Breast cancer (BC) radiotherapy (RT) and the resulting cardiac exposure is associated with early decrease of global longitudinal strain (GLS). Recent software allows multi-layer and segmental analysis of strain, which may be of interest to quantify and locate the impact of cardiac exposure on myocardial function and potentially increase the early detection of radiation-induced cardiotoxicity.

To evaluate whether decrease in GLS after BC RT is layer-specific and if it varies according to the left ventricular regional level and the coronary arterial territories.

LS was measured at baseline before radiotherapy and 6 months post-radiotherapy. The LS was obtained for each myocardial layer (endocardial, mid-myocardial, epicardial), left ventricular regional level (basal, mid, apical) and coronary artery territory (left anterior descending artery (LAD), circumflex artery, right coronary artery).

The study included 64 left sided BC patients. Mean age was 58±4 years, mean doses to the heart, the left ventricle and the LAD were respectively 3.0, 6.7 and 16.4Gy. Despite unchanged LVEF between baseline and 6 months post-RT (61±7% vs. 60±9%, P=0.07), decreased GLS was observed for the three layers (endocardial: −20.0±3.2% to −18.8±3.8%; mid-myocardial: −16.0±2.7% to −15.0±3.1%; epicardial: −12.3±2.5% to −11.4±2.8%, all P=0.02), but only the endocardial layer GLS (GLS-endo) relative change was significant (−4.7%, P=0.049). Indeed, the GLS-endo was significantly decreased for the most exposed parts of the left ventricle corresponding to the apical level (−26.3±4.0% vs. −24.2±7.1%, P=0.03) and LAD territory (−22.8±4.0% vs. −21.4±4.8%, P=0.03).

Six months post-RT, GLS decreased predominantly in the endocardial layer of the most exposed part of the left ventricle. For precise evaluation of RT-induced cardiotoxicity and early left ventricular dysfunction, the endocardial layer-based GLS might be the most sensitive parameter.