Physiologic assessment of CMR strain: afterload and contractility

Background All indices of systolic myocardial performance, including CMR strain, reflect the interplay between contractile state and loading conditions. However, CMR strains have been used largely in descriptive fashion, without consideration of physiologic determinants. We have previously demonstrated the role of increased afterload as a determinant of CMR strain using feature tracking (FT) in dilated cardiomyopathy as compared to normals, as well as the utility of an afterload index based on 3D volumetric geometric determinants (PV/M) compared to wall stress (WS) calculation. We have also shown the potential value of ratios of strain to afterload (S/A) as simple, practical contractility indices and that low dose dobutamine (Dob) can increase contractility, increasing both strain and strain rate without detectable change in blood pressure (BP) or heart rate (HR). However the relative sensitivity of CMR strain, S/A indices and strain rate to changes in contractile state and the performance of these indices with various CMR strain methods are unknown.