Doppler echocardiographic and morphologic evaluation of patients following operative repair of aortic coarctation

Aortic arch recoarctation after the Norwood stage I palliation: the comparative accuracy of blood pressure cuff and echocardiographic Doppler gradients in detecting significant obstruction

OBJECTIVE

Aortic arch recoarctation is responsible for significant morbidity and mortality after the Norwood Stage I procedure. Cuff blood pressure (BP) gradients and echocardiographic Doppler gradients are routinely used as noninvasive screening tests for early detection, but accuracy has not been systematically tested. We sought to evaluate the ability of cuff BP and Doppler gradients, measured at routine outpatient clinic visits, to predict significant arch obstruction in single ventricle patients after the Norwood operation.

DESIGN

Consecutive patients who underwent Norwood operation at our institution were identified retrospectively. Cuff and echocardiographic gradients measured prior to the pre-Glenn catheterization were compared to peak-to-peak systolic neoaortic arch gradients obtained at catheterization. Statistical analyses, including Receiver Operator Characteristic (ROC) curves, were performed using different cutpoints for cuff and echocardiographic gradients, evaluating their ability to predict a clinically significant catheter gradient.

RESULTS

Data were obtained in 68 patients. Echocardiographic gradient cutpoints were more sensitive but less specific than cuff BP gradient cutpoints at detecting a catheter gradient > or = 10 mm Hg. Echo gradients > or = 20 mm Hg showed 85% sensitivity and 95% specificity in detecting a systolic catheter gradient > or = 10 mm Hg.

CONCLUSION

chocardiographic Doppler outperforms cuff BP as a sensitive noninvasive screening tool for early detection of significant arch obstruction in infants after the Norwood operation.

Feasibility and Utility of Three-Dimensional Color Flow Echocardiography of the Aortic Arch: The “Echocardiographic Angiogram”

Two-dimensional transthoracic echocardiography (2DE) is the most commonly used diagnostic modality to evaluate congenital and acquired abnormalities of the aortic arch. However, 2DE is frequently limited in this ability due to the three-dimensional character of the arch and its interrelationships with other vascular structures. Recently, three-dimensional echocardiography (3DE) with 3D color flow Doppler became commercially available. We examined the feasibility and utility of 3DE with 3D color Doppler in the evaluation of patients with congenital (native and postoperative) abnormalities of the aortic arch. We found that 3DE color flow provides important diagnostic information in patients with aortic arch anomalies, in a manner that is quick and user-friendly. In addition, 17 of the 26 patients had their 3DE findings confirmed by additional modalities, providing reasonably significant validation for our findings with 3DE.

Evolutional aspects of children and adolescents with surgically corrected aortic coarctation: clinical, echocardiographic, and magnetic resonance image analysis of 113 patients

OBJECTIVE

The goals of this study were to determine the prevalence of hypertension and recoarctation in operated children and teenagers and to integrate clinical and imaging technique data.

METHODS

One hundred thirteen infants and children (ages 14 years or less) were retrospectively divided into 3 groups according to the age at operation and the surgical technique: 79 underwent resection with end-to-end anastomosis; 14 had patch enlargement; 13 had subclavian flap aortoplasty; and 7 had other techniques performed. The mean age at operation was 3.95 +/- 4.17 years and the mean follow-up period was 4.62 +/- 4.90 years. Each patient was clinically examined and Doppler echocardiography was performed in 112 patients. Sixty-six patients underwent magnetic resonance imaging. Diameters of aortic arch were measured at 4 levels; the ratios between each one and descendent aorta diameters were calculated. Qualitative variables and associations were studied by Fisher exact test or chi-squared test. Comparisons of measurements in different groups were performed using variance analysis, with tests of selective contrasts (nonparametric tests). The level of statistical significance was <.05.

RESULTS

The prevalence of hypertension and recoarctation was 38% and 14%, respectively. No statistical difference was found among the age groups. In 65 patients who underwent magnetic resonance imaging, the transverse aortic arch was hypoplastic in 31 (47%) patients; 41 (63%) had stenosis at the site of anastomosis (ratio < 0.9).

CONCLUSION

Hypoplasia of transverse aortic arch was highly prevalent. These data suggest that hypoplastic aortic arch should be corrected concomitantly with coarctation.

Limitations of Doppler echocardiography for the post-operative evaluation of aortic coarctation

Doppler blood flow measurements and derived pressure differences, through the Bernoulli equation, are used in the diagnosis of aortic coarctation, a congenital stenosis distal to the left subclavian artery. Doppler velocities remain elevated at the coarctation site after successful repair of coarctation, leading to high Doppler derived pressure differences without significant arm-leg pressure differences. We studied this apparent contradiction of two diagnostic methods, in vivo using patient and control data, and in vitro using a hydraulic model. Clinical and echocardiographic data from 31 patients, aged 13.0 +/- 4.0, 10.5 +/- 4.7 yr after coarctectomy by end-to-end anastomosis, and 18 age-matched healthy subjects were reviewed. Doppler peak velocities at the aortic isthmus were elevated in patients (2.2 +/- 0.4 vs. 1.2 +/- 0.2m/s, P < 0.001), corresponding to significant Doppler differences (20 +/- 7 mmHg), however, without significant arm-leg pressure differences. In all patients, a mild anatomic stenosis could still be observed. Local stiffness was increased. The hypothesis that the less distensible surgical scar in post-coarctectomy patients leads to a significant dynamic obstruction in systole was validated in a latex model of the aorta. Rigid rings (0.5-1.5 cm), matching the unloaded aortic diameter, were mounted around the aorta. Under loading conditions, Doppler peak velocities increased by 40 +/-7%, yielding Doppler differences of 21 +/- 3 mmHg, without a significant pressure drop. An alternative expression to calculate pressure differences, using both velocity and geometric information, was validated in the model. In conclusion, post-operatively, Doppler velocities remain elevated due to a mild anatomical and significant dynamic narrowing, but the specific geometry, resembling a tubular hypoplasia rather than an abrupt stenosis, permits an almost complete pressure recovery explaining the occurrence of Doppler differences in disagreement with the negligible arm-leg pressure difference.

Fixed region of nondistensibility after coarctation repair: in vitro validation of its influence on Doppler peak velocities

After coarctectomy, local loss of distensibility is noted in addition to mild anatomic narrowing. We hypothesize that the increased Doppler peak velocities measured at the aortic isthmus in these patients partly reflect obstruction secondary to the stiff surgical scar. The hypothesis was studied in a pulsatile hydraulic model. Thirty-one patients (13.0 +/- 4.0 years of age), 10.5 +/- 4.7 years after coarctectomy by end-to-end anastomosis, were studied clinically and echocardiographically. Indexes of distensibility were calculated. The effect of isolated increased stiffness was studied in vitro with a stiff and a compliant 1:1 scale latex model of the aorta mounted in a pulsatile full-scale circulation loop. Local stiffening was obtained by a rigid ring mounted around the aorta, fitted to the dimension of the unloaded aorta. For different pressure and flow regimens, pressures and Doppler velocities were measured across the ring. Mean peak velocities at the surgical scar were 2.2 +/- 0.4 m/s. Mild anatomic stenosis was present. All distensibility indexes indicated locally increased stiffness (P <.001). In the stiff latex model, Doppler peak velocities increased from 1.89 +/- 0.04 m/s to 2.32 +/- 0.06 m/s (P <.03); in the compliant model, from 1.15 +/- 0.03 m/s to 1.79 +/- 0.05 m/s (P <.001). The increase of Doppler peak velocities depends on model compliance only and is independent of flow rate, length of the noncompliant segment, and viscosity of the perfusion fluid. Velocities do not change when semicircular stiffening is applied. We have demonstrated in vitro that isolated local nondistensibility leads to vessel narrowing during vascular distension. The relative contribution of local scar stiffness in the increase of Doppler peak velocities after coarctectomy was hereby assessed.

Effects of morphologic restenosis, defined by MRI after coarctation repair, on blood pressure and arm-leg and Doppler gradients

Ten years after coarctation repair, 36 adolescents and young adults were studied in order to evaluate the relationship of anatomy at the resection site to blood pressure and arm-leg and Doppler gradients. The patients underwent magnetic resonance imaging (MRI), exercise testing, and continuous wave (CW) Doppler echocardiography. On MRI, residual narrowing at the resection site was measured as 1-(phi anastomosis/ phi descending aorta) and expressed as percent stenosis. Residual stenosis on MRI was negatively correlated with the leg pressure at rest (P = 0.0003) and during exercise (P = 0.002). Residual stenosis correlated positively with the arm-leg gradient at rest (P < 0.0001) and during exercise (P < 0.0001) and with the peak CW Doppler gradient across the anastomosis (P < 0.0001). However, residual stenosis was not related to the systolic blood pressure of the arm at rest or during exercise. The systolic arm pressures did not differ between patients with residual stenosis of less than 30% (group I), patients with residual stenosis of equal to or greater than 30% but less than 45% (group II), and patients with residual stenosis of equal to or greater than 45% (group III). In conclusion residual anatomic stenosis influences blood pressure in the legs, the arm-leg gradient, and the Doppler gradient across the anastomosis. Arm hypertension late after coarctation repair seems not to be related to residual stenosis, and the benefit of reintervention in these patients remains questionable.

Quantification of collateral blood flow in coarctation of the aorta by velocity encoded cine magnetic resonance imaging

BACKGROUND

Knowledge about the volume of collateral flow provides insight into the severity of coarctation of the aorta and may be critical in planning the operative approach. There is currently no method for the quantification of collateral flow in coarctation of the aorta. In this study, we applied velocity encoded cine magnetic resonance imaging (VENC-MR) to establish the flow pattern and volume of collateral flow in the descending thoracic aorta in normal subjects and patients with coarctation, introducing a new possibility to quantify the severity of the coarctation by determining the amount of collateral flow.

METHODS AND RESULTS

VENC-MR was used to measure flow in the proximal and distal descending thoracic aorta in 10 normal subjects. In 23 patients with coarctation, flow was measured near the coarctation site and above the diaphragm. Patients were divided into a group with moderate to severe coarctation and a group with mild coarctation on the basis of clinical gradient between upper and lower extremities and the estimation of the gradient across the coarctation by Doppler echocardiography. The gradient across the coarctation and the degree of anatomic narrowing were also assessed by MR imaging. In normal volunteers, VENC-MR showed a 7 +/- 6% decrease in total flow, from proximal to distal aorta. The interobserver reproducibility was 3.9% to 4.9% (mean, 4.4%). In patients with moderate to severe coarctation, VENC-MR demonstrated an 83 +/- 50% increase in total flow from proximal to distal aorta, yielding a significant change compared with normal subjects (P < .01). Patients with mild coarctation showed a normal flow pattern and no significant change in total flow. There was a significant relation between the amount of flow increase in the distal aorta and the reduction in luminal diameter at the coarctation site (r = .94) as well as the clinical gradient (r = .84).

CONCLUSIONS

This study shows the normal flow pattern in the descending thoracic aorta and its reversal in coarctation due to collateral flow. Thus, VENC-MR can measure collateral flow in coarctation and serves as a unique method for providing this important measurement of the severity of coarctation of the aorta.

Evaluation of anatomical obstruction by Doppler echocardiography and magnetic resonance imaging in patients with coarctation of the aorta

OBJECTIVE

To evaluate a new Doppler echocardiographic index of obstruction in patients with native coarctation or recoarctation.

PATIENTS

32 patients (mean age 20, range 3 months--50 years).

METHODS

Magnetic resonance imaging (MRI) was used to investigate the descending aorta. The cross sectional area of the obstruction was compared with the area of the abdominal aorta as an index of obstruction (CoA index). Doppler echocardiography was used to record the velocities in the coarctation jet and in the abdominal aorta. According to the continuity equation the ratio of these velocities should equal the ratios of the cross sectional areas. The gradients and diastolic half time of the Doppler curve were calculated.

RESULTS

There was a close correlation between the MRI index of obstruction and the Doppler velocity ratio (r = 0.92). The sensitivity and specificity of this ratio in detecting a CoA index equal to or less than 0.25 were better than those obtained with gradients only or the combination of gradients and diastolic half time.

CONCLUSION

The new Doppler velocity ratio correlated closely with an anatomical index of obstruction. It was easy to record in most patients and it avoided difficulties about the choice of instantaneous or peak to peak gradients and whether or not to subtract proximal velocities for the calculation of gradients.