Study Population

The study group comprised 22 patients with preoperative atrial septal defects (ASDs; mean age, 9.0 ± 4.2 years; range, 3.0–15.7 years) and 23 patients with surgically corrected tetralogy of Fallot (TOF; mean age, 7.2 ± 5.1 years; range, 2.5–16.2 years). We selected these two types of patients because these common and representative congenital heart diseases are both associated with right ventricular volume and/or pressure overload. Forty-four age-matched normal subjects with no electrocardiographic or echocardiographic abnormalities (mean age, 9.1 ± 4.1 years; range, 3.0–15.5 years) were also enrolled to serve as a control group. Cardiac catheterization was performed in the ASD and TOF groups within 7 days of undergoing echocardiography. Table 1 shows the baseline characteristics of the three groups. Left ventricular systolic function did not significantly differ among them. None of the patients in the ASD group had pulmonary hypertension or right ventricular pressure overload, whereas all those in the TOF group had right ventricular pressure with volume overload. All protocols were approved by the institutional review board of the Medical University of Tokushima, and written informed consent was obtained from the parents of all of the patients. The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki.

Standard Echocardiographic Study

Echocardiography proceeded with the subject lying in the left lateral decubitus position. Ultrasound data were acquired using an EUB8500 or a Preirus digital ultrasound system (Hitachi Medical Corporation) equipped with a 3-MHz to 7-MHz sector transducer.

Two-Dimensional Speckle-Tracking Echocardiography

Regions of interest were manually positioned on the left and right sides of the ventricular septum, and motion was then tracked throughout the cardiac cycle. The size of the sampling volume (two points of interest) was 3 mm in length. Longitudinal strain was obtained from a four-chamber view. Region of interests were positioned on both sides at the middle part of the septum. Radial and circumferential strain was analyzed in images obtained in the short-axis view at the level of the papillary muscles. We placed a sample volume on the right half and the left half of the ventricular septum for strain measurement. Furthermore, we evaluated the time interval between the peaks of the left-sided and right-sided strain curves (TLt-Rt) in each directional deformation.

Radial and longitudinal deformation of right ventricular free wall were analyzed in images obtained from a four-chamber view. Furthermore, the strain of the entire ventricular septum was also evaluated. The deformation on both sides of the septum was compared with right ventricular free wall strain and entire ventricular septal strain.

After optimizing gain, dynamic range, and time gain compensation, the images were digitally recorded at 83 to 133 frames/sec. All imaging data for one cardiac cycle were digitalized and stored on a hard disk in the ultrasound equipment and then transmitted to a personal computer for further analysis. Image analysis was performed using a novel customized software program with 2D speckle tracking (US Image Viewer version 2.0), comprising a pattern-matching algorithm that tracks changes in the distance between two points. If the tracking point is selected in the first frame of a 2D echocardiographic image, the algorithm will search the next frame for the region that is assumed to be the closest to the selected point, according to the distribution of pixel intensity. The total movement of the selected point determined by repeating this process frame by frame throughout the whole cardiac cycle is then recorded as a coordinate. The movement of the tracking point can be visualized on the screen during the analysis, and the trace of the point can be visually confirmed. When mistracking of actual wall motion was judged visually, two new points were set and tracked again. We tracked these points of interest several times, confirmed them visually, and selected the average tracking pattern for further analysis. The movements of these points during the cardiac cycle were automatically tracked. Automated tracking was started at end-diastole, defined as a Q wave on a simultaneously recorded electrocardiogram. Myocardial strain was calculated as the ratio of the length between the two points during one cardiac cycle to the initial length at end-diastole.

Cardiac Catheterization

Catheterization and angiography (Integris Allura 9 Biplane; Phillips Medical Systems, Best, The Netherlands) was performed using 4Fr to 6Fr catheters. All patients were intubated and examined under general anesthesia by biplane anteroposterior and lateral projection angiography. Volumetry was done by means of ventriculography, and it was calculated using the area-length method for the left ventricle and Simpson’s rule for the right ventricle using a commercially available quantitative cardiac analysis software package (CAW2000; ELK Corporation, Osaka, Japan). All values of end-diastolic and end-systolic volumes were expressed as percentages of the anticipated normal value calculated from the patients’ body surface areas.

Statistical Analysis

All data are expressed as mean ± SD or as medians with 5th and 95th percentiles. Statistical significance was determined using the Mann-Whitney U test or the Kruskal-Wallis test, followed by Dunn’s test as appropriate. Linear regression analyses were performed for the correlation between the myocardial strain and hemodynamic parameters, and Pearson’s correlation coefficient was calculated. All statistical calculations were performed using Microsoft Excel 2007 (Microsoft Corporation, Redmond, WA) and Prism version 5.0 (GraphPad Software, San Diego, CA) installed on a desktop computer. P values < .05 were considered statistically significant. Intraobserver and interobserver reproducibility of strain measurements was tested using Bland-Altman analysis in a blinded manner. After a 5-min interval, data recordings were performed by observer 1, observer 2, and observer 1 once again from 20 participants (five with ASD, five with tetralogy of Fallot, and 10 controls). Data were stored in digital format and transferred to a personal computer for offline analysis later.

Visualization of the Septum

Standard 2D imaging data sets were obtained from all study participants. The data were of uniformly good quality and allowed subsequent offline analysis. Figures 1 A and 1 B show representative examples of a zoomed image of the ventricular septum. Regions of interest were positioned on the left and right sides of the septum for strain analysis ( Figure 1 B). Figure 1 C shows a representative longitudinal strain curve. The time interval between the peak strain on the left and right sides (TLt-Rt) was measured as indicated.

Representative recordings of ventricular septal strain analysis by speckle-tracking strain images from a healthy 12-year-old boy. Four-chamber view shows the right (Rt) and left (Lt) components of the ventricular septum separated by a bright line ( arrow ) (A) . Two points of interest placed on the left and right sides were automatically tracked during cardiac cycles. Radial strain was obtained from the parasternal short-axis view (B) . Longitudinal strain was calculated as shown in (C) . TLt-Rt was measured as indicated. ECG , Electrocardiogram; LV , left ventricle; RV , right ventricle.

Radial Deformation

The radial deformation of both sides of the ventricular septum was quantified in the short-axis view. Figure 2 compares data on radial strain on the right versus the left side of the septum during the cardiac cycle. Strain analysis revealed significantly higher peak strain during ejection on the left than on the right in control individuals (41.7 ± 12.8% vs 22.6 ± 6.8%, P < .0001). Peak strain was detected earlier in the left than the right strain curve in 40 participants (91%). TLt-Rt was 52.9 ± 35.6 msec. Radial strain was significantly larger on the left than on the right side in the ASD group (41.8 ± 13.0% vs 22.5 ± 7.5%, P < .0001). Radial strain on both sides of the septum in this group did not significantly differ from that in the control group. TLt-Rt was 46.0 ± 39.9 msec, which also did not significantly differ from the control group. Radial strain on the right side in the TOF group was 29.9 ± 13.9%, significantly higher than that in the control group ( P < .05). On the other hand, radial strain on the left side in the TOF group was 25.2 ± 8.4%, significantly lower than that in the control and ASD groups ( P < .001 for both). The TLt-Rt of 75.7 ± 46.9 msec in the TOF group was significantly higher than that in the control and ASD groups ( P < .05 for both).

Radial strain on the right (Rt) and left (Lt) sides of the ventricular septum. Boxes describe the distribution of peak radial strain (25th and 75th percentiles; the central line represents the median). Vertical lines represent the range between the 5th and 95th percentiles. ^∗ P < .05 versus control group; ^† P < .001 versus control and ASD groups; ^‡ P < .05 versus control and ASD groups.

Longitudinal Deformation

Longitudinal strain was determined from the four-chamber view ( Figure 3 ). The longitudinal strain on the right and left sides of the ventricular septum did not significantly differ in the control group (−20.7 ± 5.2% and −22.0 ± 4.9%, respectively). Strain on the left side was significantly increased in the ASD group compared with the right side (−27.9 ± 3.4% vs −24.9 ± 4.0%, P < .05). Strain on both sides in this group was significantly increased compared with that in the control group ( P < .01 for the left side and P < .05 for the right side). Longitudinal strain did not significantly differ between the left and right sides in the TOF group (−15.7 ± 6.8% and −13.5 ± 4.5%, respectively). Strain on both sides was significantly reduced compared with the control and ASD groups (for the right side, P < .001 vs the control and ASD groups; for the left side, P < .01 vs the control group and P < .001 vs the ASD group). The TLt-Rt of longitudinal deformation did not significantly differ between the TOF and ASD groups.

Longitudinal strain on the right (Rt) and left (Lt) sides of the ventricular septum. Boxes describe the distribution of peak radial strain (25th and 75th percentiles; the central line represents the median). Vertical lines represent the range between the 5th and 95th percentiles. ^∗ P < .05 versus control group; ^† P < .01 versus control group; ^‡ P < .001 versus control and ASD groups; ^§ P < .01 versus control group and P < .001 versus ASD group.

Circumferential Deformation

Circumferential deformation of the septum was quantified in parasternal short-axis views. Figure 4 compares circumferential strain on both sides of the septum during ejection. Circumferential deformation analysis revealed significantly higher peak strain on the left side than on the right side in normal individuals (−28.0 ± 5.4% vs −22.5 ± 4.8%, P < .001) and significantly larger circumferential strain on the left than on the right side in the ASD group (−33.5 ± 4.6% vs −26.7 ± 5.2%, P < .001). Circumferential strain on both sides in this group was significantly increased compared with that in the control group ( P < .001 for both). TLt-Rt in the ASD group did not significantly differ from that in the control group. Strain on the left side of the septum was significantly higher than that on the right side in the TOF group (−30.3 ± 8.9% vs −24.1 ± 9.1%, P < .05). Circumferential strain on both sides did not significantly differ between the TOF and control groups, although TLt-Rt was significantly increased in the TOF group compared with the control and ASD groups (59.7 ± 38.1, 38.7 ± 31.0, and 33.9 ± 28.3 msec, respectively, P < .05 for both).

Circumferential strain on the right (Rt) and left (Lt) sides of the ventricular septum. Boxes describe the distribution of peak radial strain (25th and 75th percentiles; the central line represents the median). Vertical lines represent the range between the 5th and 95th percentiles. ^∗ P < .001 versus control group; ^† P < .05 versus control and ASD groups.

Reproducibility

Interobserver and intraobserver reproducibility for analysis of strain on both sides from 20 randomly selected participants (five with ASD, five with TOF, and 10 controls) was determined from Bland-Altman analysis. The Bland-Altman plots for interobserver variability (bias ± 2 SDs [95% limit of agreement]) are shown in Figure 5 . Table 2 shows interobserver and intraobserver reproducibility.

Bland-Altman plots of interobserver differences for strain on the right (Rt) and left (Lt) sides of the ventricular septum. The dotted lines show the mean difference, and the solid lines shows 95% limits of agreement in radial (A,B) , longitudinal (C,D) , and circumferential (E,F) strain.

Table 2

Interobserver and intraobserver reproducibility

Ventricular septal strain	Interobserver variability	Intraobserver variability
Radial
Right	−0.3 ± 12.6%	−0.5 ± 11.6%
Left	0.7 ± 16.6%	0.6 ± 11.5%
Longitudinal
Right	−1.6 ± 12.1%	1.4 ± 14.3%
Left	0.2 ± 9.6%	1.8 ± 7.3%
Circumferential
Right	0.2 ± 13.1%	−0.3 ± 9.1%
Left	0.8 ± 12.5%	0.5 ± 10.1%

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