Subjects

Pediatric patients with known or suspected DCM were enrolled at the time of echocardiographic presentation at each of the eight study centers (see “Acknowledgments”) between May 2005 and July 2007. Inclusion criteria were age < 22 years, known or suspected DCM, disease duration > 2 months, anticipated longitudinal follow-up to occur at the same institution, and the provision of informed consent. Exclusion criteria (listed in detail in Appendix Figure A1 ) included other forms of cardiomyopathy and congenital heart disease. Exclusion criteria also included noncompaction (due to an inability to reliably define LV endocardial borders), excessive nonsinus rhythm (due to excess beat-to-beat variance), and hemodynamic instability (due to the intent to assess longitudinal natural history).

Training

The principal investigator from each clinical site along with one or more designated site sonographers attended an in-person training session that included protocol review and demonstration of the image acquisition techniques. The measurement methods were reviewed in detail with the site principal investigator and the designated primary sonographer for the study, one of whom performed all of the local measurements. Each center performed and submitted three practice echocardiograms to the core lab for review and feedback. After approval, enrollment commenced.

Demographics

Height and weight were measured and body surface area was calculated using the Haycock formula. Systolic, diastolic, and mean blood pressures were recorded four times with the patient in a recumbent position using an automated blood pressure device. The values from the first recording were discarded, and the average value of the other three measurements was calculated for each pressure.

Echocardiographic Acquisition

All echocardiograms were obtained according to a standardized protocol, with acquisition of the images listed in Appendix Table A1 . Each center designated one or more “primary” sonographers who participated in hands-on study training sessions. For each echocardiographic evaluation, image acquisition was performed by a “primary” echocardiographer, and then a second image acquisition was independently performed by any available experienced sonographer (who had not necessarily participated in the study training sessions). The second set of images was acquired immediately after the first.

Eligibility for Longitudinal Evaluation

A standardized set of measurements was performed at the study center on the primary data acquisition, and the results of these measurements were used to determine eligibility for longitudinal echocardiographic evaluation. Patients who met criteria for the diagnosis of DCM on the basis of the inclusion and exclusion criteria listed above who also were found to have both LV dilation (defined as end-diastolic dimension > 5.5 cm or end-diastolic dimension Z score > 2) and LV dysfunction (defined as ejection fraction < 50%, shortening fraction < 28%, or Z score for either parameter < −2) were judged eligible for longitudinal assessment ( Appendix Figure A2 ). Eligible patients underwent repeat echocardiographic assessments according to the study protocol on return visits up to 18 months after enrollment, providing no indication for withdrawal from the study was met. Indications for withdrawal were death, cardiac transplantation or LV reduction surgery, institution of an LV assist device including extracorporeal membrane oxygenator support, and patient or physician preference. Each subject, therefore, was expected to have two sets of echocardiographic images at the time of study enrollment and two sets from at least one follow-up visit. The target timing for the follow-up echocardiographic assessment was 12 months, because this was considered to be a likely interval to assess change in a randomized trial. In the completed study, the mean time between paired echocardiographic assessments using the follow-up echocardiogram closest to the 12-month target was 9.1 ± 3.5 months (median, 9.6 months; range, 2–18 months).

Partial Participation Group

Subjects who underwent baseline image acquisition but were then found to not meet criteria for longitudinal evaluation were excluded from further participation, but their baseline images were included in the analyses of reproducibility, thereby permitting the evaluation of reproducibility over a broader range of ventricular size and function in addition to enhancing the analysis of the impact of severity of dysfunction on reproducibility.

Echocardiographic Analysis

A standardized measurement protocol that included a total of 150 measurements and calculated variables was performed at the core laboratory for each of three cardiac cycles (450 measurements total) for each set of echocardiographic images ( Appendix Table A2 ). Measurements were categorized as areas (nine variables); calculated variables derived from two, three, and four measured variables (19, 25, and 21 variables, respectively); dimensions (16 variables); electrocardiographic time intervals and heart rates (seven and nine variables, respectively); integrals (one variable); slopes (four variables); Doppler and M-mode time intervals (22 variables); and Doppler velocities (17 variables). A single observer at each center performed the measurements for the primary image acquisition at the initial and follow-up visits using locally available technology and submitted the results to the data coordinating center. The data sets constructed at the local centers were composed of 119 of the above 150 measurements and derived indices. The images from both the primary and secondary image acquisitions from each subject visit were submitted to the data coordinating center, where they were blinded to study date and patient identification and coded before transmission to the echocardiographic core lab for analysis ( Appendix Figure A1 ). Image capture and transfer included videotape, analog-to-digital converted images, and Digital Imaging and Communications in Medicine, depending on the date and the center. All echocardiographic measurements were performed using custom Digital Imaging and Communications in Medicine software (EchoTrace; Marcus Laboratories, Boston, MA).

At the core lab, a primary and secondary core lab observer analyzed both the primary and secondary image acquisitions using the same measurement protocol ( Appendix Table A2 ). In addition, the primary core lab observer repeated the measurements on blinded sets of the primary images at 1 month and 1 year after the original measurements. Primary and secondary image sets acquired at follow-up evaluations of fully eligible subjects were each analyzed by both the primary and secondary core lab observers. Altogether, there were 12 different categories of echocardiographic data sets for statistical comparison, as listed in Appendix Table A3 .

Image Quality Assessment

In addition to performing the measurements, the primary core lab observer performed a quality assessment for each of the images in Appendix Table A1 . The image grading system was defined as follows:

• 1.
  

  Excellent: The full extent of the structure boundary of interest was clearly defined, with no visible gaps; zoom mode was activated to maximize image resolution for two-dimensional structures; and Doppler signals were scaled proportional to image size.

  
  
• 2.
  

  Good: The full extent of the structure boundary of interest was contained within the image sector, with only brief gaps requiring interpolation, and for Doppler signals, there was minimal baseline artifact.

  
  
• 3.
  

  Fair: Nearly the entire boundary of the structure of interest was contained and adequately visible, but minor extrapolation beyond the imaging sector was required; boundaries had identifiable but indistinct borders; and prominent baseline artifact was present on Doppler recordings.

  
  
• 4.
  

  Poor: Significant portions of the boundary of interest required interpolation from visible but indistinct segments, or more than a short segment of the boundary was outside of the imaging sector.

  
  
• 5.
  

  Unusable: The structure was not recorded or was too poorly defined to be measured.

Additionally, each echocardiogram was also evaluated for (1) trabeculations that could potentially interfere with definition of the LV apical endocardium, (2) qualitative assessment of regional wall motion abnormalities, and (3) septal displacement resulting in a noncircular short-axis LV configuration.

Clinical Data Collection

The medical records of all subjects were reviewed at the time of enrollment, at each subsequent echocardiographic assessment, and at 18 months after enrollment for medical history, including medical therapy and changes in medical therapy, procedures, interventions, adverse events, and symptom and cardiac transplantation listing status.

Statistical Analysis

The primary aim of this study was to determine the interstudy variability of echocardiographically derived LV measurements in pediatric patients with DCM, in particular the variance of LV ejection fraction Z score at a single point in time and the variance of change in Z score between two time points. The required sample size to estimate the population standard deviation to within a prespecified tolerance is n = Z _1−σ/2 /(2 d ² ), where d is the allowed fractional deviation from σ, the population sample standard deviation. To construct a two-sided 95% confidence interval for σ that deviates no more than 15% from the true value requires a sample size of 86. It was estimated that 25% to 30% of subjects would withdraw, undergo echocardiography under differing sedation conditions, or have incomplete baseline or follow-up echocardiogram pairs for other reasons. Therefore, the target sample size was set to be 120 patients with qualifying baseline echocardiograms to ensure that 86 of these had paired interpretable echocardiograms (a total of 172 echocardiograms) obtained under similar conditions. In actual execution, the study enrolled 173 patients, of whom 131 were eligible for longitudinal evaluation, to ensure that 86 qualifying echocardiogram pairs would be obtained. A total of 107 of these subjects had at least one follow-up echocardiogram submitted, and 97 of these formed qualifying echocardiogram pairs. The 10 subjects with nonqualifying pairs met one of the following criteria: no secondary image acquisition, incorrect sonographer, or inconsistent sedation status between the two echocardiograms.

Ventricular Volume Variability Study Analysis Plan

On the basis of the study design shown in Appendix Table A3 , for any given echocardiographic parameter, there were 21 or 15 sets of measurements from each study visit (3 sequential cardiac cycles × 7 different readings for a baseline visit and 5 different readings for a follow-up visit). The analyses of these data sets include the following comparisons of interest to assess:

Statistical Methods: Beat Averaging

The outcome measure was the percentage error of the mean. Echocardiographic measurements using the primary image acquisition from all baseline studies were included in analysis. For each evaluation of reproducibility between two measurements of the same entity, the difference (“error”) between the two measurements was divided by the mean of those two measurements. Three settings were used to compare the following two measurements:

• •
  

  core laboratory interobserver variability: primary versus secondary observer;

  
  
• •
  

  core laboratory intraobserver variability: primary observer immediate versus 1-month reading; and

  
  
• •
  

  core versus local laboratory interobserver variability: primary core laboratory observer versus clinical center observer.

We fit a mixed-effects model with estimates obtained by restricted maximum likelihood with a compound symmetry covariance structure (fixed effect for beat-averaging method and random effect for subject) to assess whether percentage error significantly differed for single-beat versus three-beat average and two-beat versus three-beat average, for interobserver, intraobserver, and local versus core laboratory comparisons. We fit a mixed-effects model with unstructured covariance to assess whether, for each variable type, on the basis of three-beat-averaged measurements, interobserver percentage error differed for local/core versus core/core percentage error estimates and for core lab interobserver versus intraobserver percentage error.