A study caveat was that the numbers of patients were limited for several of the outcomes because of missing data, acknowledged Dr. Khush. "It is very difficult to account for center-specific differences – for example, differences in patient populations and management practices," she further noted. And unknown confounders could have influenced the findings.
Dr. Kaczmarek and his coinvestigators similarly analyzed data from the ISHLT database, but for a wider range of years (1980-2009). Their analyses were based on 67,833 heart transplant recipients.
Overall, 80% were men. On average, the men were 53 years old and the women were 51 years old. One-quarter of men received a female donor heart, and slightly fewer than one-half of women received a male donor heart.
The 15-year survival rate was best for women who were given a female heart and worst for men who were given a female heart. "The curves divide in the first year," Dr. Kaczmarek pointed out. "In the long run, they seem to be parallel, but women with female hearts do a bit better."
The 1-year rate of survival ranged from a low of 78% among men who were given a female heart to a high of 84% among men who were given a male heart. "This [latter] effect lasts for a few years, and then the better combination is female donor, female recipient," he said.
When patients who died in the first year post transplantation were excluded, the survival curves diverged gradually over time, but still arrived at the same final pattern, with long-term survival best for women who were given a female heart and worst for men who were given a female heart.
"We have seen that acute rejection contributes to that effect," Dr. Kaczmarek commented. "Acute rejection [rates] are a bit higher in male recipients who receive female donor hearts."
Results were similar when the investigators focused just on the subgroup of patients from their own institution in Munich.
"I want to carefully conclude that the combination of male recipient, female donor carries a higher risk for early mortality, whereas other gender constellations yield similar outcomes," said Dr. Kaczmarek.
"In the long-term follow-up, female recipients reveal superior results, especially the combination of female recipient and female donor," he concluded.
Dr. Khush reported having no conflicts of interest related to the research. Dr. Kaczmarek reported receiving travel or research grants from Novartis, Astellas, Roche, Orion Pharma, and Berlin Heart.