EFFECTS OF VOLUME LOADING, PROPRANOLOL, AND HEART-RATE CHANGES ON PUMP FUNCTION AND SYSTOLIC-TIME INTERVALS OF THE LEFT ATRIUM IN OPEN-CHEST DOGS

Left atrial (LA) pressure-dimension curve was constructed and the area of A-loop (AAL, in mm. mm Hg) which reflected LA stroke work was meas ured in 14 open-chest dogs before and after saline infusion, in 14 dog s before and after propranolol administration under fixed heart rate a nd in 12 dogs while atrial pacing rate was increased stepwise. The pea k +dP/dt of LA systolic pressure (LA +dP/dt, in mm Hg/s) and LA percen t fraction shortening (LA %FS) were obtained as indices of LA pump fun ction. The peak -dP/dt of X descent in LA pressure (LA -dP/dt, in mm H g/s) was measured as an index of LA relaxation. From pulsed Doppler mi tral flow velocities, A-wave acceleration (AC, in cm/s2), LA pre-eject ion period corrected by P-wave duration (LA PEPc), and LA ejection tim e (LA ET) were measured. AAL, LA +dP/dt, AC, LA %FS, and LA -dP/dt inc reased after saline infusion (AAL; 2.2+/-1.6 to 5.1+/-3.3 (p<0.05), LA +dP/dt; 34+/-16 to 52+/-23 (p<0.05), AC; 320+/-90 to 472+/-98 (p<0.05 ), LA %FS; 9+/-4 to 12+/-4 (p<0.05), and LA -dP/dt; 38+/-28 to 60+/-32 (p<0.05)) and decreased after propranolol administration (AAL; 2.9+/- 1.9 to 1.2+/-0.7 (p<0.05), and LA +dP/dt; 42+/-19 to 28+/-11 (p<0.05), AC; 332+/-92 to 254+/-102 (p<0.05), LA %FS; 14+/-5 to 8+/- 5 (p<0.05) , and LA -dP/dt; 36+/-19 to 26+/-18 (p<0.05)), but did not change sign ificantly during heart rate increments. LA PEPc decreased after saline infusion (114+/-11 to 104+/-14 (p<0.05)) and increased after proprano lol administration (108+/-8 to 129+/-13 (p < 0.05)). As pacing rate wa s increased, LA PEPc and LA ET showed no significant changes. Both AAL and LA +dP/dt correlated significantly with LA PEPc (r = -0.76 and -0 .66), but not with LA ET (r = -0.08 and -0.04). In conclusions, LA pum p function was augmented by volume loading and decreased by propranolo l, but unchanged by heart rate increments. These changes in LA pump fu nction were reflected by LA PEPc, but not by LA ET. LA PEPc is a usefu l index of LA pump function which is not heart rate dependent.