THE ROLE OF THE LEFT ATRIAL APPENDAGE - A VOLUME LOADING STUDY IN OPEN-CHEST DOGS

Although the left atrial appendage has a quite unique structure, its f unction remains unclear. To clarify the function of the left atrial ap pendage, changes in its anteroposterior, transverse and longitudinal d imensions, and in the anteroposterior dimension of the left atrial bod y were measured by a sonomicrometer during volume loading in open ches t dogs. In the control state, fractional shortening of the transverse dimension of the appendage was greater than that of the atrial body. A fter dextran infusion, each dimension of the appendage and body, measu red just before atrial contraction, increased curvilinearly. The perce nt increase in appendage dimensions was greater than that of the atria l body dimension (p < 0.05). Systolic shortenings of the appendage inc reased until mean left atrial pressure reached approximately 15 mmHg b ut after further pressure elevation, it decreased. In postmortem isola ted hearts, the appendage volume was 17.2 +/- 4.4% of the whole left a trial volume. These findings indicate that the appendage has a conside rable volume with a greater compliance and assists left ventricular fi lling during atrial contraction by a Frank-Starling mechanism.