Abnormal heart rate characteristics are associated with abnormal neuroimaging and outcomes in extremely low birth weight infants

Abstract

Objective: Brain injury in preterm infants may lead to an inflammatory response and central nervous system dysfunction reflected by abnormal heart rate characteristics (HRC). We hypothesized that a continuously monitored HRC index reflecting reduced HR variability and decelerations correlates with abnormal neuroimaging and outcomes in extremely low birth weight infants (ELBW).

Study design: We analyzed the average HRC index within 28 days after birth (aHRC28) and head ultrasound (HUS) in 384 ELBW infants. In 50 infants with brain magnetic resonance imaging (MRI) and 70 infants with Bayley neurodevelopmental testing at 1 year of age, we analyzed the relationship between aHRC28, MRI abnormalities and low Bayley scores.

Result: aHRC28 was higher in infants with severe HUS abnormalities (2.65±1.27 for Grade III-IV intraventricular hemorrhage (IVH) or cystic periventricular leukomalacia (cPVL) versus 1.72±0.95 for normal or Grade I-II IVH, P<0.001). Higher aHRC28 was also associated with white matter damage on MRI and death or Bayley motor or mental developmental index <70. Associations persisted after adjusting for gestational age, birth weight and septicemia. For every one point increase in aHRC28, the odds ratio of death or Bayley score <70 was 2.45 (95% CI 1.46, 4.05, P<0.001).

Conclusion: A continuously monitored HRC index provides an objective, noninvasive measure associated with abnormal brain imaging and adverse neurologic outcomes in ELBW infants.

Figure 1.

Examples of heart rate characteristics (HRC) index and head ultrasound (HUS) findings in two extremely low-birthweight (ELBW) infants. The hourly HRC index over the entire NICU stay is shown on the y axis. The infant represented on the left had no IVH, was in the NICU for 60 days and the average HRC index in the first 28 days from birth (aHRC28) was 0.97. The infant represented on the right had Grade 4 IVH, was in the NICU for 100 days and aHRC28 was 2.42.

Figure 2.

Heart rate characteristics (HRC) and head ultrasound findings (HUS) in extremely low-birthweight (ELBW) infants. The average HRC index in the first 28 days from birth (aHRC28) was calculated for 384 ELBW infants. HUS were classified as normal (0) or IVH grades 1–4 or cystic periventricular leukomalacia (cPVL). Asterisk indicates aHRC28 was significantly higher for infants with Grade 3–4 IVH or cPVL compared with those with normal HUS or Grade 1–2 IVH.

Figure 3.

Heart rate characteristics (HRC) and white matter damage (WMD) on brain MRI. The average HRC index in the first 28 days from birth (aHRC28) was calculated for 50 ELBW infants who underwent brain MRI near term-corrected age. Asterisk indicates aHRC28 was significantly higher for infants with moderate or severe WMD compared with those with normal MRI or mild WMD.

Figure 4.

Heart rate characteristics (HRC) and neurodevelopmental impairment. The average HRC index in the first 28 days from birth (aHRC28) was calculated for 70 extremely low-birthweight (ELBW) infants who underwent Bayley neurodevelopmental testing at 12–15 months corrected age. Asterisks indicate aHRC28 was significantly higher for infants with Bayley motor, cognitive or language score <70 or infants who died beyond 28 days of age compared with those with Bayley motor, cognitive and language scores ⩾70.