Circulatory effects of acute bradycardia in the human fetus as studied by Doppler ultrasound

Objective: To report on flow changes in fetal arterial, venous and coronary vessels during bradycardia following cordocentesis. Changes in the fetal circulation in response to acute challenges are incompletely understood. Methods: Fetal blood sampling was performed at 29 + 4 weeks for chromosome analysis in a fetus with multiple malformations including a complete atrioventricular septal defect with competent atrioventricular valve. The procedure was complicated by a 12-min bradycardia of 57 beats/min. 'Heart sparing' (sudden visualization of coronary blood flow) and 'brain sparing' (increased diastolic velocities in the middle cerebral artery) were demonstrated by Doppler examination despite marked circulatory compromise (regurgitation of atrioventricuIar valve, increased reverse flow in precordial veins and pulsatile umbilical vein flow pattern) which persisted after normalization of the fetal heart rate. The findings had resolved completely at a full cardiovascular examination 6 h after the bradycardia. Pregnancy termination was subsequently performed for partial monosomy 13q. Conclusion: Protective fetal changes producing 'heart sparing' and 'brain sparing' and may be operational during episodes of acute fetal bradycardia.