Adults born preterm showed blunted left ventricular (LV) functional responses to moderate-intensity exercise stress, despite normal LV function at rest, in a prospective observational study.
As a result, their LV ejection fractions and cardiac output were significantly lower at both 60% and 80% of peak exercise capacity compared with responses in comparable adults who had been born at term.
Also, the lower the gestational age at birth in the preterm group, the greater was their LV-functional impairment at exercise.
The findings were independent of birth weight, maternal health history, and adult health status and suggest that “preterm-born young adults have a reduced myocardial functional reserve that might help explain their increased risk of early heart failure,” Adam Lewandowski, DPhil, University of Oxford and John Radcliffe Hospital, United Kingdom, told theheart.org | Medscape Cardiology.
They also complement earlier research from his group and others suggesting that adults born preterm have increased LV mass and reduced LV volumes, adjusted for body size, he said in an emailed comment.
Altogether, the structural and functional abnormalities seen in preterm-born adults constitute a “unique phenotype” compared to other types of cardiomyopathy, according to Lewandowski.
“There’s no immediate cause for alarm, as most preterm-born individuals will not go on to develop heart failure as adults,” he said. “However, the more we start to understand how the heart works differently in people born preterm, the better we can start to implement primary prevention steps, including reducing cardiovascular risk scores and developing a healthy lifestyle.”
The findings, based on 101 normotensive adults in the Young Adult Cardiovascular Health Study (YACHT), were published March 19 in the Journal of the American College of Cardiology, with Odaro J Huckstep, MSc, University of Oxford and John Radcliffe Hospital as lead author and Lewandowski as senior author.
Although the study is observational and only hypothesis-generating, an accompanying editorial notes that “this type of mechanistic study is key to being able to direct preventive measures to those at risk.”
Also, conclusions based on case-control studies with small samples may be especially subject to confounding, but “There are factors speaking against a substantial selection bias in this study,” write Anna-Karin Edstedt Bonamy, MD, PhD, and Hanna Carr, BSc, from Karolinska Institutet, Stockholm, Sweden.
For example, differences in blood pressure between the preterm-born and full-term-born participants “are very similar to those previously reported in larger samples,” they say.
“Moreover, the gestational age distribution is close to that seen in real life, which strengthens the assumption that the results may be generalizable to other populations of preterm-born subjects.”
The mean gestational age at birth for the 47 participants born preterm was 32.8 weeks, with a range of 23 to 36 weeks; 81% had been born at 32 weeks or later.
Compared to the 54 adults born at term, the preterm-born participants had greater LV mass adjusted for body surface area (P = .015) and for end-diastolic volume (P < .001), but similar resting LV ejection fraction, all by two-dimensional echocardiography.
Nor was LV function significantly different between the two groups when they exercised to 40% of peak exercise capacity. But at that exercise level, the submaximal cardiac output reserve was 56% lower in the preterm-born adults than in the term-born control group (P = .021).
But progressing from rest to 60% of peak exercise capacity, LV ejection fraction rose 8.1 absolute percentage points in the preterm-born group and 15.2 points in the term-born control group (P = .039), to averages of 71.9% and 78.6%, respectively (P = .004). The preterm group also showed lower peak longitudinal strain (P = .004), the group reported.
Lewandowski said the magnitude of difference in LV functional reserve between the two groups was a bit surprising, given that the overwhelming majority of the preterm-born group was born only moderately preterm.
Any interventions to potentially lessen the later cardiac structural and functional impact of preterm birth would likely be most effective in the early postnatal period, he proposed.
“The neonatal and infant developmental periods are very dynamic and important for growth. Some of our recently published data from this age group would suggest that this is an important window for the development of these cardiac changes,” Lewandowski said.
His group is engaged in a randomized trial of an exercise intervention in such young adults, “including a group of individuals born preterm, to determine whether lifestyle change in young adulthood can reduce blood pressure and preferentially modify cardiac phenotype.”
Huckstep, Lewandowski, and their coauthors as well as Bonamy and Carr report that they have no relevant conflicts.
J Am Coll Cardiol. 2018;71:1347-1356, 1357-1359. Abstract, Editorial
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