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Myocardial contractility in premature neonates with and without patent ductus arteriosus
A J Barlow1, C Ward, S A Webber
1Division of Cardiology, British Columbia's Children's Hospital, 4480 Oak Street, Vancouver, B.C. V6H 3V4, Canada.
Insights
A patent ductus arteriosus (PDA) does not affect left ventricular contractility in premature infants. This study establishes a normal contractility relationship for neonates, suggesting they have a higher resting contractile state than older children.
Area of Science:
- Neonatal Cardiology
- Pediatric Cardiovascular Physiology
- Echocardiography
Background:
- Assessing ventricular contractility in premature neonates with patent ductus arteriosus (PDA) is challenging.
- Traditional load-dependent indices may not accurately reflect contractility in this population.
- Rate-corrected velocity of fiber shortening (MVCFc) adjusted for wall stress offers a preload-independent assessment.
Purpose of the Study:
- To evaluate left ventricular contractility in premature neonates with hemodynamically significant PDA.
- To establish the normal relationship between MVCFc and stress at peak systole (SPS) in premature infants.
- To determine if a significant PDA impacts ventricular contractility.
Main Methods:
- Echocardiography was used to measure MVCFc and SPS in two groups of premature infants.
- Group 1: 15 control infants (25-32 weeks' gestation).
- Group 2: 15 infants with significant PDA (26-33 weeks' gestation).
Main Results:
- A linear inverse relationship between MVCFc and SPS was observed in both groups (p < 0.001).
- Regression equations: Control group MVCFc = -0.0153SPS + 1.70; PDA group MVCFc = -0.019SPS + 1.89.
- No significant difference in the MVCFc/SPS relationship was found between groups, but slopes were steeper than in older children.
Conclusions:
- The study establishes the normal MVCFc/SPS relationship in premature neonates (25-33 weeks' gestation).
- Premature infants exhibit a higher resting contractile state compared to older children.
- A hemodynamically significant PDA does not appear to affect ventricular contractility in this population.
Abstract:
Controversy exists as to whether a hemodynamically significant left-to-right shunt due to a patent ductus arteriosus (PDA) affects ventricular contractility. Load-dependent indices such as ejection fraction and shortening fraction have traditionally been used to assess contractility, but the relationship between the rate-corrected velocity of fiber shortening (MVCFc) and wall stress may be more suitable, as it is a preload-independent, afterload-adjusted method of assessing ventricular contractility. Age-related differences have been established for these variables in normal adults and children and it has been recommended for use in the premature neonate. The study was performed to assess left ventricular contractility in premature neonates with a significant left-to-right shunt due to a PDA. Using echocardiography, we measured the relationship of MVCFc to stress at peak systole (SPS) in two groups of premature infants. Group 1 consisted of 15 controls (680-1495 g, 25-32 weeks' gestation), and Group 2 of 15 neonates with hemodynamically significant PDA (840-1635 g, 26-33 weeks' gestation). In both groups, MVCFc was linearly and inversely related to SPS ( p < 0.001). The regression equations were as follows: Group 1, MVCFc = -0.0153SPS + 1.70 ( R(2) = 0.68); and Group 2, MVCF = - 0.019SPS + 1.89 ( R(2) = 0.76). There was no significant difference in the relationship between the two groups, but their slopes were significantly steeper and had a higher Y-intercept than the relationship we previously reported for older children. This preliminary study establishes the normal MVCFc/SPS relationship in the premature neonate (25-33 weeks' gestation) and suggests that premature infants function at a higher resting contractile state than older children. A hemodynamically significant PDA has no effect on contractility. These data will be useful in assessing left ventricular contractility in premature neonates with other types of ventricular loading and noncardiac stress.
