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A 31P-nuclear magnetic resonance study of intermittent warm blood cardioplegia
1Institute for Biodiagnostics, National Research Council Canada, Winnipeg, Manitoba.
Insights
Intermittent warm blood cardioplegia (WBC) offers myocardial protection comparable to continuous WBC. Mild, reversible changes in energy metabolites and pH occurred with intermittent WBC, with no cumulative effects observed.
Area of Science:
- Cardiovascular Science
- Cardiac Surgery
- Myocardial Protection
Background:
- Optimizing myocardial protection during cardiac surgery is critical.
- Warm blood cardioplegia (WBC) is an established method for myocardial preservation.
- The impact of intermittent versus continuous WBC on myocardial energetics requires further investigation.
Purpose of the Study:
- To evaluate the effects of intermittent warm blood cardioplegia (WBC) on myocardial energy metabolites, intracellular pH, and contractile function.
- To compare the protective efficacy of intermittent WBC with continuous WBC and control perfusion.
- To determine if interruptions in WBC lead to cumulative detrimental effects.
Main Methods:
- Isolated blood-perfused pig hearts were divided into three groups: continuous WBC, intermittent WBC (with ischemic intervals), and control.
- Phosphorus 31-nuclear magnetic resonance spectroscopy was used to monitor myocardial energy metabolites and intracellular pH.
- Contractile function was assessed during reperfusion.
Main Results:
- Intermittent WBC caused transient, reversible decreases in phosphocreatine and intracellular pH, with rapid recovery upon resumption of cardioplegia.
- Subsequent interruptions of intermittent WBC did not result in cumulative changes in energy metabolites or pH.
- Hearts subjected to continuous or intermittent WBC demonstrated comparable recovery of contractile function and adenosine triphosphate levels post-reperfusion.
Conclusions:
- Antegrade intermittent warm blood cardioplegia (WBC) induces only mild and reversible changes in myocardial energy metabolism and intracellular pH.
- These metabolic changes are not cumulative, even with repeated interruptions.
- Intermittent WBC may offer equivalent myocardial protection to continuous WBC in normal hearts.
Abstract:
This study was designed to assess the effects of intermittent warm blood cardioplegia on myocardial energy metabolites, intracellular pH, and contractile function. The isolated blood-perfused pig hearts were divided into three groups. After 30 minutes of control perfusion, the hearts in group 1 (n = 10) received 90 minutes of continuous warm (37 degrees C) blood cardioplegia; the hearts in group 2 (n = 9) received six 5-minute periods of warm blood cardioplegia, interrupted by six 10-minute episodes of ischemia (37 degrees C). The hearts were then reperfused for 30 minutes. The hearts in group 3 underwent 150 minutes of control perfusion without cardioplegia or ischemic episodes. Phosphorus 31-nuclear magnetic resonance spectra showed that a 10-minute interruption of warm blood cardioplegia decreased phosphocreatine levels and intracellular pH by approximately 47% (p < 0.01) and 0.12 unit (p < 0.05), respectively, and increased inorganic phosphate levels by approximately 87%, whereas resumption of cardioplegia for 5 minutes resulted in almost 100% recovery of phosphocreatine and inorganic phosphate levels and intracellular pH. More important, subsequent interruptions did not result in any cumulative changes in phosphocreatine level, inorganic phosphate level, or intracellular pH beyond those changes observed after the initial cardioplegic interruption. Moreover, during reperfusion there were no significant differences in adenosine triphosphate and phosphocreatine levels among the three groups of hearts. Furthermore, hearts from groups 1 and 2 showed comparable recovery of contractile function. These results indicate that six 10-minute interruptions and six 5-minute restorations of warm blood cardioplegia caused only mild and reversible changes in myocardial energy metabolites and intracellular pH and these changes were not cumulative. This study suggests that antegrade intermittent warm blood cardioplegia may provide as much myocardial protection as does antegrade continuous warm blood cardioplegia in the normal heart.