Heart rate changes after acute fetal haemorrhage--a basis for the pathophysiology of the sinusoidal pattern

The sequence of fetal heart rate (FHR) changes recorded in a case of acute fetal haemorrhage is reported. Initial bradycardia progressed through an undulatory phase to tachycardia. Analysis of these patterns in the context of experimental data on intrinsic heart rate control suggests that the FHR was limited by availability of local myocardial energy, which at a critical level produced low-frequency FHR fluctuations. Extrapolation of this hypothesis to the pathophysiology of the true sinusoidal FHR pattern is discussed.