Reid reported in this very short study eight cases of midsystolic click recorded phonocardiogrphically. In seven patients, the mid-systolic click was best heard in the tricuspid or mitral area. In three patients, the click was followed by a systolic murmur continuing to the second sound and in two other patients; the click was associated with a pansystolic murmur.
In this article, Reid expressed the opinion that these mid-systolic clicks with late systolic murmurs could originate from the mitral valve.
The following brief quotation is extracted from his article:
"Association [of midsystolic click] with a murmur provides reasonable evidence of an intravascular or intracardiac origin. Because the click is characteristically heard best just within the mitral area or in the tricuspid area, and because in 3 of the present cases a murmur began with the click and continued to the second sound (implying a ventriculo-atrial regurgitation), it seems that the click may be of atrioventricular valve origin in some cases. It does not seem illogical to assume that the valves can be competent at an early stage of systole and become incompetent later."
Regarding the mechanism of the midsystolic click, Reid postulated:
"...A possible explanation of this midsystolic click is a snapping taut of a chordae tendineae during the later high -pressure phase of ventricular systole which, when resulting in mitral incompetence, is followed by a murmur that continues, like the murmur of mitral incompetence, at least to the second sound. The term 'chordal snap' is proposed for midsystolic clicks in which this explanation is thought operative."
The entire text of Reid's article is displayed here.
Mount Sinai library of medicine provided graciously the PDF file of this article.