This was a monocentric observational study conducted in one Intensive Care Unit (ICU) of the University Hospital of Nantes, France from March 1st 2014, to August the 25th 2017. Since this study was purely observational, oral and written information were provided to the patient’s next-of-kin at the early phase and to the patient when neurological recovery was deemed appropriate. This study was approved by the local ethics committee (Groupe Nantais d’Ethique dans le Domaine de la Santé – IRB N°6.02.2014). Moreover, blood samples are routinely performed in our ICU, for a biocollection in patients with brain-injury (IBIS, CPP Nantes Ouest IV, IRB approval N°46/11). For this biocollection, some patients included in the STE study provided consent. Whenever consent was not available from the patient, next-of-kin provided it.
Patients ≥ 18 years old with a TBI, a baseline Glasgow Coma Score (GCS) ≤ 12 and with anomalies on a brain computed tomography, were eligible to this study.
Patients were not included in case of ischemic cardiomyopathy, history of cardiac surgery, resuscitated cardiac arrest during initial management, thoracic trauma with an Acute Injury Score > 3, physical signs of brain death . Pregnant women were not eligible. Patients who could not benefit from a TTE in the 24 hours after ICU admission, were not included. Patients were not upheld in the final analysis if STE quality was deemed inappropriate.
Strain echocardiography protocol
TTE was performed in the first 24 hours after the patient’s ICU admission (Day 1) and on Day 3 and Day 7 after ICU admission. An electrocardiogram was systematically performed at the patient’s arrival. High sensitivity troponin-T (Hs troponin-T) was routinely measured. One anaesthetist (R.C.) performed all TTEs and STE analysis. The following loops were recorded over three cardiac cycle with a high frame rate (≥ 70.s− 1): left parasternal long and short axis views, apical two-, three-, four-, and five-chamber views. Doppler tissue imaging of the lateral and septal part of the mitral annulus, mitral inflow Doppler measurements (early (E) and late (A) peak diastolic velocities, E/A ratio) were measured. The velocity time integral (VTI) at the level of the left ventricular outflow tract was measured. Systolic function of the right ventricle (RV) was assessed through tricuspid annular plane systolic excursion (TAPSE) measurement.
Off-line and speckle-tracking analysis
The Left Ventricle (LV) end-diastolic diameter and wall thickness were measured with the M-mode in the left parasternal long axis view. The LV ejection fraction (LVEF) was evaluated with the Simpson method in the four and two-chamber views. The systolic S, diastolic E’, and A’ peak velocities, E/E’ ratio were measured at the septal and lateral part of the mitral annulus.
The LV longitudinal strain was measured in the three-, four-, and two-chamber view allowing the calculation of global longitudinal strain (GLS) according to previously described technique . TTE was performed with a Vivid S6® (GE Medical Systems, Milwaukee, WI, USA) equipped with a 2.5-MHz transducer. All echocardiographic acquisitions and off-line analyses were performed by a single anaesthetist expert in speckle-tracking analysis (R.C.) on an EchoPac® clinical workstation software (GE Medical Systems, Milwaukee, WI, USA). All speckle-tracking analyses were performed offline.
Demographic and general TBI data such as baseline GCS score, Marshall score, occurrence of intra-cranial hypertension , use of pentothal or decompressive craniectomy during hospital were recorded. General data such as ICU length of stay, duration of mechanical ventilation, in-ICU mortality, in-hospital length of stay and in-hospital mortality were recorded. Finally, neurological outcome was assessed in all patients at day-90 after ICU admission with a Glasgow Outcome Scale, collected by phone call .
The primary outcome was to evaluate the incidence of stress cardiomyopathy with GLS, in TBI patients according to previously published definitions , combining longitudinal systolic function impairment  in the course of a stressful event, a moderate cardiac biomarker increase, improvement of systolic function over time and the lack of other possible diagnosis [8, 14]. A GLS >-16% was considered an a left ventricle longitudinal systolic function impairment .
Secondary outcomes. Echocardiographic data
The secondary outcomes of the study, were to describe the evolution of GLS as well as other echocardiographic parameters (LVEF, E/A and E/E’ ratio, TAPSE) during the ICU course, and compare cardiac data between patients with moderate and severe TBI. We also described the potential link between baseline GLS and ICU mortality or 3-months neurological outcome (Glasgow Outcome Scale).
Secondary outcomes. Metanephrine and normetanephrine levels
Since the main hypothesis of stress cardiomyopathy occurrence is a major blood level catecholamine increase , we decided to explore the adrenergic response by dosing the blood levels of metanephrine and normetanephrine in patients with TBI and SAH, admitted in our institution . Metanephrine and normetanephrine were dosed at the patient’s admission, with the routine biocollection blood samples. For these dosages, patients were randomly selected in the biocollection and were matched on age and baseline GCS. Fifteen TBI and 15 SAH patients were thus selected.
Dosages of metanephrine and normetanephrine blood level
Plasma from blood samples (containing K2EDTA*) was collected and stored at − 80 °C until analysis. Plasma free metanephrine levels were measured using liquid chromatography–tandem mass detection (Waters Xevo® TQ-D mass spectrometer, Waters Corporation, Milford, MA, USA), after extraction from 50 microL of samples with a mixed-mode weak cation exchange solid-phase extraction (SPE) plate (Oasis® WCX 96-well µElution Plate, Waters Corporation), followed by rapid separation with hydrophilic interaction chromatography (ACQUITY UPLC® BEH Amide Column, Waters Corporation).
Continuous data are expressed as mean (± Standard deviation) or median (25–75 percentile) and categorical data as N(%) and are analysed with the Student or Mann-Whitney test, and χ2 tests, respectively. The evolution of GLS over time was analysed with a one-way ANOVA. Pearson test was used to assess correlation between variables. According to previously published data , 22% of patients after moderate to severe TBI could display LVEF impairment. Owing to the sensitivity of STE in neuro-ICU patients we chose to include 100 patients with moderate to severe TBI, in order to detect at least 30 patients with STE impairment along with preserved LVEF . Statistical significance was set at p = 0.05. All analyses were performed with Prism® v5, Graphpad®, California, USA.