In 1966, Criley and his colleagues published the results of their study on the potential explanation for late systolic murmur using cinenagiocardiography. This study was a duplication of Barlow"s earlier investigation in 1965. In their report, these authors commented:
"...With the onset of systole the non-opaque orifice of the valve was obliterated as the leaflets came together. As systolic contraction progressed, a well-demarcated and smooth-walled projection from the left ventricular contrast shadow extended across the atrioventricular ring into the left atrium. In mid-to-late systole, the contrast medium spread diffusely through the left atrium, producing a double density behind the more heavily opacified ventricular projection. The mitral regurgitation was slight or could not be detected in early systole, but became quite evident after 0.12 to 0.22 sec." Criley and colleagues also showed that the maximal billowing of the posterior leaflet coincided with the click in mid-late systole.
Subsequently they concluded:
"...We believe that a systolic murmur of late onset and extending to the aortic closure sound, particularly if preceded by a click, is suggestive if not diagnostic of prolapse of a portion of the mitral valve."
In this paper, Criley introduced for the first time the term "prolapse" to describe the cineangiocardiographic appearance of the posterior leaflet whereas Barlow used the term "Billowing "to describe the same entity.
Criley also made additional comments regarding surgical indications and its timings which were significantly in advance of his time:
"The type of mitral valve dysfunction described in this report may be amenable to corrective surgery without the necessity of replacing the valve, since there is more than the normal amount of valve tissue. The aneurysmal bulging may be a result of loss of chordal support, and it is possible that the process will be self-perpetuating and the incompetence will increase with time. If these assumptions are correct, early surgical indication would be indicated in patients with sign of progressive disability."