Technique with lock-in amplifier for real-time measurement of tricuspid valve annulus area

A new measuring system that permits real-time registration of the tricuspid valve annular area (TVA) using lock-in amplifier is devised and applied in open-chest anesthetized dogs. The tricuspid valve annulus was stitched with a fine, pliable, metal thread made of 10 30-micron urethane resin-coated copper wires during inflow occlusion. Both ends of the thread were guided out from the right atrium through a single pinhole in the right atrial wall. The signal intensity induced in the sense loop is linearly related to the area encircled by the thread, i.e., the area of the tricuspid annulus. During control state, TVA varied by an average of 24.5% (3.8-46.5%) of its maximum. Presystolic peak and valley of TVA due to atrial contraction and a decrease in TVA during ventricular ejection were generally observed. An increase in TVA during the initial portion of isovolumic contraction phase was prominent in dogs with filariasis, whereas in the other dogs it was not.