Venous blood flow pattern suggesting tachycardia-induced 'cardiomyopathy' in the fetus.

Studies in the fetal lamb and human fetus demonstrated that, in the late stage of supraventricular tachycardia, myocardial dysfunction (tachycardia-induced 'cardiomyopathy') may appear and even persist after drug-induced conversion to sinus rhythm. The objective of this study was to verify whether these changes in cardiac function are reflected in the venous system. In seven fetuses with supraventricular tachycardia (five with hydrops and four of these with atrioventricular valve incompetence during tachycardia) between 24 and 33 weeks of gestation, spectral Doppler analysis of flow velocity waveforms in the inferior vena cava and the ductus venosus was performed before and after drug-induced cardioversion, and was compared with reference values known from the literature and our own indices obtained in 129 normal pregnancies. After drug-induced conversion from supraventricular tachycardia to sinus rhythm associated with a change from a pulsatile to a normal biphasic forward venous blood flow pattern, abnormal venous indices resulting from increased reverse blood flow during atrial contraction persisted for 2-42 days (median 12 days). Severe functional tricuspid insufficiency can lead to a significant decrease in the systolic peak velocity with deterioration of the venous blood flow indices. In the first days after supraventricular tachycardia, rapid changes in these indices seem to depend predominantly on the decrease of tricuspid insufficiency and the increase of the systolic peak velocity. In addition to the persistence of atrioventricular valve regurgitation, abnormal indices of venous blood flow during sinus rhythm indicate the existence of altered myocardial function, suggesting reversible tachycardia-induced 'cardiomyopathy'. Blood flow indices in the venous system seem to reflect changing myocardial function very sensitively and rapidly and, therefore, appear very useful in the surveillance of the fetus with tachyarrhythmia under drug therapy, especially with regard to the assessment of cardiac function at the time of cardioversion and in the period after supraventricular tachycardia.