Background
Cancer therapy-related cardiac dysfunction and heart failure are major problems in long-term childhood cancer survivors (CCS). We hypothesize that assessment of more sensitive echo- and electrocardiographic measurements, and/or biomarkers will allow for improved recognition of patients with cardiac dysfunction before heart failure develops, and may also identify patients at lower risk for heart failure.
Objective
To describe the methodology of the Dutch LATER cardiology study (LATER CARD).
Methods
The LATER CARD study is a cross-sectional study in long-term CCS treated with (potentially) cardiotoxic cancer therapies and sibling controls. We will evaluate 1) the prevalence and associated (treatment related) risk factors of subclinical cardiac dysfunction in CCS compared to sibling controls and 2) the diagnostic value of echocardiography including myocardial strain and diastolic function parameters, blood biomarkers for cardiomyocyte apoptosis, oxidative stress, cardiac remodeling and inflammation and ECG or combinations of them in the surveillance for cancer therapy-related cardiac dysfunction. From 2017 to 2020 we expect to include 1900 CCS and 500 siblings.
Conclusions
The LATER CARD study will provide knowledge on different surveillance modalities for detection of cardiac dysfunction in long-term CCS at risk for heart failure. The results of the study will enable us to improve long-term follow-up surveillance guidelines for CCS at risk for heart failure.
The long-term survival of childhood cancer has increased considerably over the last few decades. With a 5-year overall survival of more than 80%, the majority of childhood cancer patients nowadays will become long-term survivors. Unfortunately, the improved survival is accompanied by the occurrence of late adverse effects of treatment. The cardiotoxic side effects of certain cancer treatments such as anthracyclines and chest directed radiotherapy are well-known and include heart failure, arrhythmias, coronary artery disease, valvular abnormalities and pericardial disease.
Of these cardiotoxic side effects, cancer therapy-related heart failure in childhood cancer survivors (CCS) is the most frequently encountered problem: almost 5% of all CCS develops clinical heart failure within 40 years after childhood cancer diagnosis. Moreover, mortality due to heart failure is six-fold higher in long-term CCS as compared to the general population and treatment related cardiac death is the leading cause of death after malignancies.
Before clinical heart failure, a larger proportion of long-term CCS have a subclinical decline in left ventricular (LV) systolic function. The prevalence of subclinical LV systolic dysfunction varies in the literature, and is about 30% in different follow up periods when defined as a two-dimensional ejection fraction (EF) <50% or fractional shortening (FS) <30%. In a recent study, prevalence of LV dysfunction was only 5.8% after a median follow up of 23 years but in that study LV systolic dysfunction was defined with more constraint as a three-dimensional EF <50%. The Dutch surveillance guideline for long-term CCS defines cancer therapy-related cardiac dysfunction as a FS <30% or EF< 50%.
Established treatment related risk factors for heart failure and subclinical LV systolic dysfunction in CCS are higher cumulative anthracycline doses (in a non-linear fashion with no safe dose threshold), higher cumulative mitoxantrone dose and chest directed radiotherapy (especially in combination with anthracyclines). The type of anthracycline analogue and anthracycline infusion duration might also play a role.
Surveillance for subclinical cardiac dysfunction may prevent further deterioration of LV function by timely initiating heart failure therapies.
Currently, EF measured by two-dimensional echocardiography is the main parameter used in the surveillance for cancer therapy-related cardiac dysfunction and for clinical decision making in CCS. However, the usefulness of EF is limited by a large variability of 10%.
In the general population myocardial strain imaging emerges as a valuable tool to detect subclinical LV dysfunction that is superior in predicting heart failure and all-cause mortality compared to two-dimensional EF. The prevalence of global longitudinal strain abnormalities in CCS with a preserved three-dimensional ejection fraction was 28% in a cohort study in 1820 CCS at a median of 23 years after cancer diagnosis.
Another echocardiographic tool next to LV systolic dysfunction determined by 2D echocardiography is LV diastolic dysfunction which is encountered in 9–21% of long-term CCS, with severe dysfunctions mainly after (additional) chest directed radiotherapy. Also diastolic dysfunction is a predictor of future heart failure in the general population.
Studies have been performed that identified blood biomarkers that can detect subclinical cancer-treatment related cardiac dysfunction. However, blood biomarkers are not yet recommended in the surveillance for cardiac dysfunction in long-term CCS. Recently, we reviewed the literature on blood biomarkers for the diagnosis of LV dysfunction in long-term CCS and showed that NT-proBNP and troponins have a limited diagnostic value, which underlines the need to find more accurate biomarkers.
The ability of ECG parameters to early detect cancer therapy-related cardiac dysfunction in CCS remains unknown. Several studies in long-term CCS describe a high incidence and variety of electrocardiographic abnormalities. Major ECG abnormalities were predictive for cardiac and all-cause mortality in a large CCS cohort but were not compared with echocardiographic abnormalities. In a smaller long-term CCS cohort ECG abnormalities (mainly conduction disorders, high amplitude R waves and sinus bradycardia) were not predictive for echocardiographic abnormalities. However, only one of these 340 CCS had evidence of systolic LV dysfunction with an EF< 50% and strain parameters were not measured.
There are still gaps in knowledge that needs to be addressed in order to improve the surveillance for cardiomyopathy in CCS. These gaps include 1) the use of echocardiographic parameters for early detection of cardiomyopathy, 2) the accuracy of biomarkers and ECG parameters to diagnose subclinical cardiac dysfunction, 3) the cardiotoxicity of non-anthracycline containing chemotherapy, such as high-dose cyclophosphamide, ifosfamide and vincristine, 4) the role of genetics in the susceptibility for cardiomyopathy and 5) the combined use of blood biomarkers, ECG and echocardiography for the detection of subclinical cardiac dysfunction.
Considering these knowledge gaps, more information from echocardiography including myocardial strain, blood biomarkers (including genetics) and ECG measurements for the early detection of cardiac dysfunction in CCS and their associations with cancer treatment exposures is needed. In this paper we will describe the methodological aspects of the Dutch LATER cardiology study (LATER CARD) project that focusses on subclinical cardiac dysfunction in CCS who received (potential) cardiotoxic cancer treatment(s) as detected by echocardiographic parameters including myocardial strain, blood biomarkers and ECG parameters.
Methods
Funding
The LATER CARD study is supported by grants from the Dutch Heart Foundation (CVON2015–21) and Kika/ODAS (grant 171 ‘DCOG LATER program’).
Objectives
The main objectives of the LATER CARD study are to evaluate 1) the prevalence and associated (treatment related) risk factors of subclinical cardiac dysfunction in CCS compared to sibling controls and 2) the diagnostic value of echocardiography including myocardial strain and diastolic function parameters, blood biomarkers and ECG or combinations of them in the detection of cancer therapy-related cardiac dysfunction.
The LATER CARD study is subdivided into six work packages (WPs) with different objectives that support the main objective. WP1 consists of the data collection management that is required for the other WPs and does not address a specific research question. In WP2 we will study the prevalence and treatment related risk factors for subclinical systolic cardiac dysfunction including strain and diastolic LV dysfunction identified by echocardiography. WP3 concerns the prevalence of blood biomarker abnormalities and associated treatment related risk factors. In WP4 the prevalence and associated treatment related risk factors of abnormal ECG measurements will be studied. The diagnostic tools studied in WP 2, 3 and 4 will then be compared with respect to their diagnostic value in detecting subclinical cardiac dysfunction (see “Definitions” below). WP5 will study the gender differences in the prevalence of subclinical cardiac dysfunction, abnormal blood biomarker values and ECG abnormalities. In WP6 the results of all other WPs will be combined to formulate guideline recommendations for the cardiac surveillance of long-term CCS.
Study design
The Dutch LATER CARD study, is part of the Dutch Childhood Cancer Survivors Study LATER 2 study, a cross-sectional study of a retrospective nationwide cohort of 5-year CCS ( Figures 1 and 2 ). The LATER study is a collaboration between 7 pediatric oncology centers in the Netherlands (Amsterdam University Medical Center (VU Medical Center and Academical Medical Center), Leiden University Medical Center, Erasmus Medical Center, University Medical Center Groningen, Radboudumc and University Medical Center Utrecht/Wilhelmina Children’s Hospital/Princess Máxima Center for Pediatric Oncology) and includes a close collaboration with experts for specific health problems. The study protocol was approved by the medical ethic boards of all participating centers.
Study population
Informed consent is being obtained from all participants before study inclusion. The study population is obtained from the Dutch LATER nationwide cohort (n = 6165), including all 5-year CCS diagnosed before the age of 18 years, between 1/1/1963 and 12/31/2001 with a malignancy according to the third edition of the International Classification of Childhood Cancer. We only include CCS who were living in the Netherlands at the time of childhood cancer diagnosis and who were treated in one of the Dutch pediatric oncology centers.
In the LATER CARD study we will include CCS from the LATER cohort who were treated with (potentially) cardiotoxic cancer treatments. The LATER CARD study will include four risk groups; risk group 1 (no maximum number) : CCS who received anthracyclines, mitoxantrone, or chest directed radiotherapy; risk group 2 (max n = 100) : cyclophosphamide only (no anthracyclines, mitoxantrone, or chest directed radiotherapy, ifosfamide or vincristine); risk group 3 (max n = 100) : ifosfamide only (no anthracyclines, mitoxantrone, or chest directed radiotherapy, cyclophosphamide or vincristine); risk group 4 (max n = 100) : vincristine only (no anthracyclines, mitoxantrone, or chest directed radiotherapy, ifosfamide or cyclophosphamide).
As a comparison group 500 healthy siblings recruited from the participants will be included ( Figure 1 ). We chose for siblings as the comparison group because they are of approximately the same age and share a partially common background risk for cardiac disease based on genetic make-up and early life influences.
Study timeline
Patient enrollment in the LATER CARD study started in February 2017 and we are planning to include participants until 2020. We aim to finish all the analyses in January 2022. The specific timeline per WP is displayed in Figure 3 .
Definitions
LV systolic dysfunction will be defined as a biplane EF <52% for males and a biplane EF <54% for females, in accordance with the European Association of Cardiovascular Imaging recommendations. Specific subgroups of LV dysfunction will be defined: Mid-range EF (EF 40–51% for males and EF 40–53% for females) and reduced EF (EF <40%).
LV diastolic dysfunction will be defined as grade > I diastolic dysfunction according to the European Association of Cardiovascular Imaging recommendations.
Abnormal myocardial strain values will be defined based on age, sex and vendor specific normal values and the values obtained in the sibling controls.
Data collection
The LATER CARD project is one of the 15 projects in the LATER study, each investigating different organ systems/topics (e.g. pulmonary, bone, cardiac, psychosocial, psychosexual). All study participants of the LATER CARD study will be invited once to the outpatient clinic in one of the pediatric oncology centers. A research physician will collect the following data for the LATER CARD study: (1) Medical history including family history of cardiovascular diseases, presence of hypertension, diabetes, hypercholesterolemia and life style factors such as alcohol use and smoking. (2) A comprehensive medical history including questions regarding dyspnea, chest pain, palpitations, dizziness, fainting episodes and peripheral edema. (3) Diagnostic tests: height and weight, blood pressure, echocardiographic measurements including measurements from the previous echocardiogram (if available), blood for biomarker sampling and a resting ECG. All data will be anonymized and stored in a central database.
Echocardiography
A standardized echocardiogram, will be performed in all CCS and sibling controls included in the LATER CARD study in the participating centers. Standard measurements (including LV dimensions, LV mass, FS, biplane EF, right ventricular dimensions and function, systolic pulmonary artery pressure, valve abnormalities, and diastolic function measurements) will be performed by experienced sonographers. In one of the participating centers 3-dimensional EFs will be measured. Additional echocardiographic views are obtained for strain analysis in the corelab. All measurements will be anonymized and saved on disc (DICOM format). The analyses will centrally be interpreted by the echocardiography corelab in the Radboudumc in Nijmegen, the Netherlands. The standard measurements will be reviewed and corrected by the corelab and additional measurements will be performed (including radial, circumferential and longitudinal systolic strain and strain rate, biplane EF, left atrial volume index and diastolic parameters including tissue Doppler imaging).
Blood sampling
In all CCS and siblings included in the LATER CARD study, venous blood (divided in plasma and cell portions) will be collected and stored at −80 degrees Celsius in the LATER biobank in Utrecht. Blood sample storage will be available for future biomarker evaluation including the evaluation of genetic susceptibility for cardiac dysfunction.
A panel of 184 protein biomarkers from different biological processes will be evaluated in a targeted proteomics study in a nested case–control format within the LATER CARD study cohort. The 184 markers are part of the Cardiovascular panel III and the Organ Damage panel from Olink Proteomics.
The biomarkers, their interactions and their corresponding biological processes are listed in Supplementary Table 1 and visualized in Supplementary Figure 1 . Biomarker interactions and biological processes were obtained with STRING, a database which combines data on protein interactions and biological process classifications from different curated databases (GO, KEGG, Reactome). The 184 biomarkers are mainly implicated in (myocardial) cellular damage/apoptosis, hemodynamic load, inflammation, neurohormonal activation, oxidative stress, extracellular turnover/remodeling, platelet activation/thrombosis, endothelial dysfunction and lipid metabolism.
N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and biomarkers identified in the case–control study will be evaluated in the entire LATER CARD cohort for their diagnostic value (sensitivity, specificity, negative predictive value and positive predictive value) in detecting (subclinical) LV systolic dysfunction, abnormal myocardial strain and LV diastolic dysfunction on echocardiography.
Genetic analysis will include a genome wide association study to identify susceptibility loci for cancer-therapy related cardiac dysfunction. In addition, we will evaluate the prevalence of genetic variants that are associated with dilated cardiomyopathy in CCS with cancer-therapy related cardiac dysfunction and their contribution in the risk-stratification of CCS.
ECG
In all CCS included in the LATER CARD study and sibling controls, a 12-lead resting ECG will be performed. ECGs will be stored centrally and will be analyzed by the corelab according to the Minnesota criteria.
Statistical analysis
Power analyses
The power calculations are performed with a power set at 80% and alpha set at 0.05. To detect a clinical significant difference in proportion of subjects with subclinical LV systolic dysfunction (assuming a proportion of 10% in CCS and 1.5% in the sibling controls) we need n = 128 in each group.
We assume that 13% of the CCS and 2.5% of the sibling controls will have abnormal NT-proBNP values, adjusted for age and sex. Therefore, to detect a significant difference in proportion of abnormal NT-proBNP values between the CCS and the sibling controls we need n = 108 in each group.
To detect a clinically significant difference in proportion of major ECG abnormalities of 10% (estimated proportion in the sibling controls 2.8% ) between the CCS and the sibling controls we need n = 112 in each group. However, because we aim to perform subgroup analyses according to risk factors (gender, cancer treatment) more CCS and sibling controls will be included.
Prevalence analyses
The prevalence of LV systolic dysfunction (defined as a biplane EF <52% for males and <54% for females ), LV diastolic dysfunction (grades according to the European Association of Cardiovascular Imaging ) and abnormal myocardial strain (age, sex and vendor based normal values ) will be reported and compared between the different risk groups and with the sibling controls with the χ 2 test. Likewise, the prevalence of abnormal candidate blood biomarkers and major and minor ECG abnormalities (according to the Minnesota criteria ) will be reported.
Risk factor analyses
Risk factor analyses for LV systolic dysfunction, LV diastolic dysfunction, myocardial strain abnormalities, abnormal blood biomarkers findings and abnormal ECG measurements will be evaluated using separate multivariable logistic regression models including cancer treatment(s), follow-up time, sex, age at diagnosis, lifestyle factors (including smoking, alcohol consumption) and comorbidities (including hypertension, overweight, diabetes, hypercholesterolemia). The association between cancer treatment exposures and echocardiographic measurements (including EF, strain and diastolic function), blood biomarker values and ECG measurements will be evaluated with multivariable linear regression models.
Diagnostic accuracy analyses
The association between echocardiographic indices, blood biomarker values and ECG parameters will be tested in linear regression models. The diagnostic value of blood biomarkers and ECG parameters to detect LV systolic dysfunction, LV diastolic dysfunction or strain abnormalities will be evaluated with cut-off points derived from receiver operating characteristic curves. Optimal cut-off points for confirming or excluding the presence of LV systolic dysfunction, LV diastolic dysfunction or strain abnormalities will be reported with the sensitivity, specificity, positive predictive value and negative predictive value.”
Subgroup analyses
Subgroup analyses will be performed in CCS without a (previous) diagnosis of congestive heart failure (as defined by the European Society of Cardiology heart failure guideline).
To detect early markers for subclinical cardiac dysfunction subgroup analyses will be performed in asymptomatic CCS with a normal LV function at the previous echocardiogram (within 5 years, if available) and without symptoms of heart failure.
Additional subgroup analyses will be performed for males and females to evaluate gender differences in prevalence and risk factors for cardiac dysfunction.
Non-normally distributed variables will be log-transformed or tested for with the use of non-parametric tests. Two sided p-values <0.05 will be considered as statistically significant.
Preliminary results
Study population
Table I presents the characteristics of all eligible CCS and sibling controls for the LATER CARD study who were alive on January 1, 2017. The eligible study cohort includes 3608 CCS and 1066 siblings, the majority of CCS had a primary diagnosis of leukemia, lymphoma, renal tumors, bone or soft tissue sarcomas. There are 2566 eligible CCS in risk group 1 , 48 eligible CCS in risk group 2 , 33 eligible CCS in risk group 3 and 961 eligible CCS in risk group 4 ( Figure 1 ).
