Echocardiographic analysis
All analyses were carried out offline using the GE Echopac software (version 113). S’ was derived from colour-derived TVI images where the sample volume was placed at the annulus of the septal and lateral walls. S’ was defined as the highest velocity during systole after the end of isovolumetric contraction. Three cardiac cycles were obtained and S’ was averaged for each time point. During the full protocol Simpson’s biplane was measured (in the apical 4-and 2-chamber view), global longitudinal strain (GLS) in the three apical views and the LVOT velocity time integral (VTI). Speckle-tracking strain analysis was accepted when the software and visual inspection indicated adequate tracking. If tracking was inadequate, manual adjustments were made or the analysis was excluded from overall analyses. GLS was obtained from the apical 4-chamber view (basal septum, mid septum, apical septum, basal lateral, mid lateral, and apical lateral), the apical 2-chamber view (basal inferior, mid inferior, apical inferior, basal anterior, mid anterior, apical anterior) and the apical long axis view (basal posterior, mid posterior, basal anteroseptal, mid anteroseptal). If data was of insufficient quality it was excluded from analyses. This was defined as poor TVI tracing, exclusion of the mitral valve annulus (for colour TVI measurements), or poor endocardial border definition (for biplane). Eleven participants were excluded from analysis.