ATRIAL-NATRIURETIC-FACTOR SECRETION - A ROLE FOR ATRIAL SYSTOLIC EJECTION FORCE

The increase in plasma concentration of atrial natriuretic factor in h eart transplant patients has not been fully elucidated. Besides an eve ntual pressure or volume overload leading to passive atrial distension , the atrial tension developed during atrial systole, or atrial ejecti on force, which may be increased by the transplantation procedure, is an important determinant of atrial natriuretic factor release. We ther efore determined the plasma concentration of atrial natriuretic factor and the maximal atrial ejection force in 15 heart transplant patients and 8 controls, matched for age and body mass. Atrial ejection force, as defined as the force exerted by the left atrium to accelerate bloo d into the left ventricle during atrial systole, was obtained using co mbined two-dimensional imaging and doppler echocardiography. Serum cre atinin concentrations, heart rate [91.9 (SD 13.2) vs 71.8 (SD 10.9) be ats . min(-1)], mean arterial blood pressure [103.9 (SD 9.8) vs 87.4 ( SD 5.8) mmHg, 13.85 (SD 1.31) vs 11.65 (SD 0.77) kPa], left ventricula r posterior wall thickness and interventricular septum thickness were higher in heart transplant patients compared to controls. Plasma conce ntration of atrial natriuretic factor was also elevated in heart trans plant patients [63.9 (SD 18.1) vs 34.0 (SD 3.2) pg . ml(-1); P < 0.001 ]. In contrast, although the left atrial area was greater in heart tra nsplant patients [28.2 (SD 4.8) vs 15.8 (SD 2.5) cm(2); P < 0.001], mi tral area, transmitral Doppler A-wave maximal velocity and atrial ejec tion force were similar in transplant and in control patients [7.7 (SD 3.5) vs 8.9 (SD 2.8) kdyn, 77 (SD 35) vs 89 (SD 28)mN]. No significan t correlation was observed between concentration of atrial natriuretic factor and atrial ejection force, either in heart transplant patients or in controls. Thus, the elevated plasma concentration of atrial nat riuretic factor observed in these heart transplant patients was multif actorial in origin, and was considered to depend upon an hypersecretio n rather than upon a decreased clearance rate. Moreover, it is suggest ed that the atrial ejection force was unlikely to have participated in this enhanced release of atrial natriuretic factor.