Myocardial deformation after radiotherapy: a layer-specific and territorial longitudinal strain analysis in a cohort of left-sided breast cancer patients (BACCARAT study).

Background: Radiotherapy for breast cancer (BC) and its resulting cardiac exposure are associated with subclinical left ventricular dysfunction characterized by early decrease of global longitudinal strain (LS) measurement based on 2D speckle-tracking echocardiography. 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. The aim of the study was to evaluate whether decrease in LS 6 months after radiotherapy is layer-specific and if it varies according to the left ventricular regional level and the coronary arterial territories.

Methods: 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).

Results: The study included 64 left-sided BC patients. Mean age was 58 years, mean doses to the heart, the left ventricle and the LAD were respectively 3.0, 6.7 and 16.4 Gy. The absolute decrease of LS was significant 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 relative decrease of LS in the endocardial layer was close to be significant (- 4.7%, p = 0.05). More precisely, the LS of the endocardial layer was significantly decreased for the most exposed parts of the left ventricle corresponding to the apical level (- 26.3 ± 6.0% vs. -24.2 ± 7.1%, p = 0.03) and LAD territory (- 22.8 ± 4.0% vs. -21.4 ± 4.8%, p = 0.03).

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

Trial Registration: ClinicalTrials.gov: NCT02605512 , Registered 6 November 2015 - Retrospectively registered.