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Magnesium ion is beneficial in hypothermic crystalloid cardioplegia
P S Brown1, F W Holland, G L Parenteau
1Surgery Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland.
Insights
Magnesium supplementation in cardioplegic solutions significantly improves heart function recovery after cardiac arrest. Magnesium-treated hearts showed a 96% recovery rate, compared to 52% in untreated hearts, highlighting its cardioprotective role.
Area of Science:
- Cardiovascular Science
- Biochemistry
- Physiology
Background:
- Cardioplegic solutions are used to arrest the heart during surgery.
- The optimal composition of cardioplegic solutions, particularly regarding magnesium and calcium concentrations, is crucial for myocardial protection.
Purpose of the Study:
- To reexamine the role of magnesium ion (Mg2+) in relation to calcium concentration (Ca2+) in cardioplegic solutions.
- To determine the impact of varying Mg2+ and Ca2+ levels on cardiac function recovery.
Main Methods:
- Isolated rat hearts were perfused with a modified Krebs-Henseleit bicarbonate buffer.
- Hearts underwent cardiac arrest for 20 minutes at 37°C or 90 minutes at 24°C.
- Nine different cardioplegic solutions with varying Mg2+ (0, 1.2, 15 mmol/L) and Ca2+ (0.05, 1.5, 4.5 mmol/L) concentrations were administered.
Main Results:
- Magnesium-treated hearts demonstrated a 96% recovery rate, significantly higher than the 52% recovery in hearts without magnesium.
- Addition of 15 mmol/L Mg2+ to a low Ca2+ solution (0.05 mmol/L) significantly improved systolic pressure, cardiac output, stroke work, and ATP levels.
- Increasing Ca2+ concentration from 0.05 to 4.5 mmol/L led to significant reductions in cardiac output, stroke work, and ATP recovery in groups with 0 or 15 mmol/L Mg2+.
Conclusions:
- Magnesium plays a vital role in myocardial protection during cardioplegia, enhancing functional recovery irrespective of calcium concentration.
- Optimal concentrations of both magnesium and calcium are necessary for maximizing cardiac function recovery and preserving myocardial energy levels.
- The findings suggest that magnesium-containing cardioplegic solutions are superior for preserving cardiac function post-arrest.
Abstract:
The role of magnesium ion and its relation to the calcium concentration of cardioplegic solutions was reexamined in this study. Isolated rat hearts were used with an oxygenated modified Krebs-Henseleit bicarbonate buffer as perfusion medium. The hearts were arrested for 20 minutes at 37 degrees C or 90 minutes at 24 degrees C. Treatment groups received one dose of nine possible cardioplegic solutions containing magnesium (0, 1.2, or 15 mmol/L) and calcium (0.05, 1.5, or 4.5 mmol/L). Ninety-six percent of the 75 magnesium-treated hearts recovered, regardless of the calcium concentration, in contrast to a 52% recovery rate in the 69 hearts that did not receive magnesium. The addition of 15 mmol/L Mg2+ to a cardioplegic solution containing no magnesium but 0.05 mmol/L Ca2+ significantly increased (p less than 0.01) the percent recovery of the following parameters of cardiac function: systolic pressure, 74% to 93% (37 degrees C), 64% to 98% (24 degrees C); cardiac output, 76% to 101% (37 degrees C), 71% to 102% (24 degrees C); stroke work, 64% to 104% (37 degrees C), 52% to 99% (24 degrees C); and adenosine triphosphate level, 75% to 83% (37 degrees C), 58% to 90% (24 degrees C). There were significant reductions (p less than 0.03) in percent recovery (37 degrees C and 24 degrees C) of cardiac output, stroke work, and adenosine triphosphate level in the groups that contained 0 or 15 mmol/L Mg2+ as the calcium concentration was increased from 0.05 to 4.5 mmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)