Real-time and simultaneous measurement of tricuspid orifice and tricuspid anulus areas in anesthetized dogs

Complete mapping of the tricuspid valve apparatus using three-dimensional sonomicrometry

OBJECTIVE

Many surgeons consider the tricuspid valve to be a second-class structure. Our objective was to determine the normal anatomy and dynamic characteristics of the tricuspid valve apparatus in vivo and to discern whether this would aid the design of a tricuspid valve annuloplasty ring model.

METHODS

Sixteen sonomicrometry crystals were placed around the tricuspid annulus, at the bases and tips of the papillary muscles, the free edges of the leaflets, and the right ventricular apex during cardiopulmonary bypass in 5 anesthetized York Hampshire pigs. Animals were studied after weaning of cardiopulmonary bypass on 10 cardiac cycles of normal hemodynamics.

RESULTS

Sonomicrometry array localizations demonstrate the multiplanar shape of the tricuspid annulus. The tricuspid annulus reaches its maximum area (97.9 ± 25.4 mm(2)) at the end of diastole and its minimum area (77.3 ± 22.5 mm(2)) at the end of systole, and increases again in early diastole. Papillary muscles shorten by 0.8 to 1.5 mm (11.2%) in systole, and chordae tendineae straighten by 0.8 to 1.7 mm (11.4%) in systole.

CONCLUSIONS

The shape of the tricuspid annulus is a multiplanar 3-dimensional one with its highest point at the anteroseptal commissure and its lowest point at the posteroseptal commissure, and the anteroposterior commissure is in a middle plane in between. The tricuspid annulus area reaches its maximum during diastole and its minimum during systole. The papillary muscles contract by the same amount of chordal straightening. The optimal tricuspid annuloplasty ring may be a multiplanar 3-dimensional one that mimics the normal tricuspid annulus.

Regulation of the aortic valve opening. In vivo dynamic measurement of aortic valve orifice area

Aortic valve orifice area was dynamically measured in anesthetized dogs with a new measuring system involving electromagnetic induction. This system permits us real-time measurement of the valve orifice area in beating hearts in situ. The aortic valve was already open before aortic pressure started to increase without detectable antegrade aortic flow. Maximum opening area was achieved while flow was still accelerating at a mean of 20 to 35 msec before peak blood flow. Maximum opening area was affected by not only aortic blood flow but also aortic pressure, which produced aortic root expansion. The aortic valve orifice area's decreasing curve (corresponding to valve closure) was composed of two phases: the initial decrease and late decrease. The initial decrease in aortic valve orifice area was slower (4.1 cm2/sec) than the late decrease (28.5 cm2/sec). Aortic valve orifice area was reduced from maximum to 40% of maximum (in a triangular open position) during the initial slow closing. These measurements showed that (1) initial slow closure of the aortic valve is evoked by leaflet tension which is produced by the aortic root expansion (the leaflet tension tended to make the shape of the aortic orifice triangular) and (2) late rapid closure is induced by backflow of blood into the sinus of Valsalva. Thus, cusp expansion owing to intraaortic pressure plays an important role in the opening and closing of the aortic valve and aortic blood flow.

Influence of short atrioventricular delay on late diastolic transmitral flow and stroke volume

Atrial transport function and the corresponding transmitral flow and stroke volume depend on the timing of atrial contraction. To study the influence of short atrioventricular delay (AVD) on these hemodynamic parameters, transmitral flow velocity (by pulsed wave Doppler) and aortic flow (by electromagnetic technique) were studied and compared (paired t test) during normal and short AVD at fixed rate DDD pacing (80 bpm) in AV-blocked, open-chest canine preparations (n:16). The short AVD resulted in a shorter acceleration (difference 4.1 +/- 4.9 msec, mean +/- SD, p less than 0.05), a lower peak velocity (difference: 7.1 +/- 3.2 cm/sec, p less than 0.001), a shorter (difference: 26.9 +/- 16.2 msec, p less than 0.001) and more rapid deceleration (difference: 220.7 +/- 291.7 cm/sec2, p less than 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 +/- 5.2%, p less than 0.001) during short AVD as a consequence of a reduced left ventricular filling due to the interruption of the active atrial transport by the onset of the ventricular contraction.

An in vivo area meter for real-time measurement of cross-sectional area in the cardiovascular system

A direct real-time recording of the cross-sectional area of the heart valve is useful for the fluid dynamic study of the cardiovascular system. Electronic circuitry is described that is capable of driving the transmitter coil assembly placed outside the animal and detecting an area-related signal induced in the one-turn coil in vivo. When a piece of fine pliable metal thread encircles the area of interest (e.g. the mitral/aortic valve orifice) so as to form a single loop, the electrical potential between the ends of the loop is linearly related to the size of the area irrespective of its shape. The principle of measurement, construction of transmitter coil assembly, and simple but accurate direct calibration are also described.