Comparison of the cardiac output and stroke volume response to upright exercise in children with valvular and subvalvular aortic stenosis

Abstract

Cardiac output and stroke volume were evaluated in 17 children (mean age 11.5 ± 3 years) with discrete, membranous subvalvular (Group I, n = 7) and valvular (Group II, n = 10) aortic stenosis during submaximal and maximal (>75% predicted maximal oxygen consumption) upright cycle ergometry. Patients with valvular aortic stenosis were further subdivided on the basis of their aortic valve gradient at rest determined by cardiac catheterization (Group IIA, gradient <40 mm Hg; Group IIB, gradient ≥ 40 mm Hg). These patients were matched with 17 control subjects on the basis of age, sex, height and intensity of exercise during maximal exertion. Cardiac and stroke indexes were determined by the acetylene rebreathing method at each exercise level.Stroke volume index in Group I was significantly greater at rest when compared with that in control subjects (69 ± 13 versus 53 ± 11 ml/m2, α = 0.01, p < 0.05) and that in patients in Group II (69 ± 13 versus 47 ± 12 ml/m2, α = 0.01, p < 0.05). Patients with subvalvular aortic stenosis were unable to increase their stroke volume index from rest to submaximal exercise and also decreased their stroke volume index at maximal exercise levels. In contrast, patients with mild valvular aortic stenosis (Group IIA) displayed a normal exercise response. Patients with severe valvular aortic stenosis (Group IIB) had a blunted stroke volume response at rest and at each level of exercise, as well as signs of myocardial ischemia (ST segment depression) during maximal exercise.Cardiac output measurements during exercise testing permitted analysis of stroke volume patterns that differ by anatomic type and severity of left ventricular outflow tract obstruction. These findings have implications regarding the timing of treatment and exercise prescription for children with aortic stenosis.