Objectives: We hypothesized that the physiologic response to exercise in valvular aortic stenosis could be measured by Doppler echocardiography.
Background: Data on exercise hemodynamics in patients with aortic stenosis are limited, yet Doppler echocardiography provides accurate, noninvasive measures of stenosis severity.
Methods: In 28 asymptomatic subjects with aortic stenosis maximal treadmill exercise testing was performed with Doppler recordings of left ventricular outflow tract and aortic jet velocities immediately before and after exercise. Maximal and mean volume flow rate (Qmax and Qmean), stroke volume, cardiac output, maximal and mean aortic jet velocity (Vmax, Vmean), mean pressure gradient (delta P) and continuity equation aortic valve area were calculated at rest and after exercise. The actual change from rest to exercise in Qmax and Vmax was compared with the predicted relation between these variables for a given orifice area. Subjects were classified into two groups: Group I (rest-exercise Vmax/Qmax slope > 0, n = 19) and Group II (slope < or = 0, n = 9).
Results: Mean exercise duration was 6.7 +/- 4.3 min. With exercise, Vmax increased from 3.99 +/- 0.93 to 4.61 +/- 1.12 m/s (p < 0.0001) and mean delta P increased from 39 +/- 20 to 52 +/- 26 mm Hg (p < 0.0001). Qmax rose with exercise (422 +/- 117 to 523 +/- 209 ml/s, p < 0.0001), but the systolic ejection period decreased (0.33 +/- 0.04 to 0.24 +/- 0.04, p < 0.0001), so that stroke volume decreased slightly (98 +/- 29 to 89 +/- 32 ml, p = 0.01). The increase in cardiac output with exercise (6.5 +/- 1.7 to 10.2 +/- 4.4 liters/min, p < 0.0001) was mediated by increased heart rate (71 +/- 17 to 147 +/- 28 beats/min, p < 0.0001). There was no significant change in the mean aortic valve area with exercise (1.17 +/- 0.45 to 1.28 +/- 0.65, p = 0.06). Compared with Group I patients, patients with a rest-exercise slope < or = 0 (Group II) tended to be older (69 +/- 12 vs. 58 +/- 19 years, p = 0.07) and had a trend toward a shorter exercise duration (5.3 +/- 2.9 vs. 7.3 +/- 4.9 min, p = 0.20). There was no difference between groups for heart rate at rest, blood pressure, stroke volume, cardiac output, Vmax, mean delta P or aortic valve area. With exercise, Group II subjects had a lower cardiac output (7.4 +/- 2.4 vs. 11.5 +/- 4.6 liters/min, p = 0.005) and a smaller percent increase in Vmax (3 +/- 9% vs. 22 +/- 14%, p < 0.0001).
Conclusions: Doppler echocardiography allows assessment of physiologic changes with exercise in adults with asymptomatic aortic stenosis. A majority of subjects show a rest-exercise response that closely parallels the predicted relation between Vmax and Qmax for a given orifice area. The potential utility of this approach for elucidating the relation between hemodynamic severity and clinical symptoms deserves further study.