Color M-mode propagation velocity, but not its ratio to early diastolic inflow velocity, changes throughout gestation in normal human fetuses

OBJECTIVES

Color M-mode propagation velocity (Vp) is a measure of diastolic function in adults and, when combined with early diastolic inflow velocity (E), the ratio E/Vp reflects ventricular filling pressure. Early detection of diastolic compromise may benefit fetal patients at risk for developing heart failure. The objectives of this study were to measure values for Vp and inflow peak E in a group of normal fetuses, to analyze age-dependent alterations in these measurements, and to evaluate the interobserver and intraobserver variability of the measurements.

METHODS

Thirty-two normal fetuses at between 20 and 35 weeks' gestation underwent echocardiography. Color M-mode Vp was measured from the four-chamber view for the right (RV) and left (LV) ventricles, and mitral and tricuspid inflow velocities were determined by pulsed-wave Doppler ultrasound. The values obtained were compared with previously reported findings in adults.

RESULTS

Adequate tracings were obtainable in 23 patients for the RV and 29 for the LV. Mean Vp values for the RV (15.3 +/- 3.2 cm/s) and LV (20.8 +/- 5.6 cm/s) were lower than normal adult values, and Vp values were significantly lower for the RV than the LV (P < 0.001). Applying Bazett's heart rate correction, values for RV (23.4 +/- 4.8 cm/s) and LV (31.9 +/- 8.7 cm/s) remained lower than normal adult values. There was a linear correlation of Vp with gestational age for the RV (R = 0.69, P < 0.001), and the ratio of E/Vp corrected for heart rate for the RV (1.51 +/- 0.26) remained constant throughout gestation. Interobserver bias was high but intraobserver bias low, at 19 and 1.1%, respectively.

CONCLUSIONS

Vp is lower in fetal than in adult life. Vp for the RV changes in a manner indicative of improving diastolic function throughout normal gestation, providing insight into the alterations in diastolic function with gestation that contribute to increases in cardiac output. The use of Vp to assess diastolic function disturbance in fetuses is feasible, but high interobserver variability is problematic.

Systemic venous abnormalities: embryologic and echocardiographic considerations

The echocardiographic diagnosis of systemic venous anomalies often is rendered difficult by the variety of lesions that exist. An understanding of the embryologic processes that result in these lesions is essential for accurate identification, since these lesions often are not obvious on routine echocardiographic examination. Standard echocardiographic views may demonstrate some lesions, whereas many require modified views to outline the abnormal systemic venous anatomy. This paper reviews the basic embryologic processes of the development of the normal and abnormal systemic venous system, as well as the echocardiographic identification of these major systemic venous malformations.

Radiofrequency ablation of human fetal sacrococcygeal teratoma

OBJECTIVE

Fetuses with solid, highly vascularized sacrococcygeal teratomas can die as a result of the vascular steal syndrome. This is the first report in which a percutaneous technique, radiofrequency ablation, was used to interrupt blood flow to a sacrococcygeal teratoma in 4 human fetuses.

STUDY DESIGN

A radiofrequency ablation probe was percutaneously inserted into the fetal tumor under ultrasonographic guidance. In 2 fetuses a significant portion of the tumor mass was ablated, whereas in the other 2 fetuses only the major feeding vessels were targeted.

RESULTS

Two infants were delivered at 28 and 31 weeks' gestation, respectively, and are doing well. In 2 other cases hemorrhage into the tumor led to an unfavorable fetal outcome.

CONCLUSION

Ablation of a majority of the tumor tissue in sacrococcygeal teratoma is not necessary and proved fatal in two instances. Targeted ablation of the feeding tumor vessels diminishes blood flow sufficiently to reverse high-output fetal heart failure.

Rapid enlargement of neoaortic root after the Ross procedure in children

Serial echocardiographic studies from 11 patients who underwent the Ross procedure were reviewed, and the rate of neoaortic annulus size increase was compared with that in a normal population. The rate of growth of the neoaortic annulus after the Ross procedure was significantly greater than that in the normal population.

Effect of aortic compliance on Doppler diastolic flow pattern in coarctation of the aorta

The spectral Doppler pattern at the site of an aortic coarctation (CoA) generally displays increased maximal velocity (Vmax) during systole with a slow velocity decay, resulting in the characteristic "sawtooth" pattern. If there is rapid velocity decay, the obstruction is often judged to be mild. The purpose of this study was to investigate if velocity decay is affected by proximal aortic compliance (C(p)). The relation between the velocity decay measured from the Doppler pattern and C(p) was studied with the use of an in vitro pulsatile flow model. The time (tau) between Vmax and 33% Vmax was the measure of velocity decay. The C(p) was varied from 0.7 to 2.6 mL/mm Hg for each of 4 levels of CoA severity. The various obstructions produced a Vmax range of 2.7 to 5.5 m/s. There was a positive linear relation between tau and C(p) (r(2) = 0.76). For a low C(p) (compliance = 0.7 mL/mm Hg), velocity decay was rapid (tau = 0.2 to 0.3 seconds) with no diastolic gradient. For equivalent obstructions, a high C(p) (2.6 mL/mm Hg) produced a persistent diastolic gradient and slow velocity decay (tau = 0.5 to 0.6 seconds). The Doppler pattern across a CoA is affected by C(p). Therefore, the absence of a sawtooth pattern should not exclude the diagnosis of significant CoA obstruction.

In vitro Doppler assessment of pressure gradients across modified Blalock-Taussig shunts

The relation between flow velocity and the pressure decrease is evaluated in Blalock-Taussig shunts used in congenital heart surgery and is related to the flow conditions and geometries of the shunts studied. The authors propose that the flow conditions within the shunt as well as shunt dimensions need to be taken into account when using Doppler velocimetry to predict pressure drops across these shunts.

In vitro analysis of regurgitant fraction using Doppler power-weighted sum of velocities

The power-weighted sum of velocities (PWS) is the sum of each velocity component of the Doppler signal multiplied by its power. The purpose of this study was to determine (1) whether PWS is linearly related to volume flow and (2) whether PWS can predict the regurgitant fraction in an in vitro pulsatile flow system simulating aortic regurgitation. Doppler analysis of aortic flow was performed with an intact valve and two regurgitant valves. For each valve a linear relation between the forward flow PWS and forward flow volume was demonstrated, with excellent correlation (r = 0.99). For the valves with regurgitant orifices, the values for the PWS-derived regurgitant fraction were compared with measured regurgitant fraction. A fair correlation was demonstrated (r = 0.59), with low accuracy in prediction (error 44% +/- 24%). The PWS was inaccurate in predicting flow ratios in our in vitro system despite the strong relation with forward flow volume. The error incurred may be due to effects of filters that remove low velocity and low amplitude information.

Potential role of mechanical stress in the etiology of pediatric heart disease: septal shear stress in subaortic stenosis

OBJECTIVES

The objective of this study was to show elevations in septal shear stress in response to morphologic abnormalities that have been associated with discrete subaortic stenosis (SAS) in children. Combined with the published data, this critical connection supports a four-stage etiology of SAS that is advanced in this report.

BACKGROUND

Subaortic stenosis constitutes up to 20% of left ventricular outflow obstruction in children and frequently requires surgical removal, and the lesions may reappear unpredictably after the operation. The etiology of SAS is unknown. This study proposes a four-stage etiology for SAS that I) combines morphologic abnormalities, II) elevation of septal shear stress, III) genetic predisposition and IV) cellular proliferation in response to shear stress.

METHODS

Morphologic structures of a left ventricular outflow tract were modeled based on measurements in patients with and without SAS. Septal shear stress was studied in response to changes in aortoseptal angle (AoSA) (120 degrees to 150 degrees), outflow tract convergence angle (45 degrees, 22.5 degrees and 0 degree), presence/location of a ventricular septal defect (VSD) (3-mm VSD; 2 and 6 mm from annulus) and shunt velocity (3 and 5 m/s).

RESULTS

Variations in AoSA produced marked elevations in septal shear stress (from 103 dynes/cm2 for 150 degrees angle to 150 dynes/cm2 for 120 degrees angle for baseline conditions). This effect was not dependent on the convergence angle in the outflow tract (150 to 132 dynes/cm2 over full range of angles including extreme case of 0 degree). A VSD enhanced this effect (150 to 220 dynes/cm2 at steep angle of 120 degrees and 3 m/s shunt velocity), consistent with the high incidence of VSDs in patients with SAS. The position of the VSD was also important, with a reduction of the distance between the VSD and the aortic annulus causing further increases in septal shear stress (220 and 266 dynes/cm2 for distances of 6 and 2 mm from the annulus, respectively).

CONCLUSIONS

Small changes in AoSA produce important changes in septal shear stress. The levels of stress increase are consistent with cellular flow studies showing stimulation of growth factors and cellular proliferation. Steepened AoSA may be a risk factor for the development of SAS. Evidence exists for all four stages of the proposed etiology of SAS.

Abnormalities of the left ventricular outflow tract associated with discrete subaortic stenosis in children: an echocardiographic study

OBJECTIVES

The purpose of this study was to examine the echocardiographic abnormalities of the left ventricular outflow tract associated with subaortic stenosis in children.

BACKGROUND

Considerable evidence suggests that subaortic stenosis is an acquired and progressive lesion, but the etiology remains unknown. We have proposed a four-stage etiologic process for the development of subaortic stenosis. This report addresses the first stage by defining the morphologic abnormalities of the left ventricular outflow tract present in patients who develop subaortic stenosis.

METHODS

Two study groups were evaluated-33 patients with isolated subaortic stenosis and 12 patients with perimembranous ventricular septal defect and subaortic stenosis-and were compared with a size- and lesion-matched control group. Subjects ranged in age from 0.05 to 23 years, and body surface area ranged from 0.17 to 2.3 m2. Two independent observers measured aortoseptal angle, aortic annulus diameter and mitral-aortic separation from previously recorded echocardiographic studies.

RESULTS

The aortoseptal angle was steeper in patients with isolated subaortic stenosis than in control subjects (p < 0.001). This pattern was also true for patients with ventricular septal defect and subaortic stenosis compared with control subjects (p < 0.001). Neither age nor body surface area was correlated with aortoseptal angle. A trend toward smaller aortic annulus diameter indexed to patient size was seen between patients and control subjects but failed to achieve statistical significance (p = 0.08). There was an excellent interrater correlation in aortoseptal angle and aortic annulus measurement. The mitral-aortic separation measurement was unreliable. Our results, specifically relating steep aortoseptal angle to subaortic stenosis, confirm the results of other investigators.

CONCLUSIONS

This study demonstrates that subaortic stenosis is associated with a steepened aortoseptal angle, as defined by two-dimensional echocardiography, and this association holds in patients with and without a ventricular septal defect. A steepened aortoseptal angle may be a risk factor for the development of subaortic stenosis.

Palliative arterial repair for transposition, ventricular septal defect, and pulmonary vascular disease

Failure to repair transposition of the great arteries and ventricular septal defect in the young infant results in the early development of pulmonary vascular occlusive disease. Complete repair, preferably by an arterial switch procedure and ventricular septal defect closure, may then not be possible. We report a palliative arterial switch procedure in a 5 1/2-year-old patient with transposition, ventricular septal defect, and severe pulmonary vascular obstructive disease in whom progressive hypoxemia and exercise intolerance developed. An arterial repair without ventricular septal defect closure was performed. After the operation, the child's systemic arterial oxygen saturation and exercise tolerance have substantially improved. Although the progression of pulmonary vascular disease may not be altered, arterial repair can provide effective palliation in this subset of patients.