Echocardiographic Data

All echocardiographic studies were obtained using a Vivid I or Vivid 7 machine (GE Healthcare, Wauwatosa, WI) after the patient was under general anesthesia and just before the start of the cardiac catheterization. Frame rates were maintained at >80 frames/sec in all studies. Views equivalent to a standard apical four-chamber view were obtained ( Figure 1 ). Images were optimized for the visualization of the epicardial and endocardial borders of the single RV. Postprocessing of all images was completed offline using EchoPAC version 10 (GE Healthcare), which obtains SR values via speckle-tracking analysis. All measurements were made in triplicate by a single observer blinded to the results of the cardiac catheterization measurements.

Apical four-chamber view of single RV. IVS , Interventricular septum; rLV , rudimentary left ventricle.

DTI Measurements

DTI measurements of the right ventricular free wall at the level of the atrioventricular valve annulus were obtained in the apical four-chamber view. DTI early diastolic wave (e′) and DTI late diastolic wave (a′) of the right ventricular free wall were obtained using pulsed spectral Doppler sampling in all patients. Right atrioventricular valve peak inflow velocities, early diastolic wave (E) and late diastolic wave (A), were also obtained from the same view. E/e′, e′/a′, and E/A ratios were derived from these values. Myocardial performance index was also calculated ([isovolumetric contraction time + isovolumetric relaxation time]/ejection time) using corresponding DTI values for the free right ventricular wall.

Strain Measurements

The endocardial border of the single RV in an apical four-chamber view was traced from the septal-atrioventricular annular hinge point to the apical septum and then to the right ventricular lateral wall at the lateral-atrioventricular annular hinge point. The automated epicardial-to-endocardial computer-generated border, or region of interest, was adjusted to include the epicardium. The single RV was divided automatically into a six-segment model. Borders were accepted if both visual inspection and the software indicated adequate tracking for all segments. Patients whose segments did not track well because of artifacts or inadequate visualization of the lateral borders of the RV were excluded. Longitudinal peak global SRe and global SRa were obtained on postprocessing evaluation of the global SR curve ( Figure 2 ). Global values were obtained by averaging the values of six-segment model in EchoPAC. E/SRe and SRe/SRa ratios were calculated from these variables, similarly to DTI measurements.

SR curve of a 2.5-year-old male patient with hypoplastic left heart syndrome after comprehensive stage II procedure, who presented for routine pre-Fontan cardiac catheterization. He was found to have a VEDP of 8 mm Hg.

Cardiac Catheterization

All hemodynamic measurements were performed under general anesthesia under the same steady-state conditions as for echocardiography. VEDP of the single RV was measured on the ventricular pressure tracing as the point just before the rapid rise in ventricular pressure corresponding to ventricular systole. VEDP numeric values were obtained from cardiac catheterization reports. All cardiac catheterization data were obtained before any interventional procedure was performed.

Statistical Analysis

Correlations of continuous variables with VEDP were examined using linear regression analysis and Pearson’s r correlation coefficients. Areas under the curve with χ ² difference tests were used to examine differences in logit models comparing E/SRe ratio ≥ 150 cm and E/SRe ratio ≥ 200 cm. A VEDP of 10 mm Hg was used as a cutoff value on the basis of previous studies and the increased likelihood that VEDP above this value would be suboptimal for single-ventricle palliation. P values ≤ .05 were considered significant.

To examine interobserver and intraobserver variability, three measurements were taken for each parameter on a random sample of 10 subjects and completed by one observer. An additional observer completed a single set of measurements on the same 10 subjects on all the parameters. Intraclass correlation coefficients were used to measure the levels of interobserver and intraobserver variability. Agreement was considered excellent (>0.75), good (0.60–0.74), or poor (<0.40) as defined by the intraclass correlation coefficient.

All analysis was conducted using Stata version 12 SE (StataCorp LP, College Station, TX). Results are presented as means and standard deviations unless otherwise specified.