Two sinusoidal heart rate patterns in fetal lambs undergoing extracorporeal membrane oxygenation

OBJECTIVES: The study analyzed the phase relationship between fetal heart r ate and arterial blood pressure fluctuation during sinusoidal heart rate pa tterns in fetal lambs. STUDY DESIGN: Thirty-two fetal lambs were placed on extracorporeal membrane oxygenation after cesarean delivery at ages ranging between 113 and 133 da ys' gestation. Sinusoidal heart rate patterns persisting for >10 minutes we re analyzed. The relationships between the sinusoidal heart rate cycles and the arterial blood pressure cycles were quantitatively expressed in degree s by timing the zenith and the nadir of each and assigning a phase-angle in dex (with 0 [360] and 180 degrees being synchronized and reciprocal, respec tively). Simultaneous blood samples were taken from the 4 different sites o f the fetal circulation for blood gas and acid-base analysis when the sinus oidal heart rate pattern appeared. Regional cerebral blood flow was determi ned by means of the colored microsphere technique in 8 fetuses with sinusoi dal patterns and 7 control fetuses. RESULTS: Sinusoidal heart rate patterns were observed in 13 (40.6%) of the 32 fetal lambs. Two types of fetal heart rate and arterial blood pressure r elationship could be recognized during sinusoidal pattern, the reciprocal t ype (n = 7) and the synchronized type (n = 9). A reciprocal type of sinusoi dal pattern preceded a synchronized type pattern in 3 lambs that showed sin usoidal patterns at different stages of the experiment. The reciprocal type was associated with a higher baseline heart rate and amplitude of the sinu soidal heart rate pattern than was the synchronized type. The synchronized type was associated with a lower pH and base excess than was the reciprocal type. The cerebral blood flow in the medulla oblongata was significantly l ower during the synchronized type pattern than during the reciprocal type p attern. CONCLUSION: There are 2 types of sinusoidal heart rate pattern. A synchroni zed type sinusoidal heart rate pattern may indicate more advanced fetal com promise than is associated with a reciprocal type pattern.