Strain Imaging in Aortic Stenosis

Abstract

Although aortic stenosis (AS) is a disease of poor outcomes, timely aortic valve replacement [AVR -surgical AVR (SAVR) or transcatheter AVR (TAVR)] improves the outlook with acceptable procedural risk. Survivors of AVR enjoy life expectancy that is like that of age matched controls. AVR receives a class I indication from the American and European Guidelines, in the presence of symptoms attributable to AS or when left ventricular (LV) systolic dysfunction manifests. However, there are fallacies in timing the intervention based on symptoms or LV ejection fraction. If surgery is delayed till symptoms manifest or LV dysfunction occurs, surgical risks are increased, long term outcomes are poor and in half of the patients, LV function never normalizes. Because of these reasons, pre-emptive intervention based on non-conventional parameters is expected to save more lives and prevent LV dysfunction. Data are emerging towards this approach and researchers have started focussing their attention on biomarkers like brain natriuretic peptide, multimodality imaging like estimation of extracellular volume by cardiac magnetic resonance for choosing the appropriate time for intervention in asymptomatic individuals. A relatively inexpensive way of identifying such high-risk individuals is speckle tracking imaging and in the last decade sufficient data have accumulated in favour of this modality to identify patients who may be benefited by early intervention. Speckle tracking echocardiography is a well validated technique which enables highly reproducible, angle-independent assessment of regional and global LV systolic function in longitudinal, circumferential and radial planes. Longitudinal strain, which is predominantly governed by the subendocardial layer, is most sensitive in the presence of myocardial disease and well-studied. Moreover, when discrepancies occur between gradient and valve area leading to uncertainties about the severity of AS, strain imaging would be of value in predicting outcomes particularly in those with low flow low gradient AS with normal LV ejection fraction.