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(Circulation. 2000;101:e93.)
© 2000 American Heart Association, Inc.

Circulation Electronic Pages

Physiology of Ventricular Septal Defect Shunt Flow in the Fetus Examined by Color Doppler M-Mode

Jean-Paul Lethor, MD; Francois Marçon, MD; Michael de Moor, MD; Mary Etta E. King, MD

From Massachusetts General Hospital, Pediatric Cardiology, Boston, Mass.

Correspondence to J.-P. Lethor, MD, Massachusetts General Hospital, Pediatric Cardiology, 55 Fruit St, VBK 615, Boston, MA 02114-2696. E-mail jp.lethor@chu-nancy.fr

	Introduction

 
The fetal circulation is unique in having the right ventricle perform as a systemic pump delivering oxygen-enriched placental blood to the distal fetal systemic circulation via the ductus arteriosus. Both ventricles then operate at similar systemic pressures. For this reason, the pressure gradient across the interventricular septum is known to be minimal. It has been noted, however, in fetuses with ventricular septal defects (VSDs) that shunt flow can be detected by color flow Doppler crossing the VSD, indicating that there are subtle differences in pressure between the ventricles at different times in the cardiac cycle. The isolated VSD thus provides a convenient physiological window for studying interventricular dynamics in the developing fetus.

The rapid fetal heart rate and absence of a fetal ECG make accurate timing of shunt dynamics by standard 2D echocardiography with color flow Doppler difficult. We present a case in which careful hemodynamic evaluation could be performed by combination of information from several different cardiac ultrasound modalities that possess a higher temporal resolution—continuous-wave Doppler, pulsed-wave Doppler, and color Doppler M-mode—to elucidate the temporal characteristics of VSD shunt flow.

A systematic fetal echocardiogram was performed on a 36-year-old gravida 4 woman whose previous child had been diagnosed with a perimembranous VSD. At 22 weeks of gestation in this pregnancy, a small defect of the perimembranous ventricular septum, measuring 2.1 mm in diameter (Figure 1, left), could be clearly seen in the 2D fetal echocardiogram. Accessory tissue was burgeoning close to the tricuspid region but remained rudimentary. All . . . [Full Text of this Article]