Left Ventricular Longitudinal Strain and Strain Rate Measured by 2-D Speckle Tracking Echocardiography in Neonates During Whole-Body Hypothermia

The purpose of the study was to assess changes in cardiac performance in newborn infants with hypoxic-ischemic encephalopathy during therapeutic hypothermia and rewarming with two-dimensional speckle tracking echocardiography. For eight asphyxiated neonates (median birth weight (range): 3038 (2725-3253) g; umbilical artery pH: 6.9 (6.8-7.18) undergoing whole-body hypothermia (33-34°C), left ventricular longitudinal strain and strain rate, as well as heart rate, cardiac output and left ventricular fractional shortening, were determined at four points in time: the start (T1) and end of hypothermia (T2), immediately after rewarming (T3) and the age of 5 to 7 d (T4). Mean (standard deviation) heart rate increased from 93 (12) beats/min at T1 to 133 (12) beats/min at T4 (p < 0.001). Cardiac output was low during hypothermia (T1: 207 [43] mL/kg/min, T2: 240 [70] mL/kg/min) and increased significantly (p < 0.001) afterward (T3: 329 [70] mL/kg/min, T4: 388 [78] mL/kg/min). Left ventricular fractional shortening remained unchanged. Left ventricular global longitudinal peak systolic strain did not differ significantly between hypothermia and rewarming, whereas the systolic strain rate increased from −1.1 (0.3) s-1 at T1 to −1.8 (0.26) s-1 at T4 (p = 0.001). Hypothermia affects peak systolic strain rate, heart rate and cardiac output, with complete recovery after rewarming, whereas peak systolic strain and fractional shortening remain stable.