Study Population

We retrospectively evaluated cardiac ultrasound studies in fetuses referred to Children’s Hospital Boston for fetal echocardiography for a family history of congenital heart disease or suggested fetal arrhythmia from 2004 to 2010. From these, we identified singleton fetuses between 17 and 42 weeks in gestational age (GA), with no maternal disease, fetal structural disease, or arrhythmia. After review of the echocardiographic studies, those with images felt to be sufficiently clear for STE were sequentially selected and analyzed. About 20 studies were selected for each GA subgroup (≤24, 25–29+6/7, 30–34+6/7, ≥35), with the intent of selecting a balanced distribution of fetal GA.

We identified fetuses with AS and moderate or less LV dysfunction. The AS gradient was estimated using the modified Bernoulli equation and LV volumes and LV ejection fraction using the single-plane area-length method. We selected five fetuses with AS to represent different physiologic states. Patients 1 and 2 had moderate LV dysfunction and substantial AS gradients, patients 3 and 4 had normal or mildly depressed LV function and substantial AS gradients, and patient 5 had normal LV function and a mild AS gradient. STE was performed retrospectively in these fetuses and was not used to determine whether to perform fetal aortic valvuloplasty (fAVP) or to determine the timing of fAVP.

The study was performed in conjunction with a protocol that was approved by the Children’s Hospital Committee for Clinical Investigations.

Image Acquisition

Images were acquired using Siemens Sequoia (Siemens Medical Solutions USA, Inc., Mountain View, CA) and Phillips Sonos 5500 and iE33 (Philips Medical Systems, Bothell, WA) machines. Phased-array sector or linear probes ranging from 4.0 to 7.0 Hz were used. The short-axis view was obtained by scanning perpendicular to the long axis of the heart. For circumferential strain, short-axis images containing some part of both papillary muscles without any mitral valve tissue through the whole cardiac cycle were selected as mid–papillary muscle–level images; for longitudinal strain, four-chamber views were selected. All the images were stored in Digital Imaging and Communications in Medicine format and analyzed offline. Fetal echocardiographic images were automatically stored at a frame rate of 30 Hz.

Offline Analysis

Regional cardiac function was measured using syngo Velocity Vector Imaging (VVI) software (Siemens Medical Solutions, USA, Inc.). Among images stored as Digital Imaging and Communications in Medicine clips in routine screening, well-visualized four-chamber and short-axis views were selected. Images that were acquired by Phillips Sonos 5500 or iE33 machines were reformatted to be compatible with syngo VVI software.

To define a fetal cardiac cycle, using superimposed M-mode tracings, end-diastole was defined as the point just before closure of the atrioventricular valve. For short axis, the longest LV dimension was used to define end-diastole. After manually tracing the subendocardial surface of the ventricle on the frame, VVI software calculated strain automatically using the feature-tracking algorithm ( Figure 1 ). Feature-tracking accuracy was visually confirmed, and the tracing was corrected until consistent endocardial tracking was obtained. Only one cardiac cycle was used for analysis instead of averaging over multiple cardiac cycles, to avoid artifacts due to fetal movement or change of cardiac cycle. Analysis was performed by one examiner, who was blinded to outcomes and other echocardiographic parameters.

A still frame of the short axis of the left ventricle with velocity vectors. The arrow represents magnitude of the tissue velocity and the direction of movement of the myocardium.

Because of the variable fetal cardiac location, some rearrangement was needed to match the actual segment of the fetal heart and the segment displayed on the screen. The segment consisting primarily of the septum and closest to the tricuspid valve ( Figure 2 ) was defined as septal, and other segments were defined in order.

These short-axis echocardiographic images demonstrate the method of segmenting the left ventricle (LV) into six segments. The syngo software calculates the center of the gravity of the tracing circle automatically. Segment 1 is defined by the software as the 60° region centered on a vertical line drawn upward from the center of the gravity (30° to each side of the line). Moving clockwise around the wall of the LV, successive 60° segments are defined as segments 2 to 6. In the case depicted in the figure, the segment consisting primarily of the septum and closest to the tricuspid valve was segment 1. The liver was on the right, the stomach (S) was below the heart, and the head was to the left of the image. Therefore the six segments were defined as follows: anterior, 5; lateral, 4; posterior, 3; inferior, 2; septal, 1; and anteroseptal, 6. P1 , Posteromedial papillary muscle; P2 , anterolateral papillary muscle.

Longitudinal and circumferential negative peak strains were used for strain values. Longitudinal strains for all segments were averaged to express global strain.

Data Analysis

To assess intraobserver and interobserver variability, a randomly selected subset of 15 data sets, analyzed by two examiners who were blinded to each other’s measurements, was used. Bland-Altman analysis bias was calculated and presented with the standard deviation. To assess the success rate of analysis, χ ² tests were conducted, and significance was set at P ≤ .05. To assess relationships between GA and speckle-tracking echocardiographic data, linear regression was performed. Data are presented as mean ± SD.

General Characteristics

Indications for fetal echocardiograms in the normal cohort included the following: sibling of child with congenital heart disease, possible fetal arrhythmias detected by primary obstetrician, and maternal congenital heart disease. From 150 sequential fetal studies, mothers with congenital heart disease (except for one with a small atrial septal defect), significant fetal arrhythmias, and fetuses with any anomalies were excluded. Because a majority of fetuses were evaluated in the middle of the second trimester, we selected 81 of those 150 fetuses with the intent of selecting a balanced distribution of fetal GA that met demographic and diagnostic inclusion criteria for analysis. At the time of the examination, there were no identified obstetric abnormalities. GA at the time of echocardiogram ranged from 19 to 42 weeks (mean, 29.2 ± 5.7 weeks), and the average heart rate was 140 ± 9 beats/min. Among 81 fetuses, strain analysis was performed successfully in 62 (77%) for LV longitudinal function, 64 (79%) for RV longitudinal function, and 49 (64%) for LV circumferential function ( Table 1 ). The frequency of successful analysis was lower for LV circumferential analysis, especially in late-gestation fetuses.

Longitudinal and Circumferential Strain

Global RV and LV longitudinal strains were 16.0 ± 3.3% and 15.2 ± 2.7%, respectively, and average mid-LV circumferential strain was 18.7 ± 3.3%. There was no correlation between GA and RV longitudinal strain, LV longitudinal strain, or LV circumferential strain ( Figure 3 ). Values of segmental longitudinal and circumferential strain are shown in Table 2 . Figure 4 is a representative strain curve for circumferential strain.

Peak negative global strain plotted against GA in right ventricular (RV)longitudinal (A) , LV longitudinal (B) , and LV circumferential strain (C) . Blue symbols indicate RV longitudinal strain, red symbols indicate LV longitudinal strain, and black symbols indicate LV circumferential strain.

Circumferential strain curves. Each curve represents each segmental strain and its average.

Fetuses with AS

Five fetuses with AS and no other cardiac malformation, including LV hypoplasia, were selected for analysis. Patients 1 and 2 met criteria for fetal intervention and underwent fAVP for AS soon after the echocardiographic evaluation used in this study. Patients 3 and 4 did not meet criteria for intervention and underwent fAVP 2 and 3 weeks later, respectively. Patient 5 (still in utero) was observed without intervention for 3 months.

One fetus (patient 1) that had both longitudinal and circumferential strains > 2 SDs below average underwent immediate fAVP. The two fetuses (patients 2 and 3) that had borderline low circumferential strain underwent intervention the next day ( n = 1) or after 2 weeks of observation ( n = 1). In the two fetuses with AS that had average or above-average circumferential strain (patients 4 and 5), only the fetus that had borderline high circumferential stain underwent fAVP ( Table 3 ).

Table 3

Profiles of fetal AS

Patient	GA (wk)	LV strain (%), mean ± SD		LV dysfunction	Peak ASPG (mm Hg)	LVEF (%)	Outcome
		Global longitudinal	Average mid-LV circumferential
1	22	8.8 ± −2.3	8.4 ± −3.1	Moderate	35	46	Immediate fAVP
2	22	10.8 ± −1.6	12.8 ± −1.8	Moderate	62	40	Immediate fAVP
3	23	5.3 ± −3.6	12.6 ± −1.8	Mild	63	55	2 wk to fAVP
4	23	11.5 ± −1.3	23.0 ± 1.3	None to mild	28	NA	3 wk to fAVP
5	23	13.2 ± −0.7	18.5 ± −0.1	None to mild	10	68	3-mo observation (in utero)

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Journal of the American Society of Echocardiography: 25 Years Old
2. Evaluation of Global Left Ventricular Systolic Function Using Three-Dimensional Echocardiography Speckle-Tracking Strain Parameters
3. Guidelines and standards: The DNA of a professional society and our field
4. Continuing Education and Meeting Calendar

Stay updated, free articles. Join our Telegram channel

Join