Effects of dynamic and isometric exercise on the radionuclide-determined regurgitant fraction in aortic insufficiency

Twenty-five patients with aortic insufficiency and eight asymptomatic control subjects underwent radionuclide ventriculography at rest and during dynamic and isometric exercise to clarify the mechanisms for preservation of exercise capacity in aortic insufficiency. Regardless of symptomatic state or severity of regurgitation, patients with aortic insufficiency had no significant increase in left ventricular ejection fraction or relative left ventricular end-diastolic volume during dynamic or isometric exercise. The radionuclide stroke count ratio (ratio of left ventricular to right ventricular stroke counts) progressively decreased in patients with aortic insufficiency from 2.98 ± 1.14 (mean ± 1 standard deviation) at a mean heart rate at rest of 69.6 beats/min to 2.48 ± 0.59 (p = not significant [NS]) at a mean submaximal bicycle exercise heart rate of 129 beats/min and to 1.97 ± 0.57 (p < 0.005) at a mean maximal bicycle exercise heart rate of 145 beats/min. The decrease in stroke count ratio with bicycle exercise was significantly related to the severity of valvular regurgitation at rest (p < 0.005). Although achieving lower bicycle exercise heart rates nd comparable diastolic blood pressures, symptomatic patients had a lower mean stroke count ratio compared with asymptomatic patients with aortic insufficiency, suggesting that an elevation of left ventricular diastolic pressure significantly decreased the regurgitant fraction in symptomatic patients during bicycle exercise. In patients with aortic insufficiency, the mean heart rate (92 beats/min) was significantly lower with isometric exercise than during the submaximal stage of bicycle exercise (129 beats/min). However, diastolic blood pressures, left ventricular diastolic counts and ejection fractions were comparable.Because the aortic regurgitant flow depends on heart rate, regurgitant orifice size, diastolic blood pressure and left ventricular diastolic pressure, the paradoxically lower stroke count ratio with isometric handgrip exercise compared with submaximal bicycle exercise suggests that an increase in left ventricular diastolic pressure in patients with aortic insufficiency during isometric exercise produces the observed reduction in regurgitant fraction