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Figure 4 Fetal Heart Rate Patterns in Fetal AVB
Atrial and ventricular fetal heart rate tracings from fetus #4 showing (A) reactive pattern at 28 weeks’ gestation and (B) nonreactive pattern at 32 weeks’ gestation. In the reactive pattern, the atrial and ventricular tracings were highly correlated; even variations as small as 3 beats/min (bpm) were often correlated. The degree of ventricular reactivity and the amplitude of the beat-to-beat fetal heart rate variability varied strongly with mean ventricular rate. At rates >70 beats/min, ventricular reactivity was exaggerated and the amplitude of the ventricular accelerations actually exceeded that of the atrial accelerations. As mean ventricular rate declined, the amplitude of the ventricular accelerations and the beat-to-beat fetal heart rate variability progressively decreased. Notice that atrial reactivity is present in the nonreactive pattern. Both patterns showed prominent atrial beat-to-beat variability due to the presence of ventriculophasic sinus arrhythmia. Unlike normal beat-to-beat variability, its amplitude does not diminish during heart rate acceleration. (C) Atrial and ventricular fetal heart rate tracings from fetus #3 at 30 weeks’ gestation showing abrupt transition from the nonreactive to the reactive pattern. AVB = atrioventricular block.
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