Preterm birth predisposes to the subsequent development, in adulthood, of alterations of ventricular myocardium. This is what emerges from a recent research, published in the pages of the Journal of the American College of Cardiology.
In this study young subjects, born premature, had a higher fraction of extracellular volume in the left ventricle, inversely correlated with gestational age. This myocardial alteration was then related to a worse diastolic function.
The World Health Organization (WHO) defines preterm birth as birth that occurs before the completed 37 weeks of gestation. Even in healthy women with low-risk pregnancies, some babies are born premature.
For the new-born, preterm birth is a risk factor that has an impact on health, well-being and development into adult life. Overall, the mortality and morbidity outcomes of premature babies are poorer than those of full-term babies, with the worst clinical outcomes occurring for shorter gestation periods.
Some studies have shown preterm birth rates that ranged from around 5%, in some European countries, to 18%, in some African countries. Preterm birth is usually considered to occur in about 10% of live births, worldwide.
There are many risk factors for preterm birth. This is a more frequent occurrence in adolescent and late maternal pregnancies. Other risk factors are the male gender of the baby, poor nutrition of the mother, folate depletion, in vitro fertilization, smoking in pregnancy, as well as certain genital and urinary tract infections, pre-eclampsia, and pregestational and gestational diabetes. Preterm birth in a previous pregnancy is a strong risk factor for preterm birth in a later pregnancy, as maternal nulliparity.
In the past, several studies had evaluated the impact of preterm birth on the development of cardiovascular disease, highlighting an increased risk of developing conditions such as heart failure and ischemic heart disease in childhood and adulthood.
However, these studies also highlighting morphological and functional alterations of the ventricular myocardium in subjects born preterm. Alterations that can be manifest in the neonatal period, then continuing to evolve over the years.
The YACHT study
Based on the assumption that functional damage to the ventricle was found after preterm birth in animal models, possibly due to an upregulation of myocardial fibrosis, this new study sought to determine whether there was indeed left ventricular fibrosis in preterm young adults.
For this purpose, 101 adult subjects were included in the YACHT (Young Adult Cardiovascular Health Trial) study: 54 born at term (mean 39.5 weeks of gestation) and 47 premature (mean 32.8 weeks of gestation).
Participants underwent two-dimensional echocardiography with flow Doppler and tissue Doppler sampling.
Left ventricular structure was evaluated with cardiac magnetic resonance imaging, with administration of a gadolinium-based contrast agent.
The extracellular volume fraction was higher in preterm infants
The results of the study showed that adults born preterm, compared to those at term, had a lower end-diastolic and end-systolic volume of the left ventricle. This was associated with a greater left ventricular mass and wall thickness.
In addition, longitudinal peak systolic strain and the diastolic strain rate, assessed with magnetic resonance and echocardiography, were lower in preterm births. The E/A ratio, measured by echocardiography, was also lower in preterm births than in full-term adults.
Finally, in preterm births, compared to full-term adults, a greater fraction of extracellular volume was highlighted (27.81% versus 25.48%). This same parameter was then found to be correlated with gestational age, the longitudinal systolic deformation peak and the E/A ratio.
An increased risk of heart failure
This study presents for the first time the finding in humans of myocardial fibrosis in young adults born preterm. This is a confirmation of how important the completion of the fetal maturation process is for the evolution of heart structures, even if the formation of the four-chamber heart already takes place within the seventh week of gestation.
Preterm birth seems to cause the formation of a greater proportion of fibrosis in the ventricle, causing in turn a greater rigidity of these heart chambers and an alteration of the diastole.
What significance can these alterations have for the future cardiovascular health of this preterm babies? Unfortunately, even if the information available at this time does not provide accurate data, it is possible that in the presence of a greater fraction of extracellular volume, heart failure may develop over time in some cases.
The authors thus reiterate the usefulness of this index as a prognostic marker for the stratification of the risk of early heart failure and early mortality related to cardiovascular disease.
What are the causes that lead to the development of alterations at the ventricular level? Researchers suggest that they may be due in part to the hemodynamic stress and pressure overload faced by the immature myocardium at birth. However, they prospect that other stimuli, such as inflammation and oxidative stress, are also involved in the pathogenesis of these alterations.
The authors conclude by emphasizing the need for further studies to determine whether myocardial fibrosis in preterm young adults worsens with aging and its relationship to conventional cardiovascular risk factors.
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