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Left ventricular mechanics in the preterm infant and their effect on the measurement of cardiac performance
L A Lee1, T R Kimball, S R Daniels
1Division of Cardiology, Children's Hospital Medical Center, Cincinnati, OH 45229.
Insights
Preterm infants show altered left ventricular shape and wall motion after birth, impacting cardiac function measurements. These changes improve over the first weeks of life, highlighting the need for specific assessment methods like area shortening.
Area of Science:
- Neonatal Cardiology
- Pediatric Echocardiography
- Cardiovascular Physiology
Background:
- The transition from fetal to postnatal circulation significantly impacts cardiovascular adaptation in preterm infants.
- Limited understanding exists regarding left ventricular (LV) geometry, wall motion, and function during this critical period.
- Standard echocardiographic parameters may be affected by the unique physiological state of preterm neonates.
Purpose of the Study:
- To investigate abnormalities in LV geometry and wall motion in healthy preterm infants post-birth.
- To determine the duration of these geometric and functional changes.
- To examine factors influencing these changes and their impact on cardiac performance measurements.
Main Methods:
- Serial echocardiograms were performed on 14 healthy preterm infants (gestational age 33 ± 2 weeks) at two time points: early postnatal (9.5 ± 3.5 days) and later (51 ± 16 days).
- Measurements included LV shape, wall motion, wall stress, LV mass, M-mode shortening fraction (SF), and two-dimensional area shortening (AS).
- Analysis focused on changes in LV geometry, wall motion patterns, and functional indices over the first weeks of life.
Main Results:
- Septal flattening caused LV shape distortion in early postnatal life, resolving as infants matured.
- Impaired mid-septal and anterior free wall motion at the first assessment improved by the second.
- LV mass significantly increased (24 to 41 gm/m²) and wall stress decreased (49 to 38 gm/cm²) with age. SF was lower initially (18%) compared to later (28%), while AS remained consistent (49% vs 53%).
Conclusions:
- Preterm newborns exhibit transiently distorted LV shape and abnormal wall motion in the early postnatal period.
- These findings can alter the interpretation of standard echocardiographic parameters like SF.
- Area shortening may provide a more reliable assessment of LV performance in preterm infants during the initial weeks of life.
Abstract:
The effects of the transition from fetal to postnatal circulation on left ventricular geometry, wall motion, and echocardiographic measurements of function in the human preterm infant are largely unknown. To determine whether abnormalities in left ventricular geometry are present in the normal preterm infant after birth and, if so, for how long, and to examine possible contributing factors and their effect on the measurement of cardiac performance, we obtained serial echocardiograms of 14 healthy preterm infants (gestational age, 33 +/- 2 weeks; birth weight, 1940 +/- 470 gm) at 9.5 +/- 3.5 days of age (time 1) and again at 51 +/- 16 days (time 2). Left ventricular shape and wall motion were measured and estimates of wall stress and mass were made. Performance was assessed by standard M-mode shortening fraction and by transverse two-dimensional area shortening. At time 1 septal flattening caused distortion of left ventricular shape. As the patients grew older, septal flattening resolved and the left ventricle tended to assume a circular cross-sectional shape. Wall-motion analysis demonstrated poor motion of the midseptum and anterior free wall at time 1, which improved at time 2 (p = 0.06). Left ventricular mass increased from 24 +/- 5 to 41 +/- 7 gm/m2 (p = 0.0001) and wall stress decreased from 49 +/- 21 to 38 +/- 13 gm/cm2 (p = 0.005) between time 1 and time 2. Shortening fraction was lower at time 1 than at time 2 (18% +/- 7% vs 28% +/- 8%; p = 0.001; normal limit = 28% to 45%); however, there was no significant difference in area shortening between time 1 and time 2 (49% +/- 10% vs 53% +/- 8%; normal limit = 45% to 65%). We conclude that the preterm newborn infant has distorted left ventricular shape and abnormal wall motion, which alter measurements of shortening fraction and persist for the first weeks of life. Area shortening may be necessary to assess left ventricular performance during the first weeks of life in the premature infant.