Fetal blood flow measurements during fetal cardiac arrhythmia

3 cases of fetal complete heart block, 1 case of fetal bradycardia and 2 cases of fetal supraventricular tachycardia were studied. Using an ultrasonic technique combining real-time ultrasound with a pulsed Doppler system, blood flow measurements at the lower thoracic level of the fetal descending aorta were taken. Despite alterations in rhythm, the blood flow in the aorta descendens was maintained within normal range. With a reduced heart rate, there was an increase in stroke volume, blood flow velocity, acceleration of blood flow velocity and maximum diameter change; conversely, with an increased heart rate the same four parameters were lowered. These alterations reflect changes in cardiac contraction force, and illustrate the ability of the fetal myocardium in maintaining blood flow in the growing fetus.