Nonobstructive left ventricular ejection pressure gradients in man

Abstract

Simultaneous intraventricular pressure gradients and ejection flow patterns were measured by a multisensor catheter in 6 patients with normal left ventricular function and no valve abnormalities, at rest and in exercise. Peak measured intraventricular pressure gradients were attained very early in ejection, amounted to 6.7 ± 1.9 (SD) mm Hg at rest, and were intensified to 13.0 ± 2.3 mm Hg during submaximal supine bicycle exercise. The augmentation of the gradients during exercise was associated with a pronounced accentuation of the flow acceleration and flow at the instant of peak gradient. At peak flow, the intraventricular gradients amounted to 5.4 ± 1.7 mm Hg at rest and 10.0 ± 1.8 mm Hg during submaximal exercise. The exercise-induced enhancement of the measured intraventricular pressure difference at the time of peak flow was underlain by an accentuation of the peak flow itself. A semiempirical fluid dynamic model for ejection was applied to the pressure gradient and simultaneous outflow rate and accelerated data to identify the contributions by local and convective acceleration effects to the instantaneous intraventricular gradient values. The peak intraventricular pressure gradient, which is attained very early in ejection, is mostly accounted for by local acceleration effects (85 ± 5% of the total). Conversely, at peak flow only convective acceleration effects are responsible for the measured pressure gradient. Thus, when inertial effects are augmented, as in exercise and other hyperdynamic states, the intrinsic component of the total left ventricular systolic load can be substantial, even with no outflow tract or valve abnormalities. In view of the inverse force-velocity relation of the myocardium, this implies that the intrinsic component of the left ventricular load and the corresponding component of the left ventricular muscle load must be taken into account in exploring analytically the loading feedback between the total myocardial load and the acceleration, velocity and extent of shortening, which, along with end-diastolic dimensions, determine ejection flow waveforms.