[Heart valves and cardiac ultrasound: historical perspectives]

The first studies on echocardiography (1953) and on Doppler ultrasound (1955) were intended to prove whether ultrasound methods could obtain useful diagnostic information on the heart, with no prior experience to extend. As these studies proceeded, the mitral valve emerged as a major subject in echocardiography and Doppler ultrasound, probably because of its anatomical conditions and the characteristic features of its motion. However, it took nearly 10 years before ultrasonic information on the mitral valve was definitely established near the end of the first decade of cardiac ultrasound. This review focuses on the major issues of this period, e.g., the experiences of trial and error and the establishment of the relationships between echocardiography and Doppler ultrasound. The establishment of mitral valve diagnosis by ultrasound is historically significant, because this first showed that ultrasound can provide some information on the inside of the heart, and was followed by the rapid development of echocardiography for wide application to other intracardiac structures. In the subsequent development of echocardiography, the mitral valve has been a helpful landmark. In general, we can see two directions in studies on diagnostic ultrasound; the first aims to evaluate the significance of ultrasound in medical diagnosis, to develop useful equipments and to establish the principles of ultrasonic diagnosis, and the second aims to develop a new medical field based on the established principles and equipments. These approaches may be likened to the two axes of an orthogonal coordinate system. The study on cardiac ultrasound was mainly along the first axis in its first decade, being characterized by a partnership between medicine and physico-engineering. The establishment of ultrasonic information about the mitral valve was the turning point, where the study could also be developed along the second axis.