Electrocardiographic Evidence Of Myocardial Ischaemia During Hemodilution Probably Benign

The development of the higher heart rates during haemodilution may have contributed to the development of an imbalance between myocardial supply and demand. The resulting evidence was seen on an electrocardiograph of myocardial ischaemia.

There is controversy relative to the lowest blood haemoglobin concentration, which can be safely tolerated. Consequently, researchers studied healthy resting humans to test the hypothesis that acute isovolemic reduction of blood haemoglobin concentration to 5g/dL would produce an imbalance in myocardial oxygen supply and demand. This would result in myocardial ischaemia.

Participants included 55 conscious healthy human volunteers. Blood haemoglobin concentration was reduced from 12.8-1.2 to 5.2-0.5g/dL by the isovolemic removal of aliquots of blood. There was simultaneous replacement of removed blood with intravenous fluids to maintain constant isovolemia.

Measurements of haemodynamics and arterial oxygen supply were undertaken before and after removal of each aliquot of blood. Changes in the electrocardiographs (ECG) were monitored continuously using a Holter ECG recorder for detection of myocardial ischaemia.

Transient, reversible ST-segment depression was seen on the electrocardiogram during haemodilution to develop in three subjects. These changes occurred at haemoglobin concentrations of 5-7g/dL while the subjects were asymptomatic. Two of three subjects with ECG changes had significantly higher heart rates than those without ECG changes at the same haemoglobin concentrations.

When the entire study period was evaluated, the subjects who had ECG ST-segment changes had significantly higher maximum heart rates than did those without ECG changes, despite having similar baseline values. With the acute reduction of haemoglobin concentration to 5 g/dL ECG ST-segment changes developed in three of 55 healthy conscious adults and were suggestive of, but not conclusive for, myocardial ischaemia.

Researchers concluded that the reversibility of the ECG changes and the lack of symptoms suggests that these changes were benign.