FIGURE 24-8 Grades of baseline fetal heart rate variability shown in the following five panels. 1. Undetectable, absent variability. 2. Minimal variability, ;5 bpm. 3. Moderate (normal) variability, 6 to 25 bpm. 4. Marked variability, >25 bpm. 5. Sinusoidal pattern. This differs from variability in that it has a smooth, sinelike pattern of regular fluctuation and is excluded in the definition of fetal heart rate variability. (Adapted with permission from National Institute of Child Health and Human Development Research Planning Workshop, 1997.)
FIGURE 24-9 Internal fetal monitoring at term demonstrated occasional abrupt beat-to-beat fetal heart rate spiking due to erratic extrasystoles shown in the corresponding fetal electrocardiogram. The normal newborn was delivered spontaneously and had normal cardiac rhythm in the nursery.
Most fetal arrhythmias without comorbid fetal hydrops are inconsequential during labor, but they may hinder interpretation of fetal heart rate tracings. Sonographic evaluation of fetal anatomy and echo cardiography can be useful. Generally, in the absence of fetal hydrops, neonatal outcome is not measurably improved by pregnancy intervention. At Parkland Hospital, intrapartum fetal cardiac arrhythmias, especially those associated with clear amnionic fluid, are typically managed conservatively.
A true sinusoidal pattern such as that shown in panel 5 of Figure 24-8 can be observed with fetal intracranial hemorrhage, with severe fetal asphyxia, and with severe feral anemia. he last may stem from anti-D alloimmunization, fetomaternal hemorrhage, twin-twin transusion syndrome, fetal parvoviral infection, or vasa previa with bleeding. Insigniicant sinusoidal patterns have been reported following administration of meperidine, morphine, alphaprodine, and butorphanol (Angel, 1984; Egley, 1991; Epstein, 1982). Shown in Figure 24-10 is a sinusoidal pattern seen with maternal meperidine administration. An important characteristic of this pattern when due to narcotics is the sine frequency of 6 cycles per minute. A sinusoidal pattern also has been described with chorioamnionitis, fetal distress, and umbilical cord occlusion (lvlurphy, 1991). Young (1980a) and Johnson (1981) with their coworkers concluded that intrapartum sinusoidal fetal heart patterns were not generally associated with fetal compromise. hus, management is usually dictated by the clinical setting. Modanlou and Freeman (1982), based on their extensive review, proposed adoption of a strict definition: 1.
Stable baseline heart rate of 120 to 160 bpm with regular oscillations 2.
Amplitude of 5 to 15 bpm (rarely greater)
FIGURE 24-10 Sinusoidal fetal heart rate pattern associated with maternal intravenous meperidine administration. Sine waves are occurring at a rate of 6 cycles per minute.
3.
Long-term variability frequency of 2 to 5 cycles per minute 4.
5.
Oscillation of the sinusoidal waveform above or below a baseline 6.
Absent accelerations.
Although these criteria were selected to deine a sinusoidal pattern that is most likely ominous, they observed thar the pattern associated with alphaprodine is indistinguishable. Other investigators have proposed a classiication of sinusoidal heart rate patterns into mild-amplitude 5 to 15 bpm, intermediate-16 to 24 bpm, and major-::25 bpm to quantiy fetal risk (Murphy, 1991; Neesham, 1993).