MG is directly proportional to the squared function of transvalvular flow and can be small (below 40 mmHg) despite an AVA=1.0 cm2 if transvalvular flow is significantly reduced. Low flow is usually considered when the LVEF is reduced, but should not be excluded when the LVEF is normal. Low flow has been defined as an indexed stroke volume (SVi) below 35 ml/m2. however, measures that account for the systolic ejection period (i.e. mean transvalvular flow rate below 200250 ml/s) are theoretically likely more appropriate. Hypertension, significant mitral or tricuspid valve disease, pulmonary artery hypertension and atrial fibrillation are clinical entities often co-existing with AS and associated with low flow despite a normal LVEF. Elevated blood pressure can reduce transvalvular flow and result in a smaller MG, smaller AVA and discordant measurements.31 In patients with uncontrolled hypertension, low flow and discordant data, blood pressure should be corrected and the echocardiogram repeated as normalisation of flow may resolve the discrepancy.

Low transvalvular flow can also be present in AS patients without concomitant valve disease or pulmonary artery hypertension, a clinical entity often referred to as paradoxical low flow AS, because of the paradoxical association of a low flow state despite a preserved LVEF.30 These patients tend to be older, female and have associated hypertension, metabolic syndrome, diabetes or atrial fibrillation.They also tend to have smaller left ventricular cavities with concentric remodeling, myocardial fibrosis, reduced compliance and restrictive physiology. Despite the preserved LVEF, they have evidence of intrinsic systolic dysfunction with impaired longitudinal shortening.

The Reduced Left Ventricular Ejection Fraction Patient The presence of a low flow state is often the first assumption when encountering discrepant haemodynamic data in the AS patient with a reduced LVEF. However, not all patients with a reduced LVEF have a low flow state. SVi or mean transvalvular flow rate (below 35 ml/m2 and below 200250 ml/s, respectively) should be calculated to confirm the presence of low flow and measurement error excluded.

FROM: ECR - Volume 9 Issue 2 Winter 2014 Echocardiographic Evaluation Of Aortic Stenosis Normal Flow And Low Flow Scenarios

How to find stroke volume?

Area of LVOT x VTI = SV

Compilation by Dr. Samad Ali Moradi, According to Duodecim Finnish cardiology reference book & ESC SCAD guideline & author work experience.