Human Heart Develops Slower Than Other Mammals

Lee Rannals for — Your Universe Online

The walls of the human heart develop slower than other mammals, according to a new study published in Journal of the Royal Society Interface Focus.

Researchers developed the first comprehensive model of human heart development using observations of living fetal hearts. Human hearts have walls that are a disorganized jumble of tissue until late in pregnancy, despite having the shape of a fully functioning heart.

During the study, they saw four clearly defined chambers in the fetal heart from the eighth week of pregnancy and they did not find organized muscle tissue until the 20th week.

Developing a simulation of the fetal heart is critical in helping researchers understand normal heart development in the womb. This simulation could eventually open up new ways of detecting and dealing with some functional abnormalities in early pregnancies.

The researchers used scans of healthy fetuses in the womb for the study, including a mother who volunteered to have detailed weekly electrocardiography scans from 18 weeks until just before delivery.

Data gathered during the research was used for a 3D computerized model built up using information about the structure, shape and size of the different components of the heart from two types of MRI scans of dead fetuses’ hearts.

Results from the study show the human heart may develop on different timeline from other mammals. While the tissue in the walls of a pig heart develops a highly organized structure compared to the early stage of a fetus’ development, the scientists say there is little organization of the human heart’s cells until 20 weeks into pregnancy.

A pig’s pregnancy lasts about three months, and the organized structure of the walls of the heart come up during the first month of pregnancy. The University of Leeds researchers detected similar organized structures well into the second trimester of the human pregnancy.

“For a heart to be beating effectively, we thought you needed a smoothly changing orientation of the muscle cells through the walls of the heart chambers. Such an organization is seen in the hearts of all healthy adult mammals,” said Dr. Eleftheria Pervolaraki, Visiting Research Fellow at the University of Leeds’ School of Biomedical Sciences.

She said fetal hearts in other mammals like pigs show an organization even early in gestation. However, they saw this organization was not detectable in a human fetus before 20 weeks into pregnancy.

“The development of the fetal human heart is on a totally different timeline, a slower timeline, from the model that was being used before. This upsets our assumptions and raises new questions,” Professor Arun Holden, also from Leeds’ School of Biomedical Sciences, said in a statement. “Since the wall of the heart is structurally disorganized, we might expect to find arrhythmias, which are a bad sign in an adult.”

Holden said it may be the early stages of development of the heart arrhythmias are not necessarily pathological, and there is no need to panic if we find them.

“Alternatively, we could find that the disorganization in the tissue does not actually lead to arrhythmia,” he said.

A computer model of the activity and architecture of the heart will make sense of the limited information doctors are able to obtain about the fetus using non-invasive monitoring of a pregnant woman.

“It is different from dealing with an adult, where you can look at the geometry of an individual’s heart using MRI (Magnetic Resonance Imaging) or CT (Computerised Tomography) scans,” said Holden. “You can’t squirt x-rays at a fetus and we also currently tend to avoid MRI, so we need a model into which we can put the information we do have access to.”

He said textbook descriptions of the development of the human heart are founded on animal models, and 19th century collections of abnormalities in museums.

“If you are trying to detect abnormal activity in fetal hearts, you are only talking about third trimester and postnatal care of premature babies. By looking at how the human heart actually develops in real life and creating a quantitative, descriptive model of its architecture and activity from the start of a pregnancy to birth, you are expanding electrocardiology into the fetus.”

Scientists recently published findings regarding adult hearts back in January about how they were able to reprogram scar tissue from damaged hearts into healthy muscle through gene therapy. This finding may be able to help strengthen hearts harmed due to cardiovascular events.

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