Failure of Doppler ultrasound to detect coarctation of the aorta

Abdominal aortic pulsed wave Doppler patterns reliably reflect clinical severity in patients with coarctation of the aorta

OBJECTIVE

There are situations in which standard echocardiography does not adequately define the aortic arch. We sought to determine what additional information could be gained by analyzing abdominal aortic Doppler flows in coarctation.

DESIGN

Previously recorded echocardiographic data were reviewed in 70 controls and 248 patients with coarctation, including abdominal aortic values for pulsatility indices, pulse delay, and presence of early diastolic reversal. Ability of these variables to distinguish controls from coarctation patients and to assess coarctation severity was assessed.

RESULTS

Corrected maximum instantaneous gradient and all abdominal aortic flow variables were associated with severity of obstruction. Early diastolic reversal was universally absent in significant coarctation. Threshold values for other parameters associated with significant obstruction were: corrected pulse delay >or=3.4 msec(1/2), pulsatility index <2.0, and systolic to diastolic velocity ratio <3.6. A combined abdominal aortic "variable" (absence of early diastolic reversal and corrected pulse delay >or=2.8 msec(1/2)) was found to be the best predictor of clinical coarctation status (positive predictive value = 93%, negative predictive value = 88%).

CONCLUSIONS

In the absence of a ductus arteriosus, abdominal aortic Doppler parameters can reliably predict the presence of significant coarctation. When early diastolic reversal was present, obstruction was always absent. Lack of early diastolic reversal with a prolonged pulse delay was the best predictor of significant obstruction. Abdominal aortic Doppler evaluation should become a routine part of the evaluation of patients with known or suspected coarctation.

Accuracy of Doppler methods for estimating peak-to-peak and peak instantaneous gradients across coarctation of the aorta: An In vitro study

Although data exist that address the attempt to correlate noninvasive Doppler-derived pressure gradients with invasive catheter pressure gradients in patients with coarctation of the aorta, few data exist about stiffness of the proximal descending aorta (precoarctation) and its relation to these pressure measurements. In this study, an in vitro flow model of a simulated neonatal aorta with a coarctation was developed. Three proximal descending aortas of different stiffnesses were used. The stiffness index of the proximal descending aorta was calculated as beta = ln [systolic pressure/diastolic pressure/(systolic diameter - diastolic diameter)]. We evaluated pressure gradients obtained by continuous wave Doppler and standard catheter methods and looked at acceleration of flow velocity determined by pulsed wave Doppler in the 3 precoarctation segments of differing stiffnesses. Pressures in the proximal descending aorta (precoarctation) increased with increasing stiffness, ranging from 105 mm Hg (soft) to greater than 300 mm Hg (stiff). Continuous wave Doppler instantaneous pressure gradients overestimated the catheter instantaneous pressure gradients substantially (mean 41% +/- 19%). The stiffer the precoarctation segment, the more the degree of overestimation: soft, 0% to 63% (= 3.47); medium, 13% to 54% (beta = 4.42); and stiff, 43% to 66% (beta = 5.91). Inclusion of the precoarctation velocity [V1] component in the Bernoulli equation did not significantly improve the correlation or the agreement. An additional observation was that pullback catheter peak-to-peak gradients were higher than simultaneous peak-to-peak gradients. In the stiff aorta, this difference could be greater than 22 mm Hg (>19%). Acceleration of flow velocity toward the coarctation was evident by pulsed wave Doppler interrogation. Increasing the stiffness of the precoarctation segment also increased the degree of acceleration within this proximal segment: soft, 0.4 to 0.8 m/s; medium, 0.5 to 1. 4 m/s; and stiff, 0.7 to 1.5 m/s. These data suggest that increasing stiffness of the proximal descending aorta can alter the continuous wave detected Doppler gradient and although the gradient itself has increased, it may not predict accurately the true severity of the localized, most severely obstructed segment.

Pitfalls in echocardiographic-based repair of aortic coarctation

The knowledge of echocardiographic pitfalls, which may impair the correct indication for surgery of aortic coarctation, is of great importance to pediatric cardiologists. We believe that only the suspicion of coronary artery anomalies is a clear indication to perform a cardiac catherization.

Continuous wave Doppler echocardiography after surgical repair of coarctation of the aorta

OBJECTIVE

To find how closely pressure gradients across the aortic arch derived from Doppler echocardiography reflect gradients measured by catheter after surgical repair of coarctation of the aorta.

DESIGN

Pressure drop across the aortic arch was measured simultaneously by continuous wave Doppler and double lumen catheter in 20 patients with repaired coarctation of the aorta.

RESULTS

The peak pressure drop estimated by Doppler was almost invariably higher than the peak to peak gradient measured by catheter, as might be expected. Wide variation was seen between the Doppler measured pressure drop and instantaneous peak gradient measured by catheter, ranging from +22 to -17 mm Hg. The reasons for these differences are unclear but are probably related to a combination of complex flow dynamics in the aortic arch, difficulty in closely aligning the Doppler beam with flow, and inability to measure flow velocity immediately proximal to the site of the surgical repair with continuous wave Doppler.

CONCLUSIONS

Continuous wave Doppler echocardiography may significantly overestimate or underestimate the pressure drop after repair of coarctation and it should be interpreted with caution in individual patients. Catheterisation with angiography remains the reference standard for assessment of surgical repair of the aortic arch.

Countercurrent aortography: an alternative to cardiac catheterization in infancy

Countercurrent aortography via a peripheral artery was used to clarify the aortic arch anatomy in 25 infants in whom cross-sectional and Doppler evaluation was inconclusive. Ages ranged from 3 days to 11 months (median 9 days), and 80% were neonates. The suspected diagnosis was aortic coarctation in 21 infants, interrupted aortic arch in two, recoarctation in one, and vascular ring in one. A countercurrent aortogram provided adequate diagnostic information in 24 infants. A diagnosis of coarctation was confirmed in 15, interruption of the aortic arch in two, and vascular ring in one. In six infants countercurrent aortography excluded the presence of anomalies of the aortic arch. In only one infant, who had an anomalous origin of the right subclavian artery from the descending aorta, did this technique fail to provide adequate information. The only complication observed was transient ischemia of the arm in one patient. Countercurrent aortography is a minimally invasive procedure that can provide adequate angiographic information without the need for cardiac catheterization in patients with inconclusive echocardiographic evaluation. Injection into a right upper limb artery is preferred, because it gives better opacification of the ascending and transverse aortic arch than injection into a left one.