ABSTRACT

BACKGROUND - Low-gradient severe aortic stenosis (LGSAS) with preserved ejection fraction (EF) is incompletely understood. The influence of arterial afterload and diastolic dysfunction on the hemodynamic presentation of LGSAS remains unknown.

OBJECTIVES - The authors sought to determine the acute hemodynamic response to sodium nitroprusside in LGSAS with preserved EF.

METHODS - Symptomatic patients with LGSAS and preserved EF underwent cardiac catheterization with comparison of hemodynamic measurements before and after nitroprusside.

RESULTS - Forty-one subjects (25 with low flow [LF], stroke volume index [SVI] ≤35 ml/m2, 16 with normal flow [NF]) were included. At baseline, LF patients had lower total arterial compliance (0.36 ± 0.12 ml/m2/mm Hg vs. 0.48 ± 0.16 ml/m2/mm Hg; p = 0.01) and greater effective arterial elastance (2.77 ± 0.84 mm Hg · m2/ml vs. 1.89 ± 0.82 mm Hg · m2/ml; p = 0.002). In all patients, nitroprusside reduced elastance, left ventricular filling pressures, and pulmonary artery pressures and improved compliance (p < 0.05). Aortic valve area increased to ≥1.0 cm2 in 6 LF (24%) and 4 NF (25%) subjects. Change in SVI with nitroprusside varied inversely to baseline SVI and demonstrated improvement in LF only (3 ± 6 ml/m2; p = 0.02).

CONCLUSIONS - Nitroprusside reduces afterload and left ventricular filling pressures in patients with LGSAS and preserved EF, enabling reclassification to moderate stenosis in 25% of patients. An inverse relationship between baseline SVI and change in SVI with afterload reduction was observed, suggesting that heightened sensitivity to afterload is a significant contributor to LF-LGSAS pathophysiology. These data highlight the utility of afterload reduction in the diagnostic assessment of LGSAS.