCCP (r=0.711), and azide (r=0.604; all p<0.05).

After 3 hours of ischemia, basal respiration no longer correlated with downstream respiratory parameters, while strong correlations persisted among ADP, cytochrome C, FCCP, and azide (r=0.593–0.953; p<0.05). No significant correlations were observed between 1-hour and 3-hour measurements.

Conclusions

The results of the prolonged ischemic period are influenced by other pathophysiological factors and mechanisms than the results of the moderate ischemic period. In the case of prolonged ischemia, cell membranes fail, and alterations occur at the subcellular level. Further studies are needed to elucidate what other suppressed mechanisms are activated in prolonged ischemia that have different effects.For image description, please refer to the figure legend and surrounding text.For image description, please refer to the figure legend and surrounding text.