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Postischemic [Ca2+] repletion improves cardiac performance without altering oxygen demands
H Yokoyama1, J S Julian, J Vinten-Johansen
1Department of Cardiothoracic Surgery, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27103.
Insights
Normalizing blood calcium levels after heart surgery improves left ventricular function and stiffness without increasing oxygen demand. This correction of hypocalcemia aids recovery from ischemia and reperfusion injury.
Area of Science:
- Cardiology
- Cardiovascular Surgery
- Physiology
Background:
- Postischemic hypocalcemia can impair left ventricular function.
- Reperfusion injury, particularly calcium overload, may counteract the benefits of calcium correction.
Purpose of the Study:
- To evaluate the effect of normalizing blood calcium concentration on postischemic left ventricular mechanics.
- To assess the impact of calcium correction on myocardial oxygen consumption and chamber stiffness.
Main Methods:
- Open-chest dogs on cardiopulmonary bypass underwent global ischemia followed by hypothermic, hypocalcemic blood cardioplegia.
- Left ventricular systolic and diastolic mechanics were assessed using pressure-diameter relations and oxygen consumption.
- Systemic calcium concentration was measured before and after correction.
Main Results:
- Systemic calcium concentration decreased significantly after hypocalcemic reperfusion.
- Left ventricular inotropic state, depressed post-ischemia, was restored to baseline with calcium correction.
- Chamber stiffness increased significantly after hypocalcemic reperfusion but decreased with calcium correction.
- Myocardial oxygen consumption remained unchanged after calcium correction.
Conclusions:
- Normalizing blood calcium concentration after blood cardioplegia improves postischemic left ventricular performance.
- Calcium correction enhances ventricular compliance and function without increasing myocardial oxygen consumption.
- This strategy mitigates adverse effects of hypocalcemia and potential reperfusion injury.
Abstract:
The positive inotropism expected with correction of postischemic hypocalcemia might be counterbalanced by potential aggravation of reperfusion injury, in particular by calcium overload. We evaluated the effect of normalizing blood calcium concentration ([Ca2+]) on postischemic left ventricular systolic and diastolic mechanics using oxygen consumption and indices derived from pressure-diameter relations. In 10 open-chest dogs on cardiopulmonary bypass, the hearts underwent 30 minutes of normothermic global ischemia followed by one hour of multidose hypothermic (4 degrees C), hypocalcemic (0.3 mmol/L) blood cardioplegia. After reperfusion, systemic [Ca2+] had decreased to 70% of control (p = 0.017). The left ventricular inotropic state was significantly depressed from baseline (control) values, but was restored to baseline levels by resumption of normocalcemia after one hour of reperfusion. Chamber stiffness increased by 308% (p = 0.006) after hypocalcemic reperfusion but decreased significantly after [Ca2+] correction. Recovery of left ventricular performance with [Ca2+] correction did not augment myocardial oxygen consumption from the postischemic uncorrected state (5.0 +/- 0.3 mL O2/min/100 g versus 5.3 +/- 0.3 mL O2/min/100 g). We conclude that normalizing [Ca2+] after blood cardioplegia improves postischemic left ventricular performance without adversely affecting compliance or oxygen consumption.