Global longitudinal strain by two-dimensional speckle tracking echocardiography is closely related to myocardial infarct size in chronic ischaemic heart disease: authors' reply

Abstract

We read with great interest the letter by Mr Ze-Zhou Song. Mr Song raises important issues on the impact of how deformation parameters such as strain and strain rate are influenced by several conditions and diseases other than myocardial infarction. This has previously been shown in hypertensive and diabetic patients without recognized ischaemic events as well as in other conditions. This aspect will have to be considered when interpreting our results, as well as in the clinical context. In our present study [1], we intentionally did not exclude patients with co-morbidities. We agree with Dr Hoffmann in his reply to a similar request from Mr Song in the European Heart Journal that an exclusion of patients with other conditions would reduce the applicability of the study in clinical practice [2]. The statistical power of our present study [1] was not designed for subgroup analysis, and skewness of other conditions between the groups might therefore have an influence on our results. We have therefore included information on patients' co-morbidity in our paper, and there was no co-morbidity within the reference population. When excluding severe myocardial disease, the impact of other conditions on left ventricular function is limited when compared with the impact of a transmural myocardial infarct [1]. In a clinical context, assessment of regional myocardial function would have to be performed and compared with global left ventricular function in order to distinguish regional disease (such as myocardial ischaemia) from systemic diseases affecting the global left ventricular function in a more homogeneous pattern. We agree with Mr Song that the clinician should consider other conditions resulting in impaired deformation when applying deformation imaging for the assessment of myocardial viability.The main purpose of our present study [1] was to assess the ability of longitudinal speckle tracking strain measurements to distinguish between different levels of myocardial infarct transmurality and to explore the relationship between strain measurements and infarct mass at the territorial and global levels in a chronic ischaemic population [2]. As Mr Song correctly mentions, myocardial motion is complex. The myocardial fibre orientation gradually shifts from a counter-clockwise oblique longitudinal direction in the endocardial layer to near circumferential in the mid-myocardial layer and clockwise oblique longitudinal in the subepicardial layer [3]. This results in three main deformation patterns: longitudinal shortening, circumferential shortening and rotation. Radial thickening is due to a combination of myocyte thickening and shearing of the oblique fibre layers in the subendocardium [4,5]. Assessment of circumferential shortening and radial thickening strains in an infarct population was performed on parasternal short-axis views by Becker et al. [6]. Our present study was not designed for multiple parasternal short-axes imaging, and assessment of short-axis deformation was therefore not feasible. We do agree that a direct comparison of all deformation patterns needs further echocardiographic studies, as present knowledge in this field is limited to MRI (magnetic resonance imaging) studies.