Scientists have found a way to image the very early development of the embryonic heart in research that may help them to explain how drinking alcohol in pregnancy can lead to heart defects at the baby's birth.
The researchers, based in Cleveland, OH, knew that "even one episode of heavy drinking" could lead to fetal alcohol syndrome, which is a collection of congenital (present at birth) defects, including problems with the heart.
"Alcohol-induced congenital heart defects are frequently among the most life-threatening and require surgical correction in newborns," the team, led by Ganga Karunamuni PhD, says.
But the Case Western Reserve University scientists say study of the tiny heart of an embryo had been limited, keeping reasons in the dark as to how alcohol induced these congenital heart defects.
Visualizing these developmental changes has now been made possible, however. The imaging technique is called optical coherence tomography, which works in a similar way to ultrasound, but returns high-resolution images on the micron scale and uses light waves rather than sound.
Before their use of this innovative technology, say the authors in the study abstract:
"Few studies have addressed the influential role of altered cardiac function in early embryogenesis, due to a lack of tools with the capability to assay tiny beating hearts."
Similarity of bird embryo hearts
To overcome the obvious barriers to experimenting with the effects of alcohol on human embryonic hearts, the researchers used an animal model, quail embryos - "whose heart development is very similar to that of humans."
They exposed one set of embryos to a single, large dose of alcohol and compared images of heart development with those from embryos whose eggshells had not been injected with alcohol.
The amount of alcohol given in the study, which has been published by the American Physiological Society, was "proportional to the amount that would be considered a single episode of binge drinking in a pregnant woman."
To see the alcohol effects, the optical coherence tomography gave the scientists the ability to peer through layers of tissue, and they centred this work on a particular stage of normal development when the embryo is sensitive to the induction of birth defects.
Called gastrulation, this stage sees the very early embryonic heart switch from a tube shape to a loop-shaped circuit. This is in the early days following ovulation, when the embryo has switched from being a ball of cells but is still to form the primitive neural tube that will give rise to the spinal cord and brain.
Adverse effects on blood flow
Researchers found differences in heart blood flow patterns and anatomy in the embryonic hearts of the animal models, which was caused by alcohol.
Comparing the heart blood flow patterns and anatomy at this stage, the researchers uncovered differences caused by alcohol, which they could link to the expected birth defects they subsequently found in the fully developed hearts.
"The dramatic defects close to hatching" included thinner walls separating the four chambers of the heart and damaged valves - late-stage valvuloseptal defects, in other words.
The early differences in embryonic heart blood flow that had led to these defects included a much larger portion of blood flowing backward through the heart circuit after each beat - termed a higher regurgitant flow.
The early structural differences, meanwhile, were found in smaller "atrio-ventricular cardiac cushions" - the collections of cells that later become heart chamber walls and valves.
The authors cite other research in the background to their study that has shown the heart's development can be affected by its cells being "responsive to the mechanical forces of blood flow."
They suggest the faulty function that they uncovered in the embryonic hearts may in turn steer the later developing organ in the wrong direction, "setting the stage for larger defects to arise."
Concluding their findings, the researchers point to the importance of gaining a better scientific understanding of fetal alcohol syndrome:
"With an average of 4 million US pregnancies per year, there will be approximately 10,000 cases of alcohol-induced congenital heart defects.
Continued study of the mechanisms involved in the development of alcohol-induced cardiac birth defects is warranted in order to implement effective treatments and/or prevention strategies."