Fetal cardiac asystole during labor.

A review of 14 cases of fetal cardiac asystole greater than two seconds during labor revealed two distinct patterns. Type 1 episodes developed without warning in eight apparently healthy fetuses at the nadir of a variable deceleration. These episodes were both preceded and followed by normal to increased variability, stable baseline heart rate, and less dramatic variable decelerations. Analysis of the fetal electrocardiogram (ECG) complexes during the asystole revealed a normal QRS complex, either biphasic or absent P-waves, and occasional ventricular extrasystoles. One of eight fetuses in this group died; the remainder were delivered in good condition and required minimal resuscitation. The mechanism of type 1 episodes appears to be an exuberant vagal response to umbilical cord compression. Rapid intervention probably is not warranted. Type 2 episodes developed in seriously asphyxiated infants and frequently were preceded by absent variability and, usually, severe decelerations. The fetal ECG pattern during the episode revealed bradycardia with sinus rhythm. Five of the six infants with type 2 episodes died either in utero or in the neonatal period. Despite the ominous portent of type 2 patterns, rapid delivery appears to be indicated.