Clinical studies in children have shown that girls are at higher risk for death than boys following cardiac surgery. A recent nationwide study in the US has found that females under 20 years of age are at a 31 percent greater risk of in-hospital death following heart surgery.
As studies have ruled out gender-differences based on access to and utilization of services, the Canadian team has explored a biological basis for the differences. In this study they considered whether a more rapid development of tissue acidity (acidosis) in the heart during a lack of blood flow (ischemia) might play a role.
The researchers used 20 young (3-5 days) male (n=7) and female (n=13) Yorkshire piglets to examine their theory. They took a full thickness left ventricular biopsy to compare the baseline levels of metabolites in both sexes prior to isolating the hearts. The hearts were then subjected to 60 minutes of normothermic ischemia and left ventricular biopsies were collected at the end of the period. All tissues were analyzed for adenosine adenosine triphosphate (ATP; the main energy source of the heart), creatine phosphate (CP; a readily available stored form of energy), lactate, and hydrogen ion (H+) concentration. Histidine concentration, which protects against acidosis, was also determined in baseline tissue alone.
The researchers found that the newborn female hearts had accumulated a significant 47 percent greater H+ level within 60 minutes of ischemia. This was associated with a significant 13 percent greater accumulation of lactate. They also found the CP reserve was 22 percent lower than baseline compared to males.
Based on these and other findings the investigators concluded that, for this study:
* male and female newborn hearts are not metabolically identical and have different metabolic responses to ischemia; and
* newborn female hearts can develop greater acidosis during ischemia, which may place them at greater metabolic risk
According to the research team, the results suggest that the response of the newborn female heart (i.e., myocardium) to ischemia may increase its susceptibility to injury during ischemia and offer a potential explanation for the poorer clinical outcomes found in infant females following cardiac surgery.