First-trimester fetal heart block: a marker for cardiac anomaly

Background Fetal heart block in the second and third trimesters may be caus ed by transplacental passage of autoantibodies or cardiac defects. Little i s known about the etiology of first-trimester fetal heart block. Materials and methods Fetal heart block was diagnosed in four patients (neg ative antibody serology) referred for first-trimester sonographic evaluatio n of increased fetal nuchal fold thickness with bradycardia. Two-dimensiona l echocardiography was complemented by color Doppler flow imaging of the fe tal heart. Fetal arrhythmia was verified by M-mode, pulsed wave Doppler and /or color M-mode echocardiography. Results All fetuses had congenital heart disease, atrioventricular valve re gurgitation, heart block and edema. Autopsy confirmed heterotaxy in three c ases (left atrial isomerism with atrial septal defect; left isomerism with double-outlet right ventricle, great artery malposition and ventricular sep tal defect. The third case had dextrocardia with atrioventricular canal def ect and the fourth case dextrocardia with great artery transposition. Conclusion First-trimester fetal bradycardia may result from heart block of the type associated with complex congenital heart disease. Accelerated ede ma formation in this setting may be the basis of nuchal edema formation. Fi rst-trimester fetal echocardiography offers the potential for early diagnos is and intervention in these cases with poor prognosis.