Background The 2015 neonatal resuscitation guidelines added ECG as a recommended method of assessment of an infant’s heart rate (HR) when determining the need for resuscitation at birth. However, a recent case report raised concerns about this technique in the delivery room.

Objectives To compare accuracy of ECG with auscultation to assess asystole in asphyxiated piglets.

Methods Neonatal piglets had the right common carotid artery exposed and enclosed with a real-time ultrasonic flow probe and HR was continuously measured and recorded using ECG. This set-up allowed simultaneous monitoring of HR via ECG and carotid blood flow (CBF). The piglets were exposed to 30 min normocapnic alveolar hypoxia followed by asphyxia until asystole, achieved by disconnecting the ventilator and clamping the endotracheal tube. Asystole was defined as zero carotid blood flow and was compared with ECG traces and auscultation for heart sounds using a neonatal/infant stethoscope.

Results Overall, 54 piglets were studied with a median (IQR) duration of asphyxia of 325 (200-491) s. In 14 (26%) piglets, CBF, ECG and auscultation identified asystole. In 23 (43%) piglets, we observed no CBF and no audible heart sounds, while ECG displayed an HR ranging from 15 to 80/min. Sixteen (30%) piglets remained bradycardic (defined as HR of <100/min) after 10 min of asphyxia, identified by CBF, ECG and auscultation.

Conclusion Clinicians should be aware of the potential inaccuracy of ECG assessment during asphyxia in newborn infants and should rather rely on assessment using a combination of auscultation, palpation, pulse oximetry and ECG.