Left atrial systolic and diastolic function after cessation of pacing in tachycardia-induced heart failure

Studies in the rapid-pacing model of heart failure have shown that left ventricular (LV) systolic function normalizes on cessation of pacing and LV diastolic dysfunction persists, but there is no information regarding atrial function under these conditions. To determine the effects of cessation of pacing on left atrial (LA) systolic and diastolic function, ten dogs with rapid pacing-induced heart failure (250 beats/min for 3-4 wk), six dogs with regression of heart failure (4 wk after cessation of rapid pacing), and seven control dogs were instrumented with LA sonomicrometers and micromanometers. At matched LA pressure, LA ejection (10.2 +/- 3.0 vs. 17.4 +/- 5.5%), reservoir volume fractions (19 +/- 8 vs. 35 +/- 11%), and heart rate-corrected mean normalized systolic ejection rate (1.25 +/- 0.33 vs. 1.60 +/- 0.44 EF/s) were significantly less, and the volume-normalized diastolic stiffness constant (4.9 +/- 0.8 vs. 3.2 +/- 1.1) was significantly greater, in regression versus control dogs; these changes were associated with incomplete regression of LA hypertrophy and a persistent 77.4% increase in beta-myosin heavy chain (beta-MHC) in the LA body. LV systolic function and weight were not significantly different, whereas the time constant of LV relaxation was longer (52.5 +/- 4.4 vs. 40.8 +/- 7.6 ms; P < 0.05) and LV end-diastolic pressure was greater (12.2 +/- 1.8 vs. 7.1 +/- 2.0 mmHg; P < 0.05) in regression compared with control dogs. Thus, unlike the normalization of LV systolic function observed with cessation of rapid pacing, LA systolic function is persistently abnormal, owing in part to persistent LV diastolic dysfunction, residual LA hypertrophy, and MHC isoform switches.