Low flow state masks true arterial stiffness on pulse wave analysis in patients with severe aortic stenosis.

Abstract

Background: Aortic stenosis is a common valvular disorder that shares pathophysiological principles with age-associated elevated arterial stiffness. Flow attenuation from valvular obstruction in aortic stenosis may lead to under-estimation of true arterial stiffness, particularly in aortic stenosis patients with reduced stroke volume.

Methods: Severe aortic stenosis patients were divided into high mean transvalvular gradient (HG, ≥40 mmHg) and low mean transvalvular gradient (LG, <40 mmHg) and compared with elderly controls without aortic stenosis. Aortic pressures were obtained from radial arterial tonometry calibrated to brachial cuff pressures simultaneously with aortic flows acquired via cardiac magnetic resonance phase contrast imaging. Pulse wave analysis was performed and pulsatile arterial load indices calculated using frequency domain analysis.

Results: We analysed 58 patients, with 21, 16 and 21 patients in the high gradient, low gradient and control groups, respectively. Aortic stenosis patients had higher augmentation indices (high gradient 40 ± 8%; low gradient 38 ± 7%; control 32 ± 9%, P < 0.01) despite lower mean arterial pressure (high gradient 91 ± 22 mmHg; low gradient 94 ± 23 mmHg; control 109 ± 17 mmHg, P =0.02). Cardiac output, systemic vascular resistance and aortic characteristic impedance were comparable. The high gradient group had a significantly higher stroke volume index (high gradient 39 ± 8 ml/m2; low gradient 33 ± 7 ml/m2; control 34 ± 7 ml/m2, P = 0.02), but stroke volume index was positive correlated with augmentation index only in the low gradient group (R = 0.57, P = 0.02).

Conclusion: In patients with low gradient aortic stenosis, smaller stroke volume index is associated with lower measured arterial stiffness by augmentation index on pulse wave analysis, suggesting that ventriculo-valvulo-arterial uncoupling due to elevated arterial stiffness may be more pronouncedly under-estimated in patients low-flow, low-gradient aortic stenosis.