Effect of heart failure on the mechanism of exercise-induced augmentation of mitral valve flow.

Abstract

The exercise response of left ventricular (LV) filling dynamics may be altered by congestive heart failure (CHF). Accordingly, we studied 18 conscious dogs, instrumented to measure micromanometer LV and left atrial (LA) pressures and determine LV volume from three dimensions. CHF was produced by 4-5 weeks of right ventricular rapid pacing. Before CHF, exercise (5.5-8.5 mph for 8-15 minutes) increased the maximum rate of LV filling (dV/dtmax) (197 +/- 37 versus 297 +/- 56 ml/sec [mean +/- SD], p < 0.05) in response to an increase in the maximum early diastolic LA to LV pressure gradient (5.8 +/- 2.0 versus 9.8 +/- 1.9 mm Hg, p < 0.05) produced by a fall in minimum LV pressure (1.0 +/- 2.9 versus -3.9 +/- 3.1 mm Hg, p < 0.01), whereas mean LA pressure was unchanged (6.4 +/- 3.1 versus 6.4 +/- 4.2 mm Hg, p = NS). The time constant of LV relaxation was shortened (28.1 +/- 3.2 versus 21.0 +/- 4.2 msec, p < 0.05). After CHF, dV/dtmax (141 +/- 51 versus 200 +/- 59 ml/sec, p < 0.05) and the maximum LA to LV pressure gradient (6.0 +/- 1.1 versus 11.1 +/- 2.7 mm Hg, p < 0.05) continued to increase with exercise (3-5.0 mph for 4-8 minutes). However, the time constant of LV relaxation was prolonged (35.6 +/- 4.8 versus 38.9 +/- 5.5 msec, p < 0.05), and minimum LV pressure (15.1 +/- 5.6 versus 17.6 +/- 5.9 mm Hg, p < 0.05) and mean LA pressure increased (22.6 +/- 7.2 versus 29.1 +/- 7.3 mm Hg, p < 0.05). These altered effects of exercise on LV diastolic filling dynamics persisted when heart rate and wall stress during exercise before and after CHF were matched by varying the level of exercise. We conclude that, during normal exercise, mitral valve flow is augmented by a fall of early diastolic LV pressure without a rise in LA pressure. After CHF, early diastolic LV pressure does not fall but increases during exercise. Thus, the increase in the early diastolic LA to LV pressure gradient and the rate of mitral valve flow results from an increase in LA pressure during exercise after CHF. This study suggests that the failure of the enhancement of LV relaxation and an increase in early diastolic LV pressure with exercise after CHF may contribute to exercise intolerance in CHF.