Towards assessment of left ventricular mechanics in true three dimensions

Abstract

Accurate quantification of left ventricular (LV) dimensions and systolic function is crucial for the optimal clinical management of patients with cardiovascular disease. The LV ejection fraction (LVEF) is used as a major threshold for implantation of an internal automatic defibrillator or biventricular pacemaker, whereas LV volumes are key to selecting the optimal timing for surgical valve replacement. Moreover, both the LVEF and LV volumes are important for the prognosis of patients with ischaemic heart disease. Currently, two-dimensional (2D) echocardiography is the most frequently used imaging technique for quantification of LV volumes and LVEF. Visual assessment of the LVEF is commonly used in routine clinical practice, but it requires significant expertise and remains a subjective estimation. The modified Simpson’s method calculates LV volumes by tracing the endocardial boundaries in the apical two- and four-chamber views at end-diastole and end-systole, and subsequently the LVEF is derived. However, this method is time consuming and its accuracy is limited by foreshortened apical views, inaccuracies in endocardial border detection, or LV geometric assumptions. 1 In search of an automatic, accurate, and reproducible method to quantify LV volumes and LVEF, real-time three-dimensional echocardiography (RT3DE) is an important step forward in cardiac ultrasound. Multiple studies have demonstrated the superior accuracy and reproducibility of RT3DE over 2D echocardiography for assessment of LV volumes and LVEF. 2,3 In addition, assessment of the LVEF and LV volumes by RT3DE correlated well with magnetic resonance imaging (MRI), whereas 2D echocardiography showed only a modest correlation with MRI. 2,3 Several RT3DE methods to measure LV volumes and LVEF have been proposed, with direct volumetric quantification being the most accurate approach, since this is not affected by LV foreshortening and it is independent of geometric assumptions. 4 However, beyond the assessment of LV function by simple endocardial excursion, tissue velocity and deformation analysis provides a more challenging echocardiographic approach to characterize global and regional myocardial function. The use of tissue velocity and deformation imaging has been applied increasingly in the fields of ventricular function, myocardial ischaemia and viability, valvular heart disease, and heart failure. 5‐8 Myocardial deformation imaging may be preferred over velocity assessment in patients with ischaemic heart disease and previous myocardial infarction, since deformation imaging may permit differentiation between passive motion (as can occur in infarcted tissue) and active deformation (which will discriminate between scar tissue and viable myocardium). Deformation or strain assessment was initially derived from tissue Doppler imaging, but had the disadvantage of being dependent on the ultrasound beam angle insonation, resulting in reduced applicability and diminished reproducibility. Recently, 2D speckle tracking has been introduced as a technique to measure multidirectional myocardial strain which is independent of the ultrasound beam angle insonation, and may overcome the limitations of strain derived from tissue Doppler imaging. Previous studies have validated 2D speckle tracking against sonomi