Abstract
This editorial refers to ‘Unsupervised clustering of intra-ventricular haemodynamic forces for the phenotyping of left ventricular function in non-ischaemic left ventricular cardiomyopathy’, by Lorenzo Airale et al., https://doi.org/10.1093/ehjci/jeaf009. Ejection fraction (EF) is the most basic description of cardiac mechanical function, a simple number that provides a quantitative measure of the volumetric contraction for the left ventricle (LV). EF is a reference value whose usefulness has been widely recognized useful in numerous clinical situations; nevertheless, in modern cardiology, where interest is shifting from management of overt disease to early identification of subclinical alterations in LV function, a description in terms of EF is insufficient and inconclusive.1 Last decades have witnessed a progressive refinement of techniques for the analysis of diagnostic imaging capable of following the myocardium during its motion; such techniques took the name of feature tracking in cardiac magnetic resonance (CMR) or speckle tracking in echocardiography (where images’ features are mainly speckles) and permitted to introduce additional physics-grounded measures of the effective myocardial deformation along multiple directions.2–4 The analysis of the different components of strain helps differentiating the contributions to volumetric reduction that is imputable to LV longitudinal shortening (measured by the global longitudinal strain, GLS) or to reduction of the transversal LV size (measured by global circumferential strain, GCS). Strain is not intended to supersede EF, rather to integrate it to reach an improved description of LV mechanical function and differentiate clinical conditions. A strain curve presents a relatively simple time profile: it starts from zero at end-diastole (ED, that is assumed as the instant when myocardial contraction begins), it becomes negative during systole (negative strain means that the muscle becomes shorter) reaching a minimum value about end-systole (ES), and increases during the diastolic phases to return to zero at the following ED. Thus, the time profile of strain curves is very similar to that of the LV volume and, like in the volume curve, interest is principally to the value reached at ES that describes the maximal myocardial contraction.