Ultrasonic cardiac imaging of human fetuses has been feasible only after 12 to 14 weeks gestation when the heart is completely formed. The authors' purpose was to develop a method of examining dynamic mammalian cardiogenesis with a high-resolution 9 MHz ultrasound scanner. Fetal guinea pig hearts were imaged in utero over the course of 10 days. All images were obtained after blastocyst implantation estimated to occur 8 days after fertilization with cardiogenesis occurring over the next 14 days. After laparotomies were performed on the gravid guinea pigs, sterile transducers were placed on their uterine horns and ultrasonic images were obtained. Further optical magnification of videotaped images was required to visualize cardiac details. Ten gravid guinea pigs were examined and 3 of 10 underwent serial imaging. The earliest cardiac images, recorded approximately 10 days after implantation, demonstrated a partially fused heart tube, ventricle, bulbus cordis, and first aortic arch. During the next 24 hr looping of the heart, a primitive atrium and an unfused endocardial cushion structure were observed. Midway through the first week of cardiac development, ventricular and atrial septation and development of primitive atrioventricular valve tissue were imaged. At the end of the first week of cardiac development, more distinct endocardial cushion structure and atrial and ventricular septation were noted. Additionally, a functioning foraminal flap was observed. Midway through the second week of cardiac development, spiraling and division of the bulbus cordis were complete. Scanning electron microscopic examination verified the size and configuration of ultrasonically imaged structures. The high-frequency imaging allowed dynamic recording of events in mammalian cardiogenesis.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)