Study population
This is a non-randomized, observational cohort study that included 74 asymptomatic female patients who were planned to receive chemotherapy for breast cancer in the period between November 2017 and July 2018. Exclusion criteria included a history of coronary artery disease, a hemodynamically significant valvular heart disease, and a previous chemotherapy or chest radiotherapy. Patients with known cardiovascular risk factors (old age >65 years, hypertension, diabetes, dyslipidemia, smoking, and obesity (BMI more than 30 kg/m2)) as well as patients with abnormal baseline LVEF (less than 50%) were also excluded.
This study complies with the Declaration of Helsinki (2013), and the Faculty of Medicine, Cairo University ethics committee has approved the research protocol. A written informed consent has been obtained from the patients.
Methods
The baseline visits
All patients were assessed clinically and this included oncological history, type and site of cancer, a family history of breast cancer, body weight and height measurements, body mass index (BMI) {BMI was calculated according to the following formula; BMI = body weight (kg)/height (m2)}, and heart rate and blood pressure (BP) measurements (BP was measured using the mercury sphygmomanometer).
Some data were derived from the patients’ files and the pathology report like the TNM staging, the identified receptors (progesterone, estrogen or HER receptors), the chemotherapeutic agents used (cyclophosphamide, doxorubicin, epirubicin, and docetaxel), and the doses to be given. The cardiotoxic effects have been reported with doxorubicin doses >400 mg/m2, epirubicin doses >900 mg/m2, and cyclophosphamide doses >140 mg/kg [11].
A twelve-lead ECG was done via the department machine SCHILLER, AT-101, looking out for changes in voltage, PR interval, QRS duration, QTc interval using Bazett’s formula [12] (normal corrected QT for females is 350–440 ms) [13], any arrhythmias, or any other pathological abnormalities.
Laboratory workup included complete blood count (CBC) and kidney function tests (serum creatinine and blood urea nitrogen).
* NT-pro BNP level assessment
It was measured using the enzyme-linked immunosorbent assay (ELISA) technique (the kit catalogue number is E-EL-H0902) [14]. Three milliliters of blood was withdrawn from an arm vein of the patient; samples were left to clot for 2 h at room temperature or overnight at 4°C before centrifugation for 15 min at 1000×g at 2~8 °C. The supernatant was collected for the assay and stored at – 20 °C or – 80 °C till analysis [14].
* Two-dimensional (2D) transthoracic echocardiography (TTE)
Resting conventional 2D-TTE was done by a single experienced operator using a commercially available machine (Philips IE-33), equipped with a 2.5 MHz transducer, where a 2D, M-mode and Doppler images were digitally recorded for subsequent analysis. Measurements included LV dimensions and volumes, LVEF (apical biplane modified Simpson’s method), left atrial volume index, mitral inflow Doppler parameters, and mitral lateral annulus tissue Doppler (TDI) values. The Tei index was calculated by the following formula: (IVCT+IVRT/ET), where IVCT is the isovolumetric contraction time (the time from closure of the mitral valve till the opening of the aortic valve), IVRT is the isovolumetric relaxation time (the time from closure of the aortic valve till the opening of the mitral valve), and the ET is the ejection time (the time from opening till closure of the aortic valve).
Loops of the different apical views (two (A2), four (A4), and three (A3) chamber views) were stored for offline analysis of STE and GLS using a (Q-LAB 10.0) program. A good quality ECG was ensured during recording as a prerequisite for a proper speckle tracking analysis. LV longitudinal strain parameters were measured from the apical views, and the myocardium was divided into 6 segments per view (basal, mid and apical segments for the 2 walls in each view). A2-GLS, A3-GLS, and A4-GLS were reported. The overall GLS was automatically calculated as the average of the 18 segments measured in the 3 apical views.
* Three-dimensional (3D) TTE
All patients underwent 3D echocardiography by an experienced operator using Philips IE-33 machine equipped with an xMATRIX transducer. Within a single breath-hold, 4 wedge-shaped sub-volumes were acquired from an apical view to create full-volume data sets. Care was taken to include the entire LV within the 3D scan volume by decreasing the depth and sector width as much as possible to improve the temporal and spatial resolution of the images.
Quantitative analysis was done by using (Q-LAB 10.0) software. A semi-automated border detection biplane LV analysis was performed. For the quantification of LV volumes and function, the longitudinal axes were aligned in the first frame of the loop which corresponds to LV end-diastole in both the apical four-chamber and two-chamber views. Care was taken for the proper definition of both apical views and orthogonal views to avoid foreshortening. Then, tracing was performed by marking five points: septal, lateral, anterior, and inferior points of the mitral annulus and a fifth point on the LV apex. A semi-automated blood–endocardial interface detection algorithm then automatically identified the endocardial border and calculated the LV end-diastolic volume (LVEDV). Unsatisfactory delineation of the endocardial border was manually adjusted. The end-systole was selected by visually identifying the frame with the smallest LV cavity size just before mitral valve opening where tracing was repeated in the same manner as for the end-diastole to obtain the LV end-systolic volume (LVESV). The software automatically detects the endocardial borders in the three dimensions, throughout the cardiac cycle and calculates LV volumes and EF [15,16,17].
The follow-up visits
Patients were asked to follow up after 6 weeks of the 1st chemotherapy session. Patients went through routine clinical assessment, searching for symptoms and signs of heart failure.
Electrocardiography was done and analyzed for any changes (compared to the baseline ECG). Echocardiographic assessment (conventional 2D, 2D-STE, and 3D echocardiography) was repeated, and the same study parameters were reported). Blood samples were collected for NT-pro BNP plasma level using the same ELISA technique.
End points
The primary end point for this study was the early detection of left ventricular systolic dysfunction, based on elevated NT-pro BNP plasma levels as well as reduction of the LV-GLS in breast cancer patients receiving chemotherapy.
Cardiotoxicity is defined as a decrease of LVEF from baseline values by >5% to an EF <55% (in the presence of heart failure (HF) symptoms and signs) or an asymptomatic decrease in LVEF by > 10% to an EF < 55% [18, 19]. Abnormal LV-GLS is defined by an absolute value less than 20 (less negative values) and/or a relative reduction of GLS > 15% of the baseline values [19].
Statistics
Data was analyzed using Statistical Package of Social Science (SPSS) version 20. Categorical data are described as numbers and percentages and continuous data are described as means and SD or median and range. A paired sample Student’s t test (for data that was normally distributed) or a Mann–Whitney test (for data that was not normally distributed) was used to compare data at the baselines and follow-up visits. Spearman correlation test was used to define the degree and direction of the relationship between the delta change of LV GLS and that of NT-proBNP plasma levels. The delta values of the NT-proBNP, 2D-LVEF, 3D LVEF, and 2D LV-GLS were calculated as the follow-up value minus the baseline value. The relative change of the GLS and the NT-proBNP were calculated as follows ({follow-up value − baseline value}/baseline value). A multivariate linear regression analysis was used and age, laboratory data, and echocardiographic data were introduced into the regression model to identify the independent predictors of the delta change of NT-proBNP level as well as the delta change of the GLS. A receiver operator characteristic (ROC) analysis was used to detect the relative change of NT-proBNP that was capable of defining a 15% relative change of the GLS with a good sensitivity and specificity. Two-tailed p value <0.05 was considered significant.