Dynamic mammalian cardiogenesis investigated by high-resolution ultrasound in guinea pigs.

Ultrasonic cardiac imaging ofhuman fetuses has been feasible only after 12 to 14 weeks gestation when the heart is completely formed. Our 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 three 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. Circulation 68, No. 4, 841-845, 1983. PRIOR STUDY of mammalian cardiogenesis has been accomplished by standard histologic and organ culture techniques. Serial study of dynamic cardiogenesis in mammals has not been possible since the window technique used in avian preparations' is not applicable to mammals. Echocardiographic methods are potentially useful in the study of cardiogenesis, although prior echocardiographic imaging of fetuses has been limited to study of completely formed preterm hearts, principally in humans.2 The purpose of those examinations was to detect abnormalities of the heart in utero after development was complete. The purpose of this study was to evaluate an ultrasonic method for examining dynamic mammalian cardiogenesis. Our results show that highresolution ultrasonography, a method that enabled developmental interference to be avoided, allowed study From the Departments of Pediatrics and Anatomy, University of Arizona Health Sciences Center, Tucson. Supported in part by an American Heart Association grant, NIH grant No. HL07479, and NIH grant No. lROL HL 28850-01. Address for correspondence: Stanley J. Goldberg, M.D., Department of Pediatrics, University of Arizona Health Sciences Center, Tucson, AZ 85724. Received March 21, 1983; revision accepted June 9, 1983. Vol. 68, No. 4, October 1983 of the dynamic process of mammalian cardiac development in utero.