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Phasic variations in the size, position, and geometry of the tricuspid valve annulus during the cardiac cycle were studied in five normal anethetized dogs 2-6 weeks after 8-11 lead beads had been sutured on the endocardial surface of the valve ring during cardiopulmonary bypass. Field-by-field measurements from biplane videoangiograms were used to assess changes in valve ring size and shape during control hemodynamic conditions and during increased heart rates. In addition, the percutaneous production of a complete atrioventricular block in two dogs enabled us to observe the effect of isolated atrial contractions on the valve annulus. During normal sinus rhythm, progressive narrowing of the annulus  during atrial and ventricular contractions reduced its area by 20-39% of the maximal valve circumference during diastole; approximately two-thirds of the total ring narrowing was associated with atrial systole. These findings suggest that one of the functions of atrial contraction is the reduction in size of the atrioventricular valve orifices prior to the onset of ventricular systole.

Motion of the tricuspid valve annulus in anesthetized intact dogs.