Further information from a sonometric study of the normal tricuspid valve annulus in sheep: geometric changes during the cardiac cycle.

In a previous sono-metric study, changes were described that occurred in the normal tricuspid valve during the cardiac cycle. However, the wealth of data available suggested the need for reporting further findings that should contribute to a better understanding of the dynamics of the tricuspid valve.Thirteen sonomicrometry transducers were placed in the hearts of each of seven sheep. Six transducers were placed in the tricuspid annulus (TA), at the base of each leaflet, and at each commissure; three at the tips of the papillary muscles (PMs); three in the free edges of the leaflets; and one transducer was placed at the apex. Distances between transducers, pulmonary and right ventricular pressures, and pulmonary flow were recorded simultaneously.The TA area underwent two major contractions and expansions during the cardiac cycle, reaching its maximum during isovolumic relaxation and its minimum in diastole. The TA height-to-width ratio changed from 8.4 +/- 1.9% to 15.3 +/- 4.2%. The leaflets began to open before end-systole. By the end of isovolumic relaxation, the leaflets had completed 54.1 +/- 13.4% of their opening. The PM and TA planes were not parallel, but were offset by 11.5 +/- 1.9 degrees to 17.8 +/- 2.1 degrees. The PM rotated 6.9 +/- 0.9 degrees with respect to the TA, with 3.1 +/- 1.1 degrees of the rotation occurring during ejection.The tricuspid valve is not a passive structure but rather forms a dynamic part of the right ventricle. Its orifice area changes not only due to the contraction and expansion of its perimeter but also to changes in its saddle shape. Leaflet opening and closure is not simply a response to pressure. The PMs rotate in relation to the TA. These data should impact upon the diagnosis and surgery of functional tricuspid regurgitation.