Changes in the PQRST Intervals and Heart Rate Variability Associated with Rewarming in Two Newborns Undergoing Hypothermia Therapy

Abstract

Background: Little is known about the effects of hypothermia therapy and subsequent rewarming on the PQRST intervals and heart rate variability (HRV) in term newborns with hypoxic-ischemic encephalopathy (HIE). Objectives: This study describes the changes in the PQRST intervals and HRV during rewarming to normal core body temperature of 2 newborns with HIE after hypothermia therapy. Methods: Within 6 h after birth, 2 newborns with HIE were cooled to a core body temperature of 33.5°C for 72 h using a cooling blanket, followed by gradual rewarming (0.5°C per hour) until the body temperature reached 36.5°C. Custom instrumentation recorded the electrocardiogram from the leads used for clinical monitoring of vital signs. Generalized linear mixed models were calculated to estimate temperature-related changes in PQRST intervals and HRV. Results: For every 1°C increase in body temperature, the heart rate increased by 9.2 bpm (95% CI 6.8–11.6), the QTc interval decreased by 21.6 ms (95% CI 17.3–25.9), and low and high frequency HRV decreased by 0.480 dB (95% CI 0.052–0.907) and 0.938 dB (95% CI 0.460–1.416), respectively. Conclusions: Hypothermia-induced changes in the electrocardiogram should be monitored carefully in future studies.

Effect of Temperature on Heart Rate Variability in Neonatal ICU Patients With Hypoxic-Ischemic Encephalopathy

“…Our findings of increased HRV at lower temperatures are consistent with prior animal (25) and human studies(28, 29, 33) evaluating HRV in the temperature range of moderate therapeutic hypothermia. The temperature-dependency of HRV may be explained via several possible mechanisms.…”

“…(28) Only one small study involving 2 newborns undergoing TH for HIE likewise reported a negative association between LF Power and temperature. (33) These investigators also found a negative association between HF Power and temperature as well as a positive association between LF/HF ratio and temperature. We did not evaluate LF/HF ratio as recent reports have questioned whether this measure accurately reflects the sympatho-vagal balance as originally proposed.…”

“…(12, 16) The relative low frequency (LF) and high frequency (HF) power were analyzed as measures of autonomic nervous system (ANS) regulation of HRV. (18, 19) The LF power was calculated as the sum of power in the frequency bands covering 0.05–0.25 Hz, (30, 33-35) while HF power was calculated as the sum of power in the frequency bands covering 0.3–1 Hz. (30, 33-36).…”

“…(18, 19) The LF power was calculated as the sum of power in the frequency bands covering 0.05–0.25 Hz, (30, 33-35) while HF power was calculated as the sum of power in the frequency bands covering 0.3–1 Hz. (30, 33-36). Both LF and HF power were divided by the total power (sum of power in the frequency bands covering 0.05– 2Hz) to calculate the relative LF and HF power.…”

Quantification of compensatory processes of postnatal hypoxia in newborn piglets applying short-term nonlinear dynamics analysis

“…Frequency domain indices were adapted to temporal and spectral features of neonatal cardiovascular signals [17]: very low frequency power (0.005 - 0.04 Hz), low frequency power (0.04 - 0.25 Hz) and high frequency power (0.25 - 0.85 Hz).…”