Cardiac doppler flows during fetal arrhythmias: Physiologic consequences

Eighty-six fetuses of 21-41 weeks' gestation with arrhythmias were studied with ultrasound and heart ratemonitoring. The type of arrhythmia was identified by M-mode studies and was confirmed by postnatal electrocardio-gram in 70 infants. The most common arrhythmia waspremature atrial contractions (761, followed by prematureventricular contractions (five), paroxysmal supraventriculartachycardia (four), and atrial fibrillation/flutter (one). Dop-pler echocardiography was performed in 54 fetuses to mea-sure flow velocities across the atrioventricular and semilunarvalves. After isolated premature atrial and ventricular con-tractions, post-extrasystolic potentiation was demonstratedby an increase in fractional shortening (N = 32) of 49 2 6%in the right ventricle and 64 2 7% in the left ventricle. Whenpost-extrasystolic beats were compared with normal beats, Doppler-determined time-velocity integrals increased 43%across the tricuspid valve, 41% across the mitral valve, 34%across the pulmonary valve, and 38% across the aortic valve. Mean velocity increased significantly after conversion tonormal sinus rhythm in the five fetuses with supraventricu-lar tachycardia (P <.05). By studying the physiologicconsequences of fetal arrhythmias using two-dimensional Doppler and M-mode ultrasound, we have documented thepresence of post-extrasystolic potentiation after prematurecontractions, the existence of the Frank-Starling mechanism, and an increase in mean velocity (and therefore in cardiacoutput) after conversion of fetal tachyarrhythmias to normalsinus rhythm.